WorldWideScience

Sample records for altimeters

  1. Altimeter Setting Indicator

    Data.gov (United States)

    Department of Transportation — The Altimeter Setting Indicator (ASI) is an aneroid system used at airports to provide an altimeter setting for aircraft altimeters. This indicator may be an analog...

  2. Altimeter waveform software design

    Science.gov (United States)

    Hayne, G. S.; Miller, L. S.; Brown, G. S.

    1977-01-01

    Techniques are described for preprocessing raw return waveform data from the GEOS-3 radar altimeter. Topics discussed include: (1) general altimeter data preprocessing to be done at the GEOS-3 Data Processing Center to correct altimeter waveform data for temperature calibrations, to convert between engineering and final data units and to convert telemetered parameter quantities to more appropriate final data distribution values: (2) time "tagging" of altimeter return waveform data quantities to compensate for various delays, misalignments and calculational intervals; (3) data processing procedures for use in estimating spacecraft attitude from altimeter waveform sampling gates; and (4) feasibility of use of a ground-based reflector or transponder to obtain in-flight calibration information on GEOS-3 altimeter performance.

  3. Multi-beam laser altimeter

    Science.gov (United States)

    Bufton, Jack L.; Harding, David J.; Ramos-Izquierdo, Luis

    1993-01-01

    Laser altimetry provides a high-resolution, high-accuracy method for measurement of the elevation and horizontal variability of Earth-surface topography. The basis of the measurement is the timing of the round-trip propagation of short-duration pulses of laser radiation between a spacecraft and the Earth's surface. Vertical resolution of the altimetry measurement is determined primarily by laser pulsewidth, surface-induced spreading in time of the reflected pulse, and the timing precision of the altimeter electronics. With conventional gain-switched pulses from solid-state lasers and sub-nsec resolution electronics, sub-meter vertical range resolution is possible from orbital attitudes of several hundred kilometers. Horizontal resolution is a function of laser beam footprint size at the surface and the spacing between successive laser pulses. Laser divergence angle and altimeter platform height above the surface determine the laser footprint size at the surface, while laser pulse repetition-rate, laser transmitter beam configuration, and altimeter platform velocity determine the space between successive laser pulses. Multiple laser transitters in a singlaltimeter instrument provide across-track and along-track coverage that can be used to construct a range image of the Earth's surface. Other aspects of the multi-beam laser altimeter are discussed.

  4. Satellite altimeter remote sensing of ice caps

    OpenAIRE

    Rinne, Eero Juhani

    2011-01-01

    This thesis investigates the use of satellite altimetry techniques for measuring surface elevation changes of ice caps. Two satellite altimeters, Radar Altimeter 2 (RA-2) and Geoscience Laser Altimeter System (GLAS) are used to assess the surface elevation changes of three Arctic ice caps. This is the first time the RA-2 has been used to assess the elevation changes of ice caps - targets much smaller than the ice sheets which are the instrument’s primary land ice targets. Algor...

  5. Web-based Altimeter Service

    Science.gov (United States)

    Callahan, P. S.; Wilson, B. D.; Xing, Z.; Raskin, R. G.

    2010-12-01

    We have developed a web-based system to allow updating and subsetting of TOPEX data. The Altimeter Service will be operated by PODAAC along with their other provision of oceanographic data. The Service could be easily expanded to other mission data. An Altimeter Service is crucial to the improvement and expanded use of altimeter data. A service is necessary for altimetry because the result of most interest - sea surface height anomaly (SSHA) - is composed of several components that are updated individually and irregularly by specialized experts. This makes it difficult for projects to provide the most up-to-date products. Some components are the subject of ongoing research, so the ability for investigators to make products for comparison or sharing is important. The service will allow investigators/producers to get their component models or processing into widespread use much more quickly. For coastal altimetry, the ability to subset the data to the area of interest and insert specialized models (e.g., tides) or data processing results is crucial. A key part of the Altimeter Service is having data producers provide updated or local models and data. In order for this to succeed, producers need to register their products with the Altimeter Service and to provide the product in a form consistent with the service update methods. We will describe the capabilities of the web service and the methods for providing new components. Currently the Service is providing TOPEX GDRs with Retracking (RGDRs) in netCDF format that has been coordinated with Jason data. Users can add new orbits, tide models, gridded geophysical fields such as mean sea surface, and along-track corrections as they become available and are installed by PODAAC. The updated fields are inserted into the netCDF files while the previous values are retained for comparison. The Service will also generate SSH and SSHA. In addition, the Service showcases a feature that plots any variable from files in netCDF. The

  6. Laser altimeter of CE-1 payloads system

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The design and operation of the Laser Altimeter of CE-1 Payloads System are presented in this paper.The paper includes the design of the system and spacecraft-level laser,the description of the emitting-system and receiving system,and the testing of the laser altimeter.The CE-1 laser altimeter is the first Chinese deep-space probe using a laser.It has one beam and operates at 1 Hz,with a nominal accuracy of 5 m.The laser altimeter has operated successfully in lunar orbit since November 28,2007.It has obtained 9120 thousand data values about the lunar altitude.

  7. Improved retracking algorithm for oceanic altimeter waveforms

    Institute of Scientific and Technical Information of China (English)

    Lifeng Bao; Yang Lu; Yong Wang

    2009-01-01

    Over the deep oceans without land/ice interference, the waveforms created by the return altimeter pulse generally follow the ocean model of Brown, and the corresponding range can be properly determined using the result from an onboard tracker. In the case of com-plex altimeter waveforms corrupted due to a variety of reasons, the processor on the satellite cannot properly determine the center of the leading edge, and range observations can be in error. As an efficacious method to improve the precision of those altimeter observations with complex waveforms, waveform retracking is required to reprocess the original returning pulse. Based on basic altimeter theory and the geometric feature of altimeter waveforms, we developed a new altimeter waveform retracker, which is valid for all altimeter wave-forms once there exists a reasonable returning signal. The performances of the existing Beta-5 retracker, threshold retracker, improved threshold retracker, and the new retracker are assessed in the experimental regions (China Seas and its adjacent regions), and the improvements in the accuracy of sea surface height are investigated by the difference between retracked altimeter observations and ref-erenced geoid. The comparisons denote that the new algorithm gives the best performance in both the open ocean and coastal regions. Also, the new retracker presents a uniform performance in the whole test region. Besides, there is a significant improvement in the short-wavelength precision and the spatial resolution of sea surface height after retracking process.

  8. Altimeter and gravity data analysis

    Science.gov (United States)

    Rapp, Richard H.

    1992-01-01

    The studies carried out under this grant fell into two broad areas. The first area was the analysis of surface gravity data with the ultimate goal of providing normal equations that could be used in combination with normal equations from the analysis of satellite orbit perturbations to obtain an optimal estimate of the gravitational potential coefficients of the Earth. The second main research activity was the estimation of gravity anomalies in ocean areas from satellite altimeter data. Such anomalies could enable the improved calibration of potential coefficient models derived solely from the analysis of orbital perturbation information. The studies in these two areas are discussed.

  9. Multishot laser altimeter: design and performance.

    Science.gov (United States)

    Sun, X; Abshire, J B; Davidson, F M

    1993-08-20

    The maximum measurement range of a laser altimeter can be extended by averaging the measurements from multiple laser shots at the same target. We present the principles of operation and design of such a multishot laser altimeter, which uses a Si avalanche photodiode detector. As an example, the performance of a spaceborne multishot altimeter containing components similar to those of the single-shot Mars Observer Laser Altimeter are given under operating conditions that would be encountered near Saturn. With 100-shot averages, we show that the multishot laser altimeter is capable of accurate ranging at fly-by distances of 10,000 km from an icy satellite. With 100-shot averages, the minimum optical signal level at a 90% correct-measurement probability under nighttime background is 9.8 detected signal photons per pulse as compared with 76 photons per pulse with a single shot. PMID:20830120

  10. ENVISAT Radar Altimeter Individual Echoes

    Science.gov (United States)

    Zanifé, O. Z.; Roca, M.; Rémy, F.; Legrèsy, B.; Chapron, B.; Laxon, S.; Pilar Milagro, M.; Benveniste, J.

    2006-07-01

    A unique feature of the ENVISAT RA-2 is to provide bursts of individual, unav eraged Ku band echo s ample data in phase (I) and quadrature (Q), at the full rate 1800 Hz. This data offers a unique possibility to assess the full capabilities of altimeter measurements. Both technically and scientifically, much can be expected fro m these bursts o f individual echoes, e.g., speckle characteristics over different altimeter scen es, o cean , ice, land, but also, potential blurring effects associat ed with range windo w changes during the 100 echoes on-board av eraging. Moreover, for the first time in altimetry fro m space, investigations can be carried on the direct use of phase information from backscatter signals. ENVISAT RA-2 also features a second frequency in S band. The co mbination bet ween absolutely calibrated Ku and S b and d ata can yield interesting improvement for wind speed, wav e period, g as exchang e estimates , etc. ESA has launched a study on this topic to seed the use of individual echoes by s cientists. This study is reaching completion and reconstructed echoes will be made available for the first time to the scientific community. Results fro m the technical and s cientific application of individual echoes will be pres ented.

  11. Dynamic test of radio altimeter based on IQ modulation

    Science.gov (United States)

    Pan, Hongfei; Tian, Yu; Li, Miao

    2010-08-01

    This paper based on the analysis and research of radio altimeter and its basic principles, it introduces a design for I/Q modulator's radio altimeter testing system. Further, data got from the test had been analyzed. Combined with the testing data of the altimeter, a construction of the I/Q modulator's radio altimeter testing system is built.

  12. Robust Control for the Mercury Laser Altimeter

    Science.gov (United States)

    Rosenberg, Jacob S.

    2006-01-01

    Mercury Laser Altimeter Science Algorithms is a software system for controlling the laser altimeter aboard the Messenger spacecraft, which is to enter into orbit about Mercury in 2011. The software will control the altimeter by dynamically modifying hardware inputs for gain, threshold, channel-disable flags, range-window start location, and range-window width, by using ranging information provided by the spacecraft and noise counts from instrument hardware. In addition, because of severe bandwidth restrictions, the software also selects returns for downlink.

  13. Design and Performance Measurement of the Mercury Laser Altimeter

    Science.gov (United States)

    Sun, Xiao-Li; Cavanaugh, John F.; Smith, James C.; Bartels, Arlin E.

    2004-01-01

    We report the design and test results of the Mercury Laser Altimeter on MESSENGER mission to be launched in May 2004. The altimeter will provide planet surface topography measurements via laser pulse time of flight.

  14. The Ganymede Laser Altimeter (GALA)

    Science.gov (United States)

    Hussmann, H.

    2015-12-01

    The Ganymede Laser Altimeter (GALA) is one of the instruments selected for ESA's Jupiter Icy Moons Explorer (JUICE). A fundamental goal of any exploratory space mission is to characterize and measure the shape, topography, and rotation of the target bodies. A state of the art tool for this task is laser altimetry because it can provide absolute topographic height and position with respect to a body centered reference system. With respect to Ganymede, the GALA instrument aims at mapping of global, regional and local topography; confirming the global subsurface ocean and further characterization of the water-ice/liquid shell by monitoring the dynamic response of the ice shell to tidal forces; providing constraints on the forced physical librations and spin-axis obliquity; determining Ganymede's shape; obtaining detailed topographic profiles across the linear features of grooved terrain, impact structures, possible cryo-volcanic features and other different surface units; providing information about slope, roughness and albedo (at 1064nm) of Ganymede's surface. GALA uses the direct-detection (classical) approach of laser altimetry. Laser pulses are emitted at a wavelength of 1064 nm by using an actively Q-switched Nd:Yag laser. The pulse energy and pulse repetition frequency are 17 mJ at 30 Hz, respectively. The emission time of each pulse is measured by the detector. The beam is reflected from the surface and received at a 25 cm diameter F/1 telescope. The returning laser pulse is refocused onto a silicon avalanche photodiode (APD) through back-end optics including a narrow bandpass interference filter for isolating the 1064 nm wavelength. The APD-signal is then amplified, sampled and fed to a digital range finder. The minimum acceptable SNR is approx. 1.2. This system determines the time of flight, pulse intensity, width and full shape. The GALA instrument is developed in collaboration of institutes and industry from Germany, Japan, Switzerland and Spain.

  15. High Density GEOSAT/GM Altimeter Data

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The high density Geosat/GM altimeter data south of 30 S have finally arrived. In addition, ERS-1 has completed more than 6 cycles of its 35-day repeat track. These...

  16. Analysis of Altimeter Wet Troposphere Range Correction

    Institute of Scientific and Technical Information of China (English)

    纪永刚; 张杰; 姬光荣; 张有广

    2004-01-01

    Wet path delay caused by tropospheric water vapor must be considered before altimeter data are used in oceanic application. This paper analyzed several methods of atmosphere water range correction (AWRC) using Seasat, Geosat, TOPEX and ERS-1 data, especially the calculated delay path using brightness temperature of TMR on TOPEX and EMR on ERS-1; and discussed some other problems of AWRC.

  17. Airborne laser altimeter measurements of landscape topography

    International Nuclear Information System (INIS)

    Measurements of topography can provide a wealth of information on landscape properties for managing hydrologic and geologic systems and conserving natural and agricultural resources. This article discusses the application of an airborne laser altimeter to measure topography and other landscape surface properties. The airborne laser altimeter makes 4000 measurements per second with a vertical recording resolution of 5 cm. Data are collected digitally with a personal computer. A video camera, borehole sighted with the laser, records an image for locating flight lines. GPS data are used to locate flight line positions on the landscape. Laser data were used to measure vegetation canopy topography, height, cover, and distribution and to measure microtopography of the land surface and gullies with depths of 15–20 cm. Macrotopography of landscape profiles for segments up to 4 km were in agreement with available topographic maps but provided more detail. Larger gullies with and without vegetation, and stream channel cross sections and their associated floodplains have also been measured and reported in other publications. Landscape segments for any length could be measured for either micro- or macrotopography. Airborne laser altimeter measurements of landscape profiles can provide detailed information on landscape properties or specific needs that will allow better decisions on the design and location of structures (i.e., roads, pipe, and power lines) and for improving the management and conservation of natural and agricultural landscapes. (author)

  18. Quality assessment of altimeter data through tide gauge comparisons

    Science.gov (United States)

    Prandi, Pierre; Valladeau, Guillaume; Ablain, Michael; Picot, Nicolas; Desjonquères, Jean-Damien

    2015-04-01

    Since the first altimeter missions and the improvements performed in the accuracy of sea surface height measurements from 1992 onwards, the importance of global quality assessment of altimeter data has been increasing. Global CalVal studies usually assess this performance by the analysis of internal consistency and cross-comparison between all missions. The overall quality assessment of altimeter data can be performed by analyzing their internal consistency and the cross-comparison between all missions. As a complementary approach, tide gauge measurements are used as an external and independent reference to enable further quality assessment of the altimeter sea level and provide a better estimate of the multiple altimeter performances. In this way, both altimeter and tide gauge observations, dedicated to climate applications, require a rigorous quality control. The tide gauge time series considered in this study derive from several networks (GLOSS/CLIVAR, PSMSL, REFMAR) and provide sea-level heights with a physical content comparable with altimetry sea level estimates. Concerning altimeter data, the long-term drift assessment can be evaluated thanks to a widespread network of tide gauges. Thus, in-situ measurements are compared with altimeter sea level for the main altimeter missions. If altimeter time series are long enough, tide gauge data provide a relevant estimation of the global Mean Sea Level (MSL) drift calculated for all the missions. Moreover, comparisons with sea level products merging all the altimeter missions together have also been performed using several datasets, among which the AVISO delayed-time Sea Level Anomaly grids.

  19. Initial development of a laser altimeter

    OpenAIRE

    Gilio, Joseph Paul

    1985-01-01

    A design study was carried out of a small, expendable, self-contained laser altimeter for overwater operations at low altitude. A .904 um GaAs laser was used to build a prototype transmitter/receiver at a cost of less than $600 and small enough to fit inside a 5-inch diameter cylinder, 5 inches long. Tests at a height of 120 feet above the surface of a lake resulted in a signal-to-noise ration of 6, and validated the trade-off equation used in the study. A second test model, with design im...

  20. Mars Observer Laser Altimeter: laser transmitter.

    Science.gov (United States)

    Afzal, R S

    1994-05-20

    The Mars Observer Laser Altimeter utilizes a space-qualified diode-laser-pumped Q-switched Nd:YAG laser transmitter. A simple numerical model of the laser energetics is presented, which predicts the pulse energy and pulse width. Comparisons with the measured data available are made. The temperature dependence of the laser transmitter is also predicted. This dependence prediction is particularly important in determining the operational temperature range of the transmitter. Knowing the operational temperature range is especially important for a passive, thermally controlled laser operating in space. PMID:20885685

  1. Geoscience laser altimeter system - stellar reference system

    International Nuclear Information System (INIS)

    GLAS is an EOS space-based laser altimeter being developed to profile the height of the Earth's ice sheets with ∼15 cm single shot accuracy from space under NASA's Mission to Planet Earth (MTPE). The primary science goal of GLAS is to determine if the ice sheets are increasing or diminishing for climate change modeling. This is achieved by measuring the ice sheet heights over Greenland and Antarctica to 1.5 cm/yr over 100 kmx100 km areas by crossover analysis (Zwally 1994). This measurement performance requires the instrument to determine the pointing of the laser beam to ∼5 urad (1 arcsecond), 1-sigma, with respect to the inertial reference frame. The GLAS design incorporates a stellar reference system (SRS) to relate the laser beam pointing angle to the star field with this accuracy. This is the first time a spaceborne laser altimeter is measuring pointing to such high accuracy. The design for the stellar reference system combines an attitude determination system (ADS) with a laser reference system (LRS) to meet this requirement. The SRS approach and expected performance are described in this paper

  2. Mapping Mars with a Laser Altimeter

    Science.gov (United States)

    Smith, David E.

    2001-01-01

    In November 1996 the Mars Global Surveyor (MGS) spacecraft was launched to Mars. One of the instruments on the spacecraft was a laser altimeter, MOLA, for measuring the shape and topography of the planet. The altimeter has a diode pumped Q-switched ND:YAG laser at 1064nm, operating at 10Hz with an 8 nsec pulse width. The pulse energy is 48mJ, and the instrument has a 37cm ranging precision. The laser illuminates a spot on the surface of Mars approximately 160 meters in diameter and the instrument has accumulated over 600 million range measurements of the surface since arrival at Mars in September 1997. MOLA has operated continuously for over 2 years and has mapped the planet at a horizontal resolution of about 1 km and a radial accuracy of about a meter. MOLA has measured the shape of the planet, the heights of the volcanoes, the depths of the canyons, and the volumes of the polar icecaps. It has detected carbon dioxide clouds and measured the accumulation of seasonal CO2 on the polar icecaps. This new remote sensing tool has helped transform our understanding of Mars and its geological history, and opened a new door to planetary exploration.

  3. Lunar Shape via the Apollo Laser Altimeter.

    Science.gov (United States)

    Sjogren, W L; Wollenhaupt, W R

    1973-01-19

    Data from the Apollo 15 and Apollo 16 laser altimeters reveal the first accurate elevation differences between distant features on both sides of the moon. The large far-side depression observed in the Apollo 15 data is not present in the Apollo 16 data. When the laser results are compared with elevations on maps from the Aeronautical Chart and Information Center, differences of 2 kilometers over a few hundred kilometers are detected in the Mare Nubium and Mare Tranquillitatis regions. The Apollo 16 data alone would put a 2-kilometer bulge toward the earth; however, the combined data are best fit by a sphere of radius 1737.7 kilometers. The offset of the center of gravity from the optical center is about 2 kilometers toward the earth and 1 kilometer eastward. The polar direction parameters are not well determined. PMID:17802353

  4. Photogrammetry and altimetry. Part A: Apollo 16 laser altimeter

    Science.gov (United States)

    Wollenhaupt, W. R.; Sjogren, W. L.

    1972-01-01

    The laser altimeter measures precise altitudes of the command and service module above the lunar surface and can function either with the metric (mapping) camera or independently. In the camera mode, the laser altimeter ranges at each exposure time, which varies between 20 and 28 sec (i.e., 30 to 43 km on the lunar surface). In the independent mode, the laser altimeter ranges every 20 sec. These altitude data and the spacecraft attitudes that are derived from simultaneous stellar photography are used to constrain the photogrammetric reduction of the lunar surface photographs when cartographic products are generated. In addition, the altimeter measurements alone provide broad-scale topographic relief around the entire circumference of the moon. These data are useful in investigating the selenodetic figure of the moon and may provide information regarding gravitational anomalies on the lunar far side.

  5. SIMULATION OF FULL-WAVEFORM LASER ALTIMETER ECHOWAVEFORM

    OpenAIRE

    Y. Lv; Tong, X. H.; Liu, S. J.; Xie, H; Luan, K. F.; Liu, J

    2016-01-01

    Change of globe surface height is an important factor to study human living environment. The Geoscience Laser Altimeter System (GLAS) on ICESat is the first laser-ranging instrument for continuous global observations of the Earth. In order to have a comprehensive understanding of full-waveform laser altimeter, this study simulated the operating mode of ICESat and modeled different terrains’ (platform terrain, slope terrain, and artificial terrain) echo waveforms based on the radar eq...

  6. On retrieving sea ice freeboard from ICESat laser altimeter

    OpenAIRE

    Khvorostovsky, Kirill; Rampal, Pierre

    2016-01-01

    Sea ice freeboard derived from satellite altimetry is the basis for estimation of sea ice thickness using the assumption of hydrostatic equilibrium. High accuracy of altimeter measurements and freeboard retrieval procedure are therefore required. As of today, two approaches for estimation of the freeboard using laser altimeter measurements from Ice, Cloud, and land Elevation Satellite (ICESat), referred to as tie-points (TP) and lowest-level elevation (LLE) methods, have been developed and ap...

  7. Single photon laser altimeter data processing, analysis and experimental validation

    Science.gov (United States)

    Vacek, Michael; Peca, Marek; Michalek, Vojtech; Prochazka, Ivan

    2015-10-01

    Spaceborne laser altimeters are common instruments on-board the rendezvous spacecraft. This manuscript deals with the altimeters using a single photon approach, which belongs to the family of time-of-flight range measurements. Moreover, the single photon receiver part of the altimeter may be utilized as an Earth-to-spacecraft link enabling one-way ranging, time transfer and data transfer. The single photon altimeters evaluate actual altitude through the repetitive detections of single photons of the reflected laser pulses. We propose the single photon altimeter signal processing and data mining algorithm based on the Poisson statistic filter (histogram method) and the modified Kalman filter, providing all common altimetry products (altitude, slope, background photon flux and albedo). The Kalman filter is extended for the background noise filtering, the varying slope adaptation and the non-causal extension for an abrupt slope change. Moreover, the algorithm partially removes the major drawback of a single photon altitude reading, namely that the photon detection measurement statistics must be gathered. The developed algorithm deduces the actual altitude on the basis of a single photon detection; thus, being optimal in the sense that each detected signal photon carrying altitude information is tracked and no altitude information is lost. The algorithm was tested on the simulated datasets and partially cross-probed with the experimental data collected using the developed single photon altimeter breadboard based on the microchip laser with the pulse energy on the order of microjoule and the repetition rate of several kilohertz. We demonstrated that such an altimeter configuration may be utilized for landing or hovering a small body (asteroid, comet).

  8. LASER ALTIMETER CANOPY HEIGHT PROFILES: METHODS AND VALIDATION FOR CLOSED-CANOPY, BROADLEAF FORESTS. (R828309)

    Science.gov (United States)

    AbstractWaveform-recording laser altimeter observations of vegetated landscapes provide a time-resolved measure of laser pulse backscatter energy from canopy surfaces and the underlying ground. Airborne laser altimeter waveform data was acquired using the Scanning Lid...

  9. The Mercury Laser Altimeter Instrument for the MESSENGER Mission

    Science.gov (United States)

    Cavanaugh, John F.; Smith, James C.; Sun, Xiaoli; Bartels, Arlin E.; Ramos-Izquierdo, Luis; Krebs, Danny J.; Novo-Gradac, Anne marie; McGarry, Jan F.; Trunzo, Raymond; Britt, Jamie L.

    2006-01-01

    The Mercury Laser Altimeter (MLA) is one of the payload science instruments on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission, which launched on 3 August 2004. The altimeter will measure the round trip time-of-flight of transmitted laser pulses reflected from the surface of the planet that, in combination with the spacecraft orbit position and pointing data, gives a high-precision measurement of surface topography referenced to Mercury's center of mass. The altimeter measurements will be used to determine the planet's forced librations by tracking the motion of large-scale topographic features as a function of time. MLA's laser pulse energy monitor and the echo pulse energy estimate will provide an active measurement of the surface reflectivity at 1064 nm. This paper describes the instrument design, prelaunch testing, calibration, and results of post-launch testing.

  10. Measuring canopy structure with an airborne laser altimeter

    International Nuclear Information System (INIS)

    Quantification of vegetation patterns and properties is needed to determine their role on the landscape and to develop management plans to conserve our natural resources. Quantifying vegetation patterns from the ground, or by using aerial photography or satellite imagery is difficult, time consuming, and often expensive. Digital data from an airborne laser altimeter offer an alternative method to quantify selected vegetation properties and patterns of forest and range vegetation. Airborne laser data found canopy heights varied from 2 to 6 m within even-aged pine forests. Maximum canopy heights measured with the laser altimeter were significantly correlated to measurements made with ground-based methods. Canopy shape could be used to distinguish deciduous and evergreen trees. In rangeland areas, vegetation heights, spatial patterns, and canopy cover measured with the laser altimeter were significantly related with field measurements. These studies demonstrate the potential of airborne laser data to measure canopy structure and properties for large areas quickly and quantitatively

  11. NASA Ocean Altimeter Pathfinder Project. Report 1; Data Processing Handbook

    Science.gov (United States)

    Koblinsky, C. J.; Beckley, Brian D.; Ray, Richard D.; Wang, Yan-Ming; Tsaoussi, Lucia; Brenner, Anita; Williamson, Ron

    1998-01-01

    The NOAA/NASA Pathfinder program was created by the Earth Observing System (EOS) Program Office to determine how satellite-based data sets can be processed and used to study global change. The data sets are designed to be long time-sedes data processed with stable calibration and community consensus algorithms to better assist the research community. The Ocean Altimeter Pathfinder Project involves the reprocessing of all altimeter observations with a consistent set of improved algorithms, based on the results from TOPEX/POSEIDON (T/P), into easy-to-use data sets for the oceanographic community for climate research. This report describes the processing schemes used to produce a consistent data set and two of the products derived f rom these data. Other reports have been produced that: a) describe the validation of these data sets against tide gauge measurements and b) evaluate the statistical properties of the data that are relevant to climate change. The use of satellite altimetry for earth observations was proposed in the early 1960s. The first successful space based radar altimeter experiment was flown on SkyLab in 1974. The first successful satellite radar altimeter was flown aboard the Geos-3 spacecraft between 1975 and 1978. While a useful data set was collected from this mission for geophysical studies, the noise in the radar measured and incomplete global coverage precluded ft from inclusion in the Ocean Altimeter Pathfinder program. This program initiated its analysis with the Seasat mission, which was the first satellite radar altimeter flown for oceanography.

  12. Mapping of sea bottom topography over western offshore, India using TOPEX/ERS-1 altimeter data

    Digital Repository Service at National Institute of Oceanography (India)

    Mohanty, K.K.; Majumdar, T.J.; Kunte, P.D.; Srivastava, A.K.

    convolution model using satellite altimeter data over the Indian offshore region. The study used TOPEX/POSEIDON as well as ERS-1 altimeter data, along with National Geophysical Data Centre (NGDC), USA ship-borne bathymetry data. The altimeter range data...

  13. Refinement of Phobos Ephemeris Using Mars Orbiter Laser Altimeter Radiometry

    Science.gov (United States)

    Neumann, G. A.; Bills, B. G.; Smith, D. E.; Zuber, M. T.

    2004-01-01

    Radiometric observations from the Mars Orbiter Laser Altimeter (MOLA) can be used to improve the ephemeris of Phobos, with particular interest in refining estimates of the secular acceleration due to tidal dissipation within Mars. We have searched the Mars Orbiter Laser Altimeter (MOLA) radiometry data for shadows cast by the moon Phobos, finding 7 such profiles during the Mapping and Extended Mission phases, and 5 during the last two years of radiometry operations. Preliminary data suggest that the motion of Phobos has advanced by one or more seconds beyond that predicted by the current ephemerides, and the advance has increased over the 5 years of Mars Global Surveyor (MGS) operations.

  14. First Laser Altimeter Measurements of Mercury from the MESSENGER Flyby

    Science.gov (United States)

    Sun, Xiaoli; Neumann, Gregory A.; Cavanaugh, John F.; McGarry, Jan F.; Smith, David E.; Zuber, Maria T.

    2008-01-01

    The Mercury Laser Altimeter performed the first laser ranging measurements to Mercury during the Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) flyby in January 2008. The instrument successfully ranged to 600 km at an off-nadir angle >60 and to >1600 km in the nadir direction.

  15. Optical System Design and Integration of the Mercury Laser Altimeter

    Science.gov (United States)

    Ramos-Izquierdo, Luis; Scott, V. Stanley, III; Schmidt, Stephen; Britt, Jamie; Mamakos, William; Trunzo, Raymond; Cavanaugh, John; Miller, Roger

    2005-01-01

    The Mercury Laser Altimeter (MLA). developed for the 2004 MESSENGER mission to Mercury, is designed to measure the planet's topography via laser ranging. A description of the MLA optical system and its measured optical performance during instrument-level and spacecraft-level integration and testing are presented.

  16. Geoscience Laser Altimeter System: Characteristics and Performance of the Altimeter Receiver

    Science.gov (United States)

    Sun, Xiao-Li; Yi, Dong-Hui; Abshire, James B.

    2003-01-01

    The Geoscience Laser Altimeter System (GLAS) on board ICESat spacecraft measures the surface height (altimetry) via the time of flight of its 1064 nm laser pulse. The GLAS laser transmitter produces 6 ns wide pulses with 70 mJ energy at 1064 nm at a 40 Hz rate. The altimeter receiver consists of a telescope, aft optics, a silicon avalanche photodiode, and electronic amplifiers. The transmitted and echo pulse waveforms are digitized at 1 GHz rate. The laser pulse time of flight is determined on the ground from the two digitized pulse waveforms and their positions in the full waveform record (about 5.4 ms ong) by computing the pulse centroids or by curve fitting. The GLAS receiver algorithms in on board software selects the two waveform segments containing the transmitted and the echo pulses and sends them to ground. The probability of echo pulse detection and the accuracy of time of flight measurement depend on the received signal level, the background light within the receiver field of view, the inherent detector and amplifier noise, the quantization of the digitizer, and some times by cloud obscurations. A receiver model has been developed to calculate the probability of detection and accuracy of the altimeter measurements with these noise sources. From prelaunch testing, the minimum detectable echo pulse energy for 90% detection probability was about 0.1 fj/pulse onto the detector. Such a receiver sensitivity allows GLAS to measure the surface height through clouds with optical density less than 2. The echo pulse energy required to achieve 10 cm ranging accuracy was found to be about 3 times higher than the minimum detectable signal level. The smallest single shot range measurement error, which was determined by ranging to a fixed target with strong echo pulses and no background light, was 2 to 3cm. The maximum linear response echo pulse energy was 10 fJ/pulse for the strongest echo signals, assuming a Lambertian scattering snow surface, clear sky atmosphere

  17. Geoscience Laser Altimeter System - Characteristics and Performance of the Altimeter Receiver

    Science.gov (United States)

    Sun, X.; Abshire, J. B.; Yi, D.

    2003-12-01

    The Geoscience Laser Altimeter System (GLAS) on board ICESat spacecraft measures the surface height (altimetry) via the time of flight of its 1064 nm laser pulse. The GLAS laser transmitter produces 6 ns wide pulses with 70 mJ energy at 1064 nm at a 40 Hz rate. The altimeter receiver consists of a telescope, aft optics, a silicon avalanche photodiode, and electronic amplifiers. The transmitted and echo pulse waveforms are digitized at 1 GHz rate. The laser pulse time of flight is determined on the ground from the two digitized pulse waveforms and their positions in the full digital waveform record (about 5.4 ms long) by computing the pulse centroids or by curve fitting. The GLAS receiver algorithms in on board software selects the two waveform segments containing the transmitted and the echo pulses and sends them to ground. The probability of echo pulse detection and the accuracy of time of flight measurement depend on the received signal level, the background light within the receiver field of view, the inherent detector and amplifier noise, the quantization of the digitizer, and some times by cloud obscurations. A receiver model has been developed to calculate the probability of detection and accuracy of the altimeter measurements with these noise sources. From pre-launch testing, the minimum detectable echo pulse energy for 90% detection probability was about 0.1 fJ/pulse onto the detector. Such a receiver sensitivity allows GLAS to measure the surface height through clouds with optical density less than 2. The echo pulse energy required to achieve 10cm ranging accuracy was found to be about 3 times higher than the minimum detectable signal level. The smallest single shot range measurement error, which was determined by ranging to a fixed target with strong echo pulses and no background light, was 2 to 3cm. The maximum linear response echo pulse energy was 10 fJ/pulse for the strongest echo signals, assuming a Lambertian scattering snow surface, clear sky

  18. Issues related to waveform computations for radar altimeter applications

    Science.gov (United States)

    Newkirk, Michael H.; Brown, Gary S.

    1992-12-01

    An algorithm has been developed to model the average return power waveforms available from general radar altimeter systems, such as the Multimode Airborne Radar Altimeter (MARA) system operated at NASA Goddard Space Flight Center - Wallops Flight Facility. The algorithm is based on a convolutional model comprised of three functions: the average flat surface impulse response (FSIR), the radar system point target response (PTR), and the height pdf of the specular points on the sea surface. The FSIR is modified to account for the asymmetric antenna beam used by the MARA system, and then certain properties of this modified SIR are exploited to obtain closed-form expressions that can be rapidly evaluated. An FFT convolution routine is used to further speed up the computations. The result is an algorithm that can be used to study the effects of pointing errors in surface measurements.

  19. Laser altimeter measurements at Walnut Gulch Watershed, Arizona

    International Nuclear Information System (INIS)

    Measurements of landscape surface roughness properties are necessary for understanding many watershed processes. This paper reviews the use of an airborne laser altimeter to measure topography and surface roughness properties of the landscape at Walnut Gulch Watershed in Arizona. Airborne laser data were used to measure macro and micro topography as well as canopy topography, height, cover, and distribution. Macro topography of landscape profiles for segments up to 5 km (3 mi) were measured and were in agreement with available topographic maps but provided more detail. Gullies and stream channel cross-sections and their associated floodplains were measured. Laser measurements of vegetation properties (height and cover) were highly correlated with ground measurements. Landscape segments for any length can be used to measure these landscape roughness properties. Airborne laser altimeter measurements of landscape profiles can provide detailed information on watershed surface properties for improving the management of watersheds. (author)

  20. Mars orbiter laser altimeter: receiver model and performance analysis.

    Science.gov (United States)

    Abshire, J B; Sun, X; Afzal, R S

    2000-05-20

    The design, calibration, and performance of the Mars Orbiter Laser Altimeter (MOLA) receiver are described. The MOLA measurements include the range to the surface, which is determined by the laser-pulse time of flight; the height variability within the footprint determined by the laser echo pulse width; and the apparent surface reflectivity determined by the ratio of the echo to transmitted pulse energies. PMID:18345159

  1. Initial observations from the Lunar Orbiter Laser Altimeter (LOLA)

    OpenAIRE

    Smith, David E.; Zuber, Maria T.; Neumann, Gregory A.; Lemoine, Frank G.; Mazarico, Erwan; Torrence, Mark H.; McGarry, Jan F.; Rowlands, David D.; Head, James W.; Duxbury, Thomas H.; Aharonson, Oded; Lucey, Paul G.; Robinson, Mark S.; Barnouin, Olivier S.; Cavanaugh, John F.

    2010-01-01

    As of June 19, 2010, the Lunar Orbiter Laser Altimeter, an instrument on the Lunar Reconnaissance Orbiter, has collected over 2.0 × 10^9 measurements of elevation that collectively represent the highest resolution global model of lunar topography yet produced. These altimetric observations have been used to improve the lunar geodetic grid to ~10 m radial and ~100 m spatial accuracy with respect to the Moon's center of mass. LOLA has also provided the highest resolution global maps yet produce...

  2. A stochastic approach to noise modeling for barometric altimeters.

    Science.gov (United States)

    Sabatini, Angelo Maria; Genovese, Vincenzo

    2013-11-18

    The question whether barometric altimeters can be applied to accurately track human motions is still debated, since their measurement performance are rather poor due to either coarse resolution or drifting behavior problems. As a step toward accurate short-time tracking of changes in height (up to few minutes), we develop a stochastic model that attempts to capture some statistical properties of the barometric altimeter noise. The barometric altimeter noise is decomposed in three components with different physical origin and properties: a deterministic time-varying mean, mainly correlated with global environment changes, and a first-order Gauss-Markov (GM) random process, mainly accounting for short-term, local environment changes, the effects of which are prominent, respectively, for long-time and short-time motion tracking; an uncorrelated random process, mainly due to wideband electronic noise, including quantization noise. Autoregressive-moving average (ARMA) system identification techniques are used to capture the correlation structure of the piecewise stationary GM component, and to estimate its standard deviation, together with the standard deviation of the uncorrelated component. M-point moving average filters used alone or in combination with whitening filters learnt from ARMA model parameters are further tested in few dynamic motion experiments and discussed for their capability of short-time tracking small-amplitude, low-frequency motions.

  3. A Laser Altimeter for a Planetary Flyby Mission

    Science.gov (United States)

    Smith, D. E.; Zuber, M. T.; Sun, X.; Cavanaugh, J.; Neumann, G. A.; Mazarico, E.; Genova, A.

    2014-12-01

    Several planetary missions are contemplated as flybys of planets, asteroids, and natural satellites. In many cases the option to orbit the body is impractical and observations during one or many flybys represent the only reasonable option. A laser altimeter provides measurements of topography and shape, surface roughness, and normal reflectivity at the laser wavelength and has been shown to be very effective at Mars, Mercury and the Moon when in orbit about the body and also when in proximity of an asteroid. But flyby missions are less able to provide the coverage and uniformity of the data being acquired by the instruments on the s/c because of the variation in range of the spacecraft from the body during a flyby. To address this problem, we have modified the design of our single beam Mercury Laser Altimeter (MLA), currently collecting observations on the MESSENGER mission, to provide an operating range of several thousand kilometers by increasing the output from the laser, providing a variable pulse-rate while maintaining constant electrical power, that can provide quasi-contiguous altimeter pixels during the flyby, and by storing the complete output from the detector. This approach will provide accurate topographic and shape data and enable improved orbit determination of the spacecraft by the use of orbital crossovers with minimal interpolation errors between measurements. The mass, power and data rate of the instrument is compatible with typical constraints in planetary missions.

  4. Simulation of Full-Waveform Laser Altimeter Echowaveform

    Science.gov (United States)

    Lv, Y.; Tong, X. H.; Liu, S. J.; Xie, H.; Luan, K. F.; Liu, J.

    2016-06-01

    Change of globe surface height is an important factor to study human living environment. The Geoscience Laser Altimeter System (GLAS) on ICESat is the first laser-ranging instrument for continuous global observations of the Earth. In order to have a comprehensive understanding of full-waveform laser altimeter, this study simulated the operating mode of ICESat and modeled different terrains' (platform terrain, slope terrain, and artificial terrain) echo waveforms based on the radar equation. By changing the characteristics of the system and the targets, numerical echo waveforms can be achieved. Hereafter, we mainly discussed the factors affecting the amplitude and size (width) of the echoes. The experimental results implied that the slope of the terrain, backscattering coefficient and reflectivity, target height, target position in the footprint and area reacted with the pulse all can affect the energy distribution of the echo waveform and the receiving time. Finally, Gaussian decomposition is utilized to decompose the echo waveform. From the experiment, it can be noted that the factors which can affect the echo waveform and by this way we can know more about large footprint full-waveform satellite laser altimeter.

  5. New Radar Altimeter Missions are Providing a Dramatically Sharper Image of Global Marine Tectonics

    Science.gov (United States)

    Sandwell, D. T.; Müller, D.; Garcia, E.; Matthews, K. J.; Smith, W. H. F.; Zaron, E.; Zhang, S.; Bassett, D.; Francis, R.

    2015-12-01

    Marine gravity, derived from satellite radar altimetry, is a powerful tool for mapping tectonic structures, especially in the deep ocean basins where the topography remains unmapped by ships or is buried by thick sediment. The ability to infer seafloor tectonics from space was first demonstrated in 1978 using Seasat altimeter data but the spatial coverage was incomplete because of the short three-month lifetime of the satellite. Most ocean altimeters have repeat ground tracks with spacings of hundreds of kilometers so they do not resolve tectonic structures. Adequate altimeter coverage became available in 1995 when the United States Navy declassified the Geosat radar altimeter data and the ERS-1 altimeter completed a 1-year mapping phase. These mid-1990's altimeter-derived images of the ocean basins remained static for 15 years because there were no new non-repeat altimeter missions. This situation changed dramatically in 2010 when CryoSat-2, with its advanced radar altimeter, was launched into a non-repeat orbit and continues to collect data until perhaps 2020. In addition the Jason-1 altimeter was placed into a 14-month geodetic phase at the end of its lifetime. More recently the 1.5 times higher precision measurements from the AltiKa altimeter aboard the SARAL spacecraft began to drift away from its 35-day repeat trackline. The Chinese HY-2 altimeter is scheduled to begin a dense mapping phase in early 2016. Moreover in 2020 we may enjoy significantly higher resolution maps of the ocean basins from the planned SWOT altimeter mission with its advanced swath mapping ability. All of this new data will provide a much sharper image of the tectonics of the deep ocean basins and continental margins. During this talk we will tour of the new tectonic structures revealed by CryoSat-2 and Jason-1 and speculate on the tectonic views of the ocean basins in 2020 and beyond.

  6. Wind waves in tropical cyclones: satellite altimeter observations and modeling

    Science.gov (United States)

    Golubkin, Pavel; Kudryavtsev, Vladimir; Chapron, Bertrand

    2016-04-01

    Results of investigation of wind-wave generation by tropical cyclones using satellite altimeter data are presented. Tropical cyclones are generally relatively small rapidly moving low pressure systems that are capable of generating severe wave conditions. Translation of a tropical cyclone leads to a prolonged period of time surface waves in the right sector remain under high wind forcing conditions. This effect has been termed extended fetch, trapped fetch or group velocity quasi-resonance. A tropical cyclone wave field is thus likely more asymmetrical than the corresponding wind field: wind waves in the tropical cyclone right sector are more developed with larger heights than waves in the left one. A dataset of satellite altimeter intersections of the Western Pacific tropical cyclones was created for 2010-2013. Data from four missions were considered, i.e., Jason-1, Jason-2, CryoSat-2, SARAL/AltiKa. Measurements in the rear-left and front-right sectors of tropical cyclones were examined for the presence of significant wave asymmetry. An analytical model is then derived to efficiently describe the wave energy distribution in a moving tropical cyclone. The model essentially builds on a generalization of the self-similar wave growth model and the assumption of a strongly dominant single spectral mode in a given quadrant of the storm. The model provides a criterion to anticipate wave enhancement with the generation of trapped abnormal waves. If forced during a sufficient timescale interval, also defined from this generalized self-similar wave growth model, waves can be trapped and large amplification of the wave energy will occur in the front-right storm quadrant. Remarkably, the group velocity and corresponding wavelength of outrunning wave systems will become wind speed independent and solely relate to the translating velocity. The resulting significant wave height also only weakly depends on wind speed, and more strongly on the translation velocity. Satellite

  7. NODC Standard Product: US Navy Geosat altimeter Crossover Differences (XDRs) for the Geodetic Mission (8 disc set) (NODC Accession 0054498)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This accession contains a copy of the NODC eight CD-ROMs product set of the Geosat altimeter Crossover Differences data Records (XDRs) for altimeter data obtained...

