WorldWideScience

Sample records for unit optical depth

  1. Effect of Aerosol Size and Hygroscopicity on Aerosol Optical Depth in the Southeastern United States

    Science.gov (United States)

    Brock, Charles; Wagner, Nick; Gordon, Timothy

    2016-04-01

    Aerosol optical depth (AOD) is affected by the size, optical characteristics, and hygroscopicity of particles, confounding attempts to link remote sensing observations of AOD to measured or modeled aerosol mass concentrations. In situ airborne observations of aerosol optical, chemical, microphysical and hygroscopic properties were made in the southeastern United States in the daytime in summer 2013. We use these observations to constrain a simple model that is used to test the sensitivity of AOD to the various measured parameters. As expected, the AOD was found to be most sensitive to aerosol mass concentration and to aerosol water content, which is controlled by aerosol hygroscopicity and the ambient relative humidity. However, AOD was also fairly sensitive to the mean particle diameter and the width of the size distribution. These parameters are often prescribed in global models that use simplified modal parameterizations to describe the aerosol, suggesting that the values chosen could substantially bias the calculated relationship between aerosol mass and optical extinction, AOD, and radiative forcing.

  2. Comparison of aerosol optical depth of UV-B monitoring and research program (UVMRP), AERONET and MODIS over continental united states

    Science.gov (United States)

    Tang, Hongzhao; Chen, Maosi; Davis, John; Gao, Wei

    2013-06-01

    The concern about the role of aerosols as to their effect in the Earth-Atmosphere system requires observation at multiple temporal and spatial scales. The Moderate Resolution Imaging Spectroradiameters (MODIS) is the main aerosol optical depth (AOD) monitoring satellite instrument, and its accuracy and uncertainty need to be validated against ground based measurements routinely. The comparison between two ground AOD measurement programs, the United States Department of Agriculture (USDA) Ultraviolet-B Monitoring and Research Program (UVMRP) and the Aerosol Robotic Network (AERONET) program, confirms the consistency between them. The intercomparison between the MODIS AOD, the AERONET AOD, and the UVMRP AOD suggests that the UVMRP AOD measurements are suited to be an alternative ground-based validation source for satellite AOD products. The experiments show that the spatial-temporal dependency between the MODIS AOD and the UVMRP AOD is positive in the sense that the MODIS AOD compare more favorably with the UVMRP AOD as the spatial and temporal intervals are increased. However, the analysis shows that the optimal spatial interval for all time windows is defined by an angular subtense of around 1° to 1.25°, while the optimal time window is around 423 to 483 minutes at most spatial intervals. The spatial-temporal approach around 1.25° & 423 minutes shows better agreement than the prevalent strategy of 0.25° & 60 minutes found in other similar investigations.

  3. Comparison of aerosol optical depth of UV-B Monitoring and Research Program (UVMRP), AERONET and MODIS over continental United States

    Institute of Scientific and Technical Information of China (English)

    Hongzhao TANG; Maosi CHEN; John DAVIS; Wei GAO

    2013-01-01

    The concern about the role of aerosols as to their effect in the Earth-Atmosphere system requires observation at multiple temporal and spatial scales.The Moderate Resolution Imaging Spectroradiameters (MODIS) is the main aerosol optical depth (AOD)monitoring satellite instrument,and its accuracy and uncertainty need to be validated against ground based measurements routinely.The comparison between two ground AOD measurement programs,the United States Department of Agriculture (USDA) Ultraviolet-B Monitoring and Research Program (UVMRP) and the Aerosol Robotic Network (AERONET) program,confirms the consistency between them.The intercomparison between the MODIS AOD,the AERONET AOD,and the UVMRP AOD suggests that the UVMRP AOD measurements are suited to be an alternative ground-based validation source for satellite AOD products.The experiments show that the spatial-temporal dependency between the MODIS AOD and the UVMRP AOD is positive in the sense that the MODIS AOD compare more favorably with the UVMRP AOD as the spatial and temporal intervals are increased.However,the analysis shows that the optimal spatial interval for all time windows is defined by an angular subtense of around 1° to 1.25°,while the optimal time window is around 423 to 483 minutes at most spatial intervals.The spatial-temporal approach around 1.25° & 423 minutes shows better agreement than the prevalent strategy of 0.25° & 60 minutes found in other similar investigations.Research Program (UVMRP),Aerosol Robotic Network (AERONET),Moderate Resolution Imaging Spectroradiameters (MODIS),validation,spatial-temporal approach

  4. Factors controlling contrail cirrus optical depth

    Directory of Open Access Journals (Sweden)

    B. Kärcher

    2009-08-01

    Full Text Available Aircraft contrails develop into contrail cirrus by depositional growth and sedimentation of ice particles and horizontal spreading due to wind shear. Factors controlling this development include temperature, ice supersaturation, thickness of ice-supersaturated layers, and vertical gradients in the horizontal wind field. An analytical microphysical cloud model is presented and validated that captures these processes. Many individual contrail cirrus are simulated that develop differently owing to the variability in the controlling factors, resulting in large samples of cloud properties that are statistically analyzed. Contrail cirrus development is studied over the first four hours past formation, similar to the ages of line-shaped contrails that were tracked in satellite imagery on regional scales. On these time scales, contrail cirrus optical depth and microphysical variables exhibit a marked variability, expressed in terms of broad and skewed probability distribution functions. Simulated mean optical depths at a wavelength of 0.55 μm range from 0.05-0.5 and a substantial fraction 20-50% of contrail cirrus stay subvisible (optical depth <0.02, depending on meteorological conditions.

    A detailed analysis based on an observational case study over the continental USA suggests that previous satellite measurements of line-shaped persistent contrails have missed about 89%, 50%, and 11% of contrails with optical depths 0-0.05, 0.05-0.1, and 0.1-0.2, respectively, amounting to 65% of contrail coverage of all optical depths. When comparing observations with simulations and when estimating the contrail cirrus climate impact, not only mean values but also the variability in optical depth and microphysical properties need to be considered.

  5. Diffusive low optical depth particle disks truncated by planets

    CERN Document Server

    Quillen, Alice C

    2008-01-01

    Two dimensional particle disks in proximity to a planet are numerically integrated to determine when a planet in a circular orbit can truncate a particle disk. Collisions are treated by giving each particle a series of velocity perturbations during the integration. We estimate the mass of a planet required to truncate a particle disk as a function of collision rate, related to the disk optical depth, and velocity perturbation size, related to the disk velocity dispersion. We find that for particle disks in the regime estimated for debris disks, a Neptune mass planet is sufficiently massive to truncate the disk. If both the velocity dispersion and the disk optical depth are low (dispersion less than approximately 0.02 in units of circular motion, and optical depth less than 10^-4) then an Earth mass planet suffices. We find that the disk is smooth and axisymmetric unless the velocity perturbation is small and the planet mass is of order or greater than a Neptune mass in which case azimuthal structure is seen n...

  6. Hyperspectral aerosol optical depths from TCAP flights

    Energy Technology Data Exchange (ETDEWEB)

    Shinozuka, Yohei [NASA Ames Research Center (ARC), Moffett Field, Mountain View, CA (United States); Bay Area Environmental REsearch Institute; Johnson, Roy R [NASA Ames Research Center (ARC), Moffett Field, Mountain View, CA (United States); Flynn, Connor J [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Russell, Philip B [NASA Ames Research Center (ARC), Moffett Field, Mountain View, CA (United States); Schmid, Beat [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

    2016-06-01

    4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research), a hyperspectral airborne sunphotometer, acquired aerosol optical depths (AOD) at 1 Hz during all July 2012 flights of the Two Column Aerosol Project (TCAP). Root-mean-square differences from AERONET ground-based observations were 0.01 at wavelengths between 500-1020 nm, 0.02 at 380 and 1640 nm and 0.03 at 440 nm in four clear-sky fly-over events, and similar in ground side-by-side comparisons. Changes in the above-aircraft AOD across 3- km-deep spirals were typically consistent with integrals of coincident in situ (on DOE Gulfstream 1 with 4STAR) and lidar (on NASA B200) extinction measurements within 0.01, 0.03, 0.01, 0.02, 0.02, 0.02 at 355, 450, 532, 550, 700, 1064 nm, respectively, despite atmospheric variations and combined measurement uncertainties. Finer vertical differentials of the 4STAR measurements matched the in situ ambient extinction profile within 14% for one homogeneous column. For the AOD observed between 350-1660 nm, excluding strong

  7. Improved evaluation of optical depth components from Langley plot data

    Science.gov (United States)

    Biggar, S. F.; Gellman, D. I.; Slater, P. N.

    1990-01-01

    A simple, iterative procedure to determine the optical depth components of the extinction optical depth measured by a solar radiometer is presented. Simulated data show that the iterative procedure improves the determination of the exponent of a Junge law particle size distribution. The determination of the optical depth due to aerosol scattering is improved as compared to a method which uses only two points from the extinction data. The iterative method was used to determine spectral optical depth components for June 11-13, 1988 during the MAC III experiment.

  8. Assessment and statistical modeling of the relationship between remotely sensed aerosol optical depth and PM2.5 in the eastern United States.

    Science.gov (United States)

    Paciorek, Christopher J; Liu, Yang

    2012-05-01

    Research in scientific, public health, and policy disciplines relating to the environment increasingly makes use of high-dimensional remote sensing and the output of numerical models in conjunction with traditional observations. Given the public health and resultant public policy implications of the potential health effects of particulate matter (PM*) air pollution, specifically fine PM with an aerodynamic diameter contributing a second likelihood to a Bayesian statistical model, as well as a data source on which we could directly regress. Previous consideration of satellite AOD has largely focused on the National Aeronautics and Space Administration (NASA) moderate resolution imaging spectroradiometer (MODIS) and multiangle imaging spectroradiometer (MISR) instruments. One contribution of our work is more extensive consideration of AOD derived from the Geostationary Operational Environmental Satellite East Aerosol/Smoke Product (GOES GASP) AOD and its relationship with PM2.5. In addition to empirically assessing the spatiotemporal relationship between GASP AOD and PM2.5, we considered new statistical techniques to screen anomalous GOES reflectance measurements and account for background surface reflectance. In our statistical work, we developed a new model structure that allowed for more flexible modeling of the proxy discrepancy than previous statistical efforts have had, with a computationally efficient implementation. We also suggested a diagnostic for assessing the scales of the spatial relationship between the proxy and the spatial process of interest (e.g., PM2.5). In brief, we had little success in improving predictions in our eastern-United States domain for use in epidemiologic applications. We found positive correlations of AOD with PM2.5 over time, but less correlation for long-term averages over space, unless we used calibration that adjusted for large-scale discrepancy between AOD and PM2.5 (see sections 3, 4, and 5). Statistical models that combined

  9. Towards Improved Cirrus Cloud Optical Depths from CALIPSO

    Science.gov (United States)

    Garnier, Anne; Vaughan, Mark; Pelon, Jacques; Winker, David; Trepte, Chip; Young, Stuart

    2016-06-01

    This paper reviews recent advances regarding the retrieval of optical depths of semi-transparent cirrus clouds using synergetic analyses of perfectly collocated observations from the CALIOP lidar and the IIR infrared radiometer aboard the CALIPSO satellite.

  10. Depth profilometry via multiplexed optical high-coherence interferometry

    National Research Council Canada - National Science Library

    Kazemzadeh, Farnoud; Wong, Alexander; Behr, Bradford B; Hajian, Arsen R

    2015-01-01

    ... such as defect detection, corrosion assessment, and dental assessment to name a few. In this study, we investigate the feasibility of depth profilometry using an Multiplexed Optical High-coherence Interferometry MOHI instrument...

  11. Aerosol Optical Depth Value-Added Product Report

    Energy Technology Data Exchange (ETDEWEB)

    Koontz, A; Hodges, G; Barnard, J; Flynn, C; Michalsky, J

    2013-03-17

    This document describes the process applied to retrieve aerosol optical depth (AOD) from multifilter rotating shadowband radiometers (MFRSR) and normal incidence multifilter radiometers (NIMFR) operated at the ARM Climate Research Facility’s ground-based facilities.

  12. Peripheral processing facilitates optic flow-based depth perception

    Directory of Open Access Journals (Sweden)

    Jinglin Li

    2016-10-01

    Full Text Available Flying insects, such as flies or bees, rely on consistent information regarding the depth structure of the environment when performing their flight maneuvers in cluttered natural environments. These behaviors include avoiding collisions, approaching targets or spatial navigation. Insects are thought to obtain depth information visually from the retinal image displacements (`optic flow' during translational ego-motion. Optic flow in the insect visual system is processed by a mechanism that can be modeled by correlation-type elementary motion detectors (EMDs. However, it is still an open question how spatial information can be extracted reliably from the responses of the highly contrast- and pattern-dependent EMD responses, especially if the vast range of light intensities encountered in natural environments is taken into account. This question will be addressed here by systematically modeling the peripheral visual system of flies, including various adaptive mechanisms. Different model variants of the peripheral visual system were stimulated with image sequences that mimic the panoramic visual input during translational ego-motion in various natural environments, and the resulting peripheral signals were fed into an array of EMDs. We characterized the influence of each peripheral computational unit on the representation of spatial information in the EMD responses. Our model simulations reveal that information about the overall light level needs to be eliminated from the EMD input as is accomplished under light-adapted conditions in the insect peripheral visual system. The response characteristics of large monopolar cells resemble that of a band-pass filter, which reduces the contrast dependency of EMDs strongly, effectively enhancing the representation of the nearness of objects and, especially, of their contours. We furthermore show that local brightness adaptation of photoreceptors allows for spatial vision under a wide range of dynamic light

  13. Depth-encoded synthetic aperture optical coherence tomography of biological tissues with extended focal depth.

    Science.gov (United States)

    Mo, Jianhua; de Groot, Mattijs; de Boer, Johannes F

    2015-02-23

    Optical coherence tomography (OCT) has proven to be able to provide three-dimensional (3D) volumetric images of scattering biological tissues for in vivo medical diagnostics. Unlike conventional optical microscopy, its depth-resolving ability (axial resolution) is exclusively determined by the laser source and therefore invariant over the full imaging depth. In contrast, its transverse resolution is determined by the objective's numerical aperture and the wavelength which is only approximately maintained over twice the Rayleigh range. However, the prevailing laser sources for OCT allow image depths of more than 5 mm which is considerably longer than the Rayleigh range. This limits high transverse resolution imaging with OCT. Previously, we reported a novel method to extend the depth-of-focus (DOF) of OCT imaging in Mo et al.Opt. Express 21, 10048 (2013)]. The approach is to create three different optical apertures via pupil segmentation with an annular phase plate. These three optical apertures produce three OCT images from the same sample, which are encoded to different depth positions in a single OCT B-scan. This allows for correcting the defocus-induced curvature of wave front in the pupil so as to improve the focus. As a consequence, the three images originating from those three optical apertures can be used to reconstruct a new image with an extended DOF. In this study, we successfully applied this method for the first time to both an artificial phantom and biological tissues over a four times larger depth range. The results demonstrate a significant DOF improvement, paving the way for 3D high resolution OCT imaging beyond the conventional Rayleigh range.

  14. Depth profilometry via multiplexed optical high-coherence interferometry.

    Directory of Open Access Journals (Sweden)

    Farnoud Kazemzadeh

    Full Text Available Depth Profilometry involves the measurement of the depth profile of objects, and has significant potential for various industrial applications that benefit from non-destructive sub-surface profiling such as defect detection, corrosion assessment, and dental assessment to name a few. In this study, we investigate the feasibility of depth profilometry using an Multiplexed Optical High-coherence Interferometry MOHI instrument. The MOHI instrument utilizes the spatial coherence of a laser and the interferometric properties of light to probe the reflectivity as a function of depth of a sample. The axial and lateral resolutions, as well as imaging depth, are decoupled in the MOHI instrument. The MOHI instrument is capable of multiplexing interferometric measurements into 480 one-dimensional interferograms at a location on the sample and is built with axial and lateral resolutions of 40 μm at a maximum imaging depth of 700 μm. Preliminary results, where a piece of sand-blasted aluminum, an NBK7 glass piece, and an optical phantom were successfully probed using the MOHI instrument to produce depth profiles, demonstrate the feasibility of such an instrument for performing depth profilometry.

  15. Optics for multimode lasers with elongated depth of field

    Science.gov (United States)

    Laskin, Alexander; Laskin, Vadim; Ostrun, Aleksei

    2017-02-01

    Modern multimode high-power lasers are widely used in industrial applications and control of their radiation, especially by focusing, is of great importance. Because of relatively low optical quality, characterized by high values of specifications Beam Parameter Product (BPP) or M², the depth of field by focusing of multimode laser radiation is narrow. At the same time laser technologies like deep penetration welding, cutting of thick metal sheets get benefits from elongated depth of field in area of focal plane, therefore increasing of zone along optical axis with minimized spot size is important technical task. As a solution it is suggested to apply refractive optical systems splitting an initial laser beam into several beamlets, which are focused in different foci separated along optical axis with providing reliable control of energy portions in each separate focus, independently of beam size or mode structure. With the multi-focus optics, the length of zone of material processing along optical axis is defined rather by distances between separate foci, which are determined by optical design of the optics and can be chosen according to requirements of a particular laser technology. Due to stability of the distances between foci there is provided stability of a technology process. This paper describes some design features of refractive multi-focus optics, examples of real implementations and experimental results will be presented as well.

  16. Ultrasound-modulated optical tomography at new depth

    Science.gov (United States)

    Lai, Puxiang; Xu, Xiao

    2012-01-01

    Abstract. Ultrasound-modulated optical tomography (UOT) has the potential to reveal optical contrast deep inside soft biological tissues at an ultrasonically determined spatial resolution. The optical imaging depth reported so far has, however, been limited, which prevents this technique from broader applications. Our latest experimental exploration has pushed UOT to an unprecedented imaging depth. We developed and optimized a UOT system employing a photorefractive crystal-based interferometer. A large aperture optical fiber bundle was used to enhance the efficiencies for diffuse light collection and photorefractive two-wave-mixing. Within the safety limits for both laser illumination and ultrasound modulation, the system has attained the ability to image through a tissue-mimicking phantom of 9.4 cm in thickness, which has never been reached previously by UOT. PMID:22734762

  17. On the microlensing optical depth of the galactic bar

    CERN Document Server

    Mao, S

    1996-01-01

    The microlensing probability (optical depth \\tau) toward the Galactic center carries information about the mass distribution of the Galactic bulge/bar, so can be used to constrain the very uncertain shape parameters of the bar. We find tau depends on the bar mass, radial profile, angle, axis scale lengths and boxyness by a few simple analytical formulae, which shows: (1) \\tau is proportional to the mass of the bar, M. (2) \\tau falls along the minor axis with a strong gradient. (3) An oblate bulge can have more optical depth than a triaxial bar if the bar angle \\alpha>45 degress. (4) \\tau is the largest if the angle \\alpha and the axis ratio y_0/x_0 conspires so that y_0/x_0=\\tan \\alpha. (5) At a fixed field on the minor axis but away from the center, boxy bars with a flat density profile tend to give a larger optical depth than ellipsoidal bars with a steep profile. (6) Main sequence sources should have a significantly lower (20-50\\% lower) optical depth than red clump giants if main sequence stars are not ob...

  18. Depth Compensated Spectral Domain Optical Coherence Tomography via Digital Compensation

    CERN Document Server

    Boroomand, Ameneh; Shafiee, Mohammad Javad; Bizheva, Kostadinka; Wong, Alexander

    2015-01-01

    Spectral Domain Optical Coherence Tomography (SD-OCT) is a well-known imaging modality which allows for \\textit{in-vivo} visualization of the morphology of different biological tissues at cellular level resolutions. The overall SD-OCT imaging quality in terms of axial resolution and Signal-to-Noise Ratio (SNR) degrades with imaging depth, while the lateral resolution degrades with distance from the focal plane. This image quality degradation is due both to the design of the SD-OCT imaging system and the optical properties of the imaged object. Here, we present a novel Depth Compensated SD-OCT (DC-OCT) system that integrates a Depth Compensating Digital Signal Processing (DC-DSP) module to improve the overall imaging quality via digital compensation. The designed DC-DSP module can be integrated to any SD-OCT system and is able to simultaneously compensate for the depth-dependent loss of axial and lateral resolutions, depth-varying SNR, as well as sidelobe artifact for improved imaging quality. The integrated D...

  19. Eight-year Climatology of Dust Optical Depth on Mars

    CERN Document Server

    Montabone, L; Millour, E; Wilson, R J; Lewis, S R; Cantor, B A; Kass, D; Kleinboehl, A; Lemmon, M; Smith, M D; Wolff, M J

    2014-01-01

    We have produced a multiannual climatology of airborne dust from Martian year 24 to 31 using multiple datasets of retrieved or estimated column optical depths. The datasets are based on observations of the Martian atmosphere from April 1999 to July 2013 made by different orbiting instruments: the Thermal Emission Spectrometer (TES) aboard Mars Global Surveyor, the Thermal Emission Imaging System (THEMIS) aboard Mars Odyssey, and the Mars Climate Sounder (MCS) aboard Mars Reconnaissance Orbiter (MRO). The procedure we have adopted consists of gridding the available retrievals of column dust optical depth (CDOD) from TES and THEMIS nadir observations, as well as the estimates of this quantity from MCS limb observations. Our gridding method calculates averages and uncertainties on a regularly spaced, but possibly incomplete, spatio-temporal grid, using an iterative procedure weighted in space, time, and retrieval uncertainty. In order to evaluate strengths and weaknesses of the resulting gridded maps, we validat...

  20. Evaluating UVA aerosol optical depth using a smartphone camera.

    Science.gov (United States)

    Igoe, Damien P; Parisi, Alfio V; Carter, Brad

    2013-01-01

    This research evaluates a smartphone complementary metal oxide semiconductor (CMOS) image sensor's ability to detect and quantify incident solar UVA radiation and subsequently, aerosol optical depth at 340 and 380 nm. Earlier studies revealed that the consumer grade CMOS sensor has inherent UVA sensitivities, despite attenuating effects of the lens. Narrow bandpass and neutral density filters were used to protect the image sensor and to not allow saturation of the solar images produced. Observations were made on clear days, free from clouds. The results of this research demonstrate that there is a definable response to changing solar irradiance and aerosol optical depth can be measured within 5% and 10% error margins at 380 and 340 nm respectively. The greater relative error occurs at lower wavelengths (340 nm) due to increased atmospheric scattering effects, particularly at higher air masses and due to lower signal to noise ratio in the image sensor. The relative error for solar irradiance was under 1% for observations made at 380 nm. The results indicate that the smartphone image sensor, with additional external narrow bandpass and neutral density filters can be used as a field sensor to evaluate solar UVA irradiance and aerosol optical depth. © 2013 The American Society of Photobiology.

  1. Measurement of aerosol optical depth and sub-visual cloud detection using the optical depth sensor (ODS

    Directory of Open Access Journals (Sweden)

    D. Toledo

    2015-09-01

    Full Text Available A small and sophisticated optical depth sensor (ODS has been designed to work in the atmosphere of Earth and Mars. The instrument measures alternatively the diffuse radiation from the sky and the attenuated direct radiation from the sun on the surface. The principal goals of ODS are to retrieve the daily mean aerosol optical depth (AOD and to detect very high and optically thin clouds, crucial parameters in understanding the Martian and Earth meteorology and climatology. The detection of clouds is undertaken at twilight, allowing the detection and characterization of clouds with opacities below 0.03 (sub-visual clouds. In addition, ODS is capable to retrieve the aerosol optical depth during night-time from moonlight measurements. In order to study the performance of ODS under Mars-like conditions as well as to evaluate the retrieval algorithms for terrestrial measurements, ODS was deployed in Ouagadougou (Africa between November 2004 and October 2005, a sahelian region characterized by its high dust aerosol load and the frequent occurrence of Saharan dust storms. The daily average AOD values retrieved by ODS were compared with those provided by a CIMEL Sun-photometer of the AERONET (Aerosol Robotic NETwork network localized at the same location. Results represent a good agreement between both ground-based instruments, with a correlation coefficient of 0.79 for the whole data set and 0.96 considering only the cloud-free days. From the whole dataset, a total of 71 sub-visual cirrus (SVC were detected at twilight with opacities as thin as 1.10−3 and with a maximum of occurrence at altitudes between 14 and 20 km. Although further analysis and comparisons are required, results indicate the potential of ODS measurements to detect sub-visual clouds.

  2. Measurement of aerosol optical depth and sub-visual cloud detection using the optical depth sensor (ODS)

    Science.gov (United States)

    Toledo, D.; Rannou, P.; Pommereau, J.-P.; Sarkissian, A.; Foujols, T.

    2016-02-01

    A small and sophisticated optical depth sensor (ODS) has been designed to work in the atmosphere of Mars. The instrument measures alternatively the diffuse radiation from the sky and the attenuated direct radiation from the Sun on the surface. The principal goals of ODS are to retrieve the daily mean aerosol optical depth (AOD) and to detect very high and optically thin clouds, crucial parameters in understanding the Martian meteorology and climatology. The detection of clouds is undertaken at twilight, allowing the detection and characterization of clouds with opacities below 0.03 (sub-visual clouds). In addition, ODS is capable to retrieve the aerosol optical depth during nighttime from moonlight measurements. Recently, ODS has been selected at the METEO meteorological station on board the ExoMars 2018 Lander. In order to study the performance of ODS under Mars-like conditions as well as to evaluate the retrieval algorithms for terrestrial measurements, ODS was deployed in Ouagadougou (Africa) between November 2004 and October 2005, a Sahelian region characterized by its high dust aerosol load and the frequent occurrence of Saharan dust storms. The daily average AOD values retrieved by ODS were compared with those provided by a CIMEL sunphotometer of the AERONET (Aerosol Robotic NETwork) network localized at the same location. Results represent a good agreement between both ground-based instruments, with a correlation coefficient of 0.77 for the whole data set and 0.94 considering only the cloud-free days. From the whole data set, a total of 71 sub-visual cirrus (SVC) were detected at twilight with opacities as thin as 1.10-3 and with a maximum of occurrence at altitudes between 14 and 20 km. Although further optimizations and comparisons of ODS terrestrial measurements are required, results indicate the potential of these measurements to retrieve the AOD and detect sub-visual clouds.

  3. Constraints on the Optical Depth of Galaxy Groups and Clusters

    Science.gov (United States)

    Flender, Samuel; Nagai, Daisuke; McDonald, Michael

    2017-03-01

    Future data from galaxy redshift surveys, combined with high-resolutions maps of the cosmic microwave background, will enable measurements of the pairwise kinematic Sunyaev–Zel’dovich (kSZ) signal with unprecedented statistical significance. This signal probes the matter-velocity correlation function, scaled by the average optical depth (τ) of the galaxy groups and clusters in the sample, and is thus of fundamental importance for cosmology. However, in order to translate pairwise kSZ measurements into cosmological constraints, external constraints on τ are necessary. In this work, we present a new model for the intracluster medium, which takes into account star formation, feedback, non-thermal pressure, and gas cooling. Our semi-analytic model is computationally efficient and can reproduce results of recent hydrodynamical simulations of galaxy cluster formation. We calibrate the free parameters in the model using recent X-ray measurements of gas density profiles of clusters, and gas masses of groups and clusters. Our observationally calibrated model predicts the average {τ }500 (i.e., the integrated τ within a disk of size R 500) to better than 6% modeling uncertainty (at 95% confidence level). If the remaining uncertainties associated with other astrophysical uncertainties and X-ray selection effects can be better understood, our model for the optical depth should break the degeneracy between optical depth and cluster velocity in the analysis of future pairwise kSZ measurements and improve cosmological constraints with the combination of upcoming galaxy and CMB surveys, including the nature of dark energy, modified gravity, and neutrino mass.

  4. Seasonal variability of aerosol optical depth over Indian subcontinent

    Science.gov (United States)

    Prasad, A.K.; Singh, R.P.; Singh, A.; Kafatos, M.

    2005-01-01

    Ganga basin extends 2000 km E-W and about 400 km N-S and is bounded by Himalayas in the north. This basin is unequivocally found to be affected by high aerosols optical depth (AOD) (>0.6) throughout the year. Himalayas restricts movement of aerosols toward north and as a result dynamic nature of aerosol is seen over the Ganga basin. High AOD in this region has detrimental effects on health of more than 460 million people living in this part of India besides adversely affecting clouds formation, monsoonal rainfall pattern and Normalized Difference Vegetation Index (NDVI). Severe drought events (year 2002) in Ganga basin and unexpected failure of monsoon several times, occurred in different parts of Indian subcontinent. Significant rise in AOD (18.7%) over the central part of basin (Kanpur region) have been found to cause substantial decrease in NDVI (8.1%) since 2000. A negative relationship is observed between AOD and NDVI, magnitude of which differs from region to region. Efforts have been made to determine general distribution of AOD and its dominant departure in recent years spatially using Moderate Resolution Imaging Spectroradiometer (MODIS) data. The seasonal changes in aerosol optical depth over the Indo-Gangetic basin is found to very significant as a result of the increasing dust storm events in recent years. ?? 2005 IEEE.

  5. Microlensing optical depth as a function of source apparent magnitude

    CERN Document Server

    Wood, Alexander

    2007-01-01

    Measurements of the microlensing optical depth, tau, towards the Galactic bulge appear to depend on the method used to obtain them. Those values based on the lensing of red clump giants (RCGs) appear to be significantly lower than those based on the lensing of all stars along the line of sight. This discrepancy is still not understood. Through Monte Carlo simulations, it is found that the discrepancy cannot be explained by a dependance on the flux limits of the two methods. The optical depth is expected to be generally constant as a function of source apparent magnitude for I_0 >~ 13.0, except in the range 13.5 <~ I_0 <~ 15.5. Here many RCGs are detected, causing a significant oscillation in tau. The amplitude of this oscillation is a function of the inclination angle of the Galactic bar, theta_bar, which may thus be constrained. A further constraint comes from a similar dependance of tau with theta_bar: combining the predicted trends with the measured values provides 1-sigma upper limits, which exclude...

  6. Optical depth measurements by shadow-band radiometers and their uncertainties.

    Science.gov (United States)

    Alexandrov, Mikhail D; Kiedron, Peter; Michalsky, Joseph J; Hodges, Gary; Flynn, Connor J; Lacis, Andrew A

    2007-11-20

    Shadow-band radiometers in general, and especially the Multi-Filter Rotating Shadow-band Radiometer (MFRSR), are widely used for atmospheric optical depth measurements. The major programs running MFRSR networks in the United States include the Department of Energy Atmospheric Radiation Measurement (ARM) Program, U.S. Department of Agriculture UV-B Monitoring and Research Program, National Oceanic and Atmospheric Administration Surface Radiation (SURFRAD) Network, and NASA Solar Irradiance Research Network (SIRN). We discuss a number of technical issues specific to shadow-band radiometers and their impact on the optical depth measurements. These problems include instrument tilt and misalignment, as well as some data processing artifacts. Techniques for data evaluation and automatic detection of some of these problems are described.

  7. Parameterization of cirrus optical depth and cloud fraction

    Energy Technology Data Exchange (ETDEWEB)

    Soden, B. [Princeton Univ., Princeton, NJ (United States)

    1995-09-01

    This research illustrates the utility of combining satellite observations and operational analysis for the evaluation of parameterizations. A parameterization based on ice water path (IWP) captures the observed spatial patterns of tropical cirrus optical depth. The strong temperature dependence of cirrus ice water path in both the observations and the parameterization is probably responsible for the good correlation where it exists. Poorer agreement is found in Southern Hemisphere mid-latitudes where the temperature dependence breaks down. Uncertainties in effective radius limit quantitative validation of the parameterization (and its inclusion into GCMs). Also, it is found that monthly mean cloud cover can be predicted within an RMS error of 10% using ECMWF relative humidity corrected by TOVS Upper Troposphere Humidity. 1 ref., 2 figs.

  8. Single atom visibility in STEM optical depth sectioning

    Science.gov (United States)

    Ishikawa, Ryo; Pennycook, Stephen J.; Lupini, Andrew R.; Findlay, Scott D.; Shibata, Naoya; Ikuhara, Yuichi

    2016-10-01

    The continuing development of aberration correctors for the scanning transmission electron microscope (STEM) offers the possibility of locating single atoms in crystals in 3D via optical depth sectioning. The main factors that determine the feasibility of such an approach are visibility and dose requirements. Here, we show how Poisson's statistics can be quantitatively incorporated into STEM image simulations and demonstrate that the 3D location of single cerium atoms in wurtzite-type aluminum nitride is indeed feasible under large-angle illumination conditions with a relatively low dose. We also show that chromatic aberration does not presently represent a limitation provided a cold field emission source is used. These results suggest efforts into improved aberration corrector designs for larger illumination angles that offer significant potential for 3D structure determination of materials.

  9. Constraints on the optical depth of galaxy groups and clusters

    CERN Document Server

    Flender, Samuel; McDonald, Michael

    2016-01-01

    Future data from galaxy redshift surveys, combined with high-resolutions maps of the cosmic microwave background, will enable measurements of the pairwise kinematic Sunyaev-Zel'dovich (kSZ) signal with unprecedented statistical significance. This signal probes the matter-velocity correlation function, scaled by the average optical depth ($\\tau$) of the galaxy groups and clusters in the sample, and is thus of fundamental importance for cosmology. However, in order to translate pairwise kSZ measurements into cosmological constraints, external constraints on $\\tau$ are necessary. In this work, we present a new model for the intra-cluster medium, which takes into account star-formation, feedback, non-thermal pressure, and gas cooling. Our semi-analytic model is computationally efficient and can reproduce results of recent hydrodynamical simulations of galaxy cluster formation. By calibrating the model using recent X-ray measurements of gas density profiles of clusters and $M_{\\mathrm{gas}}-M$ relations of groups ...

  10. Eight-year climatology of dust optical depth on Mars

    Science.gov (United States)

    Montabone, L.; Forget, F.; Millour, E.; Wilson, R. J.; Lewis, S. R.; Cantor, B.; Kass, D.; Kleinböhl, A.; Lemmon, M. T.; Smith, M. D.; Wolff, M. J.

    2015-05-01

    We have produced a multiannual climatology of airborne dust from martian year 24-31 using multiple datasets of retrieved or estimated column optical depths. The datasets are based on observations of the martian atmosphere from April 1999 to July 2013 made by different orbiting instruments: the Thermal Emission Spectrometer (TES) aboard Mars Global Surveyor, the Thermal Emission Imaging System (THEMIS) aboard Mars Odyssey, and the Mars Climate Sounder (MCS) aboard Mars Reconnaissance Orbiter (MRO). The procedure we have adopted consists of gridding the available retrievals of column dust optical depth (CDOD) from TES and THEMIS nadir observations, as well as the estimates of this quantity from MCS limb observations. Our gridding method calculates averages and uncertainties on a regularly spaced spatio-temporal grid, using an iterative procedure that is weighted in space, time, and retrieval quality. The lack of observations at certain times and locations introduces missing grid points in the maps, which therefore may result in irregularly gridded (i.e. incomplete) fields. In order to evaluate the strengths and weaknesses of the resulting gridded maps, we compare with independent observations of CDOD by PanCam cameras and Mini-TES spectrometers aboard the Mars Exploration Rovers "Spirit" and "Opportunity", by the Surface Stereo Imager aboard the Phoenix lander, and by the Compact Reconnaissance Imaging Spectrometer for Mars aboard MRO. We have statistically analyzed the irregularly gridded maps to provide an overview of the dust climatology on Mars over eight years, specifically in relation to its interseasonal and interannual variability, in addition to provide a basis for instrument intercomparison. Finally, we have produced regularly gridded maps of CDOD by spatially interpolating the irregularly gridded maps using a kriging method. These complete maps are used as dust scenarios in the Mars Climate Database (MCD) version 5, and are useful in many modeling

  11. Depth

    NARCIS (Netherlands)

    Koenderink, J.J.; Van Doorn, A.J.; Wagemans, J.

    2011-01-01

    Depth is the feeling of remoteness, or separateness, that accompanies awareness in human modalities like vision and audition. In specific cases depths can be graded on an ordinal scale, or even measured quantitatively on an interval scale. In the case of pictorial vision this is complicated by the f

  12. Depth

    NARCIS (Netherlands)

    Koenderink, J.J.; Van Doorn, A.J.; Wagemans, J.

    2011-01-01

    Depth is the feeling of remoteness, or separateness, that accompanies awareness in human modalities like vision and audition. In specific cases depths can be graded on an ordinal scale, or even measured quantitatively on an interval scale. In the case of pictorial vision this is complicated by the

  13. Aerosol optical depth trend over the Middle East

    Science.gov (United States)

    Klingmueller, Klaus; Pozzer, Andrea; Metzger, Swen; Abdelkader, Mohamed; Stenchikov, Georgiy; Lelieveld, Jos

    2016-04-01

    We use the combined Dark Target/Deep Blue aerosol optical depth (AOD) satellite product of the Moderate-resolution Imaging Spectroradiometer (MODIS) collection 6 to study trends over the Middle East between 2000 and 2015. Our analysis corroborates a previously identified positive AOD trend over large parts of the Middle East during the period 2001 to 2012. By relating the annual AOD to precipitation, soil moisture and surface wind, being the main factors controlling the dust cycle, we identify regions where these attributes are significantly correlated to the AOD over Saudi Arabia, Iraq and Iran. The Fertile Crescent turns out to be of prime importance for the AOD trend over these countries. Using multiple linear regression we show that AOD trend and interannual variability can be attributed to the above mentioned dust cycle parameters, confirming that the AOD increase is predominantly driven by dust. In particular, the positive AOD trend relates to a negative soil moisture trend. This suggests that increasing temperature and decreasing relative humidity in the last decade have promoted soil drying, leading to increased dust emissions and AOD; consequently an AOD increase is expected due to climate change. Based on simulations using the ECHAM/MESSy atmospheric chemistry-climate model (EMAC), we interpret the correlations identified in the observational data in terms of causal relationships.

  14. Retrieving Aerosol Optical Depth over Turbid Coastal Water

    Science.gov (United States)

    Wang, Y.; Wang, J.; Xu, X.; Levy, R. C.

    2016-12-01

    We present an approach to retrieve Aerosol Optical Depth (AOD) over turbid coastal water where operational MODerate Resolution Imaging Spectroradiometer (MODIS) Dark Target (DT) aerosol retrieval algorithm is not applied due to high water leaving radiance. Filling the coastal water AOD gap is significant because 60% of human population lives in the coastal zone. In this study, the Top of Atmosphere (TOA) reflectance at 2.1 μm observed from MODIS is used to retrieve AOD over turbid coastal water through look up table method as water leaving radiance is negligible at the band. During the retrieval process, aerosol model is substituted by the counterpart of the closest pixel retrieved through MODIS ocean DT algorithm. AOD retrievals over turbid coastal water are validated against observations from six AERONET sites at coastal region in one month. The monthly mean AERONET 440-870 nm Ångström exponent ranges from 0.597 to 1.842 for the six sites, thus they can represent from coarse-mode dominated to fine-mode dominated scenes. AOD retrievals in this study are more in agreement with AERONET observations than operational MODIS AOD (over land or clean coastal water) in terms of bias, and root-mean-square error.

  15. Depth-resolved ballistic imaging in a low-depth-of-field optical Kerr gated imaging system

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Yipeng; Tan, Wenjiang, E-mail: tanwenjiang@mail.xjtu.edu.cn; Si, Jinhai; Ren, YuHu; Xu, Shichao; Hou, Xun [Key Laboratory for Physical Electronics and Devices of the Ministry of Education and Shaanxi Key Lab of Information Photonic Technique, School of Electronics and Information Engineering, Xi' an Jiaotong University, Xianning-xilu 28, Xi' an 710049 (China); Tong, Junyi [Departments of Applied Physics, Xi' an University of Technology, Xi' an 710048 (China)

    2016-09-07

    We demonstrate depth-resolved imaging in a ballistic imaging system, in which a heterodyned femtosecond optical Kerr gate is introduced to extract useful imaging photons for detecting an object hidden in turbid media and a compound lens is proposed to ensure both the depth-resolved imaging capability and the long working distance. Two objects of about 15-μm widths hidden in a polystyrene-sphere suspension have been successfully imaged with approximately 600-μm depth resolution. Modulation-transfer-function curves with the object in and away from the object plane have also been measured to confirm the depth-resolved imaging capability of the low-depth-of-field (low-DOF) ballistic imaging system. This imaging approach shows potential for application in research of the internal structure of highly scattering fuel spray.

  16. Intercomparison of desert dust optical depth from satellite measurements

    Directory of Open Access Journals (Sweden)

    E. Carboni

    2012-08-01

    Full Text Available This work provides a comparison of satellite retrievals of Saharan desert dust aerosol optical depth (AOD during a strong dust event through March 2006. In this event, a large dust plume was transported over desert, vegetated, and ocean surfaces. The aim is to identify the differences between current datasets. The satellite instruments considered are AATSR, AIRS, MERIS, MISR, MODIS, OMI, POLDER, and SEVIRI. An interesting aspect is that the different algorithms make use of different instrument characteristics to obtain retrievals over bright surfaces. These include multi-angle approaches (MISR, AATSR, polarisation measurements (POLDER, single-view approaches using solar wavelengths (OMI, MODIS, and the thermal infrared spectral region (SEVIRI, AIRS. Differences between instruments, together with the comparison of different retrieval algorithms applied to measurements from the same instrument, provide a unique insight into the performance and characteristics of the various techniques employed. As well as the intercomparison between different satellite products, the AODs have also been compared to co-located AERONET data. Despite the fact that the agreement between satellite and AERONET AODs is reasonably good for all of the datasets, there are significant differences between them when compared to each other, especially over land. These differences are partially due to differences in the algorithms, such as assumptions about aerosol model and surface properties. However, in this comparison of spatially and temporally averaged data, it is important to note that differences in sampling, related to the actual footprint of each instrument on the heterogeneous aerosol field, cloud identification and the quality control flags of each dataset can be an important issue.

  17. Aerosol optical depth trend over the Middle East

    KAUST Repository

    Klingmüller, Klaus

    2016-04-22

    We use the combined Dark Target/Deep Blue aerosol optical depth (AOD) satellite product of the moderate-resolution imaging spectroradiometer (MODIS) collection 6 to study trends over the Middle East between 2000 and 2015. Our analysis corroborates a previously identified positive AOD trend over large parts of the Middle East during the period 2001 to 2012. We relate the annual AOD to precipitation, soil moisture and surface winds to identify regions where these attributes are directly related to the AOD over Saudi Arabia, Iraq and Iran. Regarding precipitation and soil moisture, a relatively small area in and surrounding Iraq turns out to be of prime importance for the AOD over these countries. Regarding surface wind speed, the African Red Sea coastal area is relevant for the Saudi Arabian AOD. Using multiple linear regression we show that AOD trends and interannual variability can be attributed to soil moisture, precipitation and surface winds, being the main factors controlling the dust cycle. Our results confirm the dust driven AOD trends and variability, supported by a decreasing MODIS-derived Ångström exponent and a decreasing AERONET-derived fine mode fraction that accompany the AOD increase over Saudi Arabia. The positive AOD trend relates to a negative soil moisture trend. As a lower soil moisture translates into enhanced dust emissions, it is not needed to assume growing anthropogenic aerosol and aerosol precursor emissions to explain the observations. Instead, our results suggest that increasing temperature and decreasing relative humidity in the last decade have promoted soil drying, leading to increased dust emissions and AOD; consequently an AOD increase is expected due to climate change.

  18. Deriving atmospheric visibility from satellite retrieved aerosol optical depth

    Science.gov (United States)

    Riffler, M.; Schneider, Ch.; Popp, Ch.; Wunderle, S.

    2009-04-01

    Atmospheric visibility is a measure that reflects different physical and chemical properties of the atmosphere. In general, poor visibility conditions come along with risks for transportation (e.g. road traffic, aviation) and can negatively impact human health since visibility impairment often implies the presence of atmospheric pollution. Ambient pollutants, particulate matter, and few gaseous species decrease the perceptibility of distant objects. Common estimations of this parameter are usually based on human observations or devices that measure the transmittance of light from an artificial light source over a short distance. Such measurements are mainly performed at airports and some meteorological stations. A major disadvantage of these observations is the gap between the measurements, leaving large areas without any information. As aerosols are one of the most important factors influencing atmospheric visibility in the visible range, the knowledge of their spatial distribution can be used to infer visibility with the so called Koschmieder equation, which relates visibility and atmospheric extinction. In this study, we evaluate the applicability of satellite aerosol optical depth (AOD) products from the Advanced Very High Resolution Radiometer (AVHRR) and Moderate Resolution Imaging Spectroradiometer (MODIS) to infer atmospheric visibility on large spatial scale. First results applying AOD values scaled with the planetary boundary layer height are promising. For the comparison we use a full automated and objective procedure for the estimation of atmospheric visibility with the help of a digital panorama camera serving as ground truth. To further investigate the relation between the vertical measure of AOD and the horizontal visibility data from the Aerosol Robotic Network (AERONET) site Laegeren (Switzerland), where the digital camera is mounted, are included as well. Finally, the derived visibility maps are compared with synoptical observations in central

  19. MODIS Retrieval of Aerosol Optical Depth over Turbid Coastal Water

    Directory of Open Access Journals (Sweden)

    Yi Wang

    2017-06-01

    Full Text Available We present a new approach to retrieve Aerosol Optical Depth (AOD using the Moderate Resolution Imaging Spectroradiometer (MODIS over the turbid coastal water. This approach supplements the operational Dark Target (DT aerosol retrieval algorithm that currently does not conduct AOD retrieval in shallow waters that have visible sediments or sea-floor (i.e., Class 2 waters. Over the global coastal water regions in cloud-free conditions, coastal screening leads to ~20% unavailability of AOD retrievals. Here, we refine the MODIS DT algorithm by considering that water-leaving radiance at 2.1 μm to be negligible regardless of water turbidity, and therefore the 2.1 μm reflectance at the top of the atmosphere is sensitive to both change of fine-mode and coarse-mode AODs. By assuming that the aerosol single scattering properties over coastal turbid water are similar to those over the adjacent open-ocean pixels, the new algorithm can derive AOD over these shallow waters. The test algorithm yields ~18% more MODIS-AERONET collocated pairs for six AERONET stations in the coastal water regions. Furthermore, comparison of the new retrieval with these AERONET observations show that the new AOD retrievals have equivalent or better accuracy than those retrieved by the MODIS operational algorithm’s over coastal land and non-turbid coastal water product. Combining the new retrievals with the existing MODIS operational retrievals yields an overall improvement of AOD over those coastal water regions. Most importantly, this refinement extends the spatial and temporal coverage of MODIS AOD retrievals over the coastal regions where 60% of human population resides. This expanded coverage is crucial for better understanding of impact of anthropogenic aerosol particles on coastal air quality and climate.

  20. Spatial Correlations of Aerosol Optical Depth Over Land

    Science.gov (United States)

    Radkevich, A. V.; Trishchenko, A. P.

    2009-05-01

    The accurate atmospheric correction of historical satellite long-term data is required to make them suitable for climate change application. This is essential to properly identify the impacts caused by changing surface properties, such as vegetation, soil and snow cover, rather than atmospheric effects, cloud contamination and artefacts. The correction of satellite data over land for aerosol effect constitutes the most challenging part of the processing. While a good progress in aerosol retrievals has been achieved in recent years using the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Multi-angle Imaging Spectroradiometer (MISR), the aerosol properties and their associated impact on atmospheric correction for historical data over land from the Advanced Very High Resolution Radiometer (AVHRR) onboard NOAA satellites for pre-MODIS period is still not adequately addressed. It seems promising to develop the AVHRR atmospheric correction algorithm based on the synthesis of aerosol retrievals over dark targets and optimum interpolation technique based on aerosol spatio-temporal statistics. The implementation of this approach requires the knowledge of aerosol spatial correlation function. The estimates of aerosol optical depth (AOD) spatial correlation function were obtained in this study using different data sources: MODIS level 2 and level 3 aerosol products, daily averages of ground sun photometer aerosol retrievals from Aerosol Robotic Network (AERONET) and the global chemistry and aerosol atmospheric transport model results from NASA's GOCART. The AOD correlation properties obtained from different types of MODIS aerosol products were found in reasonably good agreement with each other. The AOD correlation radius for different types of MODIS data varied from 418 km to 900 km. The AOD correlation radius obtained from AERONET data was found to be close to 500km. Substantial differences were detected between AOD spatial correlation function derived from

  1. Aerosol optical depths and their contributing sources in Taiwan

    Science.gov (United States)

    Chan, K. L.; Chan, K. L.

    2017-01-01

    In this paper, we present a quantitative investigation of the contributions of different aerosols to the aerosol optical depths (AODs) in Taiwan using a global chemical transport model (GEOS-Chem) and remote sensing measurements. The study focus is on the period from June 2012 to October 2013. Five different types of aerosols are investigated: sea salt, dust, sulfate, organic carbon and black carbon. Three of these aerosols, namely sulfate, organic carbon and black carbon, have significant anthropogenic sources. Model simulation results were compared with both ground based sun photometer measurements and MODerate resolution Imaging Spectroradiometer (MODIS) satellite observations. The model data shows good agreement with satellite observations (R = 0.72) and moderate correlation with sun photometer measurements (R = 0.52). Simulation results show the anthropogenic aerosols contribute ∼65% to the total AOD in Taipei, while natural originated aerosols only show a minor impact (∼35%). Among all the aerosols, sulfate is the dominating species, contributing 62.4% to the annual average total AOD. Organic carbon and black carbons respectively contribute 7.3% and 1.5% to the annual averaged total AOD. The annual average contributions of sea salt and dust aerosols to the total AOD are 26.4% and 2.4%, respectively. A sensitivity study was performed to identify the contributions of anthropogenic aerosol sources in each region to the AODs in Taipei. North-East Asia was identified as the major contributing source region of anthropogenic aerosols to Taipei, accounting for more than 50% of total sulfate, 32% of total organic carbon and 51% of total black carbon aerosols. South-East Asia is the second largest contributing source region, contributing 35%, 24% and 34% of total sulfate, organic carbon and black carbon aerosols, respectively. The aerosols from continents other than Asia only show minor impacts to the aerosol load in Taipei. In addition, a case study of a biomass

  2. Design of Optical Systems with Extended Depth of Field: An Educational Approach to Wavefront Coding Techniques

    Science.gov (United States)

    Ferran, C.; Bosch, S.; Carnicer, A.

    2012-01-01

    A practical activity designed to introduce wavefront coding techniques as a method to extend the depth of field in optical systems is presented. The activity is suitable for advanced undergraduate students since it combines different topics in optical engineering such as optical system design, aberration theory, Fourier optics, and digital image…

  3. The matter power spectrum from the Ly alpha forest : an optical depth estimate

    NARCIS (Netherlands)

    Zaroubi, S; Nusser, A; Haehnelt, M; Kim, TS; Viel, M.

    2006-01-01

    We measure the matter power spectrum from 31 Ly alpha spectra spanning the redshift range of 1.6-3.6. The optical depth, tau, for Ly alpha absorption of the intergalactic medium is obtained from the flux using the inversion method of Nusser & Haehnelt. The optical depth is converted to density by us

  4. Estimates of the aerosol optical depth over Pretoria using the CSIR mobile lidar

    CSIR Research Space (South Africa)

    Shikwambana, L

    2013-09-01

    Full Text Available This study shows the estimates of aerosol optical depth measured over Pretoria, South Africa, using the CSIR-NLC mobile LIDAR. The measurements are also compared with observations from the Level-3 MODIS aerosol optical depth (AOD) data...

  5. Aerosol Optical Depth over Africa retrieved from AATSR

    Science.gov (United States)

    Sogacheva, Larisa; de Leeuw, Gerrit; Kolmonen, Pekka; Sundström, Anu-Maija; Rodriques, Edith

    2010-05-01

    Aerosols produced over the African continent have important consequences for climate. In particular, large amounts of desert dust are produced over the Sahara and transported across the North Atlantic where desert dust deposition influences the eco system by iron fertilization, and further North over Europe with outbreaks as far as Scandinavia. Biomass burning occurs in most of the African continent south of the Sahara and causes a net positive radiating forcing resulting in local warming of the atmosphere layers. These effects have been studied during large field campaigns. Satellites can systematically provide information on aerosols over a large area such as Africa and beyond. To this end, we retrieved the Aerosol Optical Depth (AOD) at three wavelengths (555nm, 670nm, and 1600nm) over Africa from the reflectance measured at the top of the atmosphere by the AATSR (Advances Along Track Scanning Radiometer) flying on ENVISAT, for one year (1 May 2008 to 30 April 2009) to obtain information on the seasonal and spatial behaviour of the AOD, episodes of high AOD events and connect the retrieved AOD with the ground-based aerosol measurements. The AOD retrieval algorithm, which is applied to cloud-free pixels over land, is based on the comparison of the measured and modeled reflectance at the top of the atmosphere (TOA). The algorithm uses look-up-tables (LUTs) to compute the modeled TOA reflectance. For AOD retrieval, an aerosol in the atmosphere is assumed to be an external mixture of fine and coarse mode particles. The two aerosol types are mixed such that the spectral behavior of the reflectance due to aerosol best fits the measurements. Comparison with AERONET (Aerosol Roboric NETwork), which is a network of ground-based sun photometers which measure atmospheric aerosol properties, shows good agreement but with some overestimation of the AATSR retrieved AOD. Different aerosol models have been used to improve the comparison. The lack of AERONET stations in Africa

  6. Characteristics of spectral aerosol optical depths over India during ICARB

    Indian Academy of Sciences (India)

    S Naseema Beegum; K Krishna Moorthy; Vijayakumar S Nair; S Suresh Babu; S K Satheesh; V Vinoj; R Ramakrishna Reddy; K Rama Gopal; K V S Badarinath; K Niranjan; Santosh Kumar Pandey; M Behera; A Jeyaram; P K Bhuyan; M M Gogoi; Sacchidanand Singh; P Pant; U C Dumka; Yogesh Kant; J C Kuniyal; Darshan Singh

    2008-07-01

    Spectral aerosol optical depth (AOD) measurements, carried out regularly from a network of observatories spread over the Indian mainland and adjoining islands in the Bay of Bengal and Arabian Sea, are used to examine the spatio-temporal and spectral variations during the period of ICARB (March to May 2006). The AODs and the derived Ångström parameters showed considerable variations across India during the above period. While at the southern peninsular stations the AODs decreased towards May after a peak in April, in the north Indian regions they increased continuously from March to May. The Ångström coefficients suggested enhanced coarse mode loading in the north Indian regions, compared to southern India. Nevertheless, as months progressed from March to May, the dominance of coarse mode aerosols increased in the columnar aerosol size spectrum over the entire Indian mainland, maintaining the regional distinctiveness. Compared to the above, the island stations showed considerably low AODs, so too the northeastern station Dibrugarh, indicating the prevalence of cleaner environment. Long-range transport of aerosols from the adjoining regions leads to remarkable changes in the magnitude of the AODs and their wavelength dependencies during March to May. HYSPLIT back-trajectory analysis shows that enhanced long-range transport of aerosols, particularly from the west Asia and northwest coastal India, contributed significantly to the enhancement of AOD and in the flattening of the spectra over entire regions; if it is the peninsular regions and the island Minicoy are more impacted in April, the north Indian regions including the Indo Gangetic Plain get affected the most during May, with the AODs soaring as high as 1.0 at 500 nm. Over the islands, the Ångström exponent () remained significantly lower (∼1) over the Arabian Sea compared to Bay of Bengal (BoB) (∼1.4) as revealed by the data respectively from Minicoy and Port Blair. Occurrences of higher values of

  7. SPATIAL INTERPOLATION OF AEROSOL OPTICAL DEPTH POLLUTION: COMPARISON OF METHODS FOR THE DEVELOPMENT OF AEROSOL DISTRIBUTION

    Directory of Open Access Journals (Sweden)

    S. Safarpour

    2017-09-01

    Full Text Available Air pollution is a growing problem arising from domestic heating, high density of vehicle traffic, electricity production, and expanding commercial and industrial activities, all increasing in parallel with urban population. Monitoring and forecasting of air quality parameters are important due to health impact. One widely available metric of aerosol abundance is the aerosol optical depth (AOD. The AOD is the integrated light extinction coefficient over a vertical atmospheric column of unit cross section, which represents the extent to which the aerosols in that vertical profile prevent the transmission of light by absorption or scattering. Seasonal aerosol optical depth (AOD values at 550 nm derived from the Moderate Resolution Imaging Spectroradiometer (MODIS sensor onboard NASA’s Terra satellites, for the 10 years period of 2000 - 2010 were used to test 7 different spatial interpolation methods in the present study. The accuracy of estimations was assessed through visual analysis as well as independent validation based on basic statistics, such as root mean square error (RMSE and correlation coefficient. Based on the RMSE and R values of predictions made using measured values from 2000 to 2010, Radial Basis Functions (RBFs yielded the best results for spring, summer and winter and ordinary kriging yielded the best results for fall.

  8. Validation of MODIS aerosol optical depth over the Mediterranean Coast

    Science.gov (United States)

    Díaz-Martínez, J. Vicente; Segura, Sara; Estellés, Víctor; Utrillas, M. Pilar; Martínez-Lozano, J. Antonio

    2013-04-01

    Atmospheric aerosols, due to their high spatial and temporal variability, are considered one of the largest sources of uncertainty in different processes affecting visibility, air quality, human health, and climate. Among their effects on climate, they play an important role in the energy balance of the Earth. On one hand they have a direct effect by scattering and absorbing solar radiation; on the other, they also have an impact in precipitation, modifying clouds, or affecting air quality. The application of remote sensing techniques to investigate aerosol effects on climate has advanced significatively over last years. In this work, the products employed have been obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS). MODIS is a sensor located onboard both Earth Observing Systems (EOS) Terra and Aqua satellites, which provide almost complete global coverage every day. These satellites have been acquiring data since early 2000 (Terra) and mid 2002 (Aqua) and offer different products for land, ocean and atmosphere. Atmospheric aerosol products are presented as level 2 products with a pixel size of 10 x 10 km2 in nadir. MODIS aerosol optical depth (AOD) is retrieved by different algorithms depending on the pixel surface, distinguishing between land and ocean. For its validation, ground based sunphotometer data from AERONET (Aerosol Robotic Network) has been employed. AERONET is an international operative network of Cimel CE318 sky-sunphotometers that provides the most extensive aerosol data base globally available of ground-based measurements. The ground sunphotometric technique is considered the most accurate for the retrieval of radiative properties of aerosols in the atmospheric column. In this study we present a validation of MODIS C051 AOD employing AERONET measurements over different Mediterranean coastal sites centered over an area of 50 x 50 km2, which includes both pixels over land and ocean. The validation is done comparing spatial

  9. United assembly algorithm for optical burst switching

    Institute of Scientific and Technical Information of China (English)

    Jinhui Yu(于金辉); Yijun Yang(杨教军); Yuehua Chen(陈月华); Ge Fan(范戈)

    2003-01-01

    Optical burst switching (OBS) is a promising optical switching technology. The burst assembly algorithm controls burst assembly, which significantly impacts performance of OBS network. This paper provides a new assembly algorithm, united assembly algorithm, which has more practicability than conventional algorithms. In addition, some factors impacting selections of parameters of this algorithm are discussed and the performance of this algorithm is studied by computer simulation.

  10. Depth Profilometry via Multiplexed Optical High-Coherence Interferometry: e0121066

    National Research Council Canada - National Science Library

    Farnoud Kazemzadeh; Alexander Wong; Bradford B Behr; Arsen R Hajian

    2015-01-01

    ... such as defect detection, corrosion assessment, and dental assessment to name a few. In this study, we investigate the feasibility of depth profilometry using an Multiplexed Optical High-coherence Interferometry MOHI instrument...

  11. Retrieval of the optical depth using an all-sky CCD camera.

    Science.gov (United States)

    Olmo, Francisco J; Cazorla, Alberto; Alados-Arboledas, Lucas; López-Alvarez, Miguel A; Hernández-Andrés, Javier; Romero, Javier

    2008-12-01

    A new method is presented for retrieval of the aerosol and cloud optical depth using a CCD camera equipped with a fish-eye lens (all-sky imager system). In a first step, the proposed method retrieves the spectral radiance from sky images acquired by the all-sky imager system using a linear pseudoinverse algorithm. Then, the aerosol or cloud optical depth at 500 nm is obtained as that which minimizes the residuals between the zenith spectral radiance retrieved from the sky images and that estimated by the radiative transfer code. The method is tested under extreme situations including the presence of nonspherical aerosol particles. The comparison of optical depths derived from the all-sky imager with those retrieved with a sunphotometer operated side by side shows differences similar to the nominal error claimed in the aerosol optical depth retrievals from sunphotometer networks.

  12. Optical and thermal depth profile reconstructions of inhomogeneous photopolymerization in dental resins using photothermal waves

    Science.gov (United States)

    Martínez-Torres, P.; Mandelis, A.; Alvarado-Gil, J. J.

    2010-09-01

    Photopolymerization is a process that depends, among other factors, on the optical properties of polymerized materials. In turn, this process affects longitudinal light transport in these materials, thereby altering their optical absorption coefficient which is thus expected to exhibit depth dependence. Furthermore, polymerization affects the thermal properties of these materials. A robust theoretical approach to the study of the depth-dependent optical absorption coefficient, β(x ), and thermal diffusivity, α(x ), in materials exhibiting depth profiles of these parameters has been developed through the photothermal inverse problem based on the concept of the thermal-harmonic oscillator. Using this concept in the frequency-domain nonhomogeneous photothermal-wave boundary-value problem, the simultaneous reconstruction of arbitrary simultaneous optical and thermal depth profiles was achieved using a multiparameter fitting method to the experimental amplitude and phase. As a first application of the theory to partially polymerized Alert Composite (shade A3) dental resin, with curing induced by a blue light-emitting diode, the β(x ) and α(x ) depth profiles were reconstructed from photothermal radiometric frequency-scanned data. A strong anticorrelation of these two depth profiles was observed and was interpreted in terms of photochemical processes occurring during the optical (photocuring) creation of long polymeric chains in the resin. The photothermally reconstructed depth profiles may have implications for the optimization of blue light curing methods using such resins in dental clinical practice.

  13. Satellite and Ship-based Lidar Measurements of Optical Depth during EOPACE

    NARCIS (Netherlands)

    Jordan, M.; Wash, C.; Durkee, P.H.; Veefkind, J.P.; Leeuw, G. de; Smith, M.H.; Hill, M.K.

    1998-01-01

    Knowledge of the coastal MABL for the entire battlespace is critical for modern Navy operations. To support modern weapon and sensor systems, quantitative assessment of a number of MABL properties are needed. They include: optical depth, boundary layer depth, sea surface temperature, and surface lay

  14. Hyperscale Analysis of River Morphology Though Optical Remote Mapping of Water Depths

    Science.gov (United States)

    Fonstad, M. A.

    2007-12-01

    The science of in-channel river processes and forms has profited enormously from the introduction of specialized remote sensing tools such as LiDAR and hyperspectral imaging during the past decade. However, the cost and lack of historical data make them a less than ideal choice for many geomorphic questions. As an alternative to high-performance technology, a new analytical technique applied to older color aerial imagery allows extraction of the three-dimensional river environment over enormous distances. In clearwater rivers, some light often reaches the riverbed and returns to the surface, providing optical information about different components of the physical habitat structure. The HAB-2 transform combines the Beer-Lambert law of light absorption with hydrodynamic rules to allow the estimation of river depth at each image pixel, and it allows separation of the depth effect from the remaining image information. The widespread availability of CIR digital orthophotoquads across much of the United States allows the use of HAB approaches to extract three dimensional data for large area riverscapes at scales from about a meter to that of the entire watershed. The rapid and widespread utility of image-based river DTMs allows hitherto unparalleled investigation of geomorphic structures. As one example of this utility, HAB- calibrated high-resolution imagery of the Nueces River watershed, Texas, shows systematic deviations from the classic theory of the downstream hydraulic geometry as well as an unprecedented level of randomness at most scales.

  15. Chromatic error correction of diffractive optical elements at minimum etch depths

    Science.gov (United States)

    Barth, Jochen; Gühne, Tobias

    2014-09-01

    The integration of diffractive optical elements (DOE) into an optical design opens up new possibilities for applications in sensing and illumination. If the resulting optics is used in a larger spectral range we must correct not only the chromatic error of the conventional, refractive, part of the design but also of the DOE. We present a simple but effective strategy to select substrates which allow the minimum etch depths for the DOEs. The selection depends on both the refractive index and the dispersion.

  16. Optical probe design with extended depth-of-focus for optical coherence microscopy and optical coherence tomography

    Science.gov (United States)

    Lee, Seungwan; Choi, Minseog; Lee, Eunsung; Jung, Kyu-Dong; Chang, Jong-hyeon; Kim, Woonbae

    2013-03-01

    In this report, Optical probe system for modality, optical coherence tomography (OCT) and optical coherence microscope (OCM), is presented. In order to control the back focal length from 2.2 mm to 27 mm, optical probe is designed using two liquid lenses and several lenses. The narrow depth of focus (DOF) in microscope is extended by phase filter such as cubic filter. The filter is modified so that DOF is extended only In the OCM mode. The section for the extended DOF of probe is controlled by iris. Therefore in OCT mode, the phase filter does not affect on the DOF of lens. In OCM mode, the Gaussian light and modified light will affect the DOF. The probe dimension is less than 4 mm diameter and less than 60 mm long. The scan range of system is 0.88 mm wide, 1 mm deep in the OCT and 510 μm wide, 1 mm deep in the OCM mode. The lens curvature and iris aperture are operated by digital microelectrofluidic lens and iris.

  17. Estimating vegetation optical depth using L-band passive microwave airborne data in HiWATER

    Science.gov (United States)

    Wang, Qi; Chai, Linna

    2014-11-01

    In this study, a relationship between polarization differences of soil emissivity at different incidence angles was constructed from a large quantity of simulated soil emissivity based on the Advanced Integrated Emission Model (AIEM) input parameters include: a frequency of 1.4 GHz (L-band), incident angles varying from 1°to 60° at a 1° interval, a wide range of soil moisture content and land surface roughness parameters. Then, we used this relationship and the ω-τ zero-order radiation transfer model to develop an inversion method of low vegetation optical depth at L-band, this work were under the assumption that there was no significant polarization difference between the vegetation signals. Based on this inversion method of low vegetation optical depth, we used the land surface passive microwave brightness temperature of Heihe Watershed obtained by airborne Polarimetric L-band Multibeam Radiometer (PLMR) in 2012 Heihe Watershed Allied Telemetry Experimental Research (HiWATER) to retrieve the corn optical depth in the flight areas, then the results were compared with the measured corn LAI. Results show that the retrieved corn optical depths were consisted with the measured LAI of corn. It proved that the corn optical depth inversion method proposed in this study was feasible. Moreover, the method was promising to apply to the satellite observations.

  18. Retrieval of cloud optical depth from the cloud modification factor (CMF) for overcast skies

    Science.gov (United States)

    Serrano, David; José Marín, María; Esteve, Anna R.; Estellés, Victor; Núñez, Manuel; Utrillas, M. Pilar; Martínez-Lozano, José A.

    2014-05-01

    Clouds generally produce an attenuating effect over solar radiation (up to 80%) that depends, among other characteristics, on the type of the cloud, its optical depth and its distribution in the sky. To analyse the dependence of the atmospheric transmissivity of solar radiation with the cloud optical depth for overcast skies (τ), both in the range of ultraviolet erythemal radiation (UVER) and in the broadband, we have used the cloud optical depths obtained by a minimization process from the irradiation surface measurements. Measurements in the UVER range were obtained by means of a UVB-1 broadband radiometer by Yankee Environmental Systems, with a spectral range of 280 - 400 nm, and in the broadband with a CM-6 pyranometer by Kipp & Zonen, with a spectral range of 310 - 2800 nm. The cloud cover was obtained from cloud sky images, which were acquired at 5 minute intervals using a sky camera by SONA Sieltec Canarias S.L. A CE318 sunphotometer by CIMEL was used in this study for monitoring aerosol optical properties in a vertical column of the atmosphere. Modelled cloud optical depths obtained by the minimization process are iterated until modelled irradiances are equal to or less than 2 percent of the measured value. This study presents the relationship between the cloud optical depths, obtained by the previous minimization method, and an important atmospheric transmissivity factor, the cloud modification factor (CMF). CMF, defined as the ratio between the measured radiation in overcast sky conditions and the calculated radiation for a cloudless sky, provides a first distinction of cloud radiative effects. CMF can be evaluated for different spectral intervals, ultraviolet as well as broadband. For the estimation of CMF, we have calculated cloudless sky irradiance in two different ways: first in a simple way using the empirical expression given by Madronich's equation for UVER range and secondly using the SBDART model for both the UVER and the broadband. Data from

  19. Mapping Curie temperature depth in the western United States with a fractal model for crustal magnetization

    Science.gov (United States)

    Bouligand, C.; Glen, J.M.G.; Blakely, R.J.

    2009-01-01

    We have revisited the problem of mapping depth to the Curie temperature isotherm from magnetic anomalies in an attempt to provide a measure of crustal temperatures in the western United States. Such methods are based on the estimation of the depth to the bottom of magnetic sources, which is assumed to correspond to the temperature at which rocks lose their spontaneous magnetization. In this study, we test and apply a method based on the spectral analysis of magnetic anomalies. Early spectral analysis methods assumed that crustal magnetization is a completely uncorrelated function of position. Our method incorporates a more realistic representation where magnetization has a fractal distribution defined by three independent parameters: the depths to the top and bottom of magnetic sources and a fractal parameter related to the geology. The predictions of this model are compatible with radial power spectra obtained from aeromagnetic data in the western United States. Model parameters are mapped by estimating their value within a sliding window swept over the study area. The method works well on synthetic data sets when one of the three parameters is specified in advance. The application of this method to western United States magnetic compilations, assuming a constant fractal parameter, allowed us to detect robust long-wavelength variations in the depth to the bottom of magnetic sources. Depending on the geologic and geophysical context, these features may result from variations in depth to the Curie temperature isotherm, depth to the mantle, depth to the base of volcanic rocks, or geologic settings that affect the value of the fractal parameter. Depth to the bottom of magnetic sources shows several features correlated with prominent heat flow anomalies. It also shows some features absent in the map of heat flow. Independent geophysical and geologic data sets are examined to determine their origin, thereby providing new insights on the thermal and geologic crustal

  20. Measurement of optical penetration depth and refractive index of human tissue

    Institute of Scientific and Technical Information of China (English)

    Shusen Xie(谢树森); Hui Li(李晖); Buhong Li(李步洪)

    2003-01-01

    Experimental techniques for measurement of optical penetration depth and refractive index of human tissue are presented, respectively. Optical penetration depth can be obtained from the measurement of the relative fluence-depth distribution inside the target tissue. The depth of normal and carcinomatous human lung tissues irradiated with the wavelengths of 406.7, 632.8 and 674.4 nm in vitro are respectively determined. In addition, a novel simple method based on total internal reflection for measuring the refractive index of biotissue in vivo is developed, and the refractive indices of skin from people of different age, sex and skin color are measured. Their refractive indices are almost same and the average is 1.533.

  1. Increasing the penetration depth for ultrafast laser tissue ablation using glycerol based optical clearing

    Science.gov (United States)

    Gabay, Ilan; Subramanian, Kaushik G.; Martin, Chris; Yildirim, Murat; Tuchin, Valery V.; Ben-Yakar, Adela

    2016-03-01

    Background: Deep tissue ablation is the next challenge in ultrafast laser microsurgery. By focusing ultrafast pulses below the tissue surface one can create an ablation void confined to the focal volume. However, as the ablation depth increases in a scattering tissue, increase in the required power can trigger undesired nonlinear phenomena out of focus that restricts our ability to ablate beyond a maximum ablation depth of few scattering lengths. Optical clearing (OC) might reduce the intensity and increase the maximal ablation depth by lowering the refractive index mismatch, and therefore reducing scattering. Some efforts to ablate deeper showed out of focus damage, while others used brutal mechanical methods for clearing. Our clinical goal is to create voids in the scarred vocal folds and inject a biomaterial to bring back the tissue elasticity and restore phonation. Materials and methods: Fresh porcine vocal folds were excised and applied a biocompatible OC agent (75% glycerol). Collimated transmittance was monitored. The tissue was optically cleared and put under the microscope for ablation threshold measurements at different depths. Results: The time after which the tissue was optically cleared was roughly two hours. Fitting the threshold measurements to an exponential decay graph indicated that the scattering length of the tissue increased to 83+/-16 μm, which is more than doubling the known scattering length for normal tissue. Conclusion: Optical clearing with Glycerol increases the tissue scattering length and therefore reduces the energy for ablation and increases the maximal ablation depth. This technique can potentially improve clinical microsurgery.

  2. A disposable flexible skin patch for clinical optical perfusion monitoring at multiple depths

    Science.gov (United States)

    Farkas, Dana L.; Kolodziejski, Noah J.; Stapels, Christopher J.; McAdams, Daniel R.; Fernandez, Daniel E.; Podolsky, Matthew J.; Christian, James F.; Ward, Brent B.; Vartarian, Mark; Feinberg, Stephen E.; Lee, Seung Yup; Parikh, Urmi; Mycek, Mary-Ann; Joyner, Michael J.; Johnson, Christopher P.; Paradis, Norman A.

    2016-03-01

    Stable, relative localization of source and detection fibers is necessary for clinical implementation of quantitative optical perfusion monitoring methods such as diffuse correlation spectroscopy (DCS) and diffuse reflectance spectroscopy (DRS). A flexible and compact device design is presented as a platform for simultaneous monitoring of perfusion at a range of depths, enabled by precise location of optical fibers in a robust and secure adhesive patch. We will discuss preliminary data collected on human subjects in a lower body negative pressure model for hypovolemic shock. These data indicate that this method facilitates simple and stable simultaneous monitoring of perfusion at multiple depths and within multiple physiological compartments.

  3. Underwater Depth and Temperature Sensing Based on Fiber Optic Technology for Marine and Fresh Water Applications

    Directory of Open Access Journals (Sweden)

    Dinesh Babu Duraibabu

    2017-05-01

    Full Text Available Oceanic conditions play an important role in determining the effects of climate change and these effects can be monitored through the changes in the physical properties of sea water. In fact, Oceanographers use various probes for measuring the properties within the water column. CTDs (Conductivity, Temperature and Depth provide profiles of physical and chemical parameters of the water column. A CTD device consists of Conductivity (C, Temperature (T and Depth (D probes to monitor the water column changes with respect to relative depth. An optical fibre-based point sensor used as a combined pressure (depth and temperature sensor and the sensor system are described. Measurements accruing from underwater trials of a miniature sensor for pressure (depth and temperature in the ocean and in fresh water are reported. The sensor exhibits excellent stability and its performance is shown to be comparable with the Sea-Bird Scientific commercial sensor: SBE9Plus.

  4. Underwater Depth and Temperature Sensing Based on Fiber Optic Technology for Marine and Fresh Water Applications.

    Science.gov (United States)

    Duraibabu, Dinesh Babu; Leen, Gabriel; Toal, Daniel; Newe, Thomas; Lewis, Elfed; Dooly, Gerard

    2017-05-27

    Oceanic conditions play an important role in determining the effects of climate change and these effects can be monitored through the changes in the physical properties of sea water. In fact, Oceanographers use various probes for measuring the properties within the water column. CTDs (Conductivity, Temperature and Depth) provide profiles of physical and chemical parameters of the water column. A CTD device consists of Conductivity (C), Temperature (T) and Depth (D) probes to monitor the water column changes with respect to relative depth. An optical fibre-based point sensor used as a combined pressure (depth) and temperature sensor and the sensor system are described. Measurements accruing from underwater trials of a miniature sensor for pressure (depth) and temperature in the ocean and in fresh water are reported. The sensor exhibits excellent stability and its performance is shown to be comparable with the Sea-Bird Scientific commercial sensor: SBE9Plus.

  5. Long-wavelength optical coherence tomography at 1.7 µm for enhanced imaging depth

    OpenAIRE

    Sharma, Utkarsh; Chang, Ernest W.; Seok H Yun

    2008-01-01

    Multiple scattering in a sample presents a significant limitation to achieve meaningful structural information at deeper penetration depths in optical coherence tomography (OCT). Previous studies suggest that the spectral region around 1.7 µm may exhibit reduced scattering coefficients in biological tissues compared to the widely used wavelengths around 1.3 µm. To investigate this long-wavelength region, we developed a wavelength-swept laser at 1.7 µm wavelength and conducted OCT or optical f...