  8. 14 CFR 91.411 - Altimeter system and altitude reporting equipment tests and inspections.

    Science.gov (United States)

    2010-01-01

    ... 14 Aeronautics and Space 2 2010-01-01 2010-01-01 false Altimeter system and altitude reporting equipment tests and inspections. 91.411 Section 91.411 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION... RULES Maintenance, Preventive Maintenance, and Alterations § 91.411 Altimeter system and...

  9. Case studies of ERS-1 altimeter data applicating in China Sea

    Institute of Scientific and Technical Information of China (English)

    杨学联; 季晓阳; 黄润恒; 凌铁军

    2001-01-01

    The impact of ERS-1 altimeter significant wave height on analysis of wave field and wave predictions is tested through analysis of selected cases. Application of the altimeter data may modifg initial field and thus 24-hour prediction of significant wave height. However the variations in initial wave field almost make no effect on 48-hour predictions.

  10. Testing in a stratospheric balloon of a semiconductor detector altimeter

    International Nuclear Information System (INIS)

    An altimeter containing a semiconductor detector has been operated on flight. We have used a stratospheric balloon launched from AIRE-SUR-ADOUR with the C.N.E.S. collaboration. During this assay two apparatus have been used. The first allowed to follow the balloon during its ascension and descent, the second to follow its evolution at its maximum altitude. Informations transmitted by radio and recorded on Magnetophon, have been studied after the flight. Results are identical with these given by the barometer used by the C.N.E.S. in this essay. (authors)

  11. The BepiColombo Laser Altimeter BELA and Tx Verification

    OpenAIRE

    Althaus, Christian; Lingenauber, Kay; Michaelis, Harald

    2011-01-01

    BepiColombo is a mission to Mercury. The launch is scheduled for 2014. Onboard will be the BepiColombo Laser Altimeter (BELA) which is being developed and built in collaboration of the University Bern, Switzerland and the German Aerospace Center (DLR) in Berlin. The instrument's task is the global mapping of the planetary surface from an orbit in up to 1000 km height above the planet. Therefore the technique of measuring the travel time of light to the surface and back is used. As the s...

  12. Radar and laser altimeter measurements over Arctic sea ice.

    OpenAIRE

    Giles, K. A.

    2005-01-01

    To validate sea ice models, basin wide sea ice thickness measurements with an accuracy of 0.5 m are required to analyse trends in sea ice thickness, it is necessary to detect changes in sea ice thickness of 4 cm per year on a basin wide scale. The estimated error on satellite radar altimeter estimates of sea ice thickness is 0.45 m and the estimated error on satellite laser altimetry estimates of sea ice thickness is 0.78 m. The Laser Radar Altimetry (LaRA) field campaign took place in the Ar...

  13. Lessons Learned from the Advanced Topographic Laser Altimeter System

    Science.gov (United States)

    Garrison, Matt; Patel, Deepak; Bradshaw, Heather; Robinson, Frank; Neuberger, Dave

    2016-01-01

    The ICESat-2 Advanced Topographic Laser Altimeter System (ATLAS) instrument is an upcoming Earth Science mission focusing on the effects of climate change. The flight instrument passed all environmental testing at GSFC (Goddard Space Flight Center) and is now ready to be shipped to the spacecraft vendor for integration and testing. This presentation walks through the lessons learned from design, hardware, analysis and testing perspective. ATLAS lessons learned include general thermal design, analysis, hardware, and testing issues as well as lessons specific to laser systems, two-phase thermal control, and optical assemblies with precision alignment requirements.

  14. Inference of Altimeter Accuracy on Along-track Gravity Anomaly Recovery

    Directory of Open Access Journals (Sweden)

    LI Yang

    2015-04-01

    Full Text Available A correlation model between along-track gravity anomaly accuracy, spatial resolution and altimeter accuracy is proposed. This new model is based on along-track gravity anomaly recovery and resolution estimation. Firstly, an error propagation formula of along-track gravity anomaly is derived from the principle of satellite altimetry. Then the mathematics between the SNR (signal to noise ratio and cross spectral coherence is deduced. The analytical correlation between altimeter accuracy and spatial resolution is finally obtained from the results above. Numerical simulation results show that along-track gravity anomaly accuracy is proportional to altimeter accuracy, while spatial resolution has a power relation with altimeter accuracy. e.g., with altimeter accuracy improving m times, gravity anomaly accuracy improves m times while spatial resolution improves m0.4644 times. This model is verified by real-world data.

  15. Photon counting altimeter and lidar for air and spaceborne applications

    Science.gov (United States)

    Vacek, Michael; Michalek, Vojtech; Peca, Marek; Prochazka, Ivan; Blazej, Josef; Kodet, Jan

    2011-06-01

    We are presenting the concept and preliminary design of modular multipurpose device for space segment: single photon counting laser altimeter, atmospheric lidar, laser transponder and one way laser ranging receiver. For all the mentioned purposes, the same compact configuration of the device is appropriate. Overall estimated device weight should not exceed 5 kg with the power consumption below 10 W. The device will consists of three main parts, namely, receiver, transmitter and control and processing unit. As a transmitter a commercial solid state laser at 532 nm wavelength with 10 mW power will be used. The transmitter optics will have a diameter at most of 50 mm. The laser pulse width will be of hundreds of picoseconds order. For the laser altimeter and atmospheric lidar application, the repetition rate of 10 kHz is planned in order to obtain sufficient number of data for a distance value computing. The receiver device will be composed of active quenched Single Photon Avalanche Diode module, tiny optics, and narrow-band optical filter. The core part of the control and processing unit including high precision timing unit is implemented using single FPGA chip. The preliminary device concept includes considerations on energy balance, and statistical algorithms to meet all the mentioned purposes. Recently, the bread board version of the device is under construction in our labs. The concept, construction, and timing results will be presented.

  16. NASA Ocean Altimeter Pathfinder Project. Report 2; Data Set Validation

    Science.gov (United States)

    Koblinsky, C. J.; Ray, Richard D.; Beckley, Brian D.; Bremmer, Anita; Tsaoussi, Lucia S.; Wang, Yan-Ming

    1999-01-01

    The NOAA/NASA Pathfinder program was created by the Earth Observing System (EOS) Program Office to determine how existing satellite-based data sets can be processed and used to study global change. The data sets are designed to be long time-series data processed with stable calibration and community consensus algorithms to better assist the research community. The Ocean Altimeter Pathfinder Project involves the reprocessing of all altimeter observations with a consistent set of improved algorithms, based on the results from TOPEX/POSEIDON (T/P), into easy-to-use data sets for the oceanographic community for climate research. Details are currently presented in two technical reports: Report# 1: Data Processing Handbook Report #2: Data Set Validation This report describes the validation of the data sets against a global network of high quality tide gauge measurements and provides an estimate of the error budget. The first report describes the processing schemes used to produce the geodetic consistent data set comprised of SEASAT, GEOSAT, ERS-1, TOPEX/ POSEIDON, and ERS-2 satellite observations.

  17. Ocean state indicators from MyOcean altimeter products

    Directory of Open Access Journals (Sweden)

    L. Bessières

    2013-06-01

    Full Text Available The European MyOcean project (http://www.myocean.eu.org provides observations of the ocean dynamic topography from altimeter measurements. Three specific indicators have been developed, based on altimeter data only, in order to monitor the ocean state. The first ocean indicator observes the positive and negative phases of the ENSO events in the tropical Pacific, the El Niño/La Niña events, since 1992. The second ocean indicator tracks the contracted or extended state of the Kuroshio Extension. The last ocean indicator is dedicated to the Ionian Basin in the Mediterranean Sea and permits separation of "zonal-cyclonic" state (1998–2005 and since 2011 up to now from the "anticyclonic" state (1993–1996 usually discussed in the literature. In addition, it allows identifying a third state in which both the anticyclonic circulation around the northern part of the basin and the strong zonal Mid-Ionian Jet co-exist (2008–2010.

  18. Test Port for Fiber-Optic-Coupled Laser Altimeter

    Science.gov (United States)

    Ramos Izquierdo, Luis; Scott, V. Stanley; Rinis, Haris; Cavanaugh, John

    2011-01-01

    A test port designed as part of a fiber optic coupled laser altimeter receiver optical system allows for the back-illumination of the optical system for alignment verification, as well as illumination of the detector(s) for testing the receiver electronics and signal-processing algorithms. Measuring the optical alignment of a laser altimeter instrument is difficult after the instrument is fully assembled. The addition of a test port in the receiver aft-optics allows for the back-illumination of the receiver system such that its focal setting and boresight alignment can be easily verified. For a multiple-detector receiver system, the addition of the aft-optics test port offers the added advantage of being able to simultaneously test all the detectors with different signals that simulate the expected operational conditions. On a laser altimeter instrument (see figure), the aft-optics couple the light from the receiver telescope to the receiver detector(s). Incorporating a beam splitter in the aft-optics design allows for the addition of a test port to back-illuminate the receiver telescope and/or detectors. The aft-optics layout resembles a T with the detector on one leg, the receiver telescope input port on the second leg, and the test port on the third leg. The use of a custom beam splitter with 99-percent reflection, 1-percent transmission, and a mirrored roof can send the test port light to the receiver telescope leg as well as the detector leg, without unduly sacrificing the signal from the receiver telescope to the detector. The ability to test the receiver system alignment, as well as multiple detectors with different signals without the need to disassemble the instrument or connect and reconnect components, is a great advantage to the aft-optics test port. Another benefit is that the receiver telescope aperture is fully back-illuminated by the test port so the receiver telescope focal setting vs. pressure and or temperature can be accurately measured (as

  19. Laser altimeter observations from MESSENGER's first Mercury flyby.

    Science.gov (United States)

    Zuber, Maria T; Smith, David E; Solomon, Sean C; Phillips, Roger J; Peale, Stanton J; Head, James W; Hauck, Steven A; McNutt, Ralph L; Oberst, Jürgen; Neumann, Gregory A; Lemoine, Frank G; Sun, Xiaoli; Barnouin-Jha, Olivier; Harmon, John K

    2008-07-01

    A 3200-kilometers-long profile of Mercury by the Mercury Laser Altimeter on the MESSENGER spacecraft spans approximately 20% of the near-equatorial region of the planet. Topography along the profile is characterized by a 5.2-kilometer dynamic range and 930-meter root-mean-square roughness. At long wavelengths, topography slopes eastward by 0.02 degrees , implying a variation of equatorial shape that is at least partially compensated. Sampled craters on Mercury are shallower than their counterparts on the Moon, at least in part the result of Mercury's higher gravity. Crater floors vary in roughness and slope, implying complex modification over a range of length scales. PMID:18599773

  20. Design of A Pentagon Microstrip Antenna for Radar Altimeter Application

    Directory of Open Access Journals (Sweden)

    K. RamaDevi

    2012-11-01

    Full Text Available In the navigational applications, radar and satellite requires a device that is a radar altimeter. Theworking frequency of this system is 4.2 to 4.3GHz and also requires less weight, low profile, and high gainantennas. The above mentioned application is possible with microstrip antenna as also known as planarantenna. In this paper, the microstrip antennas are designed at 4.3GHz (C-band in rectangular andcircular shape patch antennas in single element and arrays with parasitic elements placed in H-planecoupling. The performance of all these shapes is analyzed in terms of radiation pattern, half power points,and gain and impedance bandwidth in MATLAB. This work extended here with designed in different shapeslike Rhombic, Pentagon, Octagon and Edges-12 etc. Further these parameters are simulated in ANSOFTHFSSTMV9.0 simulator.

  1. Remote sensing of Gulf Stream using GEOS-3 radar altimeter

    Science.gov (United States)

    Leitao, C. D.; Huang, N. E.; Parra, C. G.

    1978-01-01

    Radar altimeter measurements from the GEOS-3 satellite to the ocean surface indicated the presence of expected geostrophic height differences across the the Gulf Stream. Dynamic sea surface heights were found by both editing and filtering the raw sea surface heights and then referencing these processed data to a 5 minute x 5 minute geoid. Any trend between the processed data and the geoid was removed by subtracting out a linear fit to the residuals in the open ocean. The mean current velocity of 107 + or - 29 cm/sec calculated from the dynamic heights for all orbits corresponded with velocities obtained from hydrographic methods. Also, dynamic topographic maps were produced for August, September, and October 1975. Results pointed out limitations in the accuracy of the geoid, height anomaly deteriorations due to filtering, and lack of dense time and space distribution of measurements.

  2. Participation in the Mars Orbiting Laser Altimeter Experiment

    Science.gov (United States)

    Pettengil, Gordon H.; Ford, Peter

    2004-01-01

    The Mars Orbiting Laser Altimeter (MOLA) instrument [1,2] carried aboard the Mars Global Surveyor (MGS) spacecraft, has observed strong echoes from cloud tops at 1.064 microns on 61% of its orbital passes over the winter north pole (235deg L(sub S), < 315deg) and on 58% of the passes over the winter south pole (45deg < L(sub S), < 135deg). The clouds are unlikely to be composed of water ice since the vapor pressure of H2O is very low at the Martian nighttime polar temperatures measured by the Thermal Emission Spectrometer (TES) [3], and by an analysis of MGS radio occultations [4]. Dust clouds can also be ruled out since no correlation is seen between clouds and global dust storms. The virtually certain composition for the winter polar clouds is CO2 ice.

  3. Atmospheric Measurements by the 2002 Geoscience Laser Altimeter System Mission

    Science.gov (United States)

    Spinhirne, James D.; Starr, David OC. (Technical Monitor)

    2002-01-01

    The NASA Earth Observing System (EOS) program is a multiple platform NASA initiative for the study of global change. As part of the EOS project, the Geoscience Laser Altimeter System (GLAS) was selected as a laser sensor filling complementary requirements for several earth science disciplines including atmospheric and surface applications. Late in 2002, the GaAs instrument is to be launched for a three to five year observational mission. For the atmosphere, the instrument is designed to full fill comprehensive requirements for profiling of radiatively significant cloud and aerosol. Algorithms have been developed to process the cloud and aerosol data and provide standard data products. After launch there will be a three-month project to analyze and understand the system performance and accuracy of the data products. As an EOS mission, the GaAs measurements and data products will be openly available to all investigators. An overview of the instrument, data products and evaluation plan is given.

  4. An Imaging Laser Altimeter for Lunar Scientific Exploration

    Science.gov (United States)

    Smith, David E.; Zuber, M. T.; Degnan, J. J.

    2002-01-01

    A new approach to laser altimetry is offered by the development of micro-lasers and pixilated detectors that enable very high resolution measurement of topography and relatively wide swath observations. An imaging altimeter with a 8x8 array detector working at a probability of less than a single photon/shot could map the Moon or similar sized body in approximately 2 years and provide 5 meter horizontal resolution topography and a 10 centimeter vertical accuracy. In addition, it would provide surface roughness and surface slopes on similar length scales of 5 meters and be able to address a range of problems for which topography or lunar shape is important at the decimeter level. This includes the topography of the polar regions, where ice is thought to have been identified, and also the cratering history of the Moon which could be assessed with a dataset of uniform quality and high resolution.

  5. Atmospheric Measurements by the Geoscience Laser Altimeter System: Initial Results

    Science.gov (United States)

    Spinhirne, J. D.; Palm, S. P.; Hlavka, D. L.; Hart, W. D.; Mahesh, A.; Welton, E. J.

    2003-01-01

    The Geoscience Laser Altimeter System launched in early 2003 is the first satellite instrument in space to globally observe the distribution of clouds and aerosol through laser remote sensing. The instrument is a basic backscatter lidar that operates at two wavelengths, 532 and 1064 nm. The mission data products for atmospheric observations include the calibrated, observed, attenuated backscatter cross section for cloud and aerosol; height detection for multiple cloud layers; planetary boundary layer height; cirrus and aerosol optical depth and the height distribution of aerosol and cloud scattering cross section profiles. The data is expected to significantly enhance knowledge in several areas of atmospheric science, in particular the distribution, transport and influence of atmospheric aerosol. Measurements of the coverage and height of polar and cirrus cloud should be significantly more accurate than previous global measurement. Initial result from the first several months of operation will be presented.

  6. One GHz digitizer for space based laser altimeter

    Science.gov (United States)

    Staples, Edward J.

    1991-01-01

    This is the final report for the research and development of the one GHz digitizer for space based laser altimeter. A feasibility model was designed, built, and tested. Only partial testing of essential functions of the digitizer was completed. Hybrid technology was incorporated which allows analog storage (memory) of the digitally sampled data. The actual sampling rate is 62.5 MHz, but executed in 16 parallel channels, to provide an effective sampling rate of one GHz. The average power consumption of the one GHz digitizer is not more than 1.5 Watts. A one GHz oscillator is incorporated for timing purposes. This signal is also made available externally for system timing. A software package was also developed for internal use (controls, commands, etc.) and for data communication with the host computer. The digitizer is equipped with an onboard microprocessor for this purpose.

  7. Development of the Laser Altimeter (LIDAR) for Hayabusa2

    Science.gov (United States)

    Mizuno, T.; Kase, T.; Shiina, T.; Mita, M.; Namiki, N.; Senshu, H.; Yamada, R.; Noda, H.; Kunimori, H.; Hirata, N.; Terui, F.; Mimasu, Y.

    2016-02-01

    Hayabusa2 was launched on 3 December 2014 on an H-IIA launch vehicle from the Tanegashima Space Center, and is, at the time of writing, cruising toward asteroid 162137 Ryugu ( 1999JU3). After reaching the asteroid, it will stay for about 1.5 years to observe the asteroid and collect surface material samples. The light detection and ranging (LIDAR) laser altimeter on Hayabusa2 has a wide dynamic range, from 25 km to 30 m, because the LIDAR is used as a navigation sensor for rendezvous, approach, and touchdown procedures. Since it was designed for use in planetary explorers, its weight is a low 3.5 kg. The LIDAR can serve not only as a navigation sensor, but also as observation equipment for estimating the asteroid's topography, gravity and surface reflectivity (albedo). Since Hayabusa2 had a development schedule of just three years from the start of the project to launch, minimizing development time was a particular concern. A key to shortening the development period of Hayabusa2's LIDAR system was heritage technology from Hayabusa's LIDAR and the SELENE lunar explorer's LALT laser altimeter. Given that the main role of Hayabusa2's LIDAR is to serve as a navigation sensor, we discuss its development from an engineering viewpoint. However, detailed information about instrument development and test results is also important for scientific analysis of LIDAR data and for future laser altimetry in lunar and planetary exploration. Here we describe lessons learned from the Hayabusa LIDAR, as well as Hayabusa2's hardware, new technologies and system designs based on it, and flight model evaluation results. The monolithic laser used in the laser module is a characteristic technology of this LIDAR. It was developed to solve issues with low-temperature storage that were problematic when developing the LIDAR system for the first Hayabusa mission. The new module not only solves such problems but also improves reliability and miniaturization by reducing the number of parts.

  8. Lunar Geodetic Opportunities with the Laser Altimeter on LRO

    Science.gov (United States)

    Zuber, Maria T.; Smith, David E.

    2006-01-01

    The Lunar Reconnaissance Orbiter (LRO) is to be launched at the end of 2008 and will carry 7 instruments, one of which is a laser altimeter (LOLA), and obtain observations of the Moon for a period of 1 year. The orbit will be near polar and approximately circular at 50 km altitude with monthly orbital adjustments to maintain the mean altitude. The LOLA instrument has a -10 cm single-shot accuracy, with 5 beams, and operates at 28 Hz. It provides 5 adjacent profiles, each approximately 12 to 15 meters apart with a swath of approximately 65 meters. The 5 beams are arranged in a cross-shaped pattern that provides simultaneous along and cross track altimetry and providing slopes in 2 orthogonal directions every 50 meters along track. In combination with the LRO tracking data LOLA will be used to improve the model of the lunar gravity by using the altimeter on both the lunar near-side and far-side as an additional tracking system to enable precise positioning of the LRO spacecraft at about the 50 meter level rms. The instrument is expected to provide full polar coverage at very high northern and southern latitudes with spatial resolutions of 25 meters or better. In addition to the range to the surface LOLA measures the surface roughness from the spreading of the laser pulse and also the reflectance of the surface at 1064 nm. These measurements in conjunction with the altimetry will assist in the selection of future landing sites for future robotic and human missions to the Moon.

  9. Mean gravity anomalies and sea surface heights derived from GEOS-3 altimeter data

    Science.gov (United States)

    Rapp, R. H.

    1978-01-01

    Approximately 2000 GEOS-3 altimeter arcs were analyzed to improve knowledge of the geoid and gravity field. An adjustment procedure was used to fit the sea surface heights (geoid undulations) in an adjustment process that incorporated cross-over constraints. The error model used for the fit was a one or two parameter model which was designed to remove altimeter bias and orbit error. The undulations on the adjusted arcs were used to produce geoid maps in 20 regions. The adjusted data was used to derive 301 5 degree equal area anomalies and 9995 1 x 1 degree anomalies in areas where the altimeter data was most dense, using least squares collocation techniques. Also emphasized was the ability of the altimeter data to imply rapid anomaly changes of up to 240 mgals in adjacent 1 x 1 degree blocks.

  10. Two Mars Years of Clouds Detected by the Mars Orbiter Laser Altimeter

    Science.gov (United States)

    Neumann, G. A.; Smith, D. E.; Zuber, M. T.

    2002-01-01

    MOLA operated as an atmospheric lidar as well as an altimeter. We present results spanning two Mars years of observations, and some observations concerning cloud waveforms and snow. Additional information is contained in the original extended abstract.

  11. IceBridge Paroscientific L0 Pressure Altimeter Raw Air Pressure

    Data.gov (United States)

    National Aeronautics and Space Administration — The NASA IceBridge Paroscientific L0 Pressure Altimeter Raw Air Pressure (IAPRS0) data set contains air pressure readings taken over Antarctica using the...

  12. New Morphometric Measurements of Peak-Ring Basins on Mercury and the Moon: Results from the Mercury Laser Altimeter and Lunar Orbiter Laser Altimeter

    Science.gov (United States)

    Baker, David M. H.; Head, James W.; Prockter, Louise M.; Fassett, Caleb I.; Neumann, Gregory A.; Smith, David E.; Solomon, Sean C.; Zuber, Maria T.; Oberst, Juergen; Preusker, Frank; Gwiner, Klaus

    2012-01-01

    Peak-ring basins (large impact craters exhibiting a single interior ring) are important to understanding the processes controlling the morphological transition from craters to large basins on planetary bodies. New image and topography data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) and Lunar Reconnaissance Orbiter (LRO) spacecraft have helped to update the catalogs of peak-ring basins on Mercury and the Moon [1,2] and are enabling improved calculations of the morphometric properties of these basins. We use current orbital altimeter measurements from the Mercury Laser Altimeter (MLA) [3] and the Lunar Orbiter Laser Altimeter (LOLA) [4], as well as stereo-derived topography [5], to calculate the floor depths and peak-ring heights of peak-ring basins on Mercury and the Moon. We present trends in these parameters as functions of rim-crest diameter, which are likely to be related to processes controlling the onset of peak rings in these basins.

  13. A SWITCHED-ANTENNA NADIR-LOOKING INTERFEROMETRIC SAR ALTIMETER FOR TERRAIN-AIDED NAVIGATION

    OpenAIRE

    Inchan Paek; Jonghun Jang; Joohwan Chun; Jinbae Suh

    2016-01-01

    Conventional terrain-aided navigation (TAN) technique uses an altimeter to locate the position of an aerial vehicle. However, a major problem with a radar altimeter is that its beam (or pulse) footprint on the ground could be large, and therefore the nadir altitude cannot be estimated accurately. To overcome this difficulty, one may use the nadir-looking synthetic aperture radar (SAR) technique to reduce the along-track beam width, while the cross-track ambiguity is resolved wi...

  14. Waveform classification of airborne synthetic aperture radar altimeter over Arctic sea ice

    OpenAIRE

    Zygmuntowska, M.; Khvorostovsky, K.; V. Helm; S. Sandven

    2013-01-01

    Sea ice thickness is one of the most sensitive variables in the Arctic climate system. In order to quantify changes in sea ice thickness, CryoSat-2 was launched in 2010 carrying a Ku-band radar altimeter (SIRAL) designed to measure sea ice freeboard with a few centimeters accuracy. The instrument uses the synthetic aperture radar technique providing signals with a resolution of about 300m along track. In this study, airborne Ku-band radar altimeter data over different ...

  15. Towards a miniaturized photon counting laser altimeter and stereoscopic camera instrument suite for microsatellites

    OpenAIRE

    Moon, S.G.; Hannemann, S.; Collon, M.; Wielinga, K.; Kroesbergen, E.; Harris, J.; Gill, E.K.A.; Maessen, D.C.

    2009-01-01

    In the following we review the optimization for microsatellite deployment of a highly integrated payload suite comprising a high resolution camera, an additional camera for stereoscopic imaging, and a single photon counting laser altimeter. This payload suite, the `Stereo Imaging Laser Altimeter' SILAT has been designated for deployment aboard the FAST microsatellite formation mission for Earth observation. This instrument suite has been designed for a Jupiter mission, but has been redesigned...

  16. Airborne SAR/Interferometric Radar Altimeter System (ASIRAS) - Kalibrierung, Validierung und Interpretation der Messergebnisse

    OpenAIRE

    Helm, Veit

    2008-01-01

    As part of the CryoSat Calibration and Validation Experiment (CryoVEx) this work is related to the calibration and validation of ESA's AirborneSAR/Interferometric Radar Altimeter System (ASIRAS). ASIRAS was designed to simulate the CryoSat SAR Interferometric Radar Altimeter (SIRAL) for reasons of pre-launch and simultaneous accuracy and backscatter studies by using a similar instrument. The purpose of the ASIRAS calibration and data validation is to provide confidence in estimates of the unc...

  17. Mars Orbiter Laser Altimeter: Experiment summary after the first year of global mapping of Mars

    OpenAIRE

    Smith, David E.; Muhleman, Duane O.; Ivanov, Anton B.

    2001-01-01

    The Mars Orbiter Laser Altimeter (MOLA), an instrument on the Mars Global Surveyor spacecraft, has measured the topography, surface roughness, and 1.064-μm reflectivity of Mars and the heights of volatile and dust clouds. This paper discusses the function of the MOLA instrument and the acquisition, processing, and correction of observations to produce global data sets. The altimeter measurements have been converted to both gridded and spherical harmonic models for the topography and shape of ...

  18. A Next Generation Radar Altimeter: The Proposed SWOT Mission

    Science.gov (United States)

    Fu, L. L.

    2014-12-01

    Conventional nadir-looking radar altimeter is based on pulse-limited footprint approach. Near a coast the pulse limited footprint is contaminated by land within the much larger radar footprint, causing data quality to decay within 10 km from a coast. In the open ocean, the instrument noise limits the detection of dynamic ocean signals to wavelengths longer than 70 km. Using the technique of radar interferometry, the proposed Surface Water and Ocean Topography (SWOT) Mission would reduce instrument noise to resolve ocean signals to 15 km in wavelength over most of the open ocean without land contamination in the coastal zone. Sea surface height would be measured in two dimensions over a swath 120 km wide across the satellite's flight path. SWOT is under development as a joint mission of NASA and the French Space Agency, CNES, with contributions from the Canadian Space Agency and the UK Space Agency. The launch is baselined for 2020. An overview of the projected mission performance for oceanographic applications will be presented. SWOT would also measure the elevation of land surface water with hydrological applications.

  19. Tracking the attenuation and nonbreaking dissipation of swells using altimeters

    Science.gov (United States)

    Jiang, Haoyu; Stopa, Justin E.; Wang, He; Husson, Romain; Mouche, Alexis; Chapron, Bertrand; Chen, Ge

    2016-02-01

    A method for systematically tracking swells across oceanic basins is developed by taking advantage of high-quality data from space-borne altimeters and wave model output. The evolution of swells is observed over large distances based on 202 swell events with periods ranging from 12 to 18 s. An empirical attenuation rate of swell energy of about 4 × 10-7 m-1 is estimated using these observations, and the nonbreaking energy dissipation rates of swells far away from their generating areas are also estimated using a point source model. The resulting acceptance range of nonbreaking dissipation rates is -2.5 to 5.0 × 10-7 m-1, which corresponds to a dissipation e-folding scales of at least 2000 km for steep swells, to almost infinite for small-amplitude swells. These resulting rates are consistent with previous studies using in-situ and synthetic aperture radar (SAR) observations. The frequency dispersion and angular spreading effects during swell propagation are discussed by comparing the results with other studies, demonstrating that they are the two dominant processes for swell height attenuation, especially in the near field. The resulting dissipation rates from these observations can be used as a reference for ocean engineering and wave modeling, and for related studies such as air-sea and wind-wave-turbulence interactions.

  20. A Boresight Adjustment Mechanism for use on Laser Altimeters

    Science.gov (United States)

    Hakun, Claef; Budinoff, Jason; Brown, Gary; Parong, Fil; Morell, Armando

    2004-01-01

    This paper describes the development of the Boresight Adjustment Mechanism (BAM) for the Geoscience Laser Altimeter System (GLAS) Instrument. The BAM was developed late in the integration and test phase of the GLAS instrument flight program. Thermal vacuum tests of the GLAS instrument indicated that the instrument boresight alignment stability over temperature may be marginal. To reduce the risk that GLAS may not be able to meet the boresight alignment requirements, an intensive effort was started to develop a BAM. Observatory-level testing and further evaluation of the boresight alignment data indicated that sufficient margin could be obtained utilizing existing instrument resources and therefore the BAM was never integrated onto the GLAS Instrument. However, the BAM was designed fabricated and fully qualified over a 4 month timeframe to be capable of precisely steering (lasers to ensure the alignment between the transmit and receive paths of the GLAS instrument. The short timeline for the development of the mechanism resulted in several interesting design solutions. This paper discusses the requirement definition, design, and testing processes of the BAM development effort, how the design was affected by the extremely tight development schedule, and the lessons learned throughout the process.

  1. Lunar Topography: Results from the Lunar Orbiter Laser Altimeter

    Science.gov (United States)

    Neumann, Gregory; Smith, David E.; Zuber, Maria T.; Mazarico, Erwan

    2012-01-01

    The Lunar Orbiter Laser Altimeter (LOLA) onboard the Lunar Reconnaissance Orbiter (LRO) has been operating nearly continuously since July 2009, accumulating over 6 billion measurements from more than 2 billion in-orbit laser shots. LRO's near-polar orbit results in very high data density in the immediate vicinity of the lunar poles, with full coverage at the equator from more than 12000 orbital tracks averaging less than 1 km in spacing at the equator. LRO has obtained a global geodetic model of the lunar topography with 50-meter horizontal and 1-m radial accuracy in a lunar center-of-mass coordinate system, with profiles of topography at 20-m horizontal resolution, and 0.1-m vertical precision. LOLA also provides measurements of reflectivity and surface roughness down to its 5-m laser spot size. With these data LOLA has measured the shape of all lunar craters 20 km and larger. In the proposed extended mission commencing late in 2012, LOLA will concentrate observations in the Southern Hemisphere, improving the density of the polar coverage to nearly 10-m pixel resolution and accuracy to better than 20 m total position error. Uses for these data include mission planning and targeting, illumination studies, geodetic control of images, as well as lunar geology and geophysics. Further improvements in geodetic accuracy are anticipated from the use of re ned gravity fields after the successful completion of the Gravity Recovery and Interior Laboratory (GRAIL) mission in 2012.

  2. A Boresight Adjusment Mechanism For Use in Laser Altimeters

    Science.gov (United States)

    Hakun, Claef; Budinoff, Jason; Brown, Gary; Parong, Fil; Morell, Armando

    2004-01-01

    This paper describes the development of the Boresight Adjustment Mechanism (BAM) for the Geoscience Laser Altimeter System (GLAS) Instrument. The BAM was developed late in the integration and test phase of the GLAS instrument flight program. Thermal vacuum tests of the GLAS instrument indicated that the instrument-boresight alignment stability over temperature may be marginal. To reduce the risk that GLAS may not be able to meet the boresight alignment requirements an intensive effort was started to develop a BAM. Observatory-level testing and further evaluation of the boresight alignment data indicated that sufficient margin could be obtained utilizing existing instrument resources and therefore the BAM was never integrated onto the GLAS Instrument. However, the BAM was designed fabricated and fully qualified over a 4 month timeframe to be capable of precisely steering (less than 2 arcsec over plus or minus 300 arcsec) the output of three independent lasers to ensure the alignment between the transmit and receive paths of the GLAS instrument. The short timeline for the development of the mechanism resulted in several interesting design solutions. This paper discusses the requirement definition design, and testing processes of the BAM development effort how the design was affected by the extremely tight development schedule and the lessons learned throughout the process.

  3. Research Participation in the Mars Orbiter Laser Altimeter Experiment

    Science.gov (United States)

    Pettengill, Gordon H.

    2003-01-01

    This report describes the tasks that have been completed by the Principal Investigator, Gordon Pettengill, and his team during the first year of this grant. Dr. Pettengill was assisted by Dr. Peter Ford and Ms. Joan Quigley. Our main task has been to analyze the polar clouds detected by MOLA (Mars Orbiter Laser Altimeter) during the nominal mission of the Mars Global Surveyor (MGS) in 1999-2001 and to correlate the results with other data sets, in particular that from TES, the MGS thermal emission spectrometer. Starting with the Martian cloud database that we constructed prior to the start of this grant, we have examined all TES footprints that overlap MOLA clouds in time and space, correlating the thermal signature against specific categories that we assign to MOLA clouds on the basis of visual inspection. We are particularly interested in clouds in the region of "cold spots", areas of anomalously low thermal brightness temperature that have been detected in the polar winter by several instruments beginning with IRIS on Mariner 9. They are thought to indicate regions of active CO2 sublimation or snowfall, and it is hoped that MOLA measurements may tell us more about these regions.

  4. 3000 Mile Laser Altimeter Profile Across Northern Hemisphere of Mars

    Science.gov (United States)

    1997-01-01

    Topographic profile across the northern hemisphere of Mars from the Mars Orbiter Laser Altimeter (MOLA). The profile was obtained during the Mars Global Surveyor Capture Orbit Calibration Pass on September 15, 1997 and represents 20 minutes of data collection. The profile has a length of approximately 3000 miles (5000 kilometers). The large bulge is the western part of the Elysium rise, the second largest volcanic province on Mars, and shows over 3 miles (5 kilometers) of vertical relief. This area contains deep chasms that reflect tectonic, volcanic and erosional processes. In contrast is the almost 1featureless1 northern plains region of Mars, which shows only hundreds of meters of relief at scales the size of the United States. Plotted for comparison is the elevation of the Viking Lander 2 site, which is located 275 miles (445 kilometers) west of the profile. At the southernmost extent of the trace is the transition from the northern plains to the ancient southern highlands. Characterizing the fine-scale nature of topography in this chaotic region is crucial to testing theories for how the dichotomy between the geologically distinctive northern lowlands and southern uplands formed and subsequently evolved. The spatial resolution of the profile is approximately 1000 feet (330 meters) and the vertical resolution is approximately 3 feet (1 meter). When the Mars Global Surveyor mapping mission commences in March, 1998, the MOLA instrument will collect 72 times as much data every day for a period of two years.

  5. Qualification of Laser Diode Arrays for Mercury Laser Altimeter Mission

    Science.gov (United States)

    Stephen, Mark; Vasilyev, Aleksey; Schafer, John; Allan, Graham R.

    2004-01-01

    NASA's requirements for high reliability, high performance satellite laser instruments have driven the investigation of many critical components; specifically, 808 nm laser diode array (LDA) pump devices. The MESSENGER mission is flying the Mercury Laser Altimeter (MLA) which is a diode-pumped Nd:YAG laser instrument designed to map the topography of Mercury. The environment imposed on the instrument by the orbital dynamics places special requirements on the laser diode arrays. In order to limit the radiative heating of the satellite from the surface of Mercury, the satellite is designed to have a highly elliptical orbit. The satellite will heat near perigee and cool near apogee. The laser power is cycled during these orbits so that the laser is on for only 30 minutes (perigee) in a 12 hour orbit. The laser heats 10 C while powered up and cools while powered down. In order to simulate these operational conditions, we designed a test to measure the LDA performance while being temperature and power cycled. Though the mission requirements are specific to NASA and performance requirements are derived from unique operating conditions, the results are general and widely applicable. We present results on the performance of twelve LDAs operating for several hundred million pulses. The arrays are 100 watt, quasi-CW, conductively-cooled, 808 nm devices. Prior to testing, we fully characterize each device to establish a baseline for individual array performance and status. Details of this characterization can be found in reference. Arrays are divided into four groups and subjected to the temperature and power cycling matrix are shown.

  6. Improving the Altimeter Derived Geostrophic Currents Using High Resolution Sea Surface Temperature Images: A Feasibility Study

    Science.gov (United States)

    Rio, M.-H.; Santoleri, R.; Giffa, A.; Piterbarg, L.

    2015-12-01

    Accurate knowledge of spatial and temporal ocean surface currents at high resolution is essential for a variety of applications. The altimeter observing system, by providing global and repetitive measurements of the Sea Surface Height, has been by far the most exploited system to estimate ocean surface currents in the past 20 years. However it does not allow observing currents departing from the geostrophic equilibrium, nor is capable to resolve the shortest spatial scales of the currents. In order to go beyond these limits, we investigate how the high spatial and temporal resolution information from Sea Surface Temperature (SST) images can improve the altimeter currents by adapting a method first proposed by [1]. It consists in inverting the SST evolution equation for the velocity by prescribing the source and sink terms and by using the altimeter currents as background. The method feasibility is tested using simulated data based on the Mercator-Ocean system.

  7. Mean Sea Surface (mss) Model Determination for Malaysian Seas Using Multi-Mission Satellite Altimeter

    Science.gov (United States)

    Yahaya, N. A. Z.; Musa, T. A.; Omar, K. M.; Din, A. H. M.; Omar, A. H.; Tugi, A.; Yazid, N. M.; Abdullah, N. M.; Wahab, M. I. A.

    2016-09-01

    The advancement of satellite altimeter technology has generated many evolutions to oceanographic and geophysical studies. A multi-mission satellite altimeter consists with TOPEX, Jason-1 and Jason-2, ERS-2, Envisat-1, CryoSat-2 and Saral are extracted in this study and has been processed using Radar Altimeter Database System (RADS) for the period of January 2005 to December 2015 to produce the sea surface height (hereinafter referred to SSH). The monthly climatology data from SSH is generated and averaged to understand the variation of SSH during monsoon season. Then, SSH data are required to determine the localised and new mean sea surface (MSS). The differences between Localised MSS and DTU13 MSS Global Model is plotted with root mean square error value is 2.217 metres. The localised MSS is important towards several applications for instance, as a reference for sea level variation, bathymetry prediction and derivation of mean dynamic topography.

  8. GEOS-3 ocean current investigation using radar altimeter profiling. [Gulf Stream surface topography

    Science.gov (United States)

    Leitao, C. D.; Huang, N. E.; Parra, C. G.

    1978-01-01

    Both quasi-stationary and dynamic departures from the marine geoid were successfully detected using altitude measurements from the GEOS-3 radar altimeter. The quasi-stationary departures are observed either as elevation changes in single pass profiles across the Gulf Stream or at the crowding of contour lines at the western and northern areas of topographic maps generated using altimeter data spanning one month or longer. Dynamic features such as current meandering and spawned eddies can be monitored by comparing monthly mean maps. Comparison of altimeter inferred eddies with IR detected thermal rings indicates agreement of the two techniques. Estimates of current velocity are made using derived slope estimates in conjunction with the geostrophic equation.

  9. Measuring channel and gully cross-sections with an airborne laser altimeter

    International Nuclear Information System (INIS)

    A laser altimeter, making 4000 measurements per second, was used to measure channel and gully morphology. The laser measurements provide quick, accurate and readily obtained data on the cross-section and morphology of channels and gullies in relation to the adjacent landscape. Although ground based techniques can be used to make these measurements, using a laser altimeter mounted in an aircraft allows data to be collected faster, with greater density and detail, and in areas with limited access for ground surveys. The laser altimeter data are valuable for measuring channel and gully cross-sections and roughness in relation to the surrounding landscape, for assessing soil loss from gullies and channels, and for providing input to the understanding of gully and channel dynamics in the landscape. (author)

  10. Baseline Design and Performance Analysis of Laser Altimeter for Korean Lunar Orbiter

    Science.gov (United States)

    Lim, Hyung-Chul; Neumann, Gregory A.; Choi, Myeong-Hwan; Yu, Sung-Yeol; Bang, Seong-Cheol; Ka, Neung-Hyun; Park, Jong-Uk; Choi, Man-Soo; Park, Eunseo

    2016-09-01

    Korea’s lunar exploration project includes the launching of an orbiter, a lander (including a rover), and an experimental orbiter (referred to as a lunar pathfinder). Laser altimeters have played an important scientific role in lunar, planetary, and asteroid exploration missions since their first use in 1971 onboard the Apollo 15 mission to the Moon. In this study, a laser altimeter was proposed as a scientific instrument for the Korean lunar orbiter, which will be launched by 2020, to study the global topography of the surface of the Moon and its gravitational field and to support other payloads such as a terrain mapping camera or spectral imager. This study presents the baseline design and performance model for the proposed laser altimeter. Additionally, the study discusses the expected performance based on numerical simulation results. The simulation results indicate that the design of system parameters satisfies performance requirements with respect to detection probability and range error even under unfavorable conditions.

  11. Effect of the Measured Pulses Count on the Methodical Error of the Air Radio Altimeter

    Directory of Open Access Journals (Sweden)

    Ján Labun

    2010-04-01

    Full Text Available Radio altimeters are based on the principle of radio location of the earth’ssurface using a frequency-modulated standing wave. The relatively simple method ofmeasurement consists in the evaluation of the number of pulses generated as resulting fromthe mixing of the transmitted and received signals. Such a change in the number ofmodulated pulses within a certain altitude interval, however, is not so simple and is adeterminant issue in defining the precision of the radio altimeter. Being knowledgeable ofthis law in a wider context enables us to enter into discussion on the possibilities of furtherincreasing the precision of measuring low altitudes. The article deals with the lawunderlying the change in the number of radio altimeter pulses with the changing altitudemeasured.

  12. On the recovery of gravity anomalies from high precision altimeter data

    Science.gov (United States)

    Lelgemann, D.

    1976-01-01

    A model for the recovery of gravity anomalies from high precision altimeter data is derived which consists of small correction terms to the inverse Stokes' formula. The influence of unknown sea surface topography in the case of meandering currents such as the Gulf Stream is discussed. A formula was derived in order to estimate the accuracy of the gravity anomalies from the known accuracy of the altimeter data. It is shown that for the case of known harmonic coefficients of lower order the range of integration in Stokes inverse formula can be reduced very much.

  13. The Gulf Stream front - A comparison between Seasat altimeter observations and theory

    Science.gov (United States)

    Kao, T. W.; Cheney, R. E.

    1982-01-01

    A quantitative comparison is made between a model which gives a universal shape and width of the sea surface height rise anomaly across the Gulf Stream and six Gulf Stream altimeter profiles representing a range of conditions. The closeness of the fit obtained reinforces the validity of both the model and the role of satellite altimetry in ocean dynamics. Further comparisons of the data with the theories of Stommel (1966) and Charney (1955) show that the former is incomplete, accepting only one altimeter-derived parameter.

  14. 14 CFR Appendix E to Part 43 - Altimeter System Test and Inspection

    Science.gov (United States)

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Altimeter System Test and Inspection E Appendix E to Part 43 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT MAINTENANCE, PREVENTIVE MAINTENANCE, REBUILDING, AND ALTERATION Pt. 43, App. E Appendix E to...

  15. 77 FR 3323 - Airborne Radar Altimeter Equipment (For Air Carrier Aircraft)

    Science.gov (United States)

    2012-01-23

    ... [Federal Register Volume 77, Number 14 (Monday, January 23, 2012)] [Notices] [Pages 3323-3324] [FR... manufacturers currently manufacturing, advertising, or selling TSO-C67 compliant equipment. Therefore, given the... cancelling TSO-C67. Please note that TSO-C87, Airborne Low Range Radio Altimeter, is currently used for...

  16. Optical system design and integration of the Lunar Orbiter Laser Altimeter.

    Science.gov (United States)

    Ramos-Izquierdo, Luis; Scott, V Stanley; Connelly, Joseph; Schmidt, Stephen; Mamakos, William; Guzek, Jeffrey; Peters, Carlton; Liiva, Peter; Rodriguez, Michael; Cavanaugh, John; Riris, Haris

    2009-06-01

    The Lunar Orbiter Laser Altimeter (LOLA), developed for the 2009 Lunar Reconnaissance Orbiter (LRO) mission, is designed to measure the Moon's topography via laser ranging. A description of the LOLA optical system and its measured optical performance during instrument-level and spacecraft-level integration and testing are presented. PMID:19488116

  17. The Ganymede Laser Altimeter (GALA) on ESA’s JUICE Mission: Overview of the Instrument Design

    OpenAIRE

    Lingenauber, Kay; Hussmann, Hauke; Michaelis, Harald; Oberst, Jürgen; KOBAYASHI, Masanori; Namiki, Noriyuki; Thomas, Nicolas; Seiferlin, Karsten; Lara, Luisa-Maria

    2014-01-01

    The Ganymede Laser Altimeter (GALA) is one of 11 instruments selected by ESA for the JUICE mission payload. GALA will focus on geodetic and geophysical investigations of the icy satellites Europa, Callisto and, in particular, Ganymede. The instrument design is described.

  18. MOLA Science Team A Mars' Year of Topographic Mapping with the Mars Orbiter Laser Altimeter

    Science.gov (United States)

    Smith, David E.; Zuber, Maria T.

    2001-01-01

    Mars Orbiter Laser Altimeter (MOLA) has operated at Mars for a full Mars year and provided a new geodetic and geophysical view of the planet. As the spacecraft enters into the Extended Mission, MOLA will concentrate its observations on the seasonal variability of the icecaps and martian clouds. Additional information is contained in the original extended abstract.

  19. Observations of Reflectivity of the Martian Surface in the Mars Orbiter Laser Altimeter (MOLA) Investigation

    Science.gov (United States)

    Ivanov, Anton B.; Muhleman, Duane O.

    2000-01-01

    We are presenting results of calculation of the surface albedo of Mars at 1 micron wavelength from the Mars Orbiter Laser Altimeter (MOLA) reflectivity measurements. The Mars Global Surveyor Thermal Emission Spectrometer (MGS TES) 9 micron opacity is employed to remove opacity from the MOLA measurements.

  20. A Comparison of Snow Depth on Sea Ice Retrievals Using Airborne Altimeters and an AMSR-E Simulator

    Science.gov (United States)

    Cavalieri, D. J.; Marksu, T.; Ivanoff, A.; Miller, J. A.; Brucker, L.; Sturm, M.; Maslanik, J. A.; Heinrichs, J. F.; Gasiewski, A.; Leuschen, C.; Krabill, W.; Sonntag, J.

    2011-01-01

    A comparison of snow depths on sea ice was made using airborne altimeters and an Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) simulator. The data were collected during the March 2006 National Aeronautics and Space Administration (NASA) Arctic field campaign utilizing the NASA P-3B aircraft. The campaign consisted of an initial series of coordinated surface and aircraft measurements over Elson Lagoon, Alaska and adjacent seas followed by a series of large-scale (100 km ? 50 km) coordinated aircraft and AMSR-E snow depth measurements over portions of the Chukchi and Beaufort seas. This paper focuses on the latter part of the campaign. The P-3B aircraft carried the University of Colorado Polarimetric Scanning Radiometer (PSR-A), the NASA Wallops Airborne Topographic Mapper (ATM) lidar altimeter, and the University of Kansas Delay-Doppler (D2P) radar altimeter. The PSR-A was used as an AMSR-E simulator, whereas the ATM and D2P altimeters were used in combination to provide an independent estimate of snow depth. Results of a comparison between the altimeter-derived snow depths and the equivalent AMSR-E snow depths using PSR-A brightness temperatures calibrated relative to AMSR-E are presented. Data collected over a frozen coastal polynya were used to intercalibrate the ATM and D2P altimeters before estimating an altimeter snow depth. Results show that the mean difference between the PSR and altimeter snow depths is -2.4 cm (PSR minus altimeter) with a standard deviation of 7.7 cm. The RMS difference is 8.0 cm. The overall correlation between the two snow depth data sets is 0.59.

  1. Simulation of the satellite radar altimeter sea ice thickness retrieval uncertainty

    Directory of Open Access Journals (Sweden)

    R. T. Tonboe

    2009-07-01

    Full Text Available Although it is well known that radar waves penetrate into snow and sea ice, the exact mechanisms for radar-altimeter scattering and its link to the depth of the effective scattering surface from sea ice are still unknown. Previously proposed mechanisms linked the snow ice interface, i.e. the dominating scattering horizon, directly with the depth of the effective scattering surface. However, simulations using a multilayer radar scattering model show that the effective scattering surface is affected by snow-cover and ice properties. With the coming Cryosat-2 (planned launch 2009 satellite radar altimeter it is proposed that sea ice thickness can be derived by measuring its freeboard. In this study we evaluate the radar altimeter sea ice thickness retrieval uncertainty in terms of floe buoyancy, radar penetration and ice type distribution using both a scattering model and ''Archimedes' principle''. The effect of the snow cover on the floe buoyancy and the radar penetration and on the ice cover spatial and temporal variability is assessed from field campaign measurements in the Arctic and Antarctic. In addition to these well known uncertainties we use high resolution RADARSAT SAR data to simulate errors due to the variability of the effective scattering surface as a result of the sub-footprint spatial backscatter and elevation distribution sometimes called preferential sampling. In particular in areas where ridges represent a significant part of the ice volume (e.g. the Lincoln Sea the simulated altimeter thickness estimate is lower than the real average footprint thickness. This means that the errors are large, yet manageable if the relevant quantities are known a priori. A discussion of the radar altimeter ice thickness retrieval uncertainties concludes the paper.

  2. The impact of ERS-1 altimeter on the wave analysis and forecast

    International Nuclear Information System (INIS)

    The assimilation procedure has been applied to the ERS-1 altimeter data during February and March 1992. Each day a WAM wave model run consisting of an 1-day analysis and a 5-days forecast has been carried out. The data have been continuously assimilated in the model during the analysis period. Reference runs without assimilation, have been performed in parallel. The comparison between the analysis with and without ERS-1 altimeter data shows the impact of the satellite data. The effect of the ERS-1 passages on the SWH (Significant Wave Height) fields and time series, which are also compared against buoy data, is investigated. The ERS-1 data do not substantially modify the average model SWH but they affect the single values. For moderate SWH (< 4 meters) the assimilation successfully improves the agreement of model analysis and buoy data. For higher SWH values both the model and the altimeter are low with respect to the buoys. Therefore the assimilation does not compensate the discrepancies between model and buoys, indicating that altimeter data underestimate high sea states. This conclusion is also supported by a direct buoy - altimeter comparison. The comparison between the forecasts of the reference and assimilation runs shows a clear persistence of the assimilated information, improving the prediction skill. The persistence is conditioned by the presence of windsea or swell. The assimilation is very effective over large swell areas around the Equator, where the SWH has moderate values. At higher and lower latitudes the effect of the assimilation persists for a shorter time because waves are continuously developed under the action of the wind. The benefits of the assimilation on the forecast are evident in the comparison against the ERS-1 data. (orig.). 32 figs., 4 tabs

  3. Geoscience Laser Altimeter System (GLAS) for the ICESat Mission

    Science.gov (United States)

    Abshire, James B.; Sun, Xiaoli; Ketchum, Eleanor A.; Millar, Pamela S.; Riris, Haris

    2002-01-01

    The Geoscience Laser Altimeter System (GLAS) is a new generation lidar and is the primary science payload for NASA's ICESat Mission. The GLAS design combines a 10 cm precision surface lidar with a sensitive dual wavelength cloud and aerosol lidar. GLAS will precisely measure the heights of the Earth's polar ice sheets, establish a grid of accurate height profiles of the Earth's land topography, and profile the vertical distribution of clouds and aerosols on a global scale. GLAS will be integrated onto a small spacecraft built by Ball Aerospace, and will be launched into a polar orbit with a 590-630 km altitude at an inclination of 94 degrees. ICESat is is currently planned to launch in winter 2002/03 and GLAS is designed to operate continuously in space for a minimum of 3 years. GLAS will measure the vertical distance from orbit to the Earth's surface with pulses from a ND:YAG laser at a 40 Hz rate. Each 6 nsec wide 1064 nm laser pulse is used to produce a single range measurement. On the surface, the laser footprints have 66 m diameter and approx. 170 m center-center spacings. The GLAS receiver uses a I m diameter telescope to detect laser backscatter and a Si APD to detect the 1064 nm signals. The detector's output is sampled by a digital ranging receiver, which records each transmitted pulse and surface echo waveform with 1 nsec (15 cm) resolution. Each echo pulse is digitized and is reported to ground with a record length of from 200 to 544 samples, depending on the spacecraft's location . The GLAS location and epoch times are measured by a precision GPS receiver carried on the ICESat spacecraft. Initial processing of the echo waveforms within GLAS permits discrimination between cloud and surface echoes for selecting appropriate waveform samples. This selection is guided by an on-board DEM which is used to set the boundaries for the echo pulse search algorithm. Subsequent ground-based echo pulse analysis, along with GPS-based clock frequency estimates, permit

  4. The influence of rain and clouds on a satellite dual frequency radar altimeter system operating at 13 and 35 GHz

    Science.gov (United States)

    Walsh, E. J.; Monaldo, F. M.; Goldhirsh, J.

    1983-01-01

    The effects of inhomogeneous spatial attenuation resulting from clouds and rain on the altimeter estimate of the range to mean sea level are modelled. It is demonstrated that typical cloud and rain attenuation variability at commonly expected spatial scales can significantly degrade altimeter range precision. Rain cell and cloud scale sizes and attenuations are considered as factors. The model simulation of altimeter signature distortion is described, and the distortion of individual radar pulse waveforms by different spatial scales of attenuation is considered. Examples of range errors found for models of a single cloud, a rain cell, and cloud streets are discussed.

  5. Surface circulation off Somalia and western equatorial Indian Ocean during summer monsoon of 1988 from Geosat altimeter data

    Digital Repository Service at National Institute of Oceanography (India)

    Subrahmanyam, B.; RameshBabu, V.; Murty, V.S.N.; Rao, L.V.G.

    The sea level variability derived from repeating tracks of the Geosat altimeter data during the late phase (August-September) of the summer monsoon of 1988 revealed the presence of multiple meso-scale eddy features with clockwise and anti...

  6. Cloud and Aerosol Lidar Channel Design and Performance of the Geoscience Laser Altimeter System on the ICESat Mission

    Science.gov (United States)

    Sun, Xiaoli; Abshire, James B.; Krainak, Michael A.; Spinhirne, James D.; Palm, Steve S.; Lancaster, Redgie S.; Allan, Graham R.

    2004-01-01

    The design of the 532 and 1064nm wavelength atmosphere lidar channels of the Geoscience Laser Altimeter System on the ICESat spacecraft is described. The lidar channel performance per on orbit measurements data will be presented.

  7. Improving maps of ice-sheet surface elevation change using combined laser altimeter and stereoscopic elevation model data

    DEFF Research Database (Denmark)

    Fredenslund Levinsen, Joanna; Howat, I. M.; Tscherning, C. C.

    2013-01-01

    that surface to extrapolate elevations away from altimeter flight lines. This reduces the DEM registration errors and fills the gap between the altimeter paths. We use data from ICESat and ATM as well as SPOT 5 DEMs from 2007 and 2008 and apply them to the outlet glaciers Jakobshavn Isbræ (JI......We combine the complementary characteristics of laser altimeter data and stereoscopic digital elevation models (DEMs) to construct high-resolution (_100 m) maps of surface elevations and elevation changes over rapidly changing outlet glaciers in Greenland. Measurements from spaceborne and airborne......) and Kangerdlugssuaq (KL). We find that the main trunks of JI and KL lowered at rates of 30–35 and 7–20ma_1, respectively. The rates decreased inland. The corresponding errors were 0.3–5.2ma_1 for JI and 0.3–5.1ma_1 for KL, with errors increasing proportionally with distance from the altimeter paths....

  8. Offshore limit of coastal ocean variability identified from hydrography and altimeter data in the eastern Arabian Sea

    Digital Repository Service at National Institute of Oceanography (India)

    Antony, M.K.; Swamy, G.N.; Somayajulu, Y.K.

    In this communication, we describe a hitherto-unknown offshore limit to the coastal ocean variability signatures away from the continental shelf in the eastern Arabian Sea, based on hydrographic observations and satellite altimeter (TOPEX...

  9. NODC Standard Product: US Navy Geosat altimeter geophysical data records (GDRs) for the Geodetic Mission (NODC Accession 0053782)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This accession contains a complete copy of an NODC four CD-ROM product set containing all of NOAA's geophysical data records (GDRs) for the Geosat altimeter data...

  10. Validation of Chinese HY-2 satellite radar altimeter significant wave height

    Institute of Scientific and Technical Information of China (English)

    YE Xiaomin; LIN Mingsen; XU Ying

    2015-01-01

    Chinese Haiyang-2(HY-2) satellite is the first Chinese marine dynamic environment satellite. The dual-frequency (Ku and C band) radar altimeter onboard HY-2 has been working effective to provide operational significant wave height (SWH) for more than three years (October 1, 2011 to present).We validated along-track Ku-band SWH data of HY-2 satellite against National Data Buoy Center (NDBC)in-situ measurements over a time period of three years from October 1, 2011 to September 30, 2014, the root mean square error (RMSE) and mean bias of HY-2 SWH is 0.38 m and (–0.13±0.35) m, respectively. We also did cross validation against Jason-2 altimeter SWH data,the RMSE and the mean bias is 0.36m and (–0.22±0.28) m, respectively. In order to compare the statistical results between HY-2 and Jason-2 satellite SWH data, we validated the Jason-2 satellite radar altimeter along-track Ku-band SWH data against NDBC measurements using the same method. The results demonstrate the validation method in this study is scientific and the RMSE and mean bias of Jason-2 SWH data is 0.26 m and (0.00±0.26) m, respectively. We also validated both HY-2 and Jason-2 SWH data every month, the mean bias of Jason-2 SWH data almost equaled to zero all the time, while the mean bias of HY-2 SWH data was no less than –0.31m before April 2013 and dropped to zero after that time. These results indicate that the statistical results for HY-2 altimeter SWH are reliable and HY-2 altimeter along-track SWH data were steady and of high quality in the last three years. The results also indicate that HY-2 SWH data have greatly been improved and have the same accuracy with Jason-2 SWH data after April, 2013. SWH data provided by HY-2 satellite radar altimeter are useful and acceptable for ocean operational applications.

  11. ESAs new range of radar altimeters for the extraction of geophysical parameters from land, sea ice and ocean surfaces

    OpenAIRE

    Cullen, R; Davidson, M. W. J.; Drinkwater, M. R.; Francis, C. R.; Haas, Christian; R. L. Hawley; Mavrocordatos, C. M.; Morris, E. M.; Rack, Wolfgang; Ratier, G.; .P Viau; Wingham, D. J.

    2006-01-01

    Despite the loss of CryoSat, ESAs first Earthopportunity mission, during its launch sequence in Oct2005 ESA have been fortunate enough to have acquired,processed to Level 1b and analysed a significant amountof campaign data from ESAs demonstration AirborneSAR/Interferometric Radar Altimeter System (ASIRAS)designed to have similar functionality to CryoSatsSynthetic Interferometric Radar Altimeter (SIRAL).This data acquisition took place for the original purposeof validating CryoSat retrievals....

  12. A SWITCHED-ANTENNA NADIR-LOOKING INTERFEROMETRIC SAR ALTIMETER FOR TERRAIN-AIDED NAVIGATION

    Directory of Open Access Journals (Sweden)

    Inchan Paek

    2016-01-01

    Full Text Available Conventional terrain-aided navigation (TAN technique uses an altimeter to locate the position of an aerial vehicle. However, a major problem with a radar altimeter is that its beam (or pulse footprint on the ground could be large, and therefore the nadir altitude cannot be estimated accurately. To overcome this difficulty, one may use the nadir-looking synthetic aperture radar (SAR technique to reduce the along-track beam width, while the cross-track ambiguity is resolved with the interferometry technique. However, the cross-track resolution is still far from satisfactory, because of the limited aperture size of antennas. Therefore, the usual three-antenna array cannot resolve multiple terrain points in a same range bin, effectively. In this paper, we propose a technique that can increase the cross-track resolution using a large number of antennas, but in a switched fashion, not raising hardware cost.

  13. Spectral analysis of GEOS-3 altimeter data and frequency domain collocation. [to estimate gravity anomalies

    Science.gov (United States)

    Eren, K.

    1980-01-01

    The mathematical background in spectral analysis as applied to geodetic applications is summarized. The resolution (cut-off frequency) of the GEOS 3 altimeter data is examined by determining the shortest wavelength (corresponding to the cut-off frequency) recoverable. The data from some 18 profiles are used. The total power (variance) in the sea surface topography with respect to the reference ellipsoid as well as with respect to the GEM-9 surface is computed. A fast inversion algorithm for matrices of simple and block Toeplitz matrices and its application to least squares collocation is explained. This algorithm yields a considerable gain in computer time and storage in comparison with conventional least squares collocation. Frequency domain least squares collocation techniques are also introduced and applied to estimating gravity anomalies from GEOS 3 altimeter data. These techniques substantially reduce the computer time and requirements in storage associated with the conventional least squares collocation. Numerical examples given demonstrate the efficiency and speed of these techniques.

  14. ASSIMILATION OF ALTIMETER WIND DATA IN MESOSCALE NUMERICAL MODEL (MM5)

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Making use of altimeter wind data and standard sounding data in a mesoscale numerical model of PSU/NCAR (MM5), we test four-dimensional data assimilation scheme based on nudging. The purpose of this paper is to determine what meteorological fields and what assimilation method have positive effect on typhoon sea surface wind by simulating two typhoon cases in MM5. We perform seven experiments for 9608 Typhoon (Case 1): one control experiment, three analysis nudging experiments, two observation nudging experiments and one analysis and observation nudging experiment; we perform one control experiment and one analysis nudging experiment for 9711 Typhoon (Case 2). The results show assimilating wind-thermal fields can effectively improve simulation accuracy of the model; the experiment combining standard sounding data and surface observations can improve greatly the simulation accuracy of the model; the altimeter data contain lots of sea surface information and also have positive impact on typhoon sea surface wind.

  15. The 24 Million Kilometer Optical Link with the Mercury Laser Altimeter

    Science.gov (United States)

    Coyle, Donald B.

    2006-01-01

    A recent experiment has been completed at NASA Goddard Geophysical and Astronomical Observatory (GGAO) where an optical link has been achieved with the Mercury laser altimeter (MLA) instrument about the Messenger spacecraft on its way to Mercury. A pulsed laser source at 1 micron based on Earth has been recorded on MLA. Simultaneously, the spacecrafts altimeter has been properly aimed and laser pulses transmitted to earth where they were detected and recorded at the same facility. This optical link was used to calibrate and verify operation of the MLA instrument and onboard laser, as well as to gain valuable information with the methods and means of very long range optical communication pointing and receiving techniques. An overview of this experiment, the hardware, and data products will be presented.

  16. Detection of the lunar body tide by the Lunar Orbiter Laser Altimeter

    OpenAIRE

    Mazarico, Erwan Matias; Barker, Michael K.; Neumann, Gregory A.; Zuber, Maria; Smith, David Edmund

    2013-01-01

    The Lunar Orbiter Laser Altimeter instrument onboard the Lunar Reconnaissance Orbiter spacecraft collected more than 5 billion measurements in the nominal 50 km orbit over ~10,000 orbits. The data precision, geodetic accuracy, and spatial distribution enable two-dimensional crossovers to be used to infer relative radial position corrections between tracks to better than ~1 m. We use nearly 500,000 altimetric crossovers to separate remaining high-frequency spacecraft trajectory errors from the...

  17. High accuracy alignment facility for the receiver and transmitter of the BepiColombo Laser Altimeter

    OpenAIRE

    Chakraborty, Sumita; Affolter, Michael; Gunderson, Kurt; Neubert, Jakob; Thomas, Nicolas; Beck, Thomas; Gerber, Michael; Graf, Stefan; Piazza, Daniele; Pommerol, Antoine; Röthlisberger, Guillaume; Seiferlin, Karsten

    2012-01-01

    The accurate co-alignment of the transmitter to the receiver of the BepiColombo Laser Altimeter is a challenging task for which an original alignment concept had to be developed. We present here the design, construction and testing of a large collimator facility built to fulfill the tight alignment requirements. We describe in detail the solution found to attenuate the high energy of the instrument laser transmitter by an original beam splitting pentaprism group. We list the different steps o...

  18. Impact of high-frequency waves on the ocean altimeter range bias - art. no. C11006

    OpenAIRE

    D. Vandemark; Chapron, Bertrand; Elfouhaily, T; Campbell, J.

    2005-01-01

    [1] New aircraft observations are presented on the range determination error in satellite altimetry associated with ocean waves. Laser-based measurements of the cross correlation between the gravity wave slope and elevation are reported for the first time. These observations provide direct access to a long, O(10 m), gravity wave statistic central to nonlinear wave theory prediction of the altimeter sea state bias. Coincident Ka-band radar scattering data are used to estimate an electromagneti...

  19. Detection of the lunar body tide by the Lunar Orbiter Laser Altimeter

    OpenAIRE

    Mazarico, Erwan; Barker, Michael K.; Neumann, Gregory A.; Zuber, Maria T.; Smith, David E.

    2014-01-01

    The Lunar Orbiter Laser Altimeter instrument onboard the Lunar Reconnaissance Orbiter spacecraft collected more than 5 billion measurements in the nominal 50 km orbit over ∼10,000 orbits. The data precision, geodetic accuracy, and spatial distribution enable two-dimensional crossovers to be used to infer relative radial position corrections between tracks to better than ∼1 m. We use nearly 500,000 altimetric crossovers to separate remaining high-frequency spacecraft trajectory errors from the...

  20. Statistics of Mars' topography from the Mars Orbiter Laser Altimeter: Slopes, correlations, and physical Models

    OpenAIRE

    Aharonson, Oded; Zuber, Maria T.; Rothman, Daniel H.

    2001-01-01

    Data obtained recently by the Mars Orbiter Laser Altimeter (MOLA) were used to study the statistical properties of the topography and slopes on Mars. We find that the hemispheric dichotomy, manifested as an elevation difference, can be described by long baseline tilts but in places is expressed as steeper slopes. The bimodal hypsometry of elevations on Mars becomes unimodal when referenced to the center of figure, contrary to the Earth, for which the bimodality is retained. However, ruling ou...

  1. Shape of the northern hemisphere of Mars from the Mars Orbiter Laser Altimeter (MOLA)

    OpenAIRE

    Zuber, Maria T.; Smith, David E.; Phillips, Roger J.; Solomon, Sean C.; Banerdt, W. Bruce; Neumann, Gregory A.; Aharonson, Oded

    1998-01-01

    Eighteen profiles of ∼N-S-trending topography from the Mars Orbiter Laser Altimeter (MOLA) are used to analyze the shape of Mars' northern hemisphere. MOLA observations show smaller northern hemisphere flattening than previously thought. The hypsometric distribution is narrowly peaked with >20% of the surface lying within 200 m of the mean elevation. Low elevation correlates with low surface roughness, but the elevation and roughness may reflect different mechanisms. Bouguer gravity indicates...

  2. Co-registration of Laser Altimeter Tracks with Digital Terrain Models and Applications in Planetary Science

    Science.gov (United States)

    Glaeser, P.; Haase, I.; Oberst, J.; Neumann, G. A.

    2013-01-01

    We have derived algorithms and techniques to precisely co-register laser altimeter profiles with gridded Digital Terrain Models (DTMs), typically derived from stereo images. The algorithm consists of an initial grid search followed by a least-squares matching and yields the translation parameters at sub-pixel level needed to align the DTM and the laser profiles in 3D space. This software tool was primarily developed and tested for co-registration of laser profiles from the Lunar Orbiter Laser Altimeter (LOLA) with DTMs derived from the Lunar Reconnaissance Orbiter (LRO) Narrow Angle Camera (NAC) stereo images. Data sets can be co-registered with positional accuracy between 0.13 m and several meters depending on the pixel resolution and amount of laser shots, where rough surfaces typically result in more accurate co-registrations. Residual heights of the data sets are as small as 0.18 m. The software can be used to identify instrument misalignment, orbit errors, pointing jitter, or problems associated with reference frames being used. Also, assessments of DTM effective resolutions can be obtained. From the correct position between the two data sets, comparisons of surface morphology and roughness can be made at laser footprint- or DTM pixel-level. The precise co-registration allows us to carry out joint analysis of the data sets and ultimately to derive merged high-quality data products. Examples of matching other planetary data sets, like LOLA with LRO Wide Angle Camera (WAC) DTMs or Mars Orbiter Laser Altimeter (MOLA) with stereo models from the High Resolution Stereo Camera (HRSC) as well as Mercury Laser Altimeter (MLA) with Mercury Dual Imaging System (MDIS) are shown to demonstrate the broad science applications of the software tool.

  3. Calibrating mars orbiter laser altimeter pulse widths at mars science laboratory candidate landing sites

    OpenAIRE

    Poole, W.; Muller, J.-P.; S. Gupta; Grindrod, Peter M.

    2014-01-01

    Accurate estimates of surface roughness allow quantitative comparisons between planetary terrains. These comparisons enable us to improve our understanding of commonly occurring surface processes, and develop a more complete analysis of candidate landing and roving sites. A (secondary) science goal of the Mars Orbiter Laser Altimeter was to map surface roughness within the laser footprint using the backscatter pulse-widths of individual pulses, at finer scales than can be derived from the ele...

  4. Global surface slopes and roughness of the Moon from the Lunar Orbiter Laser Altimeter

    OpenAIRE

    Rosenburg, M. A.; Aharonson, O.; Head, J.W.; Kreslavsky, M. A.; Mazarico, E.; Neumann, G. A.; Smith, D E; Torrence, M. H.; Zuber, M. T.

    2011-01-01

    The acquisition of new global elevation data from the Lunar Orbiter Laser Altimeter, carried on the Lunar Reconnaissance Orbiter, permits quantification of the surface roughness properties of the Moon at unprecedented scales and resolution. We map lunar surface roughness using a range of parameters: median absolute slope, both directional (along-track) and bidirectional (in two dimensions); median differential slope; and Hurst exponent, over baselines ranging from ~17 m to ~2.7 km. We find th...

  5. Mars Orbiter Laser Altimeter pulse width measurements and footprint-scale roughness

    OpenAIRE

    Neumann, G.A.; J. B. Abshire; Aharonson, O.; Garvin, J. B.; X. Sun; Zuber, M.T.

    2003-01-01

    The Mars Orbiter Laser Altimeter (MOLA) measured the pulse width and energy of altimetric laser returns during the course of two Mars years of operations. As secondary science objectives, MOLA obtains the footprint-scale roughness and the bidirectional reflectivity of Mars. MOLA underwent extensive preflight calibration and pulse measurements were monitored continuously in flight, but anomalous values of roughness have been inferred. A calibration of pulse widths using inflight data yields a ...

  6. Validation and Variation of Upper Layer Thickness in South China Sea from Satellite Altimeter Data

    Directory of Open Access Journals (Sweden)

    Nan-Jung Kuo

    2008-06-01

    Full Text Available Satellite altimeter data from 1993 to 2005 has been used to analyze the seasonal variation and the interannual variability of upper layer thickness (ULT in the South China Sea (SCS. Base on in-situ measurements, the ULT is defined as the thickness from the sea surface to the depth of 16°C isotherm which is used to validate the result derived from satellite altimeter data. In comparison with altimeter and in-situ derived ULTs yields a correlation coefficient of 0.92 with a slope of 0.95 and an intercept of 6 m. The basin averaged ULT derived from altimeter is 160 m in winter and 171 m in summer which is similar to the in-situ measurements of 159 m in winter and 175 m in summer. Both results also show similar spatial patterns. It suggests that the sea surface height data derived from satellite sensors are usable for study the variation of ULT in the semi-closed SCS. Furthermore, we also use satellite derived ULT to detect the development of eddy. Interannual variability of two meso-scale cyclonic eddies and one anticyclonic eddy are strongly influenced by El Niño events. In most cases, there are highly positive correlations between ULT and sea surface temperature except the periods of El Niño. During the onset of El Niño event, ULT is deeper when sea surface temperature is lower.

  7. Characterization of the uncertainty of loop current metrics using a multidecadal numerical simulation and altimeter observations

    Science.gov (United States)

    Dukhovskoy, Dmitry S.; Leben, Robert R.; Chassignet, Eric P.; Hall, Cody A.; Morey, Steven L.; Nedbor-Gross, Robert

    2015-06-01

    Satellite altimetry is routinely used to monitor Loop Current intrusion and eddy shedding in the Gulf of Mexico. Statistical estimates of the location and variability of the Loop Current vary significantly among published studies and it is not obvious whether these differences are caused by observational errors, different analysis methodologies, processing and gridding of altimeter data products, or the highly variable nature of the Loop Current system itself. This study analyzes the uncertainty of basic Loop Current statistical estimates derived from altimeter observations, i.e. the northern and western extent, the mean Loop Current eddy separation period, and the relationship between the Loop Current retreat latitude and eddy separation period. The robustness of these statistics is assessed using sea surface height data from a 1/25° free-running multidecadal numerical simulation of the Gulf of Mexico HYbrid Coordinate Ocean Model. A suite of sensitivity tests is performed to identify sources of uncertainty in the Loop Current statistics. The tests demonstrate that the Loop Current metrics from the altimeter fields are less sensitive to the choice of the reference sea surface height mean field or Loop Current front definition than to satellite sampling patterns. Analysis of the model and altimetry-derived sea surface height fields shows that the Loop Current variability changes between regimes of rapid and slow eddy formation cycles. This analysis leads to a discussion of the stationarity of the LC system. The mean separation period estimated from the altimeter fields for 1993-2010 is 8±1.8 months. This uncertainty is larger than the errors introduced by the satellite data processing and gridding technique, which is on the order of O (1 month). It is shown that the available altimetry observational record is not long enough at this time to be able to estimate the mean separation period within one-month uncertainty.

  8. Numerical Simulation of Whitecaps and Foam Effects on Satellite Altimeter Response

    Directory of Open Access Journals (Sweden)

    Ferdinando Reale

    2014-04-01

    Full Text Available The determination of wave height by active satellite remote sensing, be it Synthetic Aperture Radar (SAR or altimeter, has been a common practice for many years and is now imbedded on many meteorological and oceanographic forecasting systems. Despite their differences, all active sensors are based on the measurement of the Normalized Radar Cross Section (NRCS of the sea surface, i.e., of its backscattering properties, which in turn depend on the wind velocity. At small and moderate wind speeds, the main mechanism is the formation of ripples (small scale waves; at higher speeds, whitecaps appear, and foam starts playing an essential role in determining NRCS. In the past few years much research effort has gone into clarifying these effects, thus improving the general quality of the measurements. Little work, however, has been devoted so far to consider the vertical spatial variation of backscattering properties, and in particular of the floating foam, over the sea surface. As it is shown in the present paper, the shape of the backscattered electromagnetic impulse in radar altimeters depends on the spatial distribution of foam over the water height in the sea waves and therefore the performance of these instruments in determining Significant Wave Height (Hs and Sea Surface Level (SSL is strongly affected by this effect. This work tackles these problems by making use of specially implemented numerical algorithms to simulate both sea surface processes and radar altimeter techniques. Results show that some causes of errors can be better understood and eventually corrected: in particular, the paper deals with the reconstruction of the electromagnetic Sea State Bias (SSB, the well known altimeter ranging error due to the presence of ocean waves on the sea surface.

  9. Evaluating and correcting rain effects on dual-frequency altimeter Jason-1 wind measurements

    Institute of Scientific and Technical Information of China (English)

    ZHOU Xuan; YANG Xiaofeng; HAO Yulong; ZHAO Shiwei; YU Yang; LI Ziwei

    2013-01-01

    Rain is one of the main sources of error in dual-frequency altimeter Jason-1 wind measurement.In this study,a new radar altimeter backscatter model is proposed and validated to eliminate rain effects.The model takes into account attenuation,volume backscattering,and sea surface perturbation by raindrops under rain conditions.A match-up dataset is built to evaluate rain effects,in combination with the Jason-1 normalized radar cross section,precipitation radar data from the Tropical Rainfall Measuring Mission,and sea surface wind reanalysis data from the European Centre for Medium-Range Weather Forecasts.The results show that rain-induced surface perturbation backscatter increases with rain rate at Ku-band,but their correlation at C-band is poor.In addition,rain surface perturbation and attenuation have major effects on radar altimeter wind measurements.Finally,a rain correction model for Jason-1 winds is developed and validation results prove its ability to reduce rain-induced inaccuracies in wind retrievals.

  10. ICESAT Laser Altimeter Pointing, Ranging and Timing Calibration from Integrated Residual Analysis

    Science.gov (United States)

    Luthcke, Scott B.; Rowlands, D. D.; Carabajal, C. C.; Harding, D. H.; Bufton, J. L.; Williams, T. A.

    2003-01-01

    On January 12, 2003 the Ice, Cloud and land Elevation Satellite (ICESat) was successfully placed into orbit. The ICESat mission carries the Geoscience Laser Altimeter System (GLAS), which has a primary measurement of short-pulse laser- ranging to the Earth s surface at 1064nm wavelength at a rate of 40 pulses per second. The instrument has collected precise elevation measurements of the ice sheets, sea ice roughness and thickness, ocean and land surface elevations and surface reflectivity. The accurate geolocation of GLAS s surface returns, the spots from which the laser energy reflects on the Earth s surface, is a critical issue in the scientific application of these data. Pointing, ranging, timing and orbit errors must be compensated to accurately geolocate the laser altimeter surface returns. Towards this end, the laser range observations can be fully exploited in an integrated residual analysis to accurately calibrate these geolocation/instrument parameters. ICESat laser altimeter data have been simultaneously processed as direct altimetry from ocean sweeps along with dynamic crossovers in order to calibrate pointing, ranging and timing. The calibration methodology and current calibration results are discussed along with future efforts.

  11. A Long Distance Laser Altimeter for Terrain Relative Navigation and Spacecraft Landing

    Science.gov (United States)

    Pierrottet, Diego F.; Amzajerdian, Farzin; Barnes, Bruce W.

    2014-01-01

    A high precision laser altimeter was developed under the Autonomous Landing and Hazard Avoidance (ALHAT) project at NASA Langley Research Center. The laser altimeter provides slant-path range measurements from operational ranges exceeding 30 km that will be used to support surface-relative state estimation and navigation during planetary descent and precision landing. The altimeter uses an advanced time-of-arrival receiver, which produces multiple signal-return range measurements from tens of kilometers with 5 cm precision. The transmitter is eye-safe, simplifying operations and testing on earth. The prototype is fully autonomous, and able to withstand the thermal and mechanical stresses experienced during test flights conducted aboard helicopters, fixed-wing aircraft, and Morpheus, a terrestrial rocket-powered vehicle developed by NASA Johnson Space Center. This paper provides an overview of the sensor and presents results obtained during recent field experiments including a helicopter flight test conducted in December 2012 and Morpheus flight tests conducted during March of 2014.

  12. ALTWAVE: Toolbox for use of satellite L2P altimeter data for wave model validation

    Science.gov (United States)

    Appendini, Christian M.; Camacho-Magaña, Víctor; Breña-Naranjo, José Agustín

    2016-03-01

    To characterize some of the world's ocean physical processes such as its wave height, wind speed and sea surface elevation is a major need for coastal and marine infrastructure planning and design, tourism activities, wave power and storm surge risk assessment, among others. Over the last decades, satellite remote sensing tools have provided quasi-global measurements of ocean altimetry by merging data from different satellite missions. While there is a widely use of altimeter data for model validation, practical tools for model validation remain scarce. Our purpose is to fill this gap by introducing ALTWAVE, a MATLAB user-oriented toolbox for oceanographers and coastal engineers developed to validate wave model results based on visual features and statistical estimates against satellite derived altimetry. Our toolbox uses altimetry information from the GlobWave initiative, and provides a sample application to validate a one year wave hindcast for the Gulf of Mexico. ALTWAVE also offers an effective toolbox to validate wave model results using altimeter data, as well as a guidance for non-experienced satellite data users. This article is intended for wave modelers with no experience using altimeter data to validate their results.

  13. Night and Day: The Opacity of Clouds Measured by the Mars Orbiter Laser Altimeter (MOLA)

    Science.gov (United States)

    Neumann, G. A.; Wilson, R. J.

    2006-01-01

    The Mars Orbiter Laser Altimeter (MOLA) [l] on the Mars Global Surveyor spacecraft ranged to clouds over the course of nearly two Mars years [2] using an active laser ranging system. While ranging to the surface, the instrument was also able to measure the product of the surface reflectivity with the two-way atmospheric transmission at 1064 nm. Furthermore, the reflectivity has now been mapped over seasonal cycles using the passive radiometric capability built into MOLA [3]. Combining these measurements, the column opacity may be inferred. MOLA uniquely provides these measurements both night and day. This study examines the pronounced nighttime opacity of the aphelion season tropical water ice clouds, and the indiscernibly low opacity of the southern polar winter clouds. The water ice clouds (Figure 1) do not themselves trigger the altimeter but have measured opacities tau > 1.5 and are temporally and spatially correlated with temperature anomalies predicted by a Mars Global Circulation Model (MGCM) that incorporates cloud radiative effects [4]. The south polar CO2 ice clouds trigger the altimeter with a very high backscatter cross-section over a thickness of 3-9 m and are vertically dispersed over several km, but their total column opacities lie well below the MOLA measurement limit of tau = 0.7. These clouds correspond to regions of supercooled atmosphere that may form either very large specularly reflecting particles [2] or very compact, dense concentrations (>5x10(exp 6)/cu m) of 100-p particles

  14. The validation of HY-2 altimeter measurements of a significant wave height based on buoy data

    Institute of Scientific and Technical Information of China (English)

    WANG Jichao; ZHANG Jie; YANG Jungang

    2013-01-01

    HY-2 has been launched by China on August 16, 2011 which assembles multi-microwave remote sensing payloads in a body and has the ability of monitoring ocean dynamic environments. The HY-2 satellite data need to be calibrated and validated before being put into use. Based on the in-situ buoys from the Nation-al Data Buoy Center (NDBC), Ku-band significant wave heights (SWH, hs) of HY-2 altimeter are validated. Eleven months of HY-2 altimeter Level 2 products data are chose from October 1, 2011 to August 29, 2012. Using NDBC 60 buoys yield 902 collocations for HY-2 by adopting collocation criteria of 30 min for tempo-ral window and 50 km for a spatial window. An overall RMS difference of the SWH between HY-2 and buoy data is 0.297 m. A correlation coefficient between these is 0.964. An ordinary least squares (OLS) regression is performed with the buoy data as an independent variable and the altimeter data as a dependent vari-able. The regression equation of hs is hs(HY-2)=0.891×hs(NDBC)+0.022. In addition, 2016 collocations are matched with temporal window of 30 min at the crossing points of HY-2 and Jason-2 orbits. RMS difference of Ku-band SWH between the two data sets is 0.452 m.

  15. Study on wave energy resource assessing method based on altimeter data—A case study in Northwest Pacific

    Institute of Scientific and Technical Information of China (English)

    WAN Yong; ZHANG Jie; MENG Junmin; WANG Jing; DAI Yongshou

    2016-01-01

    Wave energy resource is a very important ocean renewable energy. A reliable assessment of wave energy resources must be performed before they can be exploited. Compared with wave model, altimeter can provide more accuratein situ observations for ocean wave which can be as a novel method for wave energy assessment. The advantage of altimeter data is to provide accurate significant wave height observations for wave. In order to develop characteristic and advantage of altimeter data and apply altimeter data to wave energy assessment, in this study, we established an assessing method for wave energy in local sea area which is dedicated to altimeter data. This method includes three parts including data selection and processing, establishment of evaluation indexes system and criterion of regional division. Then a case study of Northwest Pacific was performed to discuss specific application for this method. The results show that assessing method in this paper can assess reserves and temporal and spatial distribution effectively and provide scientific references for the siting of wave power plants and the design of wave energy convertors.

  16. Shuttle Laser Altimeter (SLA): A pathfinder for space-based laser altimetry and lidar

    Science.gov (United States)

    Bufton, Jack; Blair, Bryan; Cavanaugh, John; Garvin, James

    1995-01-01

    The Shuttle Laser Altimeter (SLA) is a Hitchhiker experiment now being integrated for first flight on STS-72 in November 1995. Four Shuttle flights of the SLA are planned at a rate of about a flight every 18 months. They are aimed at the transition of the Goddard Space Flight Center airborne laser altimeter and lidar technology to low Earth orbit as a pathfinder for operational space-based laser remote sensing devices. Future alser altimeter sensors such as the Geoscience Laser Altimeter System (GLAS), an Earth Observing System facility instrument, and the Multi-Beam Laser Altimeter (MBLA), the land and vegetation laser altimeter for the NASA TOPSAT (Topography Satellite) Mission, will utilize systems and approaches being tested with SLA. The SLA Instrument measures the distance from the Space Shuttle to the Earth's surface by timing the two-way propagation of short (approximately 10 na noseconds) laser pulses. laser pulses at 1064 nm wavelength are generated in a laser transmitter and are detected by a telescope equipped with a silicon avalanche photodiode detector. The SLA data system makes the pulse time interval measurement to a precision of about 10 nsec and also records the temporal shape of the laser echo from the Earth's surface for interpretation of surface height distribution within the 100 m diam. sensor footprint. For example, tree height can be determined by measuring the characteristic double-pulse signature that results from a separation in time of laser backscatter from tree canopies and the underlying ground. This is accomplished with a pulse waveform digitizer that samples the detector output with an adjustable resolution of 2 nanoseconds or wider intervals in a 100 sample window centered on the return pulse echo. The digitizer makes the SLA into a high resolution surface lidar sensor. It can also be used for cloud and atmospheric aerosol lidar measurements by lengthening the sampling window and degrading the waveform resolution. Detailed test

  17. Measurements of land surface features using an airborne laser altimeter: the HAPEX-Sahel experiment

    International Nuclear Information System (INIS)

    An airborne laser profiling altimeter was used to measure surface features and properties of the landscape during the HAPEX-Sahel Experiment in Niger, Africa in September 1992. The laser altimeter makes 4000 measurements per second with a vertical resolution of 5 cm. Airborne laser and detailed field measurements of vegetation heights had similar average heights and frequency distribution. Laser transects were used to estimate land surface topography, gully and channel morphology, and vegetation properties ( height, cover and distribution). Land surface changes related to soil erosion and channel development were measured. For 1 km laser transects over tiger bush communities, the maximum vegetation height was between 4-5 and 6-5 m, with an average height of 21 m. Distances between the centre of rows of tiger bush vegetation averaged 100 m. For two laser transects, ground cover for tiger bush was estimated to be 225 and 301 per cent for vegetation greater than 0-5m tall and 190 and 25-8 per cent for vegetation greater than 10m tall. These values are similar to published values for tiger bush. Vegetation cover for 14 and 18 km transects was estimated to be 4 per cent for vegetation greater than 0-5 m tall. These cover values agree within 1-2 per cent with published data for short transects (⩾ 100 m) for the area. The laser altimeter provided quick and accurate measurements for evaluating changes in land surface features. Such information provides a basis for understanding land degradation and a basis for management plans to rehabilitate the landscape. (author)

  18. In-Flight Performance of the Mercury Laser Altimeter Laser Transmitter

    Science.gov (United States)

    Yu, Anthony W.; Sun, Xiaoli; Li, Steven X.; Cavanaugh, John F.; Neumann, Gregory A.