  6. Comparison of aerosol optical depth (AOD) determined from UVMRP and AERONET

    Science.gov (United States)

    Wang, Manyi; Liu, Chaoshun; Shi, Runhe; Gao, Wei

    2013-09-01

    Aerosol optical depth (AOD) is critically important for a better understanding of how Earth's climate is radiatively forced. To compensate for the conventional satellite observations, several types of ground-based radiometers are operated by AOD measurement programs. This study compares the Bratts Lake climate station's long-term AOD measurements from 1999 to 2012 which are derived from two ground-based programs with high accuracy: the United States Department of Agriculture (USDA) UV-B Monitoring and Research Program (UVMRP) and the AERONET (AErosol RObotic NETwork) program. The comparison shows that, in the 14-year period, the AOD values have an excellent agreement at six wavelengths (368, 415, 500, 610, 665, and 860 nm) with varying slopes (ranging from 0.95763 to 1.04089), intercepts (ranging from 0.0219 to 0.03945), correlation coefficients (R) (ranging from 0.82005 to 0.96155), and root mean square errors (RMSE) (ranging from 0.02639 to 0.03663). The correlations of both monthly and hourly averaged AOD measurements are highly consistent for each band. Specifically, the shorter (with larger AOD values) the wavelength is, the better the correlation is. Also, the results show that the peaks of relative errors generally occur in summer each year, and at noon each day. Our analyses suggest that AOD products derived from UVMRP are accurate and can serve as an alternative ground-based validation source for satellite AOD measurements.

  7. Light storage in a cold atomic ensemble with a high optical depth

    Science.gov (United States)

    Park, Kwang-Kyoon; Chough, Young-Tak; Kim, Yoon-Ho

    2017-06-01

    A quantum memory with a high storage efficiency and a long coherence time is an essential element in quantum information applications. Here, we report our recent development of an optical quantum memory with a rubidium-87 cold atom ensemble. By increasing the optical depth of the medium, we have achieved a storage efficiency of 65% and a coherence time of 51 μs for a weak laser pulse. The result of a numerical analysis based on the Maxwell-Bloch equations agrees well with the experimental results. Our result paves the way toward an efficient optical quantum memory and may find applications in photonic quantum information processing.

  8. Inverse problem theory in the optical depth profilometry of thin films

    Science.gov (United States)

    Power, J. F.

    2002-12-01

    The problem of nondestructive measurement of composition with depth on the scale of ˜0.1-500 μm, in polymers and related materials, has many applications in traditional and recent areas of thin film processing. This article reviews the optical depth profilometry techniques operating on this scale based on optical absorption, photoluminescence, elastic, and inelastic scattering. These methods include photoacoustic and photothermal imaging (including pulsed laser opto-acoustic profiling), attenuated total reflectance infrared, integrated optical spectroscopy methods (based on excitation of planar waveguide structures), confocal scanning microscopy, and the recent technique of light profile microscopy. The profiling of planar structures is emphasized. A common element of all of these methods is that depth mapping requires the solution of a linear inverse problem, where a map of the sample properties is mathematically reconstructed from a set of experimental measurements. This problem is to some extent ill conditioned in some or all regimes of measurement, with the result that depth maps may show sensitivity to data errors. A method is presented for assessing performance of the above experimental depth profilometry techniques in terms of ill conditioning as indicated by: spatial resolution, sensitivity to data errors, and apparent multiplicity of solutions. This method is applied a priori given a knowledge of the linear response theory and measurement parameters Application is made to individual profiling techniques, the performance of each in applications is reviewed, and an inter-comparison is made based on the conditioning of the inverse problem.

  9. Aerosol optical depth as observed by the Mars Science Laboratory REMS UV photodiodes

    Science.gov (United States)

    Smith, Michael D.; Zorzano, María-Paz; Lemmon, Mark; Martín-Torres, Javier; Mendaza de Cal, Teresa

    2016-12-01

    Systematic observations taken by the REMS UV photodiodes on a daily basis throughout the landed Mars Science Laboratory mission provide a highly useful tool for characterizing aerosols above Gale Crater. Radiative transfer modeling is used to model the approximately 1.75 Mars Years of observations taken to date taking into account multiple scattering from aerosols and the extended field of view of the REMS UV photodiodes. The retrievals show in detail the annual cycle of aerosol optical depth, which is punctuated with numerous short timescale events of increased optical depth. Dust deposition onto the photodiodes is accounted for by comparison with aerosol optical depth derived from direct imaging of the Sun by Mastcam. The effect of dust on the photodiodes is noticeable, but does not dominate the signal. Cleaning of dust from the photodiodes was observed in the season around Ls=270°, but not during other seasons. Systematic deviations in the residuals from the retrieval fit are indicative of changes in aerosol effective particle size, with larger particles present during periods of increased optical depth. This seasonal dependence of aerosol particle size is expected as dust activity injects larger particles into the air, while larger aerosols settle out of the atmosphere more quickly leading to a smaller average particle size over time.

  10. The maximum optical depth toward bulge stars from axisymmetric models of the Milky Way

    NARCIS (Netherlands)

    Kuijken, K

    1997-01-01

    It has been known that recent microlensing results toward the bulge imply mass densities that are surprisingly high, given dynamical constraints on the Milky Way mass distribution. We derive the maximum optical depth toward the bulge that may be generated by axisymmetric structures in the Milky Way,

  11. Relative skills of soil moisture and vegetation optical depth retrievals for agricultural drought monitoring

    Science.gov (United States)

    Soil moisture condition is an important indicator for agricultural drought monitoring. Through the Land Parameter Retrieval Model (LPRM), vegetation optical depth (VOD) as well as surface soil moisture (SM) can be retrieved simultaneously from brightness temperature observations from the Advanced Mi...

  12. Aerosol Optical Depth as Observed by the Mars Science Laboratory REMS UV Photodiodes

    Science.gov (United States)

    Smith, M. D.; Zorzano, M.-P.; Lemmon, M.; Martin-Torres, J.; Mendaza de Cal, T.

    2017-01-01

    Systematic observations taken by the REMS UV photodiodes on a daily basis throughout the landed Mars Science Laboratory mission provide a highly useful tool for characterizing aerosols above Gale Crater. Radiative transfer modeling is used to model the approximately two Mars Years of observations taken to date taking into account multiple scattering from aerosols and the extended field of view of the REMS UV photodiodes. The retrievals show in detail the annual cycle of aerosol optical depth, which is punctuated with numerous short timescale events of increased optical depth. Dust deposition onto the photodiodes is accounted for by comparison with aerosol optical depth derived from direct imaging of the Sun by Mastcam. The effect of dust on the photodiodes is noticeable, but does not dominate the signal. Cleaning of dust from the photodiodes was observed in the season around Ls=270deg, but not during other seasons. Systematic deviations in the residuals from the retrieval fit are indicative of changes in aerosol effective particle size, with larger particles present during periods of increased optical depth. This seasonal dependence of aerosol particle size is expected as dust activity injects larger particles into the air, while larger aerosols settle out of the atmosphere more quickly leading to a smaller average particle size over time. A full description of these observations, the retrieval algorithm, and the results can be found in Smith et al. (2016).

  13. Empirical Relationship between particulate matter and Aerosol Optical Depth over Northern Tien-Shan, Central Asia

    Science.gov (United States)

    Measurements were obtained at two sites in northern Tien-Shan in Central Asia during a 1-year period beginning July 2008 to examine the statistical relationship between aerosol optical depth (AOD) and of fine [PM2.5, particles less than 2.5 μm aerodynamic diameter (AD)] and coars...

  14. Depth evaluation of intended vs actual intacs intrastromal ring segments using optical coherence tomography.

    Science.gov (United States)

    Barbara, R; Barbara, A; Naftali, M

    2016-01-01

    PurposeEvaluation of actual vs intended intrastromal corneal ring segments (ICRS) implantation depth as measured by anterior segment optical coherence tomography (OCT)MethodsProspective study evaluating 30 Intacs segments implanted manually in 19 eyes of 15 patients suffering from keratoconus. Segment depth evaluation was performed using anterior segment OCT. Measurements were performed above and below the segment at 3 points in relation to the incision site. Statistical analysis was performed using the SAS software for ANOVA, matched t-test, and GLIMMIX procedure.ResultsIntacs segment depth was 153-μm shallower than intended (58% vs 80%). Segment layout demonstrated the proximal and distal portions to be 13-μm shallower and 12-μm deeper (on average), respectively. Intacs segment thickness does not influence implantation depth. Intacs segments implanted in the same eye do not share similar implantation depths. Stromal compression is likely to occur.ConclusionIntacs are implanted at a shallower depth than intended. The 'pocketing' stage prior to implantation most likely has a stronger effect on the segment's final implantation depth than does the incisions' depth.

  15. PAH 8μm Emission as a Diagnostic of HII Region Optical Depth

    Science.gov (United States)

    Oey, M. S.; Lopez-Hernandez, J.; Kellar, J. A.; Pellegrini, E. W.; Gordon, Karl D.; Jameson, Katherine; Li, Aigen; Madden, Suzanne C.; Meixner, Margaret; Roman-Duval, Julia; Bot, Caroline; Rubio, Monica; Tielens, A. G. G. M.

    2017-01-01

    PAHs are easily destroyed by Lyman continuum radiation and so in optically thick Stromgren spheres, they tend to be found only on the periphery of HII regions, rather than in the central volume. We therefore expect that in HII regions that are optically thin to ionizing radiation, PAHs would be destroyed beyond the primary nebular structure. Using data from the Spitzer SAGE survey of the Magellanic Clouds, we test whether 8 μm emission can serve as a diagnostic of optical depth in HII regions. We find that 8 μm emission does provide valuable constraints in the Large Magellanic Cloud, where objects identified as optically thick by their atomic ionization structure have 6 times higher median 8 μm surface brightness than optically thin objects. However, in the Small Magellanic Cloud, this differentiation is not observed. This appears to be caused by extremely low PAH production in this low-metallicity environment, such that any differentiation between optically thick and thin objects is washed out by stochastic variations, likely driven by the interplay between dust production and UV destruction. Thus, PAH emission is sensitive to nebular optical depth only at higher metallicities.

  16. High-resolution in-depth imaging of optically cleared thick samples using an adaptive SPIM

    Science.gov (United States)

    Masson, Aurore; Escande, Paul; Frongia, Céline; Clouvel, Grégory; Ducommun, Bernard; Lorenzo, Corinne

    2015-11-01

    Today, Light Sheet Fluorescence Microscopy (LSFM) makes it possible to image fluorescent samples through depths of several hundreds of microns. However, LSFM also suffers from scattering, absorption and optical aberrations. Spatial variations in the refractive index inside the samples cause major changes to the light path resulting in loss of signal and contrast in the deepest regions, thus impairing in-depth imaging capability. These effects are particularly marked when inhomogeneous, complex biological samples are under study. Recently, chemical treatments have been developed to render a sample transparent by homogenizing its refractive index (RI), consequently enabling a reduction of scattering phenomena and a simplification of optical aberration patterns. One drawback of these methods is that the resulting RI of cleared samples does not match the working RI medium generally used for LSFM lenses. This RI mismatch leads to the presence of low-order aberrations and therefore to a significant degradation of image quality. In this paper, we introduce an original optical-chemical combined method based on an adaptive SPIM and a water-based clearing protocol enabling compensation for aberrations arising from RI mismatches induced by optical clearing methods and acquisition of high-resolution in-depth images of optically cleared complex thick samples such as Multi-Cellular Tumour Spheroids.

  17. MODA: a new algorithm to compute optical depths in multi-dimensional hydrodynamic simulations

    CERN Document Server

    Perego, A; Cabezon, R; Rosswog, S; Liebendoerfer, M

    2014-01-01

    We introduce a new algorithm for the calculation of multidimensional optical depths in approximate radiative transport schemes, equally applicable to neutrinos and photons. Motivated by (but not limited to) neutrino transport in three-dimensional simulations of core-collapse supernovae and neutron star mergers, our method makes no assumptions about the geometry of the matter distribution, apart from expecting optically transparent boundaries. Based on local information about opacities, the algorithm figures out an escape route that tends to minimize the optical depth without assuming any pre-defined paths for radiation. Its adaptivity makes it suitable for a variety of astrophysical settings with complicated geometry (e.g., core-collapse supernovae, compact binary mergers, tidal disruptions, star formation, etc.). We implement the MODA algorithm into both a Eulerian hydrodynamics code with a fixed, uniform grid and into an SPH code where we make use a tree structure that is otherwise used for searching neighb...

  18. Extending the Effective Ranging Depth of Spectral Domain Optical Coherence Tomography by Spatial Frequency Domain Multiplexing

    Directory of Open Access Journals (Sweden)

    Tong Wu

    2016-11-01

    Full Text Available We present a spatial frequency domain multiplexing method for extending the imaging depth range of a spectral domain optical coherence tomography (SDOCT system without any expensive device. This method uses two galvo scanners with different pivot-offset distances in two independent reference arms for spatial frequency modulation and multiplexing. The spatial frequency contents corresponding to different depth regions of the sample can be shifted to different frequency bands. The spatial frequency domain multiplexing SDOCT system provides an approximately 1.9-fold increase in the effective ranging depth compared with that of a conventional full-range SDOCT system. The reconstructed images of phantom and biological tissue demonstrate the expected increase in ranging depth. The parameters choice criterion for this method is discussed.

  19. Fiber-optic annular detector array for large depth of field photoacoustic macroscopy.

    Science.gov (United States)

    Bauer-Marschallinger, Johannes; Höllinger, Astrid; Jakoby, Bernhard; Burgholzer, Peter; Berer, Thomas

    2017-03-01

    We report on a novel imaging system for large depth of field photoacoustic scanning macroscopy. Instead of commonly used piezoelectric transducers, fiber-optic based ultrasound detection is applied. The optical fibers are shaped into rings and mainly receive ultrasonic signals stemming from the ring symmetry axes. Four concentric fiber-optic rings with varying diameters are used in order to increase the image quality. Imaging artifacts, originating from the off-axis sensitivity of the rings, are reduced by coherence weighting. We discuss the working principle of the system and present experimental results on tissue mimicking phantoms. The lateral resolution is estimated to be below 200 μm at a depth of 1.5 cm and below 230 μm at a depth of 4.5 cm. The minimum detectable pressure is in the order of 3 Pa. The introduced method has the potential to provide larger imaging depths than acoustic resolution photoacoustic microscopy and an imaging resolution similar to that of photoacoustic computed tomography.

  20. Techniques of surface optical breakdown prevention for low-depths femtosecond waveguides writing

    Science.gov (United States)

    Bukharin, M. A.; Skryabin, N. N.; Ganin, D. V.; Khudyakov, D. V.; Vartapetov, S. K.

    2016-08-01

    We demonstrated technique of direct femtosecond waveguide writing at record low depth (2-15 μm) under surface of lithium niobate, that play a key role in design of electrooptical modulators with low operating voltage. To prevent optical breakdown of crystal surface we used high numerical aperture objectives for focusing of light and non-thermal regime of inscription in contrast to widespread femtosecond writing technique at depths of tens micrometers or higher. Surface optical breakdown threshold was measured for both x- and z- cut crystals. Inscribed waveguides were examined for intrinsic microstructure. It also reported sharp narrowing of operating pulses energy range with writing depth under the surface of crystal, that should be taken in account when near-surface waveguides design. Novelty of the results consists in reduction of inscription depth under the surface of crystals that broadens applications of direct femtosecond writing technique to full formation of near-surface waveguides and postproduction precise geometry correction of near-surfaces optical integrated circuits produced with proton-exchanged technique.

  1. Dual beam light profile microscopy: a new technique for optical absorption depth profilometry.

    Science.gov (United States)

    Power, J F; Fu, S W

    2004-02-01

    Light profile microscopy (LPM) is a recently developed technique of optical inspection that is used to record micrometer-scale images of thin-film cross-sections on a direct basis. In single beam mode, LPM provides image contrast based on luminescence, elastic, and/or inelastic scatter. However, LPM may also be used to depth profile the optical absorption coefficient of a thin film based on a method of dual beam irradiation presented in this work. The method uses a pair of collimated laser beams to consecutively irradiate a film from two opposing directions along the depth axis. An average profile of the beam's light intensity variation through the material is recovered for each direction and used to compute a depth-dependent differential absorbance profile. This latter quantity is shown from theory to be related to the film's depth-dependent optical absorption coefficient through a simple linear model that may be inverted by standard methods of numerical linear algebra. The inverse problem is relatively well posed, showing good immunity to data errors. This profilometry method is experimentally applied to a set of well-characterized materials with known absorption properties over a scale of tens of micrometers, and the reconstructed absorption profiles were found to be highly consistent with the reference data.

  2. An Optical Fibre Depth (Pressure) Sensor for Remote Operated Vehicles in Underwater Applications.

    Science.gov (United States)

    Duraibabu, Dinesh Babu; Poeggel, Sven; Omerdic, Edin; Capocci, Romano; Lewis, Elfed; Newe, Thomas; Leen, Gabriel; Toal, Daniel; Dooly, Gerard

    2017-02-19

    A miniature sensor for accurate measurement of pressure (depth) with temperature compensation in the ocean environment is described. The sensor is based on an optical fibre Extrinsic Fabry-Perot interferometer (EFPI) combined with a Fibre Bragg Grating (FBG). The EFPI provides pressure measurements while the Fibre Bragg Grating (FBG) provides temperature measurements. The sensor is mechanically robust, corrosion-resistant and suitable for use in underwater applications. The combined pressure and temperature sensor system was mounted on-board a mini remotely operated underwater vehicle (ROV) in order to monitor the pressure changes at various depths. The reflected optical spectrum from the sensor was monitored online and a pressure or temperature change caused a corresponding observable shift in the received optical spectrum. The sensor exhibited excellent stability when measured over a 2 h period underwater and its performance is compared with a commercially available reference sensor also mounted on the ROV. The measurements illustrates that the EFPI/FBG sensor is more accurate for depth measurements (depth of ~0.020 m).

  3. An Optical Fibre Depth (Pressure Sensor for Remote Operated Vehicles in Underwater Applications

    Directory of Open Access Journals (Sweden)

    Dinesh Babu Duraibabu

    2017-02-01

    Full Text Available A miniature sensor for accurate measurement of pressure (depth with temperature compensation in the ocean environment is described. The sensor is based on an optical fibre Extrinsic Fabry-Perot interferometer (EFPI combined with a Fibre Bragg Grating (FBG. The EFPI provides pressure measurements while the Fibre Bragg Grating (FBG provides temperature measurements. The sensor is mechanically robust, corrosion-resistant and suitable for use in underwater applications. The combined pressure and temperature sensor system was mounted on-board a mini remotely operated underwater vehicle (ROV in order to monitor the pressure changes at various depths. The reflected optical spectrum from the sensor was monitored online and a pressure or temperature change caused a corresponding observable shift in the received optical spectrum. The sensor exhibited excellent stability when measured over a 2 h period underwater and its performance is compared with a commercially available reference sensor also mounted on the ROV. The measurements illustrates that the EFPI/FBG sensor is more accurate for depth measurements (depth of ~0.020 m.

  4. MODA: a new algorithm to compute optical depths in multidimensional hydrodynamic simulations

    Science.gov (United States)

    Perego, Albino; Gafton, Emanuel; Cabezón, Rubén; Rosswog, Stephan; Liebendörfer, Matthias

    2014-08-01

    Aims: We introduce the multidimensional optical depth algorithm (MODA) for the calculation of optical depths in approximate multidimensional radiative transport schemes, equally applicable to neutrinos and photons. Motivated by (but not limited to) neutrino transport in three-dimensional simulations of core-collapse supernovae and neutron star mergers, our method makes no assumptions about the geometry of the matter distribution, apart from expecting optically transparent boundaries. Methods: Based on local information about opacities, the algorithm figures out an escape route that tends to minimize the optical depth without assuming any predefined paths for radiation. Its adaptivity makes it suitable for a variety of astrophysical settings with complicated geometry (e.g., core-collapse supernovae, compact binary mergers, tidal disruptions, star formation, etc.). We implement the MODA algorithm into both a Eulerian hydrodynamics code with a fixed, uniform grid and into an SPH code where we use a tree structure that is otherwise used for searching neighbors and calculating gravity. Results: In a series of numerical experiments, we compare the MODA results with analytically known solutions. We also use snapshots from actual 3D simulations and compare the results of MODA with those obtained with other methods, such as the global and local ray-by-ray method. It turns out that MODA achieves excellent accuracy at a moderate computational cost. In appendix we also discuss implementation details and parallelization strategies.

  5. Optical depth retrievals from Delta-T SPN1 measurements of broadband solar irradiance at ground

    Science.gov (United States)

    Estelles, Victor; Serrano, David; Segura, Sara; Wood, John; Webb, Nick

    2016-04-01

    The SPN1 radiometer, manufactured by Delta-T Devices Ltd., is an instrument designed for the measurement of global solar irradiance and its components (diffuse, direct) at ground level. In the present study, the direct irradiance component has been used to retrieve an effective total optical depth, by applying the Beer-Lambert law to the broadband measurements. The results have been compared with spectral total optical depths derived from two Cimel CE318 and Prede POM01 sun-sky radiometers, located at the Burjassot site in Valencia (Spain), during years 2013 - 2015. The SPN1 is an inexpensive and versatile instrument for the measurement of the three components of the solar radiation without any mobile part and without any need to azimuthally align the instrument to track the sun (http://www.delta-t.co.uk). The three components of the solar radiation are estimated from a combination of measurements performed by 7 different miniature thermopiles. In turn, the Beer-Lambert law has been applied to the broadband direct solar component to obtain an effective total optical depth, representative of the total extinction in the atmosphere. For the assessment of the total optical depth values retrieved with the SPN1, two different sun-sky radiometers (Cimel CE318 and Prede POM01L) have been employed. Both instruments belong to the international networks AERONET and SKYNET. The modified SUNRAD package has been applied in both Cimel and Prede instruments. Cloud affected data has been removed by applying the Smirnov cloud-screening procedure in the SUNRAD algorithm. The broadband SPN1 total optical depth has been analysed by comparison with the spectral total optical depth from the sun-sky radiometer measurements at wavelengths 440, 500, 675, 870 and 1020 nm. The slopes and intercepts have been estimated to be 0.47 - 0.98 and 0.055 - 0.16 with increasing wavelength. The average correlation coefficients and RMSD were 0.80 - 0.83 and 0.034 - 0.036 for all the channels. The

  6. Implications for GCM Modeling of MARCI/TES ACB Optical Depth Differences

    Science.gov (United States)

    Klassen, David R.; Kahre, Melinda A.; Wolff, Michael J.; Haberle, Robert; Hollingsworth, Jeffery L.

    2016-10-01

    The Aphelion Cloud Belt (ACB) is a well-studied phenomenon of Mars. HST violet images and microwave observations [e.g. 1–3] helped characterize its seasonal morphology and measure typical optical depths. Follow up, long-term studies by orbiting instruments [e.g. 4–6] characterized the growth and decline of the ACB as well as a baseline set of zonally averaged optical depths as a function of latitude and season. All this work provided ground-truth for the assessment and modification of Mars GCMs and current models provide good agreement with observations [e.g. 7–8].We will present recent analyses of MARCI and TES ACB optical depths that show a wavelength dependance on the timing of the peak zonal-average optical depth that implies a possible evolution in average effective radius of ACB cloud particles as the ACB ages. As we will show, this difference in timing of the optical depth peak between short and long wavelength bands is not seen in the Ames MGCM. In order to begin understanding these differences, we will present retrieved ACB cloud particle sizes from the Ames MGCM to compare to the optical depth observations and calculations and discuss possible model adjustments that may lead to better fits. Aligning model and observation results should lead to a better understanding of what is physically driving the particle size evolution.[1] James, P. B., et al. 1996, JGR, 101, 18883[2] Clancy, R. T., et al. 1996, Icarus, 122, 36[3] Wolff, M. J., et al. 1999, in The Fifth International Conference on Mars, July 19-24, 1999, Pasadena, California, 6173[4] Pearl, J. C., et al. 2001, JGR, 106, 12325[5] Smith, M. D., et al. 2003, JGR-Planets, 108, 1[6] Smith, M. D. 2004, Icarus, 167, 148[7] Montmessin, F., et al. 2004, JGR-Planets, 109, E10004[8] Haberle, R. M., et al. 2010, in BAAS, 42, 1031

  7. Diffuse optical microscopy for quantification of depth-dependent epithelial backscattering in the cervix

    Science.gov (United States)

    Bodenschatz, Nico; Lam, Sylvia; Carraro, Anita; Korbelik, Jagoda; Miller, Dianne M.; McAlpine, Jessica N.; Lee, Marette; Kienle, Alwin; MacAulay, Calum

    2016-06-01

    A fiber optic imaging approach is presented using structured illumination for quantification of almost pure epithelial backscattering. We employ multiple spatially modulated projection patterns and camera-based reflectance capture to image depth-dependent epithelial scattering. The potential diagnostic value of our approach is investigated on cervical ex vivo tissue specimens. Our study indicates a strong backscattering increase in the upper part of the cervical epithelium caused by dysplastic microstructural changes. Quantization of relative depth-dependent backscattering is confirmed as a potentially useful diagnostic feature for detection of precancerous lesions in cervical squamous epithelium.

  8. The Optical Depth of H II Regions in the Magellanic Clouds

    CERN Document Server

    Pellegrini, E W; Winkler, P F; Points, S D; Smith, R C

    2012-01-01

    We exploit ionization-parameter mapping as a powerful tool to measure the optical depth of star-forming H II regions. Our simulations based on the C LOUDY photoionization code and our new, SURFBRIGHT surface brightness simulator demonstrate that this technique can directly diagnose most density-bounded, optically thin nebulae with spatially resolved emission line data. We apply this method to the Large and Small Magellanic Clouds, using the data from the Magellanic Clouds Emission Line Survey. We generate new H II region catalogs based on photoionization criteria set by the observed ionization structure in the [SII]/[OIII] ratio and H{\\alpha} surface brightness. The luminosity functions from these catalogs generally agree with those from H{\\alpha}-only surveys. We then use ionization-parameter mapping to crudely classify all the nebulae into optically thick vs optically thin categories, yielding fundamental new insights into the Lyman continuum radiation transfer. We find that in both galaxies, the frequency ...

  9. [In-depth interviews and the Kano model to determine user requirements in a burns unit].

    Science.gov (United States)

    González-Revaldería, J; Holguín-Holgado, P; Lumbreras-Marín, E; Núñez-López, G

    To determine the healthcare requirements of patients in a Burns Unit, using qualitative techniques, such us in-depth personal interviews and Kano's methodology. Qualitative methodology using in-depth personal interviews (12 patients), Kano's conceptual model, and the SERVQHOS questionnaire (24 patients). All patients had been hospitalised in the last 12 months in the Burns Unit. Using Kano's methodology, service attributes were grouped by affinity diagrams, and classified as follows: must-be, attractive (unexpected, great satisfaction), and one-dimensional (linked to the degree of functionality of the service). The outcomes were compared with those obtained with SERVQHOS questionnaire. From the analysis of in-depth interviews, 11 requirements were obtained, referring to hotel aspects, information, need for closer staff relationship, and organisational aspects. The attributes classified as must-be were free television and automatic TV disconnection at midnight. Those classified as attractive were: individual room for more privacy, information about dressing change times in order to avoid anxiety, and additional staff for in-patients. The results were complementary to those obtained with the SERVQHOS questionnaire. In-depth personal interviews provide extra knowledge about patient requirements, complementing the information obtained with questionnaires. With this methodology, a more active patient participation is achieved and the companion's opinion is also taken into account. Copyright © 2016 SECA. Publicado por Elsevier España, S.L.U. All rights reserved.

  10. Pit Depth and Width Modulation Multilevel Run-Length Limited Read-Only Optical Storage

    Institute of Scientific and Technical Information of China (English)

    SONG Jie; PEI Jing; XU Duan-Yi; XIONG Jian-Ping; CHEN Ken; PAN Long-Ea

    2006-01-01

    When the techniques of integrating the variation of the pit depth and width simultaneously are adopted to conventional DVD, the high-density multilevel run-length limited read-only optical storage method is achieved. The dynamic range of readout signal is greatly enlarged in comparison with keeping one parameter varied, and the recording levels number can be obviously increased. The discs can be manufactured using standard photoresist mastering and replication techniques with great compatibility to conventional binary read-only discs. Experimental results show that eight-level read-only optical disc can be realized and the capacity can be increased to 20 GB.

  11. Merging Static and Dynamic Depth Cues with Optical-Flow Recovery for Creating Stereo Videos

    Directory of Open Access Journals (Sweden)

    Fang-Hsuan Cheng

    2013-01-01

    Full Text Available A method for estimating the depth information of a general monocular image sequence and then creating a 3D stereo video is proposed. Distinguishing between foreground and background is possible without additional information, and then foreground pixels are moved to create the binocular image. The proposed depth estimation method is based on coarse-to-fine strategy. By applying the CID method in the spatial domain, the sharpness and the contrast of an image can be improved by the distance of the region based on its color. Then a coarse depth map of the image can be generated. An optical-flow method based on temporal information is then used to search and compare the block motion status between previous and current frames, and then the distance of the block can be estimated according to the amount of block motion. Finally, the static and motion depth information is integrated to create the fine depth map. By shifting foreground pixels based on the depth information, a binocular image pair can be created. A sense of 3D stereo can be obtained without glasses by an autostereoscopic 3D display.

  12. Seasonal variability of cloud optical depth over northwestern China derived from CERES/MODIS satellite measurements

    Institute of Scientific and Technical Information of China (English)

    Yonghang Chen; Hongtao Bai; Jianping Huang; Hua Zhang; Jinming Ge; Xiaodan Guan; Xiaoqin Mao

    2008-01-01

    The seasonal variability of cloud optical depth over northwestern China derived from Clouds and the Earth's Radiant Energy System (CERES) Single Scanner Footprint (SSF) Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) Edition 1B data from July 2002 to June 2004 is presented. The regions of interest are those with Asia monsoon influence, the Tianshan and Qilian Mountains, and the Taklimakan Desert. The results show that the instantaneous measurements presented here are much higher than the previous results derived from International Satellite Cloud Climatology Project (ISCCP) D2 monthly mean data. Generally the measurements of cloud optical depth are the highest in summer and the lowest in winter, however, Taklimakan Desert has the lowest measurements in autumn. The regional variation is quite significant over northwestern China.

  13. Daily snow depth measurements from 195 stations in the United States

    Energy Technology Data Exchange (ETDEWEB)

    Allison, L.J. [ed.] [Oak Ridge National Lab., TN (United States). Carbon Dioxide Information Analysis Center; Easterling, D.R.; Jamason, P.; Bowman, D.P.; Hughes, P.Y.; Mason, E.H. [National Oceanic and Atmospheric Administration, Asheville, NC (United States). National Climatic Data Center

    1997-02-01

    This document describes a database containing daily measurements of snow depth at 195 National Weather Service (NWS) first-order climatological stations in the United States. The data have been assembled and made available by the National Climatic Data Center (NCDC) in Asheville, North Carolina. The 195 stations encompass 388 unique sampling locations in 48 of the 50 states; no observations from Delaware or Hawaii are included in the database. Station selection criteria emphasized the quality and length of station records while seeking to provide a network with good geographic coverage. Snow depth at the 388 locations was measured once per day on ground open to the sky. The daily snow depth is the total depth of the snow on the ground at measurement time. The time period covered by the database is 1893--1992; however, not all station records encompass the complete period. While a station record ideally should contain daily data for at least the seven winter months (January through April and October through December), not all stations have complete records. Each logical record in the snow depth database contains one station`s daily data values for a period of one month, including data source, measurement, and quality flags.

  14. Analysis of aerosol optical depth evaluation in polar regions and associated uncertainties

    Directory of Open Access Journals (Sweden)

    P. Ortiz de Galisteo

    2008-04-01

    Full Text Available Some available processing algorithms used to calculate the aerosol optical depth from radiometric measurements were tested. The aim was to evaluate the associated uncertainties in polar regions due to the data processing, in order to adjust the methodology of the calculation and illustrate the importance of these error sources. The measurements were obtained during a sun photometer campaign in Ny-Ålesund within the framework of the POLAR-AOD project.

  15. Measurements and estimation of the columnar optical depth of tropospheric aerosols in the UV spectral region

    Directory of Open Access Journals (Sweden)

    V. E. Cachorro

    Full Text Available We report values of the columnar tropospheric aerosol optical depth at UV wavelengths based on experimental measurements of the direct spectral irradiances carried out by a commercial spectroradiometer (Li1800 of Licor company covering the range from 300–1100 nm at two stations with different climate characteristics in Spain. The first station is located in a rural site in north central Spain with continental climate. The data extend from March to the end of October of 1995. The other station is a coastal site in the Gulf of Cádiz (southwest Spain of maritime climate type. This study is mainly focused on the capability of estimating aerosol optical depth values in the UV region based on the extracted information in the visible and near infrared ranges. A first method has been used based on the Ångström turbidity parameters. However, since this method requires detailed spectral information, a second method has also been used, based on the correlation between wavelengths. A correlation has been established between the experimental aerosol optical depth values at 350 nm and 500 nm wavelengths. Although the type of aerosol seems to be the key factor that determines the quality of these estimations, the evaluation of the associated error is necessary to know the behaviour of these estimations in each area of study.

    Key words. Atmospheric composition and structure (aerosols and particles; transmission and scattering of radiation; troposphere – composition and chemistry

  16. Measurements and estimation of the columnar optical depth of tropospheric aerosols in the UV spectral region

    Energy Technology Data Exchange (ETDEWEB)

    Cachorro, V.E.; Vergaz, R.; Martin, M.J.; Frutos, A.M. de [Grupo de Optica Atmosferica, Univ. de Valladolid (GOA-UVA), Valladolid (Spain); Vilaplana, J.M.; Morena, B. de la [Estacion de Sondeos Atmosfericos ESAT ' ' El Arenosillo' ' , INTA, Huelva (Spain)

    2002-04-01

    We report values of the columnar tropospheric aerosol optical depth at UV wavelengths based on experimental measurements of the direct spectral irradiances carried out by a commercial spectroradiometer (Li1800 of Licor company) covering the range from 300-1100 nm at two stations with different climate characteristics in Spain. The first station is located in a rural site in north central Spain with continental climate. The data extend from March to the end of October of 1995. The other station is a coastal site in the Gulf of Cadiz (southwest Spain) of maritime climate type. This study is mainly focused on the capability of estimating aerosol optical depth values in the UV region based on the extracted information in the visible and near infrared ranges. A first method has been used based on the Aangstroem turbidity parameters. However, since this method requires detailed spectral information, a second method has also been used, based on the correlation between wavelengths. A correlation has been established between the experimental aerosol optical depth values at 350 nm and 500 nm wavelengths. Although the type of aerosol seems to be the key factor that determines the quality of these estimations, the evaluation of the associated error is necessary to know the behavior of these estimations in each area of study. (orig.)

  17. Linking Ly-alpha and Low-Ionization Transitions at Low Optical Depth

    CERN Document Server

    Jaskot, A E

    2014-01-01

    We suggest that low optical depth in the Lyman continuum (LyC) may relate the Ly-alpha emission, C II and Si II absorption, and C II* and Si II* emission seen in high-redshift galaxies. We base this analysis on Hubble Space Telescope COS spectra of four Green Pea (GP) galaxies, which may be analogs of z>2 Ly-alpha emitters (LAEs). In the two GPs with the strongest Ly-alpha emission, the Ly-alpha line profiles do not show the typical effects of resonant scattering. Instead, the Ly-alpha profiles resemble the H-alpha line profiles of evolved star ejecta, suggesting that the Ly-alpha emission originates from a low column density and similar outflow geometry. The weak C II absorption and presence of non-resonant C II* emission in these GPs support this interpretation and imply a low LyC optical depth along the line of sight. In two additional GPs, weak Ly-alpha emission and strong C II absorption suggest a higher optical depth. These two GPs differ in their Ly-alpha profile shapes and C II* emission strengths, ho...

  18. Preliminary results of the aerosol optical depth retrieval in Johor, Malaysia

    Science.gov (United States)

    Lim, H. Q.; Kanniah, K. D.; Lau, A. M. S.

    2014-02-01

    Monitoring of atmospheric aerosols over the urban area is important as tremendous amounts of pollutants are released by industrial activities and heavy traffic flow. Air quality monitoring by satellite observation provides better spatial coverage, however, detailed aerosol properties retrieval remains a challenge. This is due to the limitation of aerosol retrieval algorithm on high reflectance (bright surface) areas. The aim of this study is to retrieve aerosol optical depth over urban areas of Iskandar Malaysia; the main southern development zone in Johor state, using Moderate Resolution Imaging Spectroradiometer (MODIS) 500 m resolution data. One of the important steps is the aerosol optical depth retrieval is to characterise different types of aerosols in the study area. This information will be used to construct a Look Up Table containing the simulated aerosol reflectance and corresponding aerosol optical depth. Thus, in this study we have characterised different aerosol types in the study area using Aerosol Robotic Network (AERONET) data. These data were processed using cluster analysis and the preliminary results show that the area is consisting of coastal urban (65%), polluted urban (27.5%), dust particles (6%) and heavy pollution (1.5%) aerosols.

  19. Constraints on primordial magnetic fields from the optical depth of the cosmic microwave background

    CERN Document Server

    Kunze, Kerstin E

    2015-01-01

    Damping of magnetic fields via ambipolar diffusion and decay of magnetohydrodynamical (MHD) turbulence in the post decoupling era heats the intergalactic medium (IGM). Collisional ionization weakly ionizes the IGM, producing an optical depth to scattering of the cosmic microwave background (CMB). The optical depth generated at $z\\gg 10$ does not affect the "reionization bump" of the CMB polarization power spectrum at low multipoles, but affects the temperature and polarization power spectra at high multipoles. Using the Planck 2013 temperature and lensing data together with the WMAP 9-year polarization data, we constrain the present-day field strength, $B_0$, smoothed over the damping length at the decoupling epoch as a function of the spectral index, $n_B$. We find the 95% upper bounds of $B_0<0.56$, 0.31, and 0.14 nG for $n_B=-2.9$, $-2.5$, and $-1.5$, respectively. For these spectral indices, the optical depth is dominated by dissipation of the decaying MHD turbulence that occurs shortly after the decou...

  20. Smartphone-Based Android app for Determining UVA Aerosol Optical Depth and Direct Solar Irradiances.

    Science.gov (United States)

    Igoe, Damien P; Parisi, Alfio; Carter, Brad

    2014-01-01

    This research describes the development and evaluation of the accuracy and precision of an Android app specifically designed, written and installed on a smartphone for detecting and quantifying incident solar UVA radiation and subsequently, aerosol optical depth at 340 and 380 nm. Earlier studies demonstrated that a smartphone image sensor can detect UVA radiation and the responsivity can be calibrated to measured direct solar irradiance. This current research provides the data collection, calibration, processing, calculations and display all on a smartphone. A very strong coefficient of determination of 0.98 was achieved when the digital response was recalibrated and compared to the Microtops sun photometer direct UVA irradiance observations. The mean percentage discrepancy for derived direct solar irradiance was only 4% and 6% for observations at 380 and 340 nm, respectively, lessening with decreasing solar zenith angle. An 8% mean percent difference discrepancy was observed when comparing aerosol optical depth, also decreasing as solar zenith angle decreases. The results indicate that a specifically designed Android app linking and using a smartphone image sensor, calendar and clock, with additional external narrow bandpass and neutral density filters can be used as a field sensor to evaluate both direct solar UVA irradiance and low aerosol optical depths for areas with low aerosol loads. © 2013 The American Society of Photobiology.

  1. Double peacock eye optical element for extended focal depth imaging with ophthalmic applications.

    Science.gov (United States)

    Romero, Lenny A; Millán, María S; Jaroszewicz, Zbigniew; Kolodziejczyk, Andrzej

    2012-04-01

    The aged human eye is commonly affected by presbyopia, and therefore, it gradually loses its capability to form images of objects placed at different distances. Extended depth of focus (EDOF) imaging elements can overcome this inability, despite the introduction of a certain amount of aberration. This paper evaluates the EDOF imaging performance of the so-called peacock eye phase diffractive element, which focuses an incident plane wave into a segment of the optical axis and explores the element's potential use for ophthalmic presbyopia compensation optics. Two designs of the element are analyzed: the single peacock eye, which produces one focal segment along the axis, and the double peacock eye, which is a spatially multiplexed element that produces two focal segments with partial overlapping along the axis. The performances of the peacock eye elements are compared with those of multifocal lenses through numerical simulations as well as optical experiments in the image space. The results demonstrate that the peacock eye elements form sharper images along the focal segment than the multifocal lenses and, therefore, are more suitable for presbyopia compensation. The extreme points of the depth of field in the object space, which represent the remote and the near object points, have been experimentally obtained for both the single and the double peacock eye optical elements. The double peacock eye element has better imaging quality for relatively short and intermediate distances than the single peacock eye, whereas the latter seems better for far distance vision.

  2. Spectral domain optical coherence tomography with extended depth-of-focus by aperture synthesis

    Science.gov (United States)

    Bo, En; Liu, Linbo

    2016-10-01

    We developed a spectral domain optical coherence tomography (SD-OCT) with an extended depth-of-focus (DOF) by synthetizing aperture. For a designated Gaussian-shape light source, the lateral resolution was determined by the numerical aperture (NA) of the objective lens and can be approximately maintained over the confocal parameter, which was defined as twice the Rayleigh range. However, the DOF was proportional to the square of the lateral resolution. Consequently, a trade-off existed between the DOF and lateral resolution, and researchers had to weigh and judge which was more important for their research reasonably. In this study, three distinct optical apertures were obtained by imbedding a circular phase spacer in the sample arm. Due to the optical path difference between three distinct apertures caused by the phase spacer, three images were aligned with equal spacing along z-axis vertically. By correcting the optical path difference (OPD) and defocus-induced wavefront curvature, three images with distinct depths were coherently summed together. This system digitally refocused the sample tissue and obtained a brand new image with higher lateral resolution over the confocal parameter when imaging the polystyrene calibration beads.

  3. A Neural Network Approach to Infer Optical Depth of Thick Ice Clouds at Night

    Science.gov (United States)

    Minnis, P.; Hong, G.; Sun-Mack, S.; Chen, Yan; Smith, W. L., Jr.

    2016-01-01

    One of the roadblocks to continuously monitoring cloud properties is the tendency of clouds to become optically black at cloud optical depths (COD) of 6 or less. This constraint dramatically reduces the quantitative information content at night. A recent study found that because of their diffuse nature, ice clouds remain optically gray, to some extent, up to COD of 100 at certain wavelengths. Taking advantage of this weak dependency and the availability of COD retrievals from CloudSat, an artificial neural network algorithm was developed to estimate COD values up to 70 from common satellite imager infrared channels. The method was trained using matched 2007 CloudSat and Aqua MODIS data and is tested using similar data from 2008. The results show a significant improvement over the use of default values at night with high correlation. This paper summarizes the results and suggests paths for future improvement.

  4. Novel optical waveguides by in-depth controlled electronic damage with swift ions

    Energy Technology Data Exchange (ETDEWEB)

    Olivares, J. [Instituto de Optica ' Daza de Valdes' , CSIC, C/Serrano 121, E-28006-Madrid (Spain)]. E-mail: j.olivares@io.cfmac.csic.es; Garcia-Navarro, A. [Centro de Microanalisis de Materiales (CMAM), UAM, Cantoblanco, E-28049-Madrid (Spain); Mendez, A. [Centro de Microanalisis de Materiales (CMAM), UAM, Cantoblanco, E-28049-Madrid (Spain); Agullo-Lopez, F. [Centro de Microanalisis de Materiales (CMAM), UAM, Cantoblanco, E-28049-Madrid (Spain); Depto. Fisica de Materiales (C-IV), UAM, E-28049-Madrid (Spain); Garcia, G. [Centro de Microanalisis de Materiales (CMAM), UAM, Cantoblanco, E-28049-Madrid (Spain); Garcia-Cabanes, A. [Depto. Fisica de Materiales (C-IV), UAM, E-28049-Madrid (Spain); Carrascosa, M. [Depto. Fisica de Materiales (C-IV), UAM, E-28049-Madrid (Spain)

    2007-04-15

    We review recent results on a novel method to modify crystalline dielectric materials and fabricate optical waveguides and integrated optics devices. It relies on irradiation with medium-mass high-energy ions (2-50 MeV) where the electronic stopping power is dominant over that one associated to nuclear collisions. By exploiting the processing capabilities of the method, novel optical structures can be achieved at moderate (10{sup 14} cm{sup -2}) and even low and ultralow (10{sup 12} cm{sup -2}) fluences. In particular, step-like waveguides with a high index jump {delta}n {approx} 0.1-0.2, guiding both ordinary and extraordinary modes, have been prepared with F and O ions (20 MeV) at moderate fluences. They present good non-linear and electrooptic perfomance and low losses. (1 dB/cm). Moreover, useful optical waveguiding has been also achieved at ultralow frequencies (isolated track regime), using Cl and Si ions (40-45 MeV). In this latter case, the individual amorphous nanotracks, whose radius increases with depth, create an effective optical medium causing optical trapping.

  5. Improvement of Aerosol Optical Depth Retrieval over Hong Kong from a Geostationary Meteorological Satellite Using Critical Reflectance with Background Optical Depth Correction

    Science.gov (United States)

    Kim, Mijin; Kim, Jhoon; Wong, Man Sing; Yoon, Jongmin; Lee, Jaehwa; Wu, Dong L.; Chan, P.W.; Nichol, Janet E.; Chung, Chu-Yong; Ou, Mi-Lim

    2014-01-01

    Despite continuous efforts to retrieve aerosol optical depth (AOD) using a conventional 5-channelmeteorological imager in geostationary orbit, the accuracy in urban areas has been poorer than other areas primarily due to complex urban surface properties and mixed aerosol types from different emission sources. The two largest error sources in aerosol retrieval have been aerosol type selection and surface reflectance. In selecting the aerosol type from a single visible channel, the season-dependent aerosol optical properties were adopted from longterm measurements of Aerosol Robotic Network (AERONET) sun-photometers. With the aerosol optical properties obtained fromthe AERONET inversion data, look-up tableswere calculated by using a radiative transfer code: the Second Simulation of the Satellite Signal in the Solar Spectrum (6S). Surface reflectance was estimated using the clear sky composite method, awidely used technique for geostationary retrievals. Over East Asia, the AOD retrieved from the Meteorological Imager showed good agreement, although the values were affected by cloud contamination errors. However, the conventional retrieval of the AOD over Hong Kong was largely underestimated due to the lack of information on the aerosol type and surface properties. To detect spatial and temporal variation of aerosol type over the area, the critical reflectance method, a technique to retrieve single scattering albedo (SSA), was applied. Additionally, the background aerosol effect was corrected to improve the accuracy of the surface reflectance over Hong Kong. The AOD retrieved froma modified algorithmwas compared to the collocated data measured by AERONET in Hong Kong. The comparison showed that the new aerosol type selection using the critical reflectance and the corrected surface reflectance significantly improved the accuracy of AODs in Hong Kong areas,with a correlation coefficient increase from0.65 to 0.76 and a regression line change from tMI [basic algorithm] = 0

  6. Studies of aerosol optical depth with use of Microtops sun photometers and MODIS detectors

    Science.gov (United States)

    Makuch, Przemyslaw; Zawadzka, Olga; Markowicz, Krzystof M.; Zielinski, Tymon; Petelski, Tomasz; Strzalkowska, Agata; Rozwadowska, Anna; Gutowska, Dorota

    2013-04-01

    We would like to describe the results of a research campaign aimed at the studies of aerosol optical properties in the regions of the open Baltic Sea as well as coastal areas. During the campaign we carried out simultaneous measurements of aerosol optical depth at 4 stations with use of the hand-held Microtops II sunphotometers. The studies were complemented with the MODIS aerosol data. In order to obtain the full picture of the aerosol situation over the study area we added air mass back-trajectories at various altitudes and wind fields. Such complex information facilitated the proper conclusions regarding aerosol optical depth and Angstroem exponent for the four locations and discussion of the changes of aerosol properties with distance and meteorological factors. We show that Microtops II sunphotometers are reliable instruments for field campaigns. They are easy to operate and provide good quality results. Acknowledgements: The support for this study was provided by the project Satellite Monitoring of the Baltic Sea Environment - SatBałtyk founded by European Union through European Regional Development Fund contract No. POIG 01.01.02-22-011/09.

  7. UVIS ring occultations show F ring feature location and optical depth correlated with Prometheus

    Science.gov (United States)

    Meinke, Bonnie K.; Esposito, L. W.; Albers, N.

    2010-05-01

    We find 24 statistically significant features in the F ring occultations using the High Speed Photometer (HSP) channel of the Cassini Ultraviolet Imaging Spectrograph (UVIS). These features are likely transient clumps of material embedded in the ring, each of which attenuates stellar signal during an occultation because the ring material is more densely packed at that location. In fact, two of these features are opaque, indicating they may be solid moonlets. Two trends are evident in the azimuthal location of these 24 F ring features with respect to that of Prometheus. First, the orbital locations of these features are mostly opposite Prometheus, as 11 of the 24 occupy the orbital region separated from Prometheus by 180° ± 20°. Second, average feature optical depth is maximum near the antipode of Prometheus in orbit. Our hypothesis is that these results show aggregation and disaggregation of clumps after Prometheus passes by. As Prometheus passes interior to the F ring, it encounters material once every synodic period, 68 days. Optical depth indicates density of ring material along the line of sight, so as material clumps together, we expect to see higher optical depths. Thus we infer that the encounter stimulates clumping of material that reaches a maximum 180° downstream. This may reinforce similar evidence that Ring-Moon interaction stimulates clumping in the F ring region from Cassini imaging (Beurle, et al., 2010) and at the B ring edge (Esposito, et al., 2010). Esposito, et al. (2010) suggest that the combined mass and velocity evolution of the ring system resembles a predator/prey model. This research was supported by the Cassini Project.

  8. In-depth quantification by using multispectral time-resolved diffuse optical tomography

    Science.gov (United States)

    Zouaoui, Judy; Hervé, Lionel; Di Sieno, Laura; Planat-Chrétien, Anne; Berger, Michel; Dalla Mora, Alberto; Pifferi, Antonio; Derouard, Jacques; Dinten, Jean-Marc

    2015-07-01

    Near-infrared diffuse optical tomography (DOT) is a medical imaging which gives the distribution of the optical properties of biological tissues. To obtain endogenous chromophore features in the depth of a scattering medium, a multiwavelength/time-resolved (MW/TR) DOT setup was used. Reconstructions of the three-dimensional maps of chromophore concentrations of probed media were obtained by using a data processing technique which manages Mellin-Laplace Transforms of their MW/TR optical signals and those of a known reference medium. The point was to put a constraint on the medium absorption coefficient by using a material basis composed of a given set of chromophores of known absorption spectra. Experimental measurements were conducted by injecting the light of a picosecond near- infrared laser in the medium of interest and by collecting, for several wavelengths and multiple positions, the backscattered light via two fibers (with a source-detector separation of 15 mm) connected to fast-gated single-photon avalanche diodes (SPAD) and coupled to a time-correlated single-photon counting (TCSPC) system. Validations of the method were performed in simulation in the same configuration as the experiments for different combination of chromophores. Evaluation of the technique in real conditions was investigated on liquid phantoms composed of an homogenous background and a 10 mm depth inclusion formed of combination of intralipid and inks scanned at 30 positions and at three wavelengths. Both numerical and preliminary phantom experiments confirm the potential of this method to determine chromophore concentrations in the depth of biological tissues.

  9. Distributed multi-hypothesis coding of depth maps using texture motion information and optical flow

    DEFF Research Database (Denmark)

    Salmistraro, Matteo; Zamarin, Marco; Rakêt, Lars Lau

    2013-01-01

    Distributed Video Coding (DVC) is a video coding paradigm allowing a shift of complexity from the encoder to the decoder. Depth maps are images enabling the calculation of the distance of an object from the camera, which can be used in multiview coding in order to generate virtual views, but also...... information, a block-based and an optical flow-based methods are employed. Finally we fuse the proposed Side Informations using a multi-hypothesis DVC decoder, which allows us to exploit the strengths of all the proposed methods at the same time....

  10. Relationship between wind speed and aerosol optical depth over remote ocean

    Directory of Open Access Journals (Sweden)

    R. G. Grainger

    2009-11-01

    Full Text Available The effect of wind speed on aerosol optical depth (AOD at 550 nm over remote ocean regions is investigated. Remote ocean regions are defined by the combination of AOD from satellite observation and wind direction from ECMWF. According to our definition, many oceanic regions cannot be taken as remote ocean regions due to long-range transportation of aerosols from continents. Highly correlated linear relationships are found in remote ocean regions with a wind speed range of 4–20 ms−1. The enhancement of AOD at high wind speed is explained as the increase of sea salt aerosol production.

  11. Ground-based aerosol optical depth inter-comparison campaigns at European EUSAAR super-sites

    Science.gov (United States)

    Nyeki, S.; Gröbner, J.; Wehrli, C.

    2013-05-01

    This work summarizes eight aerosol optical depth (AOD) inter-comparison campaigns conducted during the 2008-2011 period. A PFR (precision filter radiometer) travelling standard from the GAW-PFR network (based at PMOD/WRC, Switzerland) was run alongside existing CIMEL sun-photometers from the PHOTONS/AERONET network located at European stations. Basic statistical analysis of coincident measurements at λ = 500 and 862 nm illustrated good agreement. However, when WMO criteria for traceability were applied only one wavelength at three stations was traceable. Other stations were close to being traceable but had slight issues with window cleanliness and calibration.

  12. Intercomparison of aerosol optical depth from Brewer ozone spectrophotometers and CIMEL sunphotometers measurements

    Directory of Open Access Journals (Sweden)

    A. Cheymol

    2008-06-01

    Full Text Available The Langley plot method applied on the Brewer Ozone measurements can provide accurate Aerosol Optical Depth (AOD in the UV-B. We present seven intercomparisons between AOD retrieved from Brewer Ozone measurements and AOD measured by CIMEL sunphotometer, which are stored in the international AERONET database. Only the intercomparisons between co-located instruments can be used to validate the Langley Plot method applied to the Brewer measurements: in this case, all the correlation coefficient are above 0.83. If the instruments are not at the same site, the correlation between the AOD retrieved by both instruments is much lower.

  13. Aerosol optical depth determination in the UV using a four-channel precision filter radiometer

    Science.gov (United States)

    Carlund, Thomas; Kouremeti, Natalia; Kazadzis, Stelios; Gröbner, Julian

    2017-03-01

    The determination of aerosol properties, especially the aerosol optical depth (AOD) in the ultraviolet (UV) wavelength region, is of great importance for understanding the climatological variability of UV radiation. However, operational retrievals of AOD at the biologically most harmful wavelengths in the UVB are currently only made at very few places. This paper reports on the UVPFR (UV precision filter radiometer) sunphotometer, a stable and robust instrument that can be used for AOD retrievals at four UV wavelengths. Instrument characteristics and results of Langley calibrations at a high-altitude site were presented. It was shown that due to the relatively wide spectral response functions of the UVPFR, the calibration constants (V0) derived from Langley plot calibrations underestimate the true extraterrestrial signals. Accordingly, correction factors were introduced. In addition, the instrument's spectral response functions also result in an apparent air-mass-dependent decrease in ozone optical depth used in the AOD determinations. An adjusted formula for the calculation of AOD, with a correction term dependent on total column ozone amount and ozone air mass, was therefore introduced. Langley calibrations performed 13-14 months apart resulted in sensitivity changes of ≤ 1.1 %, indicating good instrument stability. Comparison with a high-accuracy standard precision filter radiometer, measuring AOD at 368-862 nm wavelengths, showed consistent results. Also, very good agreement was achieved by comparing the UVPFR with AOD at UVB wavelengths derived with a Brewer spectrophotometer, which was calibrated against the UVPFR at an earlier date. Mainly due to non-instrumental uncertainties connected with ozone optical depth, the total uncertainty of AOD in the UVB is higher than that reported from AOD instruments measuring in UVA and visible ranges. However, the precision can be high among instruments using harmonized algorithms for ozone and Rayleigh optical depth as

  14. Strategies to Improve the Accuracy of Mars-GRAM Sensitivity Studies at Large Optical Depths

    Science.gov (United States)

    Justh, Hilary L.; Justus, Carl G.; Badger, Andrew M.

    2010-01-01

    The poster provides an overview of techniques to improve the Mars Global Reference Atmospheric Model (Mars-GRAM) sensitivity. It has been discovered during the Mars Science Laboratory (MSL) site selection process that the Mars Global Reference Atmospheric Model (Mars-GRAM) when used for sensitivity studies for TES MapYear = 0 and large optical depth values such as tau = 3 is less than realistic. A preliminary fix has been made to Mars-GRAM by adding a density factor value that was determined for tau = 0.3, 1 and 3.

  15. Depth-resolved 3D visualization of coronary microvasculature with optical microangiography

    Science.gov (United States)

    Qin, Wan; Roberts, Meredith A.; Qi, Xiaoli; Murry, Charles E.; Zheng, Ying; Wang, Ruikang K.

    2016-11-01

    In this study, we propose a novel implementation of optical coherence tomography-based angiography combined with ex vivo perfusion of fixed hearts to visualize coronary microvascular structure and function. The extracorporeal perfusion of Intralipid solution allows depth-resolved angiographic imaging, control of perfusion pressure, and high-resolution optical microangiography. The imaging technique offers new opportunities for microcirculation research in the heart, which has been challenging due to motion artifacts and the lack of independent control of pressure and flow. With the ability to precisely quantify structural and functional features, this imaging platform has broad potential for the study of the pathophysiology of microvasculature in the heart as well as other organs.

  16. Design of the optical fiber unit for industrial equipment

    Science.gov (United States)

    Fedosov, Yuri V.; Romanova, Galina E.; Afanasev, Maxim Ya.

    2017-05-01

    Optical systems with UV lasers are widely used in various areas of manufacturing, for processing materials. To provide high operation accuracy, the equipment with high power UV laser sources requires complicated optical and mechanical unit with control electronic blocks. In order to develop successful and stable equipment and to increase accuracy, the development of each part (optical, mechanical, and electronic) is needed to solve many complex engineering problems. In this article the special features of the development of an optical unit with a high powered UV laser source are considered along with some problems and solutions.

  17. CALIPSO observations of wave-induced PSCs with near-unity optical depth over Antarctica in 2006-2007

    CERN Document Server

    Noel, Vincent; Chepfer, Hélène

    2009-01-01

    Ground-based and satellite observations have hinted at the existence of polar stratospheric clouds (PSCs) with relatively high optical depths, even if optical depth values are hard to come by. This study documents a type II PSC observed from spaceborne lidar, with visible optical depths up to 0.8. Comparisons with multiple temperature fields, including reanalyses and results from mesoscale simulations, suggest that intense small-scale temperature fluctuations due to gravity waves play an important role in its formation, while nearby observations show the presence of a potentially related type Ia PSC farther downstream inside the polar vortex. Following this first case, the geographic distribution and microphysical properties of PSCs with optical depths above 0.3 are explored over Antarctica during the 2006 and 2007 austral winters. These clouds are rare (less than 1% of profiles) and concentrated over areas where strong winds hit steep ground slopes in the Western Hemisphere, especially over the peninsula. Su...

  18. Herschel-Planck dust optical depth and column density maps - II. Perseus

    CERN Document Server

    Zari, E; Alves, J; Lada, C J; Bouy, H

    2015-01-01

    We present optical depth and temperature maps of the Perseus molecular cloud, obtained combining dust emission data from the Herschel and Planck satellites and 2MASS/NIR dust extinction maps. The maps have a resolution of 36 arcsec in the Herschel regions, and of 5 arcmin elsewhere. The dynamic range of the optical depth map ranges from $1\\times10^{-2}\\, \\mathrm{mag}$ up to $20 \\,\\mathrm{mag}$ in the equivalent K band extinction. We also evaluate the ratio between the $2.2 \\,\\mathrm{\\mu m}$ extinction coefficient and the $850 \\,\\mathrm{\\mu m}$ opacity. The value we obtain is close to the one found in the Orion B molecular cloud. We show that the cumulative and the differential area function of the data (which is proportional to the probability distribution function of the cloud column density) follow power laws with index respectively $\\simeq -2$, and $\\simeq -3$. We use WISE data to improve current YSO catalogues based mostly on \\emph{Spitzer} data and we build an up-to-date selection of Class~I/0 objects. U...

  19. CALIOP and AERONET Aerosol Optical Depth Comparisons: One Size Fits None

    Science.gov (United States)

    Omar, A. H.; Winker, D. M.; Tackett, J. L.; Giles, D. M.; Kar, J.; Liu, Z.; Vaughan, M. A.; Powell, K. A.; Trepte, C. R.

    2013-01-01

    We compare the aerosol optical depths (AOD) retrieved from backscatter measurements of the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard the Cloud Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) satellite with coincident Aerosol Robotic Network (AERONET) measurements. Overpass coincidence criteria of +/- 2 h and within a 40 km radius are satisfied at least once at 149 globally distributed AERONET sites from 2006 to 2010. Most data pairs (>80%) use AERONET measurements acquired +/- 30 min of the overpass. We examine the differences in AOD estimates between CALIOP and AERONET for various aerosol, environmental, and geographic conditions. Results show CALIOP AOD are lower than AERONET AOD especially at low optical depths as measured by AERONET (500 nm AOD0.1. Differences in AOD between CALIOP and AERONET are possibly due to cloud contamination, scene inhomogeneity, instrument view angle differences, CALIOP retrieval errors, and detection limits. Comparison of daytime to nighttime number of 5 km 60m (60m in the vertical) features detected by CALIOP show that there are 20% more aerosol features at night. We find that CALIPSO and AERONET do not agree on the cloudiness of scenes. Of the scenes that meet the above coincidence criteria, CALIPSO finds clouds in more than 45% of the coincident atmospheric columns AERONET classifies as clear.

  20. The Origin and Optical Depth of Ionizing Photons in the Green Pea Galaxies

    Science.gov (United States)

    Jaskot, A. E.; Oey, M. S.

    2014-09-01

    Our understanding of radiative feedback and star formation in galaxies at high redshift is hindered by the rarity of similar systems at low redshift. However, the recently identified Green Pea (GP) galaxies are similar to high-redshift galaxies in their morphologies and star formation rates and are vital tools for probing the generation and transmission of ionizing photons. The GPs contain massive star clusters that emit copious amounts of high-energy radiation, as indicated by intense [OIII] 5007 emission and HeII 4686 emission. We focus on six GP galaxies with high ratios of [O III] 5007,4959/[O II] 3727 ~10 or more. Such high ratios indicate gas with a high ionization parameter or a low optical depth. The GP line ratios and ages point to chemically homogeneous massive stars, Wolf-Rayet stars, or shock ionization as the most likely sources of the He II emission. Models including shock ionization suggest that the GPs may have low optical depths, consistent with a scenario in which ionizing photons escape along passageways created by recent supernovae. The GPs and similar galaxies can shed new light on cosmic reionization by revealing how ionizing photons propagate from massive star clusters to the intergalactic medium.

  1. The Origin and Optical Depth of Ionizing Photons in the Green Pea Galaxies

    CERN Document Server

    Jaskot, A E

    2014-01-01

    Our understanding of radiative feedback and star formation in galaxies at high redshift is hindered by the rarity of similar systems at low redshift. However, the recently identified Green Pea (GP) galaxies are similar to high-redshift galaxies in their morphologies and star formation rates and are vital tools for probing the generation and transmission of ionizing photons. The GPs contain massive star clusters that emit copious amounts of high-energy radiation, as indicated by intense [OIII] 5007 emission and HeII 4686 emission. We focus on six GP galaxies with high ratios of [O III] 5007,4959/[O II] 3727 ~10 or more. Such high ratios indicate gas with a high ionization parameter or a low optical depth. The GP line ratios and ages point to chemically homogeneous massive stars, Wolf-Rayet stars, or shock ionization as the most likely sources of the He II emission. Models including shock ionization suggest that the GPs may have low optical depths, consistent with a scenario in which ionizing photons escape alo...

  2. A dark-line two-dimensional magneto-optical trap of 85Rb atoms with high optical depth.

    Science.gov (United States)

    Zhang, Shanchao; Chen, J F; Liu, Chang; Zhou, Shuyu; Loy, M M T; Wong, G K L; Du, Shengwang

    2012-07-01

    We describe the apparatus of a dark-line two-dimensional (2D) magneto-optical trap (MOT) of (85)Rb cold atoms with high optical depth (OD). Different from the conventional configuration, two (of three) pairs of trapping laser beams in our 2D MOT setup do not follow the symmetry axes of the quadrupole magnetic field: they are aligned with 45° angles to the longitudinal axis. Two orthogonal repumping laser beams have a dark-line volume in the longitudinal axis at their cross over. With a total trapping laser power of 40 mW and repumping laser power of 18 mW, we obtain an atomic OD up to 160 in an electromagnetically induced transparency (EIT) scheme, which corresponds to an atomic-density-length product NL = 2.05 × 10(15) m(-2). In a closed two-state system, the OD can become as large as more than 600. Our 2D MOT configuration allows full optical access of the atoms in its longitudinal direction without interfering with the trapping and repumping laser beams spatially. Moreover, the zero magnetic field along the longitudinal axis allows the cold atoms maintain a long ground-state coherence time without switching off the MOT magnetic field, which makes it possible to operate the MOT at a high repetition rate and a high duty cycle. Our 2D MOT is ideal for atomic-ensemble-based quantum optics applications, such as EIT, entangled photon pair generation, optical quantum memory, and quantum information processing.

  3. Ultra-high modulation depth exceeding 2,400% in optically controlled topological surface plasmons.

    Science.gov (United States)

    Sim, Sangwan; Jang, Houk; Koirala, Nikesh; Brahlek, Matthew; Moon, Jisoo; Sung, Ji Ho; Park, Jun; Cha, Soonyoung; Oh, Seongshik; Jo, Moon-Ho; Ahn, Jong-Hyun; Choi, Hyunyong

    2015-10-30

    Modulating light via coherent charge oscillations in solids is the subject of intense research topics in opto-plasmonics. Although a variety of methods are proposed to increase such modulation efficiency, one central challenge is to achieve a high modulation depth (defined by a ratio of extinction with/without light) under small photon-flux injection, which becomes a fundamental trade-off issue both in metals and semiconductors. Here, by fabricating simple micro-ribbon arrays of topological insulator Bi2Se3, we report an unprecedentedly large modulation depth of 2,400% at 1.5 THz with very low optical fluence of 45 μJ cm(-2). This was possible, first because the extinction spectrum is nearly zero due to the Fano-like plasmon-phonon-destructive interference, thereby contributing an extremely small denominator to the extinction ratio. Second, the numerator of the extinction ratio is markedly increased due to the photoinduced formation of massive two-dimensional electron gas below the topological surface states, which is another contributor to the ultra-high modulation depth.

  4. On the assimilation of optical reflectances and snow depth observations into a detailed snowpack model

    Science.gov (United States)

    Charrois, Luc; Cosme, Emmanuel; Dumont, Marie; Lafaysse, Matthieu; Morin, Samuel; Libois, Quentin; Picard, Ghislain

    2016-05-01

    This paper examines the ability of optical reflectance data assimilation to improve snow depth and snow water equivalent simulations from a chain of models with the SAFRAN meteorological model driving the detailed multilayer snowpack model Crocus now including a two-stream radiative transfer model for snow, TARTES. The direct use of reflectance data, allowed by TARTES, instead of higher level snow products, mitigates uncertainties due to commonly used retrieval algorithms.Data assimilation is performed with an ensemble-based method, the Sequential Importance Resampling Particle filter, to represent simulation uncertainties. In snowpack modeling, uncertainties of simulations are primarily assigned to meteorological forcings. Here, a method of stochastic perturbation based on an autoregressive model is implemented to explicitly simulate the consequences of these uncertainties on the snowpack estimates.Through twin experiments, the assimilation of synthetic spectral reflectances matching the MODerate resolution Imaging Spectroradiometer (MODIS) spectral bands is examined over five seasons at the Col du Lautaret, located in the French Alps. Overall, the assimilation of MODIS-like data reduces by 45 % the root mean square errors (RMSE) on snow depth and snow water equivalent. At this study site, the lack of MODIS data on cloudy days does not affect the assimilation performance significantly. The combined assimilation of MODIS-like reflectances and a few snow depth measurements throughout the 2010/2011 season further reduces RMSEs by roughly 70 %. This work suggests that the assimilation of optical reflectances has the potential to become an essential component of spatialized snowpack simulation and forecast systems. The assimilation of real MODIS data will be investigated in future works.

  5. The optical detection unit for Baikal-GVD neutrino telescope

    Directory of Open Access Journals (Sweden)

    Avrorin A.D.

    2016-01-01

    Full Text Available The first stage of the GVD-cluster composed of five strings was deployed in April 2014. Each string consists of two sections with 12 optical modules per section. A section is the basic detection unit of the Baikal neutrino telescope. We will describe the section design, review its basic elements – optical modules, FADC readout units, slow control and calibration systems, and present selected results for section in-situ tests in Lake Baikal.

  6. Depth discrimination in acousto-optic cerebral blood flow measurement simulation

    Science.gov (United States)

    Tsalach, A.; Schiffer, Z.; Ratner, E.; Breskin, I.; Zeitak, R.; Shechter, R.; Balberg, M.

    2016-03-01

    Monitoring cerebral blood flow (CBF) is crucial, as inadequate perfusion, even for relatively short periods of time, may lead to brain damage or even death. Thus, significant research efforts are directed at developing reliable monitoring tools that will enable continuous, bed side, simple and cost-effective monitoring of CBF. All existing non invasive bed side monitoring methods, which are mostly NIRS based, such as Laser Doppler or DCS, tend to underestimate CBF in adults, due to the indefinite effect of extra-cerebral tissues on the obtained signal. If those are to find place in day to day clinical practice, the contribution of extra-cerebral tissues must be eliminated and data from the depth (brain) should be extracted and discriminated. Recently, a novel technique, based on ultrasound modulation of light was developed for non-invasive, continuous CBF monitoring (termed ultrasound-tagged light (UTL or UT-NIRS)), and shown to correlate with readings of 133Xe SPECT and laser Doppler. We have assembled a comprehensive computerized simulation, modeling this acousto-optic technique in a highly scattering media. Using the combination of light and ultrasound, we show how depth information may be extracted, thus distinguishing between flow patterns taking place at different depths. Our algorithm, based on the analysis of light modulated by ultrasound, is presented and examined in a computerized simulation. Distinct depth discrimination ability is presented, suggesting that using such method one can effectively nullify the extra-cerebral tissues influence on the obtained signals, and specifically extract cerebral flow data.

  7. Software-Assisted Depth Analysis of Optic Nerve Stereoscopic Images in Telemedicine.

    Science.gov (United States)

    Xia, Tian; Patel, Shriji N; Szirth, Ben C; Kolomeyer, Anton M; Khouri, Albert S

    2016-01-01

    Background. Software guided optic nerve assessment can assist in process automation and reduce interobserver disagreement. We tested depth analysis software (DAS) in assessing optic nerve cup-to-disc ratio (VCD) from stereoscopic optic nerve images (SONI) of normal eyes. Methods. In a prospective study, simultaneous SONI from normal subjects were collected during telemedicine screenings using a Kowa 3Wx nonmydriatic simultaneous stereoscopic retinal camera (Tokyo, Japan). VCD was determined from SONI pairs and proprietary pixel DAS (Kowa Inc., Tokyo, Japan) after disc and cup contour line placement. A nonstereoscopic VCD was determined using the right channel of a stereo pair. Mean, standard deviation, t-test, and the intraclass correlation coefficient (ICCC) were calculated. Results. 32 patients had mean age of 40 ± 14 years. Mean VCD on SONI was 0.36 ± 0.09, with DAS 0.38 ± 0.08, and with nonstereoscopic 0.29 ± 0.12. The difference between stereoscopic and DAS assisted was not significant (p = 0.45). ICCC showed agreement between stereoscopic and software VCD assessment. Mean VCD difference was significant between nonstereoscopic and stereoscopic (p stereoscopic VCD.

  8. Software-Assisted Depth Analysis of Optic Nerve Stereoscopic Images in Telemedicine

    Directory of Open Access Journals (Sweden)

    Tian Xia

    2016-01-01

    Full Text Available Background. Software guided optic nerve assessment can assist in process automation and reduce interobserver disagreement. We tested depth analysis software (DAS in assessing optic nerve cup-to-disc ratio (VCD from stereoscopic optic nerve images (SONI of normal eyes. Methods. In a prospective study, simultaneous SONI from normal subjects were collected during telemedicine screenings using a Kowa 3Wx nonmydriatic simultaneous stereoscopic retinal camera (Tokyo, Japan. VCD was determined from SONI pairs and proprietary pixel DAS (Kowa Inc., Tokyo, Japan after disc and cup contour line placement. A nonstereoscopic VCD was determined using the right channel of a stereo pair. Mean, standard deviation, t-test, and the intraclass correlation coefficient (ICCC were calculated. Results. 32 patients had mean age of 40±14 years. Mean VCD on SONI was 0.36±0.09, with DAS 0.38±0.08, and with nonstereoscopic 0.29±0.12. The difference between stereoscopic and DAS assisted was not significant (p=0.45. ICCC showed agreement between stereoscopic and software VCD assessment. Mean VCD difference was significant between nonstereoscopic and stereoscopic (p<0.05 and nonstereoscopic and DAS (p<0.005 recordings. Conclusions. DAS successfully assessed SONI and showed a high degree of correlation to physician-determined stereoscopic VCD.

  9. A multi-approach to the optical depth of a contrail cirrus cluster

    Science.gov (United States)

    Vazquez-Navarro, Margarita; Bugliaro, Luca; Schumann, Ulrich; Strandgren, Johan; Wirth, Martin; Voigt, Christiane

    2017-04-01

    Amongst the individual aviation emissions, contrail cirrus contribute the largest fraction to the aviation effects on climate. To investigate the optical depth from contrail cirrus, we selected a cirrus and contrail cloud outbreak on the 10th April 2014 between the North Sea and Switzerland detected during the ML-CIRRUS experiment (Voigt et al., 2017). The outbreak was not forecast by weather prediction models. We describe its origin and evolution using a combination of in-situ measurements, remote sensing approaches and contrail prediction model prognosis. The in-situ and lidar measurements were carried out with the HALO aircraft, where the cirrus was first identified. Model predictions from the contrail prediction model CoCiP (Schumann et al., 2012) point to an anthropogenic origin. The satellite pictures from the SEVIRI imager on MSG combined with the use of a contrail cluster tracking algorithm enable the automatic assessment of the origin, displacement and growth of the cloud and the correct labeling of cluster pixels. The evolution of the optical depth and particle size of the selected cluster pixels were derived using the CiPS algorithm, a neural network primarily based on SEVIRI images. The CoCiP forecast of the cluster compared to the actual cluster tracking show that the model correctly predicts the occurrence of the cluster and its advection direction although the cluster spreads faster than simulated. The optical depth derived from CiPS and from the airborne high spectral resolution lidar WALES are compared and show a remarkably good agreement. This confirms that the new CiPS algorithm is a very powerful tool for the assessment of the optical depth of even optically thinner cirrus clouds. References: Schumann, U.: A contrail cirrus prediction model, Geosci. Model Dev., 5, 543-580, doi: 10.5194/gmd-5-543-2012, 2012. Voigt, C., Schumann, U., Minikin, A., Abdelmonem, A., Afchine, A., Borrmann, S., Boettcher, M., Buchholz, B., Bugliaro, L., Costa, A

  10. Improving depth resolution of diffuse optical tomography with an exponential adjustment method based on maximum singular value of layered sensitivity

    Institute of Scientific and Technical Information of China (English)

    Haijing Niu; Ping Guo; Xiaodong Song; Tianzi Jiang

    2008-01-01

    The sensitivity of diffuse optical tomography (DOT) imaging exponentially decreases with the increase of photon penetration depth, which leads to a poor depth resolution for DOT. In this letter, an exponential adjustment method (EAM) based on maximum singular value of layered sensitivity is proposed. Optimal depth resolution can be achieved by compensating the reduced sensitivity in the deep medium. Simulations are performed using a semi-infinite model and the simulation results show that the EAM method can substantially improve the depth resolution of deeply embedded objects in the medium. Consequently, the image quality and the reconstruction accuracy for these objects have been largely improved.

  11. Development of dual-layer GSO depth-of-interaction block detector using angled optical fiber

    Energy Technology Data Exchange (ETDEWEB)

    Okumura, Satoshi, E-mail: okumura.satoshi@c.mbox.nagoya-u.ac.jp [Nagoya University Graduate School of Medicine (Japan); Yamamoto, Seiichi [Nagoya University Graduate School of Medicine (Japan); Watabe, Hiroshi [Cyclotron and Radioisotope Center (CYRIC), Tohoku University (Japan); Kato, Natsuki; Hamamura, Huka [Nagoya University Graduate School of Medicine (Japan)

    2015-05-01

    A PET system for small animals requires a small detector ring to obtain high-spatial resolution images. However, when we use a relatively large size of photodetector such as a position-sensitive photomultiplier tube (PSPMT), the detector ring is arranged in a hexagonal- or octagonal-shape, and the PET system has large gaps between the block detectors. The large gaps produce image distortion, and the reconstruction algorithm is difficult. To solve these problems, we proposed to arrange two scintillator blocks on one PSPMT using two angled optical fiber-based image guides. We could set two scintillator blocks angled at 22.5° on a PSPMT so that these scintillator blocks are arranged in a nearly circular (hexadecagonal) shape with eight developed block detectors. We used Gd{sub 2}SiO{sub 5} (GSO) scintillators with Ce concentrations of 1.5 mol% (decay time: 39 ns) and 0.4 mol% (decay time: 63 ns). Sizes of these GSO cells were 1.6×2.4×7.0 mm{sup 3} and 1.6×2.4×8.0 mm{sup 3} for 1.5 mol% Ce and 0.4 mol% Ce, respectively. These two types of GSO were arranged in an 11×15 matrix and optically coupled in the depth direction to form a depth-of-interaction (DOI) detector. Two GSO blocks and two optical fiber-based image guides were optically coupled to a 2-in. PSPMT (Hamamatsu Photonics H8500: 8×8 anodes). We measured the performances of the block detector with Cs-137 gamma photons (662-keV). We could resolve almost all pixels clearly in a two-dimensional position histogram. The average peak-to-valley ratios (P/Vs) of the two-dimensional position histogram along profiles were 2.6 and 4.8 in horizontal and vertical directions, respectively. The energy resolution was 28.4% full-width at half-maximum (FWHM). The pulse shape spectra showed good separation with a P/V of 5.2. The developed block detector performed well and shows promise for the development of high-sensitivity and high-spatial resolution PET systems.