    2014-01-01

    The Mercury Laser Altimeter (MLA) is one of the payload instruments on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, which was launched on August 3, 2004. MLA maps Mercury's shape and topographic landforms and other surface characteristics using a diode-pumped solid-state laser transmitter and a silicon avalanche photodiode receiver that measures the round-trip time of individual laser pulses. The laser transmitter has been operating nominally during planetary flyby measurements and in orbit about Mercury since March 2011. In this paper, we review the MLA laser transmitter telemetry data and evaluate the performance of solid-state lasers under extended operation in a space environment.

  19. Comparison of retrieving methods of ocean wave periods from satellite altimeter with buoy measurements

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    For validating the results of retrieved mean wave period, four empirical algorithms established previously are introduced. Based on the data of over five years derived from TOPEX satellite altimeter for the entire East China Sea, ocean wave periods were calculated and statistical comparison among them was performed. The retrieved mean wave period obtained with our new distribution parameters showed better agreement with the wave period TB measured by buoy than that calculated by other three algorithms. The difference between the mean values of and that of TB is 0.16 s and the RMSE (root mean square error) of is the lowest value (0.48).

  20. A geopotential model from satellite tracking, altimeter, and surface gravity data: GEM-T3

    Science.gov (United States)

    Lerch, F. J.; Nerem, R. S.; Putney, B. H.; Felsentreger, T. L.; Sanchez, B. V.; Marshall, J. A.; Klosko, S. M.; Patel, G. B.; Williamson, R. G.; Chinn, D. S.

    1994-01-01

    An improved model of Earth's gravitational field, Goddard Earth Model T-3 (GEM-T3), has been developed from a combination of satellite tracking, satellite altimeter, and surface gravimetric data. GEM-T3 provides a significant improvement in the modeling of the gravity field at half wavelengths of 400 km and longer. This model, complete to degree and order 50, yields more accurate satellite orbits and an improved geoid representation than previous Goddard Earth Models. GEM-T3 uses altimeter data from GEOS 3 (1975-1976), Seasat (1978) and Geosat (1986-1987). Tracking information used in the solution includes more than 1300 arcs of data encompassing 31 different satellites. The recovery of the long-wavelength components of the solution relies mostly on highly precise satellite laser ranging (SLR) data, but also includes Tracking Network (TRANET) Doppler, optical, and satellite-to-satellite tracking acquired between the ATS 6 and GEOS 3 satellites. The main advances over GEM-T2 (beyond the inclusion of altimeter and surface gravity information which is essential for the resolution of the shorter wavelength geoid) are some improved tracking data analysis approaches and additional SLR data. Although the use of altimeter data has greatly enhanced the modeling of the ocean geoid between 65 deg N and 60 deg S latitudes in GEM-T3, the lack of accurate detailed surface gravimetry leaves poor geoid resolution over many continental regions of great tectonic interest (e.g., Himalayas, Andes). Estimates of polar motion, tracking station coordinates, and long-wavelength ocean tidal terms were also made (accounting for 6330 parameters). GEM-T3 has undergone error calibration using a technique based on subset solutions to produce reliable error estimates. The calibration is based on the condition that the expected mean square deviation of a subset gravity solution from the full set values is predicted by the solutions' error covariances. Data weights are iteratively adjusted until

  1. Estimation of Ganymede's Topography, Rotation and Tidal Deformation - a Study of Synthetic Ganymede Laser Altimeter Observations

    Science.gov (United States)

    Steinke, T.; Stark, A.; Steinbrügge, G.; Hussmann, H.; Oberst, J.

    2015-10-01

    We implement an iterative least-squares inversion routine to study the estimation of several dynamic Ganymede rotation parameters by laser altimetry. Based on spherical harmonic expansions of the global topography we use simulated Ganymede Laser Al-timeter observations representing the synthetic topography of the satellite. Besides the static topography we determine the dynamical parameters, such as the rotation rate, the amplitudes of physical librations, the spin pole orientation, and the tidal deformation. This parameters may strengthen implications for a liquid ocean beneath Ganymede's icy shell and, in addition, constrain geodetic frame parameters essential for various space-borne experiments.

  2. In-Flight Thermal Performance of the Geoscience Laser Altimeter System (GLAS) Instrument

    Science.gov (United States)

    Grob, Eric; Baker, Charles; McCarthy, Tom

    2003-01-01

    The Geoscience Laser Altimeter System (GLAS) instrument is NASA Goddard Space Flight Center's first application of Loop Heat Pipe technology that provides selectable/stable temperature levels for the lasers and other electronics over a widely varying mission environment. GLAS was successfully launched as the sole science instrument aboard the Ice, Clouds, and Land Elevation Satellite (ICESat) from Vandenberg AFB at 4:45pm PST on January 12, 2003. After SC commissioning, the LHPs started easily and have provided selectable and stable temperatures for the lasers and other electronics. This paper discusses the thermal development background and testing, along with details of early flight thermal performance data.

  3. The Mars Orbiter Laser Altimeter Archive: Final Precision Experiment Data Record Release and Status of Radiometry

    Science.gov (United States)

    Neumann, Gregory A.; Lemoine, F. G.; Smith, D. E.; Zuber, M. T.

    2003-01-01

    A final release (Version L) of the Mars Orbiter Laser Altimeter (MOLA) Precision Experiment Data Record (PEDR) has been submitted to the Planetary Data System (PDS). Additional gridded data record products are forthcoming. These products have evolved since their original description, owing in part to improved gravity modeling and cartographic reference frames, and in part to refinements in calibration. An additional component, the 1064 nm narrowband radiometry data, is also being archived. These data will be invaluable for future studies by Mars explorers and scientists.

  4. Optical system design and integration of the Mars Observer Laser Altimeter.

    Science.gov (United States)

    Ramos-Izquierdo, L; Bufton, J L; Hayes, P

    1994-01-20

    The Mars Observer Laser Altimeter, developed for flight on the Mars Observer spacecraft payload in September 1992, is designed to measure the topography of the Martian surface over a 2-year period from a 400-km mapping orbit. A 40 mJ pulse diode-pumped laser together with a 0.5-m-diameter beryllium telescope and a silicon avalanche photodiode are the principal optical subassemblies of this active remote-sensing instrument. Optical design rationale and measured optical performances during assembly and integration are presented. PMID:20862020

  5. SIMULATION OF THE Ku-BAND RADAR ALTIMETER SEA ICE EFFECTIVE SCATTERING SURFACE

    DEFF Research Database (Denmark)

    Tonboe, Rasmus; Andersen, Søren; Pedersen, Leif Toudal

    2006-01-01

    A radiative transfer model is used to simulate the sea ice radar altimeter effective scattering surface variability as a function of snow depth and density. Under dry snow conditions without layering these are the primary snow parameters affecting the scattering surface variability. The model...... is initialised with in situ data collected during the May 2004 GreenIce ice camp in the Lincoln Sea (73ºW; 85ºN). Our results show that the snow cover is important for the effective scattering surface depth in sea ice and thus for the range measurement, ice freeboard and ice thickness estimation....

  6. Long term changes of altimeter range and geophysical corrections at altimetry calibration sites

    DEFF Research Database (Denmark)

    Andersen, Ole Baltazar; Cheng, Yongcun; Pascal Willis

    2013-01-01

    trends in the sum of range corrections are found for the calibrations sites both for local scales (within 50km around the selected site) and for regional scales (within 300km). However, the geophysical corrections accounting for atmospheric pressure loading and high frequency sea level variations...... (dynamic atmosphere correction) that is frequently applied to in situ gauge and the altimeter observations should be considered with care for calibration with in situ observations. Over the 18years (1993–2010), the dynamic atmosphere correction shows a regional trend close to 1mm/year at both Mediterranean...

  7. Dynamic sea surface topography, gravity and improved orbit accuracies from the direct evaluation of SEASAT altimeter data

    Science.gov (United States)

    Marsh, J. G.; Lerch, F.; Koblinsky, C. J.; Klosko, S. M.; Robbins, J. W.; Williamson, R. G.; Patel, G. B.

    1989-01-01

    A method for the simultaneous solution of dynamic ocean topography, gravity and orbits using satellite altimeter data is described. A GEM-T1 based gravitational model called PGS-3337 that incorporates Seasat altimetry, surface gravimetry and satellite tracking data has been determined complete to degree and order 50. The altimeter data is utilized as a dynamic observation of the satellite's height above the sea surface with a degree 10 model of dynamic topography being recovered simultaneously with the orbit parameters, gravity and tidal terms in this model. PGS-3337 has a geoid uncertainty of 60 cm root-mean-square (RMS) globally, with the uncertainty over the altimeter tracked ocean being in the 25 cm range. Doppler determined orbits for Seasat, show large improvements, with the sub-30 cm radial accuracies being achieved. When altimeter data is used in orbit determination, radial orbital accuracies of 20 cm are achieved. The RMS of fit to the altimeter data directly gives 30 cm fits for Seasat when using PGS-3337 and its geoid and dynamic topography model. This performance level is two to three times better than that achieved with earlier Goddard earth models (GEM) using the dynamic topography from long-term oceanographic averages. The recovered dynamic topography reveals the global long wavelength circulation of the oceans with a resolution of 1500 km. The power in the dynamic topography recovery is now found to be closer to that of oceanographic studies than for previous satellite solutions. This is attributed primarily to the improved modeling of the geoid which has occurred. Study of the altimeter residuals reveals regions where tidal models are poor and sea state effects are major limitations.

  8. Deriving Planetary Surface Characteristics from Orbiting Laser Altimeter Pulse-Widths on: Mars, the Moon, and Earth

    OpenAIRE

    Poole, W. D. B.

    2015-01-01

    A set of equations linking the time-spread of a laser altimeter echo-profile, commonly known as the pulse-width, to the variance of topography within the pulse-footprint are tested by comparing pulse-width data to surface characteristics measured from high-resolution Digital Terrain Models. The research is motivated by the advent of high-resolution Digital Terrain Models over Mars, which enables the calibration of Mars Orbiter Laser Altimeter pulse-widths, and evolves to include lunar and ter...

  9. The accuracy of satellite radar altimeter data over the Greenland ice sheet determined from airborne laser data

    DEFF Research Database (Denmark)

    Bamber, J.L.; Ekholm, Simon; Krabill, W.

    1998-01-01

    with airborne laser altimeter data an absolute accuracy typically in the range 2-10 cm +/- 10 cm. Comparison of differences between the radar and laser derived elevations, showed a correlation with surface slope. The difference between the two data sets ranged from 84 cm +/- 79 cm for slopes below 0.1 degrees......, to 10.3 m +/- 8.4 m for a slope of 0.7 degrees ( the half power beam-width of the ERS-1 radar altimeter). An explanation for the behaviour of the difference as a function of surface slope is given in terms of the pattern of surface roughness on the ice sheet....

  10. Waveform classification of airborne synthetic aperture radar altimeter over Arctic sea ice

    Directory of Open Access Journals (Sweden)

    M. Zygmuntowska

    2013-08-01

    Full Text Available Sea ice thickness is one of the most sensitive variables in the Arctic climate system. In order to quantify changes in sea ice thickness, CryoSat-2 was launched in 2010 carrying a Ku-band radar altimeter (SIRAL designed to measure sea ice freeboard with a few centimeters accuracy. The instrument uses the synthetic aperture radar technique providing signals with a resolution of about 300 m along track. In this study, airborne Ku-band radar altimeter data over different sea ice types have been analyzed. A set of parameters has been defined to characterize the differences in strength and width of the returned power waveforms. With a Bayesian-based method, it is possible to classify about 80% of the waveforms from three parameters: maximum of the returned power waveform, the trailing edge width and pulse peakiness. Furthermore, the maximum of the power waveform can be used to reduce the number of false detections of leads, compared to the widely used pulse peakiness parameter. For the pulse peakiness the false classification rate is 12.6% while for the power maximum it is reduced to 6.5%. The ability to distinguish between different ice types and leads allows us to improve the freeboard retrieval and the conversion from freeboard into sea ice thickness, where surface type dependent values for the sea ice density and snow load can be used.

  11. Oceanwide gravity anomalies from Geos-3, Seasat and Geosat altimeter data

    Science.gov (United States)

    Rapp, Richard H.; Basic, Tomislav

    1992-01-01

    Three kinds of satellite altimeter data have been combined, along with 5 x 5 arcmin bathymetric data, to calculate a 0.125 deg ocean wide gridded set of 2.3 x 10 exp 6 free-air gravity anomalies. The procedure used was least squares collocation that yields the predicted anomaly and standard deviation. The value of including the bathymetric data was shown in a test around the Dowd Seamount where the root mean square (rms) difference between ship gravity measurements decreased from +/- 40 mgal to +/- 20 mgal when the bathymetry was included. Comparisons between the predicted anomalies and ship gravity data is described in three cases. In the Banda Sea the rms differences were +/- 20 mgal for two lines. In the South Atlantic rms differences over lines of 2000 km in length were +/- 7 mgal. For cruise data in the Antarctica region the discrepancies were +/- 12 mgal. Comparisons of anomalies derived from the Geosat geodetic mission data by Marks and McAdoo (1992) with ship dta gave differences of +/- 6 mgal showing the value of the much denser Geosat geodetic mission altimeter data.

  12. Lunar topographic model CLTM-s01 from Chang'E-1 laser altimeter

    Institute of Scientific and Technical Information of China (English)

    PING JinSong; HUANG Qian; YAN JianGuo; CAO JianFeng; TANG GeShi; SHU Rong

    2009-01-01

    More than 3 million range measurements from the Chang'E-1 Laser Altimeter have been used to pro-duce a global topographic model of the Moon with improved accuracy. Our topographic model, a 360th degree and order spherical harmonic expansion of the lunar radii, is designated as Chang'E-1 Lunar Topography Model s01 (CLTM-s01). This topographic field, referenced to a mean radius of 1738 km, has an absolute vertical accuracy of approximately 31 m and a spatial resolution of 0.25° (~7.5 km). This new lunar topographic model has greatly improved previous models in spatial coverage, accuracy and spatial resolution, and also shows the polar regions with the altimeter results for the first time. From CLTM-s01, the mean, equatorial, and polar radii of the Moon are 1737103, 1737646, and 1735843 m, re-spectively. In the lunar-fixed coordinate system, this model shows a COM/COF offset to be (-1.777, -0.730, 0.237) km along the x, y, and z directions, respectively. All the basic lunar shape parameters derived from CLTM-s01 are in agreement with the results of Clementine GLTM2, but CLTM-s01 offers higher accuracy and reliability due to its better global samplings.

  13. Lunar topographic model CLTM-s01 from Chang’E-1 laser altimeter

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    More than 3 million range measurements from the Chang’E-1 Laser Altimeter have been used to produce a global topographic model of the Moon with improved accuracy. Our topographic model, a 360th degree and order spherical harmonic expansion of the lunar radii, is designated as Chang’E-1 Lunar Topography Model s01 (CLTM-s01). This topographic field, referenced to a mean radius of 1738 km, has an absolute vertical accuracy of approximately 31 m and a spatial resolution of 0.25o (~7.5 km). This new lunar topographic model has greatly improved previous models in spatial coverage, accuracy and spatial resolution, and also shows the polar regions with the altimeter results for the first time. From CLTM-s01, the mean, equatorial, and polar radii of the Moon are 1737103, 1737646, and 1735843 m, respectively. In the lunar-fixed coordinate system, this model shows a COM/COF offset to be (-1.777, -0.730, 0.237) km along the x, y, and z directions, respectively. All the basic lunar shape parameters derived from CLTM-s01 are in agreement with the results of Clementine GLTM2, but CLTM-s01 offers higher accuracy and reliability due to its better global samplings.

  14. Polarimetric, Two-Color, Photon-Counting Laser Altimeter Measurements of Forest Canopy Structure

    Science.gov (United States)

    Harding, David J.; Dabney, Philip W.; Valett, Susan

    2011-01-01

    Laser altimeter measurements of forest stands with distinct structures and compositions have been acquired at 532 nm (green) and 1064 nm (near-infrared) wavelengths and parallel and perpendicular polarization states using the Slope Imaging Multi-polarization Photon Counting Lidar (SIMPL). The micropulse, single photon ranging measurement approach employed by SIMPL provides canopy structure measurements with high vertical and spatial resolution. Using a height distribution analysis method adapted from conventional, 1064 nm, full-waveform lidar remote sensing, the sensitivity of two parameters commonly used for above-ground biomass estimation are compared as a function of wavelength. The results for the height of median energy (HOME) and canopy cover are for the most part very similar, indicating biomass estimations using lidars operating at green and near-infrared wavelengths will yield comparable estimates. The expected detection of increasing depolarization with depth into the canopies due to volume multiple-scattering was not observed, possibly due to the small laser footprint and the small detector field of view used in the SIMPL instrument. The results of this work provide pathfinder information for NASA's ICESat-2 mission that will employ a 532 nm, micropulse, photon counting laser altimeter.

  15. A BP neural network model for sea state recognition using laser altimeter

    Science.gov (United States)

    Shi, Chun-bo; Jia, Xiao-dong; Li, Sheng; Wang, Zhen

    2009-07-01

    A BP neural network method for the recognition of sea state in laser altimeter is presented in this paper. Sea wave is the typical stochastic disturbance factor of laser altimeter effecting on low-altitude defense penetration of the intelligent antiship missiles, the recognition of sea state is studied in order to satisfy the practical needs of flying over the ocean. The BP neural network fed with the feature vector of laser range-measurement presents the analysis of features and outputs the estimation result of sea state. The two most distinguishing features are the mean and the variance of the sea echo, which are extracted from the distance characteristics of sea echo using general theory of statistics. The use of a feedforward network trained with the back-propagation algorithm is also investigated. The BP neural network is trained using sample data set to the neural network, and then the BP neural network trained is tested to recognize the sea state waiting for the classification. The network output shows the recognition accuracy of the model can up to 88%, and the results of tests show that the BP neural network model for the recognition of sea state is feasible and effective.

  16. Waveform analysis of airborne synthetic aperture radar altimeter over Arctic sea ice

    Directory of Open Access Journals (Sweden)

    M. Zygmuntowska

    2013-03-01

    Full Text Available Sea ice thickness is one of the most sensitive variables in the Arctic climate system. In order to quantify changes in sea ice thickness, CryoSat was launched in 2010 carrying a Ku-band Radar Altimeter (SIRAL designed to measure sea ice freeboard with a few centimeters accuracy. The instrument uses the synthetic aperture radar technique providing signals with a resolution of about 300 m along track. In this study, airborne Ku-band radar altimeter data over different sea ice types has been analyzed. A set of parameters has been defined to characterize the difference in strength and width of the returned power waveforms. With a Bayesian based method it is possible to classify about 80% of the waveforms by three parameters: maximum of the returned power echo, the trailing edge width and pulse peakiness. Furthermore, the radar power echo maximum can be used to minimize the rate of false detection of leads compared to the widely used Pulse Peakiness parameter. The possibility to distinguish between different ice types and open water allows to improve the freeboard retrieval and the conversion into sea ice thickness where surface type dependent values for the sea ice density and snow load can be used.

  17. Analysis of GEOS-3 altimeter data and extraction of ocean wave height and dominant wavelength

    Science.gov (United States)

    Walsh, E. J.

    1979-01-01

    When the amplitude and timing biases are removed from the GEOS-3 Sample and Hold (S&H) gates, the mean return waveforms can be excellently fitted with a theoretical template which represents the convolution of: (1) the radar point target response; (2) the range noise (jitter) in the altimeter tracking loop; (3) the sea surface height distribution; and (4) the antenna pattern as a function of the range to mean sea level. Several techniques of varying complexity to remove the effect of the tracking loop jitter in computing the wave height are considered. They include: (1) realigning the S&H gates to their actual positions with respect to mean sea level before averaging; (2) using the observed standard deviation on the altitude measurement to remove the integrated effect of the tracking loop jitter, and (3) using a look-up table to correct for the expected value of range noise. Analysis of skewness in the GEOS return waveform demonstrates the potential of a satellite radar altimeter to determine the dominant wavelength of ocean waves.

  18. The Mars Orbiter Altimeter (MOLA) Investigation of the Shape and Topography of Mars

    Science.gov (United States)

    Smith, David E.; Zuber, Maria T.

    2001-01-01

    The Mars Orbiter Laser Altimeter (MOLA) is an instrument on the Mars Global Surveyor (MGS) spacecraft that has been orbiting Mars since September 1997. After some preliminary observations in Sept/Oct, 1997 and in the spring and summer of 1998, the MGS spacecraft entered its mapping orbit of 400 km above the surface of Mars in February 1999. MGS began a 2 year program of systematically mapping the planet with a camera (MOC), thermal emission spectrometer (TES), magnetometer (MAG), laser altimeter (MOLA), and a radio science investigation for gravity and radio occultations. MOLA has a 48mJ, 1064 nrn ND:YAG, diode pumped laser with a 8 nanosecond pulse width, a pulse rate of 10 Hz, and a range precision of less than 40 cm. MOLA has been operating almost continuously for over two years and obtained over 600 million measurements of the radius of Mars. Using very precise orbits for the MGS spacecraft derived from the Doppler and range tracking of MGS by the Deep Space Network a topographical map of Mars has been developed with an average radial accuracy of a meter and a horizontal accuracy of 100 meters. This topographical map has revealed a new Mars, a planet with some of the flattest areas in the solar system and one of the largest impact basins. MOLA has revealed clear evidence of the effect of past fluid action on the surface and found icecaps that contain as much water ice today as the icecap of Greenland.

  19. Precise topography assessment of Lop Nur Lake Basin using GLAS altimeter

    International Nuclear Information System (INIS)

    Lop Nur is a dried-up salt lake lying in the eastern part of Tarim basin, which used to be the second largest lagon in China. The ''ear'' rings in Lop Nur attract many interests and are regarded as the lake shorelines during its recession. The topography of the lake basin is important in understanding the formation of the ''ear'' rings. In this paper, elevation data along three transects obtained from laser altimeter were taken as the basic material of the topography in Lop Nur. Elevation data of laser altimeter show great consistency between adjacent passes. Orthometric height (OH) derived from altimetry data and the geoid model are used to analyze the elevation characteristic along ''ear'' rings. The result shows the ''ear'' rings are basically identical in elevation, supporting the statement that ''ear'' rings are former lake shorelines. A discrepancy of approximately 1 meter in OH is observed on the same ''ear'' ring, lower in the north and higher in the south, which is found for the first time. Possible explanations could be deformation of ground surface due to earthquake or tectonic movement after the ''ear'' rings are formed, or tilt of water surface due to wind stress or lake current during the formation of the rings

  20. Altimeter data assimilation in the tropical Indian Ocean using water property conserving scheme

    Indian Academy of Sciences (India)

    Bhasha M Mankad; Rashmi Sharma; Sujit Basu; P K Pal

    2012-02-01

    Altimeter data have been assimilated in an ocean general circulation model using the water property conserving scheme. Two runs of the model have been conducted for the year 2004. In one of the runs, altimeter data have been assimilated sequentially, while in another run, assimilation has been suppressed. Assimilation has been restricted to the tropical Indian Ocean. An assessment of the strength of the scheme has been carried out by comparing the sea surface temperature (SST), simulated in the two runs, with in situ derived as well as remotely sensed observations of the same quantity. It has been found that the assimilation exhibits a significant positive impact on the simulation of SST. The subsurface effect of the assimilation could be judged by comparing the model simulated depth of the 20°C isotherm (hereafter referred to as D20), as a proxy of the thermocline depth, with the same quantity estimated from ARGO observations. In this case also, the impact is noteworthy. Effect on the dynamics has been judged by comparison of simulated surface current with observed current at a moored buoy location, and finally the impact on model sea level forecast in a free run after assimilation has been quantified in a representative example.

  1. Seasonal and inter-annual sea surface height variations of the northern Indian Ocean from the TOPEX/POSEIDON altimeter

    Digital Repository Service at National Institute of Oceanography (India)

    PrasannaKumar, S.; Snaith, H.; Challenor, P.; Guymer, H.T.

    The seasonal and inter-annual variability of the northern Indian Ocean was studied by analysing 10-day snapshots of sea surface height (SSH) data from TOPEX/POSEIDON altimeter for the period November 1992 to August 1995. The large scale SSH...

  2. 20,000 Photons Under the Snow: Subsurface Scattering of Visible Laser Light and the Implications for Laser Altimeters

    Science.gov (United States)

    Greeley, A.; Kurtz, N. T.; Shappirio, M.; Neumann, T.; Cook, W. B.; Markus, T.

    2014-12-01

    Existing visible light laser altimeters such as ATM (Airborne Topographical Mapper) with NASA's Operation IceBridge and NASA's MABEL (Multiple Altimeter Beam Experimental Lidar; a simulator for NASA's ICESat-2 mission) are providing scientists with a view of Earth's ice sheets, glaciers, and sea ice with unprecedented detail. Measuring how these surfaces evolve in the face of a rapidly changing climate requires the utmost attention to detail in the design and calibration of these instruments, as well as understanding the changing optical properties of these surfaces. As single photon counting lidars, MABEL and NASA's ATLAS (Advanced Topographic Laser Altimeter System) on the upcoming ICESat-2 mission provide fundamentally different information compared with waveform lidars such as ATM, or GLAS (Geoscience Laser Altimeter System) on NASA's previous ICESat-1 mission. By recording the travel times of individual photons, more detailed information about the surface, and potentially the subsurface, are available and must be considered in elevation retrievals from the observed photon cloud. Here, we investigate possible sources of uncertainty associated with monochromatic visible light scattering in subsurface snow, which may affect the precision and accuracy of elevation estimates. We also explore the capacity to estimate snow grain size in near surface snow using experimental visible light laser data obtained in laboratory experiments.

  3. Signatures of Kelvin and Rossby wave propagation in the northern Indian Ocean from TOPEX/POSEIDON Altimeter

    Digital Repository Service at National Institute of Oceanography (India)

    PrasannaKumar, S.; Unnikrishnan, A.S.; Muraleedharan, P.M.

    The climatological monthly mean sea surface height (SSH) anomalies derived from T/P altimeter in the northern Indian Ocean, during 1993 to 1997, are used to prepare time-longitude plots. Along the equator they reveal strong semi-annual variability...

  4. Multi-Mission Cross-Calibration of Satellite Altimeters: Constructing a Long-Term Data Record for Global and Regional Sea Level Change Studies

    Directory of Open Access Journals (Sweden)

    Wolfgang Bosch

    2014-03-01

    Full Text Available Climate studies require long data records extending the lifetime of a single remote sensing satellite mission. Precise satellite altimetry exploring global and regional evolution of the sea level has now completed a two decade data record. A consistent long-term data record has to be constructed from a sequence of different, partly overlapping altimeter systems which have to be carefully cross-calibrated. This cross-calibration is realized globally by adjusting an extremely large set of single- and dual-satellite crossover differences performed between all contemporaneous altimeter systems. The total set of crossover differences creates a highly redundant network and enables a robust estimate of radial errors with a dense and rather complete sampling for all altimeter systems analyzed. An iterative variance component estimation is applied to obtain an objective relative weighting between altimeter systems with different performance. The final time series of radial errors is taken to estimate (for each of the altimeter systems an empirical auto-covariance function. Moreover, the radial errors capture relative range biases and indicate systematic variations in the geo-centering of altimeter satellite orbits. The procedure has the potential to estimate for all altimeter systems the geographically correlated mean errors which is not at all visible in single-satellite crossover differences but maps directly to estimates of the mean sea surface.

  5. Acceleration of Sea Level Rise Over Malaysian Seas from Satellite Altimeter

    Science.gov (United States)

    Hamid, A. I. A.; Din, A. H. M.; Khalid, N. F.; Omar, K. M.

    2016-09-01

    Sea level rise becomes our concern nowadays as a result of variously contribution of climate change that cause by the anthropogenic effects. Global sea levels have been rising through the past century and are projected to rise at an accelerated rate throughout the 21st century. Due to this change, sea level is now constantly rising and eventually will threaten many low-lying and unprotected coastal areas in many ways. This paper is proposing a significant effort to quantify the sea level trend over Malaysian seas based on the combination of multi-mission satellite altimeters over a period of 23 years. Eight altimeter missions are used to derive the absolute sea level from Radar Altimeter Database System (RADS). Data verification is then carried out to verify the satellite derived sea level rise data with tidal data. Eight selected tide gauge stations from Peninsular Malaysia, Sabah and Sarawak are chosen for this data verification. The pattern and correlation of both measurements of sea level anomalies (SLA) are evaluated over the same period in each area in order to produce comparable results. Afterwards, the time series of the sea level trend is quantified using robust fit regression analysis. The findings clearly show that the absolute sea level trend is rising and varying over the Malaysian seas with the rate of sea level varies and gradually increase from east to west of Malaysia. Highly confident and correlation level of the 23 years measurement data with an astonishing root mean square difference permits the absolute sea level trend of the Malaysian seas has raised at the rate 3.14 ± 0.12 mm yr-1 to 4.81 ± 0.15 mm yr-1 for the chosen sub-areas, with an overall mean of 4.09 ± 0.12 mm yr-1. This study hopefully offers a beneficial sea level information to be applied in a wide range of related environmental and climatology issue such as flood and global warming.

  6. Geoscience Laser Altimeter System (GLAS) on the ICESat Mission: Initial Science Measurement Performance

    Science.gov (United States)

    Abshire, James B.; Sun, Xiaoli; Riris, Haris; Sirota, Marcos; McGarry, J.; Palm, Steve

    2003-01-01

    The Geoscience Laser Altimeter System is the space lidar on the NASA ICESat mission. Its design combines an altimeter with 5 cm precision with a laser pointing angle determination system and a dual wavelength cloud and aerosol lidar. GLAS measures the range to the Earth s surface with 1064 nm laser pulses. Each laser pulse produces a precision pointing measurement from the stellar reference system (SRS) and an echo pulse waveform, which permits range determination and waveform spreading analysis. The single shot ranging accuracy is altimeter, inverse lidar and a stellar source simulator. It was used to simulate the range of expected optical inputs to the GLAS receiver by illuminating its telescope with simulated background light as well as laser echoes with known powers, energy levels, widths and delay times. The BCE also allowed monitoring of the transmitted laser energy, the angle measurements of the SRS, the co-alignment of the transmitted laser beam to the receiver line of sight, and performance of the flight science algorithms. Performance was evaluated during the GLAS development, before and after environmental tests, and after delivery to the spacecraft. The ICESat observatory was launched into a 94 degree inclination, 590 km altitude circular polar orbit on January 12,2003. Beginning in early February, GLAS was powered on tested in stages. Its 1064 nm optical receiver was evaluated in a several tests using both solar background light and an internal test source. Laser 1 was activated on February 20,2003. GLAS operated with Laser 1 for 38 continuous days on orbit using its 1064 nm receiver channel, producing over 130 million individual laser measurements of the Earth s surface and atmosphere. These nadir-pointed measurements fell along the ICESat s ground track, and spanned more than 4 cycles of the initial 8-day ICESat repeat orbit. The initial GLAS measurement set shows strong echo pulses from ranging to the surface topography, oceans, ice sheets and cloud

  7. ACCELERATION OF SEA LEVEL RISE OVER MALAYSIAN SEAS FROM SATELLITE ALTIMETER

    Directory of Open Access Journals (Sweden)

    A. I. A. Hamid

    2016-09-01

    Full Text Available Sea level rise becomes our concern nowadays as a result of variously contribution of climate change that cause by the anthropogenic effects. Global sea levels have been rising through the past century and are projected to rise at an accelerated rate throughout the 21st century. Due to this change, sea level is now constantly rising and eventually will threaten many low-lying and unprotected coastal areas in many ways. This paper is proposing a significant effort to quantify the sea level trend over Malaysian seas based on the combination of multi-mission satellite altimeters over a period of 23 years. Eight altimeter missions are used to derive the absolute sea level from Radar Altimeter Database System (RADS. Data verification is then carried out to verify the satellite derived sea level rise data with tidal data. Eight selected tide gauge stations from Peninsular Malaysia, Sabah and Sarawak are chosen for this data verification. The pattern and correlation of both measurements of sea level anomalies (SLA are evaluated over the same period in each area in order to produce comparable results. Afterwards, the time series of the sea level trend is quantified using robust fit regression analysis. The findings clearly show that the absolute sea level trend is rising and varying over the Malaysian seas with the rate of sea level varies and gradually increase from east to west of Malaysia. Highly confident and correlation level of the 23 years measurement data with an astonishing root mean square difference permits the absolute sea level trend of the Malaysian seas has raised at the rate 3.14 ± 0.12 mm yr-1 to 4.81 ± 0.15 mm yr-1 for the chosen sub-areas, with an overall mean of 4.09 ± 0.12 mm yr-1. This study hopefully offers a beneficial sea level information to be applied in a wide range of related environmental and climatology issue such as flood and global warming.

  8. Regional CalVal of Altimeter Range at Non-Dedicated Sites in Preparation f Sentinel-3

    Science.gov (United States)

    Cancet, M.; Watson, C.; Haines, B.; Bonnefond, P.; Lyard, F.; Femenias, P.; Guinle, T.

    2015-12-01

    In situ calibration ensures regular and long-term control of the altimeter sea surface height (SSH) time series through comparisons with independent records. Usually, in situ calibration and validation of altimeter SSH is undertaken at specific CALVAL sites through the direct comparison of the altimeter data with in situ data [1]. However, NOVELTIS has developed a regional CALVAL technique, which aims at increasing the number and the repeatability of the altimeter bias assessments by determining the altimeter bias both on overflying passes and on satellite passes located far away from the calibration site. In principle this extends the single site approach to a wider regional scale, thus reinforcing the link between the local and the global CALVAL analyses. It also provides a means to maintain a calibration time series through periods of data-outage at a specific dedicated calibration site. The regional method was initially developed at the Corsican calibration sites of Senetosa and Ajaccio. The method was used to compute the biases of Jason-1, Jason-2 and Envisat (before and after the orbit change in 2010) at both sites, and proved its stability and generality through this cross-calibration exercise [2]. These last years, the regional method was successfully implemented at the Californian site of Harvest and at the Australian site of Bass Strait, in close collaboration with JPL and the University of Tasmania, respectively. These recent studies gave the first Envisat absolute bias estimates at non-dedicated sites using the same method, and showed high consistency with the analyses of the global CALVAL teams and the work of the in situ CALVAL teams. These results highlight the numerous advantages of this technique for monitoring missions on any orbits such as the future Sentinel-3 and Jason-CS/Sentinel-6 missions.

  9. Monthly Maps of Sea Surface Height in the North Atlantic and Zonal Indices for the Gulf Stream Using TOPEX/Poseidon Altimeter Data

    Science.gov (United States)

    Singh, Sandipa; Kelly, Kathryn A.

    1997-01-01

    Monthly Maps of sea surface height are constructed for the North Atlantic Ocean using TOPEX/Poseidon altimeter data. Mean sea surface height is reconstructed using a weighted combination of historical, hydrographic data and a synthetic mean obtained by fitting a Gaussian model of the Gulf Stream jet to altimeter data. The resultant mean shows increased resolution over the hydrographic mean, and incorporates recirculation information that is absent in the synthetic mean. Monthly maps, obtained by adding the mean field to altimeter sea surface height residuals, are used to derive a set of zonal indices that describe the annual cycle of meandering as well as position and strength of the Gulf Stream.

  10. The validation of the significant wave height product of HY-2 altimeter-primary results

    Institute of Scientific and Technical Information of China (English)

    CHEN Chuntao; ZHU Jianhua; LIN Mingsen; ZHAO Yili; HUANG Xiaoqi; WANG He; ZHANG Youguang; PENG Hailong

    2013-01-01

    The HY-2 satellite was successfully launched on 16 August 2011. The HY-2 significant wave height (SWH) is validated by the data from the South China Sea (SCS) field experiment, National Data Buoy Center (NDBC) buoys and Jason-1/2 altimeters, and is corrected using a linear regression with in-situ measurements. Com-pared with NDBC SWH, the HY-2 SWH show a RMS of 0.36 m, which is similar to Jason-1 and Jason-2 SWH with the RMS of 0.35 m and 0.37 m respectively;the RMS of corrected HY-2 SWH is 0.27 m, similar to 0.27 m and 0.23 m of corrected Jason-1 and Jason-2 SWH. Therefore the accuracy of HY-2 SWH products is close to that of Jason-1/2 SWH, and the linear regression function derived can improve the accuracy of HY-2 SWH products.

  11. Determination of the Path Loss from Passenger Electronic Devices to Radio Altimeter with Additional EMI Test

    Science.gov (United States)

    Schüür, J.; Nunes, R. R.

    2012-05-01

    Emitters of current and future wireless ultra wideband technology (UWB) inside the cabin should not interfere with any aircraft system. Especially the radio altimeter (RA) system using antennas mounted outside the fuselage is potentially sensitive to UWB devices in the frequency range between 4.1 and 4.8 GHz. The measurement of the interference path loss (IPL) to the RA is therefore of interest and is presented for different aircraft. The need of a high dynamic setup with low parasitic coupling in the IPL measurement is stressed. In addition, electromagnetic interference (EMI) tests with different transmitted signals are made, showing that the susceptibility of the RA system actually increases with UWB modulation.

  12. Mercury's rotational state from combined MESSENGER laser altimeter and image data

    Science.gov (United States)

    Stark, Alexander; Oberst, Jürgen; Preusker, Frank; Margot, Jean-Luc; Phillips, Roger J.; Neumann, Gregory A.; Smith, David E.; Zuber, Maria T.; Solomon, Sean C.

    2016-04-01

    With orbital data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, we measured the rotational state of Mercury. We developed a novel approach that combined digital terrain models from stereo images (stereo DTMs) and laser altimeter data, and we applied it to 3 years of MESSENGER observations. We find a large libration amplitude, which in combination with the measured obliquity confirms that Mercury possesses a liquid outer core. Our results confirm previous Earth-based observations of Mercury's rotational state. However, we measured a rotation rate that deviates significantly from the mean resonant rotation rate. The larger rotation rate can be interpreted as the signature of a long-period libration cycle. From these findings we derived new constraints on the interior structure of Mercury. The measured rotational parameters define Mercury's body-fixed frame and are critical for the coordinate system of the planet as well as for planning the future BepiColombo spacecraft mission.

  13. Variations in transport derived from satellite altimeter data over the Gulf Stream

    Science.gov (United States)

    Molinelli, E.; Lambert, R. B.

    1981-01-01

    Variations in total change of sea surface height (delta h) across the Gulf Stream are observed using Seasat radar altimeter data. The sea surface height is related to transport within the stream by a two layer model. Variations in delta h are compared with previously observed changes in transport found to increase with distance downstream. No such increase is apparent since the satellite transports show no significant dependence on distance. Though most discrepancies are less than 50 percent, a few cases differ by about 100 percent and more. Several possible reasons for these discrepancies are advanced, including geoid error, but only two oceanographic contributions to the variability are examined, namely, limitations in the two layer model and meanders in the current. It is concluded that some of the discrepancies could be explained as changes in the density structure not accounted for by the two layer model.

  14. Large-scale Gulf Stream frontal study using GEOS 3 radar altimeter data

    Science.gov (United States)

    Huang, N. E.; Leitao, C. D.; Parra, C. G.

    1978-01-01

    From data obtained by the GEOS 3 radar altimeter, sea surface heights are found by both editing and filtering the raw sea surface height measurements and then referencing these processed data to a 5 foot by 5 foot geoid. Any trend between the processed data and the geoid is removed by subtracting out a linear fit to the residuals in the open ocean. Data from individual passes are further processed by applying a minimum variance technique at the subsatellite crossing points to produce surface topography maps for the 6 months and an overall mean map which reveal important details about the Gulf Stream system. The differences between the monthly mean and the overall mean are calculated for each of the 6 months to show the temporal and spatial changes of the Gulf Stream front and spawned eddies. The standard deviation map is even more informative and shows preferred locations of Gulf Stream meanders.

  15. Seasat altimeter observations of dynamic topography in the Gulf Stream region

    Science.gov (United States)

    Cheney, R. E.; Marsh, J. G.

    1981-01-01

    A straightforward approach to altimeter data analysis in the Gulf Stream system is presented, using a detailed geoid model to remove the gravitational component. The resulting sea surface height profiles compare remarkably well with independent oceanographic observations. Specific features such as cold rings, warm rings, and no anomaly regions are analyzed and it is shown that known positions of cyclonic and anticyclonic rings correspond with depressions and elevations, respectively, with amplitudes as large as 95 cm. The apparent fluctuation of the Gulf Stream is indicated by the results, as in the finding that on time scales of a few days, surface transport indicated by the sea surface height difference across the stream varied by nearly 30%

  16. A Mars' Year of Topographic Mapping With The Mars Orbiter Laser Altimeter

    Science.gov (United States)

    Smith, David E.; Zuber, Maria T.

    2001-01-01

    Since the end of February 1999 the Mars Orbiter Laser Altimeter (MOLA) has been mapping the planet continuously except for a 2 month period around solar conjunction in June 2000. At the end of January 2001 the Mars Global Surveyor Spacecraft (MGS) had completed its prime Mission, one Mars year of observing the planet, and begun the Extended Mission of slightly more than 14 months. MOLA will had acquired over 530 million altimetric measurements by early 2001, and continued to work perfectly. During the Extended Mission the main objective for MOLA will be observations of the seasonal variations in the locations and altitudes of clouds, the changes in the elevations of the polar icecaps due to the deposition and sublimation Of CO2, as well as supporting NASA's search for suitable future landing sites.

  17. Brightening and Volatile Distribution Within Shackleton Crater Observed by the LRO Laser Altimeter.

    Science.gov (United States)

    Smith, D. E.; Zuber, M. T.; Head, J. W.; Neumann, G. A.; Mazarico, E.; Torrence, M. H.; Aharonson, O.; Tye, A. R.; Fassett, C. I.; Rosengurg, M. A.; Melosh, H. J.

    2012-01-01

    Shackleton crater, whose interior lies largely in permanent shadow, is of interest due to its potential to sequester volatiles. Observations from the Lunar Orbiter Laser Altimeter onboard the Lunar Reconnaissance Orbiter have enabled an unprecedented topographic characterization, revealing Shackleton to be an ancient, unusually well-preserved simple crater whose interior walls are fresher than its floor and rim. Shackleton floor deposits are nearly the same age as the rim, suggesting little floor deposition since crater formation over 3 billion years ago. At 1064 nm the floor of Shackleton is brighter than the surrounding terrain and the interiors of nearby craters, but not as bright as the interior walls. The combined observations are explainable primarily by downslope movement of regolith on the walls exposing fresher underlying material. The relatively brighter crater floor is most simply explained by decreased space weathering due to shadowing, but a 1-mm-thick layer containing approx 20% surficial ice is an alternative possibility.

  18. Two-color short-pulse laser altimeter measurements of ocean surface backscatter.

    Science.gov (United States)

    Abshire, J B; McGarry, J F

    1987-04-01

    The timing and correlation properties of pulsed laser backscatter from the ocean surface have been measured with a two-color short-pulse laser altimeter. The Nd: YAG laser transmitted 70-and 35-ps wide pulses simultaneously at 532 and 355 nm at nadir, and the time-resolved returns were recorded by a receiver with 800-ps response time. The time-resolved backscatter measured at both 330- and 1291-m altitudes showed little pulse broadening due to the submeter laser spot size. The differential delay of the 355- and 532-nm backscattered waveforms were measured with a rms error of ~75 ps. The change in aircraft altitudes also permitted the change in atmospheric pressure to be estimated by using the two-color technique. PMID:20454319

  19. High accuracy alignment facility for the receiver and transmitter of the BepiColombo Laser Altimeter.

    Science.gov (United States)

    Chakraborty, Sumita; Affolter, Michael; Gunderson, Kurt; Neubert, Jakob; Thomas, Nicolas; Beck, Thomas; Gerber, Michael; Graf, Stefan; Piazza, Daniele; Pommerol, Antoine; Roethlisberger, Guillaume; Seiferlin, Karsten

    2012-07-10

    The accurate co-alignment of the transmitter to the receiver of the BepiColombo Laser Altimeter is a challenging task for which an original alignment concept had to be developed. We present here the design, construction and testing of a large collimator facility built to fulfill the tight alignment requirements. We describe in detail the solution found to attenuate the high energy of the instrument laser transmitter by an original beam splitting pentaprism group. We list the different steps of the calibration of the alignment facility and estimate the errors made at each of these steps. We finally prove that the current facility is ready for the alignment of the flight instrument. Its angular accuracy is 23 μrad. PMID:22781273

  20. Space-qualified laser system for the BepiColombo Laser Altimeter.

    Science.gov (United States)

    Kallenbach, Reinald; Murphy, Eamonn; Gramkow, Bodo; Rech, Markus; Weidlich, Kai; Leikert, Thomas; Henkelmann, Reiner; Trefzger, Boris; Metz, Bodo; Michaelis, Harald; Lingenauber, Kay; DelTogno, Simone; Behnke, Thomas; Thomas, Nicolas; Piazza, Daniele; Seiferlin, Karsten

    2013-12-20

    The space-qualified design of a miniaturized laser for pulsed operation at a wavelength of 1064 nm and at repetition rates up to 10 Hz is presented. This laser consists of a pair of diode-laser pumped, actively q-switched Nd:YAG rod oscillators hermetically sealed and encapsulated in an environment of dry synthetic air. The system delivers at least 300 million laser pulses with 50 mJ energy and 5 ns pulse width (FWHM). It will be launched in 2017 aboard European Space Agency's Mercury Planetary Orbiter as part of the BepiColombo Laser Altimeter, which, after a 6-years cruise, will start recording topographic data from orbital altitudes between 400 and 1500 km above Mercury's surface. PMID:24513938

  1. Topography of the northern hemisphere of Mars from the Mars Orbiter Laser Altimeter.

    Science.gov (United States)

    Smith, D E; Zuber, M T; Frey, H V; Garvin, J B; Head, J W; Muhleman, D O; Pettengill, G H; Phillips, R J; Solomon, S C; Zwally, H J; Banerdt, W B; Duxbury, T C

    1998-03-13

    The first 18 tracks of laser altimeter data across the northern hemisphere of Mars from the Mars Global Surveyor spacecraft show that the planet at latitudes north of 50 degrees is exceptionally flat; slopes and surface roughness increase toward the equator. The polar layered terrain appears to be a thick ice-rich formation with a non-equilibrium planform indicative of ablation near the periphery. Slope relations suggest that the northern Tharsis province was uplifted in the past. A profile across Ares Vallis channel suggests that the discharge through the channel was much greater than previously estimated. The martian atmosphere shows significant 1-micrometer atmospheric opacities, particularly in low-lying areas such as Valles Marineris. PMID:9497281

  2. Geoscience Laser Altimeter System (GLAS) on the ICESat Mission: Science Measurement Performance since Launch

    Science.gov (United States)

    Sun, Xiao-Li; Abshire, James B.; Riris, Haris; McGarry, Jan; Sirota, Marcos

    2004-01-01

    The Geoscience Laser Altimeter System is the primary space lidar on NASA's ICESat mission. Since launch in January 2003 GLAS has produced about 544 million measurements of the Earth's surface and atmosphere. It has made global measurements of the Earth's icesheets, land topography and atmosphere with unprecedented vertical resolution and accuracy. GLAS was first activated for science measurements in February 2003. Since then its operation and performance has confirmed many pre-launch expectations and exceed a few of the most optimistic expectations in vertical resolution. However GLAS also suffered an unexpected failure of its first laser, and the GLAS measurements have yielded some surprises in other areas. The talk will give a post launch assessment of the science measurement performance of the GLAS instrument, and compare the science measurements and engineering operation to pre-launch expectations. It also will address some of what has been learned from the GLAS operations and data, which may benefit future space lidar.

  3. A next generation altimeter for mapping the sea surface height variability: opportunities and challenges

    Science.gov (United States)

    Fu, Lee-Lueng; Morrow, Rosemary

    2016-07-01

    The global observations of the sea surface height (SSH) have revolutionized oceanography since the beginning of precision radar altimetry in the early 1990s. For the first time we have continuous records of SSH with spatial and temporal sampling for detecting the global mean sea level rise, the waxing and waning of El Niño, and the ocean circulation from gyres to ocean eddies. The limit of spatial resolution of the present constellation of radar altimeters in mapping SSH variability is approaching 100 km (in wavelength) with 3 or more simultaneous altimetric satellites in orbit. At scales shorter than 100 km, the circulation contains substantial amount of kinetic energy in currents, eddies and fronts that are responsible for the stirring and mixing of the ocean, especially from the vertical exchange of the upper ocean with the deep. A mission currently in development will use the technique of radar interferometry for making high-resolution measurement of the height of water over the ocean as well as on land. It is called Surface Water and Ocean Topography (SWOT), which is a joint mission of US NASA and French CNES, with contributions from Canada and UK. SWOT promises the detection of SSH at scales approaching 15 km, depending on the sea state. SWOT will make SSH measurement over a swath of 120 km with a nadir gap of 20 km in a 21-day repeat orbit. A conventional radar altimeter will provide measurement along the nadir. This is an exploratory mission with applications in oceanography and hydrology. The increased spatial resolution offers an opportunity to study ocean surface processes to address important questions about the ocean circulation. However, the limited temporal sampling poses challenges to map the evolution of the ocean variability that changes rapidly at the small scales. The measurement technique and the development of the mission will be presented with emphasis on its science program with outlook on the opportunities and challenges.

  4. ALR - Laser altimeter for the ASTER deep space mission. Simulated operation above a surface with crater

    Science.gov (United States)

    de Brum, A. G. V.; da Cruz, F. C.; Hetem, A., Jr.

    2015-10-01

    To assist in the investigation of the triple asteroid system 2001-SN263, the deep space mission ASTER will carry onboard a laser altimeter. The instrument was named ALR and its development is now in progress. In order to help in the instrument design, with a view to the creation of software to control the instrument, a package of computer programs was produced to simulate the operation of a pulsed laser altimeter with operating principle based on the measurement of the time of flight of the travelling pulse. This software Simulator was called ALR_Sim, and the results obtained with its use represent what should be expected as return signal when laser pulses are fired toward a target, reflect on it and return to be detected by the instrument. The program was successfully tested with regard to some of the most common situations expected. It constitutes now the main workbench dedicated to the creation and testing of control software to embark in the ALR. In addition, the Simulator constitutes also an important tool to assist the creation of software to be used on Earth, in the processing and analysis of the data received from the instrument. This work presents the results obtained in the special case which involves the modeling of a surface with crater, along with the simulation of the instrument operation above this type of terrain. This study points out that the comparison of the wave form obtained as return signal after reflection of the laser pulse on the surface of the crater with the expected return signal in the case of a flat and homogeneous surface is a useful method that can be applied for terrain details extraction.

  5. Investigating the Performance of the Jason-2/OSTM Radar Altimeter Over Lakes and Reservoirs

    Science.gov (United States)

    Borlett. C/ < /; Beckley, B.

    2010-01-01

    Many inland water investigations utilize archival and near-real time radar altimetry data to enable observation of the variation in surface water level. A multi-altimeter approach allows a more global outlook with improved spatial resolution, and combined long-term observations improve statistical analyses. Central to all programs is a performance assessment of each instrument. Here, we focus on data quantity and quality pertaining to the Poseidon-3 radar altimeter onboard the Jason-2/OSTM satellite.Utilizing an interim data set (IGDR), studies show that the new on-board DIODE/median and DIODE/DEM tracking modes are performing well, acquiring and maintaining the majority of lake and reservoir surfaces in varying terrains. The 20-Hz along-track resolution of the data, and particularly the availability of the range output from the ice-retracker algorithm, also improves the number of valid height measurements. Based on test-case lakes and reservoirs, output from the ice-retracker algorithm is also seen to have a clear advantage over the ocean-retracker having better height stability across calm and icy surfaces, a greater ability to gain coastline waters, and less sensitivity to loss of water surface when there is island contamination in the radar echo. Such on-board tracking and postprocessing retracking enables the lake waters to be quickly gained after coastline crossing. Values can range from lakes in the 100 C300 km2 size-category. Time series of height variations are also found to be accurate to 3 to 33 cm rms depending on target size and the presence of winter ice. These findings are an improvement over the IGDR/GDR results from the predecessor Jason-1 and TOPEX/Poseidon missions and can satisfy the accuracy requirements of both the science-related and operational lake study programs.

  6. Geosat altimeter derived sea surface wind speeds and significant wave heights for the north Indian Ocean and their comparison with in situ data

    Digital Repository Service at National Institute of Oceanography (India)

    Vethamony, P.; Vaithiyanathan, R.; Almeida, A.M.; Santanam, K.; Rao, L.V.G.; Sarkar, A.; Kumar, R.; Gairola, R.M.; Gohil, B.S.

    Geosat altimeter data for the period November 1986-October 1987 over the north Indian Ocean have been processed to retrieve wind speeds and significant wave heights. Smoothed Brown algorithm is used to retrieve wind speeds from back...

  7. The Reflectivity of Mars at 1064 nm: Derivation from Mars Orbiter Laser Altimeter Data and Application to Climatology and Meteorology

    OpenAIRE

    Heavens, Nicholas G.

    2016-01-01

    The Mars Orbiter Laser Altimeter (MOLA) on board Mars Global Surveyor (MGS) made $\\gg 10^{8}$ measurements of the reflectivity of Mars at 1064 nm ($R_{1064}$) by both active sounding and passive radiometry. Past studies of $R_{1064}$ neglected the effects of atmospheric opacity and viewing geometry on both active and passive measurements and also identified a potential calibration issue with passive radiometry. Therefore, as yet, there exists no acceptable reference $R_{1064}$ to derive a col...

  8. A sample design for globally consistent biomass estimation using lidar data from the Geoscience Laser Altimeter System (GLAS)

    OpenAIRE

    Healey Sean P; Patterson Paul L; Saatchi Sassan; Lefsky Michael A; Lister Andrew J; Freeman Elizabeth A

    2012-01-01

    Abstract Background Lidar height data collected by the Geosciences Laser Altimeter System (GLAS) from 2002 to 2008 has the potential to form the basis of a globally consistent sample-based inventory of forest biomass. GLAS lidar return data were collected globally in spatially discrete full waveform “shots,” which have been shown to be strongly correlated with aboveground forest biomass. Relationships observed at spatially coincident field plots may be used to model biomass at all GLAS shots,...

  9. Retrievals of thick cloud optical depth from the Geoscience Laser Altimeter System (GLAS) by calibration of solar background signal

    OpenAIRE

    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 spaceborne laser instruments, can only penetrate clouds to a limit of a few optical depths. As a result, only optical depths of thinner clouds (< about 3 for GLAS) are retrieved from the reflected lidar signal. This paper presents a comprehensive study of possible retrievals of optical depth of thick clouds using solar background light and treating GLAS as a solar radiometer. To do so one must first calibr...

  10. Spectral combination of land-based, airborne, shipborne and altimeter-derived gravity values: examples in Taiwan and Tahiti

    Science.gov (United States)

    Hwang, Cheinway

    2016-04-01

    Taiwan and Tahiti are bordered by seas and are islands with mountain ranges up to 4000 m height. The gravity fields here are rough due to the geodynamic processes that create the islands. On and around the two islands, gravity data have been collected by land gravimeters in relative gravity networks (point-wise), by airborne and shipborne (along-track) methods and by transformations from sea surface heights (altimeter-derived). Typically, network-adjusted land gravity values have accuracies of few tens of micro gals and contain the full gravity spectrum. Airborne gravity values are obtained by filtering original one-HZ along-track gravity values collected at varying flight altitudes that are affected by aircraft dynamics, GPS positioning error and gravimeter error. At a 5000-m flight height, along-track airborne gravity has a typical spatial resolution of 4 km and an accuracy of few mgal. Shipborne gravity is similar to airborne gravity, but with higher spatial resolutions because of ship's lower speed. Altimeter-derived gravity has varying spatial resolutions and accuracies, depending on altimeter data, processing method and extent of waveform interference. Using the latest versions of Geosat/GM, ERS-1/GM, ENVISAT, Jason-1/GM, Cryosat-2 and SARAL altimeter data, one can achieve accuracies at few mgal. The synergy of the four kinds of gravity datasets is made by the band-limited least-squares collocation, which best integrates datasets of different accuracies and spatial resolutions. The method uses the best contributions from a DEM, a global gravity model, available gravity datasets to form an optimal gravity grid. We experiment with different optimal spherical harmonic degrees of EGM08 for use around the two islands. For Tahiti, the optimal degree is 1500. New high-resolution gravity and geoid grids are constructed for the two islands and can be used in future geophysical and geodetic studies.

  11. Study of the Penetration Bias of ENVISAT Altimeter Observations over Antarctica in Comparison to ICESat Observations

    Directory of Open Access Journals (Sweden)

    Aurélie Michel

    2014-09-01

    Full Text Available The aim of this article is to characterize the penetration bias of the ENVIronmental SATellite (ENVISAT radar altimeter over the Antarctic ice sheet through comparison with the more accurate measurements of the Ice, Cloud and land Elevation Satellite (ICESat altimeter at crossover points. We studied the difference between ENVISAT and ICESat fluctuations over six years. We observed the same patterns between the leading edge width and the elevation difference. Both parameters are linked, and the major bias is due to the lengthening of the leading edge width due to the radar penetration. We show that the elevation difference between both altimeters and the leading edge width are linearly well-linked with a 0.8 Pearson correlation coefficient, whereas the slope effect over the coasts is difficult to analyze. When we analyze each crossover point temporal evolution locally, the linear correlation between the leading edge width and the elevation difference is between −0.6 and −1. Fitting a linear model between them, we find a reliability index greater than 0.7 for the Antarctic Plateau and Dronning Maud Land, which confirms that the penetration effect has a linear influence on the retrieved height. Moreover, we present results from SARAL/AltiKa (launched in February 2013 that confirm SARAL/AltiKa accuracy and the promising information it will provide.

  12. DUACS DT2014: the new multi-mission altimeter data set reprocessed over 20 years

    Science.gov (United States)

    Pujol, Marie-Isabelle; Faugère, Yannice; Taburet, Guillaume; Dupuy, Stéphanie; Pelloquin, Camille; Ablain, Michael; Picot, Nicolas

    2016-09-01

    The new DUACS DT2014 reprocessed products have been available since April 2014. Numerous innovative changes have been introduced at each step of an extensively revised data processing protocol. The use of a new 20-year altimeter reference period in place of the previous 7-year reference significantly changes the sea level anomaly (SLA) patterns and thus has a strong user impact. The use of up-to-date altimeter standards and geophysical corrections, reduced smoothing of the along-track data, and refined mapping parameters, including spatial and temporal correlation-scale refinement and measurement errors, all contribute to an improved high-quality DT2014 SLA data set. Although all of the DUACS products have been upgraded, this paper focuses on the enhancements to the gridded SLA products over the global ocean. As part of this exercise, 21 years of data have been homogenized, allowing us to retrieve accurate large-scale climate signals such as global and regional MSL trends, interannual signals, and better refined mesoscale features.An extensive assessment exercise has been carried out on this data set, which allows us to establish a consolidated error budget. The errors at mesoscale are about 1.4 cm2 in low-variability areas, increase to an average of 8.9 cm2 in coastal regions, and reach nearly 32.5 cm2 in high mesoscale activity areas. The DT2014 products, compared to the previous DT2010 version, retain signals for wavelengths lower than ˜ 250 km, inducing SLA variance and mean EKE increases of, respectively, +5.1 and +15 %. Comparisons with independent measurements highlight the improved mesoscale representation within this new data set. The error reduction at the mesoscale reaches nearly 10 % of the error observed with DT2010. DT2014 also presents an improved coastal signal with a nearly 2 to 4 % mean error reduction. High-latitude areas are also more accurately represented in DT2014, with an improved consistency between spatial coverage and sea ice edge

  13. Tropopause-level thin cirrus coverage revealed by ICESat/Geoscience Laser Altimeter System

    Science.gov (United States)

    Dessler, A. E.; Palm, S. P.; Hart, W. D.; Spinhirne, J. D.

    2006-04-01

    We analyze the distribution of thin (optical depth < 0.40) cirrus in the tropics at potential temperatures of 360, 370, 377.5, and 400 K, which are levels that bracket the tropical tropopause. The observations were obtained between 29 September and 17 November 2003 by the Geoscience Laser Altimeter System (GLAS), carried on board the Ice, Cloud, and land Elevation Satellite (ICESat). The GLAS data show that these thin, near-tropopause cirrus (TNTC) occur over broad regions of the latitude range 20°S to 30°N, with distinct maxima collocated with regions of intense convection, and that TNTC occurrence frequency decreases strongly with increasing altitude. At 377.5 K, approximately the level of the tropical tropopause, TNTC frequency over convection is two to six times larger than in the so-called "cold pool," the climatological temperature minimum located over the equatorial western Pacific where it has been suggested that dehydration of air entering the stratosphere is occurring. Comparisons between assimilated temperatures, outgoing longwave radiation (a proxy for deep convection), and TNTC frequency show that TNTC can be found where assimilated temperatures are low and deep convection is occurring. We find that assimilated temperatures, by themselves, are incomplete predictors of TNTC locations.

  14. A new lunar digital elevation model from the Lunar Orbiter Laser Altimeter and SELENE Terrain Camera

    Science.gov (United States)

    Barker, M. K.; Mazarico, E.; Neumann, G. A.; Zuber, M. T.; Haruyama, J.; Smith, D. E.

    2016-07-01

    We present an improved lunar digital elevation model (DEM) covering latitudes within ±60°, at a horizontal resolution of 512 pixels per degree (∼60 m at the equator) and a typical vertical accuracy ∼3 to 4 m. This DEM is constructed from ∼ 4.5 ×109 geodetically-accurate topographic heights from the Lunar Orbiter Laser Altimeter (LOLA) onboard the Lunar Reconnaissance Orbiter, to which we co-registered 43,200 stereo-derived DEMs (each 1° × 1°) from the SELENE Terrain Camera (TC) (∼1010 pixels total). After co-registration, approximately 90% of the TC DEMs show root-mean-square vertical residuals with the LOLA data of <5 m compared to ∼ 50% prior to co-registration. We use the co-registered TC data to estimate and correct orbital and pointing geolocation errors from the LOLA altimetric profiles (typically amounting to <10 m horizontally and <1 m vertically). By combining both co-registered datasets, we obtain a near-global DEM with high geodetic accuracy, and without the need for surface interpolation. We evaluate the resulting LOLA + TC merged DEM (designated as "SLDEM2015") with particular attention to quantifying seams and crossover errors.

  15. Space Borne Cloud and Aerosol Measurements by the Geoscience Laser Altimeter System: Initial Results

    Science.gov (United States)

    Spinhirne, James D.; Palm, Steven P.; Hlavka, Dennis L.; Hart, William D.; Mahesh, Ashwin; Welton, Ellsworth J.

    2003-01-01

    In January 2003 the Geoscience Laser Altimeter System (GLAS) was successfully launched into orbit. Beginning in March 2003 GLAS will provide global coverage lidar measurement of the height distribution of clouds and aerosol in the atmosphere for up to five years. The characteristic and value of the unique data will be presented. The instrument is a basic backscatter lidar that operates at two wavelengths, 532 and 1064 nm. The mission data products for atmospheric observations include the calibrated, observed, attenuated backscatter cross section for cloud and aerosol; height detection for multiple cloud layers; planetary boundary layer height; cirrus and aerosol optical depth and the height distribution of aerosol and cloud scattering cross section profiles. The data is expected to significantly enhance knowledge in several areas of atmospheric science, in particular the distribution, transport and influence of atmospheric aerosol and thin clouds. Measurements of the coverage and height of polar and cirrus cloud should be significantly more accurate than previous global observations. In March and April 2003, airborne and ground based data verification experiments will be carried out. Initial results from the verification experiments and the first several months of operation will be presented.

  16. Cloud Algorithm Design and Performance for the 2002 Geoscience Laser Altimeter System Mission

    Science.gov (United States)

    Spinhirne, J. D.; Palm, S. P.; Hart, W. D.; Hlavka, D. L.; Mahesh, A.; Starr, David (Technical Monitor)

    2002-01-01

    A satellite borne lidar instrument, the Geoscience Laser Altimeter System (GLAS), is to be launched in late 2002 and will provide continuous profiling of atmospheric clouds and aerosol on a global basis. Data processing algorithms have been developed to provide operational data products in near real time. Basic data products for cloud observations are the height of the top and bottom of single to multiple cloud layers and the lidar calibrated observed backscatter cross section up to the level of signal attenuation. In addition the optical depth and vertical profile of visible extinction cross section of many transmissive cloud layers and most haze layers are to be derived. The optical thickness is derivable in some cases from the attenuation of the molecular scattering below cloud base. In other cases an assumption of the scattering phase function is required. In both cases a estimated correction for multiple scattering is required. The data processing algorithms have been tested in part from aircraft measurements used to simulated satellite data. The GLAS lidar observations will be made from an orbit that will allow inter comparison with all other existing satellite cloud measurements.

  17. An Experiment to Detect Lunar Horizon Glow with the Lunar Orbit Laser Altimeter Laser Ranging Telescope

    Science.gov (United States)

    Smith, David E.; Zuber, Maria T.; Barker, Michael; Mazarico, Erwan; Neumann, Gregory A.; McClanahan, Timothy P.; Sun, Xiaoli

    2016-04-01

    Lunar horizon glow (LHG) was an observation by the Apollo astronauts of a brightening of the horizon around the time of sunrise. The effect has yet to be fully explained or confirmed by instruments on lunar orbiting spacecraft despite several attempts. The Lunar Reconnaissance Orbiter (LRO) spacecraft carries the laser altimeter (LOLA) instrument which has a 2.5 cm aperture telescope for Earth-based laser ranging (LR) mounted and bore-sighted with the high gain antenna (HGA). The LR telescope is connected to LOLA by a fiber-glass cable to one of its 5 detectors. For the LGH experiments the LR telescope is pointed toward the horizon shortly before lunar sunrise with the intent of observing any forward scattering of sunlight due to the presence of dust or particles in the field of view. Initially, the LR telescope is pointed at the dark lunar surface, which provides a measure of the dark count, and moves toward the lunar limb so as to measure the brightness of the sky just above the lunar limb immediately prior to lunar sunrise. At no time does the sun shine directly into the LR telescope, although the LR telescope is pointed as close to the sun as the 1.75-degree field of view permits. Experiments show that the LHG signal seen by the astronauts can be detected with a four-second integration of the noise counts.

  18. Observations of the north polar region of Mars from the Mars orbiter laser altimeter.

    Science.gov (United States)

    Zuber, M T; Smith, D E; Solomon, S C; Abshire, J B; Afzal, R S; Aharonson, O; Fishbaugh, K; Ford, P G; Frey, H V; Garvin, J B; Head, J W; Ivanov, A B; Johnson, C L; Muhleman, D O; Neumann, G A; Pettengill, G H; Phillips, R J; Sun, X; Zwally, H J; Banerdt, W B; Duxbury, T C

    1998-12-11

    Elevations from the Mars Orbiter Laser Altimeter (MOLA) have been used to construct a precise topographic map of the martian north polar region. The northern ice cap has a maximum elevation of 3 kilometers above its surroundings but lies within a 5-kilometer-deep hemispheric depression that is contiguous with the area into which most outflow channels emptied. Polar cap topography displays evidence of modification by ablation, flow, and wind and is consistent with a primarily H2O composition. Correlation of topography with images suggests that the cap was more spatially extensive in the past. The cap volume of 1.2 x 10(6) to 1.7 x 10(6) cubic kilometers is about half that of the Greenland ice cap. Clouds observed over the polar cap are likely composed of CO2 that condensed out of the atmosphere during northern hemisphere winter. Many clouds exhibit dynamical structure likely caused by the interaction of propagating wave fronts with surface topography. PMID:9851922

  19. Measuring tidal deformations by laser altimetry. A performance model for the Ganymede Laser Altimeter

    Science.gov (United States)

    Steinbrügge, G.; Stark, A.; Hussmann, H.; Sohl, F.; Oberst, J.

    2015-11-01

    Invaluable information about the interior of icy satellites orbiting close to the giant planets can be gained by monitoring the response of the satellite's surfaces to external tidal forces. Due to its geodetic accuracy, laser altimetry is the method of choice to measure time-dependent radial surface displacements from orbit. We present an instrument performance model with special focus on the capabilities to determine the corresponding tidal Love number h2 and apply the model to the Ganymede Laser Altimeter (GALA) on board of the Jupiter Icy Moons Explorer (JUICE). Based on the instrument and spacecraft performance, we derive the range error and the measurement capabilities of the GALA instrument to determine the amplitude of the tide induced radial displacement of Ganymede's surface using the cross-over technique. We find that h2 of Ganymede can be determined with an accuracy of better than 2% by using data acquired during the nominal mission. Furthermore, we show that this accuracy is sufficient to confirm the presence of a putative subsurface water ocean and, additionally, to constrain the thickness of the overlaying ice shell to ± 20km.

  20. Mercury's rotational parameters from MESSENGER image and laser altimeter data: A feasibility study

    Science.gov (United States)

    Stark, Alexander; Oberst, Jürgen; Preusker, Frank; Gwinner, Klaus; Peale, Stanton J.; Margot, Jean-Luc; Phillips, Roger J.; Zuber, Maria T.; Solomon, Sean C.

    2015-11-01

    A novel method has been developed to determine the rotational parameters of Mercury from data acquired by the MESSENGER spacecraft. We exploit the complementarity of laser altimeter tracks taken at different rotational phases and rigid stereo terrain models to determine a Mercury rotational model. In particular, we solve for the orientation of the spin axis, the rotation rate, and the amplitude of the forced libration. In this paper, we verify the proposed method and carry out an extensive simulation of MESSENGER data acquisition with assumed rotational parameters. To assess the uncertainty in the rotational parameters we use mission-typical assumptions for spacecraft attitude and position knowledge as well as for small-scale terrain morphology. We find that the orientation of the spin axis and the libration amplitude can be recovered with an accuracy of a few arc seconds from three years of MESSENGER orbital observations. The rotation rate can be determined to within 5 arc seconds per year. The method developed here serves as a framework for the ongoing analysis of data from the MESSENGER spacecraft. The rotational parameters of Mercury hold important constraints on the internal structure and evolution of the planet.

  1. System Accommodation of Propylene Loop Heat Pipes For The Geoscience Laser Altimeter System (GLAS) Instrument

    Science.gov (United States)

    Grob, Eric W.; Powers, Edward I. (Technical Monitor)

    2001-01-01

    Loop Heat Pipes (LHP) are used for precise temperature control for NASA Goddard Space Flight Center's Geoscience Laser Altimeter System (GLAS) Instrument in a widely varying LEO thermal environment. Two propylene LHPs are utilized to provide separate thermal control for the Nd:YAG Lasers and the remaining avionics/detector components suite. Despite a rigorous engineering development and test plan to demonstrate the performance in the restrictive GLAS design, the flight units failed initial thermal vacuum acceptance testing at GSFC. Subsequent investigation revealed that compromises in the mechanical packaging of these systems resulted in inadequate charge levels for a concentric wick LHP. The redesign effort included larger compensation chambers that provide more fluid to the wick for start-up scenarios and highlighted the need to fully understand the limitations and accommodation requirements of new technologies in a system design application. Once again, seemingly minor departures from heritage configurations and limited resources led to performance and operational issues. This paper provides details into the GLAS LHP engineering development program and acceptance testing of the flight units, including the redesign effort.

  2. Topographic roughness of the northern high latitudes of Mercury from MESSENGER Laser Altimeter data

    Science.gov (United States)

    Fa, Wenzhe; Cai, Yuzhen; Xiao, Zhiyong; Tian, Wei

    2016-04-01

    We investigated topographic roughness for the northern hemisphere (>45°N) of Mercury using high-resolution topography data acquired by the Mercury Laser Altimeter (MLA) on board the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. Our results show that there are distinct differences in the bidirectional slope and root-mean-square (RMS) height among smooth plains (SP), intercrater plains (ICP), and heavily cratered terrain (HCT), and that the ratios of the bidirectional slope and RMS height among the three geologic units are both about 1:2:2.4. Most of Mercury's surface exhibits fractal-like behavior on the basis of the linearity in the deviograms, with median Hurst exponents of 0.66, 0.80, and 0.81 for SP, ICP, and HCT, respectively. The median differential slope map shows that smooth plains are smooth at kilometer scale and become rough at hectometer scale, but they are always rougher than lunar maria at the scales studied. In contrast, intercrater plains and heavily cratered terrain are rough at kilometer scale and smooth at hectometer scale, and they are rougher than lunar highlands at scale ˜2 km. We suggest that these scale-dependent roughness characteristics are mainly caused by the difference in density and shape of impact craters between Mercury and the Moon.

  3. Initial Validation and Results of Geoscience Laser Altimeter System Optical Properties Retrievals

    Science.gov (United States)

    Hlavka, Dennis L.; Hart, W. D.; Pal, S. P.; McGill, M.; Spinhirne, J. D.

    2004-01-01

    Verification of Geoscience Laser Altimeter System (GLAS) optical retrievals is . problematic in that passage over ground sites is both instantaneous and sparse plus space-borne passive sensors such as MODIS are too frequently out of sync with the GLAS position. In October 2003, the GLAS Validation Experiment was executed from NASA Dryden Research Center, California to greatly increase validation possibilities. The high-altitude NASA ER-2 aircraft and onboard instrumentation of Cloud Physics Lidar (CPL), MODIS Airborne Simulator (MAS), and/or MODIS/ASTER Airborne Simulator (MASTER) under-flew seven orbit tracks of GLAS for cirrus, smoke, and urban pollution optical properties inter-comparisons. These highly calibrated suite of instruments are the best data set yet to validate GLAS atmospheric parameters. In this presentation, we will focus on the inter-comparison with GLAS and CPL and draw preliminary conclusions about the accuracies of the GLAS 532nm retrievals of optical depth, extinction, backscatter cross section, and calculated extinction-to-backscatter ratio. Comparisons to an AERONET/MPL ground-based site at Monterey, California will be attempted. Examples of GLAS operational optical data products will be shown.

  4. Global Lidar Measurements of Clouds and Aerosols from Space Using the Geoscience Laser Altimeter System (GLAS)

    Science.gov (United States)

    Hlavka, Dennis L.; Palm, S. P.; Welton, E. J.; Hart, W. D.; Spinhirne, J. D.; McGill, M.; Mahesh, A.; Starr, David OC. (Technical Monitor)

    2001-01-01

    The Geoscience Laser Altimeter System (GLAS) is scheduled for launch on the ICESat satellite as part of the NASA EOS mission in 2002. GLAS will be used to perform high resolution surface altimetry and will also provide a continuously operating atmospheric lidar to profile clouds, aerosols, and the planetary boundary layer with horizontal and vertical resolution of 175 and 76.8 m, respectively. GLAS is the first active satellite atmospheric profiler to provide global coverage. Data products include direct measurements of the heights of aerosol and cloud layers, and the optical depth of transmissive layers. In this poster we provide an overview of the GLAS atmospheric data products, present a simulated GLAS data set, and show results from the simulated data set using the GLAS data processing algorithm. Optical results from the ER-2 Cloud Physics Lidar (CPL), which uses many of the same processing algorithms as GLAS, show algorithm performance with real atmospheric conditions during the Southern African Regional Science Initiative (SAFARI 2000).

  5. Geoscience Laser Altimeter System (GLAS) Loop Heat Pipes: An Eventual First Year On-Orbit

    Science.gov (United States)

    Grob, E.; Baker, C.; McCarthy, T.

    2004-01-01

    Goddard Space Flight Center's Geoscience Laser Altimeter System (GLAS) is the sole scientific instrument on the Ice, Cloud and land Elevation Satellite (ICESat) that was launched on January 12, 2003 from Vandenberg AFB. A thermal control architecture based on propylene Loop Heat Pipe technology was developed to provide selectable/stable temperature control for the lasers and other electronics over the widely varying mission environment. Following a nominal LHP and instrument start-up, the mission was interrupted with the failure of the first laser after only 36 days of operation. During the 5-month failure investigation, the two GLAS LHPs and the electronics operated nominally, using heaters as a substitute for the laser heat load. Just prior to resuming the mission, following a seasonal spacecraft yaw maneuver, one of the LHPs deprimed and created a thermal runaway condition that resulted in an emergency shutdown of the GLAS instrument. This paper presents details of the LHP anomaly, the resulting investigation and recovery, along with on-orbit flight data during these critical events.

  6. On Orbit Receiver Performance Assessment of the Geoscience Laser Altimeter System (GLAS) on ICESAT

    Science.gov (United States)

    Sun, Xiaoli; Abshire, James B.; Spinhirne, James D.; McGarry, Jan; Jester, Peggy L.; Yi, Donghui; Palm, Stephen P.; Lancaster, Redgie S.

    2006-01-01

    The GLAS instrument on the NASA's ICESat mission has provided over a billion measurements of the Earth surface elevation and atmosphere backscattering at both 532 and 1064-nm wavelengths. The receiver performance has stayed nearly unchanged since ICESat launch in January 2003. The altimeter receiver has achieved a less than 3-cm ranging accuracy when excluding the effects of the laser beam pointing angle determination uncertainties. The receiver can also detect surface echoes through clouds of one-way transmission as low as 5%. The 532-nm atmosphere backscattering receiver can measure aerosol and clouds with cross section as low as 1e-7/m.sr with a 1 second integration time and molecular backscattering from upper atmosphere with a 60 second integration time. The 1064-nm atmosphere backscattering receiver can measure aerosol and clouds with a cross section as low as 4e-6/m.sr. This paper gives a detailed assessment of the GLAS receiver performance based on the in-orbit calibration tests.

  7. Measuring Directional Wave Spectra and Wind Speed with a Scanning Radar Altimeter

    Science.gov (United States)

    Walsh, E. J.; Vandemark, D.; Wright, C. W.; Swift, R. N.; Scott, J. F.; Hines, D. E.

    1999-01-01

    The geometry for the NASA Scanning Radar Altimeter (SRA) is shown. It transmits a 8-ns duration pulse at Ka-band (8.3 mm) and measures time of flight as it scans a 1 degree (two-way) beam from left to right across the aircraft ground track. The most recent configuration determines the surface elevation at 64 points spaced at uniform angular intervals of about 0.7 across a swath whose width is about 0.8 times the aircraft altitude. The system generates these raster lines of the surface topography beneath the aircraft at about a 10 Hz rate. In postflight processing the SRA wave topographic data are transformed with a two-dimensional Fast Fourier Transformation (FFT) and Doppler corrected to produce directional wave spectra. The SRA is not absolutely calibrated in power, but by measuring the relative fall-off of backscatter with increasing incidence angle, the SRA can also determine the mean square slope (mss) of the sea surface, a surrogate for wind speed. For the slope-dependent specular point model of radar sea surface scattering, an expression approximated by a geometric optics form, for the relative variation with incidence angle of the normalized backscatter radar cross section would be sigma (sup 0) (sub rel) = sec (exp 4) theta exp (-tan squared theta/mss) where theta is the off-nadir incidence angle.

  8. Altimeter-derived seasonal circulation on the southwest Atlantic shelf: 27°-43°S

    Science.gov (United States)

    Strub, P. Ted; James, Corinne; Combes, Vincent; Matano, Ricardo P.; Piola, Alberto R.; Palma, Elbio D.; Saraceno, Martin; Guerrero, Raul A.; Fenco, Harold; Ruiz-Etcheverry, Laura A.

    2015-05-01

    Altimeter sea surface height (SSH) fields are analyzed to define and discuss the seasonal circulation over the wide continental shelf in the SW Atlantic Ocean (27°-43°S) during 2001-2012. Seasonal variability is low south of the Rio de la Plata (RdlP), where winds and currents remain equatorward for most of the year. Winds and currents in the central and northern parts of our domain are also equatorward during autumn and winter but reverse to become poleward during spring and summer. Transports of shelf water to the deep ocean are strongest during summer offshore and to the southeast of the RdlP. Details of the flow are discussed using mean monthly seasonal cycles of winds, heights, and currents, along with analyses of Empirical Orthogonal Functions. Principle Estimator Patterns bring out the patterns of wind forcing and ocean response. The largest part of the seasonal variability in SSH signals is due to changes in the wind forcing (described above) and changes in the strong boundary currents that flow along the eastern boundary of the shelf. The rest of the variability contains a smaller component due to heating and expansion of the water column, concentrated in the southern part of the region next to the coast. Our results compare well to previous studies using in situ data and to results from realistic numerical models of the regional circulation.

  9. Studies of upper layer circulations of the South China Sea from Satellite altimeter observation

    International Nuclear Information System (INIS)

    Seventeen years Sea Surface Current (SSC) data from multi-satellite altimeters were used to investigate the upper layer circulation structure over the South China Sea (SCS) . And combined with QuikScat Sea Surface Wind (SSW) data, the relationship between upper layer circulation over SCS and SSW were analyzed. The results show that the largest current velocity and the greatest change of the circulation over the SCS are in the area east of the Indochina Peninsula; There are two main modes of the SCS upper layer circulation, the winter mode from October to next February and the summer mode from June to August. SCS circulations in other months are in the transitional period of the two main modes; Through the correlation analysis of the SSW and SSC, a significant positive correlation, about 0.5, between current and wind was found at the boundary area of the SCS. However, there was a significant negative correlation, about −0.5, near the middle of the SCS. The results also show that the variation of the upper layer circulation structure over the SCS is significant seasonal, and it was mostly dominated by the monsoon

  10. Stream-coordinate structure of oceanic jets based on merged altimeter data

    Institute of Scientific and Technical Information of China (English)

    SUN Che; ZHANG Linlin; YAN Xiaomei

    2011-01-01

    The jet structure of the Southern Ocean front south of Australia is studied in stream-coordinate with a new altimeter product--Absolute Dynamic Topography (ADT) from AVISO. The accuracy of the ADT data is validated with the mooring data from a two-year subantarctic-front experiment. It is demonstrated that the ADT is consistent with in-situ measurements and captures the meso-scale activity of the Antarctic Circumpolar Current (ACC). Stream-coordinate analysis of ADT surface geostrophic flows finds that ACC jets exhibit large spatio-temporal variability and do not correspond to particular streamfunction values. In the circumpolar scope ACC jets display a transient fragmented pattern controlled by topographic features. The poleward shift of jet in streamfunction space, as revealed by a streamwise correlation method, indicates the presence of meridional fluxes of zonal momentum. Such cross-stream eddy fluxes concentrate the broad ACC baroclinic flow into narrow jets. Combined with a recent discovery of gravest empirical mode (GEM) in the thermohaline fields, the study clarifies the interrelationship among front, jet and streamfunction in the Southern Ocean.

  11. Enhancements for the Geoscience Laser Altimeter System (GLAS) Data Products and Services

    Science.gov (United States)

    Fowler, D. K.; Haran, T. M.; McAllister, M.; Webster, D.

    2014-12-01

    The principle objective of the Ice, Cloud, and land Elevation Satellite (ICESat-1) mission was to measure ice sheet elevations and changes to elevation through time. Secondary objectives included measurement of cloud and aerosol height profiles, land elevation and vegetation cover, and sea ice thickness. The Geoscience Laser Altimeter System (GLAS), in operation from January 2003 through October 2009 was the sole instrument on ICESat-1. The data from this mission are archived and made available to the public at NASA's Distributed Active Archive Center located at the National Snow and Ice Data Center (NSIDC DAAC), University of Colorado in Boulder. Release 34 of ICESat-1 GLAS data completed in late 2014. These data were produced in the original binary format and also in HDF5. This release contains several important fixes to the altimetry data products which include a correction to the surface elevation, a dry tropospheric jitter correction, and adjustments to several confidence and characteristic flags. There are a variety of methods to obtain these data ranging from direct download from an online archive to using the Reverb Search and Order Tool which allows for spatial and temporal searches. Subsetting is also available for both the binary and HDF5 formats.

  12. Estimates of global M2 internal tide energy fluxes using TOPEX/POSEIDON altimeter data

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yanwei; LIANG Xinfeng; TIAN Jiwei; YANG Lifen

    2009-01-01

    TOPEX/POSEIDON altimeter data from October 1992 to June 2002 are used to calculate the global barotropic M2 tidal currents using long-term tidal harmonic analysis. The tides calculated agree well with ADCP data obtained from the South China Sea (SCS). The maximum tide velocities along the semi-major axis and semi-minor axis can be computed from the tidal ellipse. The global distribution of M2 internal tide vertical energy flux from the sea bottom is calculated based on a linear internal wave generation model. The global vertical energy flux of M2 internal tide is 0.96 TW, with 0.36 TW in the Pacific, 0.31 TW in the Atlantic and 0.29 TW in the Indian Ocean, obtained in this study. The total horizontal energy flux of M2 internal tide radiating into the open ocean from the lateral boundaries is 0.13 TW, with 0.06 TW in the Pacific, 0.04TW in the Atlantic, and 0.03 TW in the Indian Ocean. The result shows that the principal lunar semi-diurnal tide M2 provides enough energy to maintain the large-scale thermohaline circulation of the ocean.

  13. An Overview of the Topography of Mars from the Mars Orbiter Laser Altimeter (MOLA)

    Science.gov (United States)

    Smith, David E.; Zuber, Maria T.

    2000-01-01

    The Mars Global Surveyor (MGS) spacecraft has now completed more than half of its one-Mars-year mission to globally map Mars. During the MGS elliptical and circular orbit mapping phases, the Mars Orbiter Laser Altimeter (MOLA), an instrument on the MGS payload, has collected over 300 million precise elevation measurements. MOLA measures the range from the MGS spacecraft to the Martian surface and to atmospheric reflections. Range is converted to topography through knowledge of the MGS spacecraft orbit. Ranges from MOLA have resulted in a precise global topographic map of Mars. The instrument has also provided measurements of the width of the backscattered optical pulse and of the 1064 nm reflectivity of the Martian surface and atmosphere. The range resolution of the MOLA instrument is 37.5 cm and the along-track resolution of MOLA ground shots is approx. 300 m; the across-track spacing depends on latitude and time in the mapping orbit. The best current topographic grid has a spatial resolution of approx. 1/16 deg and vertical accuracy of approx. one meter. Additional information is contained in the original extended abstract.

  14. Geometric properties of Martian impact craters: Preliminary results from the Mars Orbiter Laser Altimeter

    Science.gov (United States)

    Garvin, James B.; Frawley, James J.

    1998-12-01

    The Mars Orbiter Laser Altimeter (MOLA) acquired high spatial and vertical resolution topographic data for 18 tracks across the northern hemisphere of Mars during the Fall of 1997. It sampled 98 minimally degraded impact craters between the latitudes of 80°N and 12°S The best fitting depth (d) versus diameter (D) power-law relationship for these craters is: d = 0.14 D0.90 for simple varieties, and d = 0.25 D0.49 for complex structures. The simple-to-complex transition diameter is 8 km (+/-0.5 km). The cross-sectional “shape” of the crater cavities was determined by fitting a power-function to each profile. Variation in the exponent (n) suggest the craters flatten with increasing diameter and impact energy. The ejecta thickness is skewed suggesting that use of existing empirical expressions for the expected radial decay of ejecta thickness is inappropriate for Mars in most cases.