  12. Spectral-domain optical coherence tomography enhanced depth imaging of the normal and glaucomatous nonhuman primate optic nerve head.

    Science.gov (United States)

    Yang, Hongli; Qi, Jingjing; Hardin, Christy; Gardiner, Stuart K; Strouthidis, Nicholas G; Fortune, Brad; Burgoyne, Claude F

    2012-01-25

    To test whether the enhanced depth imaging (EDI) modality improves anterior and posterior lamina cribrosa surface (ALCS and PLCS) visibility compared with conventional spectral-domain optical coherence tomography (SD-OCT). Conventional and EDI SD-OCT scans were obtained 30 minutes after IOP was manometrically lowered to 10 mm Hg in both eyes of 14 nonhuman primates (NHPs) with unilateral experimental glaucoma (EG). Thirteen horizontal and seven vertical radial B-scans of each SD-OCT data set were delineated by one operator masked to image type. Delineated ALCS and PLCS points were projected to 1 of 100 equal-sized subregions of the neural canal opening (NCO) reference plane, and the number of delineated subregions (≥2 points) was counted. Poisson regression was used to analyze the effects of image type, treatment, and quadrant. Two additional delineations were performed for three NHPs to compare reproducibility. EDI increased the number of subregions delineated for both the ALCS (by 28%; P PLCS (by 225%; P PLCS visibility was significant in all four quadrants (P PLCS depth which was deeper in the EDI data sets (P = 0.0002). ALCS and PLCS visibility within control and EG NHP ONHs increased in EDI compared to conventional SD-OCT data sets. Further study of EDI effects on PLCS parameterization is required.

  13. Reconstruction of long-term aerosol optical depth series with sunshine duration records

    Science.gov (United States)

    Sanchez-Romero, A.; Sanchez-Lorenzo, A.; González, J. A.; Calbó, J.

    2016-02-01

    We report the suitability of sunshine duration (SD) records as a proxy for the reconstruction of atmospheric aerosol content, for which little information exists, especially prior to the 1980s. Specifically, we have treated cloudless summer days in 16 stations throughout Spain. For almost all sites we find statistically significant relationships between aerosol optical depth (AOD) and daily SD. The correlation coefficient presents a mean value of -0.72, and slope values of the linear regressions are within the range [-0.11, -0.36]. The relationships are used to generate AOD series back to the 1960s (to the 1920s for Madrid). These reconstructed series show an increase in AOD from the mid-1960s to the 1980s, followed by a decrease until the present, in agreement with changes in anthropogenic aerosol emissions and with opposite trends of solar irradiance. The method can be used to reconstruct AOD from the late nineteenth century at many stations worldwide.

  14. Measurement of depth-resolved thermal deformation distribution using phase-contrast spectral optical coherence tomography.

    Science.gov (United States)

    Zhang, Yun; Dong, Bo; Bai, Yulei; Ye, Shuangli; Lei, Zhenkun; Zhou, Yanzhou

    2015-10-19

    An updated B-scan method is proposed for measuring the evolution of thermal deformation fields in polymers. In order to measure the distributions of out-of-plane deformation and normal strain field, phase-contrast spectral optical coherence tomography (PC-SOCT) was performed with the depth range and resolution of 4.3 mm and 10.7 μm, respectively, as thermal loads were applied to three different multilayer samples. The relation between temperature and material refractive index was predetermined before the measurement. After accounting for the refractive index, the thermal deformation fields in the polymer were obtained. The measured thermal expansion coefficient of silicone sealant was approximately equal to its reference value. This method allows correctly assessing the mechanical properties in semitransparent polymers.

  15. Comparing mesoscale chemistry-transport model and remote-sensed Aerosol Optical Depth

    CERN Document Server

    Carnevale, C; Pisoni, E; Volta, M

    2010-01-01

    A comparison of modeled and observed Aerosol Optical Depth (AOD) is presented. 3D Eulerian multiphase chemistry-transport model TCAM is employed for simulating AOD at mesoscale. MODIS satellite sensor and AERONET photometer AOD are used for comparing spatial patterns and temporal timeseries. TCAM simulations for year 2004 over a domain containing Po-Valley and nearly whole Northern Italy are employed. For the computation of AOD, a configuration of external mixing of the chemical species is considered. Furthermore, a parametrization of the effect of moisture affecting both aerosol size and composition is used. An analysis of the contributions of the granulometric classes to the extinction coefficient reveals the dominant role of the inorganic compounds of submicron size. For the analysis of spatial patterns, summer and winter case study are considered. TCAM AOD reproduces spatial patterns similar to those retrieved from space, but AOD values are generally smaller by an order of magnitude. However, accounting a...

  16. Intercomparison of Aerosol Optical Depth from Brewer Ozone spectrophotometers and CIMEL sunphotometers measurements

    Directory of Open Access Journals (Sweden)

    A. Cheymol

    2009-01-01

    Full Text Available The Langley plot method applied on the Brewer Ozone measurements can provide accurate Aerosol Optical Depth (AOD in the UV-B. We present seven intercomparisons between AOD retrieved from Brewer Ozone measurements at 320 nm and AOD measured by CIMEL sunphotometer at 340 nm or 440 nm (shifted to 320 nm in using the Angström's law, which are stored in the international AERONET database. Only the intercomparisons between co-located instruments can be used to validate the Langley Plot Method applied to the Brewer measurements: in this case, all the correlation coefficients are above 0.82. If the instruments are not at the same site, the correlation between the AOD retrieved by both instruments is much lower. In applying the Angström's law the intercomparison is improved compared to previous study.

  17. A comparison of two methods to measure choroidal thickness by enhanced depth imaging optical coherence tomography

    DEFF Research Database (Denmark)

    Lundberg, Lars Kristian; Vestergaard, Anders Højslet; Vergmann, Anna Stage

    coherence tomography (EDI-SD OCT) has made it possible to visualize the choroid, and it is generally accepted that Heidelberg Spectralis OCT provides valid measurements of choroidal thickness (CT), although no fully automated software is commercially available. Two methods for CT-measurement are available...... the CT: 1: Segmentation method; by the use of the thickness profile window we manually edited and moved the inner limiting membrane (ILM) line to the choroid-scleral border (CSB), while we kept the automated defined Bruchs membrane (BM). Hereafter, the software calculated the vertical distance between......Introduction The choroid is believed to be involved in the pathophysiology of several vision threatening diseases such as age-related macular degeneration, central serous chorioretinopathy, inflammatory disorders and myopic macular degeneration. Enhanced depth imaging spectral-domain optical...

  18. Preliminary investigations toward nighttime aerosol optical depth retrievals from the VIIRS day/night band

    Directory of Open Access Journals (Sweden)

    R. S. Johnson

    2013-01-01

    Full Text Available A great need exists for reliable nighttime aerosol products at high spatial and temporal resolution. In this concept demonstration study, using Visible/Infrared Imager/Radiometer Suite (VIIRS Day/Night Band (DNB observations on the Suomi National Polar-orbiting Partnership (NPP satellite, a new method is proposed for retrieving nighttime aerosol optical depth (τ using the contrast between regions with and without artificial surface lights. Evaluation of the retrieved τ values against daytime AERONET data from before and after the overpass of the VIIRS satellite over the Cape Verde, Grand Forks, and Alta Floresta AERONET stations yields a coefficient of determination (r2 of 0.71. This study suggests that the VIIRS DNB has the potential to provide useful nighttime aerosol detection and property retrievals.

  19. Measurements of UV aerosol optical depth in the French Southern Alps

    Directory of Open Access Journals (Sweden)

    J. Lenoble

    2008-11-01

    Full Text Available Routine measurements of global and diffuse UV irradiances at Briançon station (1310 m a.s.l. are used to retrieve the direct solar irradiance and the aerosol optical depth (AOD, for cloudless days. Data of three years (2003, 2004, 2005 are analyzed; the results confirm those of a preliminary analysis for 2001, 2002.

    The atmosphere is very clear in winter, with AODs between 0.05 and 0.1. The turbidity increases slowly in spring, starting end of February, with AODs around 0.2–0.3 in mid summer, some values reaching 0.4. A similar behaviour is observed for all years, with somewhat higher values in late summer for the year 2003.

  20. Automated Solar Tracking Spectrophotometer for Remote Sensing of Column Aerosol Optical Depth

    Science.gov (United States)

    Rainwater, B.; Arnott, W. P.; Moosmuller, H.; Karr, D.

    2012-12-01

    Aerosols in the atmosphere are poorly understood in terms of how they affect weather and climate. In an effort to advance this knowledge, an automated solar tracking spectrophotometer has been constructed to measure direct solar radiation from the ultraviolet to infrared. This instrument facilitates determination of solar irradiance, precipitable water, aerosol optical depth (AOD), and the Ångström turbidity exponent related to aerosol size distribution. Measurements with a CIMEL CE-318 sun photometer (part of the global NASA AERONET network) and a manual solar spectrophotometer are being used to evaluate the accuracy of our instrument. Upon successful evaluation, this instrument will provide a basis for research into spectral information that will supplement CIMEL measurements. Presented is the design of this instrument and measurement comparisons with the aforementioned instruments for the air above Reno, Nevada, USA.

  1. Assessment of error in aerosol optical depth measured by AERONET due to aerosol forward scattering

    Science.gov (United States)

    Sinyuk, Alexander; Holben, Brent N.; Smirnov, Alexander; Eck, Thomas F.; Slutsker, Ilya; Schafer, Joel S.; Giles, David M.; Sorokin, Mikhail

    2012-12-01

    We present an analysis of the effect of aerosol forward scattering on the accuracy of aerosol optical depth (AOD) measured by CIMEL Sun photometers. The effect is quantified in terms of AOD and solar zenith angle using radiative transfer modeling. The analysis is based on aerosol size distributions derived from multi-year climatologies of AERONET aerosol retrievals. The study shows that the modeled error is lower than AOD calibration uncertainty (0.01) for the vast majority of AERONET level 2 observations, ∼99.53%. Only ∼0.47% of the AERONET database corresponding mostly to dust aerosol with high AOD and low solar elevations has larger biases. We also show that observations with extreme reductions in direct solar irradiance do not contribute to level 2 AOD due to low Sun photometer digital counts below a quality control cutoff threshold.

  2. Optical gesture sensing and depth mapping technologies for head-mounted displays: an overview

    Science.gov (United States)

    Kress, Bernard; Lee, Johnny

    2013-05-01

    Head Mounted Displays (HMDs), and especially see-through HMDs have gained renewed interest in recent time, and for the first time outside the traditional military and defense realm, due to several high profile consumer electronics companies presenting their products to hit market. Consumer electronics HMDs have quite different requirements and constrains as their military counterparts. Voice comments are the de-facto interface for such devices, but when the voice recognition does not work (not connection to the cloud for example), trackpad and gesture sensing technologies have to be used to communicate information to the device. We review in this paper the various technologies developed today integrating optical gesture sensing in a small footprint, as well as the various related 3d depth mapping sensors.

  3. On how the optical depth tunes the effects of ISM neutral atom flow on debris disks

    CERN Document Server

    Marzari, Francesco

    2011-01-01

    The flux of ISM neutral atoms surrounding stars and their environment affects the motion of dust particles in debris disks, causing a significant dynamical evolution. Large values of eccentricity and inclination can be excited and strong correlations settle in among the orbital angles. This dynamical behaviour, in particular for bound dust grains, can potentially cause significant asymmetries in dusty disks around solar type stars which might be detected by observations. However, the amount of orbital changes due to this non--gravitational perturbation is strongly limited by the collisional lifetime of dust particles. We show that for large values of the disk's optical depth the influence of ISM flow on the disk shape is almost negligible because the grains are collisionally destroyed before they can accumulate enough orbital changes due to the ISM perturbations. On the other hand, for values smaller than $10^{-3}$, peculiar asymmetric patterns appear in the density profile of the disk when we consider 1-10 m...

  4. Updating Mars-GRAM to Increase the Accuracy of Sensitivity Studies at Large Optical Depths

    Science.gov (United States)

    Justh, Hiliary L.; Justus, C. G.; Badger, Andrew M.

    2010-01-01

    The Mars Global Reference Atmospheric Model (Mars-GRAM) is an engineering-level atmospheric model widely used for diverse mission applications. Mars-GRAM s perturbation modeling capability is commonly used, in a Monte-Carlo mode, to perform high fidelity engineering end-to-end simulations for entry, descent, and landing (EDL). During the Mars Science Laboratory (MSL) site selection process, it was discovered that Mars-GRAM, when used for sensitivity studies for MapYear=0 and large optical depth values such as tau=3, is less than realistic. From the surface to 80 km altitude, Mars-GRAM is based on the NASA Ames Mars General Circulation Model (MGCM). MGCM results that were used for Mars-GRAM with MapYear set to 0 were from a MGCM run with a fixed value of tau=3 for the entire year at all locations. This has resulted in an imprecise atmospheric density at all altitudes. As a preliminary fix to this pressure-density problem, density factor values were determined for tau=0.3, 1 and 3 that will adjust the input values of MGCM MapYear 0 pressure and density to achieve a better match of Mars-GRAM MapYear 0 with Thermal Emission Spectrometer (TES) observations for MapYears 1 and 2 at comparable dust loading. Currently, these density factors are fixed values for all latitudes and Ls. Results will be presented from work being done to derive better multipliers by including variation with latitude and/or Ls by comparison of MapYear 0 output directly against TES limb data. The addition of these more precise density factors to Mars-GRAM 2005 Release 1.4 will improve the results of the sensitivity studies done for large optical depths.

  5. Mars-GRAM: Increasing the Precision of Sensitivity Studies at Large Optical Depths

    Science.gov (United States)

    Justh, Hilary L.; Justus, C. G.; Badger, Andrew M.

    2010-01-01

    The Mars Global Reference Atmospheric Model (Mars-GRAM) is an engineering-level atmospheric model widely used for diverse mission applications. Mars-GRAM's perturbation modeling capability is commonly used, in a Monte-Carlo mode, to perform high fidelity engineering end-to-end simulations for entry, descent, and landing (EDL). It has been discovered during the Mars Science Laboratory (MSL) site selection process that Mars-GRAM, when used for sensitivity studies for MapYear=0 and large optical depth values such as tau=3, is less than realistic. A comparison study between Mars atmospheric density estimates from Mars-GRAM and measurements by Mars Global Surveyor (MGS) has been undertaken for locations of varying latitudes, Ls, and LTST on Mars. The preliminary results from this study have validated the Thermal Emission Spectrometer (TES) limb data. From the surface to 80 km altitude, Mars-GRAM is based on the NASA Ames Mars General Circulation Model (MGCM). MGCM results that were used for Mars-GRAM with MapYear=0 were from a MGCM run with a fixed value of tau=3 for the entire year at all locations. This has resulted in an imprecise atmospheric density at all altitudes. To solve this pressure-density problem, density factor values were determined for tau=.3, 1 and 3 that will adjust the input values of MGCM MapYear 0 pressure and density to achieve a better match of Mars-GRAM MapYear 0 with TES observations for MapYears 1 and 2 at comparable dust loading. The addition of these density factors to Mars-GRAM will improve the results of the sensitivity studies done for large optical depths.

  6. Effective cloud optical depth and enhancement effects for broken liquid water clouds in Valencia (Spain)

    Science.gov (United States)

    Marín, M. J.; Serrano, D.; Utrillas, M. P.; Núñez, M.; Martínez-Lozano, J. A.

    2017-10-01

    Partly cloudy skies with liquid water clouds have been analysed, founding that it is essential to distinguish data if the Sun is obstructed or not by clouds. Both cases can be separated considering simultaneously the Cloud Modification Factor (CMF) and the clearness index (kt). For partly cloudy skies and the Sun obstructed the effective cloud optical depth (τ) has been obtained by the minimization method for overcast skies. This method was previously developed by the authors but, in this case, taking into account partial cloud cover. This study has been conducted for the years 2011-2015 with the multiple scattering model SBDART and irradiance measurements for the UV Erythemal Radiation (UVER) and the broadband ranges. Afterwards a statistical analysis of τ has shown that the maximum value is much lower than for overcast skies and there is more discrepancy between the two spectral ranges regarding the results for overcast skies. In order to validate these results the effective cloud optical depth has been correlated with several transmission factors, giving similar fit parameters to those obtained for overcast skies except for the clearness index in the UVER range. As our method is not applicable for partly cloudy skies with the visible Sun, the enhancement of radiation caused by clouds when the Sun is visible has been studied. Results show that the average enhancement CMF values are the same for both ranges although enhancement is more frequent for low cloud cover in the UVER and medium-high cloud cover in the broadband range and it does not depend on the solar zenith angle.

  7. Proposal for loadable and erasable optical memory unit based on dual active microring optical integrators

    Science.gov (United States)

    Ding, Yunhong; Zhang, Xiaobei; Zhang, Xinliang; Huang, Dexiu

    2008-11-01

    A novel approach for loadable and erasable optical memory unit based on dual microring optical integrators is proposed and studied. The optical integrator, which can generate an optical step function for data storing, is synthesized using active media for loss compensation and a tunable phase shifter for data reading at any time. The input data into the memory is return-to-zero (RZ) signal, and the output data read from the memory is also RZ format with a narrower pulse width. An optical digital register based on the proposed optical memory unit is also investigated and simulated, which shows the potential for large scale data storage and serial-to-parallel data conversion. A great number of such memory units can be densely integrated on a photonic circuit for future large scale data storage and buffer.

  8. Modern Fiber Optic Submarine Cable Telecommunication Systems Planning for Explosive Bandwidth Needs at Different Deployment Depths

    Directory of Open Access Journals (Sweden)

    Ahmed Nabih Zaki Rashed

    2012-10-01

    Full Text Available The explosive bandwidth needs, especially in the inter data center market, have pushed transmission data rates to 100 Gbit/sec and beyond. Current terrestrial fibers are inadequate for long haul, high bandwidth deployments. To solve these problems a new fiber is introduced for terrestrial high bandwidth deployments: different polymeric core fibers with enlarged effective area with a significant optical signal to noise ratio improvement over other conventional terrestrial single mode fibers. To ensure the new fiber may be deployed robustly a new coating structure was employed. A rigorous cable structure was then chosen for evaluation. Based on experimental data, both the deep ocean water temperature and pressure are tailored as functions of the water depth. As well as the product of the transmitted bit rate and the repeater spacing is processed over wide ranges of the affecting parameters. It is taken into account the estimation of the total cost of the submarine fiber cable system for transmission technique under considerations. The system capacity as well as the spectral losses, and the dispersion effects are parametrically investigated over wide range ranges of the set of affecting parameters {wavelength, ocean depth (and consequently the ocean pressure and temperature, and the chemical structure}.

  9. Optical Estimation of Depth and Current in a Ebb Tidal Delta Environment

    Science.gov (United States)

    Holman, R. A.; Stanley, J.

    2012-12-01

    A key limitation to our ability to make nearshore environmental predictions is the difficulty of obtaining up-to-date bathymetry measurements at a reasonable cost and frequency. Due to the high cost and complex logistics of in-situ methods, research into remote sensing approaches has been steady and has finally yielded fairly robust methods like the cBathy algorithm for optical Argus data that show good performance on simple barred beach profiles and near immunity to noise and signal problems. In May, 2012, data were collected in a more complex ebb tidal delta environment during the RIVET field experiment at New River Inlet, NC. The presence of strong reversing tidal currents led to significant errors in cBathy depths that were phase-locked to the tide. In this paper we will test methods for the robust estimation of both depths and vector currents in a tidal delta domain. In contrast to previous Fourier methods, wavenumber estimation in cBathy can be done on small enough scales to resolve interesting nearshore features.

  10. Review of spectral domain enhanced depth imaging optical coherence tomography of tumors of the choroid

    Directory of Open Access Journals (Sweden)

    Carol L Shields

    2015-01-01

    Full Text Available Background: Spectral domain enhanced depth imaging optical coherence tomography (EDI-OCT can provide anatomic localization of intraocular tumors. Aims: The aim was to identify topographical and intrinsic patterns of choroidal tumors on EDI-OCT. Settings and Design: Retrospective review. Materials and Methods: Analysis of published reports and personal observations using office based EDI-OCT. Results: Using EDI-OCT, choroidal nevus displayed a smooth, dome-shaped topography with overlying retinal pigment epithelium alterations, drusen, and occasional subretinal cleft demonstrating photoreceptor loss. Small choroidal melanoma showed smooth, moderately dome-shaped topography, commonly with overlying shallow subretinal fluid that often depicted "shaggy" photoreceptors. Choroidal metastasis showed a minimally "lumpy, bumpy" surface topography and with overlying subretinal fluid and shaggy photoreceptors. Choroidal hemangioma showed a smooth, dome-shaped topography, with expansion of the affected small, medium, and large choroidal vessels. Choroidal lymphoma showed varying topography with increasing tumor thickness as "flat, rippled, or undulating (seasick" surface. Choroidal osteoma displayed a smooth undulating surface with visible intralesional horizontal lines suggestive of bone lamellae and occasional horizontal and vertical tubules with intralesional "spongy" flecks. Choroidal melanocytosis appeared as uniformly thickened choroid with increased stromal density surrounding the normal choroidal vascular structures. Conclusions: Enhanced depth imaging-OCT can depict characteristic patterns that are suggestive of various choroidal tumors.

  11. Modern Fiber Optic Submarine Cable Telecommunication Systems Planning for Explosive Bandwidth Needs at Different Deployment Depths

    Directory of Open Access Journals (Sweden)

    Ahmed Nabih Zaki Rashed

    2012-05-01

    Full Text Available The explosive bandwidth needs, especially in the inter data center market, have pushed transmission data rates to 100 Gbit/sec and beyond. Current terrestrial fibers are inadequate for long haul, high bandwidth deployments. To solve these problems a new fiber is introduced for terrestrial high bandwidth deployments: different polymeric core fibers with enlarged effective area with a significant optical signal to noise ratio improvement over other conventional terrestrial single mode fibers. To ensure the new fiber may be deployed robustly a new coating structure was employed. A rigorous cable structure was then chosen for evaluation. Based on experimental data, both the deep ocean water temperature and pressure are tailored as functions of the water depth. As well as the product of the transmitted bit rate and the repeater spacing is processed over wide ranges of the affecting parameters. It is taken into account the estimation of the total cost of the submarine fiber cable system for transmission technique under considerations. The system capacity as well as the spectral losses, and the dispersion effects are parametrically investigated over wide range ranges of the set of affecting parameters {wavelength, ocean depth (and consequently the ocean pressure and temperature, and the chemical structure}.

  12. Sensitivity of nitrate aerosols to ammonia emissions and to nitrate chemistry: implications for present and future nitrate optical depth

    Directory of Open Access Journals (Sweden)

    F. Paulot

    2015-09-01

    Full Text Available We update and evaluate the treatment of nitrate aerosols in the Geophysical Fluid Dynamics Laboratory (GFDL atmospheric model (AM3. Accounting for the radiative effects of nitrate aerosols generally improves the simulated aerosol optical depth, although nitrate concentrations at the surface are biased high. This bias can be reduced by increasing the deposition of nitrate to account for the near-surface volatilization of ammonium nitrate or by neglecting the heterogeneous production of nitric acid to account for the inhibition of N2O5 reactive uptake at high nitrate concentrations. Globally, uncertainties in these processes can impact the simulated nitrate optical depth by up to 25 %, much more than the impact of uncertainties in the seasonality of ammonia emissions (6 % or in the uptake of nitric acid on dust (13 %. Our best estimate for present-day fine nitrate optical depth at 550 nm is 0.006 (0.005–0.008. We only find a modest increase of nitrate optical depth (2 (−40 % and ammonia (+38 % from 2010 to 2050. Nitrate burden is projected to increase in the tropics and in the free troposphere, but to decrease at the surface in the midlatitudes because of lower nitric acid concentrations. Our results suggest that better constraints on the heterogeneous chemistry of nitric acid on dust, on tropical ammonia emissions, and on the transport of ammonia to the free troposphere are needed to improve projections of aerosol optical depth.

  13. Depth-Encoded Spectral Domain Phase Microscopy for Simultaneous Multi-Site Nanoscale Optical Measurements.

    Science.gov (United States)

    Hendargo, Hansford C; Bower, Bradley A; Reinstein, Alex S; Shepherd, Neal; Tao, Yuankai K; Izatt, Joseph A

    2011-09-01

    Spectral domain phase microscopy (SDPM) is an extension of spectral domain optical coherence tomography (SDOCT) that exploits the extraordinary phase stability of spectrometer-based systems with common-path geometry to resolve sub-wavelength displacements within a sample volume. This technique has been implemented for high resolution axial displacement and velocity measurements in biological samples, but since axial displacement information is acquired serially along the lateral dimension, it has been unable to measure fast temporal dynamics in extended samples. Depth-Encoded SDPM (DESDPM) uses multiple sample arms with unevenly spaced common path reference reflectors to multiplex independent SDPM signals from separate lateral positions on a sample simultaneously using a single interferometer, thereby reducing the time required to detect unique optical events to the integration period of the detector. Here, we introduce DESDPM and demonstrate the ability to acquire useful phase data concurrently at two laterally separated locations in a phantom sample as well as a biological preparation of spontaneously beating chick cardiomyocytes. DESDPM may be a useful tool for imaging fast cellular phenomena such as nervous conduction velocity or contractile motion.

  14. Motionless active depth from defocus system using smart optics for camera autofocus applications

    Science.gov (United States)

    Amin, M. Junaid; Riza, Nabeel A.

    2016-04-01

    This paper describes a motionless active Depth from Defocus (DFD) system design suited for long working range camera autofocus applications. The design consists of an active illumination module that projects a scene illuminating coherent conditioned optical radiation pattern which maintains its sharpness over multiple axial distances allowing an increased DFD working distance range. The imager module of the system responsible for the actual DFD operation deploys an electronically controlled variable focus lens (ECVFL) as a smart optic to enable a motionless imager design capable of effective DFD operation. An experimental demonstration is conducted in the laboratory which compares the effectiveness of the coherent conditioned radiation module versus a conventional incoherent active light source, and demonstrates the applicability of the presented motionless DFD imager design. The fast response and no-moving-parts features of the DFD imager design are especially suited for camera scenarios where mechanical motion of lenses to achieve autofocus action is challenging, for example, in the tiny camera housings in smartphones and tablets. Applications for the proposed system include autofocus in modern day digital cameras.

  15. Enhanced Depth Imaging Optical Coherence Tomography: A New Way Measuring Choroidal Thickness in Pregnant Women

    Directory of Open Access Journals (Sweden)

    Jun Zhang

    2017-01-01

    Full Text Available The body changes markedly during pregnancy; each system behaves differently from a nonpregnant state. As the eyes are the only windows to see directly what is going on in the internal environment, more and more researches have been done to explain the association between ocular changes and the physiological and pathological changes during pregnancy. The choroid is one of the critical parts of the eye, providing nutrition. And abnormal choroid may result in ocular dysfunction and visual problems. As the optical coherence tomography develops, a rapid, direct, noninvasive, and nontoxic way is available to obtain the choroid situation of pregnant women, which may explain the mechanism of pregnancy-related eye diseases. This review would summarize relevant original articles published from January 1, 2008 to December 1, 2016 to assess the changes of choroidal thickness (CT with enhanced depth imaging optical coherence tomography (EDI-OCT during pregnancy. And the relationship between choroidal thickness changes and pregnancy remains uncertain. To our knowledge, this is the first review of EDI-OCT in assessing the choroidal thickness of the pregnant women.

  16. Enhanced Depth Imaging Optical Coherence Tomography: A New Way Measuring Choroidal Thickness in Pregnant Women

    Science.gov (United States)

    2017-01-01

    The body changes markedly during pregnancy; each system behaves differently from a nonpregnant state. As the eyes are the only windows to see directly what is going on in the internal environment, more and more researches have been done to explain the association between ocular changes and the physiological and pathological changes during pregnancy. The choroid is one of the critical parts of the eye, providing nutrition. And abnormal choroid may result in ocular dysfunction and visual problems. As the optical coherence tomography develops, a rapid, direct, noninvasive, and nontoxic way is available to obtain the choroid situation of pregnant women, which may explain the mechanism of pregnancy-related eye diseases. This review would summarize relevant original articles published from January 1, 2008 to December 1, 2016 to assess the changes of choroidal thickness (CT) with enhanced depth imaging optical coherence tomography (EDI-OCT) during pregnancy. And the relationship between choroidal thickness changes and pregnancy remains uncertain. To our knowledge, this is the first review of EDI-OCT in assessing the choroidal thickness of the pregnant women. PMID:28630765

  17. Enhanced Depth Imaging Optical Coherence Tomography: A New Way Measuring Choroidal Thickness in Pregnant Women.

    Science.gov (United States)

    Zhang, Jun; Wang, Huiyun; Yu, Qiubo; Tong, Qihu; Lu, Qinkang

    2017-01-01

    The body changes markedly during pregnancy; each system behaves differently from a nonpregnant state. As the eyes are the only windows to see directly what is going on in the internal environment, more and more researches have been done to explain the association between ocular changes and the physiological and pathological changes during pregnancy. The choroid is one of the critical parts of the eye, providing nutrition. And abnormal choroid may result in ocular dysfunction and visual problems. As the optical coherence tomography develops, a rapid, direct, noninvasive, and nontoxic way is available to obtain the choroid situation of pregnant women, which may explain the mechanism of pregnancy-related eye diseases. This review would summarize relevant original articles published from January 1, 2008 to December 1, 2016 to assess the changes of choroidal thickness (CT) with enhanced depth imaging optical coherence tomography (EDI-OCT) during pregnancy. And the relationship between choroidal thickness changes and pregnancy remains uncertain. To our knowledge, this is the first review of EDI-OCT in assessing the choroidal thickness of the pregnant women.

  18. On X-ray Optical Depth in the Coronae of Active Stars

    CERN Document Server

    Testa, Paola; Peres, Giovanni; Huenemoerder, David P

    2007-01-01

    We have investigated the optical thickness of the coronal plasma through the analysis of high-resolution X-ray spectra of a large sample of active stars observed with the High Energy Transmission Grating Spectrometer on Chandra. In particular, we probed for the presence of significant resonant scattering in the strong Lyman series lines arising from hydrogen-like oxygen and neon ions. The active RS CVn-type binaries II Peg and IM Peg and the single M dwarf EV Lac show significant optical depth. For these active coronae, the Lya/Lyb ratios are significantly depleted as compared with theoretical predictions and with the same ratios observed in similar active stars. Interpreting these decrements in terms of resonance scattering of line photons out of the line-of-sight, we are able to derive an estimate for the typical size of coronal structures, and from these we also derive estimates of coronal filling factors. For all three sources we find that the both the photon path length as a fraction of the stellar radiu...

  19. Monitoring the Phenology of Global Agroecosystems Using SMAP Multi-temporal Vegetation Optical Depth Retrievals

    Science.gov (United States)

    Piles, M.; Entekhabi, D.; Konings, A. G.; Akbar, R.; Jagdhuber, T.; Chaparro, D.; Das, N. N.

    2016-12-01

    The first year of SMAP observations has been used to derive simultaneously soil moisture and microwave vegetation optical depth (VOD) using solely passive L-band microwave measurements, without reliance of a priori information on vegetation classification. VOD is known to be sensitive to above-ground biomass and plant water content. Unlike well-established visible-infrared indices, VOD is independent of greenness, is not affected by atmospheric conditions and remains sensitive to biomass water-uptake dynamics. A selection of global agricultural core regions (Southern Canada, US Midwest, Argentina, Spain, Sahel, South India, North India) have been selected to focus on the vegetation signal measured at L-band. First results comparing changes in SMAP VOD to changes in MODIS Enhanced Vegetation Index outline the independent and complementary information provided by microwave and optical sensors in agroecosystems. The two months of SMAP active measurements acquired over these regions have also been analyzed to further investigate the different sensitivity of active and passive measurements to vegetation properties. Measures and statistics of crop phenology in the target regions are proposed. Results provide a first evaluation of the full potential of L-band microwave sensors for global land surface phenology and eco-hydrological studies.

  20. Assessment of 10 Year Record of Aerosol Optical Depth from OMI UV Observations

    Science.gov (United States)

    Ahn, Changwoo; Torres, Omar; Jethva, Hiren

    2014-01-01

    The Ozone Monitoring Instrument (OMI) onboard the EOS-Aura satellite provides information on aerosol optical properties by making use of the large sensitivity to aerosol absorption in the near-ultraviolet (UV) spectral region. Another important advantage of using near UV observations for aerosol characterization is the low surface albedo of all terrestrial surfaces in this spectral region that reduces retrieval errors associated with land surface reflectance characterization. In spite of the 13 × 24 square kilometers coarse sensor footprint, the OMI near UV aerosol algorithm (OMAERUV) retrieves aerosol optical depth (AOD) and single-scattering albedo under cloud-free conditions from radiance measurements at 354 and 388 nanometers. We present validation results of OMI AOD against space and time collocated Aerosol Robotic Network measured AOD values over multiple stations representing major aerosol episodes and regimes. OMAERUV's performance is also evaluated with respect to those of the Aqua-MODIS Deep Blue and Terra-MISR AOD algorithms over arid and semi-arid regions in Northern Africa. The outcome of the evaluation analysis indicates that in spite of the "row anomaly" problem, affecting the sensor since mid-2007, the long-term aerosol record shows remarkable sensor stability.

  1. Variability of aerosol optical depth and aerosol radiative forcing over Northwest Himalayan region

    Science.gov (United States)

    Saheb, Shaik Darga; Kant, Yogesh; Mitra, D.

    2016-05-01

    In recent years, the aerosol loading in India is increasing that has significant impact on the weather/climatic conditions. The present study discusses the analysis of temporal (monthly and seasonal) variation of aerosol optical depth(AOD) by the ground based observations from sun photometer and estimate the aerosol radiative forcing and heating rate over selected station Dehradun in North western Himalayas, India during 2015. The in-situ measurements data illustrate that the maximum seasonal average AOD observed during summer season AOD at 500nm ≍ 0.59+/-0.27 with an average angstrom exponent, α ≍0.86 while minimum during winter season AOD at 500nm ≍ 0.33+/-0.10 with angstrom exponent, α ≍1.18. The MODIS and MISR derived AOD was also compared with the ground measured values and are good to be in good agreement. Analysis of air mass back trajectories using HYSPLIT model reveal that the transportation of desert dust during summer months. The Optical Properties of Aerosols and clouds (OPAC) model was used to compute the aerosol optical properties like single scattering albedo (SSA), Angstrom coefficient (α) and Asymmetry(g) parameter for each day of measurement and they are incorporated in a Discrete Ordinate Radiative Transfer model, i.e Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) to estimate the direct short-wave (0.25 to 4 μm) Aerosol Radiative forcing at the Surface (SUR), the top-of-atmosphere (TOA) and Atmosphere (ATM). The maximum Aerosol Radiative Forcing (ARF) was observed during summer months at SUR ≍ -56.42 w/m2, at TOA ≍-21.62 w/m2 whereas in ATM ≍+34.79 w/m2 with corresponding to heating rate 1.24°C/day with in lower atmosphere.

  2. Ultrahigh and persistent optical depths of cesium in Kagomé-type hollow-core photonic crystal fibers.

    Science.gov (United States)

    Kaczmarek, Krzysztof T; Saunders, Dylan J; Sprague, Michael R; Kolthammer, W Steven; Feizpour, Amir; Ledingham, Patrick M; Brecht, Benjamin; Poem, Eilon; Walmsley, Ian A; Nunn, Joshua

    2015-12-01

    Alkali-filled hollow-core fibers are a promising medium for investigating light-matter interactions, especially at the single-photon level, due to the tight confinement of light and high optical depths achievable by light-induced atomic desorption (LIAD). However, until now these large optical depths could only be generated for seconds, at most once per day, severely limiting the practicality of the technology. Here we report the generation of the highest observed transient (>10(5) for up to a minute) and highest observed persistent (>2000 for hours) optical depths of alkali vapors in a light-guiding geometry to date, using a cesium-filled Kagomé-type hollow-core photonic crystal fiber (HC-PCF). Our results pave the way to light-matter interaction experiments in confined geometries requiring long operation times and large atomic number densities, such as generation of single-photon-level nonlinearities and development of single photon quantum memories.

  3. Ultrahigh and persistent optical depths of cesium in Kagomé-type hollow-core photonic crystal fibers

    Science.gov (United States)

    Kaczmarek, Krzysztof T.; Saunders, Dylan J.; Sprague, Michael R.; Kolthammer, W. Steven; Feizpour, Amir; Ledingham, Patrick M.; Brecht, Benjamin; Poem, Eilon; Walmsley, Ian A.; Nunn, Joshua

    2015-12-01

    Alkali-filled hollow-core fibres are a promising medium for investigating light-matter interactions, especially at the single-photon level, due to the tight confinement of light and high optical depths achievable by light-induced atomic desorption. However, until now these large optical depths could only be generated for seconds at most once per day, severely limiting the practicality of the technology. Here we report the generation of highest observed transient ($>10^5$ for up to a minute) and highest observed persistent ($>2000$ for hours) optical depths of alkali vapours in a light-guiding geometry to date, using a caesium-filled Kagom\\'e-type hollow-core photonic crystal fibre. Our results pave the way to light-matter interaction experiments in confined geometries requiring long operation times and large atomic number densities, such as generation of single-photon-level nonlinearities and development of single photon quantum memories.

  4. Sensitivity of nitrate aerosols to ammonia emissions and to nitrate chemistry: implications for present and future nitrate optical depth

    Science.gov (United States)

    Paulot, F.; Ginoux, P.; Cooke, W. F.; Donner, L. J.; Fan, S.; Lin, M.-Y.; Mao, J.; Naik, V.; Horowitz, L. W.

    2016-02-01

    We update and evaluate the treatment of nitrate aerosols in the Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric model (AM3). Accounting for the radiative effects of nitrate aerosols generally improves the simulated aerosol optical depth, although nitrate concentrations at the surface are biased high. This bias can be reduced by increasing the deposition of nitrate to account for the near-surface volatilization of ammonium nitrate or by neglecting the heterogeneous production of nitric acid to account for the inhibition of N2O5 reactive uptake at high nitrate concentrations. Globally, uncertainties in these processes can impact the simulated nitrate optical depth by up to 25 %, much more than the impact of uncertainties in the seasonality of ammonia emissions (6 %) or in the uptake of nitric acid on dust (13 %). Our best estimate for fine nitrate optical depth at 550 nm in 2010 is 0.006 (0.005-0.008). In wintertime, nitrate aerosols are simulated to account for over 30 % of the aerosol optical depth over western Europe and North America. Simulated nitrate optical depth increases by less than 30 % (0.0061-0.010) in response to projected changes in anthropogenic emissions from 2010 to 2050 (e.g., -40 % for SO2 and +38 % for ammonia). This increase is primarily driven by greater concentrations of nitrate in the free troposphere, while surface nitrate concentrations decrease in the midlatitudes following lower concentrations of nitric acid. With the projected increase of ammonia emissions, we show that better constraints on the vertical distribution of ammonia (e.g., convective transport and biomass burning injection) and on the sources and sinks of nitric acid (e.g., heterogeneous reaction on dust) are needed to improve estimates of future nitrate optical depth.

  5. Monocular display unit for 3D display with correct depth perception

    Science.gov (United States)

    Sakamoto, Kunio; Hosomi, Takashi

    2009-11-01

    A study of virtual-reality system has been popular and its technology has been applied to medical engineering, educational engineering, a CAD/CAM system and so on. The 3D imaging display system has two types in the presentation method; one is a 3-D display system using a special glasses and the other is the monitor system requiring no special glasses. A liquid crystal display (LCD) recently comes into common use. It is possible for this display unit to provide the same size of displaying area as the image screen on the panel. A display system requiring no special glasses is useful for a 3D TV monitor, but this system has demerit such that the size of a monitor restricts the visual field for displaying images. Thus the conventional display can show only one screen, but it is impossible to enlarge the size of a screen, for example twice. To enlarge the display area, the authors have developed an enlarging method of display area using a mirror. Our extension method enables the observers to show the virtual image plane and to enlarge a screen area twice. In the developed display unit, we made use of an image separating technique using polarized glasses, a parallax barrier or a lenticular lens screen for 3D imaging. The mirror can generate the virtual image plane and it enlarges a screen area twice. Meanwhile the 3D display system using special glasses can also display virtual images over a wide area. In this paper, we present a monocular 3D vision system with accommodation mechanism, which is useful function for perceiving depth.

  6. DESIGNING FEATURES OF POWER OPTICAL UNITS FOR TECHNOLOGICAL EQUIPMENT

    Directory of Open Access Journals (Sweden)

    M. Y. Afanasiev

    2016-03-01

    Full Text Available This paper considers the question of an optical unit designing for transmitting power laser radiation through an optical fiber. The aim of this work is designing a simple construction unit with minimized reflection losses. The source of radiation in the optical unit described below is an ultraviolet laser with diode pumping. We present the general functioning scheme and designing features for the three main parts: laser beam deflecting system, laser beam dump and optical unit control system. The described laser beam deflection system is composed of a moving flat mirror and a spherical scattering mirror. Comparative analysis of the production technology for such mirrors was carried out, and, as a result, the decision was made to produce both mirrors of 99.99 % pure molybdenum without coating. A moving mirror deflects laser emission from a source through a fiber or deflects it on a spherical mirror and into the laser beam dump, moreover, switching from one position to another occurs almost immediately. It is shown that a scattering mirror is necessary, otherwise, the absorbing surface of the beam dump is being worn out irregularly. The laser beam dump is an open conical cavity, in which the conical element with its spire turned to the emission source is placed. Special microgeometry of the internal surface of the beam dump is suggested for the better absorption effect. An optical unit control system consists of a laser beam deflection system, laser temperature sensor, deflection system solenoid temperature sensor, and deflection mirror position sensor. The signal processing algorithm for signals coming from the sensors to the controller is described. The optical unit will be used in special technological equipment.

  7. Adaptive-optics Optical Coherence Tomography Processing Using a Graphics Processing Unit*

    Science.gov (United States)

    Shafer, Brandon A.; Kriske, Jeffery E.; Kocaoglu, Omer P.; Turner, Timothy L.; Liu, Zhuolin; Lee, John Jaehwan; Miller, Donald T.

    2015-01-01

    Graphics processing units are increasingly being used for scientific computing for their powerful parallel processing abilities, and moderate price compared to super computers and computing grids. In this paper we have used a general purpose graphics processing unit to process adaptive-optics optical coherence tomography (AOOCT) images in real time. Increasing the processing speed of AOOCT is an essential step in moving the super high resolution technology closer to clinical viability. PMID:25570838

  8. Adaptive-optics optical coherence tomography processing using a graphics processing unit.

    Science.gov (United States)

    Shafer, Brandon A; Kriske, Jeffery E; Kocaoglu, Omer P; Turner, Timothy L; Liu, Zhuolin; Lee, John Jaehwan; Miller, Donald T

    2014-01-01

    Graphics processing units are increasingly being used for scientific computing for their powerful parallel processing abilities, and moderate price compared to super computers and computing grids. In this paper we have used a general purpose graphics processing unit to process adaptive-optics optical coherence tomography (AOOCT) images in real time. Increasing the processing speed of AOOCT is an essential step in moving the super high resolution technology closer to clinical viability.

  9. Congestion estimation technique in the optical network unit registration process.

    Science.gov (United States)

    Kim, Geunyong; Yoo, Hark; Lee, Dongsoo; Kim, Youngsun; Lim, Hyuk

    2016-07-01

    We present a congestion estimation technique (CET) to estimate the optical network unit (ONU) registration success ratio for the ONU registration process in passive optical networks. An optical line terminal (OLT) estimates the number of collided ONUs via the proposed scheme during the serial number state. The OLT can obtain congestion level among ONUs to be registered such that this information may be exploited to change the size of a quiet window to decrease the collision probability. We verified the efficiency of the proposed method through simulation and experimental results.

  10. Fast and automatic depth control of iterative bone ablation based on optical coherence tomography data

    Science.gov (United States)

    Fuchs, Alexander; Pengel, Steffen; Bergmeier, Jan; Kahrs, Lüder A.; Ortmaier, Tobias

    2015-07-01

    Laser surgery is an established clinical procedure in dental applications, soft tissue ablation, and ophthalmology. The presented experimental set-up for closed-loop control of laser bone ablation addresses a feedback system and enables safe ablation towards anatomical structures that usually would have high risk of damage. This study is based on combined working volumes of optical coherence tomography (OCT) and Er:YAG cutting laser. High level of automation in fast image data processing and tissue treatment enables reproducible results and shortens the time in the operating room. For registration of the two coordinate systems a cross-like incision is ablated with the Er:YAG laser and segmented with OCT in three distances. The resulting Er:YAG coordinate system is reconstructed. A parameter list defines multiple sets of laser parameters including discrete and specific ablation rates as ablation model. The control algorithm uses this model to plan corrective laser paths for each set of laser parameters and dynamically adapts the distance of the laser focus. With this iterative control cycle consisting of image processing, path planning, ablation, and moistening of tissue the target geometry and desired depth are approximated until no further corrective laser paths can be set. The achieved depth stays within the tolerances of the parameter set with the smallest ablation rate. Specimen trials with fresh porcine bone have been conducted to prove the functionality of the developed concept. Flat bottom surfaces and sharp edges of the outline without visual signs of thermal damage verify the feasibility of automated, OCT controlled laser bone ablation with minimal process time.

  11. Keraring Intrastromal Segment Depth Measured by Spectral-Domain Optical Coherence Tomography in Eyes with Keratoconus

    Science.gov (United States)

    Lavia, Carlo; D'Amelio, Savino

    2017-01-01

    Purpose. To evaluate agreement between measured and intended distance of Keraring (Mediphacos, Belo Horizonte, Brazil) intracorneal ring segments from the anterior and posterior corneal surfaces. Methods. Twenty-six Keraring ICRS implanted in 24 keratoconic eyes were examined. The distance from the Keraring apex to the anterior corneal surface and the distance from the inner and the outer corners to the posterior corneal surface were measured 3 months postoperatively using spectral-domain optical coherence tomography. Agreement between measured distance and intended distance was assessed by calculating the absolute differences and 95% limits of agreement (95% LoA). Results. The mean absolute difference was significantly lower (p < 0.001) for the measurements taken at the inner corner (23.54 ± 15.90 μm) than that for those taken at the apex (108.92 ± 62.72 μm) and the outer corner (108.35 ± 56.99 μm). The measurements taken at the inner corner were within ±25 and ±50 μm of the intended distance in 15/26 (57.7%) and 24/26 (92.3%) cases, respectively, and showed the narrowest 95% LoA with the intended distance (−57.61 to 55.15 μm). Conclusions. The distance of the inner corner from the posterior corneal surface showed the best agreement with the intended distance. This measurement is suitable for determining whether the actual Keraring depth matches the intended depth. PMID:28261495

  12. On spiking units in the first optic chiasm of the blowfly. III. The sustaining unit

    NARCIS (Netherlands)

    Jansonius, N.M.; Hateren, J.H. van

    1993-01-01

    We recorded from the spiking sustaining unit in the optic chiasm between lamina and medulla in the brain of the blowfly Calliphora vicina, and investigated both temporal and spatial properties of the light-adapted cell. The sustaining unit fails to follow the highest temporal frequencies followed by

  13. ON SPIKING UNITS IN THE 1ST OPTIC CHIASM OF THE BLOWFLY .3. THE SUSTAINING UNIT

    NARCIS (Netherlands)

    JANSONIUS, NM; VANHATEREN, JH

    We recorded from the spiking sustaining unit in the optic chiasm between lamina and medulla in the brain of the blowfly Calliphora vicina, and investigated both temporal and spatial properties of the light-adapted cell. The sustaining unit fails to follow the highest temporal frequencies followed by

  14. On spiking units in the first optic chiasm of the blowfly. III. The sustaining unit

    NARCIS (Netherlands)

    Jansonius, N.M.; Hateren, J.H. van

    1993-01-01

    We recorded from the spiking sustaining unit in the optic chiasm between lamina and medulla in the brain of the blowfly Calliphora vicina, and investigated both temporal and spatial properties of the light-adapted cell. The sustaining unit fails to follow the highest temporal frequencies followed by

  15. ON SPIKING UNITS IN THE 1ST OPTIC CHIASM OF THE BLOWFLY .3. THE SUSTAINING UNIT

    NARCIS (Netherlands)

    JANSONIUS, NM; VANHATEREN, JH

    1993-01-01

    We recorded from the spiking sustaining unit in the optic chiasm between lamina and medulla in the brain of the blowfly Calliphora vicina, and investigated both temporal and spatial properties of the light-adapted cell. The sustaining unit fails to follow the highest temporal frequencies followed by

  16. ON SPIKING UNITS IN THE 1ST OPTIC CHIASM OF THE BLOWFLY .3. THE SUSTAINING UNIT

    NARCIS (Netherlands)

    JANSONIUS, NM; VANHATEREN, JH

    1993-01-01

    We recorded from the spiking sustaining unit in the optic chiasm between lamina and medulla in the brain of the blowfly Calliphora vicina, and investigated both temporal and spatial properties of the light-adapted cell. The sustaining unit fails to follow the highest temporal frequencies followed by

  17. ModelE2-TOMAS development and evaluation using aerosol optical depths, mass and number concentrations

    Directory of Open Access Journals (Sweden)

    Y. H. Lee

    2014-09-01

    Full Text Available The TwO-Moment Aerosol Sectional microphysics model (TOMAS has been integrated into the state-of-the-art general circulation model, GISS ModelE2. TOMAS has the flexibility to select a size resolution as well as the lower size cutoff. A computationally efficient version of TOMAS is used here, which has 15 size bins covering 3 nm to 10 μm aerosol dry diameter. For each bin, it simulates the total aerosol number concentration and mass concentrations of sulphate, pure elementary carbon (hydrophobic, mixed elemental carbon (hydrophilic, hydrophobic organic matter, hydrophilic organic matter, sea salt, mineral dust, ammonium, and aerosol-associated water. This paper provides a detailed description of the ModelE2-TOMAS model and evaluates the model against various observations including aerosol precursor gas concentrations, aerosol mass and number concentrations, and aerosol optical depths. Additionally, global budgets in ModelE2-TOMAS are compared with those of other global aerosol models, and the TOMAS model is compared to the default aerosol model in ModelE2, which is a bulk aerosol model. Overall, the ModelE2-TOMAS predictions are within the range of other global aerosol model predictions, and the model has a reasonable agreement with observations of sulphur species and other aerosol components as well as aerosol optical depth. However, ModelE2-TOMAS (as well as the bulk aerosol model cannot capture the observed vertical distribution of sulphur dioxide over the Pacific Ocean possibly due to overly strong convective transport. The TOMAS model successfully captures observed aerosol number concentrations and cloud condensation nuclei concentrations. Anthropogenic aerosol burdens in the bulk aerosol model running in the same host model as TOMAS (ModelE2 differ by a few percent to a factor of 2 regionally, mainly due to differences in aerosol processes including deposition, cloud processing, and emission parameterizations. Larger differences are found

  18. Improving Mars-GRAM: Increasing the Accuracy of Sensitivity Studies at Large Optical Depths

    Science.gov (United States)

    Justh, Hilary L.; Justus, C. G.; Badger, Andrew M.

    2010-01-01

    Extensively utilized for numerous mission applications, the Mars Global Reference Atmospheric Model (Mars-GRAM) is an engineering-level atmospheric model. In a Monte-Carlo mode, Mars-GRAM's perturbation modeling capability is used to perform high fidelity engineering end-to-end simulations for entry, descent, and landing (EDL). Mars-GRAM has been found to be inexact when used during the Mars Science Laboratory (MSL) site selection process for sensitivity studies for MapYear=0 and large optical depth values such as tau=3. Mars-GRAM is based on the NASA Ames Mars General Circulation Model (MGCM) from the surface to 80 km altitude. Mars-GRAM with the MapYear parameter set to 0 utilizes results from a MGCM run with a fixed value of tau=3 at all locations for the entire year. Imprecise atmospheric density and pressure at all altitudes is a consequence of this use of MGCM with tau=3. Density factor values have been determined for tau=0.3, 1 and 3 as a preliminary fix to this pressure-density problem. These factors adjust the input values of MGCM MapYear 0 pressure and density to achieve a better match of Mars-GRAM MapYear 0 with Thermal Emission Spectrometer (TES) observations for MapYears 1 and 2 at comparable dust loading. These density factors are fixed values for all latitudes and Ls and are included in Mars-GRAM Release 1.3. Work currently being done, to derive better multipliers by including variations with latitude and/or Ls by comparison of MapYear 0 output directly against TES limb data, will be highlighted in the presentation. The TES limb data utilized in this process has been validated by a comparison study between Mars atmospheric density estimates from Mars-GRAM and measurements by Mars Global Surveyor (MGS). This comparison study was undertaken for locations on Mars of varying latitudes, Ls, and LTST. The more precise density factors will be included in Mars-GRAM 2005 Release 1.4 and thus improve the results of future sensitivity studies done for large

  19. Measurement of choroid thickness in pregnant women using enhanced depth imaging optical coherence tomography.

    Science.gov (United States)

    Goktas, Sertan; Basaran, Ahmet; Sakarya, Yasar; Ozcimen, Muammer; Kucukaydin, Zehra; Sakarya, Rabia; Basaran, Mustafa; Erdogan, Erkan; Alpfidan, Ismail

    2014-01-01

    To investigate choroidal thickness in healthy pregnant women during different trimesters using enhanced depth imaging optical coherence tomography (EDI-OCT). This prospective study included 90 healthy pregnant women in their first, second, or third trimester (groups 1, 2, and 3, respectively) and 30 non-pregnant healthy women (group 4). The age range for all groups was 18-40 years. Spectral domain optical coherence tomography scans were obtained to estimate the average choroidal thickness. Using EDI-OCT, we measured choroidal thickness manually from the outer border of the retinal pigment epithelium to the inner scleral border at the subfovea, 3 mm temporal, and 3 mm nasal to the fovea. Differences among groups were analyzed by one-way ANOVA. We found a statistically significant difference between groups 2 and group 4 for subfoveal, temporal, and nasal mean choroidal thickness (p=0.007, pchoroidal thickness for group 2 was 395 ± 80 μm, 338 ± 74 μm, and 233 ± 61 μm at the regions subfoveal, temporal, and nasal to the fovea, respectively. In comparison, the mean choroidal thickness for group 4 was 335 ± 86 μm, 274 ± 54 μm, and 200 ± 53 μm at the regions subfoveal, temporal, and nasal to the fovea, respectively. No statistically significant differences were found for choroidal thickness among groups 1-4 (p=0.214, p=0.177, p=0.094, respectively) and between groups 3-4 (p=0.105, p=0.261, p=0.695, respectively) for all measured points. Our results suggest that choroidal thickening can occur at the regions subfoveal, temporal, and nasal to the fovea in the second trimester.

  20. Reducing multisensor satellite monthly mean aerosol optical depth uncertainty: 1. Objective assessment of current AERONET locations

    Science.gov (United States)

    Li, Jing; Li, Xichen; Carlson, Barbara E.; Kahn, Ralph A.; Lacis, Andrew A.; Dubovik, Oleg; Nakajima, Teruyuki

    2016-11-01

    Various space-based sensors have been designed and corresponding algorithms developed to retrieve aerosol optical depth (AOD), the very basic aerosol optical property, yet considerable disagreement still exists across these different satellite data sets. Surface-based observations aim to provide ground truth for validating satellite data; hence, their deployment locations should preferably contain as much spatial information as possible, i.e., high spatial representativeness. Using a novel Ensemble Kalman Filter (EnKF)-based approach, we objectively evaluate the spatial representativeness of current Aerosol Robotic Network (AERONET) sites. Multisensor monthly mean AOD data sets from Moderate Resolution Imaging Spectroradiometer, Multiangle Imaging Spectroradiometer, Sea-viewing Wide Field-of-view Sensor, Ozone Monitoring Instrument, and Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar are combined into a 605-member ensemble, and AERONET data are considered as the observations to be assimilated into this ensemble using the EnKF. The assessment is made by comparing the analysis error variance (that has been constrained by ground-based measurements), with the background error variance (based on satellite data alone). Results show that the total uncertainty is reduced by 27% on average and could reach above 50% over certain places. The uncertainty reduction pattern also has distinct seasonal patterns, corresponding to the spatial distribution of seasonally varying aerosol types, such as dust in the spring for Northern Hemisphere and biomass burning in the fall for Southern Hemisphere. Dust and biomass burning sites have the highest spatial representativeness, rural and oceanic sites can also represent moderate spatial information, whereas the representativeness of urban sites is relatively localized. A spatial score ranging from 1 to 3 is assigned to each AERONET site based on the uncertainty reduction

  1. Retrieval of aerosol optical depth in the visible range with a Brewer spectrophotometer in Athens

    Science.gov (United States)

    Diémoz, Henri; Eleftheratos, Kostas; Kazadzis, Stelios; Amiridis, Vassilis; Zerefos, Christos S.

    2016-04-01

    A MkIV Brewer spectrophotometer has been operating in Athens since 2004. Direct-sun measurements originally scheduled for nitrogen dioxide retrievals were reprocessed to provide aerosol optical depths (AODs) at a wavelength of about 440 nm. A novel retrieval algorithm was specifically developed and the resulting AODs were compared to those obtained from a collocated Cimel filter radiometer belonging to the Aerosol Robotic Network (AERONET). The series are perfectly correlated, with Pearson's correlation coefficients being as large as 0.996 and with 90 % of AOD deviations between the two instruments being within the World Meteorological Organisation (WMO) traceability limits. In order to reach such a high agreement, several instrumental factors impacting the quality of the Brewer retrievals must be taken into account, including sensitivity to the internal temperature, and the state of the external optics and pointing accuracy must be carefully checked. Furthermore, the long-term radiometric stability of the Brewer was investigated and the performances of in situ Langley extrapolations as a way to track the absolute calibration of the Brewer were assessed. Other sources of error, such as slight shifts of the wavelength scale, are discussed and some recommendations to Brewer operators are drawn. Although MkIV Brewers are rarely employed to retrieve AODs in the visible range, they represent a key source of information about aerosol changes in the past three decades and a potential worldwide network for present and future coordinated AOD measurements. Moreover, a better understanding of the AOD retrieval at visible wavelengths will also contribute in improving similar techniques in the more challenging UV range.

  2. Validation of aerosol optical depth and total ozone column in the ultraviolet retrieved from multifilter rotating shadowband radiometer

    Science.gov (United States)

    Liu, Chaoshun; Chen, Maosi; Gao, Wei

    2013-09-01

    Aerosol optical depth (AOD), aerosol single scattering albedo (SSA), and asymmetry factor (g) at seven ultraviolet wavelengths along with total column ozone (TOC) were retrieved based on Bayesian optimal estimation (OE) from the measurements of the UltraViolet Multifilter Rotating Shadowband Radiometer (UV-MFRSR) deployed at the Southern Great Plains (SGP) site during March to November in 2009. To assess the accuracy of the OE technique, the AOD retrievals are compared to both the Beer's law derived ones and the AErosol RObotic Network (AERONET) AOD product; and the TOC retrievals are compared to both the TOC product of the U.S. Department of Agriculture UV-B Monitoring and Research Program (USDA UVMRP) and the Ozone Monitoring Instrument (OMI) satellite data. The scatterplots of the AOD estimated by the OE method with the Beer's law derived ones and the collocated AERONET AOD product both show a very good agreement: the correlation coefficients vary between 0.98 and 0.99; the slopes range from 0.95 to 1.0; and the offsets are less than 0.02 at 368 nm. The comparison of TOC also shows a promising accuracy of the OE method: the standard deviations of the difference between the OE derived TOC and other TOC products are about 5 to 6 Dobson Units (DU). The validation of the OE retrievals on the selected dates suggests the OE technique has its merits and is a supplemental tool in analyzing UVMRP data.

  3. Retrievals of Thick Cloud Optical Depth from the Geoscience Laser Altimeter System (GLAS) by Calibration of Solar Background Signal

    Science.gov (United States)

    Yang, Yuekui; Marshak, Alexander; Chiu, J. Christine; Wiscombe, Warren J.; Palm, Stephen P.; Davis, Anthony B.; Spangenberg, Douglas A.; Nguyen, Louis; Spinhirne, James D.; Minnis, Patrick

    2008-01-01

    Laser beams emitted from the Geoscience Laser Altimeter System (GLAS), as well as other space-borne laser instruments, can only penetrate clouds to a limit of a few optical depths. As a result, only optical depths of thinner clouds (thick clouds using solar background light and treating GLAS as a solar radiometer. To do so we first calibrate the reflected solar radiation received by the photon-counting detectors of GLAS' 532 nm channel, which is the primary channel for atmospheric products. The solar background radiation is regarded as a noise to be subtracted in the retrieval process of the lidar products. However, once calibrated, it becomes a signal that can be used in studying the properties of optically thick clouds. In this paper, three calibration methods are presented: (I) calibration with coincident airborne and GLAS observations; (2) calibration with coincident Geostationary Operational Environmental Satellite (GOES) and GLAS observations of deep convective clouds; (3) calibration from the first principles using optical depth of thin water clouds over ocean retrieved by GLAS active remote sensing. Results from the three methods agree well with each other. Cloud optical depth (COD) is retrieved from the calibrated solar background signal using a one-channel retrieval. Comparison with COD retrieved from GOES during GLAS overpasses shows that the average difference between the two retrievals is 24%. As an example, the COD values retrieved from GLAS solar background are illustrated for a marine stratocumulus cloud field that is too thick to be penetrated by the GLAS laser. Based on this study, optical depths for thick clouds will be provided as a supplementary product to the existing operational GLAS cloud products in future GLAS data releases.

  4. Modeling South America regional smoke plume: aerosol optical depth variability and shortwave surface forcing

    Science.gov (United States)

    Rosário, N. E.; Longo, K. M.; Freitas, S. R.; Yamasoe, M. A.; Fonseca, R. M.

    2012-07-01

    Intra-seasonal variability of smoke aerosol optical depth (AOD) and downwelling solar irradiance at the surface during the 2002 biomass burning season in South America was modeled using the Coupled Chemistry-Aerosol-Tracer Transport model to the Brazilian developments on the Regional Atmospheric Modeling System (CCATT-BRAMS). Measurements of AOD from the AErosol RObotic NETwork (AERONET) and solar irradiance at the surface from the Solar Radiation Network (SolRad-NET) were used to evaluate model results. In general, the major features associated with AOD evolution over the southern part of the Amazon Basin and cerrado ecosystem are captured by the model. The main discrepancies were found for high aerosol loading events. In the northeastern portion of the Amazon Basin the model systematically underestimated AOD. This is likely due to the cloudy nature of the region, preventing accurate detection of the fire spots used in the emission model. Moreover, measured AOD were very often close to background conditions and emissions other than smoke were not considered in the simulation. Therefore, under the background scenario, one would expect the model to underestimate AOD. The issue of high aerosol loading events in the southern part of the Amazon and cerrado is also discussed in the context of emission shortcomings. The Cuiabá cerrado site was the only one where the highest quality AERONET data were unavailable. Thus, lower quality data were used. Root-mean-square-error (RMSE) between the model and observations decreased from 0.48 to 0.17 when extreme AOD events (AOD550 nm ≥ 1.0) and Cuiabá were excluded from analysis. Downward surface solar irradiance comparisons also followed similar trends when extremes AOD were excluded. This highlights the need to improve the modelling of the regional smoke plume in order to enhance the accuracy of the radiative energy budget. Aerosol optical model based on the mean intensive properties of smoke from the southern part of the

  5. Aerosol optical depth in a western Mediterranean site: An assessment of different methods

    Science.gov (United States)

    Sanchez-Romero, A.; González, J. A.; Calbó, J.; Sanchez-Lorenzo, A.; Michalsky, J.

    2016-06-01

    Column aerosol optical properties were derived from multifilter rotating shadowing radiometer (MFRSR) observations carried out at Girona (northeast Spain) from June 2012 to June 2014. We used a technique that allows estimating simultaneously aerosol optical depth (AOD) and Ångström exponent (AE) at high time-resolution. For the period studied, mean AOD at 500 nm was 0.14, with a noticeable seasonal pattern, i.e. maximum in summer and minimum in winter. Mean AE from 500 to 870 nm was 1.2 with a strong day-to-day variation and slightly higher values in summer. So, the summer increase in AOD seems to be linked with an enhancement in the number of fine particles. A radiative closure experiment, using the SMARTS2 model, was performed to confirm that the MFRSR-retrieved aerosol optical properties appropriately represent the continuously varying atmospheric conditions in Girona. Thus, the calculated broadband values of the direct flux show a mean absolute difference of less than 5.9 W m- 2 (0.77%) and R = 0.99 when compared to the observed fluxes. The sensitivity of the achieved closure to uncertainties in AOD and AE was also examined. We use this MFRSR-based dataset as a reference for other ground-based and satellite measurements that might be used to assess the aerosol properties at this site. First, we used observations obtained from a 100 km away AERONET station; despite a general similar behavior when compared with the in-situ MFRSR observations, certain discrepancies for AOD estimates in the different channels (R < 0.84 and slope < 1) appear. Second, AOD products from MISR and MODIS satellite observations were compared with our ground-based retrievals. Reasonable agreements are found for the MISR product (R = 0.92), with somewhat poorer agreement for the MODIS product (R = 0.70). Finally, we apply all these methods to study in detail the aerosol properties during two singular aerosol events related to a forest fire and a desert dust intrusion.

  6. Observationally-constrained estimates of aerosol optical depths (AODs) over East Asia via data assimilation techniques

    Science.gov (United States)

    Lee, K.; Lee, S.; Song, C. H.

    2015-12-01

    Not only aerosol's direct effect on climate by scattering and absorbing the incident solar radiation, but also they indirectly perturbs the radiation budget by influencing microphysics and dynamics of clouds. Aerosols also have a significant adverse impact on human health. With an importance of aerosols in climate, considerable research efforts have been made to quantify the amount of aerosols in the form of the aerosol optical depth (AOD). AOD is provided with ground-based aerosol networks such as the Aerosol Robotic NETwork (AERONET), and is derived from satellite measurements. However, these observational datasets have a limited areal and temporal coverage. To compensate for the data gaps, there have been several studies to provide AOD without data gaps by assimilating observational data and model outputs. In this study, AODs over East Asia simulated with the Community Multi-scale Air Quality (CMAQ) model and derived from the Geostationary Ocean Color Imager (GOCI) observation are interpolated via different data assimilation (DA) techniques such as Cressman's method, Optimal Interpolation (OI), and Kriging for the period of the Distributed Regional Aerosol Gridded Observation Networks (DRAGON) Campaign (March - May 2012). Here, the interpolated results using the three DA techniques are validated intensively by comparing with AERONET AODs to examine the optimal DA method providing the most reliable AODs over East Asia.

  7. Major optical depth perturbations to the stratosphere from volcanic eruptions: Steller extinction period, 1961-1978

    Science.gov (United States)

    Stothers, Richard B.

    2001-02-01

    A revised chronology of stratospheric aerosol extinction due to volcanic eruptions has been assembled for the period 1961-1978, which immediately precedes the era of dedicated satellite measurements. On the whole, the most accurate data consist of published observations of stellar extinction, supplemented in part by other kinds of observational data. The period covered encompasses the important eruptions of Agung (1963) and Fuego (1974), whose dust veils are discussed with respect to their transport, decay, and total mass. The effective (area-weighted mean) radii of the aerosols for both eruptions are found to be 0.3-0.4 μm. It is confirmed that, among known tropical eruptions, Agung's dust was unique for a low-latitude eruption in remaining almost entirely confined to the hemisphere of its production. A new table of homogeneous visual optical depth perturbations, listed by year and by hemisphere, is provided for the whole period 1881-1978, including the pyrheliometric period before 1961 that was investigated previously.

  8. Improving Calculation Accuracies of Accumulation-Mode Fractions Based on Spectral of Aerosol Optical Depths

    Science.gov (United States)

    Ying, Zhang; Zhengqiang, Li; Yan, Wang

    2014-03-01

    Anthropogenic aerosols are released into the atmosphere, which cause scattering and absorption of incoming solar radiation, thus exerting a direct radiative forcing on the climate system. Anthropogenic Aerosol Optical Depth (AOD) calculations are important in the research of climate changes. Accumulation-Mode Fractions (AMFs) as an anthropogenic aerosol parameter, which are the fractions of AODs between the particulates with diameters smaller than 1μm and total particulates, could be calculated by AOD spectral deconvolution algorithm, and then the anthropogenic AODs are obtained using AMFs. In this study, we present a parameterization method coupled with an AOD spectral deconvolution algorithm to calculate AMFs in Beijing over 2011. All of data are derived from AErosol RObotic NETwork (AERONET) website. The parameterization method is used to improve the accuracies of AMFs compared with constant truncation radius method. We find a good correlation using parameterization method with the square relation coefficient of 0.96, and mean deviation of AMFs is 0.028. The parameterization method could also effectively solve AMF underestimate in winter. It is suggested that the variations of Angstrom indexes in coarse mode have significant impacts on AMF inversions.

  9. Trends in aerosol optical depth in northern China retrieved from sunshine duration data

    Science.gov (United States)

    Li, Jun; Liu, Run; Liu, Shaw Chen; Shiu, Chein-Jung; Wang, Jingli; Zhang, Yuanhang

    2016-01-01

    A new method has been developed to retrieve aerosol optical depth (AOD) from sunshine duration (SSD). Retrieved AODs from SSD at the six stations in northern China in 2003-2005 agree reasonably well with AODs retrieved from Moderate Resolution Imaging Spectroradiometer observations near the six stations. Values and trends in AOD retrieved from SSD in Beijing and Tianjin in the period 1961-2005 also agree with those retrieved from solar radiation and visibility. These agreements allow the retrieval of credible upper and lower limits for anthropogenic AODs from SSD at the six stations during 1961-2005. The trends in anthropogenic AODs are approximately a factor of 3 to 5 lower than the trends in emissions of gas-phase precursors of aerosols in 1973-2005, implying a significant sublinear relationship between the level of aerosols and emissions of their gas phase precursors. This finding has important implications for formulating a control strategy for PM2.5 or haze pollution in northern China.

  10. Evaluating the Impact of Smoke Particle Absorption on Passive Satellite Cloud Optical Depth Retrievals

    Science.gov (United States)

    Alfaro-Contreras, R.; Zhang, J.; Reid, J. S.; Campbell, J. R.

    2013-12-01

    Absorbing aerosol particles, when lifted above clouds, can perturb top-of-atmosphere radiation radiances measured by passive satellite sensors through the absorption of reflected solar energy. This scenario, if not properly screened, impacts cloud physical retrievals, like cloud optical depth (COD), conducted using radiances/channels in the visible spectrum. We describe observations of smoke particle presence above cloud off the southwest coast of Africa, using spatially and temporally collocated Aqua Moderate Resolution Imaging Spectroradiometer (AQUA MODIS), Ozone Monitoring Instrument (OMI) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) measurements. Results from this study indicate that above cloud aerosol episodes happen rather frequent in the smoke outflow region during the Northern Hemisphere summer where above cloud aerosol plumes introduce a significant bias to MODIS COD retrievals in the visible spectrum. This suggests that individual COD retrievals as well as COD climatology from MODIS can be affected over the smoke outflow region by above cloud aerosol contamination and thus showing the need to account for the presence of above cloud absorbing aerosols in the MODIS visible COD retrievals.

  11. Validation of ASH Optical Depth and Layer Height from IASI using Earlinet Lidar Data

    Science.gov (United States)

    Balis, D.; Siomos, N.; Koukouli, M.; Clarisse, L.; Carboni, E.; Ventress, L.; Grainger, R.; Mona, L.; Pappalardo, G.

    2016-06-01

    The 2010 eruptions of the Icelandic volcano Eyjafjallajökull attracted the attention of the public and the scientific community to the vulnerability of the European airspace to volcanic eruptions. The European Space Agency project "Satellite Monitoring of Ash and Sulphur Dioxide for the mitigation of Aviation Hazards", called for the creation of an optimal End-to-End System for Volcanic Ash Plume Monitoring and Prediction. This system is based on improved and dedicated satellite-derived ash plume and sulphur dioxide level assessments, as well as an extensive validation, using among others ground-based measurements (Koukouli et al., 2014). The validation of volcanic ash levels and height extracted from IASI/MetopA is presented in this work with emphasis on the ash plume height and ash optical depth levels. European Aerosol Research Lidar Network [EARLINET] lidar measurements are compared to different satellite estimates for two eruptive episodes. The validation results are extremely promising within the estimated uncertainties of each of the comparative datasets.

  12. Nine martian years of dust optical depth observations: A reference dataset

    Science.gov (United States)

    Montabone, Luca; Forget, Francois; Kleinboehl, Armin; Kass, David; Wilson, R. John; Millour, Ehouarn; Smith, Michael; Lewis, Stephen; Cantor, Bruce; Lemmon, Mark; Wolff, Michael

    2016-07-01

    We present a multi-annual reference dataset of the horizontal distribution of airborne dust from martian year 24 to 32 using observations of the martian atmosphere from April 1999 to June 2015 made by the Thermal Emission Spectrometer (TES) aboard Mars Global Surveyor, the Thermal Emission Imaging System (THEMIS) aboard Mars Odyssey, and the Mars Climate Sounder (MCS) aboard Mars Reconnaissance Orbiter (MRO). Our methodology to build the dataset works by gridding the available retrievals of column dust optical depth (CDOD) from TES and THEMIS nadir observations, as well as the estimates of this quantity from MCS limb observations. The resulting (irregularly) gridded maps (one per sol) were validated with independent observations of CDOD by PanCam cameras and Mini-TES spectrometers aboard the Mars Exploration Rovers "Spirit" and "Opportunity", by the Surface Stereo Imager aboard the Phoenix lander, and by the Compact Reconnaissance Imaging Spectrometer for Mars aboard MRO. Finally, regular maps of CDOD are produced by spatially interpolating the irregularly gridded maps using a kriging method. These latter maps are used as dust scenarios in the Mars Climate Database (MCD) version 5, and are useful in many modelling applications. The two datasets (daily irregularly gridded maps and regularly kriged maps) for the nine available martian years are publicly available as NetCDF files and can be downloaded from the MCD website at the URL: http://www-mars.lmd.jussieu.fr/mars/dust_climatology/index.html

  13. Estimation of Aerosol Optical Depth at Different Wavelengths by Multiple Regression Method

    Science.gov (United States)

    Tan, Fuyi; Lim, Hwee San; Abdullah, Khiruddin; Holben, Brent

    2015-01-01

    This study aims to investigate and establish a suitable model that can help to estimate aerosol optical depth (AOD) in order to monitor aerosol variations especially during non-retrieval time. The relationship between actual ground measurements (such as air pollution index, visibility, relative humidity, temperature, and pressure) and AOD obtained with a CIMEL sun photometer was determined through a series of statistical procedures to produce an AOD prediction model with reasonable accuracy. The AOD prediction model calibrated for each wavelength has a set of coefficients. The model was validated using a set of statistical tests. The validated model was then employed to calculate AOD at different wavelengths. The results show that the proposed model successfully predicted AOD at each studied wavelength ranging from 340 nm to 1020 nm. To illustrate the application of the model, the aerosol size determined using measure AOD data for Penang was compared with that determined using the model. This was done by examining the curvature in the ln [AOD]-ln [wavelength] plot. Consistency was obtained when it was concluded that Penang was dominated by fine mode aerosol in 2012 and 2013 using both measured and predicted AOD data. These results indicate that the proposed AOD prediction model using routine measurements as input is a promising tool for the regular monitoring of aerosol variation during non-retrieval time.

  14. A characterization of Arctic aerosols on the basis of aerosol optical depth and black carbon measurements

    Directory of Open Access Journals (Sweden)

    R. S. Stone

    2014-06-01

    Full Text Available Abstract Aerosols, transported from distant source regions, influence the Arctic surface radiation budget. When deposited on snow and ice, carbonaceous particles can reduce the surface albedo, which accelerates melting, leading to a temperature-albedo feedback that amplifies Arctic warming. Black carbon (BC, in particular, has been implicated as a major warming agent at high latitudes. BC and co-emitted aerosols in the atmosphere, however, attenuate sunlight and radiatively cool the surface. Warming by soot deposition and cooling by atmospheric aerosols are referred to as “darkening” and “dimming” effects, respectively. In this study, climatologies of spectral aerosol optical depth AOD (2001–2011 and Equivalent BC (EBC (1989–2011 from three Arctic observatories and from a number of aircraft campaigns are used to characterize Arctic aerosols. Since the 1980s, concentrations of BC in the Arctic have decreased by more than 50% at ground stations where in situ observations are made. AOD has increased slightly during the past decade, with variations attributed to changing emission inventories and source strengths of natural aerosols, including biomass smoke and volcanic aerosol, further influenced by deposition rates and airflow patterns.

  15. Retrieval of aerosol optical depth in vicinity of broken clouds from reflectance ratios: case study

    Directory of Open Access Journals (Sweden)

    E. Kassianov

    2010-10-01

    Full Text Available A recently developed reflectance ratio (RR method for the retrieval of aerosol optical depth (AOD is evaluated using extensive airborne and ground-based data sets collected during the Cloud and Land Surface Interaction Campaign (CLASIC and the Cumulus Humilis Aerosol Processing Study (CHAPS, which took place in June 2007 over the US Department of Energy (DOE Atmospheric Radiation Measurement (ARM Southern Great Plains site. A detailed case study is performed for a field of single-layer shallow cumuli observed on 12 June 2007. The RR method is applied to retrieve the spectral values of AOD from the reflectance ratios measured by the MODIS Airborne Simulator (MAS for two pairs of wavelengths (660 and 470 nm, 870 and 470 nm collected at a spatial resolution of 0.05 km. The retrieval is compared with an independent AOD estimate from three ground-based Multi-filter Rotating Shadowband Radiometers (MFRSRs. The interpolation algorithm that is used to project MFRSR point measurements onto the aircraft flight tracks is tested using AOD derived from NASA Langley High Spectral Resolution Lidar (HSRL. The RR AOD estimates are in a good agreement (within 5% with the MFRSR-derived AOD values for the 660-nm wavelength. The AODs obtained from MAS reflectance ratios overestimate those derived from MFRSR measurements by 15–30% for the 470-nm wavelength and underestimate the 870-nm AOD by the same amount.

  16. Automatic segmentation of the choroid in enhanced depth imaging optical coherence tomography images.

    Science.gov (United States)

    Tian, Jing; Marziliano, Pina; Baskaran, Mani; Tun, Tin Aung; Aung, Tin

    2013-03-01

    Enhanced Depth Imaging (EDI) optical coherence tomography (OCT) provides high-definition cross-sectional images of the choroid in vivo, and hence is used in many clinical studies. However, the quantification of the choroid depends on the manual labelings of two boundaries, Bruch's membrane and the choroidal-scleral interface. This labeling process is tedious and subjective of inter-observer differences, hence, automatic segmentation of the choroid layer is highly desirable. In this paper, we present a fast and accurate algorithm that could segment the choroid automatically. Bruch's membrane is detected by searching the pixel with the biggest gradient value above the retinal pigment epithelium (RPE) and the choroidal-scleral interface is delineated by finding the shortest path of the graph formed by valley pixels using Dijkstra's algorithm. The experiments comparing automatic segmentation results with the manual labelings are conducted on 45 EDI-OCT images and the average of Dice's Coefficient is 90.5%, which shows good consistency of the algorithm with the manual labelings. The processing time for each image is about 1.25 seconds.

  17. Interference of Heavy Aerosol Loading on the VIIRS Aerosol Optical Depth (AOD Retrieval Algorithm

    Directory of Open Access Journals (Sweden)

    Yang Wang

    2017-04-01

    Full Text Available Aerosol optical depth (AOD has been widely used in climate research, atmospheric environmental observations, and other applications. However, high AOD retrieval remains challenging over heavily polluted regions, such as the North China Plain (NCP. The Visible Infrared Imaging Radiometer Suite (VIIRS, which was designed as a successor to the Moderate Resolution Imaging Spectroradiometer (MODIS, will undertake the aerosol observations mission in the coming years. Using the VIIRS AOD retrieval algorithm as an example, we analyzed the influence of heavy aerosol loading through the 6SV radiative transfer model (RTM with a focus on three aspects: cloud masking, ephemeral water body tests, and data quality estimation. First, certain pixels were mistakenly screened out as clouds and ephemeral water bodies because of heavy aerosols, resulting in the loss of AOD retrievals. Second, the greenness of the surface could not be accurately identified by the top of atmosphere (TOA index, and the quality of the aggregation data may be artificially high. Thus, the AOD retrieval algorithm did not perform satisfactorily, indicated by the low availability of data coverage (at least 37.97% of all data records were missing according to ground-based observations and overestimation of the data quality (high-quality data increased from 63.42% to 80.97% according to radiative simulations. To resolve these problems, the implementation of a spatial variability cloud mask method and surficial index are suggested in order to improve the algorithm.

  18. Long-term trend in aerosol optical depth from 1980 to 2001 in north China

    Institute of Scientific and Technical Information of China (English)

    Jiangxia Xie; Xiangao Xia

    2008-01-01

    Using the Total Ozone Mapping Spectrometer (TOMS) monthly aerosol optical depth (AOD) at 500 nm data from 1980 to 2001 in north China, the spatial and temporal variations of AOD were examined. Seasonal AODs in Taldimakan Desert were 0.69 and 0.44 in spring and summer,respectively, which were mainly due to frequent occurrences of dust events in this region. Dust activities in spring also led to high aerosol loading in Gobi Desert and in northeast China where spring AODs were 0.33 and 0.29, respectively. Heavily impacted by events such as volcano eruption, forest fires and extraordinary dust storms, AODs showed large inter-annual variations. A decreasing tendency in AOD was observed in north China during 1980-1991, though a reverse tendency was revealed during 1997-2001, especially for spring AOD in northeast China. Further study is required to figure out how much human activities have contributed to the AOD tendency in north China.

  19. Wave like signatures in aerosol optical depth and associated radiative impacts over the central Himalayan region

    Energy Technology Data Exchange (ETDEWEB)

    Shukla, K. K.; Phanikumar, D. V.; Kumar, K.  Niranjan; Reddy, Kishore; Kotamarthi, V. R.; Newsom, Rob K.; Ouarda, Taha B. M. J.

    2015-10-01

    In this study, we present a case study on 16 October 2011 to show the first observational evidence of the influence of short period gravity waves in aerosol transport during daytime over the central Himalayan region. The Doppler lidar data has been utilized to address the daytime boundary layer evolution and related aerosol dynamics over the site. Mixing layer height is estimated by wavelet covariance transform method and found to be ~ 0.7 km, AGL. Aerosol optical depth observations during daytime revealed an asymmetry showing clear enhancement during afternoon hours as compared to forenoon. Interestingly, Fourier and wavelet analysis of vertical velocity and attenuated backscatter showed similar 50-90 min short period gravity wave signatures during afternoon hours. Moreover, our observations showed that gravity waves are dominant within the boundary layer implying that the daytime boundary layer dynamics is playing a vital role in transporting the aerosols from surface to the top of the boundary layer. Similar modulations are also evident in surface parameters like temperature, relative humidity and wind speed indicating these waves are associated with the dynamical aspects over Himalayan region. Finally, time evolution of range-23 height indicator snapshots during daytime showed strong upward velocities especially during afternoon hours implying that convective processes through short period gravity waves plays a significant role in transporting aerosols from the nearby valley region to boundary layer top over the site. These observations also establish the importance of wave induced daytime convective boundary layer dynamics in the lower Himalayan region.

  20. Theoretical gravity darkening as a function of optical depth. A first approach to fast rotating stars

    Science.gov (United States)

    Claret, A.

    2016-04-01

    Aims: Recent observations of very fast rotating stars show systematic deviations from the von Zeipel theorem and pose a challenge to the theory of gravity-darkening exponents (β1). In this paper, we present a new insight into the problem of temperature distribution over distorted stellar surfaces to try to reduce these discrepancies. Methods: We use a variant of the numerical method based on the triangles strategy, which we previously introduced, to evaluate the gravity-darkening exponents. The novelty of the present method is that the theoretical β1 is now computed as a function of the optical depth, that is, β1 ≡ β1(τ). The stellar evolutionary models, which are necessary to obtain the physical conditions of the stellar envelopes/atmospheres inherent to the numerical method, are computed via the code GRANADA. Results: When the resulting theoretical β1(τ) are compared with the best accurate data of very fast rotators, a good agreement for the six systems is simultaneously achieved. In addition, we derive an equation that relates the locus of constant convective efficiency in the Hertzsprung-Russell (HR) diagram with gravity-darkening exponents.

  1. Flat Choroidal Nevus Inaccessible to Ultrasound Sonography Evaluated by Enhanced Depth Imaging Optical Coherence Tomography

    Directory of Open Access Journals (Sweden)

    Chrysanthi Basdekidou

    2011-06-01

    Full Text Available Purpose: To demonstrate the usefulness of enhanced depth imaging optical coherence tomography (EDI-OCT in investigating choroidal lesions inaccessible to ultrasound sonography. Methods: In a 60-year-old woman with an asymptomatic choroidal nevus, normal OCT was used to observe the macula and EDI-OCT to image the choroidal nevus that was inaccessible to ultrasound. The exact location of the lesion in the choroid and the dimensions of the nevus were measured. Results: The lesion was located in the superior macula, and the nevus was homogeneous in its reflectivity. We observed a thickened choroid delineated by the shadow cone behind it, measuring 1,376 × 325 µm in the larger vertical cut and 1,220 × 325 µm in the larger horizontal cut in an image with a 1:1 pixel mapping and automatic zoom. The macular profile and thickness were both normal. Conclusions: EDI-OCT appears to be an excellent technique for measuring choroidal nevi and all choroidal lesions accessible to OCT imaging by depicting their exact location in the choroid, their dimensions, and their demarcation from the surrounding healthy tissue, thus allowing for a more efficient and accurate follow-up.

  2. Choroid thickness in central serous chorioretinopathy using enhanced depth imaging optical coherence tomography

    Directory of Open Access Journals (Sweden)

    Xiao-Long Yu

    2013-04-01

    Full Text Available AIM: To observe the choroidal thickness in the macular area in affected and unaffected fellow eyes with central serous chorio retinopathy(CSCand in healthy controls. METHODS: Twenty-six cases with unilateral CSC and controls were recruited in this study. All eyes were divided into three groups: 26 eyes in Group A(affected eyes with CSC, 26 eyes in group B(unaffected fellow eyesand 26 eyes in group C(right eyes of age and sex matched control. Enhanced depth imaging was obtained by using spectral-domain optical coherence tomography. Subfoveal choroidal thickness and choroidal thickness at 1mm/3mm nasal, temporal, superior and inferior to the fovea were measured. RESULTS: Choroidal thickness was significantly increased in affected eyes with CSC than unaffected fellow eyes(t=5.57, P<0.01.The mean subfoveal choroidal thickness(SFCTwas 528.31±91.24μm in group A, 413.71±79.35μm in group B, and 301.31±52.46 in group C. The subfoveal choroid was significantly thicker in group A than Group C(P<0.01. SFCT in unaffected fellow eyes were thicker than the controls(P<0.01. CONCLUSION:Choroidal thickness is thicker in affected eyes with CSC and also in fellow unaffected eyes, indicating that the choroid blood vessels are high and perfusion state, may be one of the factors of the disease CSC.

  3. Repeatability of Choroidal Thickness Measurements on Enhanced Depth Imaging Optical Coherence Tomography Using Different Posterior Boundaries.

    Science.gov (United States)

    Vuong, Vivian S; Moisseiev, Elad; Cunefare, David; Farsiu, Sina; Moshiri, Ala; Yiu, Glenn

    2016-09-01

    To assess the reliability of manual choroidal thickness measurements by comparing different posterior boundary definitions of the choroidal-scleral junction on enhanced depth imaging optical coherence tomography (EDI-OCT). Reliability analysis. Two graders marked the choroidal-scleral junction with segmentation software using different posterior boundaries: (1) the outer border of the choroidal vessel lumen, (2) the outer border of the choroid stroma, and (3) the inner border of the sclera, to measure the vascular choroidal thickness (VCT), stromal choroidal thickness (SCT), and total choroidal thickness (TCT), respectively. Measurements were taken at 0.5-mm intervals from 1.5 mm nasal to 1.5 mm temporal to the fovea, and averaged continuously across the central 3 mm of the macula. Intraclass correlation coefficient (ICC) and coefficient of reliability (CR) were compared to assess intergrader and intragrader reliability. Choroidal thickness measurements varied significantly with different posterior boundaries (P choroidal-scleral junction visibility was Choroidal thickness measurements are more reproducible when measured to the border of the choroid stroma (SCT) than the vascular lumen (VCT) or sclera (TCT). Copyright © 2016 Elsevier Inc. All rights reserved.

  4. Observations of Black Carbon and Aerosol Optical Depth in the Kali Gandaki Valley, Nepal

    Science.gov (United States)

    Dhungel, S.; Panday, A. K.; Mahata, K. S.

    2012-12-01

    During recent years there has been increasing concern about the deposition of black carbon from the Indo-Gangetic Plains onto the glaciers and snowfields of the Tibetan Plateau. There has also been increasing concern about the rapid increase in air temperature at high altitudes over the Tibetan Plateau and the Himalaya. To date, there is very little knowledge about the transport pathways for pollutants traveling from the Indo-Gangetic Plains across the Himalaya to the Tibetan Plateau. The Kali Gandaki Valley in Nepal is one of the deepest gorges in the world, and has some of the highest up-valley winds in the world. It is also one of the most open connecting points for air from South Asia to reach the Tibetan Plateau. In 2010 the University of Virginia, in collaboration with ICIMOD and Nepal Wireless, established an atmospheric research station in Jomsom, Nepal (28.78N, 83.42E, 2900 m.a.s.l.). The station is equipped to measure black carbon (BC), carbon monoxide (CO), and ozone concentrations. It also has an automated weather station, a filter sampler, and a NASA Aeronet Sunphotometer. Observations of BC and aerosol optical depth (AOD) from Aeronet are analyzed and presented. Diurnal and seasonal patterns of BC have been observed with higher values during the day and lower at night and also highest during pre-monsoon and lowest during monsoon season, with observed BC concentrations exceeding 5 μg while average concentration around 3.7 μg.

  5. Aerosol optical depth under "clear" sky conditions derived from sea surface reflection of lidar signals.

    Science.gov (United States)

    He, Min; Hu, Yongxiang; Huang, Jian Ping; Stamnes, Knut

    2016-12-26

    There are considerable demands for accurate atmospheric correction of satellite observations of the sea surface or subsurface signal. Surface and sub-surface reflection under "clear" atmospheric conditions can be used to study atmospheric correction for the simplest possible situation. Here "clear" sky means a cloud-free atmosphere with sufficiently small aerosol particles. The "clear" aerosol concept is defined according to the spectral dependence of the scattering cross section on particle size. A 5-year combined CALIPSO and AMSR-E data set was used to derive the aerosol optical depth (AOD) from the lidar signal reflected from the sea surface. Compared with the traditional lidar-retrieved AOD, which relies on lidar backscattering measurements and an assumed lidar ratio, the AOD retrieved through the surface reflectance method depends on both scattering and absorption because it is based on two-way attenuation of the lidar signal transmitted to and then reflected from the surface. The results show that the clear sky AOD derived from the surface signal agrees with the clear sky AOD available in the CALIPSO level 2 database in the westerly wind belt located in the southern hemisphere, but yields significantly higher aerosol loadings in the tropics and in the northern hemisphere.

  6. Total Volcanic Stratospheric Aerosol Optical Depths and Implications for Global Climate Change

    Science.gov (United States)

    Ridley, D. A.; Solomon, S.; Barnes, J. E.; Burlakov, V. D.; Deshler, T.; Dolgii, S. I.; Herber, A. B.; Nagai, T.; Neely, R. R., III; Nevzorov, A. V.; Ritter, C.; Sakai, T.; Santer, B. D.; Sato, M.; Schmidt, A.; Uchino, O.; Vernier, J. P.

    2014-01-01

    Understanding the cooling effect of recent volcanoes is of particular interest in the context of the post-2000 slowing of the rate of global warming. Satellite observations of aerosol optical depth above 15 km have demonstrated that small-magnitude volcanic eruptions substantially perturb incoming solar radiation. Here we use lidar, Aerosol Robotic Network, and balloon-borne observations to provide evidence that currently available satellite databases neglect substantial amounts of volcanic aerosol between the tropopause and 15 km at middle to high latitudes and therefore underestimate total radiative forcing resulting from the recent eruptions. Incorporating these estimates into a simple climate model, we determine the global volcanic aerosol forcing since 2000 to be 0.19 +/- 0.09W/sq m. This translates into an estimated global cooling of 0.05 to 0.12 C. We conclude that recent volcanic events are responsible for more post-2000 cooling than is implied by satellite databases that neglect volcanic aerosol effects below 15 km.

  7. Reducing multisensor monthly mean aerosol optical depth uncertainty: 2. Optimal locations for potential ground observation deployments

    Science.gov (United States)

    Li, Jing; Li, Xichen; Carlson, Barbara E.; Kahn, Ralph A.; Lacis, Andrew A.; Dubovik, Oleg; Nakajima, Teruyuki

    2017-04-01

    Surface remote sensing of aerosol properties provides "ground truth" for satellite and model validation and is an important component of aerosol observation system. Due to the different characteristics of background aerosol variability, information obtained at different locations usually has different spatial representativeness, implying that the location should be carefully chosen so that its measurement could be extended to a greater area. In this study, we present an objective observation array design technique that automatically determines the optimal locations with the highest spatial representativeness based on the Ensemble Kalman Filter (EnKF) theory. The ensemble is constructed using aerosol optical depth (AOD) products from five satellite sensors. The optimal locations are solved sequentially by minimizing the total analysis error variance, which means that observations at these locations will reduce the background error variance to the largest extent. The location determined by the algorithm is further verified to have larger spatial representativeness than some other arbitrary location. In addition to the existing active Aerosol Robotic Network (AERONET) sites, the 40 selected optimal locations are mostly concentrated on regions with both high AOD inhomogeneity and its spatial representativeness, namely, the Sahel, South Africa, East Asia, and North Pacific Islands. These places should be the focuses of establishing future AERONET sites in order to further reduce the uncertainty in the monthly mean AOD. Observations at these locations contribute to approximately 50% of the total background uncertainty reduction.

  8. Comparison of PMCAMx aerosol optical depth predictions over Europe with AERONET and MODIS measurements

    Science.gov (United States)

    Panagiotopoulou, Antigoni; Charalampidis, Panagiotis; Fountoukis, Christos; Pilinis, Christodoulos; Pandis, Spyros N.

    2016-11-01

    The ability of chemical transport model (CTM) PMCAMx to reproduce aerosol optical depth (AOD) measurements by the Aerosol Robotic Network (AERONET) and the Moderate Resolution Imaging Spectroradiometer (MODIS) over Europe during the photochemically active period of May 2008 (EUCAARI campaign) is evaluated. Periods with high dust or sea-salt levels are excluded, so the analysis focuses on the ability of the model to simulate the mostly secondary aerosol and its interactions with water. PMCAMx reproduces the monthly mean MODIS and AERONET AOD values over the Iberian Peninsula, the British Isles, central Europe, and Russia with a fractional bias of less than 15 % and a fractional error of less than 30 %. However, the model overestimates the AOD over northern Europe, most probably due to an overestimation of organic aerosol and sulfates. At the other end, PMCAMx underestimates the monthly mean MODIS AOD over the Balkans, the Mediterranean, and the South Atlantic. These errors appear to be related to an underestimation of sulfates. Sensitivity tests indicate that the evaluation results of the monthly mean AODs are quite sensitive to the relative humidity (RH) fields used by PMCAMx, but are not sensitive to the simulated size distribution and the black carbon mixing state. The screening of the satellite retrievals for periods with high dust (or coarse particles in general) concentrations as well as the combination of the MODIS and AERONET datasets lead to more robust conclusions about the ability of the model to simulate the secondary aerosol components that dominate the AOD during this period.

  9. The Origin and Optical Depth of Ionizing Radiation in the "Green Pea" Galaxies

    CERN Document Server

    Jaskot, A E

    2013-01-01

    Although Lyman continuum (LyC) radiation from star-forming galaxies likely drove the reionization of the Universe, observations of star-forming galaxies at low redshift generally indicate low LyC escape fractions. However, the extreme [O III]/[O II] ratios of the z=0.1-0.3 Green Pea galaxies may be due to high escape fractions of ionizing radiation. To analyze the LyC optical depths and ionizing sources of these rare, compact starbursts, we compare nebular photoionization and stellar population models with observed emission lines in the Peas' SDSS spectra. We focus on the six most extreme Green Peas, the galaxies with the highest [O III]/[O II] ratios and the best candidates for escaping ionizing radiation. The Balmer line equivalent widths and He I {\\lambda}3819 emission in the extreme Peas support young ages of 3-5 Myr, and He II {\\lambda}4686 emission in five extreme Peas signals the presence of hard ionizing sources. Ionization by active galactic nuclei or high-mass X-ray binaries is inconsistent with the...

  10. Retrieval and Validation of Aerosol Optical Depth by using the GF-1 Remote Sensing Data

    Science.gov (United States)

    Zhang, L.; Xu, S.; Wang, L.; Cai, K.; Ge, Q.

    2017-05-01

    Based on the characteristics of GF-1 remote sensing data, the method and data processing procedure to retrieve the Aerosol Optical Depth (AOD) are developed in this study. The surface contribution over dense vegetation and urban bright target areas are respectively removed by using the dark target and deep blue algorithms. Our method is applied for the three serious polluted Beijing-Tianjin-Hebei (BTH), Yangtze River Delta (YRD) and Pearl River Delta (PRD) regions. The retrieved AOD are validated by ground-based AERONET data from Beijing, Hangzhou, Hong Kong sites. Our results show that, 1) the heavy aerosol loadings are usually distributed in high industrial emission and dense populated cities, with the AOD value near 1. 2) There is a good agreement between satellite-retrievals and in-site observations, with the coefficient factors of 0.71 (BTH), 0.55 (YRD) and 0.54(PRD). 3) The GF-1 retrieval uncertainties are mainly from the impact of cloud contamination, high surface reflectance and assumed aerosol model.

  11. Multiple regression method to determine aerosol optical depth in atmospheric column in Penang, Malaysia

    Science.gov (United States)

    Tan, F.; Lim, H. S.; Abdullah, K.; Yoon, T. L.; Zubir Matjafri, M.; Holben, B.

    2014-02-01

    Aerosol optical depth (AOD) from AERONET data has a very fine resolution but air pollution index (API), visibility and relative humidity from the ground truth measurements are coarse. To obtain the local AOD in the atmosphere, the relationship between these three parameters was determined using multiple regression analysis. The data of southwest monsoon period (August to September, 2012) taken in Penang, Malaysia, was used to establish a quantitative relationship in which the AOD is modeled as a function of API, relative humidity, and visibility. The highest correlated model was used to predict AOD values during southwest monsoon period. When aerosol is not uniformly distributed in the atmosphere then the predicted AOD can be highly deviated from the measured values. Therefore these deviated data can be removed by comparing between the predicted AOD values and the actual AERONET data which help to investigate whether the non uniform source of the aerosol is from the ground surface or from higher altitude level. This model can accurately predict AOD if only the aerosol is uniformly distributed in the atmosphere. However, further study is needed to determine this model is suitable to use for AOD predicting not only in Penang, but also other state in Malaysia or even global.

  12. High Resolution Aerosol Optical Depth Mapping of Beijing Using LANSAT8 Imagery

    Science.gov (United States)

    Li, Yan; Liu, Yuanliang; Wu, Jianliang

    2016-06-01

    Aerosol Optical Depth (AOD) is one of the most important parameters in the atmospheric correction of remote sensing images. We present a new method of per pixel AOD retrieval using the imagery of Landsat8. It is based on Second Simulation of the Satellite Signal in the Solar Spectrum (6S). General dark target method takes dense vegetation pixels as dark targets and derives their 550nm AODs directly from the LUT, and interpolates the AODs of other pixels according to spatial neighbourhood using those of dark target pixels. This method will down estimate the AOD levels for urban areas. We propose an innovative method to retrieval the AODs using multiple temporal data. For a pixel which has nothing change between the associated time, there must exists an intersection of surface albedo. When there are enough data to find the intersection it ought to be a value that meet the error tolerance. In this paper, we present an example of using three temporal Landsat ETM+ image to retrieve AOD taking Beijing as the testing area. The result is compared to the commonly employed dark target algorithm to show the effectiveness of the methods.

  13. Estimation of aerosol optical depth at different wavelengths by multiple regression method.

    Science.gov (United States)

    Tan, Fuyi; Lim, Hwee San; Abdullah, Khiruddin; Holben, Brent

    2016-02-01

    This study aims to investigate and establish a suitable model that can help to estimate aerosol optical depth (AOD) in order to monitor aerosol variations especially during non-retrieval time. The relationship between actual ground measurements (such as air pollution index, visibility, relative humidity, temperature, and pressure) and AOD obtained with a CIMEL sun photometer was determined through a series of statistical procedures to produce an AOD prediction model with reasonable accuracy. The AOD prediction model calibrated for each wavelength has a set of coefficients. The model was validated using a set of statistical tests. The validated model was then employed to calculate AOD at different wavelengths. The results show that the proposed model successfully predicted AOD at each studied wavelength ranging from 340 nm to 1020 nm. To illustrate the application of the model, the aerosol size determined using measure AOD data for Penang was compared with that determined using the model. This was done by examining the curvature in the ln [AOD]-ln [wavelength] plot. Consistency was obtained when it was concluded that Penang was dominated by fine mode aerosol in 2012 and 2013 using both measured and predicted AOD data. These results indicate that the proposed AOD prediction model using routine measurements as input is a promising tool for the regular monitoring of aerosol variation during non-retrieval time.

  14. Retrieval of aerosol optical depth for Chongqing using the HJ-1 satellite data

    Science.gov (United States)

    Wang, Zengwu; Yang, Shiqi; Zeng, Qiaolin; Wang, Yongqian

    2017-06-01

    Aerosol optical depth (AOD) is a common indicator applied in monitoring aerosols in the atmosphere. The hilly landscape and rapid economic growth of the megacity Chongqing have facilitated increased aerosol concentration, and it is meaningful to accurately retrieve AOD over Chongqing. The HJ-1A/B satellite of China carries a sensor/camera called the Charge Coupled Device (CCD), the spatial resolution of which meets the requirement for retrieving high resolution AOD. In this paper, analysis of the AOD retrievals from different methods using the HJ-1 satellite data revealed the most suitable algorithm. Through comparison with the AOD product of Moderate Resolution Imaging Spectroradiometer (MODIS), the AOD retrieval results using enhanced vegetation index (EVI) to estimate dark pixels showed the highest correlation. The continental aerosol model was used to build a lookup table that was able to facilitate a good AOD retrieval for both city and rural areas. Finally, the algorithm that combined dark pixels, buffer areas, and the deep blue algorithm was found to be most suitable for AOD retrieval. The AOD retrieval results based on the HJ-1 data were consistent with MODIS products, and our algorithm yields reasonable results in most cases. The results were also compared with ground-based PM10 measurements synchronized with the overpass time of the HJ-1 satellite, and high correlation was found. The findings are relevant to other Chinese satellite data used for retrieving AOD on the same channels.

  15. High Resolution Aerosol Optical Depth Retrieval Using Gaofen-1 WFV Camera Data

    Directory of Open Access Journals (Sweden)

    Kun Sun

    2017-01-01

    Full Text Available Aerosol Optical Depth (AOD is crucial for urban air quality assessment. However, the frequently used moderate-resolution imaging spectroradiometer (MODIS AOD product at 10 km resolution is too coarse to be applied in a regional-scale study. Gaofen-1 (GF-1 wide-field-of-view (WFV camera data, with high spatial and temporal resolution, has great potential in estimation of AOD. Due to the lack of shortwave infrared (SWIR band and complex surface reflectivity brought from high spatial resolution, it is difficult to retrieve AOD from GF-1 WFV data with traditional methods. In this paper, we propose an improved AOD retrieval algorithm for GF-1 WFV data. The retrieved AOD has a spatial resolution of 160 m and covers all land surface types. Significant improvements in the algorithm include: (1 adopting an improved clear sky composite method by using the MODIS AOD product to identify the clearest days and correct the background atmospheric effect; and (2 obtaining local aerosol models from long-term CIMEL sun-photometer measurements. Validation against MODIS AOD and ground measurements showed that the GF-1 WFV AOD has a good relationship with MODIS AOD (R2 = 0.66; RMSE = 0.27 and ground measurements (R2 = 0.80; RMSE = 0.25. Nevertheless, the proposed algorithm was found to overestimate AOD in some cases, which will need to be improved upon in future research.

  16. X-ray optical depth diagnostics of T Tauri accretion shocks

    CERN Document Server

    Argiroffi, C; Peres, G; Drake, J J; Santiago, J Lopez; Sciortino, S; Stelzer, B

    2009-01-01

    In classical T Tauri stars, X-rays are produced by two plasma components: a hot low-density plasma, with frequent flaring activity, and a high-density lower temperature plasma. The former is coronal plasma related to the stellar magnetic activity. The latter component, never observed in non-accreting stars, could be plasma heated by the shock formed by the accretion process. However its nature is still being debated. Our aim is to probe the soft X-ray emission from the high-density plasma component in classical T Tauri stars to check whether this is plasma heated in the accretion shock or whether it is coronal plasma. High-resolution X-ray spectroscopy allows us to measure individual line fluxes. We analyze X-ray spectra of the classical T Tauri star MP Muscae and TW Hydrae. Our aim is to evaluate line ratios to search for optical depth effects, which are expected in the accretion-driven scenario. We also derive the plasma emission measure distributions EMD, to investigate whether and how the EMD of accreting...

  17. Reflector antenna analysis using physical optics on Graphics Processing Units

    DEFF Research Database (Denmark)

    Borries, Oscar Peter; Sørensen, Hans Henrik Brandenborg; Dammann, Bernd

    2014-01-01

    The Physical Optics approximation is a widely used asymptotic method for calculating the scattering from electrically large bodies. It requires significant computational work and little memory, and is thus well suited for application on a Graphics Processing Unit. Here, we investigate...... the performance of an implementation and demonstrate that while there are some implementational pitfalls, a careful implementation can result in impressive improvements....

  18. Shipboard Sunphotometer Measurements of Aerosol Optical Depth During ACE-2 and Comparison with Selected Ship, Aircraft and Satellite Measurements

    Science.gov (United States)

    Livingston, J. M.; Kapustin, V. N.; Schmid, B.; Russell, P. B.; Quinn, P. K.; Bates, T. S.; Durkee, P. A.; Nielsen, K.; Freudenthaler, V.; Wiegner, M.; Covert, D. S.

    2000-01-01

    We present analyses of aerosol optical depth (AOD) measurements taken with a shipboard six-channel tracking sunphotometer during ACE-2. For 10 July 1997, results are also shown for measurements acquired 70 km from the ship with a fourteen-channel airborne tracking sunphotometer.

  19. Modulation Depth Based on Frequency-shift Characteristic of LiNbO3 Waveguide Electro-optic Intensity Modulator

    Institute of Scientific and Technical Information of China (English)

    Hui-juan ZHOU; Zhou MENG; Yi LIAO

    2010-01-01

    The modulation depth,defined according to practical mod-ulation results,which changes with the microwave power and its fre-quency,is significant for systems utilizing the frequency-shift charac-teristic of the LiNbO3 waveguide Electro-Optic Intensity Modulator (EOIM).By analyzing the impedance mismatch between the micro-wave source and the EOIM,the effective voltage applied to the RF port of the EOIM is deprived frcm the microwave power and its fre-quency.Associating with analyses of the phase velocity mismatch be-tween the microwave and the optical wave,the theoretical modulation depth has been obtained,which is verified by experimental results.We provide a method to choose the appropriate modulation depth to optimize the desired sideband through proper transmission bias far the system based an the frequency-shift characteristic of the EOIM.

  20. Enhanced depth imaging optical coherence tomography and fundus autofluorescence findings in bilateral choroidal osteoma: a case report

    Directory of Open Access Journals (Sweden)

    Muhammet Kazim Erol

    2013-06-01

    Full Text Available The authors present enhanced depth imaging optical coherence tomography (EDI OCT and fundus autofluorescence (FAF characteristics of a patient with bilateral choroidal osteoma and try to make a correlation between two imaging techniques. Two eyes of a patient with choroidal osteoma underwent complete ophthalmic examination. Enhanced depth imaging optical coherence tomography revealed a cage-like pattern, which corresponded to the calcified region of the tumor. Fundus autofluorescence imaging of the same area showed slight hyperautofluorescence. Three different reflectivity patterns in the decalcified area were defined. In the areas of subretinal fluid, outer segment elongations similar to central serous chorioretinopathy were observed. Hyperautofluorescent spots were evident in fundus autofluorescence in the same area. Calcified and decalcified portions of choroidal osteoma as well as the atrophy of choriocapillaris demonstrated different patterns with enhanced depth imaging and fundus autofluorescence imaging. Both techniques were found to be beneficial in the diagnosis and follow-up of choroidal osteoma.

  1. Enhanced depth imaging optical coherence tomography and fundus autofluorescence findings in bilateral choroidal osteoma: a case report.

    Science.gov (United States)

    Erol, Muhammet Kazim; Coban, Deniz Turgut; Ceran, Basak Bostanci; Bulut, Mehmet

    2013-01-01

    The authors present enhanced depth imaging optical coherence tomography (EDI OCT) and fundus autofluorescence (FAF) characteristics of a patient with bilateral choroidal osteoma and try to make a correlation between two imaging techniques. Two eyes of a patient with choroidal osteoma underwent complete ophthalmic examination. Enhanced depth imaging optical coherence tomography revealed a cage-like pattern, which corresponded to the calcified region of the tumor. Fundus autofluorescence imaging of the same area showed slight hyperautofluorescence. Three different reflectivity patterns in the decalcified area were defined. In the areas of subretinal fluid, outer segment elongations similar to central serous chorioretinopathy were observed. Hyperautofluorescent spots were evident in fundus autofluorescence in the same area. Calcified and decalcified portions of choroidal osteoma as well as the atrophy of choriocapillaris demonstrated different patterns with enhanced depth imaging and fundus autofluorescence imaging. Both techniques were found to be beneficial in the diagnosis and follow-up of choroidal osteoma.

  2. Enhanced depth imaging optical coherence tomography and fundus autofluorescence findings in bilateral choroidal osteoma: a case report

    Energy Technology Data Exchange (ETDEWEB)

    Erol, Muhammet Kazim; Coban, Deniz Turgut; Ceran, Basak Bostanci; Bulut, Mehmet, E-mail: muhammetkazimerol@gmail.com [Kazim Erol. Antalya Training and Research Hospital, Ophthalmology Department, Antalya (Turkey)

    2013-11-01

    The authors present enhanced depth imaging optical coherence tomography (EDI OCT) and fundus autofluorescence (FAF) characteristics of a patient with bilateral choroidal osteoma and try to make a correlation between two imaging techniques. Two eyes of a patient with choroidal osteoma underwent complete ophthalmic examination. Enhanced depth imaging optical coherence tomography revealed a cage-like pattern, which corresponded to the calcified region of the tumor. Fundus autofluorescence imaging of the same area showed slight hyperautofluorescence. Three different reflectivity patterns in the decalcified area were defined. In the areas of subretinal fluid, outer segment elongations similar to central serous chorioretinopathy were observed. Hyperautofluorescent spots were evident in fundus autofluorescence in the same area. Calcified and decalcified portions of choroidal osteoma as well as the atrophy of choriocapillaris demonstrated different patterns with enhanced depth imaging and fundus autofluorescence imaging. Both techniques were found to be beneficial in the diagnosis and follow-up of choroidal osteoma. (author)

  3. Thin ice clouds in the Arctic: cloud optical depth and particle size retrieved from ground-based thermal infrared radiometry

    Science.gov (United States)

    Blanchard, Yann; Royer, Alain; O'Neill, Norman T.; Turner, David D.; Eloranta, Edwin W.

    2017-06-01

    Multiband downwelling thermal measurements of zenith sky radiance, along with cloud boundary heights, were used in a retrieval algorithm to estimate cloud optical depth and effective particle diameter of thin ice clouds in the Canadian High Arctic. Ground-based thermal infrared (IR) radiances for 150 semitransparent ice clouds cases were acquired at the Polar Environment Atmospheric Research Laboratory (PEARL) in Eureka, Nunavut, Canada (80° N, 86° W). We analyzed and quantified the sensitivity of downwelling thermal radiance to several cloud parameters including optical depth, effective particle diameter and shape, water vapor content, cloud geometric thickness and cloud base altitude. A lookup table retrieval method was used to successfully extract, through an optimal estimation method, cloud optical depth up to a maximum value of 2.6 and to separate thin ice clouds into two classes: (1) TIC1 clouds characterized by small crystals (effective particle diameter ≤ 30 µm), and (2) TIC2 clouds characterized by large ice crystals (effective particle diameter > 30 µm). The retrieval technique was validated using data from the Arctic High Spectral Resolution Lidar (AHSRL) and Millimeter Wave Cloud Radar (MMCR). Inversions were performed over three polar winters and results showed a significant correlation (R2 = 0.95) for cloud optical depth retrievals and an overall accuracy of 83 % for the classification of TIC1 and TIC2 clouds. A partial validation relative to an algorithm based on high spectral resolution downwelling IR radiance measurements between 8 and 21 µm was also performed. It confirms the robustness of the optical depth retrieval and the fact that the broadband thermal radiometer retrieval was sensitive to small particle (TIC1) sizes.

  4. Relative Skills of Soil Moisutre and Vegetation Optical Depth Retrievals for Agricultural Drought Monitoring

    Science.gov (United States)

    Han, E.; Crow, W. T.; Holmes, T. R.; Bolten, J. D.

    2012-12-01

    Soil moisture condition is an important indicator for agricultural drought monitoring. Through the Land Parameter Retrieval Model (LPRM), vegetation optical depth (VOD) as well as surface soil moisture (SM) can be retrieved simultaneously from brightness temperature observations from the Advanced Microwave Scanning Radiometer (AMSR-E). This study aims to investigate added skills of VOD in addition to SM for agricultural drought monitoring using monthly LPRM-SM and VOD products from 2002 to 2011. First, the lagged rank cross-correlation between Normalized Difference Vegetation Index (NDVI) and the SM/VOD retrievals is used to evaluate the skills of the SM and VOD for drought monitoring. Interestingly, the highest rank cross-correlation between NDVI and VOD is found with lag of (+1) month (temporally lagged behind ranks of NDVI by 1 month), while the highest rank cross-correlation coefficient of SM is found with lag (-1) month (temporally precedes the ranks of NDVI by 1 month). Lagged responses of plants to the available water capacity in the root zone may explain this lagged peak of correlation of VOD. In order to understand this finding more systematically, additional analysis on the microwave polarization difference index and vertical/horizontal brightness temperature are conducted. Next, different types of observations (SM, VOD and NDVI) and hydrologic model results (Palmer model) are merged to improve predictive power. We adopt two different merging approaches (simple weighting method and auto-regressive model) to quantify the added skills of those different drought-related indices. The results show that adding more information rather than using solely SM observation increases lag (-1) month cross-correlation coefficient with NDVI. This result indicates that different observations/models have independent information to some degree. Therefore further analysis on error-correlations between the observations/model results is also conducted. This study suggests

  5. MODIS Aerosol Optical Depth retrieval over land considering surface BRDF effects

    Science.gov (United States)

    Wu, Yerong; de Graaf, Martin; Menenti, Massimo

    2016-04-01

    Aerosols in the atmosphere play an important role in the climate system and human health. Retrieval from satellite data, Aerosol Optical Depth (AOD), one of most important indices of aerosol optical properties, has been extensively investigated. Benefiting from the high resolution at spatial and temporal and the maturity of the aerosol retrieval algorithm, MOderate Resolution Imaging Spectroradiometer (MODIS) Dark Target AOD product has been extensively applied in other scientific research such as climate change and air pollution. The latest product - MODIS Collection 6 Dark Target AOD (C6_DT) has been released. However, the accuracy of C6_DT AOD (global mean ±0.03) over land is still too low for the constraint on radiative forcing in the climate system, where the uncertainty should be reduced to ±0.02. The major uncertainty mainly lies on the underestimation/overestimation of the surface contribution to the Top Of Atmosphere (TOA) radiance since a lambertian surface is assumed in the C6_DT land algorithm. In the real world, it requires considering the heterogeneity of the surface reflection in the radiative transfer process. Based on this, we developed a new algorithm to retrieve AOD by considering surface Bidirectional Reflectance Distribution Function (BRDF) effects. The surface BRDF is much more complicated than isotropic reflection, described as 4 elements: directional-directional, directional-hemispherical, hemispherical-directional and hemispherical-hemispherical reflectance, and coupled into radiative transfer equation to generate an accurate top of atmosphere reflectance. The limited MODIS measurements (three channels available) allow us to retrieve only three parameters, which including AOD, the surface directional-directional reflectance and fine aerosol ratio η. The other three elements of the surface reflectance are expected to be constrained by ancillary data and assumptions or "a priori" information since there are more unknowns than MODIS

  6. Spectral aerosol optical depths over Bay of Bengal and Chennai: I—measurements

    Science.gov (United States)

    Ramachandran, S.; Jayaraman, A.

    A cruise experiment to study the aerosol optical characteristics was conducted in February-March 2001 over the Bay of Bengal, a data void region. An analysis of aerosol optical depths (AODs) measured onboard Sagar Kanya shows that the AODs are higher when compared to those measured over the west coast of India and the Arabian Sea. The mean AODs at 0.5 μm over the Bay of Bengal are in the range of 0.2-0.7, and are found to show a variation of about 40-50% in the wavelength region of 0.4- 0.85 μm. The mean wavelength exponent α over the Bay of Bengal is found to be 1.80, higher than the Arabian Sea value of 1.46, indicating a relatively higher concentration of submicron size particles. The mean Ångström coefficient β, which represents the columnar aerosol loading, over the Bay of Bengal is found to be 0.10. Measurements of AODs, made before and after the cruise in Chennai, an urban station located on the eastern coast of India, show higher values compared to the Bay of Bengal data. The mean α for Chennai is found to be 1.53, which is lower than the Bay of Bengal value while the mean β is higher at 0.18. While a higher α value indicates the dominance of smaller size particles over Bay of Bengal, a higher β and a higher AOD at all wavelengths indicate the dominance of both bigger and smaller particles over Chennai. A comparison of AODs obtained over a coastal station Trivandrum, located on the southwest coast of India, during March 2001 showed that in the smaller wavelength range the Chennai AODs are higher while above 0.6 μm the AODs are comparable. The day-to-day variations of AODs measured at Chennai are less significant when compared to Bay of Bengal and are below 10%. As Chennai is an urban, industrial and a well-populated city, and is a constant source of aerosol particles, there are lesser day-to-day variations in the AOD, while over the Bay of Bengal the air masses come from different source regions carrying aerosols of different chemical and

  7. Strategies to Improve the Accuracy of Mars-GRAM Sensitivity Studies at Large Optical Depths

    Science.gov (United States)

    Justh, Hilary L.; Justus, Carl G.; Badger, Andrew M.

    2009-01-01

    The Mars Global Reference Atmospheric Model (Mars-GRAM) is an engineering-level atmospheric model widely used for diverse mission applications. Mars-GRAM s perturbation modeling capability is commonly used, in a Monte-Carlo mode, to perform high fidelity engineering end-to-end simulations for entry, descent, and landing (EDL). It has been discovered during the Mars Science Laboratory (MSL) site selection process that Mars-GRAM when used for sensitivity studies for MapYear=0 and large optical depth values such as tau=3 is less than realistic. A comparison study between Mars atmospheric density estimates from Mars- GRAM and measurements by Mars Global Surveyor (MGS) has been undertaken for locations of varying latitudes, Ls, and LTST on Mars. The preliminary results from this study have validated the Thermal Emission Spectrometer (TES) limb data. From the surface to 80 km altitude, Mars- GRAM is based on the NASA Ames Mars General Circulation Model (MGCM). MGCM results that were used for Mars-GRAM with MapYear=0 were from a MGCM run with a fixed value of tau=3 for the entire year at all locations. Unrealistic energy absorption by uniform atmospheric dust leads to an unrealistic thermal energy balance on the polar caps. The outcome is an inaccurate cycle of condensation/sublimation of the polar caps and, as a consequence, an inaccurate cycle of total atmospheric mass and global-average surface pressure. Under an assumption of unchanged temperature profile and hydrostatic equilibrium, a given percentage change in surface pressure would produce a corresponding percentage change in density at all altitudes. Consequently, the final result of a change in surface pressure is an imprecise atmospheric density at all altitudes. To solve this pressure-density problem, a density factor value was determined for tau=.3, 1 and 3 that will adjust the input values of MGCM MapYear 0 pressure and density to achieve a better match of Mars-GRAM MapYear=0 with MapYears 1 and 2 MGCM output

  8. MODIS 3 km and 10 km aerosol optical depth for China: Evaluation and comparison

    Science.gov (United States)

    He, Qingqing; Zhang, Ming; Huang, Bo; Tong, Xuelian

    2017-03-01

    The recently released Moderate Resolution Imaging Spectrometer (MODIS) Collection 6 introduced a fine scale aerosol optical depth (AOD) distribution, the 3 km product, which is expected to perform well in analyzing aerosols and identifying local air pollution, especially in the severely polluted atmosphere of China. However, few detailed evaluations of regional variations have been conducted. In this paper, we evaluate MODIS 3 km and 10 km AOD products for China against ground-based measurements and compare their performance with respect to spatial and temporal variations. The ground validations indicate that the two products are generally correlated well to ground-based observations. Spatially, the 3 km product slightly outperform the 10 km product in well-developed areas of southern China. Temporally, both products perform worse during spring and summer. Atmospheric clouds and underlying surface are two key factors that influence the accuracy and number of retrievals for both products. The comparison analysis reveals the newly introduced AOD product clearly shows good relationships with the coarse resolution retrievals in spatial and temporal variation but significant differences regarding details. The 3 km AOD product provides better aerosol gradients, more retrievals in bare areas of western China and some spikes of diurnal variation in cloudy days. Seasonal comparisons show the 3 km AOD product is higher than the 10 km product in all seasons, especially during spring and summer. Although the 3 km product for China generally performs slightly worse than the 10 km product, the added information of the MODIS 3 km AOD product shows potential for studying local aerosol characterization, and may facilitate studies of air pollution.

  9. Characteristics of atmospheric aerosol optical depth variation in China during 1993-2012

    Science.gov (United States)

    Xu, Xiaofeng; Qiu, Jinhuan; Xia, Xiangao; Sun, Ling; Min, Min

    2015-10-01

    The long-term variations of atmospheric aerosol optical depth (AOD) over 14 first-class solar radiation stations in China during 1993-2012 are studied. The AOD at 750 nm wavelength is retrieved with the hourly accumulated direct solar radiation by using a broadband extinction method. The retrievals are validated in comparison with AERONET (Aerosol Robotic Network) and MODIS (Moderate Resolution Imaging Spectroradiometer) AOD products. For the comparison with AERONET, the correlation coefficient (R), mean bias error (MBE) and root mean square error (RMSE) of the monthly mean AODs are respectively 0.848, 0.029 and 0.101. Based on the statistical analysis, the monthly, seasonal and annual AOD variation characteristics are categorized as follow: (1) There are three major types of the seasonal AOD variations, which shows the largest seasonal averaged AOD appearing in spring, summer and winter. The smallest seasonal averaged AOD appears mostly in autumn. (2) Beijing and Guangzhou show a significant decreasing trend of the yearly AOD, while an increasing tendency appears in Zhengzhou, Shanghai, Kunming, Kashi and Wuhan. Although no significant variation trends are found, some fluctuations appear in the 20-year period in other cities. (3) The 20-year mean AOD ranges from 0.135 (Lhasa) to 0.678 (Zhengzhou). The aerosol hygroscopic growth contributes a lot to AOD in major cities in the eastern part of China, while not in most cities in the western part. A simple correction method is applied for enhancing the relationship of AOD and PM2.5 concentration.

  10. Observations of rapid aerosol optical depth enhancements in the vicinity of polluted cumulus clouds

    Science.gov (United States)

    Eck, T. F.; Holben, B. N.; Reid, J. S.; Arola, A.; Ferrare, R. A.; Hostetler, C. A.; Crumeyrolle, S. N.; Berkoff, T. A.; Welton, E. J.; Lolli, S.; Lyapustin, A.; Wang, Y.; Schafer, J. S.; Giles, D. M.; Anderson, B. E.; Thornhill, K. L.; Minnis, P.; Pickering, K. E.; Loughner, C. P.; Smirnov, A.; Sinyuk, A.

    2014-11-01

    During the July 2011 Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) field experiment in Maryland, significant enhancements in Aerosol Robotic Network (AERONET) sun-sky radiometer measured aerosol optical depth (AOD) were observed in the immediate vicinity of non-precipitating cumulus clouds on some days. Both measured Ångström exponents and aerosol size distribution retrievals made before, during and after cumulus development often suggest little change in fine mode particle size; therefore, implying possible new particle formation in addition to cloud processing and humidification of existing particles. In addition to sun-sky radiometer measurements of large enhancements of fine mode AOD, lidar measurements made from both ground-based and aircraft-based instruments during the experiment also measured large increases in aerosol signal at altitudes associated with the presence of fair weather cumulus clouds. These data show modifications of the aerosol vertical profile as a result of the aerosol enhancements at and below cloud altitudes. The airborne lidar data were utilized to estimate the spatial extent of these aerosol enhancements, finding increased AOD, backscatter and extinction out to 2.5 km distance from the cloud edge. Furthermore, in situ measurements made from aircraft vertical profiles over an AERONET site during the experiment also showed large increases in aerosol scattering and aerosol volume after cloud formation as compared to before. The 15-year AERONET database of AOD measurements at the Goddard Space Flight Center (GSFC), Maryland site, was investigated in order to obtain a climatological perspective of this phenomenon of AOD enhancement. Analysis of the diurnal cycle of AOD in summer showed significant increases in AOD from morning to late afternoon, corresponding to the diurnal cycle of cumulus development.

  11. Choroidal vasculature characteristics based choroid segmentation for enhanced depth imaging optical coherence tomography images

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Qiang; Niu, Sijie [School of Computer Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094 (China); Yuan, Songtao; Fan, Wen, E-mail: fanwen1029@163.com; Liu, Qinghuai [Department of Ophthalmology, The First Affiliated Hospital with Nanjing Medical University, Nanjing 210029 (China)

    2016-04-15

    Purpose: In clinical research, it is important to measure choroidal thickness when eyes are affected by various diseases. The main purpose is to automatically segment choroid for enhanced depth imaging optical coherence tomography (EDI-OCT) images with five B-scans averaging. Methods: The authors present an automated choroid segmentation method based on choroidal vasculature characteristics for EDI-OCT images with five B-scans averaging. By considering the large vascular of the Haller’s layer neighbor with the choroid-sclera junction (CSJ), the authors measured the intensity ascending distance and a maximum intensity image in the axial direction from a smoothed and normalized EDI-OCT image. Then, based on generated choroidal vessel image, the authors constructed the CSJ cost and constrain the CSJ search neighborhood. Finally, graph search with smooth constraints was utilized to obtain the CSJ boundary. Results: Experimental results with 49 images from 10 eyes in 8 normal persons and 270 images from 57 eyes in 44 patients with several stages of diabetic retinopathy and age-related macular degeneration demonstrate that the proposed method can accurately segment the choroid of EDI-OCT images with five B-scans averaging. The mean choroid thickness difference and overlap ratio between the authors’ proposed method and manual segmentation drawn by experts were −11.43 μm and 86.29%, respectively. Conclusions: Good performance was achieved for normal and pathologic eyes, which proves that the authors’ method is effective for the automated choroid segmentation of the EDI-OCT images with five B-scans averaging.

  12. Standardization of choroidal thickness measurements using enhanced depth imaging optical coherence tomography

    Institute of Scientific and Technical Information of China (English)

    Nattapon; Boonarpha; Yalin; Zheng; Alexandros; N.Stangos; Huiqi; Lu; Ankur; Raj; Gabriela; Czanner; Simon; P.Harding; Jayashree; Nair-Sahni

    2015-01-01

    AIM: To describe and evaluate a standardized protocol for measuring the choroidal thickness(Ch T) using enhanced depth imaging optical coherence tomography(EDI OCT).METHODS: Single 9 mm EDI OCT line scans across the fovea were used for this study. The protocol used in this study classified the EDI OCT images into four groups based on the appearance of the choroidal-scleral interface and suprachoroidal space. Two evaluation iterations of experiments were performed: first, the protocol was validated in a pilot study of 12 healthy eyes. Afterwards, the applicability of the protocol was tested in 82 eyes of patients with diabetes. Inter-observer and intra-observer agreements on image classifications were performed using Cohen’s kappa coefficient(κ). Intraclass correlation coefficient(ICC) and Bland-Altman’s methodology were used for the measurement of the Ch T.RESULTS: There was a moderate(κ=0.42) and perfect(κ =1) inter- and intra-observer agreements on image classifications from healthy eyes images and substantial(κ =0.66) and almost perfect(κ =0.86) agreements from diabetic eyes images. The proposed protocol showed excellent inter- and intra-observer agreements for the Ch T measurements on both, healthy eyes and diabetic eyes(ICC >0.90 in all image categories). The Bland-Altman plot showed a relatively large Ch T measurement agreement in the scans that contained less visible choroidal outer boundary. CONCLUSION: A protocol to standardize Ch T measurements in EDI OCT images has been developed;the results obtained using this protocol show that the technique is accurate and reliable for routine clinical practice and research.

  13. Choroidal vasculature characteristics based choroid segmentation for enhanced depth imaging optical coherence tomography images.

    Science.gov (United States)

    Chen, Qiang; Niu, Sijie; Yuan, Songtao; Fan, Wen; Liu, Qinghuai

    2016-04-01

    In clinical research, it is important to measure choroidal thickness when eyes are affected by various diseases. The main purpose is to automatically segment choroid for enhanced depth imaging optical coherence tomography (EDI-OCT) images with five B-scans averaging. The authors present an automated choroid segmentation method based on choroidal vasculature characteristics for EDI-OCT images with five B-scans averaging. By considering the large vascular of the Haller's layer neighbor with the choroid-sclera junction (CSJ), the authors measured the intensity ascending distance and a maximum intensity image in the axial direction from a smoothed and normalized EDI-OCT image. Then, based on generated choroidal vessel image, the authors constructed the CSJ cost and constrain the CSJ search neighborhood. Finally, graph search with smooth constraints was utilized to obtain the CSJ boundary. Experimental results with 49 images from 10 eyes in 8 normal persons and 270 images from 57 eyes in 44 patients with several stages of diabetic retinopathy and age-related macular degeneration demonstrate that the proposed method can accurately segment the choroid of EDI-OCT images with five B-scans averaging. The mean choroid thickness difference and overlap ratio between the authors' proposed method and manual segmentation drawn by experts were -11.43 μm and 86.29%, respectively. Good performance was achieved for normal and pathologic eyes, which proves that the authors' method is effective for the automated choroid segmentation of the EDI-OCT images with five B-scans averaging.

  14. Standardization of choroidal thickness measurements using enhanced depth imaging optical coherence tomography

    Directory of Open Access Journals (Sweden)

    Nattapon Boonarpha

    2015-06-01

    Full Text Available AIM:To describe and evaluate a standardized protocol for measuring the choroidal thickness (ChT using enhanced depth imaging optical coherence tomography (EDI OCT.METHODS:Single 9 mm EDI OCT line scans across the fovea were used for this study. The protocol used in this study classified the EDI OCT images into four groups based on the appearance of the choroidal-scleral interface and suprachoroidal space. Two evaluation iterations of experiments were performed:first, the protocol was validated in a pilot study of 12 healthy eyes. Afterwards, the applicability of the protocol was tested in 82 eyes of patients with diabetes. Inter-observer and intra-observer agreements on image classifications were performed using Cohen’s kappa coefficient (k. Intraclass correlation coefficient (ICC and Bland-Altman’s methodology were used for the measurement of the ChT.RESULTS:There was a moderate (k=0.42 and perfect (k=1 inter- and intra-observer agreements on image classifications from healthy eyes images and substantial (k=0.66 and almost perfect (k=0.86 agreements from diabetic eyes images. The proposed protocol showed excellent inter- and intra-observer agreements for the ChT measurements on both, healthy eyes and diabetic eyes (ICC>0.90 in all image categories. The Bland-Altman plot showed a relatively large ChT measurement agreement in the scans that contained less visible choroidal outer boundary.CONCLUSIONS:A protocol to standardize ChT measurements in EDI OCT images has been developed; the results obtained using this protocol show that the technique is accurate and reliable for routine clinical practice and research.

  15. Assessment of choroidal thickness of central serous chorioretinopathy by optical coherence tomography with enhanced depth imaging

    Directory of Open Access Journals (Sweden)

    Hui Hang

    2015-01-01

    Full Text Available AIM: To evaluate the meaning of using optical coherence tomography with enhanced depth imaging(OCT-EDIto measure choroidal thickness of central serous retinopathy(CSC. METHODS: With the retrospective case control study, 65 patients(65 eyeswith CSC and 50 healthy controls(50 eyeswith age, gender and diopter-matched were recruited in this study. OCT-EDI were used to measure the subfoveal choroidal thickness(SFCTin CSC eyes, the fellow eyes and also the control eyes. Of which 40 of the 65 CSC patients self-cured, 14 of them were treated with photodynamic therapy(PDT, the left 11 accepted the laser photocoagulation(LP. SFCT were measured 3mo after that. Compared with the previous data, the statistical analysis was carried out.RESULTS: The SFCT value of 65 CSC eyes, 65 fellow eyes and 50 control eyes were 436.23±89.50, 389.45±101.03 and 329.36±95.87μm, respectively. The SFCT of suffer and fellow eyes increased significantly compared to the control eyes(P=0.008 and 0.013, respectively. There was also significant difference in SFCT between the CSC eyes and the fellow eyes(P=0.021. The SFCT were significantly decreased after PDT(P=0.032, but with no significant changes after LP or self-cured(P=0.057 and 0.076, respectively.CONCLUSION: OCT-EDI is a useful method to assess the choroidal topographic changes of CSC. The SFCT are significantly increased in the CSC eyes compared with that in the fellow eyes and the control eyes.

  16. The regional distribution characteristics of aerosol optical depth over the Tibetan Plateau

    Science.gov (United States)

    Xu, Chao; Ma, Yaoming; You, Chao; Zhu, Zhikun

    2016-04-01

    The Tibetan Plateau (TP) is representative of typical clean atmospheric conditions. Aerosol optical depth (AOD) retrieved by Multi-angle Imaging SpectroRadiometer (MISR) is higher over Qaidam Basin than the rest of the TP all the year. Different monthly variation patterns of AOD are observed over the southern and northern TP, whereby the aerosol load is usually higher in the northern TP than in the southern part. The aerosol load over the northern part increases from April to June, peaking in May. The maximum concentration of aerosols over the southern TP occurs in July. Aerosols appear to be more easily transported to the main body of the TP across the northern edge rather than the southern edge. This is may be partly because the altitude is lower at the northern edge than that of the Himalayas located along the southern edge of the TP. Three-dimensional distributions of dust, polluted dust, polluted continental and smoke are also investigated based on Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data. Dust is found to be the most prominent aerosol type on the TP, and other types of aerosols affect the atmospheric environment slightly. A dividing line of higher dust occurrence in the northern TP and lower dust occurrence in the southern TP can be observed clearly at altitude of 6-8 km above sea level, especially in spring and summer. This demarcation appears around 33-35°N in the middle of the plateau, and it is possibly associated with the high altitude terrain in the same geographic location. Comparisons of CALIPSO and MISR data show that the vertical dust occurrences are consistent with the spatial patterns of AOD. The different seasonal variation patterns between the northern and southern TP are primarily driven by atmospheric circulation, and are also related to the emission characteristics over the surrounding regions.

  17. Performance of a FieldSpec spectroradiometer for aerosol optical depth retrieval: method and preliminary results.

    Science.gov (United States)

    Bassani, Cristiana; Estellés, Víctor; Campanelli, Monica; Cavalli, Rosa Maria; Martínez-Lozano, José Antonio

    2009-04-10

    The performance of a FieldSpec spectroradiometer for retrieving aerosol optical depth (AOD) has been assessed after modifying its basic configuration in order to measure direct solar irradiance at ground level. The FieldSpec measurements were obtained during four summertime days in the years 2004 and 2005, over a Spanish agricultural site in Barrax, Albacete (30 degrees 3(') N, 2 degrees 6(') W, 700 m a.s.l.), in the framework of two European Space Agency mission remote sensing field campaigns. From the whole FieldSpec spectral domain (350-2500 nm) the AOD was extracted for channels within atmospheric windows. The instrument was calibrated by means of the standard Langley plot method, performed at a high mountain site in Italy. The AOD retrieved by the FieldSpec has been validated by comparison with the AOD obtained from a colocated CIMEL CE318 Sun photometer. The FieldSpec AOD spectra were convoluted with the CE318 filter transmission functions in order to make both datasets comparable. Our results show that both datasets are very similar (R(2) around 0.9) for all the channels from the CE318, with an average deviation of about 0.02. The temporal evolution of the AOD was accurately monitored by the FieldSpec under different atmospheric conditions, as was the case for a previously reported mineral dust intrusion. As a conclusion, the comparison performed in this study shows that the FieldSpec spectroradiometer is a suitable instrument for retrieving the AOD in different atmospheric situations.

  18. A merged aerosol dataset based on MODIS and MISR Aerosol Optical Depth products

    Science.gov (United States)

    Singh, Manoj K.; Gautam, Ritesh; Venkatachalam, Parvatham

    2016-05-01

    Aerosol Optical Depth (AOD) products available from MODIS and MISR observations are widely used for aerosol characterization, and global/environmental change studies. These products are based on different retrieval-algorithms, resolutions, sampling, and cloud-screening schemes, which have led to global/regional biases. Thus a merged product is desirable which bridges this gap by utilizing strengths from each of the sensors. In view of this, we have developed a "merged" AOD product based on MODIS and MISR AOD datasets, using Bayesian principles which takes error distributions from ground-based AOD measurements (from AERONET). Our methodology and resulting dataset are especially relevant in the scenario of combining multi-sensor retrievals for satellite-based climate data records; particularly for long-term studies involving AOD. Specifically for MISR AOD product, we also developed a methodology to produce a gap-filled dataset, using geostatistical methods (e.g. Kriging), taking advantage of available MODIS data. Merged and spatially-complete AOD datasets are inter-compared with other satellite products and with AERONET data at three stations- Kanpur, Jaipur and Gandhi College, in the Indo-Gangetic Plains. The RMSE of merged AOD (0.08-0.09) is lower than MISR (0.11-0.20) and MODIS (0.15-0.27). It is found that merged AOD has higher correlation with AERONET data (r within 0.92-0.95), compared to MISR (0.74-0.86) and MODIS (0.69-0.84) data. In terms of Expected Error, the accuracy of valid merged AOD is found to be superior as percent of merged AOD within error envelope are larger (71-92%), compared to MISR (43-61%) and MODIS (50-70%).

  19. A Synergic Algorithm for Retrieval of Aerosol Optical Depth over Land

    Institute of Scientific and Technical Information of China (English)

    GUO Jianping; XUE Yong; CAO Chunxiang; ZHANG Hao; GUANG Jie; ZHANG Xiaoye; LI Xiaowen

    2009-01-01

    In this paper,a novel algorithm for aerosol optical depth(AOD) retrieval with a 1 km spatial resolution over land is presented using the Advanced Along Track Scanning Radiometer (AATSR) dual-view capability at 0.55,0.66 and 0.87 μm,in combination with the Bi-directional Reflectance Distribution Function (BRDF) model,a product of the Moderate Resolution Imaging Spectroradiometer (MODIS).The BRDF characteristics of the land surface,i.e.prior input parameters for this algorithm,are computed by extracting the geometrical information from AATSR and reducing the kernels from the MODIS BRDF/Albedo Model Parameters Product.Finally,AOD,with a 1 km resolution at 0.55,0.66 and 0.87 μm for the forward and nadir views of AATSR,can be simultaneously obtained.Extensive validations of AOD derived from AATSR during the period from August 2005 to July 2006 in Beijing and its surrounding area,against in-situ AErosol RObotic NETwork (AERONET) measurements,were performed.The AOD difference between the retrievals from the forward and nadir views of AATSR was less than 5.72%,1.9% and 13.7%,respectively.Meanwhile,it was found that the AATSR retrievals using the synergic algorithm developed in this paper are more favorable than those by assuming a Lambert surface,for the coefficient of determination between AATSR derived AOD and AERONET mearured AOD,decreased by 15.5% and 18.5%,compared to those derived by the synergic algorithm.This further suggests that the synergic algorithm can be potentially used in climate change and air quality monitoring.

  20. A consistent aerosol optical depth (AOD) dataset over mainland China by integration of several AOD products

    Science.gov (United States)

    Xu, H.; Guang, J.; Xue, Y.; de Leeuw, Gerrit; Che, Y. H.; Guo, Jianping; He, X. W.; Wang, T. K.

    2015-08-01

    The Moderate Resolution Imaging Spectroradiometer (MODIS), the Multiangle Imaging Spectroradiometer (MISR) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) provide validated aerosol optical depth (AOD) products over both land and ocean. However, the values of the AOD provided by each of these satellites may show spatial and temporal differences due to the instrument characteristics and aerosol retrieval algorithms used for each instrument. In this article we present a method to produce an AOD data set over Asia for the year 2007 based on fusion of the data provided by different instruments and/or algorithms. First, the bias of each satellite-derived AOD product was calculated by comparison with ground-based AOD data derived from the AErosol RObotic NETwork (AERONET) and the China Aerosol Remote Sensing NETwork (CARSNET) for different values of the surface albedo and the AOD. Then, these multiple AOD products were combined using the maximum likelihood estimate (MLE) method using weights derived from the root mean square error (RMSE) associated with the accuracies of the original AOD products. The original and merged AOD dataset has been validated by comparison with AOD data from the CARSNET. Results show that the mean bias error (MBE) and mean absolute error (MAE) of the merged AOD dataset are not larger than that of any of the original AOD products. In addition, for the merged AOD dataset the fraction of pixels with no data is significantly smaller than that of any of the original products, thus increasing the spatial coverage. The fraction of retrievable area is about 50% for the merged AOD dataset and between 5% and 20% for the MISR, SeaWiFS, MODIS-DT and MODIS-DB algorithms.

  1. Estimating aerosol emissions by assimilating observed aerosol optical depth in a global aerosol model

    Directory of Open Access Journals (Sweden)

    N. Huneeus

    2012-01-01

    Full Text Available This study estimates the emission fluxes of a range of aerosol species and aerosol precursor at the global scale. These fluxes are estimated by assimilating daily total and fine mode aerosol optical depth (AOD at 550 nm from the Moderate Resolution Imaging Spectroradiometer (MODIS into a global aerosol model of intermediate complexity. Monthly emissions are fitted homogenously for each species over a set of predefined regions. The performance of the assimilation is evaluated by comparing the AOD after assimilation against the MODIS observations and against independent observations. The system is effective in forcing the model towards the observations, for both total and fine mode AOD. Significant improvements for the root mean square error and correlation coefficient against both the assimilated and independent datasets are observed as well as a significant decrease in the mean bias against the assimilated observations. The assimilation is more efficient over land than over ocean. The impact of the assimilation of fine mode AOD over ocean demonstrates potential for further improvement by including fine mode AOD observations over continents. The Angström exponent is also improved in African, European and dusty stations. The estimated emission flux for black carbon is 14.5 Tg yr−1, 119 Tg yr−1 for organic matter, 17 Pg yr−1 for sea salt, 82.7 TgS yr−1 for SO2 and 1383 Tg yr−1 for desert dust. They represent a difference of +45%, +40%, +26%, +13% and −39% respectively, with respect to the a priori values. The initial errors attributed to the emission fluxes are reduced for all estimated species.

  2. Estimating aerosol emissions by assimilating observed aerosol optical depth in a global aerosol model

    Directory of Open Access Journals (Sweden)

    N. Huneeus

    2012-05-01

    Full Text Available This study estimates the emission fluxes of a range of aerosol species and one aerosol precursor at the global scale. These fluxes are estimated by assimilating daily total and fine mode aerosol optical depth (AOD at 550 nm from the Moderate Resolution Imaging Spectroradiometer (MODIS into a global aerosol model of intermediate complexity. Monthly emissions are fitted homogenously for each species over a set of predefined regions. The performance of the assimilation is evaluated by comparing the AOD after assimilation against the MODIS observations and against independent observations. The system is effective in forcing the model towards the observations, for both total and fine mode AOD. Significant improvements for the root mean square error and correlation coefficient against both the assimilated and independent datasets are observed as well as a significant decrease in the mean bias against the assimilated observations. These improvements are larger over land than over ocean. The impact of the assimilation of fine mode AOD over ocean demonstrates potential for further improvement by including fine mode AOD observations over continents. The Angström exponent is also improved in African, European and dusty stations. The estimated emission flux for black carbon is 15 Tg yr−1, 119 Tg yr−1 for particulate organic matter, 17 Pg yr−1 for sea salt, 83 TgS yr−1 for SO2 and 1383 Tg yr−1 for desert dust. They represent a difference of +45 %, +40 %, +26 %, +13 % and −39 % respectively, with respect to the a priori values. The initial errors attributed to the emission fluxes are reduced for all estimated species.

  3. Climatology of aerosol optical depth in north-central Oklahoma: 1992–2008

    Energy Technology Data Exchange (ETDEWEB)

    Michalsky, Joseph; Denn, Frederick; Flynn, Connor; Hodges, Gary; Kiedron, Piotr; Koontz, Annette; Schlemmer, James; Schwartz, Stephen E.

    2010-04-13

    Aerosol optical depth (AOD) has been measured at the Atmospheric Radiation Measurement Program central facility near Lamont, Oklahoma, since the fall of 1992. Most of the data presented are from the multifilter rotating shadowband radiometer, a narrow-band, interference-filter Sun radiometer with five aerosol bands in the visible and near infrared; however, AOD measurements have been made simultaneously and routinely at the site by as many as three different types of instruments, including two pointing Sun radiometers. Scatterplots indicate high correlations and small biases consistent with earlier comparisons. The early part of this 16 year record had a disturbed stratosphere with residual Mt. Pinatubo aerosols, followed by the cleanest stratosphere in decades. As such, the last 13 years of the record reflect changes that have occurred predominantly in the troposphere. The field calibration technique is briefly described and compared to Langley calibrations from Mauna Loa Observatory. A modified cloudscreening technique is introduced that increases the number of daily averaged AODs retrieved annually to about 250 days compared with 175 days when a more conservative method was employed in earlier studies. AODs are calculated when the air mass is less than six; that is, when the Sun’s elevation is greater than 9.25°. The more inclusive cloud screen and the use of most of the daylight hours yield a data set that can be used to more faithfully represent the true aerosol climate for this site. The diurnal aerosol cycle is examined month-by-month to assess the effects of an aerosol climatology on the basis of infrequent sampling such as that from satellites.

  4. Climatology of aerosol optical depth in North-Central Oklahoma: 1992-2008

    Energy Technology Data Exchange (ETDEWEB)

    Michalsky, J.; Schwartz, S.; Denn, F.; Flynn, C.; Hodges, G.; Kiedron, P.; Koontz, A.; Schlemmer, J., and Schwartz, S. E

    2010-04-01

    Aerosol optical depth (AOD) has been measured at the Atmospheric Radiation Measurement Program central facility near Lamont, Oklahoma, since the fall of 1992. Most of the data presented are from the multifilter rotating shadowband radiometer, a narrow-band, interference-filter Sun radiometer with five aerosol bands in the visible and near infrared; however, AOD measurements have been made simultaneously and routinely at the site by as many as three different types of instruments, including two pointing Sun radiometers. Scatterplots indicate high correlations and small biases consistent with earlier comparisons. The early part of this 16 year record had a disturbed stratosphere with residual Mt. Pinatubo aerosols, followed by the cleanest stratosphere in decades. As such, the last 13 years of the record reflect changes that have occurred predominantly in the troposphere. The field calibration technique is briefly described and compared to Langley calibrations from Mauna Loa Observatory. A modified cloud-screening technique is introduced that increases the number of daily averaged AODs retrieved annually to about 250 days compared with 175 days when a more conservative method was employed in earlier studies. AODs are calculated when the air mass is less than six; that is, when the Sun's elevation is greater than 9.25{sup o}. The more inclusive cloud screen and the use of most of the daylight hours yield a data set that can be used to more faithfully represent the true aerosol climate for this site. The diurnal aerosol cycle is examined month-by-month to assess the effects of an aerosol climatology on the basis of infrequent sampling such as that from satellites.

  5. Retrieval of Aerosol Optical Depth over Arid Areas from MODIS Data

    Directory of Open Access Journals (Sweden)

    Xin-peng Tian

    2016-10-01

    Full Text Available Moderate Resolution Imaging Spectroradiometer (MODIS data have been widely applied for the remote sensing of aerosol optical depth (AOD because the MODIS sensor features a short revisit period and a moderate spatial resolution. The Dense Dark Vegetation (DDV method is the most popular retrieval method. However, the DDV method can only be used to retrieve the AOD with high precision when the surface reflectance in the visible spectrum is low, such as over dense vegetation or water. To obtain precise AOD values in areas with higher reflectance, such as arid areas, Land Surface Reflectance (LSR must be estimated accurately. This paper proposes a method of estimating LSR for AOD retrieval over arid areas from long-term series of MODIS images. According to the atmospheric parameters (AOD and water vapor, the clearest image without clouds was selected from the long-term series of continuous MODIS images. Atmospheric correction was conducted based on similar ground-measured atmospheric parameters and was used to estimate the LSR and retrieve the AOD at adjacent times. To validate this method, aerosol inversion experiments were performed in northern Xinjiang, in which the inverted AOD was compared to ground-measured AOD and MODIS aerosol products (MOD04. The AOD retrieved using the new algorithm was highly consistent with the AOD derived from ground-based measurements, with a correlation coefficient of 0.84. Additionally, 82.22% of the points fell within the expected error defined by NASA. The precision of the retrieved AOD data was better than that of MOD04 AOD products over arid areas.

  6. Some implications of sampling choices on comparisons between satellite and model aerosol optical depth fields

    Directory of Open Access Journals (Sweden)

    A. M. Sayer

    2010-11-01

    Full Text Available The comparison of satellite and model aerosol optical depth (AOD fields provides useful information on the strengths and weaknesses of both. However, the sampling of satellite and models is very different and some subjective decisions about data selection and aggregation must be made in order to perform such comparisons. This work examines some implications of these decisions, using GlobAerosol AOD retrievals at 550 nm from Advanced Along-Track Scanning Radiometer (AATSR measurements, and aerosol fields from the GEOS-Chem chemistry transport model. It is recommended to sample the model only where the satellite flies over on a particular day; neglecting this can cause regional differences in model AOD of up to 0.1 on monthly and annual timescales. The comparison is observed to depend strongly upon thresholds for sparsity of satellite retrievals in the model grid cells. Requiring at least 25% coverage of the model grid cell by satellite data decreases the observed difference between the two by approximately half over land. The impact over ocean is smaller. In both model and satellite datasets, there is an anticorrelation between the proportion p of a model grid cell covered by satellite retrievals and the AOD. This is attributed to small p typically occuring due to high cloud cover and lower AODs being found in large clear-sky regions. Daily median AATSR AODs were found to be closer to GEOS-Chem AODs than daily means (with the root mean squared difference being approximately 0.05 smaller. This is due to the decreased sensitivity of medians to outliers such as cloud-contaminated retrievals, or aerosol point sources not included in the model.

  7. Assembling optically active and nonactive metamaterials with chiral units

    Directory of Open Access Journals (Sweden)

    Xiang Xiong

    2012-12-01

    Full Text Available Metamaterials constructed with chiral units can be either optically active or nonactive depending on the spatial configuration of the building blocks. For a class of chiral units, their effective induced electric and magnetic dipoles, which originate from the induced surface electric current upon illumination of incident light, can be collinear at the resonant frequency. This feature provides significant advantage in designing metamaterials. In this paper we concentrate on several examples. In one scenario, chiral units with opposite chiralities are used to construct the optically nonactive metamaterial structure. It turns out that with linearly polarized incident light, the pure electric or magnetic resonance (and accordingly negative permittivity or negative permeability can be selectively realized by tuning the polarization of incident light for 90°. Alternatively, units with the same chirality can be assembled as a chiral metamaterial by taking the advantage of the collinear induced electric and magnetic dipoles. It follows that for the circularly polarized incident light, negative refractive index can be realized. These examples demonstrate the unique approach to achieve certain optical properties by assembling chiral building blocks, which could be enlightening in designing metamaterials.