  15. A new lunar digital elevation model from the Lunar Orbiter Laser Altimeter and SELENE Terrain Camera

    Science.gov (United States)

    Barker, M. K.; Mazarico, E.; Neumann, G. A.; Zuber, M. T.; Haruyama, J.; Smith, D. E.

    2016-07-01

    We present an improved lunar digital elevation model (DEM) covering latitudes within ±60°, at a horizontal resolution of 512 pixels per degree (∼60 m at the equator) and a typical vertical accuracy ∼3 to 4 m. This DEM is constructed from ∼ 4.5 ×109 geodetically-accurate topographic heights from the Lunar Orbiter Laser Altimeter (LOLA) onboard the Lunar Reconnaissance Orbiter, to which we co-registered 43,200 stereo-derived DEMs (each 1° × 1°) from the SELENE Terrain Camera (TC) (∼1010 pixels total). After co-registration, approximately 90% of the TC DEMs show root-mean-square vertical residuals with the LOLA data of profiles (typically amounting to <10 m horizontally and <1 m vertically). By combining both co-registered datasets, we obtain a near-global DEM with high geodetic accuracy, and without the need for surface interpolation. We evaluate the resulting LOLA + TC merged DEM (designated as "SLDEM2015") with particular attention to quantifying seams and crossover errors.

  16. Qualification testing of the laser transmitter part for ESA's BepiColombo Laser Altimeter (BELA)

    Science.gov (United States)

    Weidlich, K.; Rech, M.; Kallenbach, R.

    2011-10-01

    The BepiColombo Laser Altimeter (BELA) is one of 11 instruments aboard ESA's Mercury Planetary Orbiter (MPO) scheduled for launch in 2014. BELA will record the surface profile of the planet while orbiting around it at a distance of 400km to 1500km1. The altimetry data constitute an important prerequisite for a number of remote sensing and observation techniques residing on the same orbiter. The BELA instrument comprises a laser transmitter and a receiver part, the design of the former is being presented and discussed in this paper. The laser transmitter encompasses a pair of diode-pumped, actively Q-switched Nd:YAG rod oscillators which have been miniaturized, light-weighted and dimensioned for high electrical to optical efficiency. The key performance parameters of the laser will be presented. Laser design trades which are relevant for a space mission to Mercury and the BELA instrument in particular are discussed. An overview is given to the laser qualification programme which includes performance and environmental tests. Test results are presented which have been recorded during the qualification test campaign currently in progress at Carl Zeiss Optronics.

  17. Performance Assessment of the Mercury Laser Altimeter on MESSENGER from Mercury Orbit

    Science.gov (United States)

    Sun, Xiaoli; Cavanaugh, John F.; Neumann, Gregory A.; Mazarico, Edward M.

    2009-01-01

    The Mercury Laser Altimeter (MLA) is one of seven instruments on the MErcury Surface, Space ENvironment GEochemistry, and Ranging (MESSENGER) spacecraft,a mission in NASA's Discovery Program. MESSENGER was launched on August 3, 2004, and entered into orbit about Mercury on March 29, 2011. As of June 30, 2011 MLA started to collect science Measurements on March 29, 2011. As of June 30, 2011 MLA had accumulated about 3 million laser ranging measurements to the Mercury surface through one Mercury year, i.e ., one complete cycle of the spacecraft thermal environment. The average MLA laser output-pulse energy remained steady despite the harsh thermal environment, in which the laser bench temperature changed by as much as 15 C over a 35 min operating period . The laser beam-collimating telescope experienced a 30 C temperature swing over the same period, and the thermal cycling repeated every 12 hours. Nonetheless, MLA receiver optics appeared to be aligned and in focus throughout these temperature excursions. The maximum ranging distance of MLA was 1500 km at near-zero laser-beam incidence angle (and emission angle) and 600 km at 60 deg incidence angle. The MLA instrument performance in Mercury orbit has been consistent with the performance demonstrated during MESSENGER's Mercury flybys in January and October 2008 and during pre-launch testing. In addition to range measurements, MLA data are being used to estimate the surface reflectance of Mercury at 1064 nm wavelength, including regions of permanent shadow on the floors of polar craters. MLA also provides a measurement of the surface reflectance of sunlight at 1064 nm wavelength by its noise counters, for which output is a monotonic function of the background light.

  18. Improve the ZY-3 Height Accuracy Using Icesat/glas Laser Altimeter Data

    Science.gov (United States)

    Li, Guoyuan; Tang, Xinming; Gao, Xiaoming; Zhang, Chongyang; Li, Tao

    2016-06-01

    ZY-3 is the first civilian high resolution stereo mapping satellite, which has been launched on 9th, Jan, 2012. The aim of ZY-3 satellite is to obtain high resolution stereo images and support the 1:50000 scale national surveying and mapping. Although ZY-3 has very high accuracy for direct geo-locations without GCPs (Ground Control Points), use of some GCPs is still indispensible for high precise stereo mapping. The GLAS (Geo-science Laser Altimetry System) loaded on the ICESat (Ice Cloud and land Elevation Satellite), which is the first laser altimetry satellite for earth observation. GLAS has played an important role in the monitoring of polar ice sheets, the measuring of land topography and vegetation canopy heights after launched in 2003. Although GLAS has ended in 2009, the derived elevation dataset still can be used after selection by some criteria. In this paper, the ICESat/GLAS laser altimeter data is used as height reference data to improve the ZY-3 height accuracy. A selection method is proposed to obtain high precision GLAS elevation data. Two strategies to improve the ZY-3 height accuracy are introduced. One is the conventional bundle adjustment based on RFM and bias-compensated model, in which the GLAS footprint data is viewed as height control. The second is to correct the DSM (Digital Surface Model) straightly by simple block adjustment, and the DSM is derived from the ZY-3 stereo imaging after freedom adjustment and dense image matching. The experimental result demonstrates that the height accuracy of ZY-3 without other GCPs can be improved to 3.0 meter after adding GLAS elevation data. What's more, the comparison of the accuracy and efficiency between the two strategies is implemented for application.

  19. Wind-driven circulation in the subarctic north Pacific using altimeter data

    Indian Academy of Sciences (India)

    Osamu Isoguchi; Hiroshi Kawamura

    2002-09-01

    Time-dependent wind-driven circulation in the subarctic north Pacific is investigated by using Topex/Poseidon (T/P) altimeter data and European Centre for Medium-Range Weather Forecasts (ECMWF) wind data for about 6 years. The first empirical orthogonal function (EOF) of the T/P- derived sea level anomaly (SLA) without the variation related to the steric height change (SLA1) and the first EOF of the ECMWF-based wind stress curl fields represent basin-sized south-north oscillations and their time series agree well with a correlation of 0.49. They appear to express the spin-up and spin-down of the subarctic gyre. The third EOF of SLA (SLA3) and the second EOF of the wind stress curl are also related to the variation of the subarctic gyre. Though the correlation of their time series is 0.27, drastic changes in early winter coincide well. The two EOF pairs can be considered to mean that the SLA variation followed by the latitudinal migration of the Aleutian low is separated into two standing oscillation patterns, that is, the sea level variation combined with SLA1 and SLA3 expresses seasonal variations of the wind-driven circulation of the subarctic gyre. The interannual SLAs constructed by subtracting the SLA1 and SLA3 components clearly show trans-pacific westward propagation even in the high-latitudes. The time series of SLA1 is in agreement with that of in situ SLAs measured with the tide gauge at Petropavlovsk (53-01N, 158-38E), which implies the possibility to monitor the subarctic circulation using tide gauge data.

  20. Atmospheric and Surface Reflectance Measurements by the Geoscience Laser Altimeter System

    Science.gov (United States)

    Spinhirne, James D.; Palm, Steven P.; Hlavka, Dennis L.; Hart, William D.; Mehesh, Ashwin; Welton, Ellsworth J.

    2004-01-01

    The Geoscience Laser Altimeter System launched in early 2003 is the first satellite instrument IC space to globally observe the distribution of clouds and aerosol through laser remote sensing. The instrument is a basic backscatter lidar that operates at two wavelengths, 532 and 1064 nm. The mission data products for atmospheric observations include the calibrated, observed, attenuated backscatter cross section for cloud and aerosol; height detection for multiple cloud layers; planetary boundary layer height; cirrus and aerosol optical depth and the height distribution of aerosol and cloud scattering cross section profiles. The data will enhance knowledge in several areas of atmospheric science: the distribution, transport and influence of atmospheric aerosol, significantly more accurate measurements of the coverage and height of cirrus and other clouds, polar cloud climatology and radiation influence, the dynamics planetary boundary layer and others. An overview and summary of initial results are presented. Initial results from the first months of operation show the detailed height structure of clouds and aerosol on a global basis as expected. The 532 nm channel was expected to be the more sensitive and primary channel for aerosol measurements, but extensive aerosol loading in many regions are observed by the 1064 nm channel. Sensitivities are down to a few times l0(exp 6) l/(m-sr), much better than originally expected. The 532 channel adds an order of magnitude addition sensitivity. Initial comparisons to aerosol models have been done. Similarly for global cloud cover, good results are obtained just from the 1064 nm channel and from both channels, a measurement of multiple layers and cloud overlap has been made. Antarctica observations show high levels of total cloud cover including unique low-level cirrus and blowing snow. Data products have been generated for cloud, aerosol and PBL presence and heights in addition to the basic scattering cross section profiles.

  1. Polar Dunes Resolved by the Mars Orbiter Laser Altimeter Gridded Topography and Pulse Widths

    Science.gov (United States)

    Neumann, Gregory A.

    2003-01-01

    The Mars Orbiter Laser Altimeter (MOLA) polar data have been refined to the extent that many features poorly imaged by Viking Orbiters are now resolved in densely gridded altimetry. Individual linear polar dunes with spacings of 0.5 km or more can be seen as well as sparsely distributed and partially mantled dunes. The refined altimetry will enable measurements of the extent and possibly volume of the north polar ergs. MOLA pulse widths have been recalibrated using inflight data, and a robust algorithm applied to solve for the surface optical impulse response. It shows the surface root-mean-square (RMS) roughness at the 75-m-diameter MOLA footprint scale, together with a geological map. While the roughness is of vital interest for landing site safety studies, a variety of geomorphological studies may also be performed. Pulse widths corrected for regional slope clearly delineate the extent of the polar dunes. The MOLA PEDR profile data have now been re-released in their entirety (Version L). The final Mission Experiment Gridded Data Records (MEGDR's) are now provided at up to 128 pixels per degree globally. Densities as high as 512 pixels per degree are available in a polar stereographic projection. A large computational effort has been expended in improving the accuracy of the MOLA altimetry themselves, both in improved orbital modeling and in after-the-fact adjustment of tracks to improve their registration at crossovers. The current release adopts the IAU2000 rotation model and cartographic frame recommended by the Mars Cartography Working Group. Adoption of the current standard will allow registration of images and profiles globally with an uncertainty of less than 100 m. The MOLA detector is still operational and is currently collecting radiometric data at 1064 nm. Seasonal images of the reflectivity of the polar caps can be generated with a resolution of about 300 m per pixel.

  2. 激光测高技术的发展趋势%Progress and prospect of laser altimeter technology

    Institute of Scientific and Technical Information of China (English)

    季云飞; 耿林; 冯国旭; 王鹏飞

    2011-01-01

    Study on laser altimeter technology has had a history of decades. It has also been used in wide application fields such as topography, geodesy, astronautics, resource survey, etc. Although the technology is relatively mature, it still has a wide developing space as the laser technology and application requirements develop fast. By studying several practical systems which are developed recently or under research, the developing tendency and prospect of laser altimeter are summarized. The technology of multi-beam, single photon detection, multi-shot counting and multi-function system are introduced,which might offer reference for the research of new type laser altimeter.%激光测高技术作为一种的先进测量手段,已广泛应用于地形地貌测绘、地球科学研究、航天工程、城市规划、森林资源调查等诸多方面.虽然激光测高技术已相对成熟,但随着激光技术的发展和应用需求的拓展,激光测高技术仍有很大的发展空间.通过对国外近期研制或正在研究的几个具体激光测高设备的介绍和分析,总结了激光测高技术的一些典型技术特点和发展趋势,介绍了多光束发射和接收、单光子探测、多回波测量和多功能集成等技术在激光测高仪的应用.这对开展新型激光测高技术的研究具有一定参考价值.

  3. Mars 1064 nm spectral radiance measurements determined from the receiver noise response of the Mars Orbiter Laser Altimeter.

    Science.gov (United States)

    Sun, Xiaoli; Neumann, Gregory A; Abshire, James B; Zuber, Maria T

    2006-06-10

    A technique was developed to compute the radiance of the scene viewed by the optical receiver of the Mars Orbiter Laser Altimeter. The technique used the detection threshold and the false detection rate of the receiver to provide a passive radiometry measurement of Mars at the 1064 nm wavelength over a 2 nm bandwidth and subkilometer spatial resolution in addition to the altimetry and active radiometry measurements. The passive radiometry measurement is shown to have a 2% or better precision and has been stable over several Martian years. We describe the principle of operation of the instrument and its calibration and assess its performance from sample orbital measurements. PMID:16761033

  4. Airborne Polarimetric, Two-Color Laser Altimeter Measurements of Lake Ice Cover: A Pathfinder for NASA's ICESat-2 Spaceflight Mission

    Science.gov (United States)

    Harding, David; Dabney, Philip; Valett, Susan; Yu, Anthony; Vasilyev, Aleksey; Kelly, April

    2011-01-01

    The ICESat-2 mission will continue NASA's spaceflight laser altimeter measurements of ice sheets, sea ice and vegetation using a new measurement approach: micropulse, single photon ranging at 532 nm. Differential penetration of green laser energy into snow, ice and water could introduce errors in sea ice freeboard determination used for estimation of ice thickness. Laser pulse scattering from these surface types, and resulting range biasing due to pulse broadening, is assessed using SIMPL airborne data acquired over icecovered Lake Erie. SIMPL acquires polarimetric lidar measurements at 1064 and 532 nm using the micropulse, single photon ranging measurement approach.

  5. ICESat Laser Altimeter Pointing, Ranging and Timing Calibration from Integrated Residual Analysis: A Summary of Early Mission Results

    Science.gov (United States)

    Lutchke, Scott B.; Rowlands, David D.; Harding, David J.; Bufton, Jack L.; Carabajal, Claudia C.; Williams, Teresa A.

    2003-01-01

    On January 12, 2003 the Ice, Cloud and land Elevation Satellite (ICESat) was successfUlly placed into orbit. The ICESat mission carries the Geoscience Laser Altimeter System (GLAS), which consists of three near-infrared lasers that operate at 40 short pulses per second. The instrument has collected precise elevation measurements of the ice sheets, sea ice roughness and thickness, ocean and land surface elevations and surface reflectivity. The accurate geolocation of GLAS's surface returns, the spots from which the laser energy reflects on the Earth's surface, is a critical issue in the scientific application of these data Pointing, ranging, timing and orbit errors must be compensated to accurately geolocate the laser altimeter surface returns. Towards this end, the laser range observations can be fully exploited in an integrated residual analysis to accurately calibrate these geolocation/instrument parameters. Early mission ICESat data have been simultaneously processed as direct altimetry from ocean sweeps along with dynamic crossovers resulting in a preliminary calibration of laser pointing, ranging and timing. The calibration methodology and early mission analysis results are summarized in this paper along with future calibration activities

  6. Multiresolution fusion of radar sounder and altimeter data for the generation of high resolution DEMs of ice sheets

    Science.gov (United States)

    Ilisei, Ana-Maria; Bruzzone, Lorenzo

    2015-10-01

    Understanding the dynamics and processes of the ice sheets is crucial for predicting the behavior of climate change. A potential approach to achieve this is by using high resolution (HR) digital elevation models (DEMs) of the ice surface derived from remote sensing radar or laser altimeters. Unfortunately, at present HR DEMs of large portions of the ice sheets are not available. To address this issue, in this paper we propose a multisensor data fusion technique for the generation of a HR DEM of the ice sheets, which fuses two types of data, i.e., radargrams acquired by radar sounder (RS) instruments and ice surface elevation data measured by altimeter (ALT) instruments. The aim of the technique is to generate a DEM of the ice surface at the best possible horizontal resolution by exploiting the complementary characteristics of the RS and ALT data. This is done by defining a novel processing scheme that involves image processing techniques based on data rescaling, geostatistical interpolation and multiresolution analysis (MRA). The method has been applied to a subset of RS and ALT data acquired over a portion of the Byrd Glacier in Antarctica. Experimental results confirm the effectiveness of the proposed method.

  7. Lunar phase function at 1064 nm from Lunar Orbiter Laser Altimeter passive and active radiometry

    Science.gov (United States)

    Barker, M. K.; Sun, X.; Mazarico, E.; Neumann, G. A.; Zuber, M. T.; Smith, D. E.

    2016-07-01

    We present initial calibration and results of passive radiometry collected by the Lunar Orbiter Laser Altimeter onboard the Lunar Reconnaissance Orbiter over the course of 12 months. After correcting for time- and temperature-dependent dark noise and detector responsivity variations, the LOLA passive radiometry measurements are brought onto the absolute radiance scale of the SELENE Spectral Profiler. The resulting photometric precision is estimated to be ∼5%. We leverage the unique ability of LOLA to measure normal albedo to explore the 1064 nm phase function's dependence on various geologic parameters. On a global scale, we find that iron abundance and optical maturity (quantified by FeO and OMAT) are the dominant controlling parameters. Titanium abundance (TiO2), surface roughness on decimeter to decameter scales, and soil thermophysical properties have a smaller effect, but the latter two are correlated with OMAT, indicating that exposure age is the driving force behind their effects in a globally-averaged sense. The phase function also exhibits a dependence on surface slope at ∼300 m baselines, possibly the result of mass wasting exposing immature material and/or less space weathering due to reduced sky visibility. Modeling the photometric function in the Hapke framework, we find that, relative to the highlands, the maria exhibit decreased backscattering, a smaller opposition effect (OE) width, and a smaller OE amplitude. Immature highlands regolith has a higher backscattering fraction and a larger OE width compared to mature highlands regolith. Within the maria, the backscattering fraction and OE width show little dependence on TiO2 and OMAT. Variations in the phase function shape at large phase angles are observed in and around the Copernican-aged Jackson crater, including its dark halo, a putative impact melt deposit. Finally, the phase function of the Reiner Gamma Formation behaves more optically immature than is typical for its composition and OMAT

  8. Geoscience Laser Altimeter System (GLAS) Instrument: Flight Loop Heat Pipe (LHP) Acceptance Thermal Vacuum Test

    Science.gov (United States)

    Baker, Charles; Butler, Dan; Ku, Jentung; Grob, Eric; Swanson, Ted; Nikitkin, Michael; Powers, Edward I. (Technical Monitor)

    2001-01-01

    Two loop heat pipes (LHPs) are to be used for tight thermal control of the Geoscience Laser Altimeter System (GLAS) instrument, planned for flight in late 2001. The LHPs are charged with Propylene as a working fluid. One LHP will be used to transport 110 W from a laser to a radiator, the other will transport 160 W from electronic boxes to a separate radiator. The application includes a large amount of thermal mass in each LHP system and low initial startup powers. The initial design had some non-ideal flight design compromises, resulted in a less than ideal charge level for this design concept with a symmetrical secondary wick. This less than ideal charge was identified as the source of inadequate performance of the flight LHPs during the flight thermal vacuum test in October of 2000. We modified the compensation chamber design, re-built and charged the LHPs for a final LHP acceptance thermal vacuum test. This test performed March of 2001 was 100% successful. This is the last testing to be performed on the LHPs prior to instrument thermal vacuum test. This sensitivity to charge level was shown through varying the charge on a Development Model Loop Heat Pipe (DM LHP) and evaluating performance at various fill levels. At lower fills similar to the original charge in the flight units, the same poor performance was observed. When the flight units were re-designed and filled to the levels similar to the initial successful DM LHP test, the flight units also successfully fulfilled all requirements. This final flight Acceptance test assessed performance with respect to startup, low power operation, conductance, and control heater power, and steady state control. The results of the testing showed that both LHPs operated within specification. Startup on one of the LHPs was better than the other LHP because of the starter heater placement and a difference in evaporator design. These differences resulted in a variation in the achieved superheat prior to startup. The LHP with

  9. Radiometry Measurements of Mars at 1064 nm Using the Mars Orbiter Laser Altimeter

    Science.gov (United States)

    Sun, Xiao-Li; Abshire, James B.; Neumann, Gregory A.; Zuber, Maria T.; Smith, David E. (Technical Monitor)

    2001-01-01

    Measurements by the Mars Orbiter Laser Altimeter (MOLA) on board the Mars Global Surveyor (MGS) may be used to provides a radiometric measurement of Mars in addition to the topographic measurement. We will describe the principle of operation, a mathematical model, and the receiver calibration in this presentation. MOLA was designed primarily to measure Mars topography, surface roughness end the bidirectional reflectance to the laser beam. To achieve the highest sensitivity the receiver detection threshold is dynamically adjusted to be as low as possible while keeping a predetermined false alarm rate. The average false alarm rate 29 monitored in real time on board MOLA via a noise counter, whose output is fed to the threshold control loop. The false alarm rate at a given threshold is a function of the detector output noise which is the sum of the photo detector, shot noise due to the background light seen by the detector and the dark noise. A mathematical model has been developed that can be used to numerically solve for the optical background power given the MOLA threshold setting and the average noise count. The radiance of Mars can then be determined by dividing the optical power by the solid angle subtended by the MOLA receiver, the receiver optical band-width, end the Mars surface area within the receiver field of view. The phase angle which is the sun-Mars-MOLA angle is available from the MGS database. MOLA also measures simultaneously the bidirectional reflectance of Mars vie its 106-lum loser beam at nadir with nearly zero phase angle. The optical bandwidth of the MOLA receiver is 2um full width at half maximum (FWHM) and centered at 106-lum. The receiver field of view is 0.95mrad FWHM. The nominated spacecraft altitude is 100km and the ground track speed is about 3km/s. Under normal operation, the noise counter are read and the threshold levels are updated at 1Hz. The receiver sensitivity is limited by the detector dark noise to about 0.1nW, which

  10. Geoscience Laser Altimeter System (GLAS) Final Test Report of DM LHP TV Testing

    Science.gov (United States)

    Baker, Charles

    2000-01-01

    Two loop heat pipes (LHPs) are to be used for thermal control of the Geoscience Laser Altimeter System (GLAS), planned for flight in 2001. One LHP will be used to transport 100 W from a laser to the radiator, the other will transport 210 W from electronic boxes to the radiator. In order to verify the LHP design for the GLAS application, an LHP Development Model has been fabricated, and ambient and thermal vacuum tested. Two aluminum blocks of 15 kg and 30 kg, respectively, were attached to the LHP to simulate the thermal masses connected to the heat sources. A 20 W starter heater was installed on the evaporator to aid the loop startup. A new concept to thermally couple the vapor and liquid line was also incorporated in the LHP design. Such a thermal coupling would reduce the power requirement on the compensation chamber in order to maintain the loop set point temperature. To avoid freezing of the liquid in the condenser during cold cases, propylene was selected as the working fluid. The LHP was tested under reflux mode and with adverse elevation. Tests conducted included start-up, power cycle, steady state and transient operation during hot and cold cases, and heater power requirements for the set point temperature control of the LHP. Test results showed very successful operation of the LHP under all conditions. The 20 W starter heater proved necessary in order to start the loop when a large thermal mass was attached to the evaporator. The thermal coupling between the liquid line and the vapor line significantly reduced the heater power required for loop temperature control, which was less than 5 watts in all cases, including a cold radiator. The test also demonstrated successful operation with a propylene working fluid, with successful startups with condenser temperatures as low as 100 C. Furthermore, the test demonstrated accurate control of the loop operating temperature within +/- 0.2 C, and a successful shutdown of the loop during the survival mode of

  11. Global Geometric Properties of Martian Impact Craters: A Preliminary Assessment Using Mars Orbiter Laser Altimeter (MOLA)

    Science.gov (United States)

    Garvin, J. B.; Sakimoto, S. E. H.; Schnetzler, C.; Frawley, J. J.

    1999-01-01

    Impact craters on Mars have been used to provide fundamental insights into the properties of the martian crust, the role of volatiles, the relative age of the surface, and on the physics of impact cratering in the Solar System. Before the three-dimensional information provided by the Mars Orbiter Laser Altimeter (MOLA) instrument which is currently operating in Mars orbit aboard the Mars Global Surveyor (MGS), impact features were characterized morphologically using orbital images from Mariner 9 and Viking. Fresh-appearing craters were identified and measurements of their geometric properties were derived from various image-based methods. MOLA measurements can now provide a global sample of topographic cross-sections of martian impact features as small as approx. 2 km in diameter, to basin-scale features. We have previously examined MOLA cross-sections of Northern Hemisphere and North Polar Region impact features, but were unable to consider the global characteristics of these ubiquitous landforms. Here we present our preliminary assessment of the geometric properties of a globally-distributed sample of martian impact craters, most of which were sampled during the initial stages of the MGS mapping mission (i.e., the first 600 orbits). Our aim is to develop a framework for reconsidering theories concerning impact cratering in the martian environment. This first global analysis is focused upon topographically-fresh impact craters, defined here on the basis of MOLA topographic profiles that cross the central cavities of craters that can be observed in Viking-based MDIM global image mosaics. We have considered crater depths, rim heights, ejecta topologies, cross-sectional "shapes", and simple physical models for ejecta emplacement. To date (May, 1999), we have measured the geometric properties of over 1300 impact craters in the 2 to 350 km diameter size interval. A large fraction of these measured craters were sampled with cavity-center cross-sections during the first

  12. Lunar Phase Function at 1064 Nm from Lunar Orbiter Laser Altimeter Passive and Active Radiometry

    Science.gov (United States)

    Barker, M. K.; Sun, X.; Mazarico, E.; Neumann, G. A.; Zuber, M. T.; Smith, D. E.

    2016-01-01

    We present initial calibration and results of passive radiometry collected by the Lunar Orbiter Laser Altimeter onboard the Lunar Reconnaissance Orbiter over the course of 12 months. After correcting for time- and temperature-dependent dark noise and detector responsivity variations, the LOLA passive radiometry measurements are brought onto the absolute radiance scale of the SELENE Spectral Profiler. The resulting photometric precision is estimated to be 5%. We leverage the unique ability of LOLA to measure normal albedo to explore the 1064 nm phase function's dependence on various geologic parameters. On a global scale, we find that iron abundance and optical maturity (quantified by FeO and OMAT) are the dominant controlling parameters. Titanium abundance (TiO2), surface roughness on decimeter to decameter scales, and soil thermo- physical properties have a smaller effect, but the latter two are correlated with OMAT, indicating that exposure age is the driving force behind their effects in a globally-averaged sense. The phase function also exhibits a dependence on surface slope at approximately 300 m baselines, possibly the result of mass wasting exposing immature material and/or less space weathering due to reduced sky visibility. Modeling the photometric function in the Hapke framework, we find that, relative to the highlands, the maria exhibit decreased backscattering, a smaller opposition effect (OE) width, and a smaller OE amplitude. Immature highlands regolith has a higher backscattering fraction and a larger OE width compared to mature highlands regolith. Within the maria, the backscattering fraction and OE width show little dependence on TiO2 and OMAT. Variations in the phase function shape at large phase angles are observed in and around the Copernican-aged Jackson crater, including its dark halo, a putative impact melt deposit. Finally, the phase function of the Reiner Gamma Formation behaves more optically immature than is typical for its composition

  13. Ocean surface waves and winds over the north Indian Ocean from satellite altimeter - preliminary results of SAC-NIO joint project

    Digital Repository Service at National Institute of Oceanography (India)

    Sarkar, A.; Rajkumar, R.; Gairola, R.M.; Gohil, B.S.; Vethamony, P.; Rao, L.V.G.

    With the aim of retrieving, validating and mapping ocean surface winds and waves in the north Indian Ocean, GEOSAT altimeter data for the period November 1986 to October 1987 and available sea truth data for the above period were processed in SAC...

  14. The Keck "Mars 2000" Project: Using Mars Orbiter Laser Altimeter Data to Assess Geological Processes and Regional Stratigraphy Near Orcus Patera and Marte Vallis on Mars

    Science.gov (United States)

    Grosfils, E. B.; Sakimoto, S. E. H.; Mendelson, C. V.; Bleacher, J. E.

    2001-01-01

    During the Keck 'Mars 2000' summer project 10 undergraduates (rising juniors) used Mars Orbiter Laser Altimeter (MOLA) data to study a 19x14 degree region they identified as a potential Mars 2003 landing site. Here we introduce the project science and organization. Additional information is contained in the original extended abstract.

  15. NODC Standard Product: US Navy Geosat altimeter T2 Geophysical Data Records for the Exact Repeat Mission (6 disc set) (NODC Accession 0053521)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This accession contains a copy of the NODC CD-ROM product titled US Navy Geosat altimeter T2 GDRs for the Exact Repeat Mission for the time period of November 08,...

  16. Seafloor spreading pattern of the North Atlantic between 10o and 40o N : a reconstruction based on shipborne measurements and satellite altimeter data

    NARCIS (Netherlands)

    Roest, W.R.

    1987-01-01

    The history of the relative motion between North America and Africa is recorded in the floor of the central North Atlantic Ocean. The resulting pattern of magnetic anomalies and fracture zones in the area between 10° and 40° N was analysed using shipborne measurements and Seasat altimeter data. This

  17. Seafloor spreading pattern of the North Atlantic between 10⁰ and 40⁰ N : a reconstruction based on shipborne measurements and satellite altimeter data

    NARCIS (Netherlands)

    Roest, W.R.

    1987-01-01

    The history of the relative motion between North America and Africa is recorded in the floor of the central North Atlantic Ocean. The resulting pattern of magnetic anomalies and fracture zones in the area between 10° and 40° N was analysed using shipborne measurements and Seasat altimeter data. This

  18. Relative performance of future altimeter systems and tide gauges in constraining a model of North Sea high-frequency barotropic dynamics

    Science.gov (United States)

    Mourre, Baptiste; de Mey, Pierre; Ménard, Yves; Lyard, Florent; Le Provost, Christian

    2006-12-01

    We evaluate in this paper the ability of several altimeter systems, considered separately as well as together with tide gauges, to control the time evolution of a barotropic model of the North Sea shelf. This evaluation is performed in the framework of the particular model errors due to uncertainties in bathymetry. An Ensemble Kalman Filter (EnKF) data assimilation approach is adopted, and observing-systems simulation experiments (OSSEs) are carried out using ensemble spread statistics. The skill criterion for the comparison of observing networks is, therefore, not based on the misfit between two simulations, as done in classic twin experiments, but on the reduction of ensemble variance occurring as a consequence of the assimilation. Future altimeter systems, such as the Wide Swath Ocean Altimeter (WSOA) and satellite constellations, are considered in this work. A single WSOA exhibits, for instance, similar performance as two-nadir satellites in terms of sea-level correction, and is better than three satellites in terms of model velocity control. Generally speaking, the temporal resolution of observations is shown to be of major importance for controlling the model error in these experiments. This result is clearly related to the focus adopted in this study on the specific high-frequency response of the ocean to meteorological forcing. Altimeter systems lack adequate temporal sampling for properly correcting the major part of model error in this context, whereas tide gauges, which provide a much finer time resolution, lead to better global statistical performance. When looking into further detail, tide gauges and altimetry are demonstrated to exhibit an interesting complementary character over the whole shelf, as tide gauge networks make it possible to properly control model error in a ˜100-km coastal band, while high-resolution altimeter systems are more efficient farther from the coast.

  19. Detailed geoid computations for GEOS-C altimeter experiment areas. [gravimetric geoid for Atlantic and northeast Pacific Ocean areas

    Science.gov (United States)

    Marsh, J. G.; Vincent, S.

    1973-01-01

    The GEOS-C spacecraft is scheduled to carry onboard a radar altimeter for the purpose of measuring the geoid undulations in oceanic areas. An independently derived geoid map will provide a valuable complement to these experiments. A detailed gravimetric geoid is presented for the Atlantic and northeast Pacific Ocean areas based upon a combination of the Goddard Space Flight Center GEM-6 earth model and surface 1 deg x 1 deg gravity data. As part of this work a number of satellite derived gravity models were evaluated to establish the model which best represented the long wave length features of the geoid in the above mentioned area. Comparisons of the detailed geoid with the astrogeodetic data provided by the National Ocean Survey and dynamically derived tracking station heights indicate that the accuracy of this combined geoid is on the order of 2 meters or better where data was dense and 5 to 7 meters where data was less dense.

  20. Mars 1064-nm Spectral Radiance Measurements from the Receiver Noise Response of the Mars Orbiter Laser Altimeter

    Science.gov (United States)

    Sun, Xiaoli; Neumann, Gregory A.; Abshire, James B.; Zuber, Maria T.

    2005-01-01

    The Mars Orbiter Laser Altimeter not only provides surface topography from the laser pulse time-of-flight, but also two radiometric measurements, the active measurement of transmitted and reflected laser pulse energy, and the passive measurement of reflected solar illumination. The passive radiometry measurement is accomplished in a novel fashion by monitoring the noise density at the output of the photodetector and solving for the amount of background light. The passive radiometry measurements provide images of Mars at 1064-nm wavelength over a 2 nm bandwidth with sub-km spatial resolution and with 2% or better precision under full illumination. We describe in this paper the principle of operation, the receiver mathematical model, its calibration, and performance assessment from sample measurement data.

  1. The Reflectivity of Mars at 1064 nm: Derivation from Mars Orbiter Laser Altimeter Data and Application to Climatology and Meteorology

    CERN Document Server

    Heavens, Nicholas G

    2016-01-01

    The Mars Orbiter Laser Altimeter (MOLA) on board Mars Global Surveyor (MGS) made $\\gg 10^{8}$ measurements of the reflectivity of Mars at 1064 nm ($R_{1064}$) by both active sounding and passive radiometry. Past studies of $R_{1064}$ neglected the effects of atmospheric opacity and viewing geometry on both active and passive measurements and also identified a potential calibration issue with passive radiometry. Therefore, as yet, there exists no acceptable reference $R_{1064}$ to derive a column opacity product from surface returns during active sounding for the purposes of atmospheric studies. Here, such a reference $R_{1064}$ is derived by seeking $R^{M,N}_{1064}$: a Minnaert-corrected normal albedo under clear conditions and assuming minimal phase angle dependence. Over darker surfaces, $R^{M,N}_{1064}$ and the absolute level of atmospheric opacity were estimated from active sounding. Over all surfaces, the opacity derived from active sounding were used to filter out the cloudiest passive radiometry measur...

  2. Effects of surface roughness on sea ice freeboard retrieval with an Airborne Ku-Band SAR radar altimeter

    DEFF Research Database (Denmark)

    Hendricks, Stefan; Stenseng, Lars; Helm, Veit;

    2010-01-01

    Results from two years of the CryoSat Validation Experiment (CryoVEx) over sea ice in the western Arctic Ocean are presented. The estimation of freeboard, the height of sea ice floating above the water level, is one the main goals of the CryoSat-2 mission of the European Space Agency (ESA) in order...... to investigate sea ice volume changes on an Arctic wide scale. Freeboard retrieval requires precise radar range measurements to the ice surface, therefore we investigate the penetration of the Ku-Band radar waves into the overlying snow cover as well as the effects of sub-footprint-scale surface roughness using...... airborne radar and laser altimeters. We find regional variable penetration of the radar signal at late spring conditions, where the difference of the radar and the reference laser range measurement never agrees with the expected snow thickness. In addition, a rough surface can lead to biases...

  3. A new, high-resolution digital elevation model of Greenland fully validated with airborne laser altimeter data

    DEFF Research Database (Denmark)

    Bamber, J.L.; Ekholm, Simon; Krabill, W.B.

    2001-01-01

    A new digital elevation model of the Greenland ice sheet and surrounding rock outcrops has been produced at 1-km postings from a comprehensive suite of satellite remote sensing and cartographic data sets. Height data over the ice sheet were mainly from ERS-1 and Geosat radar altimetry. These data...... were corrected for a slope-dependent bias that had been identified in a previous study. The radar altimetry was supplemented with stereophotogrammetric data sets, synthetic aperture radar interferometry, and digitized cartographic maps over regions of bare rock and where gaps in the satellite altimeter...... the bare rock areas the accuracy ranged from 20 to 200 m, dependent on the data source available. The new digital elevation model was used as an input data set for a positive degree day model of ablation. The new elevation model was found to reduce ablation by only 2% compared with using an older, 2.5-km...

  4. The application of the ITRF2014 Product Center solutions with respect to Altimeter Satellite Precise Orbit Determination

    Science.gov (United States)

    Lemoine, Frank G.; Zelensky, Nikita P.; Couhert, Alexandre; Jalabert, Eva; Chinn, Douglas S.

    2016-04-01

    The IERS product centers, IGN, DGFI, and JPL, have prepared new solution realizations of the International Terrestrial Reference Frame (ITRF), based on the analysis and the combination SINEX solutions submitted by the individual geodetic techniques: Satellite Laser Ranging (SLR), Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), Very Long Baseline Interferometry (VLBI), and Global Navigation Satellite Systems (GNSS). We evaluate these solutions with respect to their orbit determination performance, including RMS of fit, and other orbit metrics, including altimeter crossovers, focusing on the altimeter satellites, in particular TOPEX/Poseidon, Jason-1, and Jason-2, but also Cryosat-2 and Envisat. We also evaluate the POD performance using the Jason-2 JPL/reduced-dynamic orbits as a reference. We have conducted a preliminary evaluation of the new solutions so far released, ITRF2014P (IGN), and DTRF2014 (DGFI) with respect to the Jason-2 satellite, and find a significant improvement in the DORIS satellite RMS of fit for DORIS-only orbit computations. Over 260 orbit cycles (July 2008 to August 2015) the RMS of fit improves from 0.3667 mm/s for DPOD2008 to 0.3646 and 0.3645 mm/s for the two new ITRF2014 realizations. The following stations show improvements in RMS of fit of more than 0.02 mm/s, which is significant for DORIS data: KRUB/KRWB (Kourou), CIDB (Cibinong), JIUB (Jiufeng), YEMB (Yellowknife), MATB (Marion Island), FUTB (Futuna), and ARFB (Arequipa). In this paper we also focus on the SLR performance, and we evaluate how the new ITRF2014 reference frame realization can be integrated into the next generation of precision orbit improvements for the Jason series of satellites.

  5. Improved calibration of reflectance data from the LRO Lunar Orbiter Laser Altimeter (LOLA) and implications for space weathering

    Science.gov (United States)

    Lemelin, M.; Lucey, P. G.; Neumann, G. A.; Mazarico, E. M.; Barker, M. K.; Kakazu, A.; Trang, D.; Smith, D. E.; Zuber, M. T.

    2016-07-01

    The Lunar Orbiter Laser Altimeter (LOLA) experiment on Lunar Reconnaissance Orbiter (LRO) is a laser altimeter that also measures the strength of the return pulse from the lunar surface. These data have been used to estimate the reflectance of the lunar surface, including regions lacking direct solar illumination. A new calibration of these data is presented that features lower uncertainties overall and more consistent results in the polar regions. We use these data, along with newly available maps of the distribution of lunar maria, also derived from LRO instrument data, to investigate a newly discovered dependence of the albedo of the lunar maria on latitude (Hemingway et al., [2015]). We confirm that there is an increase in albedo with latitude in the lunar maria, and confirm that this variation is not an artifact arising from the distribution of compositions within the lunar maria, using data from the Lunar Prospector Neutron Spectrometer. Radiative transfer modeling of the albedo dependence within the lunar maria is consistent with the very weak to absent dependence of albedo on latitude in the lunar highlands; the lower abundance of the iron source for space weathering products in the lunar highlands weakens the latitude dependence to the extent that it is only weakly detectable in current data. In addition, photometric models and normalization may take into account the fact that the lunar albedo is latitude dependent, but this dependence can cause errors in normalized reflectance of at most 2% for the majority of near-nadir geometries. We also investigate whether the latitude dependent albedo may have obscured detection of small mare deposits at high latitudes. We find that small regions at high latitudes with low roughness similar to the lunar maria are not mare deposits that may have been misclassified owing to high albedos imposed by the latitude dependence. Finally, we suggest that the only modest correlations among space weathering indicators defined

  6. Design of a laser altimeter applied to terrain matching guidance%应用于地形匹配导航的激光高度计设计

    Institute of Scientific and Technical Information of China (English)

    张翼飞; 杨辉; 王孝通

    2011-01-01

    The terrain matching guidance system equipped with radar altimeter has low detection precision and is susceptible to electromagnetic interference. Moreover, it can not work over the sea. In order to resolve these problems, a scheme of laser al-timeter is designed to take the place of the radar altimeter. The technology of diode-pumped solid-state laser is adopted to design laser transmitter, outputting infrared/blue-green dual-wavelength laser. The altimeter with dual-wavelength output can detect both the land terrain and the seabed terrain. To promote the performance of the laser altimeter, the detectors are selected careful-ly, and the optics system, the scanning system and the signal processing system are designed optimally. The designed laser altim-eter features small size, light weight, high repetition rate, high detection sensitivity and strong anti-interference ability.%为解决基于雷达高度表探测的地形匹配导航系统探测精度不高、易受电子干扰影响而失效、且在跨海飞行时无法导航的难题,设计了一种激光高度计来代替雷达高度表进行地形探测.采用二极管泵浦固体激光器技术设计激光发射装置,输出近红外/蓝绿双波长激光,既可以测量陆地地形高度,又可以穿透海水探测海底地形;并根据激光高度计拟达到的性能指标选择合适的光电探测器,优化设计了光学系统、扫描系统和信号处理系统.所设计的激光高度计具有体积小、重量轻、高重频、探测灵敏度高、抗电磁干扰能力强等特点.

  7. A Study on Sea Level Variations of the Korean Peninsula and Surrounding Areas Based on Tide Gauge, GPS and Satellite Altimeter Measurements

    Science.gov (United States)

    Kim, K.; Park, K.; Won, J.

    2010-12-01

    Sea level variations of the Korean peninsula and surrounding areas in the ranges of 20-40 °N and 110-145 °E were investigated for the purpose of understanding the regional characteristics of the abnormal sea level rise near the Jeju island located in the southern edge of the Korean peninsula. For this study, we used tide gauge (TG) data, Global Positioning System (GPS) observations, and satellite altimeter measurements taken in the study area. We used the data at 194 TG stations. We obtained the TG data from 38 stations operated by Korea Hydrographic and Oceanographic Administration (KHOA) in Korea. We also collected monthly mean sea level observations from 139 and 17 TG stations of Japan and China, respectively. The data of Japan and China are from Global Sea Level Observing System (GLOSS) and Permanent Service for Mean Sea Level (PSMSL) services. We computed sea level rates using monthly mean sea level measurements, and analyzed spatial-temporal correlation through the Empirical Orthogonal Function (EOF) and Fast Fourier Transform (FFT) analysis. As the second part of our study, we derived absolute sea level rise rates by correcting the TG data for crustal deformation rates. To obtain the uplift rates in the area, we used continuous measurements at permanent GPS stations located at the TG site. For GPS data processing high-precision GPS data processing program GIPSY-OASIS II was used. To analyze local signatures of crustal deformation, we subtracted the primary EOF mode signal from the GPS height time series. Furthermore, we compared the obtained absolute sea level rates with satellite altimeter measurements. We obtained and analyzed TOPEX/Poseidon, Jason-1, and Jason-2 satellite altimeter data provided by AVISO from 1993 to 2010. We found that the absolute sea level rates from geodetic measurements are generally in good agreement with radar altimeter rates.