  8. Modeling the South American regional smoke plume: aerosol optical depth variability and surface shortwave flux perturbation

    Directory of Open Access Journals (Sweden)

    N. E. Rosário

    2013-03-01

    Full Text Available Intra-seasonal variability of smoke aerosol optical depth (AOD and downwelling solar irradiance at the surface during the 2002 biomass burning season in South America was modeled using the Coupled Chemistry-Aerosol-Tracers Transport model with the Brazilian developments on the Regional Atmospheric Modeling System (CCATT-BRAMS. Measurements of total and fine mode fraction (FMF AOD from the AErosol RObotic NETwork (AERONET and solar irradiance at the surface from the Solar Radiation Network (SolRad-NET were used to evaluate model results. In general, the major features associated with AOD evolution over the southern part of the Amazon basin and cerrado ecosystem are captured by the model. The main discrepancies were found for high aerosol loading events. In the northeastern portion of the Amazon basin the model systematically underestimated total AOD, as expected, since smoke contribution is not dominant as it is in the southern portion and emissions other than smoke were not considered in the simulation. Better agreement was obtained comparing the model results with observed FMF AOD, which pointed out the relevance of coarse mode aerosol emission in that region. Likewise, major discrepancies over cerrado during high AOD events were found to be associated with coarse mode aerosol omission in our model. The issue of high aerosol loading events in the southern part of the Amazon was related to difficulties in predicting the smoke AOD field, which was discussed in the context of emissions shortcomings. The Cuiabá cerrado site was the only one where the highest quality AERONET data were unavailable for both total and FMF AOD. Thus, lower quality data were used. Root-mean-square error (RMSE between the model and observed FMF AOD decreased from 0.34 to 0.19 when extreme AOD events (FMF AOD550 nm ≥ 1.0 and Cuiabá were excluded from the analysis. Downward surface solar irradiance comparisons also followed similar trends when extreme AOD were excluded

  9. Signal and depth enhancement for in vivo flow cytometer measurement of ear skin by optical clearing agents.

    Science.gov (United States)

    Ding, Yimin; Wang, Jing; Fan, Zhichao; Wei, Dan; Shi, Rui; Luo, Qingming; Zhu, Dan; Wei, Xunbin

    2013-01-01

    The in vivo flow cytometry (IVFC) has shown a great potential for detecting circulating tumor cells quantitatively in the bloodstream. However, the detection depth suffers from the strong light scattering of tissue. In this study, an innovative ear skin optical clearing agent (ESOCA) is employed to improve the signal quality of the IVFC. Our results show that compared with commonly used glycerol, topical application of ESOCA can enhance the transmittance of rat ear significantly in vivo. The labeled red blood cells can be detected by the IVFC with higher signal quality and greater detection depth. This study is very helpful for potential tumor metastasis studies by the IVFC in deep tissues.

  10. Spatio-Temporal Variations in the Associations between Hourly PM2.5 and Aerosol Optical Depth (AOD) from MODIS Sensors on Terra and Aqua.

    Science.gov (United States)

    Kim, Minho; Zhang, Xingyou; Holt, James B; Liu, Yang

    2013-10-01

    Recent studies have explored the relationship between aerosol optical depth (AOD) measurements by satellite sensors and concentrations of particulate matter with aerodynamic diameters less than 2.5 μm (PM2.5). However, relatively little is known about spatial and temporal patterns in this relationship across the contiguous United States. In this study, we investigated the relationship between US Environmental Protection Agency estimates of PM2.5 concentrations and Moderate Resolution Imaging Spectroradiometer (MODIS) AOD measurements provided by two NASA satellites (Terra and Aqua) across the contiguous United States during 2005. We found that the combined use of both satellite sensors provided more AOD coverage than the use of either satellite sensor alone, that the correlation between AOD measurements and PM2.5 concentrations varied substantially by geographic location, and that this correlation was stronger in the summer and fall than that in the winter and spring.

  11. Remote Access Unit for Optic-to-Wireless Conversion

    DEFF Research Database (Denmark)

    Chorchos, Łukasz; Rommel, Simon; Turkiewicz, J. P.

    In this paper we propose a design of a reconfigurable Remote Access Unit (RAU) interfacing optical dense wavelength division multiplexed (DWDM) networks with radio communication links. To generate a radio signal the device utilizes a principles of incoherent heterodyne signal upconversion...... to the chosen radio frequency. Both signals are fed into a photodiode with 90GHz bandwidth and transmitted with antenas. The local oscillator and tunable filter are controlled over processing unit that can be easily connected to the management network. The filter and local oscillator are widely tunable what...

  12. A surface reflectance scheme for retrieving aerosol optical depth over urban surfaces in MODIS Dark Target retrieval algorithm

    Science.gov (United States)

    Gupta, Pawan; Levy, Robert C.; Mattoo, Shana; Remer, Lorraine A.; Munchak, Leigh A.

    2016-07-01

    The MODerate resolution Imaging Spectroradiometer (MODIS) instruments, aboard the two Earth Observing System (EOS) satellites Terra and Aqua, provide aerosol information with nearly daily global coverage at moderate spatial resolution (10 and 3 km). Almost 15 years of aerosol data records are now available from MODIS that can be used for various climate and air-quality applications. However, the application of MODIS aerosol products for air-quality concerns is limited by a reduction in retrieval accuracy over urban surfaces. This is largely because the urban surface reflectance behaves differently than that assumed for natural surfaces. In this study, we address the inaccuracies produced by the MODIS Dark Target (MDT) algorithm aerosol optical depth (AOD) retrievals over urban areas and suggest improvements by modifying the surface reflectance scheme in the algorithm. By integrating MODIS Land Surface Reflectance and Land Cover Type information into the aerosol surface parameterization scheme for urban areas, much of the issues associated with the standard algorithm have been mitigated for our test region, the continental United States (CONUS). The new surface scheme takes into account the change in underlying surface type and is only applied for MODIS pixels with urban percentage (UP) larger than 20 %. Over the urban areas where the new scheme has been applied (UP > 20 %), the number of AOD retrievals falling within expected error (EE %) has increased by 20 %, and the strong positive bias against ground-based sun photometry has been eliminated. However, we note that the new retrieval introduces a small negative bias for AOD values less than 0.1 due to the ultra-sensitivity of the AOD retrieval to the surface parameterization under low atmospheric aerosol loadings. Global application of the new urban surface parameterization appears promising, but further research and analysis are required before global implementation.

  13. Perception of scene-relative object movement: Optic flow parsing and the contribution of monocular depth cues.

    Science.gov (United States)

    Warren, Paul A; Rushton, Simon K

    2009-05-01

    We have recently suggested that the brain uses its sensitivity to optic flow in order to parse retinal motion into components arising due to self and object movement (e.g. Rushton, S. K., & Warren, P. A. (2005). Moving observers, 3D relative motion and the detection of object movement. Current Biology, 15, R542-R543). Here, we explore whether stereo disparity is necessary for flow parsing or whether other sources of depth information, which could theoretically constrain flow-field interpretation, are sufficient. Stationary observers viewed large field of view stimuli containing textured cubes, moving in a manner that was consistent with a complex observer movement through a stationary scene. Observers made speeded responses to report the perceived direction of movement of a probe object presented at different depths in the scene. Across conditions we varied the presence or absence of different binocular and monocular cues to depth order. In line with previous studies, results consistent with flow parsing (in terms of both perceived direction and response time) were found in the condition in which motion parallax and stereoscopic disparity were present. Observers were poorer at judging object movement when depth order was specified by parallax alone. However, as more monocular depth cues were added to the stimulus the results approached those found when the scene contained stereoscopic cues. We conclude that both monocular and binocular static depth information contribute to flow parsing. These findings are discussed in the context of potential architectures for a model of the flow parsing mechanism.

  14. Estimating Ground-Level Particulate Matter (PM) Concentration using Satellite-derived Aerosol Optical Depth (AOD)

    Science.gov (United States)

    Park, Seohui; Im, Jungho

    2017-04-01

    Atmospheric aerosols are strongly associated with adverse human health effects. In particular, particulate matter less than 10 micrometers and 2.5 micrometers (i.e., PM10 and PM2.5, respectively) can cause cardiovascular and lung diseases such as asthma and chronic obstructive pulmonary disease (COPD). Air quality including PM has typically been monitored using station-based in-situ measurements over the world. However, in situ measurements do not provide spatial continuity over large areas. An alternative approach is to use satellite remote sensing as it provides data over vast areas at high temporal resolution. The literature shows that PM concentrations are related with Aerosol Optical Depth (AOD) that is derived from satellite observations, but it is still difficult to identify PM concentrations directly from AOD. Some studies used statistical approaches for estimating PM concentrations from AOD while some others combined numerical models and satellite-derived AOD. In this study, satellite-derived products were used to estimate ground PM concentrations based on machine learning over South Korea. Satellite-derived products include AOD from Geostationary Ocean Color Imager (GOCI), precipitation from Tropical Rainfall Measuring Mission (TRMM), soil moisture from AMSR-2, elevation from Shuttle Radar Topography Mission (SRTM), and land cover, land surface temperature and normalized difference vegetation index (NDVI) from Moderate Resolution Imaging Spectroradiometer (MODIS). PM concentrations data were collected from 318 stations. A statistical ordinary least squares (OLS) approach was also tested and compared with the machine learning approach (i.e., random forest). PM concentration was estimated during spring season (from March to May) in 2015 that typically shows high concentration of PM. The randomly selected 80% of data were used for model calibration and the remaining 20% were used for validation. The developed models were further tested for prediction of PM

  15. Improved MODIS Dark Target aerosol optical depth algorithm over land: angular effect correction

    Science.gov (United States)

    Wu, Yerong; de Graaf, Martin; Menenti, Massimo

    2016-11-01

    Aerosol optical depth (AOD) product retrieved from MODerate Resolution Imaging Spectroradiometer (MODIS) measurements has greatly benefited scientific research in climate change and air quality due to its high quality and large coverage over the globe. However, the current product (e.g., Collection 6) over land needs to be further improved. The is because AOD retrieval still suffers large uncertainty from the surface reflectance (e.g., anisotropic reflection) although the impacts of the surface reflectance have been largely reduced using the Dark Target (DT) algorithm. It has been shown that the AOD retrieval over dark surface can be improved by considering surface bidirectional distribution reflectance function (BRDF) effects in previous study. However, the relationship of the surface reflectance between visible and shortwave infrared band that applied in the previous study can lead to an angular dependence of the AOD retrieval. This has at least two reasons. The relationship based on the assumption of isotropic reflection or Lambertian surface is not suitable for the surface bidirectional reflectance factor (BRF). However, although the relationship varies with the surface cover type by considering the vegetation index NDVISWIR, this index itself has a directional effect and affects the estimation of the surface reflection, and it can lead to some errors in the AOD retrieval. To improve this situation, we derived a new relationship for the spectral surface BRF in this study, using 3 years of data from AERONET-based Surface Reflectance Validation Network (ASRVN). To test the performance of the new algorithm, two case studies were used: 2 years of data from North America and 4 months of data from the global land. The results show that the angular effects of the AOD retrieval are largely reduced in most cases, including fewer occurrences of negative retrievals. Particularly, for the global land case, the AOD retrieval was improved by the new algorithm compared to the

  16. Retrieval of aerosol optical depth over land surfaces from AVHRR data

    Directory of Open Access Journals (Sweden)

    L. Mei

    2013-02-01

    Full Text Available The Advanced Very High Resolution Radiometer (AVHRR radiance data provide a global, long-term, consistent time series having high spectral and spatial resolution and thus being valuable for the retrieval of surface spectral reflectance, albedo and surface temperature. Long term time series of such data products are necessary for studies addressing climate change, sea ice distribution and movement, and ice sheet coastal configuration. These data have also been used to retrieve aerosol properties over ocean and land surfaces. However, the retrieval of aerosol over land and land surface albedo are challenging because of the information content of the measurement is limited and the inversion of these data products being ill defined. Solving the radiative transfer equations requires additional information and knowledge to reduce the number of unknowns. In this contribution we utilise an empirical linear relationship between the surface reflectances in the AVHRR channels at wavelengths of 3.75 μm and 2.1 μm, which has been identified in Moderate Resolution Imaging Spectroradiometer (MODIS data. Next, following the MODIS dark target approach, the surface reflectance at 0.64 μm was obtained. The comparison of the estimated surface reflectance at 0.64 μm with MODIS reflectance products (MOD09 shows a strong correlation (R = 0.7835. Once this was established, the MODIS "dark-target" aerosol retrieval method was adapted to Advanced Very High Resolution Radiometer (AVHRR data. A simplified Look-Up Table (LUT method, adopted from Bremen AErosol Retrieval (BAER algorithm, was used in the retrieval. The Aerosol Optical Depth (AOD values retrieved from AVHRR with this method compare favourably with ground-based measurements, with a correlation coefficient R = 0.861 and Root Mean Square Error (RMSE = 0.17. This method can be easily applied to other satellite instruments which do not have a 2.1 μm channel, such as those currently planned to

  17. Prediction of Aerosol Optical Depth in West Asia: Machine Learning Methods versus Numerical Models

    Science.gov (United States)

    Omid Nabavi, Seyed; Haimberger, Leopold; Abbasi, Reyhaneh; Samimi, Cyrus

    2017-04-01

    Dust-prone areas of West Asia are releasing increasingly large amounts of dust particles during warm months. Because of the lack of ground-based observations in the region, this phenomenon is mainly monitored through remotely sensed aerosol products. The recent development of mesoscale Numerical Models (NMs) has offered an unprecedented opportunity to predict dust emission, and, subsequently Aerosol Optical Depth (AOD), at finer spatial and temporal resolutions. Nevertheless, the significant uncertainties in input data and simulations of dust activation and transport limit the performance of numerical models in dust prediction. The presented study aims to evaluate if machine-learning algorithms (MLAs), which require much less computational expense, can yield the same or even better performance than NMs. Deep blue (DB) AOD, which is observed by satellites but also predicted by MLAs and NMs, is used for validation. We concentrate our evaluations on the over dry Iraq plains, known as the main origin of recently intensified dust storms in West Asia. Here we examine the performance of four MLAs including Linear regression Model (LM), Support Vector Machine (SVM), Artificial Neural Network (ANN), Multivariate Adaptive Regression Splines (MARS). The Weather Research and Forecasting model coupled to Chemistry (WRF-Chem) and the Dust REgional Atmosphere Model (DREAM) are included as NMs. The MACC aerosol re-analysis of European Centre for Medium-range Weather Forecast (ECMWF) is also included, although it has assimilated satellite-based AOD data. Using the Recursive Feature Elimination (RFE) method, nine environmental features including soil moisture and temperature, NDVI, dust source function, albedo, dust uplift potential, vertical velocity, precipitation and 9-month SPEI drought index are selected for dust (AOD) modeling by MLAs. During the feature selection process, we noticed that NDVI and SPEI are of the highest importance in MLAs predictions. The data set was divided

  18. Influence of observed diurnal cycles of aerosol optical depth on aerosol direct radiative effect

    Directory of Open Access Journals (Sweden)

    A. Arola

    2013-08-01

    Full Text Available The diurnal variability of aerosol optical depth (AOD can be significant, depending on location and dominant aerosol type. However, these diurnal cycles have rarely been taken into account in measurement-based estimates of aerosol direct radiative forcing (ADRF or aerosol direct radiative effect (ADRE. The objective of our study was to estimate the influence of diurnal aerosol variability at the top of the atmosphere ADRE estimates. By including all the possible AERONET sites, we wanted to assess the influence on global ADRE estimates. While focusing also in more detail on some selected sites of strongest impact, our goal was to also see the possible impact regionally. We calculated ADRE with different assumptions about the daily AOD variability: taking the observed daily AOD cycle into account and assuming diurnally constant AOD. Moreover, we estimated the corresponding differences in ADREs, if the single AOD value for the daily mean was taken from the the Moderate Resolution Imaging Spectroradiometer (MODIS Terra or Aqua overpass times, instead of accounting for the true observed daily variability. The mean impact of diurnal AOD variability on 24 h ADRE estimates, averaged over all AERONET sites, was rather small and it was relatively small even for the cases when AOD was chosen to correspond to the Terra or Aqua overpass time. This was true on average over all AERONET sites, while clearly there can be much stronger impact in individual sites. Examples of some selected sites demonstrated that the strongest observed AOD variability (the strongest morning afternoon contrast does not typically result in a significant impact on 24 h ADRE. In those cases, the morning and afternoon AOD patterns are opposite and thus the impact on 24 h ADRE, when integrated over all solar zenith angles, is reduced. The most significant effect on daily ADRE was induced by AOD cycles with either maximum or minimum AOD close to local noon. In these cases, the impact on

  19. Partitioning aerosol optical depth between the boundary layer and the free troposphere

    Science.gov (United States)

    Bourgeois, Quentin; Ekman, Annica; Krejci, Radovan; Devasthale, Abhay; Renard, Jean-Baptiste

    2017-04-01

    Aerosols are short-lived (about a week) compounds in the atmosphere due to the efficient removal by dry and wet deposition in the boundary layer (BL) where a majority of the emission sources are located. As a consequence, most of the aerosol mass should be found in the BL and the aerosol optical depth (AOD) integrated over the atmospheric column should be dominated by the BL contribution. As a consequence, BL aerosols would most likely have the largest climate effect. However, aerosols advected to the free troposphere (FT) have a much longer residence time (typically a few weeks) than those in the BL, potentially inducing a more long-term effect on climate. Light-absorbing aerosols may in addition have an enhanced absorption, and thereby climate warming effect, if they are located above low-level reflective clouds. Light-absorbing aerosols above clouds may also modify below cloud formation and transformation. In this study, the global AOD has been retrieved using satellite observations from CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) over a nine-year period (2007-2015) and partitioned between the BL and FT using BL heights obtained from the ERA-Interim re-analysis data. The results show that the vertical distribution of AOD does not follow the diurnal cycle of the BL but remains similar between day and night highlighting the role of a residual layer during night. The BL and FT contribute 71% and 29%, respectively, to the global AOD during daytime. The FT AOD contribution is larger in the tropics than at mid-latitudes which indicates that convective transport largely controls the vertical profile of aerosols, and the FT AOD contribution over oceans is governed by neighboring continents. According to the CALIOP aerosol classification, dust and smoke particles are the main aerosol types transported into the FT. Overall, the study shows that the fraction of AOD in the FT - and thus potentially located above low-level clouds - is substantial and should

  20. Influence of Observed Diurnal Cycles of Aerosol Optical Depth on Aerosol Direct Radiative Effect

    Science.gov (United States)

    Arola, A.; Eck, T. F.; Huttunen, J.; Lehtinen, K. E. J.; Lindfors, A. V.; Myhre, G.; Smirinov, A.; Tripathi, S. N.; Yu, H.

    2013-01-01

    The diurnal variability of aerosol optical depth (AOD) can be significant, depending on location and dominant aerosol type. However, these diurnal cycles have rarely been taken into account in measurement-based estimates of aerosol direct radiative forcing (ADRF) or aerosol direct radiative effect (ADRE). The objective of our study was to estimate the influence of diurnal aerosol variability at the top of the atmosphere ADRE estimates. By including all the possible AERONET sites, we wanted to assess the influence on global ADRE estimates. While focusing also in more detail on some selected sites of strongest impact, our goal was to also see the possible impact regionally.We calculated ADRE with different assumptions about the daily AOD variability: taking the observed daily AOD cycle into account and assuming diurnally constant AOD. Moreover, we estimated the corresponding differences in ADREs, if the single AOD value for the daily mean was taken from the the Moderate Resolution Imaging Spectroradiometer (MODIS) Terra or Aqua overpass times, instead of accounting for the true observed daily variability. The mean impact of diurnal AOD variability on 24 h ADRE estimates, averaged over all AERONET sites, was rather small and it was relatively small even for the cases when AOD was chosen to correspond to the Terra or Aqua overpass time. This was true on average over all AERONET sites, while clearly there can be much stronger impact in individual sites. Examples of some selected sites demonstrated that the strongest observed AOD variability (the strongest morning afternoon contrast) does not typically result in a significant impact on 24 h ADRE. In those cases, the morning and afternoon AOD patterns are opposite and thus the impact on 24 h ADRE, when integrated over all solar zenith angles, is reduced. The most significant effect on daily ADRE was induced by AOD cycles with either maximum or minimum AOD close to local noon. In these cases, the impact on 24 h ADRE was

  1. Ultra-high and persistent optical depths of caesium in Kagom\\'e-type hollow-core photonic crystal fibres

    CERN Document Server

    Kaczmarek, Krzysztof T; Sprague, Michael R; Kolthammer, W Steven; Feizpour, Amir; Ledingham, Patrick M; Brecht, Benjamin; Poem, Eilon; Abdolvand, Amir; Russell, Philip St J; Walmsley, Ian A; Nunn, Joshua

    2015-01-01

    Alkali-filled hollow-core fibres are a promising medium for investigating light-matter interactions, especially at the single-photon level, due to the tight confinement of light and high optical depths achievable by light-induced atomic desorption. However, until now these large alkali vapour densities could only be generated for seconds at most once per day, severely limiting the practicality of the technology. Here we report the generation of highest observed transient ($>10^5$ for minutes) and highest observed persistent (>2000 for hours) optical depths of alkali vapours in hollow-core fibres to date, using a caesium-filled Kagom\\'e-type hollow-core photonic crystal fibre. Our results pave the way to light-matter interaction experiments in confined geometries requiring long operation times and large atomic number densities, such as single-photon-level light-matter interaction experiments and fundamental investigations of hot dense atomic gases.

  2. Statistics Analysis of the Uncertainties in Cloud Optical Depth Retrievals Caused by Three-Dimensional Radiative Effects

    Science.gov (United States)

    Varnai, Tamas; Marshak, Alexander

    2000-01-01

    This paper presents a simple approach to estimate the uncertainties that arise in satellite retrievals of cloud optical depth when the retrievals use one-dimensional radiative transfer theory for heterogeneous clouds that have variations in all three dimensions. For the first time, preliminary error bounds are set to estimate the uncertainty of cloud optical depth retrievals. These estimates can help us better understand the nature of uncertainties that three-dimensional effects can introduce into retrievals of this important product of the MODIS instrument. The probability distribution of resulting retrieval errors is examined through theoretical simulations of shortwave cloud reflection for a wide variety of cloud fields. The results are used to illustrate how retrieval uncertainties change with observable and known parameters, such as solar elevation or cloud brightness. Furthermore, the results indicate that a tendency observed in an earlier study, clouds appearing thicker for oblique sun, is indeed caused by three-dimensional radiative effects.

  3. Depth-dependent global properties of a sunspot observed by Hinode using the Solar Optical Telescope/Spectropolarimeter

    Science.gov (United States)

    Tiwari, Sanjiv K.; van Noort, Michiel; Solanki, Sami K.; Lagg, Andreas

    2015-11-01

    Context. For the past two decades, the three-dimensional structure of sunspots has been studied extensively. A recent improvement in the Stokes inversion technique prompts us to revisit the depth-dependent properties of sunspots. Aims: In the present work, we aim to investigate the global depth-dependent thermal, velocity, and magnetic properties of a sunspot, as well as the interconnection between various local properties. Methods: We analysed high-quality Stokes profiles of the disk-centred, regular, leading sunspot of NOAA AR 10933, acquired by the Solar Optical Telescope/Spectropolarimeter (SOT/SP) on board the Hinode spacecraft. To obtain depth-dependent stratification of the physical parameters, we used the recently developed, spatially coupled version of the SPINOR inversion code. Results: First, we study the azimuthally averaged physical parameters of the sunspot. We find that the vertical temperature gradient in the lower- to mid-photosphere is at its weakest in the umbra, while it is considerably stronger in the penumbra, and stronger still in the spot's surroundings. The azimuthally averaged field becomes more horizontal with radial distance from the centre of the spot, but more vertical with height. At continuum optical depth unity, the line-of-sight velocity shows an average upflow of ~300 ms-1 in the inner penumbra and an average downflow of ~1300 ms-1 in the outer penumbra. The downflow continues outside the visible penumbral boundary. The sunspot shows, at most, a moderate negative twist of qualitative similarity to that of a standard penumbral filament and its surrounding spines. Conclusions: The large-scale variation in the physical parameters of a sunspot at various optical depths is presented. Our results suggest that the spines in the penumbra are basically the outward extension of the umbra. The spines and the penumbral filaments, together, are the basic elements that form a sunspot penumbra.

  4. Fine Particulate Matter Predictions Using High Resolution Aerosol Optical Depth (AOD) Retrievals

    Science.gov (United States)

    Chudnovsky, Alexandra A.; Koutrakis, Petros; Kloog, Itai; Melly, Steven; Nordio, Francesco; Lyapustin, Alexei; Wang, Jujie; Schwartz, Joel

    2014-01-01

    To date, spatial-temporal patterns of particulate matter (PM) within urban areas have primarily been examined using models. On the other hand, satellites extend spatial coverage but their spatial resolution is too coarse. In order to address this issue, here we report on spatial variability in PM levels derived from high 1 km resolution AOD product of Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm developed for MODIS satellite. We apply day-specific calibrations of AOD data to predict PM(sub 2.5) concentrations within the New England area of the United States. To improve the accuracy of our model, land use and meteorological variables were incorporated. We used inverse probability weighting (IPW) to account for nonrandom missingness of AOD and nested regions within days to capture spatial variation. With this approach we can control for the inherent day-to-day variability in the AOD-PM(sub 2.5) relationship, which depends on time-varying parameters such as particle optical properties, vertical and diurnal concentration profiles and ground surface reflectance among others. Out-of-sample "ten-fold" cross-validation was used to quantify the accuracy of model predictions. Our results show that the model-predicted PM(sub 2.5) mass concentrations are highly correlated with the actual observations, with out-of- sample R(sub 2) of 0.89. Furthermore, our study shows that the model captures the pollution levels along highways and many urban locations thereby extending our ability to investigate the spatial patterns of urban air quality, such as examining exposures in areas with high traffic. Our results also show high accuracy within the cities of Boston and New Haven thereby indicating that MAIAC data can be used to examine intra-urban exposure contrasts in PM(sub 2.5) levels.

  5. Retrieval of Cirrus Cloud Optical Depth under Day and Night Conditions from MODIS Collection 6 Cloud Property Data

    Directory of Open Access Journals (Sweden)

    Andrew K. Heidinger

    2015-06-01

    Full Text Available This paper presents a technique to generate cirrus optical depth and particle effective size estimates from the cloud emissivities at 8.5, 11 and 12 μm contained in the Collection-6 (C6 MYD06 cloud product. This technique employs the latest scattering models and scattering radiative transfer approximations to estimate cloud optical depth and particle effective size using efficient analytical formulae. Two scattering models are tested. The first is the same scattering model as that used in the C6 MYD06 solar reflectance products. The second model is an empirical model derived from radiometric consistency. Both models are shown to generate optical depths that compare well to those from constrained CALIPSO retrievals and MYD06. In terms of effective radius retrievals, the results from the radiometric empirical model agree more closely with MYD06 than those from the C6 model. This analysis is applied to AQUA/MODIS data collocated with CALIPSO/CALIOP during January 2010.

  6. An improved algorithm for the determination of aerosol optical depth in the ultraviolet spectral range from Brewer spectrophotometer observations

    Science.gov (United States)

    Sellitto, P.; di Sarra, A.; Siani, A. M.

    2006-10-01

    Methods to derive aerosol optical depth in the UV spectral range from ground-based remote-sensing stations equipped with Brewer spectrophotometers have been recently developed. In this study a modified Langley plot method has been implemented to retrieve aerosol optical depth from direct sun Brewer measurements. The method uses measurements over an extended range of atmospheric airmasses obtained with two different neutral density filters, and accounts for short-term variations of total ozone, derived from the same direct sun observations. The improved algorithm has been applied to data collected with a Brewer mark IV, operational in Rome, Italy, and with a Brewer mark III, operational in Lampedusa, Italy, in the Mediterranean. The efficiency of the improved algorithm has been tested comparing the number of determinations of the extraterrestrial constant against those obtained with a standard Langley plot procedure. The improved method produces a larger number of reliable Langley plots, allowing for a better statistical characterization of the extraterrestrial constant and a better study of its temporal variability. The values of aerosol optical depth calculated in Rome and Lampedusa compare well with simultaneous determinations in the 416-440 nm interval derived from MFRSR and CIMEL measurements.

  7. Annual cycle of global distributions of aerosol optical depth from integration of MODIS retrievals and GOCART model simulations

    Science.gov (United States)

    Yu, Hongbin; Dickinson, R. E.; Chin, M.; Kaufman, Y. J.; Holben, B. N.; Geogdzhayev, I. V.; Mishchenko, M. I.

    2003-02-01

    The Moderate-Resolution Imaging Spectroradiometer (MODIS) instrument onboard the Earth Observing System (EOS) satellites provides an unprecedented opportunity to study aerosols from space with high accuracy and on a nearly global scale. However, difficulty with highly reflective arid and snow-covered lands introduces significant gaps in global or regional coverage that must be filled by some other means. This study provides a complete global coverage of an annual cycle of aerosol optical depth by combining the MODIS retrievals and Georgia Tech/Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) simulations weighted with the uncertainties in each product. The assimilated aerosol optical depths over land are better correlated with the ground-based Aerosol Robotic Network (AERONET) measurements than are either the MODIS retrievals or the GOCART simulations alone. The gaps in the MODIS retrievals are filled with values that are generally consistent with the AERONET aerosol climatology. The assimilated aerosol optical depths are in good agreement with the Advanced Very High Resolution Radiometer (AVHRR) aerosol climatology over the Atlantic and North Indian Oceans. In spring, large discrepancies between the MODIS retrievals in 2001 and the AVHRR climatology over the North Pacific are likely a result of extremely active transcontinental transport of Asian dust/pollutants to North America in the year 2001. Large model-satellite differences in the South Pacific and South Indian Oceans may be attributable to missing or underestimated sources in the model and/or cloud, whitecap, and glint contamination in satellite retrievals.

  8. Aerosol optical depth over central north Asia based on MODIS-Aqua data

    Science.gov (United States)

    Avgousta Foutsi, Athina; Korras Carraca, Marios Bruno; Matsoukas, Christos; Biskos, George

    2016-04-01

    Atmospheric aerosols, both natural and anthropogenic, can affect the regional and global climate through their direct, indirect, and semi-direct effects on the radiative energy budget of the Earth-atmosphere system. To quantify these effects it is important to determine the aerosol load, and an effective way to do that is by measuring the aerosol optical depth (AOD). The central Asia region (mainly the Caspian and Aral sea basins), the arid and semi-arid regions of Western China as well as Siberia are of great interest due to the significant natural sources of mineral aerosols originating from local deserts and biomass burning from wildfires in boreal forests. What is of particular interest in the region is the phenomenal shrinking and desertification of the Aral Sea that drives an intense salt and dust transport from the exposed sea-bed to the surrounding regions with important implications in regional air quality. Anthropogenic particles are also observed due to fossil-fuel combustion occurring mainly at oil refineries in the Caspian Sea basin. Here we investigate the spatial and temporal variability of the AOD at 550 nm over central Asia, Siberia and western China, in the region located between 35° N - 65° N and 45° E - 110° E. For our analysis we use Level-3 daily MODIS - Aqua Dark Target - Deep Blue combined product, from the latest collection (006), available in a 1°×1° resolution (ca. 100 km × 100 km) over the period 2002-2014. Our results indicate a significant spatial variability of the aerosol load over the study region. The highest AODs are observed over the Aral Sea year-round, with extreme values reaching 2.1 during July. In the rest of our study region a clear seasonal cycle with highest AOD values (up to 1.2 over the Taklamakan Desert) during spring and summer is observed. The arid parts of central north Asia are characterized by larger aerosol loads during spring, lower but still high AOD in summer and much lower values in autumn and spring

  9. Micropulse lidar-derived aerosol optical depth climatology at ARM sites worldwide

    Science.gov (United States)

    Kafle, D. N.; Coulter, R. L.

    2013-07-01

    This paper focuses on climatology of the vertical distribution of aerosol optical depth (AOD (z)) from micropulse lidar (MPL) observations for climatically different locations worldwide. For this, a large data set obtained by MPL systems operating at 532 nm during the 4 year period 2007-2010 was used to derive vertical profiles of AOD (z) by combining the corresponding AOD data as an input from an independent measurement using nearly colocated multifilter rotating shadowband radiometer (MFRSR) systems at five different U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Program sites—three permanent sites (SGP in north-central Oklahoma, at 36.6°N, 97.5°W, 320 m; TWP-Darwin in the tropical western Pacific, at 12.4°S, 130.9°E, 30 m; and NSA at Barrow on the North Slope of Alaska, at 71.3°N, 156.6°W, 8 m) and two mobile facility sites (GRW at Graciosa Island in the Azores, at 39°N, 28°W, 15 m; and FKB in the Black Forest of Germany, at 48.5°N, 8.4°E, 511 m). Therefore, amount of data used in this study is constrained by the availability of the MFRSR data. The MPL raw data were averaged for 30 s in time and 30 m in altitude. The diurnally averaged AOD (z) profiles from 4 years were combined to obtain a multiyear vertical profile of AOD (z) climatology at various ARM sites, including diurnal, day-to-day, and seasonal variabilities. Most aerosols were found to be confined to 0-2 km (approximately the planetary boundary layer region) at all sites; however, all sites exhibited measurable aerosols well above the mixed layer, with different height maxima. The entire data set demonstrates large day-to-day variability at all sites. However, there is no significant diurnal variation in AOD (z) at all sites. Significant interannual variability was observed at the SGP site. Clear seasonal variations in AOD (z) profiles exist for all five sites, but seasonal behavior was distinct. Moreover, the different seasonal variability for the lower level (0 to ~2

  10. Evaluating Nighttime CALIOP 0.532 micron Aerosol Optical Depth and Extinction Coefficient Retrievals

    Science.gov (United States)

    Campbell, J. R.; Tackett, J. L.; Reid, J. S.; Zhang, J.; Curtis, C. A.; Hyer, E. J.; Sessions, W. R.; Westphal, D. L.; Prospero, J. M.; Welton, E. J.; Omar, A. H.; Vaughan, M. A.; Winker, D. M.

    2012-01-01

    NASA Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) Version 3.01 5-km nighttime 0.532 micron aerosol optical depth (AOD) datasets from 2007 are screened, averaged and evaluated at 1 deg X 1 deg resolution versus corresponding/co-incident 0.550 micron AOD derived using the US Navy Aerosol Analysis and Prediction System (NAAPS), featuring two-dimensional variational assimilation of quality-assured NASA Moderate Resolution Imaging Spectroradiometer (MODIS) and Multi-angle Imaging Spectroradiometer (MISR) AOD. In the absence of sunlight, since passive radiometric AOD retrievals rely overwhelmingly on scattered radiances, the model represents one of the few practical global estimates available from which to attempt such a validation. Daytime comparisons, though, provide useful context. Regional-mean CALIOP vertical profiles of night/day 0.532 micron extinction coefficient are compared with 0.523/0.532 micron ground-based lidar measurements to investigate representativeness and diurnal variability. In this analysis, mean nighttime CALIOP AOD are mostly lower than daytime (0.121 vs. 0.126 for all aggregated data points, and 0.099 vs. 0.102 when averaged globally per normalised 1 deg. X 1 deg. bin), though the relationship is reversed over land and coastal regions when the data are averaged per normalised bin (0.134/0.108 vs. 0140/0.112, respectively). Offsets assessed within single bins alone approach +/- 20 %. CALIOP AOD, both day and night, are higher than NAAPS over land (0.137 vs. 0.124) and equal over water (0.082 vs. 0.083) when averaged globally per normalised bin. However, for all data points inclusive, NAAPS exceeds CALIOP over land, coast and ocean, both day and night. Again, differences assessed within single bins approach 50% in extreme cases. Correlation between CALIOP and NAAPS AOD is comparable during both day and night. Higher correlation is found nearest the equator, both as a function of sample size and relative signal magnitudes inherent at

  11. The regime of aerosol optical depth over Central Asia based on MODIS Aqua Deep Blue data

    Science.gov (United States)

    Floutsi, Athina; KorrasCarraca, Marios; Matsoukas, Christos; Biskos, George

    2015-04-01

    Atmospheric aerosols, both natural and anthropogenic, can affect the regional and global climate through their direct, indirect, and semi-direct effects on the radiative energy budget of the Earth-atmosphere system. To quantify these effects it is therefore important to determine the aerosol load, and an effective way to do that is by measuring the aerosol optical depth (AOD). In this study we investigate the spatial and temporal variability of the AOD over the climatically sensitive region of Central Asia (36° N - 50° N, 46° E - 75° E), which has significant sources of both natural and anthropogenic particles. The primary source of anthropogenic particles is fossil fuel combustion occurring mainly at oil refineries in the Caspian Sea basin. Natural particles originate mostly from the two deserts in the region (namely Kara-Kum and Kyzyl-Kum), where persistent dust activity is observed. Another source is the Aral Sea region, which due to its phenomenal desertification also drives an intense salt and dust transport from the exposed sea-bed to the surrounding regions. This transport is of particular interest because of health-hazardous materials contained in the Aral Sea sea-bed. For our analysis we use Level-3 daily MODIS - Aqua Dark Target - Deep Blue combined product, from the latest MODIS collection (006), available in 1° x 1° resolution (about 100 km x 100 km) over the period 2002-2014.Our first results indicate a significant spatial variability of the aerosol load over the study region. The data also show a clear seasonal cycle, with large aerosol load being associated with strong dust activity during spring and summer (AOD up to 0.5), and low during autumn and winter (AOD up to 0.4). In spring and summer significant aerosol load is observed in the Garabogazköl basin, Northeast and South-southeast Caspian Sea (offshore North Iran and Azerbaijan), as well as southwest of the Aral Sea. In the later region, the high AOD values can be explained by export of

  12. Validation of aerosol optical depth uncertainties within the ESA Climate Change Initiative

    Science.gov (United States)

    Stebel, Kerstin; Povey, Adam; Popp, Thomas; Capelle, Virginie; Clarisse, Lieven; Heckel, Andreas; Kinne, Stefan; Klueser, Lars; Kolmonen, Pekka; de Leeuw, Gerrit; North, Peter R. J.; Pinnock, Simon; Sogacheva, Larisa; Thomas, Gareth; Vandenbussche, Sophie

    2017-04-01

    Uncertainty is a vital component of any climate data record as it provides the context with which to understand the quality of the data and compare it to other measurements. Therefore, pixel-level uncertainties are provided for all aerosol products that have been developed in the framework of the Aerosol_cci project within ESA's Climate Change Initiative (CCI). Validation of these estimated uncertainties is necessary to demonstrate that they provide a useful representation of the distribution of error. We propose a technique for the statistical validation of AOD (aerosol optical depth) uncertainty by comparison to high-quality ground-based observations and present results for ATSR (Along Track Scanning Radiometer) and IASI (Infrared Atmospheric Sounding Interferometer) data records. AOD at 0.55 µm and its uncertainty was calculated with three AOD retrieval algorithms using data from the ATSR instruments (ATSR-2 (1995-2002) and AATSR (2002-2012)). Pixel-level uncertainties were calculated through error propagation (ADV/ASV, ORAC algorithms) or parameterization of the error's dependence on the geophysical retrieval conditions (SU algorithm). Level 2 data are given as super-pixels of 10 km x 10 km. As validation data, we use direct-sun observations of AOD from the AERONET (AErosol RObotic NETwork) and MAN (Maritime Aerosol Network) sun-photometer networks, which are substantially more accurate than satellite retrievals. Neglecting the uncertainty in AERONET observations and possible issues with their ability to represent a satellite pixel area, the error in the retrieval can be approximated by the difference between the satellite and AERONET retrievals (herein referred to as "error"). To evaluate how well the pixel-level uncertainty represents the observed distribution of error, we look at the distribution of the ratio D between the "error" and the ATSR uncertainty. If uncertainties are well represented, D should be normally distributed and 68.3% of values should

  13. Optical depth sectioning in self-mixing lasers for biomedical applications

    OpenAIRE

    Cabedo Bru, Josep

    2015-01-01

    Illumination in scattering media provides a general means to provide optical diagnosis in a noninvasive, painless and low cost approach, which has pushed forward the interest of the field both in biomedical and industrial applications. Several biophotonics techniques are based on the use of the therapeutic window of skin, where diffusion of light is dominant and the classical geometrical optics approach gets lost, with only radiometric methods being valid in practice. A comparable analysis is...

  14. Quality parameters analysis of optical imaging systems with enhanced focal depth using the Wigner distribution function

    Science.gov (United States)

    Zalvidea; Colautti; Sicre

    2000-05-01

    An analysis of the Strehl ratio and the optical transfer function as imaging quality parameters of optical elements with enhanced focal length is carried out by employing the Wigner distribution function. To this end, we use four different pupil functions: a full circular aperture, a hyper-Gaussian aperture, a quartic phase plate, and a logarithmic phase mask. A comparison is performed between the quality parameters and test images formed by these pupil functions at different defocus distances.

  15. A pinhole gamma camera with optical depth-of-interaction elimination

    NARCIS (Netherlands)

    Korevaar, M.A.N.; Heemskerk, J.W.T.; Beekman, F.J.

    2009-01-01

    The performance of pinhole single photon emission computed tomography (SPECT) depends on the spatial resolution of the gamma-ray detectors used. Pinhole cameras suffer from strong resolution loss due to the varying depth-of-interaction (DOI) of gamma quanta that enter the detector material at an ang

  16. Aerosol spectral optical depths and size characteristics at a coastal industriallocation in India - effect of synoptic and mesoscale weather

    Directory of Open Access Journals (Sweden)

    K. Niranjan

    2004-06-01

    Full Text Available The aerosol spectral optical depths at ten discrete channels in the visible and near IR bands, obtained from a ground-based passive multi-wavelength solar radiometer at a coastal industrial location, Visakhapatnam, on the east coast of India, are used to study the response of the aerosol optical properties and size distributions to the changes in atmospheric humidity, wind speed and direction. It is observed that during high humidity conditions, the spectral optical depths show about 30% higher growth factors, and the size distributions show the generation of a typical new mode around 0.4 microns. The surface wind speed and direction also indicate the formation of new particles when the humid marine air mass interacts with the industrial air mass. This is interpreted in terms of new particle formation and subsequent particle growth by condensation and self-coagulation. The results obtained on the surface-size segregated aerosol mass distribution from a co-located Quartz Crystal Microbalance during different humidity conditions also show a large mass increase in the sub-micron size range with an increase in atmospheric humidity, indicating new particle formation at the sub-micron size range.

  17. Nocturnal aerosol optical depth measurements with a small-aperture automated photometer using the moon as a light source

    Science.gov (United States)

    Berkoff, T.A.; Sorokin, M.; Stone, T.; Eck, T.F.; Hoff, R.; Welton, E.; Holben, B.

    2011-01-01

    A method is described that enables the use of lunar irradiance to obtain nighttime aerosol optical depth (AOD) measurements using a small-aperture photometer. In this approach, the U.S. Geological Survey lunar calibration system was utilized to provide high-precision lunar exoatmospheric spectral irradiance predictions for a ground-based sensor location, and when combined with ground measurement viewing geometry, provided the column optical transmittance for retrievals of AOD. Automated multiwavelength lunar measurements were obtained using an unmodified Cimel-318 sunphotometer sensor to assess existing capabilities and enhancements needed for day/night operation in NASA's Aerosol Robotic Network (AERONET). Results show that even existing photometers can provide the ability for retrievals of aerosol optical depths at night near full moon. With an additional photodetector signal-to-noise improvement of 10-100, routine use over the bright half of the lunar phase and a much wider range of wavelengths and conditions can be achieved. Although the lunar cycle is expected to limit the frequency of observations to 30%-40% compared to solar measurements, nevertheless this is an attractive extension of AERONET capabilities. ?? 2011 American Meteorological Society.

  18. The "RED Versa NIR" Plane to Retrieve Broken-Cloud Optical Depth from Ground-Based Measurements"

    Science.gov (United States)

    Marshak, A.; Knyazikhin, Y.; Evans, K.; Wiscombe, W.

    2003-01-01

    A new method for retrieving cloud optical depth from ground-based measurements of zenith radiance in the RED and near infrared (MR) spectral regions is introduced. Because zenith radiance does not have a one-to-one relationship with optical depth, it is absolutely impossible to use a monochromatic retrieval. On the other side, algebraic combinations of spectral radiances such as NDCI while largely removing nouniquiness and the radiative effects of cloud inhomogeneity, can result in poor retrievals due to its insensitivity to cloud fraction. Instead, both RED and NIR radiances as points on the 'RED vs. NIR' plane are proposed to be used for retrieval. The proposed retrieval method is applied to Cimel measurements at the Atmospheric Radiation Measurements (ARM) site in Oklahoma. Cimel, a multi-channel sunphotometer, is a part of AERONET - a ground-based network for monitoring aerosol optical properties. The results of retrieval are compared with the ones from Microwave Radiometer (MWR) and Multi-Filter Rotating Shadowband Radiometers (MFRSR) located next to Cimel at the ARM site. In addition, the performance of the retrieval method is assessed using a fractal model of cloud inhomogeneity and broken cloudiness. The preliminary results look very promising both theoretically and from measurements.

  19. Nocturnal Aerosol Optical Depth Measurements with a Small-Aperture Automated Photometer Using the Moon as a Light Source

    Science.gov (United States)

    Berkoff, Timothy A.; Sorokin, Mikail; Stone, Tom; Eck, Thomas F.; Hoff, Raymond; Welton, Ellsworth; Holben, Brent

    2011-01-01

    A method is described that enables the use of lunar irradiance to obtain nighttime aerosol optical depth (AOD) measurements using a small-aperture photometer. In this approach, the U.S. Geological Survey lunar calibration system was utilized to provide high-precision lunar exoatmospheric spectral irradiance predictions for a ground-based sensor location, and when combined with ground measurement viewing geometry, provided the column optical transmittance for retrievals of AOD. Automated multiwavelength lunar measurements were obtained using an unmodified Cimel-318 sunphotometer sensor to assess existing capabilities and enhancements needed for day/night operation in NASA s Aerosol Robotic Network (AERONET). Results show that even existing photometers can provide the ability for retrievals of aerosol optical depths at night near full moon. With an additional photodetector signal-to-noise improvement of 10-100, routine use over the bright half of the lunar phase and a much wider range of wavelengths and conditions can be achieved. Although the lunar cycle is expected to limit the frequency of observations to 30%-40% compared to solar measurements, nevertheless this is an attractive extension of AERONET capabilities.

  20. Nocturnal Aerosol Optical Depth Measurements with a Small-Aperture Automated Photometer Using the Moon as a Light Source

    Science.gov (United States)

    Berkoff, Timothy A.; Sorokin, Mikail; Stone, Tom; Eck, Thomas F.; Hoff, Raymond; Welton, Ellsworth; Holben, Brent

    2011-01-01

    A method is described that enables the use of lunar irradiance to obtain nighttime aerosol optical depth (AOD) measurements using a small-aperture photometer. In this approach, the U.S. Geological Survey lunar calibration system was utilized to provide high-precision lunar exoatmospheric spectral irradiance predictions for a ground-based sensor location, and when combined with ground measurement viewing geometry, provided the column optical transmittance for retrievals of AOD. Automated multiwavelength lunar measurements were obtained using an unmodified Cimel-318 sunphotometer sensor to assess existing capabilities and enhancements needed for day/night operation in NASA s Aerosol Robotic Network (AERONET). Results show that even existing photometers can provide the ability for retrievals of aerosol optical depths at night near full moon. With an additional photodetector signal-to-noise improvement of 10-100, routine use over the bright half of the lunar phase and a much wider range of wavelengths and conditions can be achieved. Although the lunar cycle is expected to limit the frequency of observations to 30%-40% compared to solar measurements, nevertheless this is an attractive extension of AERONET capabilities.

  1. Relationship between vessel diameter and depth measurements within the limbus using ultra-high resolution optical coherence tomography.

    Science.gov (United States)

    Alabi, Emmanuel; Hutchings, Natalie; Bizheva, Kostadinka; Simpson, Trefford

    2017-06-16

    To establish a relationship between the diameter and depth position of vessels in the superior and inferior corneo-scleral limbus using ultra-high resolution optical coherence tomography (UHR-OCT). Volumetric OCT images of the superior and inferior limbus were acquired from 14 healthy subjects with a research-grade UHR-OCT system. Differences in vessel diameter and depth between superior and inferior limbus were analyzed using repeated measured ANOVA in SPSS and R. The mean (± SD) superior and inferior diameters were 29±18μm and 24±18μm respectively, and the mean (± SD) superior and inferior depths were 177±109μm and 207±132μm respectively. The superior limbal vessels were larger than the inferior ones (RM-ANOVA, p=0.004), and the inferior limbal vessels were deeper than the superior vessels (RM-ANOVA, p=0.041). There was a positive linear association between limbal vessel depth and size within the superior and inferior limbus with Pearson correlation coefficients of 0.803 and 0.754, respectively. This study demonstrated that the UHR-OCT was capable of imaging morphometric characteristics such as the size and depth of vessels in the limbus. The results of this study suggest a difference in the size and depth of vessels across different positions of the limbus, which may be indicative of adaptations to chronic hypoxia caused by the covering of the superior limbus by the upper eyelid. UHR-OCT may be a useful tool to evaluate the effect of contact lenses on the microvascular properties within the limbus. Copyright © 2017 Spanish General Council of Optometry. All rights reserved.

  2. Depth Estimation of Submerged Aquatic Vegetation in Clear Water Streams Using Low-Altitude Optical Remote Sensing

    Directory of Open Access Journals (Sweden)

    Fleur Visser

    2015-09-01

    Full Text Available UAVs and other low-altitude remote sensing platforms are proving very useful tools for remote sensing of river systems. Currently consumer grade cameras are still the most commonly used sensors for this purpose. In particular, progress is being made to obtain river bathymetry from the optical image data collected with such cameras, using the strong attenuation of light in water. No studies have yet applied this method to map submergence depth of aquatic vegetation, which has rather different reflectance characteristics from river bed substrate. This study therefore looked at the possibilities to use the optical image data to map submerged aquatic vegetation (SAV depth in shallow clear water streams. We first applied the Optimal Band Ratio Analysis method (OBRA of Legleiter et al. (2009 to a dataset of spectral signatures from three macrophyte species in a clear water stream. The results showed that for each species the ratio of certain wavelengths were strongly associated with depth. A combined assessment of all species resulted in equally strong associations, indicating that the effect of spectral variation in vegetation is subsidiary to spectral variation due to depth changes. Strongest associations (R2-values ranging from 0.67 to 0.90 for different species were found for combinations including one band in the near infrared (NIR region between 825 and 925 nm and one band in the visible light region. Currently data of both high spatial and spectral resolution is not commonly available to apply the OBRA results directly to image data for SAV depth mapping. Instead a novel, low-cost data acquisition method was used to obtain six-band high spatial resolution image composites using a NIR sensitive DSLR camera. A field dataset of SAV submergence depths was used to develop regression models for the mapping of submergence depth from image pixel values. Band (combinations providing the best performing models (R2-values up to 0.77 corresponded with the

  3. Depth Estimation of Submerged Aquatic Vegetation in Clear Water Streams Using Low-Altitude Optical Remote Sensing.

    Science.gov (United States)

    Visser, Fleur; Buis, Kerst; Verschoren, Veerle; Meire, Patrick

    2015-09-30

    UAVs and other low-altitude remote sensing platforms are proving very useful tools for remote sensing of river systems. Currently consumer grade cameras are still the most commonly used sensors for this purpose. In particular, progress is being made to obtain river bathymetry from the optical image data collected with such cameras, using the strong attenuation of light in water. No studies have yet applied this method to map submergence depth of aquatic vegetation, which has rather different reflectance characteristics from river bed substrate. This study therefore looked at the possibilities to use the optical image data to map submerged aquatic vegetation (SAV) depth in shallow clear water streams. We first applied the Optimal Band Ratio Analysis method (OBRA) of Legleiter et al. (2009) to a dataset of spectral signatures from three macrophyte species in a clear water stream. The results showed that for each species the ratio of certain wavelengths were strongly associated with depth. A combined assessment of all species resulted in equally strong associations, indicating that the effect of spectral variation in vegetation is subsidiary to spectral variation due to depth changes. Strongest associations (R²-values ranging from 0.67 to 0.90 for different species) were found for combinations including one band in the near infrared (NIR) region between 825 and 925 nm and one band in the visible light region. Currently data of both high spatial and spectral resolution is not commonly available to apply the OBRA results directly to image data for SAV depth mapping. Instead a novel, low-cost data acquisition method was used to obtain six-band high spatial resolution image composites using a NIR sensitive DSLR camera. A field dataset of SAV submergence depths was used to develop regression models for the mapping of submergence depth from image pixel values. Band (combinations) providing the best performing models (R²-values up to 0.77) corresponded with the OBRA

  4. Deriving depth-dependent light escape efficiency and optical Swank factor from measured pulse height spectra of scintillators.

    Science.gov (United States)

    Howansky, Adrian; Peng, Boyu; Lubinsky, Anthony R; Zhao, Wei

    2017-03-01

    Pulse height spectroscopy has been used by investigators to deduce the imaging properties of scintillators. Pulse height spectra (PHS) are used to compute the Swank factor, which describes the variation in scintillator light output per x-ray interaction. The spread in PHS measured below the K-edge is related to the optical component of the Swank factor, i.e., variations in light escape efficiency from different depths of x-ray interaction in the scintillator, denoted ε¯(z). Optimizing scintillators for medical imaging applications requires understanding of these optical properties, as they determine tradeoffs between parameters such as x-ray absorption, light yield, and spatial resolution. This work develops a model for PHS acquisition such that the effect of measurement uncertainty can be removed. This method allows ε¯(z) to be quantified on an absolute scale and permits more accurate estimation of the optical Swank factor of scintillators. The pulse height spectroscopy acquisition chain was modeled as a linear system of stochastic gain stages. Analytical expressions were derived for signal and noise propagation through the PHS chain, accounting for deterministic and stochastic aspects of x-ray absorption, scintillation, and light detection with a photomultiplier tube. The derived expressions were used to calculate PHS of thallium-doped cesium iodide (CsI) scintillators using parameters that were measured, calculated, or known from literature. PHS were measured at 25 and 32 keV of CsI samples designed with an optically reflective or absorptive backing, with or without a fiber-optic faceplate (FOP), and with thicknesses ranging from 150-1000 μm. Measured PHS were compared with calculated PHS, then light escape model parameters were varied until measured and modeled results reached agreement. Resulting estimates of ε¯(z) were used to calculate each scintillator's optical Swank factor. For scintillators of the same optical design, only minor differences in

  5. Depth Profile of Optically Recorded Patterns in Light-Sensitive Liquid Crystal Elastomers

    CERN Document Server

    Gregorc, Marko; Domenici, Valentina; Ambrožič, Gabriela; Drevenšek-Olenik, Irena; Fally, Martin; Čopič, Martin

    2011-01-01

    We investigated nonlinear absorption and photobleaching processes in a liquid crystal elastomer (LCE) doped with light-sensitive azobenzene moiety. A conventional one-dimensional holographic grating was recorded in the material with the use of two crossed UV laser beams and the angular dependence of the diffraction efficiency in the vicinity of the Bragg peak was analyzed. These measurements gave information on the depth to which trans to cis isomerisation had progressed into the sample as a function of the UV irradiation time. Using a numerical model that takes into account the propagation of writing beams and rate equations for the local concentration of the absorbing trans conformer, we computed the expected spatial distribution of the trans and cis conformers and the shape of the corresponding Bragg diffraction peak for different irradiation doses. Due to residual absorption of the cis conformers the depth of the recording progresses logarithmically with time and is limited by the thermal relaxation from ...

  6. Influence and compensation of autocorrelation terms in depth-resolved spectroscopic Fourier-domain optical coherence tomography.

    Science.gov (United States)

    Steiner, Patrick; Meier, Christoph; Koch, Volker M

    2010-12-20

    We demonstrate depth-resolved spectral absorption measurements in the wavelength range from 750 to 850 nm using a broadband light source consisting of three spectrally shifted superluminescent light-emitting diode modules and a low-cost spectrometer-based Fourier-domain optical coherence tomography system. We present the theoretical model and experimental verification of interferences between autocorrelation terms and the signal carrying cross-correlation terms, strongly affecting the absorption measurements. A simple background subtraction, minimizing the artifacts caused by the interferences of autocorrelation and cross-correlation terms, is presented.

  7. Evidence for Three-Dimensional Radiative Effects in MODIS Cloud Optical Depths Retrieved at Back Scattering View Angles

    Science.gov (United States)

    Varnai, Tamas; Marshak, Alexander

    2003-01-01

    This study addresses the question whether 1D radiative transfer theory describes well the angular distribution of shortwave cloud reflection. The statistical analysis of a large set of MODIS observations indicates that in oblique backward scattering directions, cloud reflection is stronger than 1D theory would predict. After considering a variety of possible causes, the paper concludes that the most likely reason for the increase lies in 3D radiative interactions. The results' main implication is that cloud optical depths retrieved at back scattering view angles larger than about 50 degrees tend to be overestimated and should be used only with great caution.

  8. Enhanced depth imaging optical coherence tomography of choroidal osteoma with secondary neovascular membranes: report of two cases

    Directory of Open Access Journals (Sweden)

    Patrícia Correa de Mello

    2016-06-01

    Full Text Available ABSTRACT We report enhanced depth imaging optical coherence tomography (EDI-OCT features based on clinical and imaging data from two newly diagnosed cases of choroidal osteoma presenting with recent visual loss secondary to choroidal neovascular membranes. The features described in the two cases, compression of the choriocapillaris and disorganization of the medium and large vessel layers, are consistent with those of previous reports. We noticed a sponge-like pattern previously reported, but it was subtle. Both lesions had multiple intralesional layers and a typical intrinsic transparency with visibility of the sclerochoroidal junction.

  9. Use of satellite-based aerosol optical depth and spatial clustering to predict ambient PM2.5 concentrations

    OpenAIRE

    2012-01-01

    Satellite-based PM2.5 monitoring has the potential to complement ground PM2.5 monitoring networks, especially for regions with sparsely distributed monitors. Satellite remote sensing provides data on aerosol optical depth (AOD), which reflects particle abundance in the atmospheric column. Thus AOD has been used in statistical models to predict ground-level PM2.5 concentrations. However, previous studies have shown that AOD may not be a strong predictor of PM2.5 ground levels. Another shortcom...

  10. Evaluation of optical imaging and spectroscopy approaches for cardiac tissue depth assessment

    Energy Technology Data Exchange (ETDEWEB)

    Lin, B; Matthews, D; Chernomordik, V; Gandjbakhche, A; Lane, S; Demos, S G

    2008-02-13

    NIR light scattering from ex vivo porcine cardiac tissue was investigated to understand how imaging or point measurement approaches may assist development of methods for tissue depth assessment. Our results indicate an increase of average image intensity as thickness increases up to approximately 2 mm. In a dual fiber spectroscopy configuration, sensitivity up to approximately 3 mm with an increase to 6 mm when spectral ratio between selected wavelengths was obtained. Preliminary Monte Carlo results provided reasonable fit to the experimental data.

  11. Rotational Diffusion of Plasmon-Resonant Gold Nanorods for Depth-Resolved Microrheology Using Optical Coherence Tomography

    Science.gov (United States)

    Oldenburg, Amy; Chhetri, Raghav; Kozek, Krystian; Johnston-Peck, Aaron; Tracy, Joseph

    2011-03-01

    The ability to perform microrheology in optically thick samples would enable analysis of bulk tissues. Optical coherence tomography (OCT) provides imaging several mean free scattering path lengths into tissue. In this study we report the use of plasmon-resonant gold nanorods as microrheological sensors in OCT. Nanorods exhibit a longitudinal mode that is excited when they are oriented parallel to the polarization of the incident light, which is favorable for passive microrheology using polarized light to monitor their rotational diffusion. We demonstrate measurements of the rotational diffusion of unconfined, colloidal gold nanorods using polarization-sensitive OCT, and validate the Stokes-Einstein relationship for the nanorods in simple fluids of varying viscosity. We then show that OCT provides depth-resolved imaging of fluid viscosity through measurements of the rotational diffusion rate of the nanorods. We acknowledge support from the Carolina Cancer Center for Nanotechnology Excellence (C-CCNE NIH (NCI) #U54CA119343).

  12. A Perceptual Matching Technique for Depth Judgements in Optical, See-Through Augmented Reality

    Science.gov (United States)

    2006-03-01

    a perceptual matching task. Figure 1 shows the experimental setting. We seated observers on a tall stool 3.4 meters from one end of a 50.1-meter...center of each lens was 147.3 cm above the floor, and we adjusted the height of the stool so that observers could comforta- bly look through the display...234–250. [15] MON-WILLIAMS, M, TRESILIAN, JR, “Ordinal depth information from accommodation?”, Ergonomics , 43(3), March 2000, pages 391–404. [16

  13. PRECISE MEASUREMENT OF THE REIONIZATION OPTICAL DEPTH FROM THE GLOBAL 21 cm SIGNAL ACCOUNTING FOR COSMIC HEATING

    Energy Technology Data Exchange (ETDEWEB)

    Fialkov, Anastasia; Loeb, Abraham, E-mail: anastasia.fialkov@cfa.harvard.edu, E-mail: aloeb@cfa.harvard.edu [Department of Astronomy, Harvard University, 60 Garden Street, MS-51, Cambridge, MA 02138 (United States)

    2016-04-10

    As a result of our limited data on reionization, the total optical depth for electron scattering, τ, limits precision measurements of cosmological parameters from the Cosmic Microwave Background (CMB). It was recently shown that the predicted 21 cm signal of neutral hydrogen contains enough information to reconstruct τ with sub-percent accuracy, assuming that the neutral gas was much hotter than the CMB throughout the entire epoch of reionization (EoR). Here we relax this assumption and use the global 21 cm signal alone to extract τ for realistic X-ray heating scenarios. We test our model-independent approach using mock data for a wide range of ionization and heating histories and show that an accurate measurement of the reionization optical depth at a sub-percent level is possible in most of the considered scenarios even when heating is not saturated during the EoR, assuming that the foregrounds are mitigated. However, we find that in cases where heating sources had hard X-ray spectra and their luminosity was close to or lower than what is predicted based on low-redshift observations, the global 21 cm signal alone is not a good tracer of the reionization history.

  14. Interpreting the cloud cover – aerosol optical depth relationship found in satellite data using a general circulation model

    Directory of Open Access Journals (Sweden)

    J. Quaas

    2010-07-01

    Full Text Available Statistical analysis of satellite data shows a positive correlation between aerosol optical depth (AOD and total cloud cover (TCC. Reasons for this relationship have been disputed in recent literature. The aim of this study is to explore how different processes contribute to one model's analog of the positive correlation between aerosol optical depth and total cloud cover seen in the satellite retrievals. We compare the slope of the linear regression between the logarithm of TCC and the logarithm of AOD, or the strength of the relationship, as derived from three satellite data sets to the ones simulated by a global aerosol-climate model. We analyse model results from two different simulations with and without a parameterisation of aerosol indirect effects, and using dry compared to humidified AOD. Perhaps not surprisingly we find that no single one of the hypotheses discussed in the literature is able to uniquely explain the positive relationship. However the dominant contribution to the model's AOD-TCC relationship can be attributed to aerosol swelling in regions where humidity is high and clouds are coincidentally found. This finding leads us to hypothesise that much of the AOD-TCC relationship seen in the satellite data is also carried by such a process, rather than the direct effects of the aerosols on the cloud fields themselves.

  15. Swept source/Fourier domain polarization sensitive optical coherence tomography with a passive polarization delay unit.

    Science.gov (United States)

    Baumann, Bernhard; Choi, WooJhon; Potsaid, Benjamin; Huang, David; Duker, Jay S; Fujimoto, James G

    2012-04-23

    Polarization sensitive optical coherence tomography (PS-OCT) is a functional imaging method that provides additional contrast using the light polarizing properties of a sample. This manuscript describes PS-OCT based on ultrahigh speed swept source / Fourier domain OCT operating at 1050 nm at 100 kHz axial scan rates using single mode fiber optics and a multiplexing approach. Unlike previously reported PS-OCT multiplexing schemes, the method uses a passive polarization delay unit and does not require active polarization modulating devices. This advance decreases system cost and avoids complex synchronization requirements. The polarization delay unit was implemented in the sample beam path in order to simultaneously illuminate the sample with two different polarization states. The orthogonal polarization components for the depth-multiplexed signals from the two input states were detected using dual balanced detection. PS-OCT images were computed using Jones calculus. 3D PS-OCT imaging was performed in the human and rat retina. In addition to standard OCT images, PS-OCT images were generated using contrast form birefringence and depolarization. Enhanced tissue discrimination as well as quantitative measurements of sample properties was demonstrated using the additional contrast and information contained in the PS-OCT images.

  16. Retrieval, Inter-Comparison, and Validation of Above-Cloud Aerosol Optical Depth from A-train Sensors

    Science.gov (United States)

    Jethva, Hiren; Torres, Omar; Bhartia, Pawan K.; Remer, Lorraine; Redemann, Jens; Dunagan, Stephen E.; Livingston, John; Shinozuka, Yohei; Kacenelenbogen, Meloe; Segal-Rosenbeimer, Michal; hide

    2014-01-01

    Absorbing aerosols produced from biomass burning and dust outbreaks are often found to overlay lower level cloud decks and pose greater potentials of exerting positive radiative effects (warming) whose magnitude directly depends on the aerosol loading above cloud, optical properties of clouds and aerosols, and cloud fraction. Recent development of a 'color ratio' (CR) algorithm applied to observations made by the Aura/OMI and Aqua/MODIS constitutes a major breakthrough and has provided unprecedented maps of above-cloud aerosol optical depth (ACAOD). The CR technique employs reflectance measurements at TOA in two channels (354 and 388 nm for OMI; 470 and 860 nm for MODIS) to retrieve ACAOD in near-UV and visible regions and aerosol-corrected cloud optical depth, simultaneously. An inter-satellite comparison of ACAOD retrieved from NASA's A-train sensors reveals a good level of agreement between the passive sensors over the homogeneous cloud fields. Direct measurements of ACA such as carried out by the NASA Ames Airborne Tracking Sunphotometer (AATS) and Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) can be of immense help in validating ACA retrievals. We validate the ACA optical depth retrieved using the CR method applied to the MODIS cloudy-sky reflectance against the airborne AATS and 4STAR measurements. A thorough search of the historic AATS-4STAR database collected during different field campaigns revealed five events where biomass burning, dust, and wildfire-emitted aerosols were found to overlay lower level cloud decks observed during SAFARI-2000, ACE-ASIA 2001, and SEAC4RS- 2013, respectively. The co-located satellite-airborne measurements revealed a good agreement (RMSE less than 0.1 for AOD at 500 nm) with most matchups falling within the estimated uncertainties in the MODIS retrievals. An extensive validation of satellite-based ACA retrievals requires equivalent field measurements particularly over the regions where ACA are often

  17. Multimodal adaptive optics for depth-enhanced high-resolution ophthalmic imaging

    Science.gov (United States)

    Hammer, Daniel X.; Mujat, Mircea; Iftimia, Nicusor V.; Lue, Niyom; Ferguson, R. Daniel

    2010-02-01

    We developed a multimodal adaptive optics (AO) retinal imager for diagnosis of retinal diseases, including glaucoma, diabetic retinopathy (DR), age-related macular degeneration (AMD), and retinitis pigmentosa (RP). The development represents the first ever high performance AO system constructed that combines AO-corrected scanning laser ophthalmoscopy (SLO) and swept source Fourier domain optical coherence tomography (SSOCT) imaging modes in a single compact clinical prototype platform. The SSOCT channel operates at a wavelength of 1 μm for increased penetration and visualization of the choriocapillaris and choroid, sites of major disease activity for DR and wet AMD. The system is designed to operate on a broad clinical population with a dual deformable mirror (DM) configuration that allows simultaneous low- and high-order aberration correction. The system also includes a wide field line scanning ophthalmoscope (LSO) for initial screening, target identification, and global orientation; an integrated retinal tracker (RT) to stabilize the SLO, OCT, and LSO imaging fields in the presence of rotational eye motion; and a high-resolution LCD-based fixation target for presentation to the subject of stimuli and other visual cues. The system was tested in a limited number of human subjects without retinal disease for performance optimization and validation. The system was able to resolve and quantify cone photoreceptors across the macula to within ~0.5 deg (~100-150 μm) of the fovea, image and delineate ten retinal layers, and penetrate to resolve targets deep into the choroid. In addition to instrument hardware development, analysis algorithms were developed for efficient information extraction from clinical imaging sessions, with functionality including automated image registration, photoreceptor counting, strip and montage stitching, and segmentation. The system provides clinicians and researchers with high-resolution, high performance adaptive optics imaging to help

  18. Retrieval of volcanic ash particle size, mass and optical depth from a ground-based thermal infrared camera

    Science.gov (United States)

    Prata, A. J.; Bernardo, C.

    2009-09-01

    Volcanoes can emit fine-sized ash particles (1-10 μm radii) into the atmosphere and if they reach the upper troposphere or lower stratosphere, these particles can have deleterious effects on the atmosphere and climate. If they remain within the lowest few kilometers of the atmosphere, the particles can lead to health effects in humans and animals and also affect vegetation. It is therefore of some interest to be able to measure the particle size distribution, mass and other optical properties of fine ash once suspended in the atmosphere. A new imaging camera working in the infrared region between 7-14 μm has been developed to detect and quantify volcanic ash. The camera uses passive infrared radiation measured in up to five spectral channels to discriminate ash from other atmospheric absorbers (e.g. water molecules) and a microphysical ash model is used to invert the measurements into three retrievable quantities: the particle size distribution, the infrared optical depth and the total mass of fine particles. In this study we describe the salient characteristics of the thermal infrared imaging camera and present the first retrievals from field studies at an erupting volcano. An automated ash alarm algorithm has been devised and tested and a quantitative ash retrieval scheme developed to infer particle sizes, infrared optical depths and mass in a developing ash column. The results suggest that the camera is a useful quantitative tool for monitoring volcanic particulates in the size range 1-10 μm and because it can operate during the night, it may be a very useful complement to other instruments (e.g. ultra-violet spectrometers) that only operate during daylight.

  19. Optical depth estimates and effective critical densities of dense gas tracers in the inner parts of nearby galaxy discs

    Science.gov (United States)

    Jiménez-Donaire, M. J.; Bigiel, F.; Leroy, A. K.; Cormier, D.; Gallagher, M.; Usero, A.; Bolatto, A.; Colombo, D.; García-Burillo, S.; Hughes, A.; Kramer, C.; Krumholz, M. R.; Meier, D. S.; Murphy, E.; Pety, J.; Rosolowsky, E.; Schinnerer, E.; Schruba, A.; Tomičić, N.; Zschaechner, L.

    2017-04-01

    High critical density molecular lines like HCN (1-0) or HCO+ (1-0) represent our best tool to study currently star-forming, dense molecular gas at extragalactic distances. The optical depth of these lines is a key ingredient to estimate the effective density required to excite emission. However, constraints on this quantity are even scarcer in the literature than measurements of the high-density tracers themselves. Here, we combine new observations of HCN, HCO+ and HNC (1-0) and their optically thin isotopologues H13CN, H13CO+ and HN13C (1-0) to measure isotopologue line ratios. We use IRAM 30-m observations from the large programme EMPIRE and new Atacama Large Millimetre/submillimetre Array observations, which together target six nearby star-forming galaxies. Using spectral stacking techniques, we calculate or place strong upper limits on the HCN/H13CN, HCO+/H13CO+ and HNC/HN13C line ratios in the inner parts of these galaxies. Under simple assumptions, we use these to estimate the optical depths of HCN (1-0) and HCO+ (1-0) to be τ ∼ 2-11 in the active, inner regions of our targets. The critical densities are consequently lowered to values between 5 and 20 × 105 cm-3, 1 and 3 × 105 cm-3 and 9 × 104 cm-3 for HCN, HCO+ and HNC, respectively. We study the impact of having different beam-filling factors, η, on these estimates and find that the effective critical densities decrease by a factor of η _{12}/η _{13} τ_{12}. A comparison to existing work in NGC 5194 and NGC 253 shows the HCN/H13CN and HCO+/H13CO+ ratios in agreement with our measurements within the uncertainties. The same is true for studies in other environments such as the Galactic Centre or nuclear regions of active galactic nucleus dominated nearby galaxies.

  20. Determination of Backscatter-Extinction Coefficient Ratio for LIDAR-Retrieved Aerosol Optical Depth Based on Sunphotometer Data

    Directory of Open Access Journals (Sweden)

    Pak Wai Chan

    2010-09-01

    Full Text Available Backscattered power data from the Doppler LIght Detection And Ranging (LIDAR systems at the Hong Kong International Airport (HKIA could be used to obtain the extinction coefficient of the troposphere by combining with the meteorological optical range (MOR data from the nearby forward scatter sensor. The Range-height Indicator (RHI scan of the LIDAR is then utilized to derive the vertical profile of extinction coefficient, which is integrated with height to obtain the aerosol optical depth (AOD. In the retrieval of extinction coefficient profile, there is a power exponent of unknown value relating the backscattered power and the extinction coefficient. This exponent (called the backscatter-extinction coefficient ratio depends on the optical properties of the aerosol in the air, and is normally assumed to be 1. In the present study, the value of this ratio is established by comparing the AOD measurements by a hand-held sunphotometer and the LIDAR-based AOD estimate in one winter (October 2008 to January 2009, which is the season with the largest number of haze episodes, and one summer-winter-spring period of the following year (July 2009 to May 2010 at HKIA. It is found to be about 1.4. The sensitivity of extinction coefficient profile to the value of the ratio is also examined for two cases in the study period, one good visibility day and one hazy day.

  1. Depth probing of the hydride formation process in thin Pd films by combined electrochemistry and fiber optics-based in situ UV/vis spectroscopy.

    Science.gov (United States)

    Wickman, Björn; Fredriksson, Mattias; Feng, Ligang; Lindahl, Niklas; Hagberg, Johan; Langhammer, Christoph

    2015-07-15

    We demonstrate a flexible combined electrochemistry and fiber optics-based in situ UV/vis spectroscopy setup to gain insight into the depth evolution of electrochemical hydride and oxide formation in Pd films with thicknesses of 20 and 100 nm. The thicknesses of our model systems are chosen such that the films are thinner or significantly thicker than the optical skin depth of Pd to create two distinctly different situations. Low power white light is irradiated on the sample and analyzed in three different configurations; transmittance through, and, reflectance from the front and the back side of the film. The obtained optical sensitivities correspond to fractions of a monolayer of adsorbed or absorbed hydrogen (H) and oxygen (O) on Pd. Moreover, a combined simultaneous readout obtained from the different optical measurement configurations provides mechanistic insights into the depth-evolution of the studied hydrogenation and oxidation processes.

  2. Optics optimization in high-resolution imaging module with extended depth of field

    Science.gov (United States)

    Chen, Xi; Bakin, Dmitry; Liu, Changmeng; George, Nicholas

    2008-08-01

    The standard imaging lens for a high resolution sensor was modified to achieve the extended depth of field (EDoF) from 300 mm to infinity. In the module the raw sensor outputs are digitally processed to obtain high contrast images. The overall module is considered as an integrated computational imaging system (ICIS). The simulation results for illustrative designs with different amount of spherical aberrations are provided and compared. Based on the results of simulations we introduced the limiting value of the PSF Strehl ratio as the integral threshold criteria to be used during EDoF lens optimization. A four-element standard lens was modified within the design constraints to achieve the EDoF performance. Two EDoF designs created with different design methods are presented. The imaging modules were compared in terms of Strehl ratios, limiting resolution, modulation frequencies at 50% contrast, and SNR. The output images were simulated for EDoF modules, passed through the image processing pipeline, and compared against the images obtained with the standard lens module.

  3. Using the OMI aerosol index and absorption aerosol optical depth to evaluate the NASA MERRA Aerosol Reanalysis

    Science.gov (United States)

    Buchard, V.; da Silva, A. M.; Colarco, P. R.; Darmenov, A.; Randles, C. A.; Govindaraju, R.; Torres, O.; Campbell, J.; Spurr, R.