  8. Ku- and Ka-band altimeter data in the northwestern mediterranean sea : impact on the observation of the coastal ocean variability

    OpenAIRE

    Birol, F.; Nino, Fernando

    2015-01-01

    The strong increase in altimeter measurement errors near land surfaces is a limiting factor for coastal applications. We analyze the performance of the new Ka-band SARAL/AltiKa (SRL) mission in the northwestern Mediterranean Sea. SRL sea surface height (SSH) measurements are compared with those from the Jason-2 Ku-band satellite mission. The results show a significant increase in both quantity and quality of SSH data available near coastlines when using SRL data. Available edited data are 95....

  9. A method for separating Antarctic postglacial rebound and ice mass balance using future ICESat Geoscience Laser Altimeter System, Gravity Recovery and Climate Experiment, and GPS satellite data

    OpenAIRE

    I. Velicogna; J. Wahr

    2002-01-01

    Measurements of ice elevation from the Geoscience Laser Altimeter System (GLAS) aboard the Ice, Cloud, and Land Elevation Satellite can be combined with time-variable geoid measurements from the Gravity Recovery and Climate Experiment (GRACE) satellite mission to learn about ongoing changes in polar ice mass and viscoelastic rebound of the lithosphere under the ice sheet. We estimate the accuracy in recovering the spatially varying ice mass trend and postglacial rebound signals for Antarctica...

  10. Rain and cloud effects on a satellite dual-frequency radar altimeter system operating at 13.5 and 35 GHz

    Science.gov (United States)

    Walsh, E. J.; Monaldo, F. M.; Goldhirsh, J.

    1984-01-01

    The influence of clouds and rain on the return waveform signatures from satellite borne radar altimeters operating at 13.5 and 35 GHz are examined. It is specifically demonstrated that spatial nonuniformity in the cloud liquid water content or variations of the rain rate may result in significant distortions of the altimeter signature. The distorted signal is produced as a result of nonuniform attenuation occurring at the different range bins associated with the reflected signal. Determination of the mean sea height by employing tracking algorithms on these distorted echoes may result in gross errors. Although the influence of clouds on the altimeter signature and hence tracking precision is minimal at 13.5 GHz (e.g., less than 4 cm for a 1-s average), it may produce unacceptable mean sea level uncertainties at 35 GHz (e.g., 20 cm for a 1-s average) assuming a significant waveheight of 4 m. On the other hand, the signatures at both 13.5 GHz and 35 GHz become grossly distorted for rain rates of 10 mm/h and higher resulting in mean sea height errors of 46 and 65 cm, respectively, for significant wave heights of 2 m.

  11. 高度表宽多普勒频宽回波研究%Study of Altimeter Wide Doppler Frequency Band Echo

    Institute of Scientific and Technical Information of China (English)

    刘浩淼; 卞树檀; 朱守保

    2012-01-01

    分析了PD雷达高度表的地回波特性。总结了高度表的工作特征,通过网格映像法借助数字地图思想建立了地面的距离-多普勒关系。考虑回波的影响因素,如散射系数、天线模型等,通过Matlab建模仿真分析了高度表回波的时域和频域特征。研究结果对研制和地面测试弹载雷达高度表提供了技术支持。%This paper analyzes the features of the PD radar altimeter.It summarizes the performance characteristics of the altimeter.Based on the idea of the digital map,it sets up the ground distance-doppler relation by the grid method.Considering the effects of the crossing factor,such as the scattering parameter and antenna model,a simulation model is built with Matlab,which can analyze the features of the time-zone and frequency-zone.The result can provide technical support to the development and test of the altimeter for missiles.

  12. A wave energy resource assessment in the China's seas based on multi-satellite merged radar altimeter data

    Institute of Scientific and Technical Information of China (English)

    WAN Yong; ZHANG Jie; MENG Junmin; WANG Jing

    2015-01-01

    Wave energy resources are abundant in both offshore and nearshore areas of the China's seas. A reliable assessment of the wave energy resources must be performed before they can be exploited. First, for a water depth in offshore waters of China, a parameterized wave power density model that considers the effects of the water depth is introduced to improve the calculating accuracy of the wave power density. Second, wave heights and wind speeds on the surface of the China's seas are retrieved from an AVISO multi-satellite altim-eter data set for the period from 2009 to 2013. Three mean wave period inversion models are developed and used to calculate the wave energy period. Third, a practical application value for developing the wave energy is analyzed based on buoy data. Finally, the wave power density is then calculated using the wave field data. Using the distribution of wave power density, the energy level frequency, the time variability indexes, the to-tal wave energy and the distribution of total wave energy density according to a wave state, the offshore wave energy in the China's seas is assessed. The results show that the areas of abundant and stable wave energy are primarily located in the north-central part of the South China Sea, the Luzon Strait, southeast of Taiwan in the China's seas; the wave power density values in these areas are approximately 14.0–18.5 kW/m. The wave energy in the China’s seas presents obvious seasonal variations and optimal seasons for a wave energy utilization are in winter and autumn. Except for very coastal waters, in other sea areas in the China's seas, the energy is primarily from the wave state with 0.5 m≤Hs≤4 m, 4 s≤Te≤10 s whereHs is a significant wave height andTe is an energy period; within this wave state, the wave energy accounts for 80% above of the total wave energy. This characteristic is advantageous to designing wave energy convertors (WECs). The practical application value of the wave energy is higher

  13. Prediction of bathymetry from satellite altimeter based gravity in the Arabian Sea: Mapping of two unnamed deep seamounts

    Science.gov (United States)

    Jena, B.; Kurian, P. J.; Swain, D.; Tyagi, A.; Ravindra, R.

    2012-06-01

    This work attempts to predict bathymetry from satellite altimeter based gravity in the Arabian Sea. A collocated match-up database (n = 17,016) was created on Multibeam Echosounder (MBES) bathymetry and satellite gravity values (˜1 min spatial resolution) derived from remote sensing satellites. A Radial Basis Function (RBF) based Artificial Neural Network (ANN) model was developed to predict bathymetry from satellite gravity values. The ANN model was trained with variable undersea features such as seamount, knoll, abyssal plain, hill, etc. to familiarize the network with all possible geomorphic features as inputs through learning and the corresponding target outputs. The performance of the predictive model was evaluated by comparing bathymetric values with MBES datasets that were not used during the training and verification steps of the ANN model formulation. The model was then compared with MBES surveyed seamount observations (those were not used during ANN analysis) and global model bathymetry products. Results demonstrate better performance of ANN model compared to global model products for mapping of two unnamed seamounts in the Arabian Sea. These two unnamed seamounts have been predicted, mapped and their morphology is reported for the first time through this work.

  14. The steepest slopes on the Moon from Lunar Orbiter Laser Altimeter (LOLA) Data: Spatial Distribution and Correlation with Geologic Features

    Science.gov (United States)

    Kreslavsky, Mikhail A.; Head, James W.

    2016-07-01

    We calculated topographic gradients over the surface of the Moon at a 25 m baseline using data obtained by the Lunar Orbiter Laser Altimeter (LOLA) instrument onboard the Lunar Reconnaissance Orbiter (LRO) spacecraft. The relative spatial distribution of steep slopes can be reliably obtained, although some technical characteristics of the LOLA dataset preclude statistical studies of slope orientation. The derived slope-frequency distribution revealed a steep rollover for slopes close to the angle of repose. Slopes significantly steeper than the angle of repose are almost absent on the Moon due to (1) the general absence of cohesion/strength of the fractured and fragmented megaregolith of the lunar highlands, and (2) the absence of geological processes producing steep-slopes in the recent geological past. The majority of slopes steeper than 32°-35° are associated with relatively young large impact craters. We demonstrate that these impact craters progressively lose their steepest slopes. We also found that features of Early Imbrian and older ages have almost no slopes steeper than 35°. We interpret this to be due to removal of all steep slopes by the latest basin-forming impact (Orientale), probably by global seismic shaking. The global spatial distribution of the steepest slopes correlates moderately well with the predicted spatial distribution of impact rate; however, a significant paucity of steep slopes in the southern farside remains unexplained.

  15. Observations of Dust Using the NASA Geoscience Laser Altimeter System (GLAS): New New Measurements of Aerosol Vertical Distribution From Space

    Science.gov (United States)

    Welton, Ellsworth; Spinhirne, James D.; Palm, Steven P.; Hlavka, Dennis; Hart, William

    2003-01-01

    On January 12, 2003 NASA launched the first satellite-based lidar, the Geoscience Laser -Altimeter System (GLAS), onboard the ICESat spacecraft. The GLAS atmospheric measurements introduce a fundamentally new and important tool for understanding the atmosphere and climate. In the past, aerosols have only been studied from space using images gathered by passive sensors. Analysis of this passive data has lead to an improved understanding of aerosol properties, spatial distribution, and their effect on the earth's climate. However, these images do not show the aerosol's vertical distribution. As a result, a key piece of information has been missing. The measurements now obtained by GLAS will provide information on the vertical distribution of aerosols and clouds, and improve our ability to study their transport processes and aerosol-cloud interactions. Here we show an overview of GLAS, provide an update of its current status, and present initial observations of dust profiles. In particular, a strategy of characterizing the height profile of dust plumes over source regions will be presented.

  16. The Algorithm Theoretical Basis Document for the Atmospheric Delay Correction to GLAS Laser Altimeter Ranges. Volume 8

    Science.gov (United States)

    Herring, Thomas A.; Quinn, Katherine J.

    2012-01-01

    NASA s Ice, Cloud, and Land Elevation Satellite (ICESat) mission will be launched late 2001. It s primary instrument is the Geoscience Laser Altimeter System (GLAS) instrument. The main purpose of this instrument is to measure elevation changes of the Greenland and Antarctic icesheets. To accurately measure the ranges it is necessary to correct for the atmospheric delay of the laser pulses. The atmospheric delay depends on the integral of the refractive index along the path that the laser pulse travels through the atmosphere. The refractive index of air at optical wavelengths is a function of density and molecular composition. For ray paths near zenith and closed form equations for the refractivity, the atmospheric delay can be shown to be directly related to surface pressure and total column precipitable water vapor. For ray paths off zenith a mapping function relates the delay to the zenith delay. The closed form equations for refractivity recommended by the International Union of Geodesy and Geophysics (IUGG) are optimized for ground based geodesy techniques and in the next section we will consider whether these equations are suitable for satellite laser altimetry.

  17. Validation of the“HY-2”altimeter wet tropospheric path delay correction based on radiosonde data

    Institute of Scientific and Technical Information of China (English)

    WANG Jin; ZHANG Jie; FAN Chenqing; WANG Jing

    2014-01-01

    Wet tropospheric path delay (PD) is a highly variable term for the altimeter measurement of a sea surface height, caused by the refraction effect of atmospheric water vapor and cloud liquid water. In order to esti-mate PD values, the“HY-2”system includes a calibration microwave radiometer (CMR) operating at 18.7, 23.8 and 37 GHz. The PD data of the CMR were compared and validated by coincident radiosonde profiles from ten globally distributed radiosonde stations during October 2011 to August 2012. The temporal interval was 1 h. In order to avoid land contamination, different spatial intervals between these two data sets were tested. The empirical fit function of PD uncertainty and spatial interval was found and extrapolated to the ideal situation that the data of CMR and radiosonde were totally coincident. The stability of the brightness temperature of the CMR and its impact on the PD correction was also studied. Consequently, the uncer-tainty of the PD algorithm of the CMR was estimated to be 2.1 cm.

  18. Thule to Summit: Accumulation variability, surface elevation, and satellite altimeter validation from ground-penetrating radar and GPS profiles

    Science.gov (United States)

    Overly, T. B.; Wong, G. J.; Courville, Z.; Hawley, R. L.; Lutz, E.; Osterberg, E. C.

    2011-12-01

    The spatial variability of accumulation rates, elevation, and near-surface firn physical properties on the Greenland Ice Sheet (GIS) are of interest in the context of mass balance studies, remote sensing studies, and climate studies. In the springs of 2010 and 2011, we traversed from Thule Air Base to Summit Station on the GIS. Along the traverse route, we collected continuous Ground-penetrating radar data with a 400 MHz commercial (GSSI) instrument, and continuous kinematic geodetic-quality GPS data. Here, we present these data and preliminary analysis. In the GPR data, continuous reflection horizons persist along the entire traverse path through the dry-snow zone. We calculate near-surface radar velocity from snowpit and shallow core density measurements collected along the traverse route. Our 400 MHz radar data yields accumulation rates along the traverse route to a depth of 60 meters. The continuous geodetic-quality GPS data provides the most accurate representation of surface elevation along our traverse route. We compare our GPS elevation data with surface elevations from remote-sensing platforms such as ESA's CryoSat-2 and the altimeters aboard the NASA Operation IceBridge aircraft.

  19. Study on Space-borne Laser Altimeter Supported Satellite Photogrammetry%星载激光测高仪辅助卫星摄影测量浅析

    Institute of Scientific and Technical Information of China (English)

    岳春宇; 郑永超; 陶宇亮

    2013-01-01

    激光测高仪可以快速高精度获取地面高程信息,弥补卫星光学遥感影像三维信息获取能力的不足。采用高精度激光测高数据作为控制信息,符合卫星摄影测量尽量减少地面控制点的发展趋势。文章首先介绍了实际卫星立体测绘中难以解决的问题,结合激光测高的特点,设计了星载激光测高仪辅助空中三角测量立体测绘的方案。根据摄影测量观测方程和激光测高仪对地观测方程,以及卫星影像和激光测高数据外方位元素之间的联系,由光束法平差原理建立观测误差方程。对星载激光测高仪进行定位精度理论分析,采用高精度激光测高数据可以作为高程控制,提高高程观测精度。最后对卫星摄影测量数据与星载激光测高数据联合平差仿真实验,实验结果表明定位精度明显提高。%As a way of acquiring elevation with high accuracy and effectiveness, laser altimeter can im-prove the capability of 3-dimensional earth observation of satellite optical remote sensing imagery. And using high accuracy elevation observation of space-borne laser altimeter as control points accords with the trend of satellite photogrammetry without ground control points. In this paper, the problems of satellite photogrammetry are firstly introduced, and then the method of space-borne laser altimeter supported aerotriangulation is de-scribed, which can solve these problems due to the characteristics of laser altimeter. The bundle adjustment er-ror equations are established according to the earth observation of satellite image and space-borne laser altime-ter, as well as the relationship of their exterior orientation elements. Elevation observations supplied by laser altimeter can be used as elevation control points to improve the accuracy of aerotriangulation and the position-ing accuracy. Finally, the improvement of positioning accuracy is shown in simulation aerotriangulation ex

  20. Application of Reconfigurable Computing Technology to Multi-KiloHertz Micro-Laser Altimeter (MMLA) Data Processing

    Science.gov (United States)

    Powell, Wesley; Dabney, Philip; Hicks, Edward; Pinchinat, Maxime; Day, John H. (Technical Monitor)

    2002-01-01

    The Multi-KiloHertz Micro-Laser Altimeter (MMLA) is an aircraft based instrument developed by NASA Goddard Space Flight Center with several potential spaceflight applications. This presentation describes how reconfigurable computing technology was employed to perform MMLA signal extraction in real-time under realistic operating constraints. The MMLA is a "single-photon-counting" airborne laser altimeter that is used to measure land surface features such as topography and vegetation canopy height. This instrument has to date flown a number of times aboard the NASA P3 aircraft acquiring data at a number of sites in the Mid-Atlantic region. This instrument pulses a relatively low-powered laser at a very high rate (10 kHz) and then measures the time-of-flight of discrete returns from the target surface. The instrument then bins these measurements into a two-dimensional array (vertical height vs. horizontal ground track) and selects the most likely signal path through the array. Return data that does not correspond to the selected signal path are classified as noise returns and are then discarded. The MMLA signal extraction algorithm is very compute intensive in that a score must be computed for every possible path through the two dimensional array in order to select the most likely signal path. Given a typical array size with 50 x 6, up to 33 arrays must be processed per second. And for each of these arrays, roughly 12,000 individual paths must be scored. Furthermore, the number of paths increases exponentially with the horizontal size of the array, and linearly with the vertical size. Yet, increasing the horizontal and vertical sizes of the array offer science advantages such as improved range, resolution, and noise rejection. Due to the volume of return data and the compute intensive signal extraction algorithm, the existing PC-based MMLA data system has been unable to perform signal extraction in real-time unless the array is limited in size to one column, This

  1. 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.

  2. Assimilation of Altimeter Data into a Quasigeostrophic Model of the Gulf Stream System. Part 1; Dynamical Considerations

    Science.gov (United States)

    Capotondi, Antonietta; Malanotte-Rizzoli, Paola; Holland, William R.

    1995-01-01

    The dynamical consequences of constraining a numerical model with sea surface height data have been investigated. The model used for this study is a quasigeostrophic model of the Gulf Stream region. The data that have been assimilated are maps of sea surface height obtained as the superposition of sea surface height variability deduced from the Geosat altimeter measurements and a mean field constructed from historical hydrographic data. The method used for assimilating the data is the nudging technique. Nudging has been implemented in such a way as to achieve a high degree of convergence of the surface model fields toward the observations. The assimilation of the surface data is thus equivalent to the prescription of a surface pressure boundary condition. The authors analyzed the mechanisms of the model adjustment and the characteristics of the resultant equilibrium state when the surface data are assimilated. Since the surface data are the superposition of a mean component and an eddy component, in order to understand the relative role of these two components in determining the characteristics of the final equilibrium state, two different experiments have been considered: in the first experiment only the climatological mean field is assimilated, while in the second experiment the total surface streamfunction field (mean plus eddies) has been used. It is shown that the model behavior in the presence of the surface data constraint can be conveniently described in terms of baroclinic Fofonoff modes. The prescribed mean component of the surface data acts as a 'surface topography' in this problem. Its presence determines a distortion of the geostrophic contours in the subsurface layers, thus constraining the mean circulation in those layers. The intensity of the mean flow is determined by the inflow/outflow conditions at the open boundaries, as well as by eddy forcing and dissipation.

  3. Assimilation of Altimeter Data into a Quasigeostrophic Model of the Gulf Stream System. Part 2; Assimilation Results

    Science.gov (United States)

    Capotondi, Antonietta; Holland, William R.; Malanotte-Rizzoli, Paola

    1995-01-01

    The improvement in the climatological behavior of a numerical model as a consequence of the assimilation of surface data is investigated. The model used for this study is a quasigeostrophic (QG) model of the Gulf Stream region. The data that have been assimilated are maps of sea surface height that have been obtained as the superposition of sea surface height variability deduced from the Geosat altimeter measurements and a mean field constructed from historical hydrographic data. The method used for assimilating the data is the nudging technique. Nudging has been implemented in such a way as to achieve a high degree of convergence of the surface model fields toward the observations. Comparisons of the assimilation results with available in situ observations show a significant improvement in the degree of realism of the climatological model behavior, with respect to the model in which no data are assimilated. The remaining discrepancies in the model mean circulation seem to be mainly associated with deficiencies in the mean component of the surface data that are assimilated. On the other hand, the possibility of building into the model more realistic eddy characteristics through the assimilation of the surface eddy field proves very successful in driving components of the mean model circulation that are in relatively good agreement with the available observations. Comparisons with current meter time series during a time period partially overlapping the Geosat mission show that the model is able to 'correctly' extrapolate the instantaneous surface eddy signals to depths of approximately 1500 m. The correlation coefficient between current meter and model time series varies from values close to 0.7 in the top 1500 m to values as low as 0.1-0.2 in the deep ocean.

  4. In Orbit Performance of Si Avalanche Photodiode Single Photon Counting Modules in the Geoscience Laser Altimeter System on ICESat

    Science.gov (United States)

    Sun, X.; Jester, P. L.; Palm, S. P.; Abshire, J. B.; Spinhime, J. D.; Krainak, M. A.

    2006-01-01

    Si avalanche photodiode (APD) single photon counting modules (SPCMs) are used in the Geoscience Laser Altimeter System (GLAS) on Ice, Cloud, anti land Elevation Satellite (ICESat), currently in orbit measuring Earth surface elevation and atmosphere backscattering. These SPCMs are used to measure cloud and aerosol backscatterings to the GLAS laser light at 532-nm wavelength with 60-70% quantum efficiencies and up to 15 millions/s maximum count rates. The performance of the SPCMs has been closely monitored since ICESat launch on January 12, 2003. There has been no measurable change in the quantum efficiency, as indicated by the average photon count rates in response to the background light from the sunlit earth. The linearity and the afterpulsing seen from the cloud and surface backscatterings profiles have been the same as those during ground testing. The detector dark count rates monitored while the spacecraft was in the dark side of the globe have increased almost linearly at about 60 counts/s per day due to space radiation damage. The radiation damage appeared to be independent of the device temperature and power states. There was also an abrupt increase in radiation damage during the solar storm in 28-30 October 2003. The observed radiation damage is a factor of two to three lower than the expected and sufficiently low to provide useful atmosphere backscattering measurements through the end of the ICESat mission. To date, these SPCMs have been in orbit for more than three years. The accumulated operating time to date has reached 290 days (7000 hours). These SPCMs have provided unprecedented receiver sensitivity and dynamic range in ICESat atmosphere backscattering measurements.

  5. A high resolution salinity time series 1993-2012 in the North Atlantic from Argo and Altimeter data

    Science.gov (United States)

    Stendardo, I.; Rhein, M.; Hollmann, R.

    2016-04-01

    The study of salinity changes has been hampered by the lack of temporal and spatial resolution of the observations. In order to improve the spatial and temporal distribution of salinity observations, we used the Gravest Empirical Mode (GEM) technique to calculate high-resolution salinity distributions as a function of dynamic height for the period 1993-2012. This technique combined Argo and altimeter data to exploit the relationship between T/S profiles and dynamic height in the North Atlantic. The method was valid in the upper 700 m mainly at and near the pathways of the North Atlantic Current (NAC), but failed in regions with weak stratification or with ambiguities in the T/S relationships. Coherent, multiannual large-scale variability was observed, with many features present in all regions, albeit with weaker amplitudes in the eastern basins. Some of the interannual features in the northeastern Atlantic basins were unrelated to the variability further south and west, pointing to an occasional advection of subtropical water in the eastern Atlantic. Origin and advection of salinity anomalies with the NAC from the North American Basin into the western subpolar North Atlantic are correlated with the state of the North Atlantic Oscillation (NAO) and dampened by the surface freshwater fluxes. Other mechanisms influencing the salinity pattern are the changing location of the subpolar front, also related to the NAO. The large multiyear variability in the 20 year time series obscured any potential trends caused by global warming. Only the Rockall Trough showed a salinity increase of 0.03 per decade.

  6. Lunar Impact Basins: Stratigraphy, Sequence and Ages from Superposed Impact Crater Populations Measured from Lunar Orbiter Laser Altimeter (LOLA) Data

    Science.gov (United States)

    Fassett, C. I.; Head, J. W.; Kadish, S. J.; Mazarico, E.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

    2012-01-01

    Impact basin formation is a fundamental process in the evolution of the Moon and records the history of impactors in the early solar system. In order to assess the stratigraphy, sequence, and ages of impact basins and the impactor population as a function of time, we have used topography from the Lunar Orbiter Laser Altimeter (LOLA) on the Lunar Reconnaissance Orbiter (LRO) to measure the superposed impact crater size-frequency distributions for 30 lunar basins (D = 300 km). These data generally support the widely used Wilhelms sequence of lunar basins, although we find significantly higher densities of superposed craters on many lunar basins than derived by Wilhelms (50% higher densities). Our data also provide new insight into the timing of the transition between distinct crater populations characteristic of ancient and young lunar terrains. The transition from a lunar impact flux dominated by Population 1 to Population 2 occurred before the mid-Nectarian. This is before the end of the period of rapid cratering, and potentially before the end of the hypothesized Late Heavy Bombardment. LOLA-derived crater densities also suggest that many Pre-Nectarian basins, such as South Pole-Aitken, have been cratered to saturation equilibrium. Finally, both crater counts and stratigraphic observations based on LOLA data are applicable to specific basin stratigraphic problems of interest; for example, using these data, we suggest that Serenitatis is older than Nectaris, and Humboldtianum is younger than Crisium. Sample return missions to specific basins can anchor these measurements to a Pre-Imbrian absolute chronology.

  7. Deep Ocean Warming Assessed from Altimeters, GRACE, 3 In-situ Measurements, and a Non-Boussinesq OGCM

    Science.gov (United States)

    Song, Y. Tony; Colberg, Frank

    2011-01-01

    Observational surveys have shown significant oceanic bottom water warming, but they are too spatially and temporally sporadic to quantify the deep ocean contribution to the present-day sea level rise (SLR). In this study, altimetry sea surface height (SSH), Gravity Recovery and Climate Experiment (GRACE) ocean mass, and in situ upper ocean (0-700 m) steric height have been assessed for their seasonal variability and trend maps. It is shown that neither the global mean nor the regional trends of altimetry SLR can be explained by the upper ocean steric height plus the GRACE ocean mass. A non-Boussinesq ocean general circulation model (OGCM), allowing the sea level to rise as a direct response to the heat added into the ocean, is then used to diagnose the deep ocean steric height. Constrained by sea surface temperature data and the top of atmosphere (TOA) radiation measurements, the model reproduces the observed upper ocean heat content well. Combining the modeled deep ocean steric height with observational upper ocean data gives the full depth steric height. Adding a GRACE-estimated mass trend, the data-model combination explains not only the altimetry global mean SLR but also its regional trends fairly well. The deep ocean warming is mostly prevalent in the Atlantic and Indian oceans, and along the Antarctic Circumpolar Current, suggesting a strong relation to the oceanic circulation and dynamics. Its comparison with available bottom water measurements shows reasonably good agreement, indicating that deep ocean warming below 700 m might have contributed 1.1 mm/yr to the global mean SLR or one-third of the altimeter-observed rate of 3.11 +/- 0.6 mm/yr over 1993-2008.

  8. Validation of Sea Level Data in the East Asian Marginal Seas: Comparison between TOPEX/POSEIDON Altimeter and In-Situ Tide Gauges

    Institute of Scientific and Technical Information of China (English)

    Yong-HoonYOUN; ImSangOH; Ki-HyunKIM; Young-HyangPARK; JongWooKIM

    2003-01-01

    In an effort to assess the reliability of satellite altimeter systems, the authors conduct a comparative analysis of sea level data that were collected from the TOPEX/POSEIDON (T/P) altimeter and 10 tide gauges (TG) near the satellite passing ground tracks. The analysis is made using datasets collected from marginal sea regions surrounding the Korean Peninsula at T/P cycles of 2 to 230, which correspond to October 1992 to December 1998. Proper treatment of tidal errors is a very critical step in data processing because the study area has very strong tide. When the T/P data are processed, the procedures of Park and Gamberoni (1995) are adapted to reduce errors associated with the tide. When the T/P data are processed in this way, the alias periods of M2, $2, and K1 constituents are found to be 62.1, 58.7, and 173 days repectively. The compatibility of the T/P and TG datasets are examined at various filtering periods.The results indicate that the low-frequency signals of the T/P data can be interpreted more safely with longer filtering periods (such as up to the maximum selected value of 200 days). When RMS errors for the 200-day low-pass filter period are compared with all 10 tidal stations, the values span the range of 2.8 to 6.7 cm. The results of a correlation analysis for this filtering period also show a strong agreement between the T/P and TG datasets across all stations investigated (e.g., p-values consistently less than 0.001). Hence according to the analysis, the conclusion is made that the analysis of surface sea level using satellite altimeter data can be made safely with reasonably extended filtering periods such as 200 days.

  9. New Measurements of Aerosol Vertical Structure from Space using the NASA Geoscience Laser Altimeter System (GLAS): Applications for Aerosol Transport Models

    Science.gov (United States)

    Welton, E. J.; Spinhime, J.; Palm, S.; Hlavka, D.; Hart, W.; Ginoux, P.; Chin, M.; Colarco, P.

    2004-01-01

    In the past, satellite measurements of aerosols have only been possible using passive sensors. Analysis of passive satellite data has lead to an improved understanding of aerosol properties, spatial distribution, and their effect on the earth,s climate. However, direct measurement of aerosol vertical distribution has not been possible using only the passive data. Knowledge of aerosol vertical distribution is important to correctly assess the impact of aerosol absorption, for certain atmospheric correction procedures, and to help constrain height profiles in aerosol transport models. On January 12,2003 NASA launched the first satellite-based lidar, the Geoscience Laser Altimeter System (GLAS), onboard the ICESat spacecraft. GLAS is both an altimeter and an atmospheric lidar, and obtains direct measurements of aerosol and cloud heights. Here we show an overview of GLAS, provide an update of its current status, and discuss how GLAS data will be useful for modeling efforts. In particular, a strategy of using GLAS to characterize the height profile of dust plumes over source regions will be presented, along with initial results. Such information can be used to validate and improve output from aerosol transport models. Aerosol height profile comparisons between GLAS and transport models will be shown for regions downwind of aerosol sources. We will also discuss the feasibility of assimilating GLAS profiles into the models in order to improve their output.

  10. A fixed full-matrix method for determining ice sheet height change from satellite altimeter: an ENVISAT case study in East Antarctica with backscatter analysis

    Science.gov (United States)

    Yang, Yuande; Hwang, Cheinway; E, Dongchen

    2014-09-01

    A new method, called the fixed full-matrix method (FFM), is used to compute height changes at crossovers of satellite altimeter ground tracks. Using the ENVISAT data in East Antarctica, FFM results in crossovers of altimeter heights that are 1.9 and 79 times more than those from the fixed half method (FHM) and the one-row method (ORM). The mean standard error of height changes is about 14 cm from ORM, which is reduced to 7 cm by FHM and to 3 cm by FFM. Unlike FHM, FFM leads to uniform errors in the first-half and second-half height-change time series. FFM has the advantage in improving the accuracy of the change of height and backscattered power over ORM and FHM. Assisted by the ICESat-derived height changes, we determine the optimal threshold correlation coefficient (TCC) for a best correction for the backscatter effect on ENVISAT height changes. The TCC value of 0.92 yields an optimal result for FFM. With this value, FFM yields ENVISAT-derived height change rates in East Antarctica mostly falling between and 3 cm/year, and matching the ICESat result to 0.94 cm/year. The ENVISAT result will provide a constraint on the current mass balance result along the Chinese expedition route CHINARE.

  11. Design of Parameters for Missile-borne Laser Altimeter with Dual-wavelength Outputs%弹载双波长输出激光高度计参数设计

    Institute of Scientific and Technical Information of China (English)

    张翼飞; 杨辉; 王孝通

    2011-01-01

    采用雷达高度表的巡航导弹地形匹配导航系统易受电子干扰影响而失效.针对该问题,提出应用红外/蓝绿双波长输出的激光高度计代替雷达高度表进行地形探测的方案,该方案还可解决巡航导弹在跨海攻击时无法制导的难题.根据激光测高和测深方程及探测器输出信噪比计算公式,采用数字仿真的方法对高度计性能进行了评价.仿真结果表明,红外和蓝绿激光的峰值功率分别达到50 kW和450 kW左右时,可基本满足测高和测深的要求,并确定了激光高度计单脉冲能量、脉冲宽度、脉冲重复频率、光束发散角等参数值.%The terrain matching navigation system with radar altimeter is prone to be influenced by electronic interference, so the laser altimeter with infra-red/blue-green dual-wavelength outputs was designed to replace the radar altimeter for cruise missile. Furthermore, the hard problem could be resolved, i.e., the radar altimeter couldn't work over the sea, but the laser altimeter could. Based on laser altimetry/bathymetry equations and the output SNR expression, the digital simulation calculation was used to assess the performance of the laser altimeter. The simulation results show: the laser altimeter can satisfy the need of altimetry and bathymetry when the peak power of infra-red and blue-green pulses respectively reach 50 kW and 450 kW. At the same time, such parameters can be decided, including pulse energy, pulse width, pulse repetition rate, and divergence angle of laser beam, etc.

  12. 星载激光高度计几何定位误差传播分析%Study on Error Propagation of Space-borne Laser Altimeter Geometric Positioning

    Institute of Scientific and Technical Information of China (English)

    岳春宇; 何红艳; 鲍云飞; 邢坤; 周楠

    2014-01-01

    As a way of acquiring elevation with high accuracy, space-borne laser altimeter improves the capability of 3-dimensional cartography of satellite optical remote sensing imagery. However, the plane accu-racy of space-borne laser altimeter is not so high as its elevation accuracy. Accordingly, the error sources and their influences on space-borne laser altimeter geometric positioning are studied in this paper. The geometric positioning of space-borne laser altimeter is first modeled, then error propagation of the model is studied, and the main error sources of space-borne laser altimeter geometric positioning are obtained. Finally the influences of each error sources on space-borne laser altimeter geometric positioning are analysed, which can be as the references for space-borne laser altimeter designing and application.%星载激光高度计能够获取高精度的地面高程信息,可作为卫星光学遥感影像三维测图的补充。星载激光高度计的高程测量精度很高,但是平面精度较低。为了能够更有效的利用星载激光测高数据,需要研究星载激光高度计几何定位的误差源及其对定位精度的影响。文章从星载激光高度计几何定位模型出发,推导了星载激光高度计定位误差传播模型,得到影响星载激光高度计测高数据定位精度的主要误差源,并分析了各误差源对定位精度的影响,可以为星载激光高度计的设计和应用提供一定参考。

  13. Performance Considerations for the SIMPL Single Photon, Polarimetric, Two-Color Laser Altimeter as Applied to Measurements of Forest Canopy Structure and Composition

    Science.gov (United States)

    Dabney, Philip W.; Harding, David J.; Valett, Susan R.; Vasilyev, Aleksey A.; Yu, Anthony W.

    2012-01-01

    The Slope Imaging Multi-polarization Photon-counting Lidar (SIMPL) is a multi-beam, micropulse airborne laser altimeter that acquires active and passive polarimetric optical remote sensing measurements at visible and near-infrared wavelengths. SIMPL was developed to demonstrate advanced measurement approaches of potential benefit for improved, more efficient spaceflight laser altimeter missions. SIMPL data have been acquired for wide diversity of forest types in the summers of 2010 and 2011 in order to assess the potential of its novel capabilities for characterization of vegetation structure and composition. On each of its four beams SIMPL provides highly-resolved measurements of forest canopy structure by detecting single-photons with 15 cm ranging precision using a narrow-beam system operating at a laser repetition rate of 11 kHz. Associated with that ranging data SIMPL provides eight amplitude parameters per beam unlike the single amplitude provided by typical laser altimeters. Those eight parameters are received energy that is parallel and perpendicular to that of the plane-polarized transmit pulse at 532 nm (green) and 1064 nm (near IR), for both the active laser backscatter retro-reflectance and the passive solar bi-directional reflectance. This poster presentation will cover the instrument architecture and highlight the performance of the SIMPL instrument with examples taken from measurements for several sites with distinct canopy structures and compositions. Specific performance areas such as probability of detection, after pulsing, and dead time, will be highlighted and addressed, along with examples of their impact on the measurements and how they limit the ability to accurately model and recover the canopy properties. To assess the sensitivity of SIMPL's measurements to canopy properties an instrument model has been implemented in the FLIGHT radiative transfer code, based on Monte Carlo simulation of photon transport. SIMPL data collected in 2010 over

  14. Simulation Analysis of Spaceborne Laser Altimeter Echo Signal%星载激光测高仪回波信号仿真分析

    Institute of Scientific and Technical Information of China (English)

    朱近; 孙世君

    2013-01-01

    为研究不同地形、地物对激光回波信号的变化状况和星载激光测高仪的实际测量精度等问题,文章采用计算机仿真技术建立了立体地物数字模型、激光脉冲数学模型和噪声信号模型;设计了针对光栅网格地形数据的激光回波近似算法,避免了三角面片的划分、面片间遮挡测试和消隐处理,简化了计算过程.对理想平面目标的激光回波仿真结果与理论结果一致.利用在Matlab环境下开发的仿真程序,对平面型、阶梯型和高斯起伏型3种典型地物模型进行了仿真实验,估算了星载激光测高仪对不同目标区域的实际测量精度.%In this paper, the computer simulation technology is used,to research the laser echo signals change in different terrains and the actual measurement accuracy of laser altimeter are researched. Three-dimensional digital models in the terrains and mathematical models of the laser pulse and noise signal are established. The laser echo approximation algorithm for grid terrain data is innovated, which can avoid the division of the triangular facets, the test of facet blocks and blanking processing to simplify the calculation process. The simulated results of laser echo for the ideal planar targets are identical with the theoretical results.The simulation program is developed and run in the Matlab environment. It can simulate the spaceborne laser altimeter echo signals in a variety of conditions, and the results can be applied in quantitative analysis and study. Three typical terrain models of plane, stairs and Gaussian Wave types are designed in simulation experiments, and the actual measurement accuracy of spaceborne laser altimeter for the different areas are estimated.

  15. Cryosat-2数据的大地水准面分辨能力研究%Estimation of the Resolution Capability of the Cryosat-2 Altimeter

    Institute of Scientific and Technical Information of China (English)

    张胜军; 金涛勇; 褚永海; 孔祥雪

    2016-01-01

    Cryosat-2卫星首次提供了369 d重复周期的密集漂移轨道测高数据,可用于改进海洋重力场反演精度和分辨率.从信号和噪声两个角度对其沿轨数据进行自回归建模,给出了一种以重复轨道观测序列差分加和确定信号谱和噪声谱,并比较分析测高数据大地水准面分辨能力的方法(称为信噪比分析法).对全球5个试验区域采用谱关联性法和信噪比法来分析Cryosat-2沿轨数据的大地水准面,其分辨能力约为23~33 km,均值约为27 km,优于单周期Geosat/ERM、ERS-1/ERM和T/P数据的38 km、43 km和37 km.研究表明,Cryosat-2数据具有更低噪声水平和更高大地水准面信号辨识度,可以为构建海洋重力场模型提供更高分辨率的短波信息.%The cryosat-2 satellite recently published its first altimeter dataincluding periodically drifting orbit and dense ground tracks.These data can be used to improve the accuracy and resolution of the marine gravity field.In this paper,we constructs auto-regressive models of the altimeter data series by considering two aspects of signal and noise,and propose a new method called the signal-to-noise ratio analytical method for estimating the resolution capability of Cryosat-2 data.in five test cases,this new method offers a consistent alternative to the traditional spectral correlation method.The resolution capability of Cryostat-2 altimeter data from single cycle is in the range of 23 km~33 km,with an average value of 27 kn,and better than 38 km,43 km and 37 km of the Geosat/ERM,ERS 1/ERM and T/P data.This result shows that the Cryosat 2 altimeter data has a lower noise level and a higher geoid signal recognition.Therefore,it is reasonable to believe that the Cryostat-2 could provide shorter wavelength information for the construction of marine gravity field with higher resolution.

  16. Stratigraphy, Sequence, and Crater Populations of Lunar Impact Basins from Lunar Orbiter Laser Altimeter (LOLA) Data: Implications for the Late Heavy Bombardment

    Science.gov (United States)

    Fassett, C. I.; Head, J. W.; Kadish, S. J.; Mazarico, E.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

    2012-01-01

    New measurements of the topography of the Moon from the Lunar Orbiter Laser Altimeter (LOLA)[1] provide an excellent base-map for analyzing the large crater population (D.20 km)of the lunar surface [2, 3]. We have recently used this data to calculate crater size-frequency distributions (CSFD) for 30 lunar impact basins, which have implications for their stratigraphy and sequence. These data provide an avenue for assessing the timing of the transitions between distinct crater populations characteristic of ancient and young lunar terrains, which has been linked to the late heavy bombardment (LHB). We also use LOLA data to re-examine relative stratigraphic relationships between key lunar basins.

  17. Comparison of TOPEX/POSEIDON altimeter derived wave period with ocean buoy data in the East China Sea and South China Sea

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Altimeter wave period data obtained from continental shelf seas are analyzed in this paper.Empirical models are introduced for zero up-crossing and peak wave period calculation with TOPEX/POSEIDON data. Their performances are assessed using independent validation dataset in four sites in the open ocean of China. To provide more accurate wave period estimation, new coefficients are applied to reliable in situ data. Comparison of our estimated the wave periods with new linear calibrations based on independent data of Seapac 2100 deployed in the East China Sea and South China Sea showed that the accuracy was improved over estimates determined from earlier empirical models. Regional analysis indicated that the wave period model works better under wind sea condition.

  18. Full-waveform, Laser Altimeter Measurements of Vegetation Vertical Structure and Sub-canopy Topography in Support of the North American Carbon Program

    Science.gov (United States)

    Blair, B.; Hofton, M.; Rabine, D.; Padden, P.; Rhoads, J.

    2004-01-01

    Full-waveform, scanning laser altimeters (i.e. lidar) provide a unique and precise view of the vertical and horizontal structure of vegetation across wide swaths. These unique laser altimeters systems are able to simultaneously image sub-canopy topography and the vertical structure of any overlying vegetation. These data reveal the true 3-D distribution of vegetation in leaf-on conditions enabling important biophysical parameters such as canopy height and aboveground biomass to be estimated with unprecedented accuracy. An airborne lidar mission was conducted in the summer of 2003 in support of preliminary studies for the North America Carbon Program. NASA's Laser Vegetation Imaging Sensor (LVIS) was used to image approximately 2,000 sq km in Maine, New Hampshire, Massachusetts and Maryland. Areas with available ground and other data were included (e.g., experimental forests, FLUXNET sites) in order to facilitate numerous bio- and geophysical investigations. Data collected included ground elevation and canopy height measurements for each laser footprint, as well as the vertical distribution of intercepted surfaces (i.e. the return waveform). Data are currently available at the LVIS website (http://lvis.gsfc.nasa.gov/). Further details of the mission, including the lidar system technology, the locations of the mapped areas, and examples of the numerous data products that can be derived from the return waveform data products are available on the website and will be presented. Future applications including potential fusion with other remote sensing data sets and a spaceborne implementation of wide-swath, full-waveform imaging lidar will also be discussed.

  19. 无线电/激光高度表复合测高技术研究%Research into Composite Altimetry Technology Based on Radio/Laser Altimeter

    Institute of Scientific and Technical Information of China (English)

    毕开波; 姚申茂; 谢春思

    2016-01-01

    无线电高度表和激光高度表是巡航导弹上用于探测地形高度的2种主要传感器,激光高度表具有探测精度高、抗电磁干扰能力强的优点;而无线电高度表不受天气和环境的影响,可全天候使用。因而,将无线电高度表与激光高度表进行复合探测,有利于提高地形探测精度,并增强系统抗干扰能力。在高度表测量方程的基础上,基于卡尔曼滤波公式和简单融合算法,给出了无线电/激光多传感器的滤波及融合模型;并利用M atlab对多传感器融合效果进行了仿真。仿真结果表明:基于多传感器融合的高度测量系统的精度比单个传感器的测量精度要高,且系统的稳定性和可靠性更强,所设计的基于无线电/激光高度表多传感器数据融合的高度测量算法是有效的。%Radio altimeter and laser altimeter are two main sensors which is applied to detect terrain altitude of the cruise missiles .Laser altimeter has high detection precision ,strong anti-electromag-netism-jamming ability .However radio altimeter can work under the condition of all-weather , which is immune for weather and environment .Detection system combining radio altimeter with la-ser altimeter can improve terrain detection precision and anti-jamming ability .On the basis of altim-eter measuring equation ,this paper presents radio/laser multi-sensor filtering model and fusion model based on Kalman filtering formula and simple fusion arithmetic ;simulates the fusion effect of multi-sensor by means of Matlab .The simulation results show that the altimetry system based on multi-sensor fusion has higher detection precision than single sensor ,and has good stability and re-liability ,the multi-sensor data fusion altimetry arithmetic based on radio altimeter/laser is effec-tive .