    2015-05-01

    A radiative transfer interface has been developed to simulate the UV aerosol index (AI) from the NASA Goddard Earth Observing System version 5 (GEOS-5) aerosol assimilated fields. The purpose of this work is to use the AI and aerosol absorption optical depth (AAOD) derived from the Ozone Monitoring Instrument (OMI) measurements as independent validation for the Modern Era Retrospective analysis for Research and Applications Aerosol Reanalysis (MERRAero). MERRAero is based on a version of the GEOS-5 model that is radiatively coupled to the Goddard Chemistry, Aerosol, Radiation, and Transport (GOCART) aerosol module and includes assimilation of aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. Since AI is dependent on aerosol concentration, optical properties and altitude of the aerosol layer, we make use of complementary observations to fully diagnose the model, including AOD from the Multi-angle Imaging SpectroRadiometer (MISR), aerosol retrievals from the AErosol RObotic NETwork (AERONET) and attenuated backscatter coefficients from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission to ascertain potential misplacement of plume height by the model. By sampling dust, biomass burning and pollution events in 2007 we have compared model-produced AI and AAOD with the corresponding OMI products, identifying regions where the model representation of absorbing aerosols was deficient. As a result of this study over the Saharan dust region, we have obtained a new set of dust aerosol optical properties that retains consistency with the MODIS AOD data that were assimilated, while resulting in better agreement with aerosol absorption measurements from OMI. The analysis conducted over the southern African and South American biomass burning regions indicates that revising the spectrally dependent aerosol absorption properties in the near-UV region improves the modeled-observed AI comparisons

  4. Characteristics of Aerosol Spectral Optical Depths over Manora Peak, Nainital $-$ A High Altitude Station in the Central Himalayas

    CERN Document Server

    Sagar, R; Dumka, U C; Moorthy, K K; Pant, P

    2003-01-01

    We present for the first time spectral behaviour of aerosol optical depths (AODs) over Manora Peak, Nainital located at an altitude of ~2 km in the central Himalayas. The observations were carried out using a Multi-Wavelength Solar Radiometer during January to December 2002. The primary features of the study are (i) larger AOD during afternoon periods compared to forenoon, attributable to change in the ray path from comparatively cleaner environment in the forenoon to polluted environment in the afternoon (ii) extremely low AODs during local winter and a remarkable increase to high values in summer (iii) a distinct change in the spectral dependencies of AODs from a relatively steeper spectra during winter to a shallower one in summer representing both transparent (meteorological aerosols) and polluted summer (urban haze aerosols) skies.The mean aerosol extinction law at Nainital during 2002 is best represented by $0.10 \\lambda^{-0.61}$.

  5. Impact of continental meteorology and atmospheric circulation in the modulation of Aerosol Optical Depth over the Arabian Sea

    Indian Academy of Sciences (India)

    Sandhya K Nair; S Sijikumar; S S Prijith

    2012-04-01

    Time series analysis of Aerosol Optical Depth (AOD) derived from NOAA-AVHRR data during the period 1996–1999 and the MODIS data during 2000–2009 over the Arabian Sea revealed a systematic biennial variability in the high AOD during summer months. The variability is more prominent over the northern and central parts of the Arabian Sea and became less significant towards southern latitudes. The possible mechanisms for these are examined by estimating the source strength over coastal Arabia and AOD flow rate through the western boundary of the Arabian Sea. Both these show clear signatures of biennial variability with same phase as AOD for most of the years. This result indicates that the observed biennial variability in AOD is likely to be the outcome of combined effects of biennial variability in wind generated sea-salt aerosols and dust transported from Arabia.

  6. Estimating nocturnal opaque ice cloud optical depth from MODIS multispectral infrared radiances using a neural network method

    Science.gov (United States)

    Minnis, Patrick; Hong, Gang; Sun-Mack, Szedung; Smith, William L.; Chen, Yan; Miller, Steven D.

    2016-05-01

    Retrieval of ice cloud properties using IR measurements has a distinct advantage over the visible and near-IR techniques by providing consistent monitoring regardless of solar illumination conditions. Historically, the IR bands at 3.7, 6.7, 11.0, and 12.0 µm have been used to infer ice cloud parameters by various methods, but the reliable retrieval of ice cloud optical depth τ is limited to nonopaque cirrus with τ water path in the future. Factors affecting the uncertainties and potential improvements are discussed. With improved techniques for discriminating between opaque and semitransparent ice clouds, the method can ultimately improve cloud property monitoring over the entire diurnal cycle.

  7. The effect of aerosol optical depth on rainfall with reference to meteorology over metro cities in India.

    Science.gov (United States)

    Gunaseelan, Indira; Bhaskar, B Vijay; Muthuchelian, K

    2014-01-01

    Rainfall is a key link in the global water cycle and a proxy for changing climate; therefore, proper assessment of the urban environment's impact on rainfall will be increasingly important in ongoing climate diagnostics and prediction. Aerosol optical depth (AOD) measurements on the monsoon seasons of the years 2008 to 2010 were made over four metro regional hotspots in India. The highest average of AOD was in the months of June and July for the four cities during 3 years and lowest was in September. Comparing the four regions, Kolkata was in the peak of aerosol contamination and Chennai was in least. Pearson correlation was made between AOD with climatic parameters. Some changes in the parameters were found during drought year. Temperature, cloud parameters, and humidity play an important role for the drought conditions. The role of aerosols, meteorological parameters, and their impacts towards the precipitation during the monsoon was studied.

  8. Enhanced-Depth Imaging Optical Coherence Tomography of the Human Choroid In Vivo Compared With Histology After Enucleation

    DEFF Research Database (Denmark)

    Li, Xiao Qiang; Heegaard, Steffen; Kiilgaard, Jens Folke

    2016-01-01

    PURPOSE: This study compared in vivo enhanced-depth imaging optical coherence tomography (EDI-OCT) with ex vivo histology of the choroid in human eyes. METHODS: Three eyes in three patients with advanced iris melanoma without posterior segment involvement underwent EDI-OCT less than 24 hours prior...... to enucleation and, in one eye, immediately after enucleation. Following fixation in 4% buffered formaldehyde and paraffin embedding, serial sections of the whole eye were cut horizontally, mounted, stained with hematoxylin-eosin and digitized. Alignment between histology and EDI-OCT was made on landmarks...... such as retinal vessel, the foveal depression, ciliary arteries, drusen, and nevi. RESULTS: Intra- and interindividual variations in relative choroidal thickness were comparable between the two modalities. After histologic fixation of the three melanoma eyes, the fullness of the choroidal vessels was reduced...

  9. Fast temporal adaptation of on-off units in the first optic chiasm of the blowfly

    NARCIS (Netherlands)

    Jansonius, N.M.; Hateren, J.H. van

    1991-01-01

    We recorded from spiking units in the first optic chiasm between lamina and medulla in the brain of the blowfly (Calliphora vicina). Both previously characterized neuron types, on-off units and sustaining units, were encountered. On-off units had a temporal frequency response with a lower cut-off

  10. Fast temporal adaptation of on-off units in the first optic chiasm of the blowfly

    NARCIS (Netherlands)

    Jansonius, N.M.; Hateren, J.H. van

    1991-01-01

    We recorded from spiking units in the first optic chiasm between lamina and medulla in the brain of the blowfly (Calliphora vicina). Both previously characterized neuron types, on-off units and sustaining units, were encountered. On-off units had a temporal frequency response with a lower cut-off fr

  11. Effect of Uveal Melanocytes on Choroidal Morphology in Rhesus Macaques and Humans on Enhanced-Depth Imaging Optical Coherence Tomography

    Science.gov (United States)

    Yiu, Glenn; Vuong, Vivian S.; Oltjen, Sharon; Cunefare, David; Farsiu, Sina; Garzel, Laura; Roberts, Jeffrey; Thomasy, Sara M.

    2016-01-01

    Purpose To compare cross-sectional choroidal morphology in rhesus macaque and human eyes using enhanced-depth imaging optical coherence tomography (EDI-OCT) and histologic analysis. Methods Enhanced-depth imaging–OCT images from 25 rhesus macaque and 30 human eyes were evaluated for choriocapillaris and choroidal–scleral junction (CSJ) visibility in the central macula based on OCT reflectivity profiles, and compared with age-matched histologic sections. Semiautomated segmentation of the choriocapillaris and CSJ was used to measure choriocapillary and choroidal thickness, respectively. Multivariate regression was performed to determine the association of age, refractive error, and race with choriocapillaris and CSJ visibility. Results Rhesus macaques exhibit a distinct hyporeflective choriocapillaris layer on EDI-OCT, while the CSJ cannot be visualized. In contrast, humans show variable reflectivities of the choriocapillaris, with a distinct CSJ seen in many subjects. Histologic sections demonstrate large, darkly pigmented melanocytes that are densely distributed in the macaque choroid, while melanocytes in humans are smaller, less pigmented, and variably distributed. Optical coherence tomography reflectivity patterns of the choroid appear to correspond to the density, size, and pigmentation of choroidal melanocytes. Mean choriocapillary thickness was similar between the two species (19.3 ± 3.4 vs. 19.8 ± 3.4 μm, P = 0.615), but choroidal thickness may be lower in macaques than in humans (191.2 ± 43.0 vs. 266.8 ± 78.0 μm, P morphology on EDI-OCT in rhesus macaque and human eyes. Racial differences in pigmentation may affect choriocapillaris and CSJ visibility, and may influence the accuracy of choroidal thickness measurements. PMID:27792810

  12. The choroid and lamina cribrosa is affected in patients with Parkinson's disease: enhanced depth imaging optical coherence tomography study.

    Science.gov (United States)

    Eraslan, Muhsin; Cerman, Eren; Yildiz Balci, Sevcan; Celiker, Hande; Sahin, Ozlem; Temel, Ahmet; Suer, Devran; Tuncer Elmaci, Nese

    2016-02-01

    To compare lamina cribrosa (LC) and choroidal thicknesses using enhanced depth imaging optical coherence tomography (EDI-OCT) in patients with Parkinson's disease (PD) and healthy controls. A total number of 44 eyes of 22 patients with PD and 50 eyes of 25 healthy subjects were utilized in this institutional cross-sectional study. After a complete ophthalmic examination, all eyes were imaged with OCT (RTVue-100 version 5.1 Fourier-domain optical coherence tomography; Optovue Inc., Fremont, CA, USA); LC and choroidal thickness were assessed. The mean LC thicknesses were 209.4 ± 40.2 μm in patients with PD and 292.5 ± 33.7 μm in control subjects. There was a significant difference in the mean LC thickness between the groups (p choroidal thickness measurements of the PD group at the subfoveal region and 1.5 mm temporal and 1.5 mm nasal to the fovea were 228.1 ± 44.3, 193.2 ± 41.4 and 188.4 ± 49.0 μm, respectively, whereas measurements for the controls were, respectively, 246.5 ± 38.2, 227.3 ± 34.7 and 216.7 ± 51.4 μm. The choroid was significantly thinner in eyes of the PD group compared to that of the controls (p = 0.001, p choroid thicknesses (rs[94] = -0.282, p = 0.006; rs[94] = -0.324, p = 0.001, rs[94] = -0.240, and p = 0.020, respectively). Regardless of the disease severity, PD may cause atrophy and volume loss in the lamina cribrosa, and choroid. An enhanced depth imaging technique may be used as an additional modality in the diagnosis and follow-up of patients with PD. © 2015 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.

  13. Algorithms and uncertainties for the determination of multispectral irradiance components and aerosol optical depth from a shipborne rotating shadowband radiometer

    Science.gov (United States)

    Witthuhn, Jonas; Deneke, Hartwig; Macke, Andreas; Bernhard, Germar

    2017-03-01

    The 19-channel rotating shadowband radiometer GUVis-3511 built by Biospherical Instruments provides automated shipborne measurements of the direct, diffuse and global spectral irradiance components without a requirement for platform stabilization. Several direct sun products, including spectral direct beam transmittance, aerosol optical depth, Ångström exponent and precipitable water, can be derived from these observations. The individual steps of the data analysis are described, and the different sources of uncertainty are discussed. The total uncertainty of the observed direct beam transmittances is estimated to be about 4 % for most channels within a 95 % confidence interval for shipborne operation. The calibration is identified as the dominating contribution to the total uncertainty. A comparison of direct beam transmittance with those obtained from a Cimel sunphotometer at a land site and a manually operated Microtops II sunphotometer on a ship is presented. Measurements deviate by less than 3 and 4 % on land and on ship, respectively, for most channels and in agreement with our previous uncertainty estimate. These numbers demonstrate that the instrument is well suited for shipborne operation, and the applied methods for motion correction work accurately. Based on spectral direct beam transmittance, aerosol optical depth can be retrieved with an uncertainty of 0.02 for all channels within a 95 % confidence interval. The different methods to account for Rayleigh scattering and gas absorption in our scheme and in the Aerosol Robotic Network processing for Cimel sunphotometers lead to minor deviations. Relying on the cross calibration of the 940 nm water vapor channel with the Cimel sunphotometer, the column amount of precipitable water can be estimated with an uncertainty of ±0.034 cm.

  14. Optical depth distribution of optically thin clouds and surface elevation variability derived from CALIPSO lidar measurements (Conference Presentation)

    Science.gov (United States)

    Liu, Zhaoyan; Lin, Bing; Obland, Michael D.; Campbell, Joel

    2016-12-01

    Atmospheric carbon dioxide (CO2) is one of the major greenhouse gases in the Earth's climate system. The CO2 concentration in the atmosphere has been significantly increased over the last 150 years, due mainly to anthropogenic activities. Comprehensive measurements of global atmospheric CO2 distributions are urgently needed to develop a more complete understanding of CO2 sources and sinks. Because of the importance of the atmospheric CO2 measurements, satellite missions with passive sensors such as GOSAT and OCO-2 have been launched, and those with active sensors like Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) using an integrated path differential absorption (IPDA) lidar are being studied. The required accuracy and precision for the column-integrated CO2 mixing ratios (XCO2) is high, within 1.0 ppm or approximately 0.26%, which calls for unbiased CO2 measurements and accurate determinations of the path length. The presence of clouds and aerosols can make the measurement complicated, especially for passive instruments. The heterogeneity generated by the surface elevation changes within the field of view of the sensors and the grid boxes of averaged values of atmospheric CO2 would also cause significant uncertainties in XCO2 estimates if the path length is not accurately known. Thus, it is required to study the cloud and aerosol distributions as well as the surface elevation variability in assessing the performance of the CO2 measurements from both active and passive instruments. The CALIPSO lidar has acquired nearly 10 years of global measurement data. It provides a great opportunity to study the global distribution of clouds and aerosols as well as the statistics of the surface elevation variations. In this study we have analyzed multiple years of the CALIPSO Level 2 data to derive the global occurrence of aerosols and optically thin clouds. The results show that clear sky does not occur as frequently as expected. The global average

  15. Validation of MODIS Aerosol Optical Depth Retrievals over a Tropical Urban Site, Pune, India

    Science.gov (United States)

    More, Sanjay; Kuman, P. Pradeep; Gupta, Pawan; Devara, P. C. S.; Aher, G. R.

    2011-01-01

    In the present paper, MODIS (Terra and Aqua; level 2, collection 5) derived aerosoloptical depths (AODs) are compared with the ground-based measurements obtained from AERONET (level 2.0) and Microtops - II sun-photometer over a tropical urban station, Pune (18 deg 32'N; 73 deg 49'E, 559 m amsl). This is the first ever systematic validation of the MODIS aerosol products over Pune. Analysis of the data indicates that the Terra and Aqua MODIS AOD retrievals at 550 nm have good correlations with the AERONET and Microtops - II sun-photometer AOD measurements. During winter the linear regression correlation coefficients for MODIS products against AERONET measurements are 0.79 for Terra and 0.62 for Aqua; however for premonsoon, the corresponding coefficients are 0.78 and 0.74. Similarly, the linear regression correlation coefficients for Microtops measurements against MODIS products are 0.72 and 0.93 for Terra and Aqua data respectively during winter and are 0.78 and 0.75 during pre-monsoon. On yearly basis in 2008-2009, correlation coefficients for MODIS products against AERONET measurements are 0.80 and 0.78 for Terra and Aqua respectively while the corresponding coefficients are 0.70 and 0.73 during 2009-2010. The regressed intercepts with MODIS vs. AERONET are 0.09 for Terra and 0.05 for Aqua during winter whereas their values are 0.04 and 0.07 during pre-monsoon. However, MODIS AODs are found to underestimate during winter and overestimate during pre-monsoon with respect to AERONET and Microtops measurements having slopes 0.63 (Terra) and 0.74 (Aqua) during winter and 0.97 (Terra) and 0.94 (Aqua) during pre-monsoon. Wavelength dependency of Single Scattering Albedo (SSA) shows presence of absorbing and scattering aerosol particles. For winter, SSA decreases with wavelength with the values 0.86 +/- 0.03 at 440 nm and 0.82 +/- 0.04 at 1020nm. In pre-monsoon, it increases with wavelength (SSA is 0.87 +/- 0.02 at 440nm; and 0.88 +/-0.04 at 1020 nm).

  16. Changes in choroidal thickness after prophylactic iridectomy in primary angle closure suspect eyes using enhanced depth imaging optical coherence tomography

    Directory of Open Access Journals (Sweden)

    Wei Wang

    2015-01-01

    Full Text Available Purpose: The aim of the present study was to evaluate the effect of surgical peripheral iridectomy (SPI on choroidal thickness in primary angle-closure suspect (PACS eyes. Materials and Methods: This was a prospective observational case series of 30 subjects with PACS. Ocular biometry was performed before SPI (baseline and then 1 week later. Choroid was imaged by enhanced depth imaging optical coherence tomography (EDI-OCT. The choroidal thickness of the subfoveal area at 1 and 3 mm diameter around the fovea was determined. Central anterior chamber depth (ACD, lens thickness (LT, vitreous chamber depth (VCD, and axial length (AL were measured by A-scan ultrasound. Parameters were compared before SPI (baseline and 1 week later. Results: Thirty eyes of 30 patients with mean age of 61.53 ± 7.98 years were studied. There was no significant difference in the choroidal thickness at all macular locations before and after SPI (all P > 0.05. Mean subfoveal choroidal thickness was 279.61 μm ± 65.50 μm before and 274.54 μm ± 63.36 μm after SPI (P = 0.308. There was also no significant change in central ACD, LT, VCD, and LT after SPI (all P > 0.05. Conclusions: SPI does not appear to alter choroidal thickness in PACS eyes, as assessed using EDI-OCT. Long-term follow-up of PACS eyes treated with SPI may provide further insight into the effects of this treatment modality on the choroid.

  17. Efficient optical pumping and high optical depth in a hollow-core photonic-crystal fibre for a broadband quantum memory

    Science.gov (United States)

    Sprague, Michael R.; England, Duncan G.; Abdolvand, Amir; Nunn, Joshua; Jin, Xian-Min; Kolthammer, W. Steven; Barbieri, Marco; Rigal, Bruno; Michelberger, Patrick S.; Champion, Tessa F. M.; Russell, Philip St. J.; Walmsley, Ian A.

    2013-05-01

    The generation of large multiphoton quantum states—for applications in computing, metrology and simulation—requires a network of high-efficiency quantum memories capable of storing broadband pulses. Integrating these memories into a fibre offers a number of advantages towards realizing this goal: strong light-matter coupling at low powers, simplified alignment and compatibility with existing photonic architectures. Here, we introduce a large-core kagome-structured hollow-core fibre as a suitable platform for an integrated fibre-based quantum memory with a warm atomic vapour. We demonstrate, for the first time, efficient optical pumping in such a system, where 90 ± 1% of atoms are prepared in the ground state. We measure high optical depths (3 × 104) and narrow homogeneous linewidths (6 ± 2 MHz) that do not exhibit significant transit-time broadening, showing that we can prepare a Λ-level system in a pure state. Our results establish that kagome fibres are suitable for implementing a broadband, room-temperature quantum memory, as well as a range of nonlinear optical effects.

  18. Variations of aerosol optical depth and Angstrom parameters at a suburban location in Iran During 2009–2010

    Indian Academy of Sciences (India)

    M Khoshsima; A A Bidokhti; F Ahmadi-Giv

    2014-02-01

    Solar irradiance is attenuated spectrally when passing through the earth’s atmosphere and it is strongly dependent on sky conditions, cleanliness of the atmosphere, composition of aerosols and gaseous constituents. In this paper, aerosol optical properties including aerosol optical depth (AOD), Angstrom exponent () and Angstrom turbidity coefficient () have been investigated during December 2009 to October 2010, in a suburban area of Zanjan (36°N, 43°E, 1700 m), in the north–west of Iran, using meteorological and sun photometric data. Results show that turbidity varies on all time scales, from the seasonal to hourly, because of changes in the atmospheric meteorological parameters. The values of range from near zero to 1.67. The diurnal variation of AOD in Zanjan is about 15%. The diurnal variability of AOD, showed a similar variation pattern in spring (including March, April, May) and winter (December, January, February) and had a different variation pattern in summer (June, July, August) and autumn (September and October). During February, spring and early summer winds transport continental aerosols mostly from the Iraq (dust events) and cause the increase of beta and turbidity of atmosphere of Zanjan.

  19. Combining Gabor and Talbot bands techniques to enhance the sensitivity with depth in Fourier domain optical coherence tomography

    Science.gov (United States)

    Bradu, Adrian; Marques, Manuel J.; Bouchal, Petr; Podoleanu, Adrian Gh.

    2013-03-01

    The purpose of this study was to show how to favorably mix two e_ects to improve the sensitivity with depth in Fourier domain optical coherence tomography (OCT): Talbot bands (TB) and Gabor-based fusion (GF) technique. TB operation is achieved by directing the two beams, from the object arm and from the reference arm in the OCT interferometer, along parallel separate paths towards the spectrometer. By changing the lateral gap between the two beams in their path towards the spectrometer, the position for the maximum sensitivity versus the optical path difference in the interferometer is adjusted. For five values of the focus position, the gap between the two beams is readjusted to reach maximum sensitivity. Then, similar to the procedure employed in the GF technique, a composite image is formed by edging together the parts of the five images that exhibited maximum brightness. The combined procedure, TB/GF is examined for four different values of the beam diameters of the two beams. Also we demonstrate volumetric FD-OCT images with mirror term attenuation and sensitivity profile shifted towards higher OPD values by applying a Talbot bands configuration.

  20. Retrieval of Aerosol Optical Depth Using the Empirical Orthogonal Functions (EOFs Based on PARASOL Multi-Angle Intensity Data

    Directory of Open Access Journals (Sweden)

    Yang Zhang

    2017-06-01

    Full Text Available Aerosol optical depth (AOD is a widely used aerosol optical parameter in atmospheric physics. To obtain this parameter precisely, many institutions plan to launch satellites with multi-angle measurement sensors, but one important step in aerosol retrieval, the estimation of surface reflectance, is still a pressing issue. This paper presents an AOD retrieval method based on the multi-angle intensity data from the Polarization and Anisotropy of Reflectances for Atmospheric Science coupled with Observations from a Lidar (PARASOL platform using empirical orthogonal functions (EOFs, which can be universally applied to multi-angle observations. The function of EOFs in this study is to estimate surface intensity contributions, associated with aerosol lookup tables (LUTs, so that the retrieval of AOD can be implemented. A comparison of the retrieved AODs for the Beijing, Xianghe, Taihu, and Hongkong_PolyU sites with those from the Aerosol Robotic Network (AERONET ground-based observations produced high correlation coefficients (r of 0.892, 0.915, 0.831, and 0.897, respectively, while the corresponding root mean square errors (RMSEs are 0.095, 0.093, 0.099, and 0.076, respectively.

  1. An analysis of the collection 5 MODIS over-ocean aerosol optical depth product for its implication in aerosol assimilation

    Directory of Open Access Journals (Sweden)

    Y. Shi

    2011-01-01

    Full Text Available As an update to our previous use of the collection 4 Moderate Resolution Imaging Spectroradiometer (MODIS over-ocean aerosol optical depth (AOD data, we examined ten years of Terra and eight years of Aqua collection 5 data for its potential usage in aerosol assimilation. Uncertainties in the over-ocean MODIS AOD were studied as functions of observing conditions, such as surface characteristics, aerosol optical properties, and cloud artifacts. Empirical corrections and quality assurance procedures were developed and compared to collection 4 data. After applying these procedures, the Root-Mean-Square-Error (RMSE in the MODIS Terra and Aqua AOD are reduced by 30% and 10–20%, respectively, with respect to AERONET data. Ten years of Terra and eight years of Aqua quality-assured level 3 MODIS over-ocean aerosol products were produced. The newly developed MODIS over-ocean aerosol products will be used in operational aerosol assimilation and aerosol climatology studies, as well as other research based on MODIS products.

  2. Advanced Optical Inertial Reference Unit with 100 Nanoradian Stability, Two-axis

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    ATA Sensors and Systems produces precision angular rate sensors, state-of-the-art optical inertial reference units, fast steering mirrors, inertial measurement u-nits, actuators and controls used in long-range optical systems and laser communications and space qualified subsystems for satellite imaging and inertial guidance.

  3. Fast ray-tracing of human eye optics on Graphics Processing Units.

    Science.gov (United States)

    Wei, Qi; Patkar, Saket; Pai, Dinesh K

    2014-05-01

    We present a new technique for simulating retinal image formation by tracing a large number of rays from objects in three dimensions as they pass through the optic apparatus of the eye to objects. Simulating human optics is useful for understanding basic questions of vision science and for studying vision defects and their corrections. Because of the complexity of computing such simulations accurately, most previous efforts used simplified analytical models of the normal eye. This makes them less effective in modeling vision disorders associated with abnormal shapes of the ocular structures which are hard to be precisely represented by analytical surfaces. We have developed a computer simulator that can simulate ocular structures of arbitrary shapes, for instance represented by polygon meshes. Topographic and geometric measurements of the cornea, lens, and retina from keratometer or medical imaging data can be integrated for individualized examination. We utilize parallel processing using modern Graphics Processing Units (GPUs) to efficiently compute retinal images by tracing millions of rays. A stable retinal image can be generated within minutes. We simulated depth-of-field, accommodation, chromatic aberrations, as well as astigmatism and correction. We also show application of the technique in patient specific vision correction by incorporating geometric models of the orbit reconstructed from clinical medical images. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

  4. Study of total column atmospheric aerosol optical depth, ozone and precipitable water content over Bay of Bengal during BOBMEX-99

    Indian Academy of Sciences (India)

    K K Dani; R S Maheskumar; P C S Devara

    2003-06-01

    The spatial and temporal variations in aerosols and precursor gases over oceanic regions have special importance in the estimation of radiative forcing parameters and thereby in the refinement of general circulation models. Extensive observations of the columnar aerosol optical depth (AOD), total column ozone (TCO) and precipitable water content (PWC) have been carried out using the on-line, multi-band solar radiometers onboard ORV Sagar Kanya (Cruise#SK 147B) over Bay of Bengal during 11th-28th August 1999. Aerosol optical and physical properties (optical depth and angstrom parameter) have been estimated at six wavelengths covering from UV to NIR (380-1020 nm) while TCO and PWC have been determined using the UV band around 300nm and NIR band around 940 nm, respectively. Added, concurrent meteorological and satellite observations during this field phase of BOBMEX-99 have been utilized to investigate spectral-temporal variations of AOD, TCO and PWC in marine environment. The results indicate lower AODs (around 0.4 at characteristic wavelength of 500 nm) and size distributions with abundance of coarse-mode particles as compared to those aerosols of typical land origin. An interesting result that is found in the present study is the significant reduction in AOD at all wavelengths from initial to later part of observation period due to cloud-scavenging and rain-washout effects as well as signature of coastal aerosol loading. The clear-sky daytime diurnal variation of TCO shows gradual increase during post-sunrise hours, broad maximum during afternoon hours and gradual decrease during pre-sunset hours, which is considered to be due to photochemical reactions. The diurnal variation curve of PWC showed maximum (∼4cm) during morning hours and gradual decrease (∼3.5cm) towards evening hours, which are found to be greater as compared to typical values over land. Another interesting feature observed is that although the PWC values are very high, there was no proportionate

  5. On the correlation between aerosol optical depth and precipitation over hyperarid regions: A case study from the Arabian Peninsula

    Science.gov (United States)

    Rodrigo Vargas Godoy, Mijael; Reddy Marpu, Prashanth; Chiesa, Matteo; Molini, Annalisa

    2017-04-01

    Atmospheric turbidity plays a crucial - and controversial - role in the hydroclimatology of arid regions, with atmospheric aerosols both acting as rainfall inhibitors and enhancers. Aircraft observations and model simulations show that cloud development is strongly modulated by dust-cloud interactions at the microscales, during the drop formation process. However, the influence of aerosols and dust on precipitation remains poorly understood, mainly due to our limited knowledge of the dynamical processes that - acting over a wider range of spatial and temporal scales - drive cloud formation and trigger precipitation. The effects of dust and aerosols on precipitation mostly depend on the concentration of dust particles acting as cloud condensation nuclei (CCNs) and ice nuclei (IN), their chemical composition, size and morphology. In the recent years, the application of satellite data to characterize aerosol distribution has advanced dramatically through the systematic acquisition of aerosol optical depth (AOD) data over land from space borne sensors like MODIS onboard the EOS-Terra satellite. Although AOD is not a direct measure of the aerosol concentration in atmosphere, but rather an estimate of the atmospheric optical thickness due to scattering and absorption by aerosols, it is frequently used as a proxy of dust concentration in the atmospheric column. Many studies have analyzed the coupling between dust/aerosol abundance and precipitation through the use of remotely sensed data of AOD and precipitation. However, their focus has been mainly on the long-term influence (at monthly or annual scales) of dust/aerosols on precipitation onset, and on the influence of transport processes (through Lagrangian tracking). In this contribution, we move our attention to hyperarid regions - and in particular to a large region centered on the Arabian Peninsula, Persia and Eastern Africa - where precipitation events are highly sporadic and scattered in space. We use aerosol

  6. En face enhanced-depth swept-source optical coherence tomography features of chronic central serous chorioretinopathy.

    Science.gov (United States)

    Ferrara, Daniela; Mohler, Kathrin J; Waheed, Nadia; Adhi, Mehreen; Liu, Jonathan J; Grulkowski, Ireneusz; Kraus, Martin F; Baumal, Caroline; Hornegger, Joachim; Fujimoto, James G; Duker, Jay S

    2014-03-01

    To characterize en face features of the retinal pigment epithelium (RPE) and choroid in eyes with chronic central serous chorioretinopathy (CSCR) using a high-speed, enhanced-depth swept-source optical coherence tomography (SS-OCT) prototype. Consecutive patients with chronic CSCR were prospectively examined with SS-OCT. Fifteen eyes of 13 patients. Three-dimensional 6×6 mm macular cube raster scans were obtained with SS-OCT operating at 1050 nm wavelength and 100000 A-lines/sec with 6 μm axial resolution. Segmentation of the RPE generated a reference surface; en face SS-OCT images of the RPE and choroid were extracted at varying depths every 3.5 μm (1 pixel). Abnormal features were characterized by systematic analysis of multimodal fundus imaging, including color photographs, fundus autofluorescence, fluorescein angiography, and indocyanine-green angiography (ICGA). En face SS-OCT morphology of the RPE and individual choroidal layers. En face SS-OCT imaging at the RPE level revealed absence of signal corresponding to RPE detachment or RPE loss in 15 of 15 (100%) eyes. En face SS-OCT imaging at the choriocapillaris level showed focally enlarged vessels in 8 of 15 eyes (53%). At the level of Sattler's layer, en face SS-OCT documented focal choroidal dilation in 8 of 15 eyes (53%) and diffuse choroidal dilation in 7 of 15 eyes (47%). At the level of Haller's layer, these same features were observed in 3 of 15 eyes (20%) and 12 of 15 eyes (80%), respectively. In all affected eyes, these choroidal vascular abnormalities were seen just below areas of RPE abnormalities. In 2 eyes with secondary choroidal neovascularization (CNV), distinct en face SS-OCT features corresponded to the neovascular lesions. High-speed, enhanced-depth SS-OCT at 1050 nm wavelength enables the visualization of pathologic features of the RPE and choroid in eyes with chronic CSCR not usually appreciated with standard spectral domain (SD) OCT. En face SS-OCT imaging seems to be a useful tool in

  7. Development of Extended-Depth Swept Source Optical Coherence Tomography for Applications in Ophthalmic Imaging of the Anterior and Posterior Eye

    Science.gov (United States)

    Dhalla, Al-Hafeez Zahir

    Optical coherence tomography (OCT) is a non-invasive optical imaging modality that provides micron-scale resolution of tissue micro-structure over depth ranges of several millimeters. This imaging technique has had a profound effect on the field of ophthalmology, wherein it has become the standard of care for the diagnosis of many retinal pathologies. Applications of OCT in the anterior eye, as well as for imaging of coronary arteries and the gastro-intestinal tract, have also shown promise, but have not yet achieved widespread clinical use. The usable imaging depth of OCT systems is most often limited by one of three factors: optical attenuation, inherent imaging range, or depth-of-focus. The first of these, optical attenuation, stems from the limitation that OCT only detects singly-scattered light. Thus, beyond a certain penetration depth into turbid media, essentially all of the incident light will have been multiply scattered, and can no longer be used for OCT imaging. For many applications (especially retinal imaging), optical attenuation is the most restrictive of the three imaging depth limitations. However, for some applications, especially anterior segment, cardiovascular (catheter-based) and GI (endoscopic) imaging, the usable imaging depth is often not limited by optical attenuation, but rather by the inherent imaging depth of the OCT systems. This inherent imaging depth, which is specific to only Fourier Domain OCT, arises due to two factors: sensitivity fall-off and the complex conjugate ambiguity. Finally, due to the trade-off between lateral resolution and axial depth-of-focus inherent in diffractive optical systems, additional depth limitations sometimes arises in either high lateral resolution or extended depth OCT imaging systems. The depth-of-focus limitation is most apparent in applications such as adaptive optics (AO-) OCT imaging of the retina, and extended depth imaging of the ocular anterior segment. In this dissertation, techniques for

  8. Some features of columnar aerosol optical depth, ozone and precipitable water content observed over land during the INDOEX-IFP99

    Directory of Open Access Journals (Sweden)

    Panuganti China Sattilingam Devara

    2001-04-01

    Full Text Available Columnar aerosol optical depth (AOD, ozone and precipitable water content measurements have been made under different atmospheric conditions on a total of 46 days at the Indian Institute of Tropical Meteorology (IITM, Pune during the Intensive Field Phase (IFP of the Indian Ocean Experiment INDOEX (January-March 1999. These observations have been obtained using two compact, on-line, multi-band solar radiometers (MICROTOPS-II simultaneously. The results indicate higher aerosol optical depth (more than double on hazy days as compared to clear stable days. Further increase in aerosol optical depth and markable changes in the size spectrum are also noticed during the occasions of smoke particles' emission from combustion processes in proximity to the experimental site and high water content in the atmosphere. Size spectra of aerosols exhibit characteristic bimodal distribution with mode radii between 0.1 and 1.0 μm on the days associated with hazy-sky conditions and combustion activity. However, the mean aerosol optical depth over the entire IFP shows almost exponential decrease with increase in wavelength, and corresponding size spectrum portrays power law distribution, which may be due to the averaging effect of time variations such as forenoon, afternoon and day-to-day. Moreover, the daily values of columnar aerosol optical depth and water content show almost similar variations. Besides an increasing trend in the total column ozone variations throughout the period of study, it shows opposite variation with those observed in AOD and water content. These interesting features reveal the influence of water content on the growth processes of aerosol particles, and relationship between the increase in aerosol extinction and reduction in ozone amount and vice versa. The columnar aerosol optical depth or content or loading during the IFP99 exhibit higher values as compared to those during the First Field Phase (FFP98.

  9. Optical depths of semi-transparent cirrus clouds over oceans from CALIPSO infrared radiometer and lidar measurements, and an evaluation of the lidar multiple scattering factor

    Directory of Open Access Journals (Sweden)

    A. Garnier

    2015-02-01

    Full Text Available This paper provides a detailed evaluation of cloud absorption optical depths retrieved at 12.05 μm and comparisons to extinction optical depths retrieved at 0.532 μm from perfectly co-located observations of single-layered semi-transparent cirrus over ocean made by the Imaging Infrared Radiometer (IIR and the Cloud and Aerosol Lidar with Orthogonal Polarization (CALIOP flying on-board the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations satellite. The blackbody radiance taken in the IIR Version 3 algorithm is evaluated, and IIR retrievals are corrected accordingly. IIR infrared absorption optical depths are then compared to CALIOP visible extinction optical depths when the latter can be directly derived from the measured apparent 2-way transmittance through the cloud. Numerical simulations and IIR retrievals of ice crystal sizes suggest that the ratios of CALIOP extinction and IIR absorption optical depths should remain roughly constant with respect to temperature. Instead, these ratios are found to increase quasi-linearly by about 40% as the temperature at the layer centroid altitude decreases from 240 to 200 K. This behavior is explained by variations of the multiple scattering factor ηT to be applied to correct the measured transmittance, which is taken equal to 0.6 in the CALIOP Version 3 algorithm, and which is found here to vary with temperature (and hence cloud particle size from ηT = 0.8 at 200 K to ηT = 0.5 at 240 K for clouds with optical depth larger than 0.3. The revised parameterization of ηT introduces a concomitant temperature dependence in the simultaneously derived CALIOP lidar ratios that is consistent with observed changes in CALIOP depolarization ratios and particle habits derived from IIR measurements.

  10. Comparison between a New Optical Biometry Device and an Anterior Segment Optical Coherence Tomographer for Measuring Central Corneal Thickness and Anterior Chamber Depth

    Directory of Open Access Journals (Sweden)

    Jinhai Huang

    2016-01-01

    Full Text Available Purpose. To compare between a new optical biometer (AL-Scan, Nidek Co., Aichi, Japan and an anterior segment optical coherence tomographer (Visante AS-OCT, Carl Zeiss Meditec, Dublin, USA for measuring central corneal thickness (CCT, anterior chamber depth (ACD, and aqueous depth (AD. Methods. Sixty-three eyes of 63 normal subjects were examined with AL-Scan and Visante AS-OCT in this prospective study. One eye per subject was measured three times with both devices to record their CCT, ACD, and AD. All procedures were performed by the same operator. Agreement between the two devices was assessed using paired t-tests, Bland-Altman plots, and 95% limits of agreement (LoA. Results. The mean CCT, ACD, and AD measured by AL-Scan were 538.59±27.37 μm, 3.70±0.30 mm, and 3.16±0.30 mm, respectively. The mean values obtained by the Visante OCT were 536.14±26.61 μm for CCT, 3.71±0.29 mm for ACD, and 3.17±0.29 mm for AD. The mean CCT by the AL-Scan was higher than that obtained by the Visante AS-OCT (difference = 2.45±6.07 μm, P<0.05. The differences in ACD and AD measurements were not statistically significant. The 95% LoA of CCT, ACD, and AD were between −9.44 and 14.35 μm, −0.15 and 0.12 mm, and −0.15 and 0.12 mm, respectively. Conclusions. Since these two devices were comparable for measuring CCT, ACD, and AD, their results can be interchangeably used in the clinic.

  11. Comparison between a New Optical Biometry Device and an Anterior Segment Optical Coherence Tomographer for Measuring Central Corneal Thickness and Anterior Chamber Depth

    Science.gov (United States)

    Huang, Jinhai; Lu, Weicong; Savini, Giacomo; Chen, Hao; Wang, Chengfang; Yu, Xinxin; Bao, Fangjun; Wang, Qinmei

    2016-01-01

    Purpose. To compare between a new optical biometer (AL-Scan, Nidek Co., Aichi, Japan) and an anterior segment optical coherence tomographer (Visante AS-OCT, Carl Zeiss Meditec, Dublin, USA) for measuring central corneal thickness (CCT), anterior chamber depth (ACD), and aqueous depth (AD). Methods. Sixty-three eyes of 63 normal subjects were examined with AL-Scan and Visante AS-OCT in this prospective study. One eye per subject was measured three times with both devices to record their CCT, ACD, and AD. All procedures were performed by the same operator. Agreement between the two devices was assessed using paired t-tests, Bland-Altman plots, and 95% limits of agreement (LoA). Results. The mean CCT, ACD, and AD measured by AL-Scan were 538.59 ± 27.37 μm, 3.70 ± 0.30 mm, and 3.16 ± 0.30 mm, respectively. The mean values obtained by the Visante OCT were 536.14 ± 26.61 μm for CCT, 3.71 ± 0.29 mm for ACD, and 3.17 ± 0.29 mm for AD. The mean CCT by the AL-Scan was higher than that obtained by the Visante AS-OCT (difference = 2.45 ± 6.07 μm, P < 0.05). The differences in ACD and AD measurements were not statistically significant. The 95% LoA of CCT, ACD, and AD were between −9.44 and 14.35 μm, −0.15 and 0.12 mm, and −0.15 and 0.12 mm, respectively. Conclusions. Since these two devices were comparable for measuring CCT, ACD, and AD, their results can be interchangeably used in the clinic. PMID:27403339

  12. Depth dependent modification of optical constants arising from H+ implantation in n-type 4H-SiC measured using coherent acoustic phonons

    Directory of Open Access Journals (Sweden)

    Andrey Baydin

    2016-06-01

    Full Text Available Silicon carbide (SiC is a promising material for new generation electronics including high power/high temperature devices and advanced optical applications such as room temperature spintronics and quantum computing. Both types of applications require the control of defects particularly those created by ion bombardment. In this work, modification of optical constants of 4H-SiC due to hydrogen implantation at 180 keV and at fluences ranging from 1014 to 1016 cm−2 is reported. The depth dependence of the modified optical constants was extracted from coherent acoustic phonon spectra. Implanted spectra show a strong dependence of the 4H-SiC complex refractive index depth profile on H+ fluence. These studies provide basic insight into the dependence of optical properties of 4H silicon carbide on defect densities created by ion implantation, which is of relevance to the fabrication of SiC-based photonic and optoelectronic devices.

  13. Efficient optical pumping and high optical depth in a hollow-core photonic-crystal fibre for a broadband quantum memory

    CERN Document Server

    Sprague, Michael R; Abdolvand, Amir; Nunn, Joshua; Jin, Xian-Min; Kolthammer, W Steven; Barbieri, Marco; Rigal, Bruno; Michelberger, Patrick S; Champion, Tessa F M; Russell, Philip St J; Walmsley, Ian A

    2012-01-01

    The generation of large multiphoton quantum states - for applications in computing, metrology, and simulation - requires a network of high-efficiency quantum memories capable of storing broadband pulses. Integrating these memories into a fibre offers a number of advantages towards realising this goal: strong light-matter coupling at low powers, simplified alignment, and compatibility with existing photonic architectures. Here, we introduce a large-core kagome-structured hollow-core fibre as a suitable platform for an integrated fibre-based quantum memory with a warm atomic vapour. We demonstrate, for the first time, efficient optical pumping in a hollow-core photonic-crystal fibre with a warm atomic vapour, where (90 $\\pm$ 1)% of atoms are prepared in the ground state. We measure high optical depths (3$\\times 10^{4}$) and, also, narrow homogeneous linewidths that do not exhibit significant transit-time broadening. Our results establish that kagome fibres are suitable for implementing a broadband, room-tempera...

  14. AERONET-based microphysical and optical properties of smoke-dominated aerosol near source regions and transported over oceans, and implications for satellite retrievals of aerosol optical depth

    Science.gov (United States)

    Sayer, A. M.; Hsu, N. C.; Eck, T. F.; Smirnov, A.; Holben, B. N.

    2013-09-01

    Smoke aerosols from biomass burning are an important component of the global aerosol cycle. Analysis of Aerosol Robotic Network (AERONET) retrievals of size distribution and refractive index reveals variety between biomass burning aerosols in different global source regions, in terms of aerosol particle size and single scatter albedo (SSA). Case studies of smoke transported to coastal/island AERONET sites also mostly lie within the range of variability at near-source sites. Two broad ''families'' of aerosol properties are found, corresponding to sites dominated by boreal forest burning (larger, broader fine mode, with midvisible SSA ∼0.95), and those influenced by grass, shrub, or crop burning with additional forest contributions (smaller, narrower particles with SSA ∼0.88-0.9 in the midvisible). The strongest absorption is seen in southern African savannah at Mongu (Zambia), with average SSA ∼0.85 in the midvisible. These can serve as candidate sets of aerosol microphysical/optical properties for use in satellite aerosol optical depth (AOD) retrieval algorithms. The models presently adopted by these algorithms over ocean are often insufficiently absorbing to represent these biomass burning aerosols. A corollary of this is an underestimate of AOD in smoke outflow regions, which has important consequences for applications of these satellite datasets.

  15. Variations in optical properties of aerosols on monsoon seasonal change and estimation of aerosol optical depth using ground-based meteorological and air quality data

    Directory of Open Access Journals (Sweden)

    F. Tan

    2014-07-01

    Full Text Available In this study, the optical properties of aerosols in Penang, Malaysia were analyzed for four monsoonal seasons (northeast monsoon, pre-monsoon, southwest monsoon, and post-monsoon based on data from the AErosol RObotic NETwork (AERONET from February 2012 to November 2013. The aerosol distribution patterns in Penang for each monsoonal period were quantitatively identified according to the scattering plots of the aerosol optical depth (AOD against the Angstrom exponent. A modified algorithm based on the prototype model of Tan et al. (2014a was proposed to predict the AOD data. Ground-based measurements (i.e., visibility and air pollutant index were used in the model as predictor data to retrieve the missing AOD data from AERONET because of frequent cloud formation in the equatorial region. The model coefficients were determined through multiple regression analysis using selected data set from in situ data. The predicted AOD of the model was generated based on the coefficients and compared against the measured data through standard statistical tests. The predicted AOD in the proposed model yielded a coefficient of determination R2 of 0.68. The corresponding percent mean relative error was less than 0.33% compared with the real data. The results revealed that the proposed model efficiently predicted the AOD data. Validation tests were performed on the model against selected LIDAR data and yielded good correspondence. The predicted AOD can beneficially monitor short- and long-term AOD and provide supplementary information in atmospheric corrections.

  16. Variations in optical properties of aerosols on monsoon seasonal change and estimation of aerosol optical depth using ground-based meteorological and air quality data

    Science.gov (United States)

    Tan, F.; Lim, H. S.; Abdullah, K.; Yoon, T. L.; Holben, B.

    2014-07-01

    In this study, the optical properties of aerosols in Penang, Malaysia were analyzed for four monsoonal seasons (northeast monsoon, pre-monsoon, southwest monsoon, and post-monsoon) based on data from the AErosol RObotic NETwork (AERONET) from February 2012 to November 2013. The aerosol distribution patterns in Penang for each monsoonal period were quantitatively identified according to the scattering plots of the aerosol optical depth (AOD) against the Angstrom exponent. A modified algorithm based on the prototype model of Tan et al. (2014a) was proposed to predict the AOD data. Ground-based measurements (i.e., visibility and air pollutant index) were used in the model as predictor data to retrieve the missing AOD data from AERONET because of frequent cloud formation in the equatorial region. The model coefficients were determined through multiple regression analysis using selected data set from in situ data. The predicted AOD of the model was generated based on the coefficients and compared against the measured data through standard statistical tests. The predicted AOD in the proposed model yielded a coefficient of determination R2 of 0.68. The corresponding percent mean relative error was less than 0.33% compared with the real data. The results revealed that the proposed model efficiently predicted the AOD data. Validation tests were performed on the model against selected LIDAR data and yielded good correspondence. The predicted AOD can beneficially monitor short- and long-term AOD and provide supplementary information in atmospheric corrections.

  17. Enhanced depth imaging optical coherence tomography of the choroid in migraine patients: implications for the association of migraine and glaucoma.

    Science.gov (United States)

    Dadaci, Zeynep; Doganay, Fatma; Oncel Acir, Nursen; Aydin, Hacer Doganay; Borazan, Mehmet

    2014-07-01

    To compare the choroidal thickness measurements obtained during the attack period and during the pain-free interval in migraine patients using enhanced depth imaging optical coherence tomography (OCT). 58 eyes of 29 subjects with a diagnosis of migraine with or without aura were enrolled in this observational, cross-sectional study. Two OCT scans were performed for each patient, one during the peak period of the migraine attack and the other during the headache-free interval, using the enhanced depth imaging mode. Choroidal thicknesses were measured at the fovea, at three locations nasal and at three locations temporal to the fovea at 500 μm intervals. In patients with unilateral headaches, the choroidal thickness measurements obtained during the attack period were significantly increased only in the eyes on the headache side (pchoroidal thickness measured in the pain-free interval was 373.45 ± 76.47 μm (mean ± SD), which increased to 408.80 ± 77.70 μm during the attack period (pchoroidal thickness measurements of patients with bilateral headaches were compared to basal levels, a statistically significant increase was observed at five out of the seven measured points in the right eyes (pChoroidal thickness was found to be significantly increased in migraine patients during the attack period when compared to basal levels. The possible implications of this finding on the association between migraine and glaucoma are discussed. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

  18. Probing into the aging dynamics of biomass burning aerosol by using satellite measurements of aerosol optical depth and carbon monoxide

    Science.gov (United States)

    Konovalov, Igor B.; Beekmann, Matthias; Berezin, Evgeny V.; Formenti, Paola; Andreae, Meinrat O.

    2017-04-01

    Carbonaceous aerosol released into the atmosphere from open biomass burning (BB) is known to undergo considerable chemical and physical transformations (aging). However, there is substantial controversy about the nature and observable effects of these transformations. A shortage of consistent observational evidence on BB aerosol aging processes under different environmental conditions and at various temporal scales hinders development of their adequate representations in chemistry transport models (CTMs). In this study, we obtain insights into the BB aerosol dynamics by using available satellite measurements of aerosol optical depth (AOD) and carbon monoxide (CO). The basic concept of our method is to consider AOD as a function of the BB aerosol photochemical age (that is, the time period characterizing the exposure of BB aerosol emissions to atmospheric oxidation reactions) predicted by means of model tracers. We evaluate the AOD enhancement ratio (ER) defined as the ratio of optical depth of actual BB aerosol with respect to that of a modeled aerosol tracer that is assumed to originate from the same fires as the real BB aerosol but that is not affected by any aging processes. To limit possible effects of model transport errors, the AOD measurements are normalized to CO column amounts that are also retrieved from satellite measurements. The method is applied to the analysis of the meso- and synoptic-scale evolution of aerosol in smoke plumes from major wildfires that occurred in Siberia in summer 2012. AOD and CO retrievals from MODIS and IASI measurements, respectively, are used in combination with simulations performed with the CHIMERE CTM. The analysis indicates that aging processes strongly affected the evolution of BB aerosol in the situation considered, especially in dense plumes (with spatial average PM2. 5 concentration exceeding 100 µg m-3). For such plumes, the ER is found to increase almost 2-fold on the scale of ˜ 10 h of daytime aerosol evolution

  19. Design of the Secondary Optical Elements for Concentrated Photovoltaic Units with Fresnel Lenses

    Directory of Open Access Journals (Sweden)

    Yi-Cheng Chen

    2015-10-01

    Full Text Available The goal of this presented study was to determine the optimum parameters of secondary optical elements (SOEs for concentrated photovoltaic (CPV units with flat Fresnel lenses. Three types of SOEs are under consideration in the design process, including kaleidoscope with equal optical path design (KOD, kaleidoscope with flat top surface (KFTS, and open-truncated tetrahedral pyramid with specular walls (SP. The function of using a SOE with a Fresnel lens in a CPV unit is to achieve high optical efficiency, low sensitivity to the sun tracking error, and improved uniformity of irradiance distribution on the solar cell. Ray tracing technique was developed to simulate the optical characteristics of the CPV unit with various design parameters of each type of SOE. Finally, an optimum KOD-type SOE was determined by parametric design process. The resulting optical performance of the CPV unit with the optimum SOE was evaluated in both single-wavelength and broadband simulation of solar spectrum.

  20. Regional trends of aerosol optical depth and their impact on cloud properties over Southern India using MODIS data

    Science.gov (United States)

    Gopal, K. Rama; Obul Reddy, K. Raja; Balakrishnaiah, G.; Arafath, S. MD.; Kumar Reddy, N. Siva; Rao, T. Chakradhar; Reddy, T. Lokeswara; Reddy, R. Ramakrishna

    2016-08-01

    Remote sensing of global aerosols has constituted a great scientific interest in a variety of applications related to global warming and climatic change. In the present study we investigate the spatial and temporal variations of aerosol optical properties and its impact on various properties of clouds over Southern India for the last ten years (2005-2014) by using Moderate Resolution Imaging Spectroradiometer (MODIS) data retrieved from the onboard Terra and Aqua satellites. The spatial distributions of annual mean lowest Aerosol Optical Depth (AOD) value is observed in Bangalore (BLR) (0.22±0.04) and the highest AOD value is noted in Visakhapatnam (VSK) (0.39±0.05). Similarly high Fine Mode Fraction (FMF) is noticed over VSK and Thiruvananthapuram (TVM), while lower values are observed in Anantapur (ATP), Hyderabad (HYD), Pune (PUNE) and BLR. From the results, a negative correlation was found between AOD and Cloud Top Temperature (CTT), Cloud Top Pressure (CTP) where as, a positive correlation was observed between AOD and Cloud Fraction (CF), Water Vapor (WV) over the selected regions. Monthly average AOD and FMF are plotted for analysis of the trends of aerosol loading in a long-term scale and both values showed statistically significant enhancing trend over all regions as derived from the MODIS measurements. Further, the annual variation of spatial correlation between MODIS and MISR (Multi - Angle Imaging Spectro Radiometer) AOD has been analyzed and the correlation coefficients are found to be higher in two of the regions VSK and PUNE (>0.8), and considerably lower for TVM (<0.7).

  1. A global comparison of GEOS-Chem predicted and remotely-sensed mineral dust aerosol optical depth

    Directory of Open Access Journals (Sweden)

    Matthew S Johnson

    2012-07-01

    Full Text Available Dust aerosol optical depth (AOD and vertical distribution of aerosol extinction predicted by a global chemical transport model (GEOS-Chem are compared to space-borne data from the Moderate-resolution Imaging Spectroradiometer (MODIS, Multi-Angle Imaging SpectroRadiometer (MISR, and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO for March 2009 to February 2010. Model-predicted and remotely-sensed AOD/aerosol extinction profiles are compared over six regions where aerosol abundances are dominated by mineral dust. Calculations indicate that over the regions examined in this study (with the exception of Middle Eastern dust sources GEOS-Chem predicts higher AOD values compared to MODIS and MISR. The positive bias is particularly pronounced over the Saharan dust source regions, where model-predicted AOD values are a factor of 2 to 3 higher. The comparison with CALIPSO-derived dust aerosol extinction profiles revealed that the model overestimations of dust abundances over the study regions primarily occur below ~4 km, suggesting excessive emissions of mineral dust and/or uncertainties in dust optical properties. The implementation of a new dust size distribution scheme into GEOS-Chem reduced the yearly-mean positive bias in model-predicted AOD values over the study regions. The results were most noticeable over the Saharan dust source regions where the differences between model-predicted and MODIS/MISR retrieved AOD values were reduced from 0.22 and 0.17 to 0.02 and -0.04, respectively. Our results suggest that positive/negative biases between satellite and model-predicted aerosol extinction values at different altitudes can sometimes even out, giving a false impression for the agreement between remotely-sensed and model-predicted column-integrated AOD data.

  2. Dust aerosol, clouds, and the atmospheric optical depth record over 5 Mars years of the Mars Exploration Rover mission

    CERN Document Server

    Lemmon, Mark T; Bell, James F; Smith, Michael D; Cantor, Bruce A; Smith, Peter H

    2014-01-01

    Dust aerosol plays a fundamental role in the behavior and evolution of the Martian atmosphere. The first five Mars years of Mars Exploration Rover data provide an unprecedented record of the dust load at two sites. This record is useful for characterization of the atmosphere at the sites and as ground truth for orbital observations. Atmospheric extinction optical depths have been derived from solar images after calibration and correction for time-varying dust that has accumulated on the camera windows. The record includes local, regional, and globally extensive dust storms. Comparison with contemporaneous thermal infrared data suggests significant variation in the size of the dust aerosols, with a 1 {\\mu}m effective radius during northern summer and a 2 {\\mu}m effective radius at the onset of a dust lifting event. The solar longitude (LS) 20-136{\\deg} period is also characterized by the presence of cirriform clouds at the Opportunity site, especially near LS=50 and 115{\\deg}. In addition to water ice clouds, ...

  3. A revisit to decadal change of aerosol optical depth and its impact on global radiation over China

    Science.gov (United States)

    Tang, Wenjun; Yang, Kun; Qin, Jun; Niu, Xiaolei; Lin, Changgui; Jing, Xianwen

    2017-02-01

    Global radiation over China decreased between the 1960s and 1990, since when it has remained stable. As the total cloud cover has continued to decrease since the 1960s, variations in aerosols were suggested in previous studies to be the primary cause for variations in global radiation over China. However, the effect of aerosols on global radiation on a decadal scale has not been physically quantified over China. In this study, aerosol optical depth (AOD) data since 1980 are estimated by combining horizontal visibility data at stations in China and AOD observed by the moderate resolution imaging spectroradiometer (MODIS). It is found that the AOD exhibits decadal changes, with two decreasing periods (before the end of 1980s and after 2006) and one increasing period (from 1990 to 2006). With the derived AOD, a clear-sky model is then applied to quantify the role of aerosols in the variations in global radiation over China. The results show that aerosol direct effect cannot fully explain the decadal variations in the global radiation over China between 1980 and 2010, though it has a considerable effect on global radiation climatology. There are significant differences between the trends of clear-sky global radiation impacted by aerosols and those of all-sky global radiation impacted by aerosols and clouds, and the correlation coefficient for the comparison is very low. Therefore, the variations in all-sky global radiation over China are likely to be due to changes in cloud properties and to interactions between clouds and aerosols.

  4. Evaluation of the MODIS aerosol optical depth retrieval over different ecosystems in China during EAST-AIRE

    Science.gov (United States)

    Wang, Lili; Xin, Jinyuan; Wang, Yuesi; Li, Zhanqing; Liu, Guangren; Li, Jing

    The accuracy of the Moderate Resolution Imaging Spectroradiometer's (MODIS) aerosol products is still uncertain in China, due to a lack of validation by long-term and large-scale ground-based observations. In this paper, the MODIS aerosol optical depth (AOD) product is evaluated using Chinese Sun Hazemeter Network (CSHNET) data as ground truths over different ecological regions in China during the East Asian Study of Tropospheric Aerosols—an International Regional Experiment (EAST-AIRE). The evaluation results show very large differences in the MODIS AOD retrieval between different ecosystems and geographic locations. The most agreement between the MODIS data and that of the CSHNET was in farmland sites in central-southern China, where high correlation ( R>0.82) and large percentages ( R2>72%) within the expected error lines issued by NASA were found. In temperate forest, coastal regions, and northeast and central farmlands, there appeared moderate agreement, with R˜0.64-0.80 and 45-73% of retrieval data falling within the expected errors. The poorest agreement existed in northern arid and semiarid regions, in remote northeast farmlands, in the Tibetan and Loess Plateau, and in southern forests, with 13-54% of retrieval data falling within the expected errors. In addition, the MODIS AOD retrievals were significantly overestimated in the northern arid and semiarid regions and underestimated in remote northeast farmlands and southern forests.

  5. Comparative measurements of total ozone amount and aerosol optical depth during a campaign at El Arenosillo, Huelva, Spain

    Directory of Open Access Journals (Sweden)

    A. de La Casinière

    2005-12-01

    Full Text Available A one week field campaign took place in September 2002 at El Arenosillo, Spain. The objective was to compare total ozone column (TOC and aerosol optical depth (AOD from near ultraviolet to near infrared, measured by several Spanish and French instruments. Three spectroradiometers, Brewer, SPUV02, and LICOR, and a CIMEL photometer, have been used simultaneously and the results are presented for four clear days. TOC values are given by the Brewer instrument, and by SPUV02, using two different methods. The ground instruments compare satisfactorily (within 5 DU and the values are consistent with TOMS data (within 10 DU.

    AOD from the various instruments are compared at seven different wavelengths between 320 nm and 1020 nm: the agreement is very good at 350, 380, and 870 nm; at the four other wavelengths the difference is smaller than 0.03, which can be explained by a relative difference of 4% only between the calibrations of the various instruments. Larger AOD diurnal variations were observed at short wavelengths than in the visible and near infrared; this is most likely due to changes in aerosol size along the day, during the campaign.

  6. The GAW-PFR aerosol optical depth network: The 2008-2013 time series at Cape Point Station, South Africa

    Science.gov (United States)

    Nyeki, S.; Wehrli, C.; Gröbner, J.; Kouremeti, N.; Wacker, S.; Labuschagne, C.; Mbatha, N.; Brunke, E.-G.

    2015-05-01

    A ground-based aerosol optical depth (AOD) climatology is presented for Cape Point (CPT) station, South Africa, for the 2008-2013 period. CPT is part of the Global Atmosphere Watch-Precision Filter Radiometer network which conducts long-term AOD measurements at remote background sites. AOD (λ = 500 nm) and Ångström exponent (368 to 862 nm; α368-862) averages for the entire period were 0.059 and 0.68, displaying only a weak seasonality. Based on an established method for air mass classification using the in situ wind direction and 222Rn concentration, the following four air mass types were used to further investigate AOD: background marine, marine, mixed, and continental. AOD was similar for all types, but α368-862 was distinctly lower (0.43) for background marine and higher (1.07) for continental air masses, illustrating the presence of coarse mode and anthropogenic aerosols, respectively. Trajectory cluster analysis of 5 day back trajectories confirmed/augmented this classification. AOD for background marine and marine air mass types were consistent with ship-based (Maritime Aerosol Network) and island (AErosol RObotic NETwork) measurements, suggesting that CPT is a suitable site to monitor pristine conditions in the South Atlantic and Southern Oceans when 222Rn concentrations are < 100 mBq m-3.

  7. Enhanced-Depth Imaging Optical Coherence Tomography of the Human Choroid In Vivo Compared With Histology After Enucleation.

    Science.gov (United States)

    Li, Xiao Qiang; Heegaard, Steffen; Kiilgaard, Jens Folke; Munch, Inger Christine; Larsen, Michael

    2016-07-01

    This study compared in vivo enhanced-depth imaging optical coherence tomography (EDI-OCT) with ex vivo histology of the choroid in human eyes. Three eyes in three patients with advanced iris melanoma without posterior segment involvement underwent EDI-OCT less than 24 hours prior to enucleation and, in one eye, immediately after enucleation. Following fixation in 4% buffered formaldehyde and paraffin embedding, serial sections of the whole eye were cut horizontally, mounted, stained with hematoxylin-eosin and digitized. Alignment between histology and EDI-OCT was made on landmarks such as retinal vessel, the foveal depression, ciliary arteries, drusen, and nevi. Intra- and interindividual variations in relative choroidal thickness were comparable between the two modalities. After histologic fixation of the three melanoma eyes, the fullness of the choroidal vessels was reduced and subfoveal choroid thickness reduced to 56%, 45%, and 56%, respectively, of its in vivo thickness on EDI-OCT. There were no identifiable discrepancies in choroidal structural patterns between clinical EDI-OCT and histologic sections except that after enucleation and histologic fixation choroidal thickness was reduced to roughly half of its in vivo value, a phenomenon that may reflect the high content of blood vessels in the choroid.

  8. Lack of Association between Glaucoma and Macular Choroidal Thickness Measured with Enhanced Depth-Imaging Optical Coherence Tomography

    Science.gov (United States)

    Mwanza, Jean-Claude; Hochberg, Jessica T.; Banitt, Michael R.; Feuer, William J.

    2011-01-01

    Purpose. To compare choroidal thickness measurements among normal eyes, eyes with normal tension glaucoma (NTG), and those with primary open-angle glaucoma (POAG), and to correlate choroidal thickness with demographic and clinical ocular parameters. Methods. Choroidal thickness was measured with enhanced depth-imaging (EDI) optical coherence tomography (OCT) in one eye of 38 normal, 20 NTG, and 56 POAG subjects and compared among groups. The mean age was 69.3 ± 13.6 years (60.1 ± 13.4 years for normal subjects and 73.8 ± 11.3 years for glaucoma subjects; P choroid every 0.5 mm up to 3 mm away from the fovea. Univariate and multivariate linear regression analyses were performed to assess the association between choroidal thickness and demographic and ocular parameters. Results. There were no differences in foveal, temporal, or nasal choroidal thickness between normal, NTG, and POAG subjects (all P > 0.05) after adjusting for age, axial length, and intraocular pressure. Similarly, glaucoma severity groups did not differ from each other in all choroidal thickness measurements (all P > 0.05). Age (β = −1.78; P choroidal thickness in the entire group, followed by axial length (β = −11.8; P = 0.002). Conclusions. Choroidal thickness does not differ among normal, NTG, and POAG subjects, suggesting a lack of relationship between choroidal thickness and glaucoma based on EDI OCT measurements. PMID:21357398

  9. Inversion of Aerosol Optical Depth Based on the CCD and IRS Sensors on the HJ-1 Satellites

    Directory of Open Access Journals (Sweden)

    Yang Zhang

    2014-09-01

    Full Text Available To perform a high-resolution aerosol optical depth (AOD inversion from the HJ-1 satellites, a dark pixel algorithm utilizing the HJ-1 satellite data was developed based on the Moderate-Resolution Imaging Spectroradiometer (MODIS algorithm. By analyzing the relationship between the apparent reflectance from the 1.65 μm and 2.1 μm channels of MODIS, a method for estimating albedo using the 1.65 μm channel data of the HJ-1 satellites was established, and a high-resolution AOD inversion in the Chengdu region based on the HJ-1 satellite was completed. A comparison of the inversion results with CE318 measured data produced a correlation of 0.957, respectively, with an absolute error of 0.106. An analysis of the AOD inversion results from different aerosol models showed that the rural aerosol model was suitable as a general model for establishing an aerosol inversion look-up table for the Chengdu region.

  10. Application of oxygen A-band equivalent width to disambiguate downwelling radiances for cloud optical depth measurement

    Science.gov (United States)

    Niple, Edward R.; Scott, Herman E.; Conant, John A.; Jones, Stephen H.; Iannarilli, Frank J.; Pereira, Wellesley E.

    2016-08-01

    This paper presents the three-waveband spectrally agile technique (TWST) for measuring cloud optical depth (COD). TWST is a portable field-proven sensor and retrieval method offering a unique combination of fast (1 Hz) cloud-resolving (0.5° field of view) real-time-reported COD measurements. It entails ground-based measurement of visible and near-infrared (VNIR) zenith spectral radiances much like the Aerosol Robotic Network (AERONET) cloud-mode sensors. What is novel in our approach is that we employ absorption in the oxygen A-band as a means of resolving the COD ambiguity inherent in using up-looking spectral radiances. We describe the TWST sensor and algorithm, and assess their merits by comparison to AERONET cloud-mode measurements collected during the US Department of Energy's Atmospheric Radiation Measurements (ARM) Two-Column Aerosol Project (TCAP). Spectral radiance agreement was better than 1 %, while a linear fit of COD yielded a slope of 0.905 (TWST reporting higher COD) and offset of -2.1.

  11. MODIS derived fire characteristics and aerosol optical depth variations during the agricultural residue burning season, north India

    Energy Technology Data Exchange (ETDEWEB)

    Vadrevu, Krishna Prasad, E-mail: krisvkp@yahoo.com [Department of Geography, University of Maryland, College Park, Maryland (United States); Ellicott, Evan [Department of Geography, University of Maryland, College Park, Maryland (United States); Badarinath, K.V.S. [National Remote Sensing Center, Atmospheric Science Section, Hyderabad (India); Vermote, Eric [Department of Geography, University of Maryland, College Park, Maryland (United States)

    2011-06-15

    Agricultural residue burning is one of the major causes of greenhouse gas emissions and aerosols in the Indo-Ganges region. In this study, we characterize the fire intensity, seasonality, variability, fire radiative energy (FRE) and aerosol optical depth (AOD) variations during the agricultural residue burning season using MODIS data. Fire counts exhibited significant bi-modal activity, with peak occurrences during April-May and October-November corresponding to wheat and rice residue burning episodes. The FRE variations coincided with the amount of residues burnt. The mean AOD (2003-2008) was 0.60 with 0.87 (+1{sigma}) and 0.32 (-1{sigma}). The increased AOD during the winter coincided well with the fire counts during rice residue burning season. In contrast, the AOD-fire signal was weak during the summer wheat residue burning and attributed to dust and fossil fuel combustion. Our results highlight the need for 'full accounting of GHG's and aerosols', for addressing the air quality in the study area. - Highlights: > MODIS data could capture rice and wheat residue burning events. > The total FRP was high during the rice burning season than the wheat. > MODIS AOD variations coincided well with rice burning events than wheat. > AOD values exceeding one suggested intense air pollution. - This research work highlights the satellite derived fire products and their potential in characterizing the agricultural residue burning events and air pollution.

  12. Assessment of the aerosol optical depths measured by satellite-based passive remote sensors in the Alberta oil sands region

    Science.gov (United States)

    Sioris, Christopher E.; McLinden, Chris A.; Shephard, Mark W.; Fioletov, Vitali E.; Abboud, Ihab

    2017-02-01

    Several satellite aerosol optical depth (AOD) products are assessed in terms of their data quality in the Alberta oil sands region. The instruments consist of MODIS (Moderate Resolution Imaging Spectroradiometer), POLDER (Polarization and Directionality of Earth Reflectances), MISR (Multi-angle Imaging SpectroRadiometer), and AATSR (Advanced Along-Track Scanning Radiometer). The AOD data products are examined in terms of multiplicative and additive biases determined using local Aerosol Robotic Network (AERONET) (AEROCAN) stations. Correlation with ground-based data is used to assess whether the satellite-based AODs capture day-to-day, month-to-month, and spatial variability. The ability of the satellite AOD products to capture interannual variability is assessed at Albian mine and Shell Muskeg River, two neighbouring sites in the northern mining region where a statistically significant positive trend (2002-2015) in PM2.5 mass density exists. An increasing trend of similar amplitude (˜ 5 % year-1) is observed in this northern mining region using some of the satellite AOD products.

  13. Dust Aerosol, Clouds, and the Atmospheric Optical Depth Record over 5 Mars Years of the Mars Exploration Rover Mission

    Science.gov (United States)

    Lemmon, Mark T.; Wolff, Michael J.; Bell, James F., III; Smith, Michael D.; Cantor, Bruce A.; Smith, Peter H.

    2014-01-01

    Dust aerosol plays a fundamental role in the behavior and evolution of the Martian atmosphere. The first five Mars years of Mars Exploration Rover data provide an unprecedented record of the dust load at two sites. This record is useful for characterization of the atmosphere at the sites and as ground truth for orbital observations. Atmospheric extinction optical depths have been derived from solar images after calibration and correction for time-varying dust that has accumulated on the camera windows. The record includes local, regional, and globally extensive dust storms. Comparison with contemporaneous thermal infrared data suggests significant variation in the size of the dust aerosols, with a 1 micrometer effective radius during northern summer and a 2 micrometer effective radius at the onset of a dust lifting event. The solar longitude (L (sub s)) 20-136 degrees period is also characterized by the presence of cirriform clouds at the Opportunity site, especially near LS = 50 and 115 degrees. In addition to water ice clouds, a water ice haze may also be present, and carbon dioxide clouds may be present early in the season. Variations in dust opacity are important to the energy balance of each site, and work with seasonal variations in insolation to control dust devil frequency at the Spirit site.

  14. Analysis of marine aerosol optical depth retrieved from IRS-P4 OCM sensor and comparison with the aerosol derived from SeaWiFS and MODIS sensor

    Indian Academy of Sciences (India)

    A K Mishra; V K Dadhwal; C B S Dutt

    2008-07-01

    Aerosol optical depth is regularly derived from SeaWiFS and MODIS sensor and used by the scientific community in various climatic studies. In the present study an attempt has been made to retrieve the aerosol optical depth using the IRS-P4 OCM sensor data and a comparison has been carried out using few representative datasets. The results show that the IRS-P4 OCM retrieved aerosol optical depth is in good agreement with the aerosols retrieved from SeaWiFS as well as MODIS. The RMSE are found to be ± 0.0522 between OCM and SeaWIFS and ± 0.0638 between OCM and MODIS respectively. However, IRS-P4 OCM sensor retrieved aerosol optical depth is closer to SeaWiFS (correlation = 0.88, slope = 0.96 and intercept = −0.013) compared to MODIS (correlation = 0.75, slope = 0.91 and intercept = 0.0198). The mean percentage difference indicates that OCM retrieved AOD is +12% higher compared to SeaWiFS and +8% higher compared to MODIS. The mean absolute percentage between OCM derived AOD and SeaWiFS is found to be less (16%) compared to OCM and MODIS (20%).

  15. Lidar multiple scattering factors inferred from CALIPSO lidar and IIR retrievals of semi-transparent cirrus cloud optical depths over oceans

    Science.gov (United States)

    Garnier, A.; Pelon, J.; Vaughan, M. A.; Winker, D. M.; Trepte, C. R.; Dubuisson, P.

    2015-07-01

    Cirrus cloud absorption optical depths retrieved at 12.05 μm are compared to extinction optical depths retrieved at 0.532 μm from perfectly co-located observations of single-layered semi-transparent cirrus over ocean made by the Imaging Infrared Radiometer (IIR) and the Cloud and Aerosol Lidar with Orthogonal Polarization (CALIOP) flying on board the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite. IIR infrared absorption optical depths are compared to CALIOP visible extinction optical depths when the latter can be directly derived from the measured apparent two-way transmittance through the cloud. An evaluation of the CALIOP multiple scattering factor is inferred from these comparisons after assessing and correcting biases in IIR and CALIOP optical depths reported in version 3 data products. In particular, the blackbody radiance taken in the IIR version 3 algorithm is evaluated, and IIR retrievals are corrected accordingly. Numerical simulations and IIR retrievals of ice crystal sizes suggest that the ratios of CALIOP extinction and IIR absorption optical depths should remain roughly constant with respect to temperature. Instead, these ratios are found to increase quasi-linearly by about 40 % as the temperature at the layer centroid altitude decreases from 240 to 200 K. It is discussed that this behavior can be explained by variations of the multiple scattering factor ηT applied to correct the measured apparent two-way transmittance for contribution of forward-scattering. While the CALIOP version 3 retrievals hold ηT fixed at 0.6, this study shows that ηT varies with temperature (and hence cloud particle size) from ηT = 0.8 at 200 K to ηT = 0.5 at 240 K for single-layered semi-transparent cirrus clouds with optical depth larger than 0.3. The revised parameterization of ηT introduces a concomitant temperature dependence in the simultaneously derived CALIOP lidar ratios that is consistent with observed changes in CALIOP

  16. Optical Properties of Boreal Region Biomass Burning Aerosols in Central Alaska and Seasonal Variation of Aerosol Optical Depth at an Arctic Coastal Site

    Science.gov (United States)

    Eck, T. F.; Holben, B. N.; Reid, J. S.; Sinyuk, A.; Hyer, E. J.; O'Neill, N. T.; Shaw, G. E.; VandeCastle, J. R.; Chapin, F. S.; Dubovik, O.; hide

    2010-01-01

    Long-term monitoring of aerosol optical properties at a boreal forest AERONET site in interior Alaska was performed from 1994 through 2008 (excluding winter). Large interannual variability was observed, with some years showing near background aerosol optical depth (AOD) levels (burning regions. Single scattering albedo (omega (sub 0); 440 nm) at the boreal forest site ranged from approximately 0.91 to 0.99 with an average of approximately 0.96 for observations in 2004 and 2005. This suggests a significant amount of smoldering combustion of woody fuels and peat/soil layers that would result in relatively low black carbon mass fractions for smoke particles. The fine mode particle volume median radius during the heavy burning years was quite large, averaging approximately 0.17 micron at AOD(440 nm) = 0.1 and increasing to approximately 0.25 micron at AOD(440 nm) = 3.0. This large particle size for biomass burning aerosols results in a greater relative scattering component of extinction and, therefore, also contributes to higher omega (sub 0). Additionally, monitoring at an Arctic Ocean coastal site (Barrow, Alaska) suggested transport of smoke to the Arctic in summer resulting in individual events with much higher AOD than that occurring during typical spring Arctic haze. However, the springtime mean AOD(500 nm) is higher during late March through late May (approximately 0.150) than during summer months (approximately 0.085) at Barrow partly due to very few days with low background AOD levels in spring compared with many days with clean background conditions in summer.

  17. Monsoonal variations in aerosol optical properties and estimation of aerosol optical depth using ground-based meteorological and air quality data in Peninsular Malaysia

    Science.gov (United States)

    Tan, F.; Lim, H. S.; Abdullah, K.; Yoon, T. L.; Holben, B.

    2015-04-01

    Obtaining continuous aerosol-optical-depth (AOD) measurements is a difficult task due to the cloud-cover problem. With the main motivation of overcoming this problem, an AOD-predicting model is proposed. In this study, the optical properties of aerosols in Penang, Malaysia were analyzed for four monsoonal seasons (northeast monsoon, pre-monsoon, southwest monsoon, and post-monsoon) based on data from the AErosol RObotic NETwork (AERONET) from February 2012 to November 2013. The aerosol distribution patterns in Penang for each monsoonal period were quantitatively identified according to the scattering plots of the Ångström exponent against the AOD. A new empirical algorithm was proposed to predict the AOD data. Ground-based measurements (i.e., visibility and air pollutant index) were used in the model as predictor data to retrieve the missing AOD data from AERONET due to frequent cloud formation in the equatorial region. The model coefficients were determined through multiple regression analysis using selected data set from in situ data. The calibrated model coefficients have a coefficient of determination, R2, of 0.72. The predicted AOD of the model was generated based on these calibrated coefficients and compared against the measured data through standard statistical tests, yielding a R2 of 0.68 as validation accuracy. The error in weighted mean absolute percentage error (wMAPE) was less than 0.40% compared with the real data. The results revealed that the proposed model efficiently predicted the AOD data. Performance of our model was compared against selected LIDAR data to yield good correspondence. The predicted AOD can enhance measured short- and long-term AOD and provide supplementary information for climatological studies and monitoring aerosol variation.

  18. Real-time display on Fourier domain optical coherence tomography system using a graphics processing unit.

    Science.gov (United States)

    Watanabe, Yuuki; Itagaki, Toshiki

    2009-01-01

    Fourier domain optical coherence tomography (FD-OCT) requires resampling of spectrally resolved depth information from wavelength to wave number, and the subsequent application of the inverse Fourier transform. The display rates of OCT images are much slower than the image acquisition rates due to processing speed limitations on most computers. We demonstrate a real-time display of processed OCT images using a linear-in-wave-number (linear-k) spectrometer and a graphics processing unit (GPU). We use the linear-k spectrometer with the combination of a diffractive grating with 1200 lines/mm and a F2 equilateral prism in the 840-nm spectral region to avoid calculating the resampling process. The calculations of the fast Fourier transform (FFT) are accelerated by the GPU with many stream processors, which realizes highly parallel processing. A display rate of 27.9 frames/sec for processed images (2048 FFT size x 1000 lateral A-scans) is achieved in our OCT system using a line scan CCD camera operated at 27.9 kHz.

  19. Fiber-fault protection WDM-PON using new apparatus in optical networking unit

    Science.gov (United States)

    Yeh, C. H.; Chow, C. W.; Shih, F. Y.; Wu, Y. F.; Sung, J. Y.

    2012-04-01

    In this study, we propose and experimentally demonstrate a simple self-protection architecture for WDM passive optical network (PON) by adding a novel 2 × 2 optical switch design in each optical networking unit (ONU). Two adjacent ONUs are interconnected into a group. By using the proposed protection architecture, the affected traffic can be restored immediately against fiber fault in the feeder and distributed fibers. Moreover, the performance of proposed self-protection WDM-PON is also discussed and analyzed.

  20. Determination of Aerosol Optical Depth with a Multifilter Rotating Shadowband Radiometer using in-place calibrations at a coastal site

    Science.gov (United States)

    Denn, F. M.; Fabbri, B. E.; Schuster, G. L.

    2012-12-01

    Direct and indirect aerosol effects are identified among the largest sources of uncertainty in model projections of climate change (IPCC AR-4). Even though aerosol optical depths (AODs) are currently derived on a global scale from satellite measurements as well as within data assimilation models, ground-based sun photometer measurements of AOD are extremely important for validating these indirect retrievals. Calibration of surface sun photometers requires knowledge of the instrument-specific solar signal at each measurement channel (V0), determined by doing Langley extrapolations. V0s are often difficult to determine at ground sites, and are very difficult to obtain at the Clouds and the Earth's Radiant Energy (CERES) Ocean Validation Experiment (COVE) site. Some reasons for this difficulty are varying humidity, aerosol loading, and generally unstable atmospheric conditions. For these reasons, many researchers prefer to determine instrument V0s at pristine mountain sites, such as Mauna Loa Observatory (MLO) Hawaii, where these problems are greatly reduced. However, taking an instrument to a mountain top location can introduce a new set of problems, such as shipping damage and potential environmental influences on the instrument (temperature). For instruments with an exposed Spectralon diffuser such as the Multifilter Rotating Shadowband radiometer (MFRSR), diffuser bleaching by ultraviolet radiation and possible distortion of the diffuser by changes in atmospheric pressure can occur. For these reasons, our goal is to determine AODs for our MFRSR using V0s determined in-place at the COVE site. The reference AOD data is from a co-located CIMEL sun photometer, which is part of NASA's Aerosol Robotic NETwork (AERONET). We show that in-place V0s can be determined with nearly the same precision as at a mountain site, and that the resultant AODs obtained using these in-place V0s agree better with AERONET than the AODs determined using the mountain derived V0s. The

  1. Exploring the effects of landscape structure on aerosol optical depth (AOD) patterns using GIS and HJ-1B images.

    Science.gov (United States)

    Ye, Luping; Fang, Linchuan; Tan, Wenfeng; Wang, Yunqiang; Huang, Yu

    2016-02-01

    A GIS approach and HJ-1B images were employed to determine the effect of landscape structure on aerosol optical depth (AOD) patterns. Landscape metrics, fractal analysis and contribution analysis were proposed to quantitatively illustrate the impact of land use on AOD patterns. The high correlation between the mean AOD and landscape metrics indicates that both the landscape composition and spatial structure affect the AOD pattern. Additionally, the fractal analysis demonstrated that the densities of built-up areas and bare land decreased from the high AOD centers to the outer boundary, but those of water and forest increased. These results reveal that the built-up area is the main positive contributor to air pollution, followed by bare land. Although bare land had a high AOD, it made a limited contribution to regional air pollution due to its small spatial extent. The contribution analysis further elucidated that built-up areas and bare land can increase air pollution more strongly in spring than in autumn, whereas forest and water have a completely opposite effect. Based on fractal and contribution analyses, the different effects of cropland are ascribed to the greater vegetation coverage from farming activity in spring than in autumn. The opposite effect of cropland on air pollution reveals that green coverage and human activity also influence AOD patterns. Given that serious concerns have been raised regarding the effects of built-up areas, bare land and agricultural air pollutant emissions, this study will add fundamental knowledge of the understanding of the key factors influencing urban air quality.

  2. Monitoring and tracking the trans-Pacific transport of aerosols using multi-satellite aerosol optical depth composites

    Science.gov (United States)

    Naeger, Aaron R.; Gupta, Pawan; Zavodsky, Bradley T.; McGrath, Kevin M.

    2016-06-01

    The primary goal of this study was to generate a near-real time (NRT) aerosol optical depth (AOD) product capable of providing a comprehensive understanding of the aerosol spatial distribution over the Pacific Ocean, in order to better monitor and track the trans-Pacific transport of aerosols. Therefore, we developed a NRT product that takes advantage of observations from both low-earth orbiting and geostationary satellites. In particular, we utilize AOD products from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Suomi National Polar-orbiting Partnership (NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) satellites. Then, we combine these AOD products with our own retrieval algorithms developed for the NOAA Geostationary Operational Environmental Satellite (GOES-15) and Japan Meteorological Agency (JMA) Multi-functional Transport Satellite (MTSAT-2) to generate a NRT daily AOD composite product. We present examples of the daily AOD composite product for a case study of trans-Pacific transport of Asian pollution and dust aerosols in mid-March 2014. Overall, the new product successfully tracks this aerosol plume during its trans-Pacific transport to the west coast of North America as the frequent geostationary observations lead to a greater coverage of cloud-free AOD retrievals equatorward of about 35° N, while the polar-orbiting satellites provide a greater coverage of AOD poleward of 35° N. However, we note several areas across the domain of interest from Asia to North America where the GOES-15 and MTSAT-2 retrieval algorithms can introduce significant uncertainties into the new product.

  3. Merging aerosol optical depth data from multiple satellite missions to view agricultural biomass burning in Central and East China

    Directory of Open Access Journals (Sweden)

    Y. Xue

    2012-04-01

    Full Text Available Agricultural biomass burning (ABB in Central and East China occurs every year from May to October and peaks in June. The biomass burning event in June 2007 was very strong. During the period from 26 May to 16 June 2007, ABB occurred mainly in Anhui, Henan, Jiangsu and Shandong provinces. A comprehensive set of aerosol optical depth (AOD data, produced by a merger of AOD product data from the Moderate Resolution Imaging Spectroradiometer (MODIS and the Multiangle Imaging Spectroradiometer (MIRS, is used to study the spatial and temporal distribution of agricultural biomass aerosols in Central and East China combining with ground observations from both AErosol RObotic NETwork (AERONET and China Aerosol Remote Sensing NETwork (CARSNET measurements. We compared merged AOD data with single-sensor single-algorithm AOD data (MODIS Dark Target AOD data, MODIS Deep Blue AOD data, SRAP-MODIS AOD data and MISR AOD data. In this comparison, we found merged AOD products can improve the quality of AOD products from single-sensor single-algorithm data sets by expanding the spatial coverage of the study area and keeping the statistical confidence in AOD parameters. There existed high correlation (0.8479 between the merged AOD data and AERONET measurements. Our merged AOD data make use of synergetic information conveyed in all of the available satellite data. The merged AOD data were used for the analysis of the biomass burning event from 26 May to 16 June 2007 together with meteorological data. The merged AOD products and the ground observations from China suggest that biomass burning in Central and East China has had great impact on AOD over China. Influenced by this ABB, the highest AOD value in Beijing on 12 June 2007 reached 5.71.

  4. Spatio-temporal variability of aerosols over East China inferred by merged visibility-GEOS-Chem aerosol optical depth

    Science.gov (United States)

    Lin, Jintai; Li, Jing

    2016-05-01

    Long-term visibility measurements offer useful information for aerosol and climate change studies. Recently, a new technique to converting visibility measurements to aerosol optical depth (AOD) has been developed on a station-to-station basis (Lin et al., 2014). However, factors such as human observation differences and local meteorological conditions often impair the spatial consistency of the visibility converted AOD dataset. Here we further adopt AOD spatial information from a chemical transport model GEOS-Chem, and merge visibility inferred and modeled early-afternoon AOD over East China on a 0.667° long. × 0.5° lat. grid for 2005-2012. Comparisons with MODIS/Aqua retrieved AOD and subsequent spectral decomposition analyses show that the merged dataset successfully corrects the low bias in the model while preserving its spatial pattern, resulting in very good agreement with MODIS in both magnitude and spatio-temporal variability. The low bias is reduced from 0.10 in GEOS-Chem AOD to 0.04 in the merged data averaged over East China, and the correlation in the seasonal and interannual variability between MODIS and merged AOD is well above 0.75 for most regions. Comparisons between the merged and AERONET data also show an overall small bias and high correlation. The merged dataset reveals four major pollution hot spots in China, including the North China Plain, the Yangtze River Delta, the Pearl River Delta and the Sichuan Basin, consistent with previous works. AOD peaks in spring-summer over the North China Plain and Yangtze River Delta and in spring over the Pearl River Delta, with no distinct seasonal cycle over the Sichuan Basin. The merged AOD has the largest difference from MODIS over the Sichuan Basin. We also discuss possible benefits of visibility based AOD data that correct the sampling bias in MODIS retrievals related to cloud-free sampling and misclassified heavy haze conditions.

  5. Merging aerosol optical depth data from multiple satellite missions to view agricultural biomass burning in Central and East China

    Science.gov (United States)

    Xue, Y.; Xu, H.; Mei, L.; Guang, J.; Guo, J.; Li, Y.; Hou, T.; Li, C.; Yang, L.; He, X.

    2012-04-01

    Agricultural biomass burning (ABB) in Central and East China occurs every year from May to October and peaks in June. The biomass burning event in June 2007 was very strong. During the period from 26 May to 16 June 2007, ABB occurred mainly in Anhui, Henan, Jiangsu and Shandong provinces. A comprehensive set of aerosol optical depth (AOD) data, produced by a merger of AOD product data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Multiangle Imaging Spectroradiometer (MIRS), is used to study the spatial and temporal distribution of agricultural biomass aerosols in Central and East China combining with ground observations from both AErosol RObotic NETwork (AERONET) and China Aerosol Remote Sensing NETwork (CARSNET) measurements. We compared merged AOD data with single-sensor single-algorithm AOD data (MODIS Dark Target AOD data, MODIS Deep Blue AOD data, SRAP-MODIS AOD data and MISR AOD data). In this comparison, we found merged AOD products can improve the quality of AOD products from single-sensor single-algorithm data sets by expanding the spatial coverage of the study area and keeping the statistical confidence in AOD parameters. There existed high correlation (0.8479) between the merged AOD data and AERONET measurements. Our merged AOD data make use of synergetic information conveyed in all of the available satellite data. The merged AOD data were used for the analysis of the biomass burning event from 26 May to 16 June 2007 together with meteorological data. The merged AOD products and the ground observations from China suggest that biomass burning in Central and East China has had great impact on AOD over China. Influenced by this ABB, the highest AOD value in Beijing on 12 June 2007 reached 5.71.

  6. The comparison of MODIS-Aqua (C5 and CALIOP (V2 & V3 aerosol optical depth

    Directory of Open Access Journals (Sweden)

    J. Redemann

    2012-03-01

    Full Text Available We assess the consistency between instantaneously collocated level-2 aerosol optical depth (AOD retrievals from MODIS-Aqua (C5 and CALIOP (Version 2 & 3, comparing the standard MODIS AOD (MYD04_L2 data to the AOD calculated from CALIOP aerosol extinction profiles for both the previous release (V2 and the latest release (V3 of CALIOP data. Based on data collected in January 2007, we investigate the most useful criteria for screening the MODIS and CALIOP retrievals to achieve the best agreement between the two data sets. Applying these criteria to eight months of data (Jan, Apr, Jul, Oct 2007 and 2009, we find an order of magnitude increase for the CALIOP V3 data density (by comparison to V2, that is generally accompanied by equal or better agreement with MODIS AOD. Differences in global, monthly mean, over-ocean AOD (532 nm between CALIOP and MODIS range between 0.03 and 0.04 for CALIOP V3, with CALIOP generally biased low, when all available data from both sensors are considered. Root-mean-squares (RMS differences in instantaneously collocated AOD retrievals by the two instruments are reduced from values ranging between 0.14 and 0.19 using the unscreened V3 data to values ranging from 0.09 to 0.1 for the screened data. A restriction to scenes with cloud fractions less than 1% (as defined in the MODIS aerosol retrievals generally results in improved correlation (R2>0.5, except for the month of July when correlations remain relatively lower. Regional assessments show hot spots in disagreement between the two sensors in Asian outflow during April and off the coast of South Africa in July.

  7. Inter-comparison of model-simulated and satellite-retrieved componential aerosol optical depths in China

    Science.gov (United States)

    Li, Shenshen; Yu, Chao; Chen, Liangfu; Tao, Jinhua; Letu, Husi; Ge, Wei; Si, Yidan; Liu, Yang

    2016-09-01

    China's large aerosol emissions have major impacts on global climate change as well as regional air pollution and its associated disease burdens. A detailed understanding of the spatiotemporal patterns of aerosol components is necessary for the calculation of aerosol radiative forcing and the development of effective emission control policy. Model-simulated and satellite-retrieved aerosol components can support climate change research, PM2.5 source appointment and epidemiological studies. This study evaluated the total and componential aerosol optical depth (AOD) from the GEOS-Chem model (GC) and the Global Ozone Chemistry Aerosol Radiation and Transport model (GOCART), and the Multiangle Imaging Spectroradiometer (MISR) from 2006 to 2009 in China. Linear regression analysis between the GC and AErosol RObotic NETwork (AERONET) in China yielded similar correlation coefficients (0.6 daily, 0.71 monthly) but lower slopes (0.41 daily, 0.58 monthly) compared with those in the U.S. This difference was attributed to GC's underestimation of water-soluble AOD (WAOD) west of the Heihe-Tengchong Line, the dust AOD (DAOD) in the fall and winter, and the soot AOD (SAOD) throughout the year and throughout the country. GOCART exhibits the strongest dust estimation capability among all datasets. However, the GOCART soot distribution in the Northeast and Southeast has significant errors, and its WAOD in the polluted North China Plain (NCP) and the South is underestimated. MISR significantly overestimates the water-soluble aerosol levels in the West, and does not capture the high dust loadings in all seasons and regions, and the SAOD in the NCP. These discrepancies can mainly be attributed to the uncertainties in the emission inventories of both models, the poor performance of GC under China's high aerosol loading conditions, the omission of certain aerosol tracers in GOCART, and the tendency of MISR to misidentify dust and non-dust mixtures.

  8. Aerosol optical depths at Mohal-Kullu in the northwestern Indian Himalayan high altitude station during ICARB

    Indian Academy of Sciences (India)

    Jagdish C Kuniyal; Alpana Thakur; Harinder K Thakur; Sanjeev Sharma; P Pant; Pan S Rawat; K Krishna Moorthy

    2009-02-01

    First time observations of spectral aerosol optical depths (AODs) at Mohal (31.9°N, 77.11°E; altitude 1154m amsl) in the Kullu valley, located in the northwestern Indian Himalayan region, have been carried out during Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB), as a part of the Indian Space Research Organisation–Geosphere Biosphere Program (ISRO–GBP). AODs at six wavelengths are obtained using Microtops-II Sunphotometer and Ozonometer. The monthly mean values of AOD at 500 nm are found to be 0.27 ± 0.04 and 0.24 ± 0.02 during March and April, 2006 respectively. However, their monthly mean values are 0.33 ± 0.04 at 380 nm and 0.20 ± 0.03 nm at 870 nm during March 2006 and 0.31 ± 0.3 at 380 nm and 0.17 ± 0.2 at 870 nm during April 2006, showing a gradual decrease in AOD with wavelength. The Ångstrom wavelength exponent '' had a mean value of 0.72 ± 0.05, implying reduced dominance of fine particles. Further, the afternoon AOD values are higher as compared to forenoon values by ∼33.0% during March and by ∼9.0% during April 2006 and are attributed to the pollutant lifted up from the valley by the evolving boundary layer. Besides the long-range transportation of aerosol particles by airmass from the Great Sahara and the Thar Desert regions to the observing site, the high values of AODs have also been influenced by biomass burning and frequent incidents of forest fire at local levels.

  9. Spatiotemporal variability and contribution of different aerosol types to the aerosol optical depth over the Eastern Mediterranean

    Science.gov (United States)

    Georgoulias, Aristeidis K.; Alexandri, Georgia; Kourtidis, Konstantinos A.; Lelieveld, Jos; Zanis, Prodromos; Pöschl, Ulrich; Levy, Robert; Amiridis, Vassilis; Marinou, Eleni; Tsikerdekis, Athanasios

    2016-11-01

    This study characterizes the spatiotemporal variability and relative contribution of different types of aerosols to the aerosol optical depth (AOD) over the Eastern Mediterranean as derived from MODIS (Moderate Resolution Imaging Spectroradiometer) Terra (March 2000-December 2012) and Aqua (July 2002-December 2012) satellite instruments. For this purpose, a 0.1° × 0.1° gridded MODIS dataset was compiled and validated against sun photometric observations from the AErosol RObotic NETwork (AERONET). The high spatial resolution and long temporal coverage of the dataset allows for the determination of local hot spots like megacities, medium-sized cities, industrial zones and power plant complexes, seasonal variabilities and decadal averages. The average AOD at 550 nm (AOD550) for the entire region is ˜ 0.22 ± 0.19, with maximum values in summer and seasonal variabilities that can be attributed to precipitation, photochemical production of secondary organic aerosols, transport of pollution and smoke from biomass burning in central and eastern Europe and transport of dust from the Sahara and the Middle East. The MODIS data were analyzed together with data from other satellite sensors, reanalysis projects and a chemistry-aerosol-transport model using an optimized algorithm tailored for the region and capable of estimating the contribution of different aerosol types to the total AOD550. The spatial and temporal variability of anthropogenic, dust and fine-mode natural aerosols over land and anthropogenic, dust and marine aerosols over the sea is examined. The relative contribution of the different aerosol types to the total AOD550 exhibits a low/high seasonal variability over land/sea areas, respectively. Overall, anthropogenic aerosols, dust and fine-mode natural aerosols account for ˜ 51, ˜ 34 and ˜ 15 % of the total AOD550 over land, while, anthropogenic aerosols, dust and marine aerosols account ˜ 40, ˜ 34 and ˜ 26 % of the total AOD550 over the sea, based on

  10. Evaluation of choroidal thickness via enhanced depth-imaging optical coherence tomography in patients with systemic hypertension

    Directory of Open Access Journals (Sweden)

    Mustafa Gök

    2015-01-01

    Full Text Available Purpose: The purpose was to evaluate choroidal thickness via spectral domain optical coherence tomography (SD-OCT and to compare the data with those of 24-h blood pressure monitoring, elastic features of the aorta, and left ventricle systolic functions, in patients with systemic hypertension. Materials and Methods: This was a case-control, cross-sectional prospective study. A total of 116 patients with systemic hypertension, and 116 healthy controls over 45 years of age, were included. Subfoveal choroidal thickness (SFCT was measured using a Heidelberg SD-OCT platform operating in the enhanced depth imaging mode. Patients were also subjected to 24-h ambulatory blood pressure monitoring (ABPM and standard transthoracic echocardiography (STTE. Patients were divided into dippers and nondippers using ABPM data and those with or without left ventricular hypertrophy (LVH+ and LVH- based on STTE data. The elastic parameters of the aorta, thus aortic strain (AoS, the beta index (BI, aortic distensibility (AoD, and the left ventricular mass index (LVMI, were calculated from STTE data. Results: No significant difference in SFCT was evident between patients and controls (P ≤ 0.611. However, a significant negative correlation was evident between age and SFCT in both groups (r = −0.66/−0.56, P ≤ 0.00. No significant SFCT difference was evident between the dipper and nondipper groups (P ≤ 0.67, or the LVH (+ and LVH (- groups (P ≤ 0.84. No significant correlation was evident between SFCT and any of AoS, BI, AoD, or LVMI. Discussion : The choroid is affected by atrophic changes associated with aging. Even in the presence of comorbid risk factors including LVH and arterial stiffness, systemic hypertension did not affect SFCT.

  11. The Two-Column Aerosol Project: Phase I - Overview and Impact of Elevated Aerosol Layers on Aerosol Optical Depth

    Energy Technology Data Exchange (ETDEWEB)

    Berg, Larry K.; Fast, Jerome D.; Barnard, James C.; Burton, Sharon; Cairns, Brian; Chand, Duli; Comstock, Jennifer M.; Dunagan, Stephen; Ferrare, Richard A.; Flynn, Connor J.; Hair, John; Hostetler, Chris A.; Hubbe, John M.; Jefferson, Anne; Johnson, Roy; Kassianov, Evgueni I.; Kluzek, Celine D.; Kollias, Pavlos; Lamer, Katia; Lantz, K.; Mei, Fan; Miller, Mark A.; Michalsky, Joseph; Ortega, Ivan; Pekour, Mikhail S.; Rogers, Ray; Russell, P.; Redemann, Jens; Sedlacek, Art; Segal Rozenhaimer, Michal; Schmid, Beat; Shilling, John E.; Shinozuka, Yohei; Springston, Stephen R.; Tomlinson, Jason M.; Tyrrell, Megan; Wilson, Jacqueline; Volkamer, Rainer M.; Zelenyuk, Alla; Berkowitz, Carl M.

    2016-01-08

    The Two-Column Aerosol Project (TCAP), which was conducted from June 2012 through June 2013, was a unique field study that was designed to provide a comprehensive data set that can be used to investigate a number of important climate science questions, including those related to aerosol mixing state and aerosol radiative forcing. The study was designed to sample the atmosphere at a number of altitudes, from near the surface to as high as 8 km, within two atmospheric columns; one located near the coast of North America (over Cape Cod, MA) and a second over the Atlantic Ocean several hundred kilometers from the coast. TCAP included the yearlong deployment of the U.S. Department of Energy’s (DOE) Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) that was located at the base of the Cape Cod column, as well as summer and winter aircraft intensive observation periods of the ARM Aerial Facility. One important finding from TCAP is the relatively common occurrence (on four of six nearly cloud-free flights) of elevated aerosol layers in both the Cape Cod and maritime columns that were detected using the nadir pointing second-generation NASA high-spectral resolution lidar (HSRL-2). These layers contributed up to 60% of the total aerosol optical depth (AOD) observed in the column. Many of these layers were also intercepted by the aircraft configured for in situ sampling, and the aerosol in the layers was found to have increased amounts of biomass burning aerosol and nitrate compared to the aerosol found near the surface.

  12. Airborne observation of aerosol optical depth during ARCTAS: vertical profiles, inter-comparison and fine-mode fraction

    Directory of Open Access Journals (Sweden)

    Y. Shinozuka

    2011-04-01

    Full Text Available We describe aerosol optical depth (AOD measured during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS experiment, focusing on vertical profiles, inter-comparison with correlative observations and fine-mode fraction. Arctic haze observed in <2 km and 2–4 km over Alaska in April 2008 originated mainly from anthropogenic emission and biomass burning, respectively, according to aerosol mass spectrometry and black carbon incandescence measurements. The Ångström exponent for these air masses is 1.4 ± 0.3 and 1.7 ± 0.1, respectively, when derived at 499 nm from a second-order polynomial fit to the AOD spectra measured with the 14-channel Ames Airborne Tracking Sunphotometer (AATS-14 over 354–2139 nm. We examine 55 vertical profiles selected from all phases of the experiment. For two thirds of them, the AOD spectra are within 3% + 0.02 of the vertical integral of local visible-light scattering and absorption. The horizontal structure of smoke plumes from local biomass burning observed in central Canada in June and July 2008 explains most outliers. The differences in mid-visible Ångström exponent are <0.10 for 63% of the profiles with 499-nm AOD > 0.1. The retrieved fine-mode fraction of AOD is mostly between 0.7 and 1.0, and its root mean square difference (in both directions from column-integral submicron fraction (measured with nephelometers, absorption photometers and an impactor is 0.12. These AOD measurements from the NASA P-3 aircraft, after compensation for below-aircraft light attenuation by vertical extrapolation, mostly fall within ±0.02 of AERONET ground-based measurements between 340–1640 nm for five overpass events.

  13. Validation of MODIS and Deep Blue aerosol optical depth retrievals in an arid/semi-arid region of northwest China

    Institute of Scientific and Technical Information of China (English)

    Xia Li; Xiangao Xia; Shengli Wang; Jietai Mao; Yan Liu

    2012-01-01

    The global aerosol optical depth (AOD or τ) has been retrieved using the Dark Target algorithm (the C004 and C005 products) and the Deep Blue algorithm (DB product).Few validations have thus far been performed in arid/semi-arid regions,especially in northwest China.The ground-based remote sensing of AOD from sun photometers at four sites in Xinjiang during the years 2002-2003 is used to validate aerosol products,including C004,C005 and DB of the Moderate Resolution Imaging Spectroradiometer (MODIS).The results show substantial improvement in the C005 aerosol product over the C004 product.The average correlation coefficient of regression with ground measurements increased from 0.59 to 0.69,and the average offset decreased from 0.28 to 0.13.The slopes of the linear regressions tended to be close to unity.The percentage of AODs falling within the retrieval errors of 30% (or △τ =±0.1 ± 0.2τ)increased from 16.1% to 45.6%.The best retrievals are obtained over an oasis region,whereas the worst are obtained over urban areas.Both the MODIS C004 and C005 products overestimate AOD,which is likely related to improper assumptions of the aerosol model and of the estimation of surface reflectance.An encouraging result has been derived with regard to validation of the DB AOD.Overall,the average offset,slope and correlation coefficient of regression with sun-photometer measurements are -0.04,0.88 and 0.85,respectively.Approximately 73% of the DB AOD retrievals fall within the expected error of 30%.Underestimation of the AOD by the DB products is observed.The aerosol model and estimations of surface reflectance in this region require further improvements.

  14. Assessment of nocturnal aerosol optical depth from lunar photometry at the Izaña high mountain observatory

    Science.gov (United States)

    Barreto, África; Román, Roberto; Cuevas, Emilio; Berjón, Alberto J.; Almansa, A. Fernando; Toledano, Carlos; González, Ramiro; Hernández, Yballa; Blarel, Luc; Goloub, Philippe; Guirado, Carmen; Yela, Margarita

    2017-08-01

    This work is a first approach to correct the systematic errors observed in the aerosol optical depth (AOD) retrieved at nighttime using lunar photometry and calibration techniques dependent on the lunar irradiance model. To this end, nocturnal AOD measurements were performed in 2014 using the CE318-T master Sun-sky-lunar photometer (lunar Langley calibrated) at the Izaña high mountain observatory. This information has been restricted to 59 nights characterized as clean and stable according to lidar vertical profiles. A phase angle dependence as well as an asymmetry within the Moon's cycle of the Robotic Lunar Observatory (ROLO) model could be deduced from the comparison in this 59-night period of the CE318-T calibration performed by means of the lunar Langley calibration and the calibration performed every single night by means of the common Langley technique. Nocturnal AOD has also been compared in the same period with a reference AOD based on daylight AOD extracted from the AErosol RObotic NETwork (AERONET) at the same station. Considering stable conditions, the difference ΔAODfit, between AOD from lunar observations and the linearly interpolated AOD (the reference) from daylight data, has been calculated. The results show that ΔAODfit values are strongly affected by the Moon phase and zenith angles. This dependency has been parameterized using an empirical model with two independent variables (Moon phase and zenith angles) in order to correct the AOD for these residual dependencies. The correction of this parameterized dependency has been checked at four stations with quite different environmental conditions (Izaña, Lille, Carpentras and Dakar) showing a significant reduction of the AOD dependence on phase and zenith angles and an improved agreement with daylight reference data. After the correction, absolute AOD differences for day-night-day clean and stable transitions remain below 0.01 for all wavelengths.

  15. Monitoring and tracking the trans-Pacific transport of aerosols using multi-satellite aerosol optical depth retrievals

    Directory of Open Access Journals (Sweden)

    A. R. Naeger

    2015-10-01

    Full Text Available The primary goal of this study was to generate a near-real time (NRT aerosol optical depth (AOD product capable of providing a comprehensive understanding of the aerosol spatial distribution over the Pacific Ocean in order to better monitor and track the trans-Pacific transport of aerosols. Therefore, we developed a NRT product that takes advantage of observations from both low-earth orbiting and geostationary satellites. In particular, we utilize AOD products from the Moderate Resolution Imaging Spectroradiometer (MODIS and Suomi National Polar-orbiting Partnership (NPP Visible Infrared Imaging Radiometer Suite (VIIRS satellites. Then, we combine these AOD products with our own retrieval algorithms developed for the NOAA Geostationary Operational Environmental Satellite (GOES-15 and Japan Meteorological Agency (JMA Multi-functional Transport Satellite (MTSAT-2 to generate a NRT daily AOD composite product. We present examples of the daily AOD composite product for a case study of trans-Pacific transport of Asian pollution and dust aerosols in mid-March 2014. Overall, the new product successfully tracks this aerosol plume during its trans-Pacific transport to the west coast of North America. However, we identify several areas across the domain of interest from Asia to North America where the new product can encounter significant uncertainties due to the inclusion of the geostationary AOD retrievals. The uncertainties associated with geostationary AOD retrievals are expected to be minimized after the successful launch of the next-generation advanced NOAA GOES-R and recently launched JMA Himawari satellites. Observations from these advanced satellites will ultimately provide an enhanced understanding of the spatial and temporal distribution of aerosols over the Pacific.

  16. A simplified method to measure choroidal thickness using adaptive compensation in enhanced depth imaging optical coherence tomography.

    Directory of Open Access Journals (Sweden)

    Preeti Gupta

    Full Text Available PURPOSE: To evaluate a simplified method to measure choroidal thickness (CT using commercially available enhanced depth imaging (EDI spectral domain optical coherence tomography (SD-OCT. METHODS: We measured CT in 31 subjects without ocular diseases using Spectralis EDI SD-OCT. The choroid-scleral interface of the acquired images was first enhanced using a post-processing compensation algorithm. The enhanced images were then analysed using Photoshop. Two graders independently graded the images to assess inter-grader reliability. One grader re-graded the images after 2 weeks to determine intra-grader reliability. Statistical analysis was performed using intra-class correlation coefficient (ICC and Bland-Altman plot analyses. RESULTS: Using adaptive compensation both the intra-grader reliability (ICC: 0.95 to 0.97 and inter-grader reliability (ICC: 0.93 to 0.97 were perfect for all five locations of CT. However, with the conventional technique of manual CT measurements using built-in callipers provided with the Heidelberg explorer software, the intra- (ICC: 0.87 to 0.94 and inter-grader reliability (ICC: 0.90 to 0.93 for all the measured locations is lower. Using adaptive compensation, the mean differences (95% limits of agreement for intra- and inter-grader sub-foveal CT measurements were -1.3 (-3.33 to 30.8 µm and -1.2 (-36.6 to 34.2 µm, respectively. CONCLUSIONS: The measurement of CT obtained from EDI SD-OCT using our simplified method was highly reliable and efficient. Our method is an easy and practical approach to improve the quality of choroidal images and the precision of CT measurement.

  17. Investigating relationships between aerosol optical depth and cloud fraction using satellite, aerosol reanalysis and general circulation model data

    Directory of Open Access Journals (Sweden)

    B. S. Grandey

    2013-03-01

    Full Text Available Strong positive relationships between cloud fraction (fc and aerosol optical depth (τ have been reported. Data retrieved from the MODerate resolution Imaging Spectroradiometer (MODIS instrument show positive fc–τ relationships across most of the globe. A global mean fc increase of approximately 0.2 between low and high τ conditions is found for both ocean and land. However, these relationships are not necessarily due to cloud–aerosol interactions. Using state-of-the-art Monitoring Atmospheric Composition and Climate (MACC reanalysis-forecast τ data, which should be less affected by retrieval artefacts, it is demonstrated that a large part of the observed fc–τ signal may be due to cloud contamination of satellite-retrieved τ. For longer MACC forecast time steps of 24 h, which likely contain less cloud contamination, some negative fc–τ relationships are found. The global mean fc increase between low and high τ conditions is reduced to 0.1, suggesting that cloud contamination may account for approximately one half of the satellite-retrieved increase in fc. ECHAM5-HAM general circulation model (GCM simulations further demonstrate that positive fc–τ relationships may arise due to covariation with relative humidity. Widespread negative simulated fc–τ relationships in the tropics are shown to arise due to scavenging of aerosol by convective precipitation. Wet scavenging events are likely poorly sampled in satellite-retrieved data, because the properties of aerosol below clouds cannot be retrieved. Quantifying the role of wet scavenging, and assessing GCM representations of this important process, remains a challenge for future observational studies of aerosol–cloud–precipitation interactions.

  18. Assessment of nocturnal aerosol optical depth from lunar photometry at the Izaña high mountain observatory

    Directory of Open Access Journals (Sweden)

    Á. Barreto

    2017-08-01

    Full Text Available This work is a first approach to correct the systematic errors observed in the aerosol optical depth (AOD retrieved at nighttime using lunar photometry and calibration techniques dependent on the lunar irradiance model. To this end, nocturnal AOD measurements were performed in 2014 using the CE318-T master Sun–sky–lunar photometer (lunar Langley calibrated at the Izaña high mountain observatory. This information has been restricted to 59 nights characterized as clean and stable according to lidar vertical profiles. A phase angle dependence as well as an asymmetry within the Moon's cycle of the Robotic Lunar Observatory (ROLO model could be deduced from the comparison in this 59-night period of the CE318-T calibration performed by means of the lunar Langley calibration and the calibration performed every single night by means of the common Langley technique. Nocturnal AOD has also been compared in the same period with a reference AOD based on daylight AOD extracted from the AErosol RObotic NETwork (AERONET at the same station. Considering stable conditions, the difference ΔAODfit, between AOD from lunar observations and the linearly interpolated AOD (the reference from daylight data, has been calculated. The results show that ΔAODfit values are strongly affected by the Moon phase and zenith angles. This dependency has been parameterized using an empirical model with two independent variables (Moon phase and zenith angles in order to correct the AOD for these residual dependencies. The correction of this parameterized dependency has been checked at four stations with quite different environmental conditions (Izaña, Lille, Carpentras and Dakar showing a significant reduction of the AOD dependence on phase and zenith angles and an improved agreement with daylight reference data. After the correction, absolute AOD differences for day–night–day clean and stable transitions remain below 0.01 for all wavelengths.

  19. Area- and Depth-Weighted Averages of Selected SSURGO Variables for the Conterminous United States and District of Columbia

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This digital data release consists of seven national data files of area- and depth-weighted averages of select soil attributes for every available county in the...

  20. Spectral Discrimination of Fine and Coarse Mode Aerosol Optical Depth from AERONET Direct Sun Data of Singapore and South-East Asia

    Science.gov (United States)

    Salinas Cortijo, S.; Chew, B.; Liew, S.

    2009-12-01

    Aerosol optical depth combined with the Angstrom exponent and its derivative, are often used as a qualitative indicator of aerosol particle size, with Angstrom exp. values greater than 2 indicating small (fine mode) particles associated with urban pollution and bio-mass burning. Around this region, forest fires are a regular occurrence during the dry season, specially near the large land masses of Sumatra and Borneo. The practice of clearing land by burning the primary and sometimes secondary forest, results in a smog-like haze covering large areas of regional cities such as cities Singapore, Kuala Lumpur and sometimes the south of Thailand, often reducing visibility and increasing health problems for the local population. In Singapore, the sources of aerosols are mostly from fossil fuel burning (energy stations, incinerators, urban transport etc.) and from the industrial and urban areas. The proximity to the sea adds a possible oceanic source. However, as stated above and depending on the time of the year, there can be a strong bio-mass component coming from forest fires from various regions of the neighboring countries. Bio-mass related aerosol particles are typically characterized by showing a large optical depth and small, sub-micron particle size distributions. In this work, we analyze three years of direct Sun measurements performed with a multi-channel Cimel Sun-Photometer (part of the AERONET network) located at our site. In order to identify bio-mass burning events in this region, we perform a spectral discrimination between coarse and fine mode optical depth; subsequently, the fine mode parameters such as optical depth, optical ratio and fine mode Angstrom exponents (and its derivative) are used to identify possible bio-mass related events within the data set.

  1. Neutral Hydrogen Optical Depth near Star-forming Galaxies at z ≈ 2.4 in the Keck Baryonic Structure Survey

    Science.gov (United States)

    Rakic, Olivera; Schaye, Joop; Steidel, Charles C.; Rudie, Gwen C.

    2012-06-01

    We study the interface between galaxies and the intergalactic medium by measuring the absorption by neutral hydrogen in the vicinity of star-forming galaxies at z ≈ 2.4. Our sample consists of 679 rest-frame UV-selected galaxies with spectroscopic redshifts that have impact parameters background QSOs and that fall within the redshift range of its Lyα forest. We present the first two-dimensional maps of the absorption around galaxies, plotting the median Lyα pixel optical depth as a function of transverse and line-of-sight separation from galaxies. The Lyα optical depths are measured using an automatic algorithm that takes advantage of all available Lyman series lines. The median optical depth, and hence the median density of atomic hydrogen, drops by more than an order of magnitude around 100 kpc, which is similar to the virial radius of the halos thought to host the galaxies. The median remains enhanced, at the >3σ level, out to at least 2.8 Mpc (i.e., >9 comoving Mpc), but the scatter at a given distance is large compared with the median excess optical depth, suggesting that the gas is clumpy. Within 100 (200) kpc, and over ±165 km s-1, the covering fraction of gas with Lyα optical depth greater than unity is 100+0 - 32% (66% ± 16%). Absorbers with τLyα > 0.1 are typically closer to galaxies than random. The mean galaxy overdensity around absorbers increases with the optical depth and also as the length scale over which the galaxy overdensity is evaluated is decreased. Absorbers with τLyα ~ 1 reside in regions where the galaxy number density is close to the cosmic mean on scales >=0.25 Mpc. We clearly detect two types of redshift space anisotropies. On scales 3σ significance), an effect that we attribute to large-scale infall (i.e., the Kaiser effect). Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made

  2. Perception of scene-relative object movement: Optic flow parsing and the contribution of monocular depth cues

    National Research Council Canada - National Science Library

    Warren, Paul A; Rushton, Simon K

    2009-01-01

    ...). Here, we explore whether stereo disparity is necessary for flow parsing or whether other sources of depth information, which could theoretically constrain flow-field interpretation, are sufficient...

  3. Comparison of GOES and MODIS aerosol optical depth (AOD) to aerosol robotic network (AERONET) AOD and IMPROVE PM2.5 mass at Bondville, Illinois.

    Science.gov (United States)

    Green, Mark; Kondragunta, Shobha; Ciren, Pubu; Xu, Chuanyu

    2009-09-01

    Collocated Interagency Monitoring of Protected Visual Environments (IMPROVE) particulate matter (PM) less than 2.5 microm in aerodynamic diameter (PM2.5) chemically speciated data, mass of PM less than 10 microm in aerodynamic diameter (PM10), and Aerosol Robotic Network (AERONET) aerosol optical depth (AOD) and size distribution at Bondville, IL, were compared with satellite-derived AOD. This was done to evaluate the quality of the Geostationary Operational Environmental Satellite (GOES) and Moderate Resolution Imaging Spectroradiometer (MODIS) AOD data and their potential to predict surface PM2.5 concentrations. MODIS AOD correlated better to AERONET AOD (r = 0.835) than did GOES AOD (r = 0.523). MODIS and GOES AOD compared better to AERONET AOD when the particle size distribution was dominated by fine mode. For all three AOD methods, correlation between AOD and PM2.5 concentration was highest in autumn and lowest in winter. The AERONET AOD-PM2.5 relationship was strongest with moderate relative humidity (RH). At low RH, AOD attributable to coarse mass degrades the relationship; at high RH, added AOD from water growth appears to mask the relationship. For locations such as many in the central and western United States with substantial coarse mass, coarse mass contributions to AOD may make predictions of PM2.5 from AOD data problematic. Seasonal and diurnal variations in particle size distributions, RH, and seasonal changes in boundary layer height need to be accounted for to use satellite AOD to predict surface PM2.5.

  4. Retrievals of aerosol optical depth and total column ozone from Ultraviolet Multifilter Rotating Shadowband Radiometer measurements based on an optimal estimation technique

    Science.gov (United States)

    Liu, Chaoshun; Chen, Maosi; Shi, Runhe; Gao, Wei

    2014-12-01

    A Bayesian optimal estimation (OE) retrieval technique was used to retreive aerosol optical depth (AOD), aerosol single scattering albedo (SSA), and an asymmetry factor ( g) at seven ultraviolet wavelengths, along with total column ozone (TOC), from the measurements of the UltraViolet Multifilter Rotating Shadowband Radiometer (UV-MFRSR) deployed at the Southern Great Plains (SGP) site during March through November in 2009. The OE technique specifies appropriate error covariance matrices and optimizes a forward model (Tropospheric ultraviolet radiative transfer model, TUV), and thus provides a supplemental method for use across the network of the Department of Agriculture UV-B Monitoring and Research Program (USDA UVMRP) for the retrieval of aerosol properties and TOC with reasonable accuracy in the UV spectral range under various atmospheric conditions. In order to assess the accuracy of the OE technique, we compared the AOD retreivals from this method with those from Beer's Law and the AErosol RObotic Network (AERONET) AOD product. We also examine the OE retrieved TOC in comparison with the TOC from the U.S. Department of Agriculture UV-B Monitoring and Research Program (USDA UVMRP) and the Ozone Monitoring Instrument (OMI) satellite data. The scatterplots of the estimated AOD from the OE method agree well with those derived from Beer's law and the collocated AERONETAOD product, showing high values of correlation coefficients, generally 0.98 and 0.99, and large slopes, ranging from 0.95 to 1.0, as well as small offsets, less than 0.02 especially at 368 nm. The comparison of TOC retrievals also indicates the promising accuracy of the OE method in that the standard deviations of the difference between the OE derived TOC and other TOC products are about 5 to 6 Dobson Units (DU). Validation of the OE retrievals on these selected dates suggested that the OE technique has its merits and can serve as a supplemental tool in further analyzing UVMRP data.

  5. Real-time Graphics Processing Unit Based Fourier Domain Optical Coherence Tomography and Surgical Applications

    Science.gov (United States)

    Zhang, Kang

    2011-12-01

    In this dissertation, real-time Fourier domain optical coherence tomography (FD-OCT) capable of multi-dimensional micrometer-resolution imaging targeted specifically for microsurgical intervention applications was developed and studied. As a part of this work several ultra-high speed real-time FD-OCT imaging and sensing systems were proposed and developed. A real-time 4D (3D+time) OCT system platform using the graphics processing unit (GPU) to accelerate OCT signal processing, the imaging reconstruction, visualization, and volume rendering was developed. Several GPU based algorithms such as non-uniform fast Fourier transform (NUFFT), numerical dispersion compensation, and multi-GPU implementation were developed to improve the impulse response, SNR roll-off and stability of the system. Full-range complex-conjugate-free FD-OCT was also implemented on the GPU architecture to achieve doubled image range and improved SNR. These technologies overcome the imaging reconstruction and visualization bottlenecks widely exist in current ultra-high speed FD-OCT systems and open the way to interventional OCT imaging for applications in guided microsurgery. A hand-held common-path optical coherence tomography (CP-OCT) distance-sensor based microsurgical tool was developed and validated. Through real-time signal processing, edge detection and feed-back control, the tool was shown to be capable of track target surface and compensate motion. The micro-incision test using a phantom was performed using a CP-OCT-sensor integrated hand-held tool, which showed an incision error less than +/-5 microns, comparing to >100 microns error by free-hand incision. The CP-OCT distance sensor has also been utilized to enhance the accuracy and safety of optical nerve stimulation. Finally, several experiments were conducted to validate the system for surgical applications. One of them involved 4D OCT guided micro-manipulation using a phantom. Multiple volume renderings of one 3D data set were

  6. Changes in ground-level PM mass concentration and column aerosol optical depth over East Asia during 2004-2014

    Science.gov (United States)

    Nam, J.; Kim, S. W.; Park, R.; Yoon, S. C.; Sugimoto, N.; Park, J. S.; Hong, J.

    2015-12-01

    Multi-year records of moderate resolution imaging spectroradiometer (MODIS), ground-level particulate matter (PM) mass concentration, cloud-aerosol lidar with orthogonal polarization (CALIOP), and ground-level lidar were analyzed to investigate seasonal and annual changes of aerosol optical depth (AOD) and PM mass concentration over East Asia. Least mean square fit method is applied to detect the trends and their magnitudes for each selected regions and stations. Eleven-year MODIS measurements show generally increasing trends in both AOD (1.18 % yr-1) and Ångström exponent (0.98 % yr-1), especially over the east coastal industrialized region in China. Monthly variation of AOD show maximum value at April-July, which were related to the progress of summer monsoon rain band and stationary continental air mass on the northeast of Asia. Increasing trends of AOD were found for eight cites in China (0.80 % yr-1) and Seoul site, Korea (0.40 % yr-1), whereas no significant change were shown in Gosan background site (0.04 % yr-1) and decreasing trend at five background sites in Japan (-0.42 % yr-1). Contrasting to AOD trend, all fifteen sites in China (-1.28 % yr-1), Korea (-2.77 % yr-1), and Japan (-2.03 % yr-1) showed decreasing trend of PM10 mass concentration. Also, PM2.5 mass concentration at Beijing, Seoul, Rishiri, and Oki show significant decreasing trend of -1.16 % yr-1. To further discuss the opposite trend of surface PM mass concentration and column AOD, we investigate vertical aerosol profile from lidar measurements. AOD estimated for planetary boundary layer (surface~1.5 km altitude; AODPBL) from CALIOP measurements over East China show decreasing trend of -1.71 % yr-1 over the period of 2007-2014, wherever AOD estimated for free troposphere (1.5 km~5 km altitude; AODFT) show increasing trend of 2.92 % yr-1. In addition, ground-level lidar measurements in Seoul show decreasing AODPBL trend of -2.57 % yr-1, whereas, AODFT show no significant change (-0.44 % yr

  7. Constraining Black Carbon Aerosol over Asia using OMI Aerosol Absorption Optical Depth and the Adjoint of GEOS-Chem

    Science.gov (United States)

    Zhang, Li; Henze, David K.; Grell, Georg A.; Carmichael. Gregory R.; Bousserez, Nicolas; Zhang, Qiang; Torres, Omar; Ahn, Changwoo; Lu, Zifeng; Cao, Junji; Mao, Yuhao

    2015-01-01

    Accurate estimates of the emissions and distribution of black carbon (BC) in the region referred to here as Southeastern Asia (70degE-l50degE, 11degS-55degN) are critical to studies of the atmospheric environment and climate change. Analysis of modeled BC concentrations compared to in situ observations indicates levels are underestimated over most of Southeast Asia when using any of four different emission inventories. We thus attempt to reduce uncertainties in BC emissions and improve BC model simulations by developing top-down, spatially resolved, estimates of BC emissions through assimilation of OMI observations of aerosol absorption optical depth (AAOD) with the GEOS-Chem model and its adjoint for April and October of 2006. Overwhelming enhancements, up to 500%, in anthropogenic BC emissions are shown after optimization over broad areas of Southeast Asia in April. In October, the optimization of anthropogenic emissions yields a slight reduction (1-5%) over India and parts of southern China, while emissions increase by 10-50% over eastern China. Observational data from in situ measurements and AERONET observations are used to evaluate the BC inversions and assess the bias between OMI and AERONET AAOD. Low biases in BC concentrations are improved or corrected in most eastern and central sites over China after optimization, while the constrained model still underestimates concentrations in Indian sites in both April and October, possibly as a. consequence of low prior emissions. Model resolution errors may contribute up to a factor of 2.5 to the underestimate of surface BC concentrations over northern India. We also compare the optimized results using different anthropogenic emission inventories and discuss the sensitivity of top-down constraints on anthropogenic emissions with respect to biomass burning emissions. In addition, the impacts of brown carbon, the formulation of the observation operator, and different a priori constraints on the optimization are

  8. A new zenith-looking narrow-band radiometer-based system (ZEN) for dust aerosol optical depth monitoring

    Science.gov (United States)

    Almansa, A. Fernando; Cuevas, Emilio; Torres, Benjamín; Barreto, África; García, Rosa D.; Cachorro, Victoria E.; de Frutos, Ángel M.; López, César; Ramos, Ramón

    2017-02-01

    A new zenith-looking narrow-band radiometer based system (ZEN), conceived for dust aerosol optical depth (AOD) monitoring, is presented in this paper. The ZEN system comprises a new radiometer (ZEN-R41) and a methodology for AOD retrieval (ZEN-LUT). ZEN-R41 has been designed to be stand alone and without moving parts, making it a low-cost and robust instrument with low maintenance, appropriate for deployment in remote and unpopulated desert areas. The ZEN-LUT method is based on the comparison of the measured zenith sky radiance (ZSR) with a look-up table (LUT) of computed ZSRs. The LUT is generated with the LibRadtran radiative transfer code. The sensitivity study proved that the ZEN-LUT method is appropriate for inferring AOD from ZSR measurements with an AOD standard uncertainty up to 0.06 for AOD500 nm ˜ 0.5 and up to 0.15 for AOD500 nm ˜ 1.0, considering instrumental errors of 5 %. The validation of the ZEN-LUT technique was performed using data from AErosol RObotic NETwork (AERONET) Cimel Electronique 318 photometers (CE318). A comparison between AOD obtained by applying the ZEN-LUT method on ZSRs (inferred from CE318 diffuse-sky measurements) and AOD provided by AERONET (derived from CE318 direct-sun measurements) was carried out at three sites characterized by a regular presence of desert mineral dust aerosols: Izaña and Santa Cruz in the Canary Islands and Tamanrasset in Algeria. The results show a coefficient of determination (R2) ranging from 0.99 to 0.97, and root mean square errors (RMSE) ranging from 0.010 at Izaña to 0.032 at Tamanrasset. The comparison of ZSR values from ZEN-R41 and the CE318 showed absolute relative mean bias (RMB) < 10 %. ZEN-R41 AOD values inferred from ZEN-LUT methodology were compared with AOD provided by AERONET, showing a fairly good agreement in all wavelengths, with mean absolute AOD differences < 0.030 and R2 higher than 0.97.

  9. Recovering Long-term Aerosol Optical Depth Series (1976–2012 from an Astronomical Potassium-based Resonance Scattering Spectrometer

    Directory of Open Access Journals (Sweden)

    A. Barreto

    2014-04-01

    Full Text Available A 37 year long-term series of monochromatic Aerosol Optical Depth (AOD has been recovered from solar irradiance measurements performed with the solar spectrometer Mark-I, deployed at Izaña mountain since 1976. The instrument operation is based on the method of resonant scattering, which presents a long-term stability and high precision in comparison to other instruments based on interference filters. However, it has been specifically designed as a reference instrument for helioseismology, and its ability to determine AOD from transmitted and scattered monochromatic radiation at 769.9 nm inside a potassium vapor cell in the presence of a permanent magnetic field is evaluated in this paper. Particularly, the use of an exposed mirrors arrangement to collect sunlight as well as the Sun-laboratory velocity dependence of the scattered component introduces some inconveniences when we perform the instrument's calibration. We have solved this problem using a quasi-continuous Langley calibration technique and a refinement procedure to correct for calibration errors as well as for the fictitious diurnal cycle on AOD data. Our results showed that calibration errors associated to the quasi-continuous Langley technique are not dependent on aerosol load, provided aerosol concentration remains constant throughout the day, assuring the validity of this technique for those periods with relatively high aerosol content required to calibrate the scattered component. The comparative analysis between the recovered AOD dataset from Mark-I and collocated quasi-simultaneous data from Cimel AErosol RObotic NETwork (AERONET and Precision Filter Radiometer (PFR instruments showed an absolute mean bias ≤ 0.01 in the 11 year and 12 year comparison, respectively. High correlation coefficients between AERONET/Mark-I and PFR/Mark-I pairs confirmed a very good linear relationship between instruments, proving that recovered AOD data series from Mark-I can be used together PFR

  10. Utility of MODIS Aerosol Optical Depth for Estimating PM2.5 Exposure in Environmental Public Health Surveillance

    Science.gov (United States)

    Al-Hamdan, Mohammad; Crosson, William; Limaye, Ashutosh; Rickman, Doug; Quattrochi, Dale; Estes, Maury; Adeniyi, Kafayat; Qualters, Judith; Niskar, Amanda Sue

    2006-01-01

    , including PM(2.5). Thus, HELIX-Atlanta is focusing on methods for characterizing population exposure to PM(2.5) for the Atlanta metropolitan area that could be used in on-going surveillance. While use of the Air Quality System, (AQS) PM(2.5) data alone could meet HELIX Atlanta, specifications, there are only five AQS sites in the Atlanta area, thus the spatial coverage is not ideal. Also, the AQS ground observations are made at time intervals ranging from one hour to six days leaving some temporal gaps. NASA Moderate Resolution Imaging Spectroradiometer (MODIS) satellite Aerosol Optical Depth (AOD) data have the potential for estimating daily ground level PM(2.5) at 10 km resolution over the metropolitan Atlanta area supplementing the AQS ground observations and filling their spatial and temporal gaps.

  11. Aerosol data assimilation in the chemical transport model MOCAGE during the TRAQA/ChArMEx campaign: aerosol optical depth

    Science.gov (United States)

    Sič, Bojan; El Amraoui, Laaziz; Piacentini, Andrea; Marécal, Virginie; Emili, Emanuele; Cariolle, Daniel; Prather, Michael; Attié, Jean-Luc

    2016-11-01

    In this study, we describe the development of the aerosol optical depth (AOD) assimilation module in the chemistry transport model (CTM) MOCAGE (Modèle de Chimie Atmosphérique à Grande Echelle). Our goal is to assimilate the spatially averaged 2-D column AOD data from the National Aeronautics and Space Administration (NASA) Moderate-resolution Imaging Spectroradiometer (MODIS) instrument, and to estimate improvements in a 3-D CTM assimilation run compared to a direct model run. Our assimilation system uses 3-D-FGAT (first guess at appropriate time) as an assimilation method and the total 3-D aerosol concentration as a control variable. In order to have an extensive validation dataset, we carried out our experiment in the northern summer of 2012 when the pre-ChArMEx (CHemistry and AeRosol MEditerranean EXperiment) field campaign TRAQA (TRAnsport à longue distance et Qualité de l'Air dans le bassin méditerranéen) took place in the western Mediterranean basin. The assimilated model run is evaluated independently against a range of aerosol properties (2-D and 3-D) measured by in situ instruments (the TRAQA size-resolved balloon and aircraft measurements), the satellite Spinning Enhanced Visible and InfraRed Imager (SEVIRI) instrument and ground-based instruments from the Aerosol Robotic Network (AERONET) network. The evaluation demonstrates that the AOD assimilation greatly improves aerosol representation in the model. For example, the comparison of the direct and the assimilated model run with AERONET data shows that the assimilation increased the correlation (from 0.74 to 0.88), and reduced the bias (from 0.050 to 0.006) and the root mean square error in the AOD (from 0.12 to 0.07). When compared to the 3-D concentration data obtained by the in situ aircraft and balloon measurements, the assimilation consistently improves the model output. The best results as expected occur when the shape of the vertical profile is correctly simulated by the direct model. We

  12. Prediction of Hourly Particulate Matter Concentrations in Chiangmai, Thailand Using MODIS Aerosol Optical Depth and Ground-Based Meteorological Data

    Directory of Open Access Journals (Sweden)

    Thongchai Kanabkaew

    2013-07-01

    Full Text Available Various extreme events recorded over the world have been recognized as scientific-based evidence from possible climate change and variability. The incidence of increasing forest fires and intensive agricultural field burning in Chiangmai and Northern Thailand due to favor conditions may also due to a likely increase of droughts caused by the changing climate. Smog from biomass burning, particularly particulate matter (PM seriously affects health and the environment. Lack and sparse of ground monitors may cause unreliability for warning information. Satellite remote sensing is now a promising technology for air quality prediction at ground level. This study was to investigate the statistical model for predicting PM concentration using satellite data. Aerosol optical depth (AOD data were gathered from MODIS-Terra platform while hourly PM2.5 and PM10 data were collected from the Pollution Control Department. The relationship between AOD and hourly PM over Chiangmai was addressed by Model I-Simple linear regression and Model II-Multiple linear regression with ground-based meteorological data correction. The data used for the statistical analyses were from smog period in 2012 (January-April. Results revealed that AOD and hourly PM in Model I were positively correlated with the coefficient of determination (R2 of 0.22 and 0.21, respectively for PM2.5 and PM10. The relationship between AOD and hourly PM was improved significantly when correcting with relative humidity and temperature data. The model II gave R2 of 0.77 and 0.71, respectively for PM2.5 and PM10. To investigate the validity of model, the regression equation obtained from Model II was then applied with smog data over Chiangmai in March 2007. The model performed reasonably with R2 of 0.74. The model applications would provide supplementary data to other areas with similar conditions and without air quality monitoring stations, and reduce false warning the level of air pollution associated

  13. Simultaneous Retrieval of Aerosol Optical Depth and Surface Reflectance over Land within Short Temporal Interval Using MSG Data

    Science.gov (United States)

    Li, C.; Xue, Y.; Li, Y. J.; Yang, L. K.; Hou, T. T.

    2012-04-01

    Aerosols cause a major uncertainty in the research of climatology and global change, whereas satellite aerosol remote sensing over land still remains a big challenge. Due to their short time repeat cycle, geostationary satellites are capable of monitoring the temporal features of aerosols, while its limited number of visible bands is an obstacle. On the other hand, a main uncertainty in aerosol retrieval is the difficulty to separate the relatively weaker contribution of the atmosphere to the signal received by the satellite from the contribution of the Earth's surface. In this paper, an analytical retrieval strategy is presented to solve the both problems above. For the lack of surface reflectance, we use the Ross-Li BRDF (Bidirectional Reflectance Distribution Function) model and assume that the surface reflective property changes mainly due to the change of illumination geometry in a short time interval while the kernals of Ross-Li model remain the same. For the limited visible band, we take advantage of the Aerosol Optical Depth (AOD) consistence within short distances, thus to reduce the number of unknown parameters. A parameterization of the atmospheric radiative transfer model is used which is proved to be proper to retrieve aerosol and surface parameters by sensitivity analysis. Taking the three kernels of kernel-driven BRDF model and AOD as unknown parameters and based on prior knowledge of aerosol types, a series of nonlinear equations can be established then. Both AOD and surface reflectance can be obtained by using a numerical method to solve these equations. By applying this method, called LABITS-MSG (Land Aerosol and Bidirectional reflectance Inversion by Time Series technique for MSG), to data from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) observations on board Meteosat Second Generation (MSG), we obtain regional maps of AOD and surface reflectance in July 11, 2010 within a temporal interval of as short as 1 hour, and a spatial

  14. Airborne observation of aerosol optical depth during ARCTAS: vertical profiles, inter-comparison, fine-mode fraction and horizontal variability

    Directory of Open Access Journals (Sweden)

    Y. Shinozuka

    2010-08-01

    Full Text Available We describe aerosol optical depth (AOD measured during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS experiment, conducted in North America in April and June–July 2008, focusing on vertical profiles, inter-comparison with correlative observations, fine-mode fraction and horizontal variability. The AOD spectra spanning 354–2139 nm measured with the 14-channel Ames Airborne Tracking Sunphotometer (AATS-14 are generally less wavelength-dependent below 2 km (499-nm Angstrom exponent 1.4 ± 0.3 than in 2–4 km (1.6–1.8 for Alaska in April 2008. Together with concurrent aerosol mass spectrometry and black carbon incandescence measurements, this corroborates the hypothesis that Arctic haze in these layers originates mainly from anthropogenic emission and biomass burning, respectively. The spectra are within 3%+0.02 of the vertical integral of local visible-light scattering and absorption for two thirds of the 55 vertical profiles examined. The horizontal structure of smoke plumes in central Canada in June and July 2008 explains most outliers. The differences in mid-visible Angstrom exponent are <0.10 for 63% of the profiles with 499-nm AOD>0.1. The retrieved fine-mode fraction of AOD is mostly between 0.7 and 1.0, and its root mean square difference from column-integral submicron fraction (measured with nephelometers, absorption photometers and an impactor is 0.12. These AOD measurements from the NASA P-3 aircraft, after compensation for below-aircraft light attenuation by vertical extrapolation, mostly fall within 0.02 of AERONET ground-based measurements for five overpass events. Evidently, the fresh local emission in Canada in June and July makes the horizontal distribution of AOD highly heterogeneous (standard deviation ~19% of the mean over 20 km and random (autocorrelation r=0.37 across 20 km, in contrast to long-range transport to Alaska in April (std~2%, r=0.95. The

  15. Detailed Aerosol Optical Depth Intercomparison between Brewer and Li-Cor 1800 Spectroradiometers and a Cimel Sun Photometer

    Energy Technology Data Exchange (ETDEWEB)

    Cachorro, V. E.; Berjon, A.; Toledano, C.; Mogo, S.; Prats, N.; de Frutos, A. M.; Sorribas, M.; Vilaplana, J. M.; de la Morena, B. A.; Grobner, Julian; Laulainen, Nels

    2009-08-01

    We present here representative results about a comparison of aerosol optical depth (AOD) using different instruments during three short and intensive campaigns carried out from 1999 to 2001 at El Arenosillo (Huelva, Spain). The specific aim of this study is to determine the level of agreement between three different instruments operating at our station. This activity, however, is part of a broader objective to recover an extended data series of AOD in the UV range obtained from a Brewer spectroradiometer. This instrument may be used to obtain AOD at the same five UV wavelengths used during normal operation for ozone content determination. As part of the validation of the Brewer AOD data recovery process, a Cimel sun photometer and another spectroradiometer, a Licor1800, were used. The Licor1800 spectroradiometer (which covers the spectral range 300-1100 nm) was the first instrument used at this station for aerosol monitoring (1996-99) and it was operated during these intercomparison campaigns (1999-2001) specifically to assess the continuity of the AOD data series. The Cimel sunphotometer was installed at our station at the beginning of 2000 as part of AERONET to provide AOD data over the visible and near infrared spectrum. A detailed comparison of these three instruments is carried out by means of near-simultaneous measurements, with particular emphasis on examining any diurnal AOD variability that may be linked with calibration and/or measurement errors or real atmospheric variability. Because the comparison is carried out from UV (320nm) to near infrared (1020nm) wavelengths under all possible atmospheric conditions (including clouds), AOD values range from near zero up to 1. Absolute AOD uncertainties range from 0.02 for the Cimel to 0.08 for the Brewer, with intermediate values for the Licor1800. All the values during the comparison are in reasonable agreement, when taking into account the different performance characteristics of each instrument. The

  16. Spatial distribution and temporal variation of aerosol optical depth in the Sichuan basin, China, the recent ten years

    Science.gov (United States)

    Liu, Xinyu; Chen, Quanliang; Che, Huizheng; Zhang, Renjian; Gui, Ke; Zhang, Huan; Zhao, Tianliang

    2016-12-01

    The applicability of the MODIS (Moderate Resolution Imaging Spectroradiometer) aerosol optical depth (AOD) product was verified using CE-318 sun photometric data for the Sichuan area. The results show that MODIS_3K AOD agrees well with the AOD derived from the CE-318 sun photometer, with a high correlation coefficient (R2 = 0.91). And we used the MODIS AOD product analyzed the spatial distribution and temporal variation of the annual, seasonal and monthly distribution of AOD in the Sichuan area over the last ten years (2006-2015). In the Sichuan area, the mean change of AOD over the 10-year period showed a significant decreasing trend, reaching its maximum in 2010 and its minimum in 2015. Considering only the first five years, the lowest value was reached in 2008 and the overall trend was a standard symmetrical "V" type. Over the later five years, the annual average AOD value showed an overall decreasing trend. The monthly averaged AOD indicated a "double peaks" fluctuation trend; the two peaks appeared in March and August, and AOD changes were relatively small between September and January. Overall, the average value of AOD reached its highest values in spring, and its lowest values in autumn. In the city of Chengdu, the monthly and seasonal changes in the trend were essentially the same as those of the whole Sichuan area; However, the Chengdu AOD monthly and seasonal average change rate was higher than that of Sichuan as a whole. This shows that Chengdu is still the main contributor to the enhanced AOD value for the entire Sichuan region. The spatial distribution of AOD values indicates an "east high, west low" situation across the Sichuan area and Chengdu is one of three cities with the highest AOD values. However, the spatial variation of AOD trend value indicated an "east low, west high" the spatial distribution across the Sichuan region, opposite to the spatial distribution. Moreover, in the past 10 years, the overall AOD changes in Sichuan showed a downward

  17. Recovering long-term aerosol optical depth series (1976–2012 from an astronomical potassium-based resonance scattering spectrometer

    Directory of Open Access Journals (Sweden)

    A. Barreto

    2014-12-01

    Full Text Available A 37-year long-term series of monochromatic aerosol optical depth (AOD has been recovered from solar irradiance measurements performed with the solar spectrometer Mark-I, deployed at Izaña mountain since 1976. The instrument operation is based on the method of resonant scattering, which affords wavelength absolute reference and stability (long-term stability and high precision in comparison to other instruments based purely on interference filters. However, it has been specifically designed as a reference instrument for helioseismology, and its ability to determine AOD from transmitted and scattered monochromatic radiation at 769.9 nm inside a potassium vapour cell in the presence of a permanent magnetic field is evaluated in this paper. Particularly, the use of an exposed mirror arrangement to collect sunlight as well as the Sun–laboratory velocity dependence of the scattered component introduces some important inconveniences to overcome when we perform the instrument's calibration. We have solved this problem using a quasi-continuous Langley calibration technique and a refinement procedure to correct for calibration errors as well as for the fictitious diurnal cycle on AOD data. Our results showed similar calibration errors retrieved by means of this quasi-continuous Langley technique applied in different aerosol load events (from 0.04 to 0.3, provided aerosol concentration remains constant throughout the calibration interval. It assures the validity of this technique when it is applied in those periods with relatively high aerosol content. The comparative analysis between the recovered AOD data set from the Mark-I and collocated quasi-simultaneous data from the Cimel-AErosol RObotic NETwork (AERONET and Precision Filter Radiometer (PFR instruments showed an absolute mean bias ≤ 0.01 in the 10- and 12-year comparison, respectively. High correlation coefficients between AERONET and Mark-I and PFR/Mark-I pairs confirmed a very good linear

  18. Aerosol optical depth thresholds as a tool to assess diffuse radiation fertilization of the land carbon uptake in China

    Science.gov (United States)

    Yue, Xu; Unger, Nadine

    2017-01-01

    China suffers from frequent haze pollution episodes that alter the surface solar radiation and influence regional carbon uptake by the land biosphere. Here, we apply combined vegetation and radiation modeling and multiple observational datasets to assess the radiative effects of aerosol pollution in China on the regional land carbon uptake for the 2009-2011 period. First, we assess the inherent sensitivity of China's land biosphere to aerosol pollution by defining and calculating two thresholds of aerosol optical depth (AOD) at 550 nm, (i) AODt1, resulting in the maximum net primary productivity (NPP), and (ii) AODt2, such that if local AOD fertilization effect (DFE) always promotes local NPP compared with aerosol-free conditions. Then, we apply the thresholds, satellite data, and interactive vegetation modeling to estimate current impacts of aerosol pollution on land ecosystems. In the northeast, observed AOD is 55 % lower than AODt1, indicating a strong aerosol DFE on local NPP. In the southeastern coastal regions, observed AOD is close to AODt1, suggesting that regional NPP is promoted by the current level of aerosol loading, but that further increases in AOD in this region will weaken the fertilization effects. The North China Plain experiences limited enhancement of NPP by aerosols because observed AOD is 77 % higher than AODt1 but 14 % lower than AODt2. Aerosols always inhibit regional NPP in the southwest because of the persistent high cloud coverage that already substantially reduces the total light availability there. Under clear-sky conditions, simulated NPP shows widespread increases of 20-60 % (35.0 ± 0.9 % on average) by aerosols. Under all-sky conditions, aerosol pollution has spatially contrasting opposite sign effects on NPP from -3 % to +6 % (1.6 ± 0.5 % on average), depending on the local AOD relative to the regional thresholds. Stringent aerosol pollution reductions motivated by public health concerns, especially in the North China Plain and

  19. Aerosol Optical Depth measurements at 340 nm with a Brewer spectrophotometer and comparison with Cimel sunphotometer observations at Uccle, Belgium

    Directory of Open Access Journals (Sweden)

    V. De Bock

    2010-11-01

    Full Text Available The Langley Plot Method (LPM is adapted for the retrieval of Aerosol Optical Depth (AOD values at 340 nm from Brewer#178 sun scan measurements between 335 and 345 nm (convoluted with the band pass function of the Cimel sunphotometer filter at 340 nm performed in Uccle, Belgium. The use of sun scans instead of direct sun measurements simplifies the comparison of the AOD values with quasi-simultaneous Cimel sunphotometer values. Also, the irradiance at 340 nm is larger than the one at 320.1 nm due to lower ozone absorption, thus improving the signal to noise ratio. For the selection of the cloudless days (from now on referred to as calibration quality clear days, a new set of criteria is proposed. With the adapted method, individual clear sky AOD values, for which the selection criteria are also presented in this article, are calculated for a period from September 2006 until the end of August 2010. These values are then compared to quasi-simultaneous Cimel sunphotometer measurements, showing a very good agreement (the correlation coefficient, the slope and the intercept of the regression line are respectively 0.974, 0.968 and 0.011, which proves that good quality observations can be obtained from Brewer sun scan measurements at 340 nm. The analysis of the monthly and seasonal Brewer AODs at Uccle is consistent with studies at other sites reporting on the seasonal variation of AODs in Europe. The highest values can be observed in summer and spring, whereas more than 50% of the winter AODs are lower than 0.3. On a monthly scale, the lowest AOD are observed in December and the highest values occur in June and April. No clear weekly cycle is observed for Uccle. The current cloud-screening algorithm is still an issue, which means that some AOD values can still be influenced by scattered clouds. This effect can be seen when comparing the calculated monthly mean values of the Brewer with the AERONET measurements.

  20. Determination of effective droplet radius and optical depth of liquid water clouds over a tropical site in northern Thailand using passive microwave soundings, aircraft measurements and spectral irradiance data

    Science.gov (United States)

    Nimnuan, P.; Janjai, S.; Nunez, M.; Pratummasoot, N.; Buntoung, S.; Charuchittipan, D.; Chanyatham, T.; Chantraket, P.; Tantiplubthong, N.

    2017-08-01

    This paper presents an algorithm for deriving the effective droplet radius and optical depth of liquid water clouds using ground-based measurements, aircraft observations and an adiabatic model of cloud liquid water. The algorithm derives cloud effective radius and cloud optical depth over a tropical site at Omkoi (17.80°N, 98.43°E), Thailand. Monthly averages of cloud optical depth are highest in April (54.5), which is the month with the lowest average cloud effective radius (4.2 μm), both occurring before the start of the rainy season and at the end of the high contamination period. By contrast, the monsoon period extending from May to October brings higher cloud effective radius and lower cloud optical depth to the region on average. At the diurnal scale there is a gradual increase in average cloud optical depth and decrease in cloud effective radius as the day progresses.

  1. Retrievals of aerosol optical depth and Angström exponent from ground-based Sun-photometer data of Singapore.

    Science.gov (United States)

    Salinas, Santo V; Chew, Boon N; Liew, Soo C

    2009-03-10

    The role of aerosols in climate and climate change is one of the factors that is least understood at the present. Aerosols' direct interaction with solar radiation is a well understood mechanism that affects Earth's net radiative forcing. However, quantifying its magnitude is more problematic because of the temporal and spatial variability of aerosol particles. To enhance our understanding of the radiative effects of aerosols on the global climate, Singapore has joined the AERONET (Aerosol Robotic Network) worldwide network by contributing ground-based direct Sun measurements performed by means of a multiwavelength Sun-photometer instrument. Data are collected on an hourly basis, then are uploaded to be fully screened and quality assured by AERONET. We use a one year data record (level 1.5/2.0) of measured columnar atmospheric optical depth, spanning from November 2006 to October 2007, to study the monthly and seasonal variability of the aerosol optical depth and the Angström exponent. We performed independent retrievals of these parameters (aerosol optical depth and Angström exponent) by using the photometer's six available bands covering the near-UV to near-IR (380-1080 nm). As a validation, our independent retrievals were compared with AERONET 1.5/2.0 level direct Sun product.

  2. Planck early results. XIX. All-sky temperature and dust optical depth from Planck and IRAS. Constraints on the "dark gas" in our Galaxy

    DEFF Research Database (Denmark)

    Bucher, M.; Delabrouille, J.; Giraud-Héraud, Y.;

    2011-01-01

    An all sky map of the apparent temperature and optical depth of thermal dust emission is constructed using the Planck-HFI (350μm to 2 mm) andIRAS(100μm) data. The optical depth maps are correlated with tracers of the atomic (Hi) and molecular gas traced by CO. The correlation with the column...... density of observed gas is linear in the lowest column density regions at high Galactic latitudes. At high NH, the correlation is consistent with that of the lowest NH, for a given choice of the CO-to-H2 conversion factor. In the intermediate NH range, a departure from linearity is observed, with the dust...... optical depth in excess of the correlation. This excess emission is attributed to thermal emission by dust associated with a dark gas phase, undetected in the available Hi and CO surveys. The 2D spatial distribution of the dark gas in the solar neighbourhood (|bII| > 10°) is shown to extend around known...

  3. RDA Implementation and Training Issues across United States Academic Libraries: An In-Depth E-Mail Interview Study

    Science.gov (United States)

    Park, Jung-ran; Tosaka, Yuji

    2015-01-01

    This study aims at providing in-depth perspectives on the ways in which cataloging and metadata professionals have coped with RDA training and implementation through an e-mail interview method. Results show that the performance-based, "learn-as-you-go," peer learning method is found by practitioners to be most effective in acquiring and…

  4. Compact MEMS/NEMS characterization platform using a DVD optical pick-up unit with optical imaging function

    DEFF Research Database (Denmark)

    Liao, Hsien-Shun; Hwang, Ing-Shouh; Chen, Ching-Hsiu

    2013-01-01

    In this work, we present a compact, simple and efficient platform for Micro-electromechanical systems (MEMS)/Nano-electromechanical systems (NEMS) characterization. In this platform, a CCD camera is combined with a DVD optical pick-up unit (OPU). The CCD camera captures optical image of MEMS....../NEMS samples and detection laser spot, which makes laser alignment on measurement target easier. The DVD OPU is used for detection of resonant frequency measurements of the samples. Working bandwidth and noise level of the OPU are 100 MHz and 1.3 pmHz"2, respectively. Furthermore, the OPU has a laser spot size...

  5. Retrieval of aerosol optical depth over land based on a time series technique using MSG/SERIVI data

    Directory of Open Access Journals (Sweden)

    L. Mei

    2012-02-01

    Full Text Available A novel approach for the joint retrieval of aerosol optical depth (AOD and surface reflectance, using Meteosat Second Generation – Spinning Enhanced Visible and Infrared Imagers (MSG/SEVIRI observations in two solar channels, is presented. The retrieval is based on a time series (TS technique, which makes use of the two visible bands at 0.6 μm and 0.8 μm in three orderly scan times (15 min interval between two scans to retrieve the AOD over land. Using the radiative transfer equation for plane-parallel atmospheres two coupled differential equations for the upward and downward fluxes are derived. The boundary conditions for the upward and downward fluxes at the top and at the bottom of the atmosphere are used in these equations to provide an analytic solution for the surface reflectance. To derive these fluxes, the aerosol single scattering albedo (SSA and asymmetry factor are required to provide a solution. These are provided from a set of six pre-defined aerosol types with the SSA and asymmetry factor (g. We assume one aerosol type for a grid of 1° × 1° and the surface reflectance changes little between two consequent scans. A k approximation was used in the inversion to find the best solution of atmospheric properties and surface reflectance. The algorithm makes use of numerical minimisation routines to obtain the optimal solution of atmospheric properties and surface reflectance by selection of the most suitable aerosol type from pre-defined sets. Also, it is assumed that the surface reflectance is little influenced by aerosol scattering at 1.6 μm and therefore the ratio of surface reflectances in the solar band for two consequent scans can be well-approximated by the ratio of the reflectances at 1.6 μm. A further assumption is that the surface reflectance varies only slightly over a period of 30 min.

    A detailed analysis of the retrieval results show that it is suitable for AOD retrieval over land. Six Aerosol

  6. Daily spectral effects on concentrating PV solar cells as affected by realistic aerosol optical depth and other atmospheric conditions

    Science.gov (United States)

    Gueymard, Christian A.

    2009-08-01

    provides a preliminary quantitative assessment of how local atmospheric conditions interact with the spectral response of different CPV technologies. Most importantly, it is shown that the effect of aerosol optical depth (AOD, also referred to as atmospheric turbidity) has the largest impact on both the average direct normal irradiance (DNI) during a given month and the cell's DSEF. It is found that DSEF can be as low as 0.993 under clean conditions (low AOD), and as high as 1.215 under hazy conditions (high AOD). Under most conditions, all simulated solar cells perform significantly better than under rating conditions due to the spectral effect alone. There is no important difference in DSEF from cell to cell, except in one instance of very high AOD. The methodology and results proposed here constitute a step towards a better performance prediction of CPV systems, by assessing the variable spectral effect more accurately. It is anticipated that a more detailed simulation, which would also model temperature effects, as well as current-limiting effects in multijunction cells, would indicate even larger DSEF values than found here. Accurate aerosol data with higher spatial resolution in the "sun belt" than what exists today would also be desirable for the development of CPV applications.

  7. Post-processing to remove residual clouds from aerosol optical depth retrieved using the Advanced Along Track Scanning Radiometer

    Science.gov (United States)

    Sogacheva, Larisa; Kolmonen, Pekka; Virtanen, Timo H.; Rodriguez, Edith; Saponaro, Giulia; de Leeuw, Gerrit

    2017-02-01

    Cloud misclassification is a serious problem in the retrieval of aerosol optical depth (AOD), which might considerably bias the AOD results. On the one hand, residual cloud contamination leads to AOD overestimation, whereas the removal of high-AOD pixels (due to their misclassification as clouds) leads to underestimation. To remove cloud-contaminated areas in AOD retrieved from reflectances measured with the (Advanced) Along Track Scanning Radiometers (ATSR-2 and AATSR), using the ATSR dual-view algorithm (ADV) over land or the ATSR single-view algorithm (ASV) over ocean, a cloud post-processing (CPP) scheme has been developed at the Finnish Meteorological Institute (FMI) as described in Kolmonen et al. (2016). The application of this scheme results in the removal of cloud-contaminated areas, providing spatially smoother AOD maps and favourable comparison with AOD obtained from the ground-based reference measurements from the AERONET sun photometer network. However, closer inspection shows that the CPP also removes areas with elevated AOD not due to cloud contamination, as shown in this paper. We present an improved CPP scheme which better discriminates between cloud-free and cloud-contaminated areas. The CPP thresholds have been further evaluated and adjusted according to the findings. The thresholds for the detection of high-AOD regions (> 60 % of the retrieved pixels should be high-AOD (> 0.6) pixels), and cloud contamination criteria for low-AOD regions have been accepted as the default for AOD global post-processing in the improved CPP. Retaining elevated AOD while effectively removing cloud-contaminated pixels affects the resulting global and regional mean AOD values as well as coverage. Effects of the CPP scheme on both spatial and temporal variation for the period 2002-2012 are discussed. With the improved CPP, the AOD coverage increases by 10-15 % with respect to the existing scheme. The validation versus AERONET shows an improvement of the correlation

  8. Retrieval of aerosol optical depth over land based on a time series technique using MSG/SEVIRI data

    Directory of Open Access Journals (Sweden)

    L. Mei

    2012-10-01

    Full Text Available A novel approach for the joint retrieval of aerosol optical depth (AOD and aerosol type, using Meteosat Second Generation – Spinning Enhanced Visible and Infrared Imagers (MSG/SEVIRI observations in two solar channels, is presented. The retrieval is based on a Time Series (TS technique, which makes use of the two visible bands at 0.6 μm and 0.8 μm in three orderly scan times (15 min interval between two scans to retrieve the AOD over land. Using the radiative transfer equation for plane-parallel atmosphere, two coupled differential equations for the upward and downward fluxes are derived. The boundary conditions for the upward and downward fluxes at the top and at the bottom of the atmosphere are used in these equations to provide an analytic solution for the AOD. To derive these fluxes, the aerosol single scattering albedo (SSA and asymmetry factor are required to provide a solution. These are provided from a set of six pre-defined aerosol types with the SSA and asymmetry factor. We assume one aerosol type for a grid of 1°×1° and the surface reflectance changes little between two subsequent observations. A k-ratio approach is used in the inversion to find the best solution of atmospheric properties and surface reflectance. The k-ratio approach assumes that the surface reflectance is little influenced by aerosol scattering at 1.6 μm and therefore the ratio of surface reflectances in the solar band for two subsequent observations can be well-approximated by the ratio of the reflectances at 1.6 μm. A further assumption is that the surface reflectance varies only slightly over a period of 30 min. The algorithm makes use of numerical minimisation routines to obtain the optimal solution of atmospheric properties and surface reflectance by selection of the most suitable aerosol type from pre-defined sets.

    A detailed analysis of the retrieval results shows that it is suitable for AOD retrieval over land from SEVIRI data

  9. Aerosol optical depth over a remote semi-arid region of South Africa from spectral measurements of the daytime solar extinction and the nighttime stellar extinction

    Science.gov (United States)

    Formenti, P.; Winkler, H.; Fourie, P.; Piketh, S.; Makgopa, B.; Helas, G.; Andreae, M. O.

    Spectral daytime aerosol optical depths have been measured at Sutherland, South Africa (32°22'S, 20°48'E), from January 1998 to November 1999. Sutherland is located in the semi-arid Karoo desert, approximately 400-km northeast from Cape Town. The site, remote from major sources of aerosols, hosts the South African Astronomical Observatory (SAAO), where nighttime stellar extinction is being measured. The comparison of daytime and nighttime measurements for the years 1998-1999 makes it possible to validate the astronomical dataset of aerosol optical depth ( τa) dating back to 1991. The 1998 and 1999 annually averaged daytime τa at 500 nm are 0.04±0.04 and 0.06±0.06, respectively. Half-day averages vary between 0.03 and 0.44, with peak values in August-September. This pronounced seasonality is linked to the biomass-burning season in the Southern Hemisphere. Smoke haze layers transported to Sutherland originated primarily on the African landmass at latitudes between 10° and 20°S and passed over Namibia and Angola. On one occasion, aerosols from fires in Brazil transported across the Atlantic Ocean were likely detected. The haze layers reaching Sutherland are therefore at least 2-3 days old. The spectral dependence of the aerosol optical depth for the smoke layers supports the bimodality of the volume size distribution for biomass burning aerosols. The accumulation mode has a volume modal diameter of 0.32 μm, consistent with the hypothesis of aged haze. The stellar measurements (1991-2001) show that, due to the eruption of Mt. Pinatubo, the atmospheric extinction depth at 550 nm in the years 1991-1993 increased by 33% with respect to the average value (0.14±0.03) for the period 1994-2001. Outside the Pinatubo event, extinction is largest in the period 1997-1999.

  10. Depth information in natural environments derived from optic flow by insect motion detection system: A model analysis

    Directory of Open Access Journals (Sweden)

    Alexander eSchwegmann

    2014-08-01

    Full Text Available Knowing the depth structure of the environment is crucial for moving animals in many behavioral contexts, such as collision avoidance, targeting objects, or spatial navigation. An important source of depth information is motion parallax. This powerful cue is generated on the eyes during translatory self-motion with the retinal images of nearby objects moving faster than those of distant ones. To investigate how the visual motion pathway represents motion-based depth information we analyzed its responses to image sequences recorded in natural cluttered environments with a wide range of depth structures. The analysis was done on the basis of an experimentally validated model of the visual motion pathway of insects, with its core elements being correlation-type elementary motion detectors (EMDs. It is the key result of our analysis that the absolute EMD responses, i.e. the motion energy profile, represent the contrast-weighted nearness of environmental structures during translatory self-motion at a roughly constant velocity. In other words, the output of the EMD array highlights contours of nearby objects. This conclusion is largely independent of the scale over which EMDs are spatially pooled and was corroborated by scrutinizing the motion energy profile after eliminating the depth structure from the natural image sequences. Hence, the well-established dependence of correlation-type EMDs on both velocity and textural properties of motion stimuli appears to be advantageous for representing behaviorally relevant information about the environment in a computationally parsimonious way.

  11. Aerosol optical depth and fine-mode fraction retrieval over East Asia using multi-angular total and polarized remote sensing

    Science.gov (United States)

    Cheng, T.; Gu, X.; Xie, D.; Li, Z.; Yu, T.; Chen, H.

    2012-03-01

    A new aerosol retrieval algorithm using multi-angular total and polarized measurements is presented. The algorithm retrieves aerosol optical depth (AOD), fine-mode fraction (FMF) for studying the impact of aerosol on climate change. The retrieval algorithm is based on a lookup table (LUT) method, which assumes that one fine and one coarse lognormal aerosol modes can be combined with proper weightings to represent the ambient aerosol properties. To reduce the ambiguity in retrieval algorithm, the key characteristics of aerosol model over East Asia are constrained using the cluster analysis technique based on the AERONET sun-photometer observation over East Asia, and the fine and coarse modes are not fixed but can vary. A mixing model of bare soil and green vegetation spectra and the Nadal and Breon model for the bidirectional polarized reflectance factor (BPDF) were used to simulate total and polarized surface reflectance of East Asia. By applying the present algorithm to POLDER measurements, three different aerosol cases of clear, polluted and dust are analyzed to test the algorithm. The comparison of retrieved aerosol optical depth (AOD) and fine-mode fraction (FMF) with those of AERONET sun-photometer observations show reliable results. Preliminary validation is encouraging. Using the new aerosol retrieval algorithm for multi-angular total and polarized measurements, the spatial and temporal variability of anthropogenic aerosol optical properties over East Asia, which were observed during a heavy polluted event, were analyzed. Exceptionally high values of aerosol optical depth contributed by fine mode of up to 0.5 (at 0.865 μm), and high values of fine-mode fraction of up to 0.9, were observed in this case study.

  12. Aerosol optical depth and fine-mode fraction retrieval over East Asia using multi-angular total and polarized remote sensing

    Directory of Open Access Journals (Sweden)

    T. Cheng

    2012-03-01

    Full Text Available A new aerosol retrieval algorithm using multi-angular total and polarized measurements is presented. The algorithm retrieves aerosol optical depth (AOD, fine-mode fraction (FMF for studying the impact of aerosol on climate change. The retrieval algorithm is based on a lookup table (LUT method, which assumes that one fine and one coarse lognormal aerosol modes can be combined with proper weightings to represent the ambient aerosol properties. To reduce the ambiguity in retrieval algorithm, the key characteristics of aerosol model over East Asia are constrained using the cluster analysis technique based on the AERONET sun-photometer observation over East Asia, and the fine and coarse modes are not fixed but can vary. A mixing model of bare soil and green vegetation spectra and the Nadal and Breon model for the bidirectional polarized reflectance factor (BPDF were used to simulate total and polarized surface reflectance of East Asia. By applying the present algorithm to POLDER measurements, three different aerosol cases of clear, polluted and dust are analyzed to test the algorithm. The comparison of retrieved aerosol optical depth (AOD and fine-mode fraction (FMF with those of AERONET sun-photometer observations show reliable results. Preliminary validation is encouraging. Using the new aerosol retrieval algorithm for multi-angular total and polarized measurements, the spatial and temporal variability of anthropogenic aerosol optical properties over East Asia, which were observed during a heavy polluted event, were analyzed. Exceptionally high values of aerosol optical depth contributed by fine mode of up to 0.5 (at 0.865 μm, and high values of fine-mode fraction of up to 0.9, were observed in this case study.

  13. Optical and radiative properties of aerosols over Abu Dhabi in the United Arab Emirates

    Science.gov (United States)

    Beegum, S. Naseema; Romdhane, Haifa Ben; Ali, Mohammed Tauha; Armstrong, Peter; Ghedira, Hosni

    2016-12-01

    The present study is on the aerosol optical and radiative properties in the short-wave radiation and its climate implications at the arid city of Abu Dhabi (24.42 ∘N, 54.61 ∘E, 4.5 m MSL), in the United Arab Emirates. The direct aerosol radiative forcings (ARF) in the short-wave region at the top (TOA) and bottom of the atmosphere (BOA) are estimated using a hybrid approach, making use of discrete ordinate radiative transfer method in conjunction with the short-wave flux and spectral aerosol optical depth (AOD) measurements, over a period of 3 years (June 2012-July 2015), at Abu Dhabi located at the south-west coast of the Arabian Gulf. The inferred microphysical properties of aerosols at the measurement site indicate strong seasonal variations from the dominance of coarse mode mineral dust aerosols during spring (March-May) and summer (June-September), to the abundance of fine/accumulation mode aerosols mainly from combustion of fossil-fuel and bio-fuel during autumn (October-November) and winter (December-February) seasons. The monthly mean diurnally averaged ARF at the BOA (TOA) varies from -13.2 Wm-2 (˜-0.96 Wm-2) in November to -39.4 Wm-2 (-11.4 Wm-2) in August with higher magnitudes of the forcing values during spring/summer seasons and lower values during autumn/winter seasons. The atmospheric aerosol forcing varies from + 12.2 Wm-2 (November) to 28.2 Wm-2 (June) with higher values throughout the spring and summer seasons, suggesting the importance of mineral dust aerosols towards the solar dimming. Seasonally, highest values of the forcing efficiency at the surface are observed in spring (-85.0 ± 4.1 W m-2 τ -1) followed closely by winter (-79.2 ± 7.1 W m-2 τ -1) and the lowest values during autumn season (-54 ± 4.3 W m-2 τ -1). The study concludes with the variations of the atmospheric heating rates induced by the forcing. Highest heating rate is observed in June (0.39 K day -1) and the lowest in November (0.17 K day -1) and the temporal

  14. Optical and radiative properties of aerosols over Abu Dhabi in the United Arab Emirates

    Indian Academy of Sciences (India)

    S Naseema Beegum; Haifa Ben Romdhane; Mohammed Tauha Ali; Peter Armstrong; Hosni Ghedira

    2016-12-01

    The present study is on the aerosol optical and radiative properties in the short-wave radiation and its climate implications at the arid city of Abu Dhabi (24.42°N, 54.61°E, 4.5 m MSL), in the United Arab Emirates. The direct aerosol radiative forcings (ARF) in the short-wave region at the top (TOA) and bottom of the atmosphere (BOA) are estimated using a hybrid approach, making use of discrete ordinate radiative transfer method in conjunction with the short-wave flux and spectral aerosol optical depth (AOD) measurements, over a period of 3 years (June 2012–July 2015), at Abu Dhabi located at the southwest coast of the Arabian Gulf. The inferred microphysical properties of aerosols at the measurementsite indicate strong seasonal variations from the dominance of coarse mode mineral dust aerosols during spring (March–May) and summer (June–September), to the abundance of fine/accumulation modeaerosols mainly from combustion of fossil-fuel and bio-fuel during autumn (October–November) and winter(December–February) seasons. The monthly mean diurnally averaged ARF at the BOA (TOA) varies from −13.2Wm⁻² (∼ −0.96 Wm⁻²) in November to −39.4 Wm⁻² (−11.4 Wm⁻²) in August with higher magnitudes of the forcing values during spring/summer seasons and lower values during autumn/winter seasons. The atmospheric aerosol forcing varies from +12.2 Wm⁻² (November) to 28.2 Wm⁻² (June) with higher values throughout the spring and summer seasons, suggesting the importance of mineral dust aerosols towards the solar dimming. Seasonally, highest values of the forcing efficiency at the surfaceare observed in spring (−85.0± 4.1Wm⁻²τ⁻¹) followed closely by winter (−79.2±7.1 W m⁻²τ⁻¹) and the lowest values during autumn season (−54±4.3W m⁻²τ⁻¹). The study concludes with the variations of the atmospheric heating rates induced by the forcing. Highest heating rate is observed in June (0.39 K day⁻¹) and the lowest in November

  15. A Simplified Measurement Method of Solar-Optical Properties of Multi-Pane Glazing Units

    Directory of Open Access Journals (Sweden)

    Zhuolun Chen

    2013-07-01

    Full Text Available Energy-efficient windows with double- or triple-pane glazing units are currently widely utilized in building applications. The solar-optical properties of glazing units can greatly affect their energy and daylighting performance. However, it is generally difficult to measure the solar-optical properties of glazings using the current ISO standards, especially for multi-pane units. This paper presents a simplified test method suitable for multi-pane glazing. Three sets of double-pane Low-Emissivity (LOW-E glazing units were tested under ISO standard and proposed methods. Good agreement between the two testing methods was obtained. However, the simplified method required much less experimental time and labor..

  16. Studies of aerosol optical depth with the use of Microtops II sun photometers and MODIS detectors in coastal areas of the Baltic Sea

    Science.gov (United States)

    Zawadzka, Olga; Makuch, Przemysław; Markowicz, Krzysztof; Zieliński, Tymon; Petelski, Tomasz; Ulevičius, Vidmantas; Strzałkowska, Agata; Rozwadowska, Anna; Gutowska, Dorota

    2014-04-01

    In this paper we describe the results of a research campaign dedicated to the studies of aerosol optical properties in different regions of both the open Baltic Sea and its coastal areas. During the campaign we carried out simultaneous measurements of aerosol optical depth at 4 stations with the use of the hand-held Microtops II sun photometers. The studies were complemented with aerosol data provided by the MODIS. In order to obtain the full picture of aerosol situation over the study area, we added to our analyses the air mass back-trajectories at various altitudes as well as wind fields. Such complex information facilitated proper conclusions regarding aerosol optical depth and Ångström exponent for the four locations and discussion of the changes of aerosol properties with distance and with changes of meteorological factors. We also show that the Microtops II sun photometers are reliable instruments for field campaigns. They are easy to operate and provide good quality results.

  17. Validating MODIS above-cloud aerosol optical depth retrieved from "color ratio" algorithm using direct measurements made by NASA's airborne AATS and 4STAR sensors

    Science.gov (United States)

    Jethva, Hiren; Torres, Omar; Remer, Lorraine; Redemann, Jens; Livingston, John; Dunagan, Stephen; Shinozuka, Yohei; Kacenelenbogen, Meloe; Segal Rosenheimer, Michal; Spurr, Rob

    2016-10-01

    We present the validation analysis of above-cloud aerosol optical depth (ACAOD) retrieved from the "color ratio" method applied to MODIS cloudy-sky reflectance measurements using the limited direct measurements made by NASA's airborne Ames Airborne Tracking Sunphotometer (AATS) and Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) sensors. A thorough search of the airborne database collection revealed a total of five significant events in which an airborne sun photometer, coincident with the MODIS overpass, observed partially absorbing aerosols emitted from agricultural biomass burning, dust, and wildfires over a low-level cloud deck during SAFARI-2000, ACE-ASIA 2001, and SEAC4RS 2013 campaigns, respectively. The co-located satellite-airborne matchups revealed a good agreement (root-mean-square difference < 0.1), with most matchups falling within the estimated uncertainties associated the MODIS retrievals (about -10 to +50 %). The co-retrieved cloud optical depth was comparable to that of the MODIS operational cloud product for ACE-ASIA and SEAC4RS, however, higher by 30-50 % for the SAFARI-2000 case study. The reason for this discrepancy could be attributed to the distinct aerosol optical properties encountered during respective campaigns. A brief discussion on the sources of uncertainty in the satellite-based ACAOD retrieval and co-location procedure is presented. Field experiments dedicated to making direct measurements of aerosols above cloud are needed for the extensive validation of satellite-based retrievals.

  18. Validating MODIS Above-Cloud Aerosol Optical Depth Retrieved from Color Ratio Algorithm Using Direct Measurements Made by NASA's Airborne AATS and 4STAR Sensors

    Science.gov (United States)

    Jethva, Hiren; Torres, Omar; Remer, Lorraine; Redemann, Jens; Livingston, John; Dunagan, Stephen; Shinozuka, Yohei; Kacenelenbogen, Meloe; Segal Rozenhaimer, Michal; Spurr, Rob

    2016-01-01

    We present the validation analysis of above-cloud aerosol optical depth (ACAOD) retrieved from the color ratio method applied to MODIS cloudy-sky reflectance measurements using the limited direct measurements made by NASAs airborne Ames Airborne Tracking Sunphotometer (AATS) and Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) sensors. A thorough search of the airborne database collection revealed a total of five significant events in which an airborne sun photometer, coincident with the MODIS overpass, observed partially absorbing aerosols emitted from agricultural biomass burning, dust, and wildfires over a low-level cloud deck during SAFARI-2000, ACE-ASIA 2001, and SEAC4RS 2013 campaigns, respectively. The co-located satellite-airborne match ups revealed a good agreement (root-mean-square difference less than 0.1), with most match ups falling within the estimated uncertainties associated with the MODIS retrievals (about -10 to +50 ). The co-retrieved cloud optical depth was comparable to that of the MODIS operational cloud product for ACE-ASIA and SEAC4RS, however, higher by 30-50% for the SAFARI-2000 case study. The reason for this discrepancy could be attributed to the distinct aerosol optical properties encountered during respective campaigns. A brief discussion on the sources of uncertainty in the satellite-based ACAOD retrieval and co-location procedure is presented. Field experiments dedicated to making direct measurements of aerosols above cloud are needed for the extensive validation of satellite based retrievals.

  19. Depth-resolved multilayer pigment identification in paintings: combined use of laser-induced breakdown spectroscopy (LIBS) and optical coherence tomography (OCT).

    Science.gov (United States)

    Kaszewska, Ewa A; Sylwestrzak, Marcin; Marczak, Jan; Skrzeczanowski, Wojciech; Iwanicka, Magdalena; Szmit-Naud, Elżbieta; Anglos, Demetrios; Targowski, Piotr

    2013-08-01

    A detailed feasibility study on the combined use of laser-induced breakdown spectroscopy with optical coherence tomography (LIBS/OCT), aiming at a realistic depth-resolved elemental analysis of multilayer stratigraphies in paintings, is presented. Merging a high spectral resolution LIBS system with a high spatial resolution spectral OCT instrument significantly enhances the quality and accuracy of stratigraphic analysis. First, OCT mapping is employed prior to LIBS analysis in order to assist the selection of specific areas of interest on the painting surface to be examined in detail. Then, intertwined with LIBS, the OCT instrument is used as a precise profilometer for the online determination of the depth of the ablation crater formed by individual laser pulses during LIBS depth-profile analysis. This approach is novel and enables (i) the precise in-depth scaling of elemental concentration profiles, and (ii) the recognition of layer boundaries by estimating the corresponding differences in material ablation rate. Additionally, the latter is supported, within the transparency of the object, by analysis of the OCT cross-sectional views. The potential of this method is illustrated by presenting results on the detailed analysis of the structure of an historic painting on canvas performed to aid planned restoration of the artwork.

  20. A bio-inspired, computational model suggests velocity gradients of optic flow locally encode ordinal depth at surface borders and globally they encode self-motion.

    Science.gov (United States)

    Raudies, Florian; Ringbauer, Stefan; Neumann, Heiko

    2013-09-01

    Visual navigation requires the estimation of self-motion as well as the segmentation of objects from the background. We suggest a definition of local velocity gradients to compute types of self-motion, segment objects, and compute local properties of optical flow fields, such as divergence, curl, and shear. Such velocity gradients are computed as velocity differences measured locally tangent and normal to the direction of flow. Then these differences are rotated according to the local direction of flow to achieve independence of that direction. We propose a bio-inspired model for the computation of these velocity gradients for video sequences. Simulation results show that local gradients encode ordinal surface depth, assuming self-motion in a rigid scene or object motions in a nonrigid scene. For translational self-motion velocity, gradients can be used to distinguish between static and moving objects. The information about ordinal surface depth and self-motion can help steering control for visual navigation.

  1. ON-OFF UNITS IN THE 1ST OPTIC CHIASM OF THE BLOWFLY .2. SPATIAL PROPERTIES

    NARCIS (Netherlands)

    JANSONIUS, NM; VANHATEREN, JH

    We recorded from the spiking on-off unit in the first optic chiasm (between lamina and medulla) in the blowfly Calliphora vicina, and investigated its spatial properties. The receptive field extends over (11.4+/-0.9)-degrees horizontally and (8.7+/-0.6)-degrees vertically, i.e. about 7 by 5

  2. On-off units in the first optic chiasm of the blowfly. II. Spatial properties

    NARCIS (Netherlands)

    Jansonius, N.M.; Hateren, J.H. van

    1993-01-01

    We recorded from the spiking on-off unit in the first optic chiasm (between lamina and medulla) in the blowfly Calliphora vicina, and investigated its spatial properties. The receptive field extends over (11.4±0.9)° horizontally and (8.7±0.6)° vertically, i.e. about 7 by 5 interommatidial angles.

  3. ON-OFF UNITS IN THE 1ST OPTIC CHIASM OF THE BLOWFLY .2. SPATIAL PROPERTIES

    NARCIS (Netherlands)

    JANSONIUS, NM; VANHATEREN, JH

    1993-01-01

    We recorded from the spiking on-off unit in the first optic chiasm (between lamina and medulla) in the blowfly Calliphora vicina, and investigated its spatial properties. The receptive field extends over (11.4+/-0.9)-degrees horizontally and (8.7+/-0.6)-degrees vertically, i.e. about 7 by 5 interomm

  4. On-off units in the first optic chiasm of the blowfly. II. Spatial properties

    NARCIS (Netherlands)

    Jansonius, N.M.; Hateren, J.H. van

    1993-01-01

    We recorded from the spiking on-off unit in the first optic chiasm (between lamina and medulla) in the blowfly Calliphora vicina, and investigated its spatial properties. The receptive field extends over (11.4±0.9)° horizontally and (8.7±0.6)° vertically, i.e. about 7 by 5 interommatidial angles. Th

  5. ON-OFF UNITS IN THE 1ST OPTIC CHIASM OF THE BLOWFLY .2. SPATIAL PROPERTIES

    NARCIS (Netherlands)

    JANSONIUS, NM; VANHATEREN, JH

    1993-01-01

    We recorded from the spiking on-off unit in the first optic chiasm (between lamina and medulla) in the blowfly Calliphora vicina, and investigated its spatial properties. The receptive field extends over (11.4+/-0.9)-degrees horizontally and (8.7+/-0.6)-degrees vertically, i.e. about 7 by 5 interomm

  6. FAST TEMPORAL ADAPTATION OF ON-OFF UNITS IN THE 1ST OPTIC CHIASM OF THE BLOWFLY

    NARCIS (Netherlands)

    JANSONIUS, NM; VANHATEREN, JH

    1991-01-01

    1. We recorded from spiking units in the first optic chiasm between lamina and medulla in the brain of the blowfly (Calliphora vicina). Both previously characterized neuron types, on-off units and sustaining units, were encountered. On-off units had a temporal frequency response with a lower cut-off

  7. Biogenic Aerosols – Effects on Climate and Clouds. Cloud Optical Depth (COD) Sensor Three-Waveband Spectrally-Agile Technique (TWST) Field Campaign Report

    Energy Technology Data Exchange (ETDEWEB)

    Niple, E. R. [Aerodyne Research, Inc., Billerica, MA (United States); Scott, H. E. [Aerodyne Research, Inc., Billerica, MA (United States)

    2016-04-01

    This report describes the data collected by the Three-Waveband Spectrally-agile Technique (TWST) sensor deployed at Hyytiälä, Finland from 16 July to 31 August 2014 as a guest on the Biogenic Aerosols Effects on Climate and Clouds (BAECC) campaign. These data are currently available from the Atmospheric Radiation Measurement (ARM) Data Archive website and consists of Cloud Optical Depth (COD) measurements for the clouds directly overhead approximately every second (with some dropouts described below) during the daylight periods. A good range of cloud conditions were observed from clear sky to heavy rainfall.

  8. Design of a Shadowband Spectral Radiometer for the Retrieval of Thin Cloud Optical Depth, Liquid Water Path, and the Effective Radius

    Energy Technology Data Exchange (ETDEWEB)

    Bartholomew M. J.; Reynolds, R. M.; Vogelmann, A. M.; Min, Q.; Edwards, R.; Smith, S.

    2011-11-01

    The design and operation of a Thin-Cloud Rotating Shadowband Radiometer (TCRSR) described here was used to measure the radiative intensity of the solar aureole and enable the simultaneous retrieval of cloud optical depth, drop effective radius, and liquid water path. The instrument consists of photodiode sensors positioned beneath two narrow metal bands that occult the sun by moving alternately from horizon to horizon. Measurements from the narrowband 415-nm channel were used to demonstrate a retrieval of the cloud properties of interest. With the proven operation of the relatively inexpensive TCRSR instrument, its usefulness for retrieving aerosol properties under cloud-free skies and for ship-based observations is discussed.

  9. Localization of Objects Using the Ms Windows Kinect 3D Optical Device with Utilization of the Depth Image Technology

    OpenAIRE

    Ján VACHÁLEK; Marian GÉCI; Oliver ROVNÝ; Tomáš VOLENSKÝ

    2015-01-01

    The paper deals with the problem of object recognition for the needs of mobile robotic systems (MRS). The emphasis was placed on the segmentation of an in-depth image and noise filtration. MS Kinect was used to evaluate the potential of object location taking advantage of the indepth image. This tool, being an affordable alternative to expensive devices based on 3D laser scanning, was deployed in series of experiments focused on object location in its field of vision. In our ca...

  10. Discovery & Depth

    CERN Document Server

    Kulkarni, S R

    2012-01-01

    In the United States, the National Science Foundation (NSF), anticipating the no growth in funding, has commissioned a review of NSF-funded astronomy assets with the goal of determining how to best allocate funding for this decade. Inputs from members of the US community were sought. It is a matter of simple arithmetic that for a fixed level of funding many significant aspirations of Astro2010 cannot be met. Here, accepting the boundary conditions posed above, I have focused on fields centered on optical astronomy which offer the best opportunity for progress in this decade and thus offer the highest cost-benefit ratio. Readers may profit from reading the first seven sections.

  11. Lidar Ratios for Dust Aerosols Derived From Retrievals of CALIPSO Visible Extinction Profiles Constrained by Optical Depths from MODIS-Aqua and CALIPSO/CloudSat Ocean Surface Reflectance Measurements

    Science.gov (United States)

    Young, Stuart A.; Josset, Damien B.; Vaughan, Mark A.

    2010-01-01

    CALIPSO's (Cloud Aerosol Lidar Infrared Pathfinder Satellite Observations) analysis algorithms generally require the use of tabulated values of the lidar ratio in order to retrieve aerosol extinction and optical depth from measured profiles of attenuated backscatter. However, for any given time or location, the lidar ratio for a given aerosol type can differ from the tabulated value. To gain some insight as to the extent of the variability, we here calculate the lidar ratio for dust aerosols using aerosol optical depth constraints from two sources. Daytime measurements are constrained using Level 2, Collection 5, 550-nm aerosol optical depth measurements made over the ocean by the MODIS (Moderate Resolution Imaging Spectroradiometer) on board the Aqua satellite, which flies in formation with CALIPSO. We also retrieve lidar ratios from night-time profiles constrained by aerosol column optical depths obtained by analysis of CALIPSO and CloudSat backscatter signals from the ocean surface.

  12. Polarization-dependent all-optical modulator with ultra-high modulation depth based on a stereo graphene-microfiber structure

    CERN Document Server

    Xu, Fei; Zheng, Bi-cai; Shao, Guang-hao; Ge, Shi-jun; Lu, Yan-qing

    2015-01-01

    We report an in-line polarization-dependent all-optical fiber modulator based on a stereo graphene-microfiber structure (GMF) by utilizing the lab-on-rod technique. Owing to the unique spring-like geometry, an ultra-long GMF interaction length can be achieved, and an ultra-high modulation depth (MD) of ~7.5 dB and a high modulation efficiency (ME) of ~0.2 dB/mW were demonstrated for one polarization state. The MD and ME are more than one order larger than those of other graphene-waveguide hybrid all-optical modulators. By further optimizing the transferring and cleaning process, the modulator can quickly switch between transparent and opaque states for both the two polarization states with a maximized MD of tens of decibels. This modulator is compatible with current fiber-optic communication systems and may be applied in the near future to meet the impending need for ultrafast optical signal processing.

  13. Near Real-Time Estimation of Super-Resolved Depth and All-In-Focus Images from a Plenoptic Camera Using Graphics Processing Units

    Directory of Open Access Journals (Sweden)

    J. P. Lüke

    2010-01-01

    Full Text Available Depth range cameras are a promising solution for the 3DTV production chain. The generation of color images with their accompanying depth value simplifies the transmission bandwidth problem in 3DTV and yields a direct input for autostereoscopic displays. Recent developments in plenoptic video-cameras make it possible to introduce 3D cameras that operate similarly to traditional cameras. The use of plenoptic cameras for 3DTV has some benefits with respect to 3D capture systems based on dual stereo cameras since there is no need for geometric and color calibration or frame synchronization. This paper presents a method for simultaneously recovering depth and all-in-focus images from a plenoptic camera in near real time using graphics processing units (GPUs. Previous methods for 3D reconstruction using plenoptic images suffered from the drawback of low spatial resolution. A method that overcomes this deficiency is developed on parallel hardware to obtain near real-time 3D reconstruction with a final spatial resolution of 800×600 pixels. This resolution is suitable as an input to some autostereoscopic displays currently on the market and shows that real-time 3DTV based on plenoptic video-cameras is technologically feasible.

  14. Temporal and spatial variability of aerosol optical depth in the Sahel region in relation to vegetation remote sensing

    Science.gov (United States)

    Holben, B. N.; Fraser, R. S.; Eck, T. F.

    1991-01-01

    In order to monitor the aerosol characteristics needed for atmospheric correction of remotely sensed data, a network of sun photometers was established in the Sahel region of Senegal, Mali, and Niger. Data analysis suggests that there is a high spatial variability of the aerosol optical thickness tau(a) in the western Sahel region. At a 67 percent confidence level the instantaneous values of tau(a) can be extrapolated approximately 270-400 km with an error tolerance of 50 percent. Spatial variability in the dry season is found to be of a similar magnitude. The ranges of variations in the NDVI in the Sahel region are shown to be approximately 0.02 and 0.01, respectively, due to commonly observed fluctuations in the aerosol optical thickness and aerosol size distribution.

  15. Localization of Objects Using the Ms Windows Kinect 3D Optical Device with Utilization of the Depth Image Technology

    Directory of Open Access Journals (Sweden)

    Ján VACHÁLEK

    2015-11-01

    Full Text Available The paper deals with the problem of object recognition for the needs of mobile robotic systems (MRS. The emphasis was placed on the segmentation of an in-depth image and noise filtration. MS Kinect was used to evaluate the potential of object location taking advantage of the indepth image. This tool, being an affordable alternative to expensive devices based on 3D laser scanning, was deployed in series of experiments focused on object location in its field of vision. In our case, balls with fixed diameter were used as objects for 3D location.

  16. Depth dose deposition measurement in electronics packages using optically stimulated luminescence films; Mesure du rendement en profondeur dans un boitier de composant electronique au moyen de films luminescents stimulables optiquement

    Energy Technology Data Exchange (ETDEWEB)

    Ranchoux, G.; Dusseau, L.; Gensanne, D.; Plattard, D.; Polge, G.; Saigne, F.; Fesquet, J.; Gasiot, J. [Montpellier-2 Univ., CEMM2, 34 (France); Menduina, X. [Universite Autonome de Barcelone (Spain); Bessiere, J.C. [CORAD P.I.T. Pompignane, 34 - Montpelliers (France)

    1999-07-01

    The energy deposited by electrons versus depth inside molded Epoxy packages is measured using optically stimulated luminescence (OSL) dose mapping technique. Longitudinal and transversal depth dose curves are investigated under various angles of irradiation. Experimental results are compared with PENELOPE transport code calculations. Preliminary results are in good agreement with simulations.

  17. Evaluation of Optical Depths and Self-Absorption of Strontium and Aluminum Emission Lines in Laser-Induced Breakdown Spectroscopy (LIBS).

    Science.gov (United States)

    Alfarraj, Bader A; Bhatt, Chet R; Yueh, Fang Yu; Singh, Jagdish P

    2017-04-01

    Laser-induced breakdown spectroscopy (LIBS) is a widely used laser spectroscopic technique in various fields, such as material science, forensic science, biological science, and the chemical and pharmaceutical industries. In most LIBS work, the analysis is performed using radiative transitions from atomic emissions. In this study, the plasma temperature and the product [Formula: see text] (the number density N and the absorption path length [Formula: see text]) were determined to evaluate the optical depths and the self-absorption of Sr and Al lines. A binary mixture of strontium nitrate and aluminum oxide was used as a sample, consisting of variety of different concentrations in powder form. Laser-induced breakdown spectroscopy spectra were collected by varying various parameters, such as laser energy, gate delay time, and gate width time to optimize the LIBS signals. Atomic emission from Sr and Al lines, as observed in the LIBS spectra of different sample compositions, was used to characterize the laser induced plasma and evaluate the optical depths and self-absorption of LIBS.

  18. Development and assessment of a higher-spatial-resolution (4.4 km) MISR aerosol optical depth product using AERONET-DRAGON data

    Science.gov (United States)

    Garay, Michael J.; Kalashnikova, Olga V.; Bull, Michael A.

    2017-04-01

    Since early 2000, the Multi-angle Imaging SpectroRadiometer (MISR) instrument on NASA's Terra satellite has been acquiring data that have been used to produce aerosol optical depth (AOD) and particle property retrievals at 17.6 km spatial resolution. Capitalizing on the capabilities provided by multi-angle viewing, the current operational (Version 22) MISR algorithm performs well, with about 75 % of MISR AOD retrievals globally falling within 0.05 or 20 % × AOD of paired validation data from the ground-based Aerosol Robotic Network (AERONET). This paper describes the development and assessment of a prototype version of a higher-spatial-resolution 4.4 km MISR aerosol optical depth product compared against multiple AERONET Distributed Regional Aerosol Gridded Observations Network (DRAGON) deployments around the globe. In comparisons with AERONET-DRAGON AODs, the 4.4 km resolution retrievals show improved correlation (r = 0. 9595), smaller RMSE (0.0768), reduced bias (-0.0208), and a larger fraction within the expected error envelope (80.92 %) relative to the Version 22 MISR retrievals.

  19. THE EFFECT OF DEPTH OF HOOKS, SET AND SOAK TIME TO THE CATCH PER UNIT OF EFFORT OF TUNA IN THE EASTERN INDIAN OCEAN

    Directory of Open Access Journals (Sweden)

    Bram Setyadji

    2017-01-01

    Full Text Available Yellowfin (Thunnus albacares and bigeye (T. obesus tuna have been intensively exploited by longline fleets since 1980’s, however, a large proportion of zero catch per set of target species still accurred. Zero catch data contributed significantly to the low catch per unit of effort (CPUE compared to other countries at the same fishing area. Therefore, understanding the factors contributed to the CPUE of tuna is essential, in order to improve longline fishing efficiency. A total of 2.115 set-by-set data were obtained from Indonesian Scientific Observer Program. The onboard observations were carried out at commercial tuna longline operated in Eastern Indian Ocean from August 2005 to December 2014. Several analytical approaches were conducted in this paper. First, General Linear Model (GLM was applied in order to model the relationship between CPUE with all the variables involved. Second, boxplot diagram, polynomial and linear regression were applied to fit the relationship between CPUE with set time, soak time and depth (represented by hook position respectively. The result showed that, there was no significant relationship between set time and CPUE of bigeye and yellowfin tuna. Soak time was positively related with CPUE of yellowfin and affect adversely on bigeye. Depth also have significant relationship with CPUE of tuna, where catch of yellowfin decreased linearly with hook depth, whereas catch of bigeye was performed the opposite. Improvement in tuna longline fishery in eastern Indian Ocean can be achieved through implementation of the specific soak time and hook depth for each target species, i.e. yellowfin and bigeye tuna.

  20. Scanning micromechanical mirror for fine-pointing units of intersatellite optical links

    Science.gov (United States)

    Suhonen, Mika; Graeffe, Jussi; Sillanpää, Teuvo; Sipola, Hannu; Eiden, Michael

    2001-12-01

    A light and fast two-axial fine-pointing mirror has a number of space applications, especially in intersatellite optical links. The fine pointing of laser beams in optical links is currently realized with electromagnetic or piezoelectric actuators, which are relatively large and heavy. Micro-electro-mechanical system technology bears a high potential in space applications, offering a reduction in device size, mass and power consumption. Microtechnology facilitates batch mode fabrication, yielding a low cost per unit. VTT Automation has designed and partially tested a silicon micromachined electrostatically actuated two-axial mirror, which can be controlled with microradian resolution and large bandwidth over the angular range of +/-3 mrad.

  1. In-depth imaging and quantification of degenerative changes associated with Achilles ruptured tendons by polarization-sensitive optical coherence tomography

    Science.gov (United States)

    Bagnaninchi, P. O.; Yang, Y.; Bonesi, M.; Maffulli, G.; Phelan, C.; Meglinski, I.; El Haj, A.; Maffulli, N.

    2010-07-01

    The objective of this study was to develop a method based on polarization-sensitive optical coherent tomography (PSOCT) for the imaging and quantification of degenerative changes associated with Achilles tendon rupture. Ex vivo PSOCT examinations were performed in 24 patients. The study involved samples from 14 ruptured Achilles tendons, 4 tendinopathic Achilles tendons and 6 patellar tendons (collected during total knee replacement) as non-ruptured controls. The samples were imaged in both intensity and phase retardation modes within 24 h after surgery, and birefringence was quantified. The samples were fixed and processed for histology immediately after imaging. Slides were assessed twice in a blind manner to provide a semi-quantitative histological score of degeneration. In-depth micro structural imaging was demonstrated. Collagen disorganization and high cellularity were observable by PSOCT as the main markers associated with pathological features. Quantitative assessment of birefringence and penetration depth found significant differences between non-ruptured and ruptured tendons. Microstructure abnormalities were observed in the microstructure of two out of four tendinopathic samples. PSOCT has the potential to explore in situ and in-depth pathological change associated with Achilles tendon rupture, and could help to delineate abnormalities in tendinopathic samples in vivo.

  2. In-depth imaging and quantification of degenerative changes associated with Achilles ruptured tendons by polarization-sensitive optical coherence tomography

    Energy Technology Data Exchange (ETDEWEB)

    Bagnaninchi, P O; Yang, Y; Maffulli, G; El Haj, A; Maffulli, N [Institute for Science and Technology in Medicine, Keele University, Thornburrow Drive, Hartshill, Stoke-on-Trent ST4 7QB (United Kingdom); Bonesi, M; Meglinski, I [Cranfield Health, Cranfield University, Cranfield MK43 0AL (United Kingdom); Phelan, C, E-mail: pierre.bagnaninchi@ed.ac.u [Department of Pathology, University Hospital of North Staffordshire, Stoke-on-Trent ST4 7QB (United Kingdom)

    2010-07-07

    The objective of this study was to develop a method based on polarization-sensitive optical coherent tomography (PSOCT) for the imaging and quantification of degenerative changes associated with Achilles tendon rupture. Ex vivo PSOCT examinations were performed in 24 patients. The study involved samples from 14 ruptured Achilles tendons, 4 tendinopathic Achilles tendons and 6 patellar tendons (collected during total knee replacement) as non-ruptured controls. The samples were imaged in both intensity and phase retardation modes within 24 h after surgery, and birefringence was quantified. The samples were fixed and processed for histology immediately after imaging. Slides were assessed twice in a blind manner to provide a semi-quantitative histological score of degeneration. In-depth micro structural imaging was demonstrated. Collagen disorganization and high cellularity were observable by PSOCT as the main markers associated with pathological features. Quantitative assessment of birefringence and penetration depth found significant differences between non-ruptured and ruptured tendons. Microstructure abnormalities were observed in the microstructure of two out of four tendinopathic samples. PSOCT has the potential to explore in situ and in-depth pathological change associated with Achilles tendon rupture, and could help to delineate abnormalities in tendinopathic samples in vivo.

  3. Quantum dot imaging in the second near-infrared optical window: studies on reflectance fluorescence imaging depths by effective fluence rate and multiple image acquisition.

    Science.gov (United States)

    Jung, Yebin; Jeong, Sanghwa; Nayoun, Won; Ahn, Boeun; Kwag, Jungheon; Geol Kim, Sang; Kim, Sungjee

    2015-04-01

    Quantum dot (QD) imaging capability was investigated by the imaging depth at a near-infrared second optical window (SOW; 1000 to 1400 nm) using time-modulated pulsed laser excitations to control the effective fluence rate. Various media, such as liquid phantoms, tissues, and in vivo small animals, were used and the imaging depths were compared with our predicted values. The QD imaging depth under excitation of continuous 20 mW/cm(2) laser was determined to be 10.3 mm for 2 wt%hemoglobin phantom medium and 5.85 mm for 1 wt% intralipid phantom, which were extended by more than two times on increasing the effective fluence rate to 2000 mW/cm(2). Bovine liver and porcine skin tissues also showed similar enhancement in the contrast-to-noise ratio (CNR) values. A QD sample was inserted into the abdomen of a mouse.With a higher effective fluence rate, the CNR increased more than twofold and the QD sample became clearly visualized, which was completely undetectable under continuous excitation.Multiple acquisitions of QD images and averaging process pixel by pixel were performed to overcome the thermal noise issue of the detector in SOW, which yielded significant enhancement in the imaging capability, showing up to a 1.5 times increase in the CNR.

  4. AERONET-based models of smoke-dominated aerosol near source regions and transported over oceans, and implications for satellite retrievals of aerosol optical depth

    Science.gov (United States)

    Sayer, A. M.; Hsu, N. C.; Eck, T. F.; Smirnov, A.; Holben, B. N.

    2014-10-01

    Smoke aerosols from biomass burning are an important component of the global aerosol system. Analysis of Aerosol Robotic Network (AERONET) retrievals of aerosol microphysical/optical parameters at 10 sites reveals variety between biomass burning aerosols in different global source regions, in terms of aerosol particle size and single scatter albedo (SSA). Case studies of smoke observed at coastal/island AERONET sites also mostly lie within the range of variability at the near-source sites. Differences between sites tend to be larger than variability at an individual site, although optical properties for some sites in different regions can be quite similar. Across the sites, typical midvisible SSA ranges from ~ 0.95-0.97 (sites dominated by boreal forest or peat burning, typically with larger fine-mode particle radius and spread) to ~ 0.88-0.9 (sites most influenced by grass, shrub, or crop burning, typically smaller fine-mode particle radius and spread). The tropical forest site Alta Floresta (Brazil) is closer to this second category, although with intermediate SSA ~ 0.92. The strongest absorption is seen in southern African savannah at Mongu (Zambia), with average midvisible SSA ~ 0.85. Sites with stronger absorption also tend to have stronger spectral gradients in SSA, becoming more absorbing at longer wavelengths. Microphysical/optical models are presented in detail so as to facilitate their use in radiative transfer calculations, including extension to UV (ultraviolet) wavelengths, and lidar ratios. One intended application is to serve as candidate optical models for use in satellite aerosol optical depth (AOD) retrieval algorithms. The models presently adopted by these algorithms over ocean often have insufficient absorption (i.e. too high SSA) to represent these biomass burning aerosols. The underestimates in satellite-retrieved AOD in smoke outflow regions, which have important consequences for applications of these satellite data sets, are consistent with

  5. Total ozone column, aerosol optical depth and precipitable water effects on solar erythemal ultraviolet radiation recorded in Malta.

    Science.gov (United States)

    Bilbao, Julia; Román, Roberto; Yousif, Charles; Mateos, David; Miguel, Argimiro

    2013-04-01

    The Universities of Malta and Valladolid (Spain) developed a measurement campaign, which took place in the Institute for Energy Technology in Marsaxlokk (Southern Malta) between May and October 2012, and it was supported by the Spanish government through the Project titled "Measurement campaign about Solar Radiation, Ozone, and Aerosol in the Mediterranean area" (with reference CGL2010-12140-E). This campaign provided the first ground-based measurements in Malta of erythemal radiation and UV index, which indicate the effectiveness of the sun exposure to produce sunburn on human skin. A wide variety of instruments was involved in the campaign, providing a complete atmospheric characterization. Data of erythemal radiation and UV index (from UVB-1 pyranometer), total shortwave radiaton (global and diffuse components from CM-6B pyranometers), and total ozone column, aerosol optical thickness, and precitable water column (from a Microtops-II sunphotometer) were available in the campaign. Ground-based and satellite instruments were used in the analysis, and several intercomparisons were carried out to validate remote sensing data. OMI, GOME, GOME-2, and MODIS instruments, which provide data of ozone, aerosol load and optical properties, were used to this end. The effects on solar radiation, ultraviolet and total shortwave ranges, of total ozone column, aerosol optical thickness and precipitable water column were obtained using radiation measurements at different fixed solar zenith angles. The empirical results shown a determinant role of the solar position, a negligible effect of ozone on total shortwave radiation, and a stronger attenuation provided by aerosol particles in the erythemal radiation. A variety of aerosol types from different sources (desert dust, biomass burning, continental, and maritime) reach Malta, in this campaign several dust events from the Sahara desert occurred and were analyzed establishing the air mass back-trajectories ending at Malta at

  6. Medical diagnosis system and method with multispectral imaging. [depth of burns and optical density of the skin

    Science.gov (United States)

    Anselmo, V. J.; Reilly, T. H. (Inventor)

    1979-01-01

    A skin diagnosis system includes a scanning and optical arrangement whereby light reflected from each incremental area (pixel) of the skin is directed simultaneously to three separate light filters, e.g., IR, red, and green. As a result, the three devices simultaneously produce three signals which are directly related to the reflectance of light of different wavelengths from the corresponding pixel. These three signals for each pixel after processing are used as inputs to one or more output devices to produce a visual color display and/or a hard copy color print, for one usable as a diagnostic aid by a physician.

  7. Towards a first ground-based validation of aerosol optical depths from Sentinel-2 over the complex topography of the Alps

    Science.gov (United States)

    Marinelli, Valerio; Cremonese, Edoardo; Diémoz, Henri; Siani, Anna Maria

    2017-04-01

    The European Space Agency (ESA) is spending notable effort to put in operation a new generation of advanced Earth-observation satellites, the Sentinel constellation. In particular, the Sentinel-2 host an instrumental payload mainly consisting in a MultiSpectral Instrument (MSI) imaging sensor, capable of acquiring high-resolution imagery of the Earth surface and atmospheric reflectance at selected spectral bands, hence providing complementary measurements to ground-based radiometric stations. The latter can provide reference data for validating the estimates from spaceborne instruments such as Sentinel-2A (operating since October 2015), whose aerosol optical thickness (AOT) values, can be obtained from correcting SWIR (2190 nm) reflectance with an improved dense dark vegetation (DDV) algorithm. In the Northwestern European Alps (Saint-Christophe, 45.74°N, 7.36°E) a Prede POM-02 sun/sky aerosol photometer has been operating for several years within the EuroSkyRad network by the Environmental Protection Agency of Aosta Valley (ARPA Valle d'Aosta), gathering direct sun and diffuse sky radiance for retrieving columnar aerosol optical properties. This aerosol optical depth (AOD) dataset represents an optimal ground-truth for the corresponding Sentinel-2 estimates obtained with the Sen2cor processor in the challenging environment of the Alps (complex topography, snow-covered surfaces). We show the deviations between the two measurement series and propose some corrections to enhance the overall accuracy of satellite estimates.

  8. A comparison of two methods to measure choroidal thickness by enhanced depth imaging optical coherence tomography -Letter to the Editor

    DEFF Research Database (Denmark)

    Lundberg, Kristian; Vergmann, Anna Stage; Vestergaard, Anders Højslet;

    2016-01-01

    -domain optical coherence tomography (EDI-SD OCT) has made it possible to visualize the choroid, and it is generally accepted that Heidelberg Spectralis OCT provides valid measurements of choroidal thickness (CT) (Li et al. 2014), although no fully automated software is commercially available. In the literature...... different approaches and software programs are described for manual measurement of the CT. Unfortunately many investigators do not report in details which method they use. Two methods for CT-measurement are available in the Heidelberg software, but to our knowledge these methods have not been compared....... Hence, the purpose of this study was to evaluate and validate the Segmentation method and the Ruler method for CT-measurement. We obtained data from 10 healthy subjects, aged 15 to 17 years (mean 16.3) and 10 patients with macular pathology, aged 59 to 79 years (mean 71.8). The diseases included wet age...

  9. Analysis of SMOS brightness temperature and vegetation optical depth data with coupled land surface and radiative transfer models in Southern Germany

    Directory of Open Access Journals (Sweden)

    F. Schlenz

    2012-10-01

    Full Text Available Soil Moisture and Ocean Salinity (SMOS L1c brightness temperature and L2 optical depth data are analysed with a coupled land surface (PROMET and radiative transfer model (L-MEB. The coupled models are validated with ground and airborne measurements under contrasting soil moisture, vegetation and land surface temperature conditions during the SMOS Validation Campaign in May and June 2010 in the SMOS test site Upper Danube Catchment in southern Germany. The brightness temperature root-mean-squared errors are between 6 K and 9 K. The L-MEB parameterisation is considered appropriate under local conditions even though it might possibly be further optimised. SMOS L1c brightness temperature data are processed and analysed in the Upper Danube Catchment using the coupled models in 2011 and during the SMOS Validation Campaign 2010 together with airborne L-band brightness temperature data. Only low to fair correlations are found for this comparison (R between 0.1–0.41. SMOS L1c brightness temperature data do not show the expected seasonal behaviour and are positively biased. It is concluded that RFI is responsible for a considerable part of the observed problems in the SMOS data products in the Upper Danube Catchment. This is consistent with the observed dry bias in the SMOS L2 soil moisture products which can also be related to RFI. It is confirmed that the brightness temperature data from the lower SMOS look angles and the horizontal polarisation are less reliable. This information could be used to improve the brightness temperature data filtering before the soil moisture retrieval. SMOS L2 optical depth values have been compared to modelled data and are not considered a reliable source of information about vegetation due to missing seasonal behaviour and a very high mean value. A fairly strong correlation between SMOS L2 soil moisture and optical depth was found (R = 0.65 even though the two variables are considered independent in the

  10. Optimal depth of cure for nanohybrid resin composite using quartz tungsten halogen and new high intensity light-emitting diode curing units.

    Science.gov (United States)

    Tanthanuch, Saijai; Ruengsri, Prapansri; Kukiattrakoon, Boonlert

    2013-08-01

    This study sought to evaluate the effects of quartz tungsten halogen (QTH) and light-emitting diode (LED) photocuring units on the degree of conversion (DC) and surface microhardness of a resin composite that had been cured for optimal depth of cure (DoC) assessment. Two hundred and forty cylindrical specimens (4.0 mm in diameter, 2.0-4.0 mm thick) of shade A2 resin composite were prepared and cured with either a QTH or an LED. The DC and top and bottom surface hardness were recorded, and data were analyzed using 2-way ANOVA, Tukey's test, t-test (α = 0.05) and linear regression analysis. The results showed that surface microhardness values and DC were affected by light intensity (P resin composite thickness (2, 3, and 4 mm) (P Resin composite polymerized by the QTH had an optimal DoC of 3 mm, compared to 4 mm for the LED.

  11. Planck 2016 intermediate results. XLVI. Reduction of large-scale systematic effects in HFI polarization maps and estimation of the reionization optical depth

    CERN Document Server

    Aghanim, N; Aumont, J; Baccigalupi, C; Ballardini, M; Banday, A J; Barreiro, R B; Bartolo, N; Basak, S; Battye, R; Benabed, K; Bernard, J -P; Bersanelli, M; Bielewicz, P; Bock, J J; Bonaldi, A; Bonavera, L; Bond, J R; Borrill, J; Bouchet, F R; Boulanger, F; Bucher, M; Burigana, C; Butler, R C; Calabrese, E; Cardoso, J -F; Carron, J; Challinor, A; Chiang, H C; Colombo, L P L; Combet, C; Comis, B; Coulais, A; Crill, B P; Curto, A; Cuttaia, F; Davis, R J; de Bernardis, P; de Rosa, A; de Zotti, G; Delabrouille, J; Delouis, J -M; Di Valentino, E; Dickinson, C; Diego, J M; Doré, O; Douspis, M; Ducout, A; Dupac, X; Efstathiou, G; Elsner, F; Enßlin, T A; Eriksen, H K; Falgarone, E; Fantaye, Y; Finelli, F; Forastieri, F; Frailis, M; Fraisse, A A; Franceschi, E; Frolov, A; Galeotta, S; Galli, S; Ganga, K; Génova-Santos, R T; Gerbino, M; Ghosh, T; González-Nuevo, J; Górski, K M; Gratton, S; Gruppuso, A; Gudmundsson, J E; Hansen, F K; Helou, G; Henrot-Versillé, S; Herranz, D; Hivon, E; Huang, Z; Ilic, S; Jaffe, A H; Jones, W C; Keihänen, E; Keskitalo, R; Kisner, T S; Knox, L; Krachmalnicoff, N; Kunz, M; Kurki-Suonio, H; Lagache, G; Lamarre, J -M; Langer, M; Lasenby, A; Lattanzi, M; Lawrence, C R; Jeune, M Le; Leahy, J P; Levrier, F; Liguori, M; Lilje, P B; López-Caniego, M; Ma, Y -Z; Macías-Pérez, J F; Maggio, G; Mangilli, A; Maris, M; Martin, P G; Martínez-González, E; Matarrese, S; Mauri, N; McEwen, J D; Meinhold, P R; Melchiorri, A; Mennella, A; Migliaccio, M; Miville-Deschênes, M -A; Molinari, D; Moneti, A; Montier, L; Morgante, G; Moss, A; Mottet, S; Naselsky, P; Natoli, P; Oxborrow, C A; Pagano, L; Paoletti, D; Partridge, B; Patanchon, G; Patrizii, L; Perdereau, O; Perotto, L; Pettorino, V; Piacentini, F; Plaszczynski, S; Polastri, L; Polenta, G; Puget, J -L; Rachen, J P; Racine, B; Reinecke, M; Remazeilles, M; Renzi, A; Rocha, G; Rossetti, M; Roudier, G; Rubiño-Martín, J A; Ruiz-Granados, B; Salvati, L; Sandri, M; Savelainen, M; Scott, D; Sirri, G; Sunyaev, R; Suur-Uski, A -S; Tauber, J A; Tenti, M; Toffolatti, L; Tomasi, M; Tristram, M; Trombetti, T; Valiviita, J; Van Tent, F; Vibert, L; Vielva, P; Villa, F; Vittorio, N; Wandelt, B D; Watson, R; Wehus, I K; White, M; Zacchei, A; Zonca, A

    2016-01-01

    This paper describes the identification, modelling, and removal of previously unexplained systematic effects in the polarization data of the Planck High Frequency Instrument (HFI) on large angular scales, including new mapmaking and calibration procedures, new and more complete end-to-end simulations, and a set of robust internal consistency checks on the resulting maps. These maps, at 100, 143, 217, and 353 GHz, are early versions of those that will be released in final form later in 2016. The improvements allow us to determine the cosmic reionization optical depth $\\tau$ using, for the first time, the low-multipole $EE$ data from HFI, reducing significantly the central value and uncertainty, and hence the upper limit. Two different likelihood procedures are used to constrain $\\tau$ from two estimators of the CMB $E$- and $B$-mode angular power spectra at 100 and 143 GHz, after debiasing the spectra from a small remaining systematic contamination. These all give fully consistent results. A further consistenc...

  12. Time Series of Aerosol Column Optical Depth at the Barrow, Alaska, ARM Climate Research Facility for 2008 Fourth Quarter 2009 ARM and Climate Change Prediction Program Metric Report

    Energy Technology Data Exchange (ETDEWEB)

    C Flynn; AS Koontz; JH Mather

    2009-09-01

    The uncertainties in current estimates of anthropogenic radiative forcing are dominated by the effects of aerosols, both in relation to the direct absorption and scattering of radiation by aerosols and also with respect to aerosol-related changes in cloud formation, longevity, and microphysics (See Figure 1; Intergovernmental Panel on Climate Change, Assessment Report 4, 2008). Moreover, the Arctic region in particular is especially sensitive to changes in climate with the magnitude of temperature changes (both observed and predicted) being several times larger than global averages (Kaufman et al. 2009). Recent studies confirm that aerosol-cloud interactions in the arctic generate climatologically significant radiative effects equivalent in magnitude to that of green house gases (Lubin and Vogelmann 2006, 2007). The aerosol optical depth is the most immediate representation of the aerosol direct effect and is also important for consideration of aerosol-cloud interactions, and thus this quantity is essential for studies of aerosol radiative forcing.

  13. Planck early results. XIX. All-sky temperature and dust optical depth from Planck and IRAS. Constraints on the "dark gas" in our Galaxy

    DEFF Research Database (Denmark)

    Bucher, M.; Delabrouille, J.; Giraud-Héraud, Y.;

    2011-01-01

    mass fraction is relatively constant down to a few degrees from the Galactic plane. A possible explanation for the dark gas lies in a dark molecular phase, where H2 survives photodissociation but CO does not. The observed transition for the onsetof this phase in the solar neighbourhood (AV = 0.4mag...... density of observed gas is linear in the lowest column density regions at high Galactic latitudes. At high NH, the correlation is consistent with that of the lowest NH, for a given choice of the CO-to-H2 conversion factor. In the intermediate NH range, a departure from linearity is observed, with the dust......) appears consistent with recent theoretical predictions. It is also possible that up to half of the dark gas could be in atomic form, due to optical depth effects in the Hi measurements. © ESO, 2011....

  14. UNITED STABILIZING SCHEME FOR EDGE DELAY IN OPTICAL BURST SWITCHED NETWORKS

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    A novel scheme, namely united stabilizing scheme for edge delay, is introduced in optical burst switched networks. In the scheme, the limits of burst length and assembly time are both set according to certain qualifications. For executing the scheme, the conception for unit input bit rate is introduced to improve universality, and the assembly algorithm with a buffer safety space under the self-similar traffic model at each ingress edge router is proposed. Then, the components of burst and packet delay are concluded, and the equations that limits of burst length and assembly time should satisfy to stabilize the burst edge delay under different buffer offered loads are educed. The simulation results show that united stabilizing scheme stabilizes both burst and packet edge delay to a great extent when buffer offered load changes from 0.1 to 1, and the edge delay of burst and packet are near the limit values under larger offered load, respectively.

  15. Review of spectral domain-enhanced depth imaging optical coherence tomography of tumors of the retina and retinal pigment epithelium in children and adults

    Directory of Open Access Journals (Sweden)

    Carol L Shields

    2015-01-01

    Full Text Available Background: Spectral domain (SD enhanced depth imaging optical coherence tomography (EDI-OCT is a useful tool for anatomic, cross-sectional imaging of retinal conditions. Aims: The aim was to identify characteristic patterns of retinal and retinal pigment epithelial tumors on EDI-OCT in children and adults. Settings and Design: Retrospective review. Materials and Methods: Analysis of published reports and personal observations using office-based EDI-OCT for adults and portable hand-held SD OCT for infants and children. Results: Using EDI-OCT, retinal tumors such as small retinoblastoma, astrocytic hamartoma, and hemangioblastoma arose abruptly from the retina, immediately adjacent to normal retina. Small exophytic retinoblastoma and retinal hemangioblastoma showed the full-thickness, homogeneous retinal disorganization with surrounding normal retina "draping" over the margins. Retinoblastoma occasionally had intralesional cavities and surrounding subretinal fluid. Hemangioblastoma often had adjacent intraretinal edema and subretinal fluid. Astrocytic hamartoma arose within the nerve fiber layer and sometimes with a "moth-eaten" or cavitary appearance. Retinal pigment epithelial (RPE lesions such as congenital hypertrophy of RPE appeared flat with shadowing, occasional subretinal cleft, and abrupt photoreceptor loss. Congenital simple hamartoma showed an abrupt elevation from the inner retina with crisp, dark posterior shadowing. Combined hamartoma of the retina/RPE showed vitreoretinal traction causing "sawtooth mini-peak" or gently "maxi-peak" folding of the retina. RPE adenoma often produces remote macular edema or epiretinal membrane and the tumor has an irregular, "rugged" surface with deep shadowing. Conclusions: Enhanced depth imaging optical coherence tomography shows characteristic patterns that are suggestive of certain retinal and RPE tumors.

  16. Ultra-high-sensitive optical micro-angiography provides depth resolved visualization of microcirculations within human skin under psoriatic conditions

    Science.gov (United States)

    Qin, Jia; An, Lin; Wang, Ruikang

    2011-03-01

    Adequate functioning of the peripheral micro vascular in human skin is necessary to maintain optimal tissue perfusion and preserve normal hemodynamic function. There is a growing body of evidence suggests that vascular abnormalities may directly related to several dermatologic diseases, such as psoriasis, port-wine stain, skin cancer, etc. New in vivo imaging modalities to aid volumetric microvascular blood perfusion imaging are there for highly desirable. To address this need, we demonstrate the capability of ultra-high sensitive optical micro angiography to allow blood flow visualization and quantification of vascular densities of lesional psoriasis area in human subject in vivo. The microcirculation networks of lesion and non-lesion skin were obtained after post processing the data sets captured by the system. With our image resolution (~20 μm), we could compare these two types of microcirculation networks both qualitatively and quantitatively. The B-scan (lateral or x direction) cross section images, en-face (x-y plane) images and the volumetric in vivo perfusion map of lesion and non-lesion skin areas were obtained using UHS-OMAG. Characteristic perfusion map features were identified between lesional and non-lesional skin area. A statistically significant difference between vascular densities of lesion and non-lesion skin area was also found using a histogram based analysis. UHS-OMAG has the potential to differentiate the normal skin microcirculation from abnormal human skin microcirculation non-invasively with high speed and sensitivity. The presented data demonstrates the great potential of UHS-OMAG for detecting and diagnosing skin disease such as psoriasis in human subjects.

  17. Characterization of penetration depth as a function of optical fiber separation at various absorption and scatter coefficients for a noninvasive metabolic sensor

    Science.gov (United States)

    DeMilo, Charles; Brukilacchio, Thomas; Soller, Babs R.; Soyemi, Olusola

    2004-06-01

    A visible-near IR (500-1,000nm) fiber optic sensor is under development that is intended to non-invasively assess muscle metabolism through the measurement of tissue pH and oxygen partial pressure. These parameters are calculated from the spectra of hemoglobin and myoglobin in muscle. The sensor consists of transmit (illumination) fibers and receive (detection) fibers that are coupled to a spectrometer. Light from the probe must penetrate below the surface of the skin and into a 5-10mm thick layer of muscle. A study was conducted to quantify the relationship between transmit and receive fiber separation and sensor penetration depth below the surface of the skin. A liquid phantom was created to replicate the absorption (μa) and reduced scatter coefficient (μs') profiles typically found in human blood and tissue. The phantom consisted of a solution of Intralipid and India ink in the appropriate concentrations to achieve desired reduced scatter coefficient and absorption profiles. The reduced scatter coefficient of the liquid phantom was achieved to an accuracy of +/-10% compared to previously published data. A fixed illumination fiber and translatable detector fiber were placed in the liquid phantom, and the fiber separation was varied from 3-40mm. Values of μa and μs' varied from 0.03-0.40 cm-1 and 5.0-15.0 cm-1 respectively. Results from the experiment demonstrate a strong correlation between penetration depth and fiber separation. Additionally, it was found that penetration depth was not substantially influenced by absorption and scatter concentration. As signal-to-noise is an important parameter in many non-invasive biomedical applications, the relative signal as a function of fiber separation was determined to follow an exponential relationship.

  18. Network coding based joint signaling and dynamic bandwidth allocation scheme for inter optical network unit communication in passive optical networks

    Science.gov (United States)

    Wei, Pei; Gu, Rentao; Ji, Yuefeng

    2014-06-01

    As an innovative and promising technology, network coding has been introduced to passive optical networks (PON) in recent years to support inter optical network unit (ONU) communication, yet the signaling process and dynamic bandwidth allocation (DBA) in PON with network coding (NC-PON) still need further study. Thus, we propose a joint signaling and DBA scheme for efficiently supporting differentiated services of inter ONU communication in NC-PON. In the proposed joint scheme, the signaling process lays the foundation to fulfill network coding in PON, and it can not only avoid the potential threat to downstream security in previous schemes but also be suitable for the proposed hybrid dynamic bandwidth allocation (HDBA) scheme. In HDBA, a DBA cycle is divided into two sub-cycles for applying different coding, scheduling and bandwidth allocation strategies to differentiated classes of services. Besides, as network traffic load varies, the entire upstream transmission window for all REPORT messages slides accordingly, leaving the transmission time of one or two sub-cycles to overlap with the bandwidth allocation calculation time at the optical line terminal (the OLT), so that the upstream idle time can be efficiently eliminated. Performance evaluation results validate that compared with the existing two DBA algorithms deployed in NC-PON, HDBA demonstrates the best quality of service (QoS) support in terms of delay for all classes of services, especially guarantees the end-to-end delay bound of high class services. Specifically, HDBA can eliminate queuing delay and scheduling delay of high class services, reduce those of lower class services by at least 20%, and reduce the average end-to-end delay of all services over 50%. Moreover, HDBA also achieves the maximum delay fairness between coded and uncoded lower class services, and medium delay fairness for high class services.

  19. Validation of MODIS Aerosol Optical Depth Retrieval over Mountains in Central China Based on a Sun-Sky Radiometer Site of SONET

    Directory of Open Access Journals (Sweden)

    Yan Ma

    2016-02-01

    Full Text Available The 3 km Dark Target (DT aerosol optical depth (AOD products, 10 km DT and Deep Blue (DB AOD products from the Collection 6 (C6 product data of Moderate Resolution Imaging Spectroradiometer (MODIS are compared with Sun-sky Radiometer Network (SONET measurements at Song Mountain in central China, where ground-based remote sensing measurements of aerosol properties are still very limited. The seasonal variations of AODs are significant in the Song Mountain region, with higher AODs in spring and summer and lower AODs in autumn and winter. Annual mean AODs (0.55 µm vary in the range of 0.5–0.7, which indicates particle matter (PM pollutions in this mountain region. Validation against one-year ground-based measurements shows that AOD retrievals from the MODIS onboard Aqua satellite are better than those from the Terra satellite in Song Mountain. The 3 km and 10 km AODs from DT algorithms are comparable over this region, while the AOD accuracy of DB algorithm is relatively lower. However, the spatial coverage of DB products is higher than that of 10 km DT products. Moreover, the optical and microphysical characteristics of aerosols at Song Mountain are analyzed on the basis of SONET observations. It suggests that coarse-mode aerosol particles dominate in spring, and fine-mode particles dominate in summer. The aerosol property models are also established and compared to aerosol types used by MODIS algorithm.

  20. Long-term analysis of aerosol optical depth over Northeast Asia using a satellite-based measurement: MI Yonsei Aerosol Retrieval Algorithm (YAER)

    Science.gov (United States)

    Kim, Mijin; Kim, Jhoon; Yoon, Jongmin; Chung, Chu-Yong; Chung, Sung-Rae

    2017-04-01

    In 2010, the Korean geostationary earth orbit (GEO) satellite, the Communication, Ocean, and Meteorological Satellite (COMS), was launched including the Meteorological Imager (MI). The MI measures atmospheric condition over Northeast Asia (NEA) using a single visible channel centered at 0.675 μm and four IR channels at 3.75, 6.75, 10.8, 12.0 μm. The visible measurement can also be utilized for the retrieval of aerosol optical properties (AOPs). Since the GEO satellite measurement has an advantage for continuous monitoring of AOPs, we can analyze the spatiotemporal variation of the aerosol using the MI observations over NEA. Therefore, we developed an algorithm to retrieve aerosol optical depth (AOD) using the visible observation of MI, and named as MI Yonsei Aerosol Retrieval Algorithm (YAER). In this study, we investigated the accuracy of MI YAER AOD by comparing the values with the long-term products of AERONET sun-photometer. The result showed that the MI AODs were significantly overestimated than the AERONET values over bright surface in low AOD case. Because the MI visible channel centered at red color range, contribution of aerosol signal to the measured reflectance is relatively lower than the surface contribution. Therefore, the AOD error in low AOD case over bright surface can be a fundamental limitation of the algorithm. Meanwhile, an assumption of background aerosol optical depth (BAOD) could result in the retrieval uncertainty, also. To estimate the surface reflectance by considering polluted air condition over the NEA, we estimated the BAOD from the MODIS dark target (DT) aerosol products by pixel. The satellite-based AOD retrieval, however, largely depends on the accuracy of the surface reflectance estimation especially in low AOD case, and thus, the BAOD could include the uncertainty in surface reflectance estimation of the satellite-based retrieval. Therefore, we re-estimated the BAOD using the ground-based sun-photometer measurement, and

  1. An Improved Retrieval Algorithm of Aerosol Optical Depth%一种反演气溶胶光学厚度的改进方法

    Institute of Scientific and Technical Information of China (English)

    何涛; 赵凤生

    2011-01-01

    The algorithm to retrieve the aerosol optical depth over land has been completely restructured to produce the collection 005 products based on the algorithm by Levy et al. But the accuracy of the MODIS aerosol optical depth (AOD) products still has very large differences for different seasons and geographic locations in China. In order to improve the accuracy of aerosol retrieval products, an easier and faster algorithm for retrieval of aerosol optical depth over land with MODIS IB data is introduced. This algorithm deals with the surface reflectance relationships is the same way as MODIS V5. 2 algorithm. In order to better represent aerosol properties in China, the size distribution and refractive index of aerosol have been improved. Considering the fine structure of the aerosol size distribution has a little effect on satellite remote sensing of aerosol optical depth, this algorithm use the Junge aerosol size distribution to approximate the aerosol size distribution in an actual atmosphere. The real and imaginary index of refractive is 1. 5 and 0. 005, respectively. The complex refractive index is assumed for all wavelengths(0. 47,0. 55,0. 66 ^m and 2. 1 fjLm).In order to verify the accuracy and regional applicability of this algorithm, aerosol optical depth is derived with this algorithm using the MODIS IB data at Taihu and Xianghe, and this retrieval result is compared with equivalent measurements from AERONET (Aerosol Robotic NETwork) site (Level 2. 0 data). The MODIS/AOD product and IB data from September 2006 to June 2008 at Taihu (MODISI/AOD product and IB data from May 2008 to July 2009 at Xianghe) has been matched with L2. 0 AOD product from AERONET stations during the same period. Data from the AERONET are averaged within 30 min before and after the satellite's passing, and the MODIS data are averaged over a 10 km (15 km at Xianghe) area centered at the ground stations.The comparison results show that the standard deviation of the new algorithm inversion

  2. Accelerating frequency-domain diffuse optical tomographic image reconstruction using graphics processing units.

    Science.gov (United States)

    Prakash, Jaya; Chandrasekharan, Venkittarayan; Upendra, Vishwajith; Yalavarthy, Phaneendra K

    2010-01-01

    Diffuse optical tomographic image reconstruction uses advanced numerical models that are computationally costly to be implemented in the real time. The graphics processing units (GPUs) offer desktop massive parallelization that can accelerate these computations. An open-source GPU-accelerated linear algebra library package is used to compute the most intensive matrix-matrix calculations and matrix decompositions that are used in solving the system of linear equations. These open-source functions were integrated into the existing frequency-domain diffuse optical image reconstruction algorithms to evaluate the acceleration capability of the GPUs (NVIDIA Tesla C 1060) with increasing reconstruction problem sizes. These studies indicate that single precision computations are sufficient for diffuse optical tomographic image reconstruction. The acceleration per iteration can be up to 40, using GPUs compared to traditional CPUs in case of three-dimensional reconstruction, where the reconstruction problem is more underdetermined, making the GPUs more attractive in the clinical settings. The current limitation of these GPUs in the available onboard memory (4 GB) that restricts the reconstruction of a large set of optical parameters, more than 13,377.

  3. MEGARA optical design: the new integral field unit and multi-object spectrograph for the GTC 10m telescope

    Science.gov (United States)

    García-Vargas, María. Luisa; Sánchez-Blanco, Ernesto; Carrasco, Esperanza; Gil de Paz, Armando; Páez, Gonzalo; Pérez, Ana; Gallego, Jesús; Sánchez, Francisco; Vílchez, José M.

    2012-12-01

    We describe the optical design of MEGARA, the future optical Integral Field Unit (IFU) and Multi-Object Spectrograph (MOS) for the 10.4-m Gran Telescopio CANARI