  20. RESEARCH ON LASER ALTIMETER'S FIELD OF VIEW%激光高度计探测视场角的测试研究

    Institute of Scientific and Technical Information of China (English)

    狄慧鸽; 王建宇; 方抗美; 舒嵘

    2009-01-01

    激光高度计的探测视场角是影响系统性能的一个重要参数,论述了视场角对系统探测性能的影响.受到回波杂散光和探测器响应不均匀性的影响,激光高度计的探测视场会随回波能量的改变而发生变化,而回波能量随探测距离发生变化.本文提出了测试激光高度计整机探测视场角的方法,并且模拟了系统在实际工作状态时的情况;对于有近程延时保护的系统,给出了测试的解决方案.对设计视场角为1.5mrad的激光高度计进行了测试,调节模拟回波信号能量至5×10~(-8)W,模拟其工作距离为200km时的工作状态,得出系统的探测视场角为1.46mrad.%Laser altimeter' s field of view (FOV) is an important parameter affecting system' s performance.The effect of the field of view on the detection performance of system was discussed.Because of the straylight and the sensor' s nonunifor-mity, the FOV changes as the echo' s power changes.At the same time the echo' s power will be varied with the detecting distance.The testing way of detecting FOV was put forward, and the factual working status was simulated.For system with inner short-range delay protecting circuit, a new method was brought forward.A laser altimeter with the FOV of 1.5mrad was tested.The FOV of the system is 1.46mrad when its detecting distance is 200km and the echo's power is 5 ×10~(-8)W.

  1. Algorithm of laser altimeter reflecting waveform based on Gaussian decomposition%激光测高仪高斯回波分解算法

    Institute of Scientific and Technical Information of China (English)

    赵欣; 张毅; 张黎明; 王相京; 赵平建; 涂碧海

    2012-01-01

    地球表面地形的复杂多样可对激光测高仪回波波形产生显著影响,造成多峰叠加形状,该波形通过经典的阈值比较或重心点等算法很难精确得到激光足印内每个反射面的海拔高度.通过高斯分解法把测高回波波形分解成一系列连续的高斯波形,通过拟合得到每个高斯波形的宽度、中心点、幅度等基本参数来估计激光足印内起伏地形的不同反射面的海拔高度.将该算法应用于激光测高仪原理样机,并通过采集不同地形的多模回波数据对该算法进行了验证.%The reflecting waveform will interact with complex terrain on the earth and cause superposition peak shape. The classic algorithm of threshold comparison or focus point is difficult to accurately obtain the desired reflecting surface elevation. To decompose a return waveform into a series of Gaussian components, the number of the Gaussian components and the position, half-width and amplitude of each Gaussian component were obtained. From these basic parameters, the topographic information as the elevations and distributions, the surface slope and roughness, and the albedos of distinct reflecting surfaces within the laser footprint were got by fitting. At last, the Gaussian decomposition method by a prototype of laser altimeter which was used to collect the signal in the country was validated. The results show that this method is adapted to fit the echo signal of laser altimeter on different earth surface.

  2. CE-1立体相机与激光高度计数据联合平差%Combined Adjustment of CE-1 Stereo Camera Image and Laser Altimeter Data

    Institute of Scientific and Technical Information of China (English)

    赵双明; 冉晓雅; 付建红; 郭秋燕

    2014-01-01

    CE‐1三线阵立体相机和激光高度计主要用于获取月球形貌信息。CE‐1沿轨运动过程中,可同时获取高分辨率的三线阵扫描影像和高精度的激光测高数据。在分析立体影像与激光高度计数据不一致性的基础上,为提高定位精度,将激光测距数据引入三线阵立体影像光束法平差处理。本文提出一种改进的外定向参数模型,采用3阶Lagrange多项式模型(LPM)建立外定向线元素内插模型,采用四元数球面线性内插建立外定向角元素模型,并根据改进模型建立激光高度计数据与影像数据的联合平差数学模型。试验表明,本文立体相机和激光高度计数据联合平差模型是有效的。%CE‐1 carries two types of mapping equipments:CE‐1 Lunar laser altimeter and three‐line‐array stereo camera .Laser altimeter collects accurate laser altimetry data over the Lunar surface ,while stereo camera acquires high resolution three‐line‐array CCD images .By means of an inconsistency analysis of stereo image and laser altimeter data ,the CE‐1 Laser altimeter ranges are expected to be incorporated into the bundle adjustment as measurements to improve accuracy of CE‐1 image photogrammetric reduction .An improved exterior orientation model is proposed in which exterior orientation line element interpol ation model is established with the 3 order Lagrange polynomi al and the attitude interpol ation model is established using spherical linear interpolation of quaternion .Secondly , a bundle combined adjustment of CE‐1 stereo camera image and laser altimeter data is developed and implemented in this paper .experiment results show that the bundle combined adjustment model is effective .

  3. Frequency of tropical precipitating clouds as observed by the Tropical Rainfall Measuring Mission Precipitation Radar and ICESat/Geoscience Laser Altimeter System

    Science.gov (United States)

    Casey, Sean P. F.; Dessler, Andrew E.; Schumacher, Courtney

    2007-07-01

    Convective clouds in the tropics can be grouped into three categories: shallow clouds with cloud top heights near 2 km above the surface, midlevel congestus clouds with tops near the 0°C level, and deep convective clouds capped by the tropopause. This trimodal distribution is visible in cloud data from the Geoscience Laser Altimeter System (GLAS), carried aboard the Ice, Cloud, and land Elevation Satellite (ICESat), as well as in precipitation data from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR). Fractional areal coverage (FAC) data is calculated at each of the three levels to describe how often optically thick clouds or precipitation are seen at each level. By dividing the FAC of TRMM PR-observed precipitation by the FAC of thick GLAS/ICESat-observed clouds, we derive the fraction of clouds that are precipitating. We find that the tropical mean precipitating cloud fraction is low: 3.7% for shallow clouds, 6.5% for midlevel clouds, and 24.1% for deep clouds.

  4. The meandering Gulf Stream as seen by the Geosat altimeter - Surface transport, position, and velocity variance from 73 deg to 46 deg W

    Science.gov (United States)

    Kelly, Kathryn A.

    1991-01-01

    Results are presented of an analysis of the surface geostrophic velocity field for the Gulf Stream region for the position, structure, and surface transport of the Gulf Stream for 2.5 yr of the Geosat altimeter Exact Repeat Mission. Synthetic data using a Gaussian velocity profile were generated and fit to the sea surface residual heights to create a synthetic mean sea surface height field and profiles of absolute geostrophic currents. An analysis of the model parameters and the actual geostrophic velocity profiles revealed two different flow regimes for the Gulf Stream connected by a narrow transition region coincident with the New England Seamount Chain. The upstream region was found to exhibit relatively straight Gulf Stream paths, long Eulerian time scales, and eastward propagating meanders. The downstream region had more large meanders, no consistent propagation direction, and shorter Eulerian time scales. A 25-percent reduction in surface transport occurred in the transition region, with a corresponding reduction in current speed and no change in Gulf Stream width.

  5. Influence of noise on range error for satellite laser altimeter%噪声对星载激光测高仪测距误差的影响

    Institute of Scientific and Technical Information of China (English)

    周辉; 李松; 王良训; 郑国兴

    2015-01-01

    噪声是影响星载激光测高仪测距误差的重要因素。根据星载激光测高仪接收脉冲回波和噪声的分布特点,推导出接收脉冲回波信号时间重心的方差的理论表达形式,建立了噪声对激光测距误差的影响模型。基于激光测距误差最小化的原则,提出了一种星载激光测高仪低通滤波器的优化设计方法。以Geosicence Laser Altimeter System(GLAS)激光测高仪基本测量参数为输入条件,仿真分析了激光测距误差和低通滤波器均方根脉宽的优化结果的分布规律。对于倾斜度为0º~40º且粗糙度为0~15 m范围内的目标而言,噪声所导致的激光测距误差范围为0.28~32.49 cm,相应地,低通滤波器均方根脉宽优化值的范围为1.4~57.4 ns。针对倾斜度在1º范围内的目标,解算得到GLAS星载激光测高仪低通滤波器均方根脉宽为2.2 ns,这与其实际公布的2 ns很接近。同时,低通滤波器的优化结果所对应的激光测距误差发生大幅减小,其最大值减小至10.93 cm,减小幅度接近3倍。结果表明,噪声是影响星载激光测高仪测距误差的重要因素,合理设计低通滤波器的参数可以消除其部分影响,这对于星载激光测高仪的硬件设计和性能评估具有一定实际应用价值。%Noise is an important factor of affecting range error for satellite laser altimeter with recording waveform. According to the distribution characteristic of received pulse signal and noise, the theoretical expression form about variance of time-centroid for received pulse signal was deduced. Thereby, the impact model of noise on range error was built-up. Base on the principle of minimizing range error, an optimization design method for low-pass filter was put forward. In terms of basic measurement parameters for Geoscience Laser Altimeter System(GLAS), the distribution regularities of range error and RMS pulse width for low-pass filter were

  6. Vegetation and topography mapping with an airborne laser altimeter using a high-efficiency laser and a scannable field-of-view telescope

    Energy Technology Data Exchange (ETDEWEB)

    Blair, J.B. [NASA Goddard Space Flight Center, Greenbelt, MD (United States); Coyle, D. B.

    1996-11-01

    A medium altitude airborne laser altimeter system has been designed and developed at NASA`s Goddard Space Flight Center to map surface height distributions (SHDs) across wide, nadir-centered, swaths. Instrument performance, data product quality, and the satellite-like footprint sizes are maintained using novel laser output and receiver field of view (FOV) scanning techniques. The laser transmitter was custom designed and built at GSFC to achieve 10% wallplug efficiency in a compact, rugged package. The laser output pulse is 2 nsec full width half max (FWHM) at a repetition rate of 500 Hz and with 6 mJ of output power evenly split into 1.064 nm and 0.532 nm wavelengths. A multiple-pass pump scheme along with variable conductance heatpipes (VCHPs) combine to increase the laser efficiency. The telescope was custom designed to have a throughput of > 85%, 20 cm aperture, 6{degrees} potential FOV, 0.5 {degrees} instantaneous FOV that is rapidly positioned anywhere in the potential FOV within 2 msec, permitting wide-swath scanning as well as real-time nadir control of the scan swath. The return echoes are recorded using a 500 MHz, 8-bit waveform digitizer. Possible applications range from simple topographic mapping to 3-dimensional vegetation structure determination. Tree heights, canopy architecture, and surface roughness can easily be extracted from the return echo. 3 refs., 3 figs.

  7. Thickness of Proximal Ejecta from the Orientale Basin from Lunar Orbiter Laser Altimeter (LOLA) Data: Implications for Multi-Ring Basin Formation

    Science.gov (United States)

    Fassett, Caleb I.a; Head, James W.; Smith, David E.; Zuber, Maria T.; Neumann, Gregory A.

    2011-01-01

    Quantifying the ejecta distribution around large lunar basins is important to understanding the origin of basin rings, the volume of the transient cavity, the depth of sampling, and the nature of the basin formation processes. We have used newly obtained altimetry data of the Moon from the Lunar Orbiter Laser Altimeter (LOLA) instrument to estimate the thickness of ejecta in the region surrounding the Orientale impact basin, the youngest and best preserved large basin on the Moon. Our measurements yield ejecta thicknesses of approx.2900 m near the Cordillera Mountains, the topographic rim of Orientale, decaying to approx.1 km in thickness at a range of 215 km. These measurements imply a volume of ejecta in the region from the Cordillera ring to a radial range of one basin diameter of approx.2.9 x 10(exp 6)cu km and permit the derivation of an ejecta-thickness decay model, which can be compared with estimates for the volume of excavation and the size of the transient cavity. These data are consistent with the Outer Rook Mountains as the approximate location of the transient cavity s rim crest and suggest a volume of approx.4.8 x 10(exp 6)cu km for the total amount of basin ejecta exterior to this location.

  8. Use of high frequency radiometer and altimeter on board AMSU-B, AMSR-E and Altika/SARAL for observations of the Antarctic ice sheet surface.

    Science.gov (United States)

    Adodo, Fifi; Picard, Ghislain; Remy, Frederique

    2016-04-01

    Snow surface properties quickly evolved according to local weather conditions, therefore are climate change indicator. These snow surface properties such as grain size, density, accumulation rate etc... are very important for evaluation and monitoring of the impact of global warming on the polar ice sheet. In order to retrieve these snowpack properties, we explore the high frequency microwave radiometer variable( Brightness Temperature (Tb)) on the Antarctic ice sheet on-board AMSU-B , AMSR-E in combination with the ALTIKA altimeter (37GHz) waveform parameters (Backscatter coefficient, Trailing edge Slope(TeS) and Leading edge Width(LeW)). We compare the radiometer brightness temperature to calculations with the DMRT- ML radiative transfer model which simulates brightness temperature in vertical and horizontal polarizations. With some assumptions, this combination allows a good retrieval of snowpack properties. We showed positive trend of the grains size on the Antarctic plateau especially at Dome C during the two last decades. This work will provide a higher accuracy of the estimation of snowpack surfaces properties and contribute to monitoring the ice sheet surface mass balance, well constraining of meteorological and glaciological models.

  9. Computation of a new Mean Dynamic Topography for the Mediterranean Sea from model outputs, altimeter measurements and oceanographic in-situ data

    Directory of Open Access Journals (Sweden)

    M.-H. Rio

    2014-02-01

    Full Text Available The accurate knowledge of the ocean Mean Dynamic Topography (MDT is a crucial issue for a number of oceanographic applications and in some areas of the Mediterranean Sea, important limitations have been found pointing to the need of an upgrade. We present a new Mean Dynamic Topography (MDT that was computed for the Mediterranean Sea. It takes profit of improvements made possible by the use of extended datasets and refined processing. The updated dataset spans the 1993–2012 period and consists of: drifter velocities, altimetry data, hydrological profiles and model data. The methodology is similar to the previous MDT Rio et al. (2007. However, in Rio et al. (2007 no hydrological profiles had been taken into account. This has required the development of dedicated processing. A number of sensitivity studies have been carried out to obtain the most accurate MDT as possible. The main results from these sensitivity studies are the following: moderate impact to the choice of correlation scales but almost negligible sensitivity to the choice of the first guess (model solution. A systematic external validation to independent data has been made to evaluate the performance of the new MDT. Compared to previous version, SMDT-MED-2014 features shorter scales structures, which results in an altimeter velocity variance closer to the observed velocity variance and, at the same time, gives better Taylor skills.

  10. Global air-sea surface carbon dioxide transfer velocity and flux estimated using 17 a altimeter data and a new algorithm

    Institute of Scientific and Technical Information of China (English)

    YU Tan; HE Yijun; YAN Xiaohai

    2013-01-01

    The global distributions of the air-sea CO2 transfer velocity and flux are retrieved from TOPEX/Poseidon and Jason altimeter data from October 1992 to December 2009 using a combined algorithm. The 17 a average global, area-weighted, Schmidt number-corrected mean gas transfer velocity is 21.26 cm/h, and the full exploration of the uncertainty of this estimate awaits further data. The average total CO2 flux (calculated by carbon) from atmosphere to ocean during the 17 a was 2.58 Pg/a. The highest transfer velocity is in the circumpolar current area, because of constant high wind speeds and currents there. This results in strong CO2 fluxes. CO2 fluxes are strong but opposite direction in the equatorial east Pacific Ocean, because the air-sea CO2 partial pressure difference is the largest in the global oceans. The results differ from the previous studies calculated using the wind speed. It is demonstrated that the air-sea transfer velocity is very important for estimating air-sea CO2 flux. It is critical to have an accurate estimation for improving calculation of CO2 flux within climate change studies.

  11. Integrated analysis of PALSAR/Radarsat-1 InSAR and ENVISAT altimeter data for mapping of absolute water level changes in Louisiana wetlands

    Science.gov (United States)

    Kim, J.-W.; Lu, Zhiming; Lee, H.; Shum, C.K.; Swarzenski, C.M.; Doyle, T.W.; Baek, S.-H.

    2009-01-01

    Interferometric Synthetic Aperture Radar (InSAR) has been used to detect relative water level changes in wetlands. We developed an innovative method to integrate InSAR and satellite radar altimetry for measuring absolute or geocentric water level changes and applied the methodology to remote areas of swamp forest in coastal Louisiana. Coherence analysis of InSAR pairs suggested that the HH polarization is preferred for this type of observation, and polarimetric analysis can help to identify double-bounce backscattering areas in the wetland. ENVISAT radar altimeter-measured 18-Hz (along-track sampling of 417 m) water level data processed with regional stackfile method have been used to provide vertical references for water bodies separated by levees. The high-resolution (~ 40 m) relative water changes measured from ALOS PALSAR L-band and Radarsat-1 C-band InSAR are then integrated with ENVISAT radar altimetry to obtain absolute water level. The resulting water level time series were validated with in situ gauge observations within the swamp forest. We anticipate that this new technique will allow retrospective reconstruction and concurrent monitoring of water conditions and flow dynamics in wetlands, especially those lacking gauge networks. ?? 2009 Elsevier Inc.

  12. 星载激光测高仪大气干项延迟校正%Hydrostatic delay correction for satellite laser altimeter

    Institute of Scientific and Technical Information of China (English)

    马跃; 李松; 翁寅侃; 周辉

    2013-01-01

    星载激光测高仪发射的激光脉冲在通过地球大气层时发生折射,导致激光路径的延长,为了获得高精度的测距结果,必须对大气延迟进行修正;而大气干项延迟在大气延迟中占主导作用,仅由测量位置的地表大气压力决定.通过推导静态大气在非理想气体条件下的流体静力学方程,得出地表气压与位势高度有关的大气压力模型,结合NCEP基于标准大气压层的气象数据和GLAS测量的时间经纬度和高程数据,对位势高度使用4阶Runge-Kutta算法进行数值积分得出地表气压,进而计算大气干项延迟.通过该方法和NCEP地表气压估计得出的干项延迟分别与GLAS官方公布的干项延迟对比,该方法计算结果的趋势与准确程度均占优,且最大干项延迟误差小于2 cm.证明通过流体静力学方程数值积分计算地表气压的方法能够得出对星载激光测高仪较为准确的大气干项延迟.%The laser pulse transmitted by satellite laser altimeter bends for atmospheric refraction and extends the ray paths,and it is necessary to correct the atmospheric delay to get accurate ranging results.The hydrostatic delay is the major component of total zenith delay,which is only decided by surface pressure.The hydrostatic equation of static atmosphere was deduced under the condition of non-ideal gas,and surface pressure model was established relevant to geopotential height.Combined with the meteorological data of NCEP and position and elevation data of GLAS,the surface pressure was calculated by numerical integration of 4 order Runge-Kutta algorithm,and then the hydrostatic delay was obtained.Through the respective comparisons between the hydrostatic delays got by this method and the NCEP estimated surface pressure with the GLAS official results,the trend and accuracy of this method are both better with the maximum error less than 2 cm.It is concluded that the hydrostatic delay of satellite laser altimeter can

  13. Tropical cloud-top height distributions revealed by the Ice, Cloud, and Land Elevation Satellite (ICESat)/Geoscience Laser Altimeter System (GLAS)

    Science.gov (United States)

    Dessler, A. E.; Palm, S. P.; Spinhirne, J. D.

    2006-06-01

    We analyze cloud-top height data obtained at tropical latitudes between 29 September and 17 November, 2003, from the Geoscience Laser Altimeter System (GLAS), carried onboard the Ice, Cloud, and Land Elevation Satellite (ICESat). About 66% of the tropical observations show one or more cloud layers. Of those observations that do show a cloud, about half show two or more cloud layers. Maxima in the cloud-top height distribution occur in the upper troposphere, between 12 and 17 km, and in the lower troposphere, below about 4 km. A less prominent maximum occurs in the midtroposphere, between 6 and 8 km. The occurrence of cloud layers tends to be consistent with the well-known diurnal cycles of continental and oceanic convection, and we find that cloud layers tend to occur more frequently over land than ocean, except in the lower troposphere, where the opposite is true. A particular emphasis of this paper is the convection that penetrates into the so-called tropical tropopause layer (TTL). We find more frequent occurrence of thick clouds in the TTL and above the tropopause than other studies, with 3.0% and 19% of the thick and thin cloud observations, respectively, showing a cloud top in the TTL and 0.34% and 3.1% showing a cloud top above the average level of the tropopause. These values are higher than those found in other data sets and suggest that an upward revision of TTL cloud frequency might be necessary. TTL clouds are observed more frequently in the evening than in the morning and more frequently over land than over ocean.

  14. 激光测高仪的回波信号理论模型%Theoretical model for return signal of laser altimeter

    Institute of Scientific and Technical Information of China (English)

    李松; 周辉; 石岩; 郭耀

    2007-01-01

    利用菲涅尔衍射理论推导出高斯型激光脉冲的回波计算方法,建立了斜坡、阶梯和植被三种标准漫反射地物的回波模型,以GLAS(Geoscience Laser Altimeter System)系统为例,通过数值计算得到了标准漫反射地物的回波信号波形,分析了回波波形与三种地物模型参数、光束扫描角之间的关系.仿真计算结果表明:斜坡回波信号波形近似为单个高斯波形,其峰值和脉宽与斜坡倾角、光束扫描角有关;阶梯回波信号波形近似为多个高斯波形,其峰值与光斑内阶梯分布有关;波形的中心位置差与阶梯高度和光束扫描角有关;植被回波信号波形呈现出多个类高斯型,其峰值不仅与植被的位置有关,还与植被的面积有关.这些结论为地形地貌的反演及地表资源分布的分析提供了理论基础.

  15. Received Waveform Model for Satellite Laser Altimeter Measuring Ocean Surface%星载激光测高仪海洋表面回波计算的理论模型

    Institute of Scientific and Technical Information of China (English)

    马跃; 李松; 周辉; 郑国兴

    2012-01-01

    不同地表目标的模拟回波波形对测高仪系统参数设计具有重要意义,而海洋回波参数在Tsai之后很少被研究.根据菲涅耳衍射理论、海洋表面镜面反射性质以及海洋表面波高和斜率的统计规律,推导出与Tsai结果不同的近天顶方向入射时星载海洋测高仪探测器输出的回波解析表达式和回波总光子数;并用该推导结果建立了适用于激光测高仪亚毫弧度量级发散角的回波解析式.将模拟波形与地球科学激光测高系统(GLAS)真实海洋回波做对比,其能量、脉宽、振幅和形状都非常接近,误差均小于6%;分析得出海洋测高仪回波与测高系统参数和海平面上方平均风速有关,以GLAS参数为例,在风速大于12 m/s的条件下将很难收到有效海洋回波.该结论对海洋激光测高仪的系统设计参数及海平面上方风速的反演提供了重要的理论依据.%The received waveform model for different earth surfaces is significant for altimeter system design, and the model of ocean surface is rarely researched after Tsai. According to the theory of Fresnel diffraction, the character of specular reflection and statistical regularity of the ocean surface profile, the analytic expression of detector output and the average received photons are deduced which are used for ocean altimeter and different from the results of Tsai under the condition of near-normal incidence. The simulated waveform is established for laser altimeter with microradian beam divergence and compared with the real geoscience laser altimeter system (GLAS) received signal. The energy, root mean square (RMS) width, amplitude and shape are very similar and the errors between simulated and real waveforms are all less than 6 % . The parameters of received signal are related to the altimeter systems and the wind speed over the ocean surface, and taking the GLAS parameters for example, the valid ocean waveforms can be hardly got when the

  16. Mesoscale ocean variability signal recovered from altimeter data in the SW Atlantic Ocean: a comparison of orbit error correction in three Geosat data sets

    Directory of Open Access Journals (Sweden)

    Gustavo Goni

    1995-01-01

    Full Text Available Orbit error is one of the largest sources of uncertainty in studies of ocean dynamics using satellite altimeters. The sensitivity of GEOSAT mesoscale ocean variability estimates to altimeter orbit precision in the SW Atlantic is analyzed using three GEOSAT data sets derived from different orbit estimation methods: (a the original GDR data set, which has the lowest orbit precision, (b the GEM-T2 set, constructed from a much more precise orbital model, and (c the Sirkes-Wunsch data set, derived from additional spectral analysis of the GEM-T2 data set. Differences among the data sets are investigated for two tracks in dynamically dissimilar regimes of the Southwestern Atlantic Ocean, by comparing: (a distinctive features of the average power density spectra of the sea height residuals and (b space-time diagrams of sea height residuals. The variability estimates produced by the three data sets are extremely similar in both regimes after removal of the time-dependent component of the orbit error using a quadratic fit. Our results indicate that altimeter orbit precision with appropriate processing plays only a minor role in studies of mesoscale ocean variability.Erro orbital tem sido a principal fonte de incerteza no processamento de dados altimétricos. Recentes conjuntos de dados, baseados em modelos de predição orbital mais avançados c em novas metodologias de correção de erro, já foram capazes de reduzir o erro orbital de ate uma ordem de magnitude em comparação com os GDRs originais. Ncslc trabalho nós avaliamos os resultados dessas melhores eslimativas na descrição da variabilidade "meso- escalar" na parte sudoeste do oceano Atlântico Sul. Comparamos resultados obtidos cm tres conjuntos de dados: os GDRs originais c os conjuntos de dados GEM-T2 c Sirkes-Wunsch. Para garantir a "sensibilidade" das estimativas dc variabilidade mcso-cscalar quanto às mudanças na precisão orbital, utilizamos as mesmas "correções ambientais" c o

  17. Influence of terrain and surface features on waveforms of returned signal of satellite laser altimeter%地形地物对星载激光测高仪回波信号的影响

    Institute of Scientific and Technical Information of China (English)

    颜国强; 王睿星; 牛燕雄; 崔云霞; 王彩丽; 张鹏; 和婷; 牛海莎

    2012-01-01

    The ranging performance of satellite laser altimeter is influenced to a great extent by the waveforms of returned signals reflecting the target surface characteristics. The analysis of the return signal of satellite laser altimeter was presented. The mathematical and physical mode of typical landforms regarding different kinds of terrains was established. Based on computer simulations of return signal representing these modes of the landforms, an analysis of the variance of the return signal waveform was made. Using different signal detection methods, including the centroid method and the threshold method, ranging deviation caused by variance of the returned signal waveforms under different characteristics of target surface were provided. The conclusion of the analysis plays an important role in guaranteeing the ranging accuracy of satellite laser altimeter.%地形地物的回波信号特性影响着星载激光测高仪测量精度.对星载激光测高仪回波脉冲信号进行了理论分析,建立了地形地物数学物理模型,对不同地形地物的回波信号进行了数值模拟研究;在采用不同回波信号检测的情况下,分析了不同地形地物造成回波信号的变化所引起的测量误差.研究结果对保证星载激光测高仪测量精度具有重要的意义.

  18. Study on global average colinear sea surface height based on Satelite Altimeter%基于卫星高度计的全球平均共线海表面高度研究

    Institute of Scientific and Technical Information of China (English)

    王鑫; 苗洪利

    2015-01-01

    Satelite altimeter can measure global ocean dynamic environment around the clock.The important data product is the sea surface height (SSH). In this paper we compute the SSH of al the points based on the satelite altimeter data. Then we use the reference orbit to colinear processing with SSH and average the result. Finaly we get the mean sea surface height (MSSH). This method can get the sea surface height information of different time ranges in a short period of time. And it can provide the data support for the long term change of sea level.%卫星高度计可以实现全球范围的全天候海洋动力环境测量,其中重要的数据产品为海表面高度(SSH)。本文基于高度计测量数据,计算出每个测量点的海表面高度。利用参考轨道对数据采用共线处理得到全球的平均共线海表面高度。这一方法可以在短时间内获得全球范围的不同时间尺度下的海表面高度信息,能够为海平面长期变化研究提供数据支持。

  19. The Transition from Complex Crater to Peak-Ring Basin on the Moon: New Observations from the Lunar Orbiter Laser Altimeter (LOLA) Instrument

    Science.gov (United States)

    Baker, David M. H.; Head, James W.; Fassett, Caleb I.; Kadish, Seth J.; Smith, Dave E.; Zuber, Maria T.; Neumann, Gregory A.

    2012-01-01

    Impact craters on planetary bodies transition with increasing size from simple, to complex, to peak-ring basins and finally to multi-ring basins. Important to understanding the relationship between complex craters with central peaks and multi-ring basins is the analysis of protobasins (exhibiting a rim crest and interior ring plus a central peak) and peak-ring basins (exhibiting a rim crest and an interior ring). New data have permitted improved portrayal and classification of these transitional features on the Moon. We used new 128 pixel/degree gridded topographic data from the Lunar Orbiter Laser Altimeter (LOLA) instrument onboard the Lunar Reconnaissance Orbiter, combined with image mosaics, to conduct a survey of craters >50 km in diameter on the Moon and to update the existing catalogs of lunar peak-ring basins and protobasins. Our updated catalog includes 17 peak-ring basins (rim-crest diameters range from 207 km to 582 km, geometric mean = 343 km) and 3 protobasins (137-170 km, geometric mean = 157 km). Several basins inferred to be multi-ring basins in prior studies (Apollo, Moscoviense, Grimaldi, Freundlich-Sharonov, Coulomb-Sarton, and Korolev) are now classified as peak-ring basins due to their similarities with lunar peak-ring basin morphologies and absence of definitive topographic ring structures greater than two in number. We also include in our catalog 23 craters exhibiting small ring-like clusters of peaks (50-205 km, geometric mean = 81 km); one (Humboldt) exhibits a rim-crest diameter and an interior morphology that may be uniquely transitional to the process of forming peak rings. Comparisons of the predictions of models for the formation of peak-ring basins with the characteristics of the new basin catalog for the Moon suggest that formation and modification of an interior melt cavity and nonlinear scaling of impact melt volume with crater diameter provide important controls on the development of peak rings. In particular, a power-law model of

  20. Diode-pumped laser altimeter

    Science.gov (United States)

    Welford, D.; Isyanova, Y.

    1993-01-01

    TEM(sub 00)-mode output energies up to 22.5 mJ with 23 percent slope efficiencies were generated at 1.064 microns in a diode-laser pumped Nd:YAG laser using a transverse-pumping geometry. 1.32-micron performance was equally impressive at 10.2 mJ output energy with 15 percent slope efficiency. The same pumping geometry was successfully carried forward to several complex Q-switched laser resonator designs with no noticeable degradation of beam quality. Output beam profiles were consistently shown to have greater than 90 percent correlation with the ideal TEM(sub 00)-order Gaussian profile. A comparison study on pulse-reflection-mode (PRM), pulse-transmission-mode (PTM), and passive Q-switching techniques was undertaken. The PRM Q-switched laser generated 8.3 mJ pulses with durations as short as 10 ns. The PTM Q-switch laser generated 5 mJ pulses with durations as short as 5 ns. The passively Q-switched laser generated 5 mJ pulses with durations as short as 2.4 ns. Frequency doubling of both 1.064 microns and 1.32 microns with conversion efficiencies of 56 percent in lithium triborate and 10 percent in rubidium titanyl arsenate, respectively, was shown. Sum-frequency generation of the 1.064 microns and 1.32 microns radiations was demonstrated in KTP to generate 1.1 mJ of 0.589 micron output with 11.5 percent conversion efficiency.

  1. Inconsistency Analysis of CE-1 Stereo Camera Images and Laser Altimeter Data%CE-1立体相机影像与激光高度计数据不一致性分析

    Institute of Scientific and Technical Information of China (English)

    赵双明; 李德仁; 牟伶俐

    2011-01-01

    直接利用CE-1激光高度计测高数据制作月球表面模型,分辨率、精度都较低。利用激光测高数据改善三线阵CCD数据立体定位精度是一种有效方法。通过计算立体影像外定向参数、激光脚印(footprint)月固坐标,基于物方空间到像方空间的快速反投影算法,分析研究立体影像与激光高度计数据不一致性,目的是为后续CE-1探月三线阵影像数据与激光测高数据联合平差处理提供相对基准控制。通过不一致性分析试验,得到一些有益的结论,这些分析结果有望在下一步联合平差处理中获得应用。%Direct georeferencing lunar~sDSM. The use of laser to CE-1 laser altimetry data results altimetry data to improve three-line n relatively low resolution and accuracy for array CCD data positioning accuracy is an effective method, An analysis approach of stereo image and laser altimeter data inconsistency is proDosed which project each CE-1 laser footprints to CE-1 CCD three scan images using their exterior orientation parameters obtained from satellite auxiliary data about time and the laser footprints moon-fixed coordinate. The inconsistency analysis is for the purposes of subsequent lunar image and laser altimeter data combined adjustment constraints, Some useful conclusions are drawn by analyzing inconsistency experiments. The results show that the CE-1 laser altimeter ranges are expected to be incorporated into the bundle adjustment as measurements to improve accuracy of CE-1 image photogrammetric reduction in the next step.

  2. 激光高度计接收脉冲回波信号分析器%Analyzer on received waveforms of laser altimeter

    Institute of Scientific and Technical Information of China (English)

    周辉; 李松; 明先顺; 陈舒杭; 陈梦竹; 胡磊

    2012-01-01

    The received waveforms of laser altimeter were composed of multiple non-Gaussian waveforms appended with noise. It was absolutely crucial for retrieving the height and category of target by extracting the statistical parameters of non-Gaussian waveforms. Based on the feature of received pulse signal, its mathematics model was described with generalized Gaussian function. Using the method of smoothing filtering and calculating initial parameters on received waveforms, and the non-linear least squares algorithm, an analyzer with extracting the statistical parameters for received waveforms was developed. In terms of the analyzer, simulated waveforms processing and statistical parameters extraction were performed well. The analyzed results show that the maximal extraction error for statistical parameters is less than 1% for the single generalized Gaussian waveforms with 15 dB signal to noise ratio (SNR). Meanwhile, with the increase of the number of generalized Gaussian components and the decrease of SNR, extraction error for statistical parameters becomes larger. The statistical parameters can be extracted effectively with waveforms analyzer, which provides data gist for retrieving the target information.%激光高度计接收脉冲回波是叠加有噪声的多重非高斯波形,有效提取非高斯波形的统计参量对于反演目标高度和种类信息是十分关键的.基于接收脉冲回波信号的特点,利用广义高斯函数模型完成接收脉冲回波信号的数学建模.通过对接收脉冲回波的平滑滤波和初始参数获取,并采用非线性最小二乘算法,开发了一种提取接收脉冲回波统计参量的波形分析器.利用波形分析器对仿真的回波波形进行了处理,结果表明,对于15dB的单个广义高斯波形,其统计参量的最大提取误差不超过1%.随着广义高斯分量个数的增加以及回波信噪比的降低,统计参量的提取误差有所增加.利用波形分析器能够有效地提

  3. Effect of system parameters on ranging and pulse width in ocean satellite laser altimeter system%系统参数对激光测高仪海洋测距和回波脉宽影响

    Institute of Scientific and Technical Information of China (English)

    马跃; 李松; 周辉; 易洪

    2013-01-01

    星载激光测高仪的回波时间重心和脉冲宽度等系统参数对常见海态条件下的测距和反演精度有重要影响.本文根据菲涅尔衍射理论、海洋表面镜面反射理论、海洋波高和斜率统计特性以及激光测高仪回波误差理论,推导并更正了激光测高仪海洋回波光子数表达式.首次完整推导出了影响海洋回波重心和脉宽因素的表达式,证明了回波参数主要受发射脉冲宽度、测量天底角、指向角抖动和海洋表面上方风速的影响.除风速为表面特性影响外,其余为系统参数影响.结合地球科学激光测高系统(GLAS)参数对其海洋回波的测距和脉宽精度做了定量分析,得出不同风速GLAS的海洋表面单回波测距误差为2~15 cm,脉宽标准差为0.5~3.5 ns.推导结果对优化设计用于海洋表面测量的星载激光测高仪系统参数、提高回波反演目标特性精度很有意义.%The system parameters such as the centroid and pulse width of a laser altimeter system have great effects on its accuracy in ranging and inversion under the condition of a common sea state. Therefore, this paper deduces the functions referred to influencing factors of centroid and pulse width and corrects the received photon function of ocean surface according to the theory of Fresnel diffraction, the character of specular reflection, the statistical regularity of ocean surface profile and the error theory of laser altimeter systems. It gives complete influencing factors on the centroid and pulse width, which include the transmitted and received instruments, nadir angles, pointing jitters and wind speeds. Among them, the first three factors are all system parameters, and the wind speed is a surface characteristic. Combined with the parameters of Geoscience Laser Altimeter System) GLAS, the error of range and the accuracy of pulse width are calculated and analyzed. The results show that the ranging error of GLAS is from 2 to 15 cm

  4. 基于匹配滤波技术的特征信号提取的仿真和实现%Simulation and realization of the fidelity of the signal of laser altimeter based on matched filter

    Institute of Scientific and Technical Information of China (English)

    李洋; 刘元廷; 任萍; 张建秋; 汤永新

    2012-01-01

    The laser altimeter contains the information of target such as harshness, gradient, reflectivity and etc.The multichannel matching filter technique is used to automatically acquire best signal-to-noise ratio from different targets and to ensure the exactitude of the signal.%激光测高仪的回波信号中包含目标物的粗糙度、倾斜度、反射率等信息,对于复杂地物特征的回波信号,采用多通道匹配滤波技术不仅可以获得高的信噪比,还可以保证信号的保真度。

  5. Simulation of terrestrial target response function for satellite laser altimeter%面向星载激光测高仪的陆地目标响应函数仿真

    Institute of Scientific and Technical Information of China (English)

    王良训; 周辉; 李子乐; 刘国根; 王虹; 王雅培

    2015-01-01

    面向星载激光测高仪的陆地目标响应函数的时间分布是评价星载激光测高仪使用性能的重要因素.根据星载激光测高仪发射的高斯激光束和目标响应函数的分布特点,采用等间隔同心圆环与等分圆周的方法实现目标的离散化三角网格划分,基于三角网格的均匀性与目标响应函数特征参数的误差模型,以目标响应函数的仿真误差指标为依据,提出一种全新的目标响应函数的时空域参数选取方法.以对地观测星载激光测高仪GLAS的系统参数为输入条件,针对三种典型倾斜度(3°、12.5°和28.5°)的平面目标和多平面目标,通过限定目标响应函数特征参数的2%容限误差,仿真了对应的波形分布,并解算出其特征参数的最大误差不超过1.16%,有效验证了陆地目标响应函数仿真方法的正确性.所得结果对于星载激光测高仪接收脉冲回波的分析、数据反演及其性能评价具有一定的实际应用价值.%The Terrestrial Target Response Function(TTRF) of satellite laser altimeter is the key factor for evaluating its performance. According to the distribution characteristics of transmitted Gaussian laser beam and the target response function, the methods of using equal-interval concentric rings and dividing circumference uniformly were utilized to achieve the discrete triangular mesh of target. Based on the homogeneity of the triangular mesh and error model about characteristic parameters of TTRF, a new parameter selection method of TTRF was presented in terms of the simulation error index. In light of geosciences laser altimeter system (GLAS) parameters, the TTRF waveform distribution of planar target with three typical slope targets (3° and 12.5° and 12.5°) and multiple planar targets were simulated, by restricting the allowance error of its characteristic parameters within 2%. The calculated error is less than 1.16%, which proved that the method on simulation of TTRF is

  6. Influence of atmospheric transmission delay of satellite laser altimeter on ranging precision%星载激光测高仪大气传输延迟对测距精度的影响

    Institute of Scientific and Technical Information of China (English)

    赵欣; 张毅; 赵平建; 涂碧海

    2011-01-01

    地球表层的大气折射可对激光测高仪的激光脉冲传输造成延迟,该延迟对激光飞行时间的测量精度以及地球表面三维轮廓的监测造成显著影响.因此,激光测高仪测距精度需要通过大气传播误差函数进行修正.着重讨论了激光脉冲基于天顶延迟的计算方法和相关映射函数模型的选择,并采用NMF连分式映射函数分别对干项和湿项进行计算.结果表明,在1.064 μm波长,指向角偏差不超过10°的激光测高仪系统中,干项延迟可达2.35 m,为主要误差源,湿项延迟变化从1~4 mm不等,基本可以忽略.%Atmospheric delay of laser pulse is the dominant error source for high precision range measurements of laser altimeter arisen from atmospheric refraction, the error source will greatly influence the measurement precision for pulse laser flight time, and faulty estimation in the three-dimension prediction.So the atmospheric model is needed to correct the propagation delay of the laser transmission in air.How to calculate the ray paths delay in atmosphere near zenith was presented, and some models of relative map function were given out.Through calculating and comparing these functions, the NMF function in a continued fraction was used to calculate separately for hydrostatic and wet components of the air.Result shows that laser altimeter transmitting with 1.064 μm laser and point angle under 10° off nadir, the zenith hydrostatic delay is approximately 2.35 m and is the major component of total delay; the corresponding zenith wet delay varing from 1 mm to 4 mm can be ignored.

  7. Noise suppression method for received waveform of satellite laser altimeter based on adaptive filter%利用自适应滤波星载激光测高仪回波噪声抑制方法

    Institute of Scientific and Technical Information of China (English)

    马跃; 李松; 周辉; 翁寅侃

    2012-01-01

    For satellite laser altimeter, the range between earth surface and satellite platform could be calculated, and the target characters could be inversed through extracting the parameters of received waveforms. The signal degradations emerge on the noise suppression process of returned pulse using the fixed width Gaussian filter, which influences seriously the extracting of the effective parameters. Based on the different statistical regularities among blocked signal, a new method is presented to estimate the mean and standard deviation of returned waveforms, and a width adaptive Gaussian filter is designed according to the statistical characters of returned pulse. The received digital counts data of GLAS were used to the Noise estimation, adaptive Gaussian filter, and Gaussian fitting were measured by GLAS system. The calculation results accord with GLAS official statstics. The errors of estimated noise mean were less than 0.4 digitized unit, and the effective Gaussian parameter errors are less dian 1%. The conclusion is that the returned pulse parameters of laser altimeter could be extracted effectively and accurately through this noise suppression method.%具有波形记录功能的星载激光测高仪,通过回波信息解算地表与卫星平台距离和反演地物特性.目前广泛采用的固定宽度高斯滤波方法在抑制回波噪声过程中造成有效信号变形,对提取信号有效参量造成严重干扰.根据分块信号统计特性不同的规律,提出了激光测高仪回波噪声均值和方差的估计方法;根据回波信号的统计特性,设计了一种宽度自适应的高斯滤波器.通过GLAS系统实测回波信号的噪声估计与自适应高斯滤波、高斯拟合,得到的波形处理结果与GLAS官方数据有很好的吻合度,噪声均值估计误差小于0.4个数字化仪单位,有效高斯参数计算误差小于1%.该方法能准确地提取波形参量,为地表高程解算和目标表面信息反演提供有效数据.

  8. Analysis on atmospheric ref raction delay for satellite laser altimeter system%星载激光测高系统大气折射延迟的影响分析

    Institute of Scientific and Technical Information of China (English)

    李松; 马跃; 周辉; 鲜勇

    2014-01-01

    The laser pulse transmitted from satellite laser altimeter system would be refracted by atmosphere and the range error in the system was about a few meters .In this paper the atmos-pheric refraction delay based on refraction models and mapping function was calculated ,and the method of air pressure correction were discussed .Combined with the elevation data of geo-science laser altimeter system (GLAS) and meteorological parameters of national center for en-vironment prediction (NCEP ) , the atmospheric delay was calculated and compared to the GLAS results .The comparison shows the deviation of hydrostatic and wet atmospheric delay are less than 2 cm and 1 mm respectively .%星载激光测高系统发出的测距光束经过大气层时会发生折射,由此产生的与大气延迟相关的测距误差在数米量级。讨论了激光测高系统大气延迟修正理论及实现算法,通过使用沿天顶方向的大气传输延迟值与非天顶方向相应映射函数乘积的方法来计算大气延迟,并对影响大气延迟主要气象参数地表气压进行修正。结合全球首个对地观测星载激光测高系统GLAS测量数据和美国国家环境预报中心NCEP气象数据进行大气延迟修正,并与GLAS系统公布延迟数据对比。结果表明:大气干项延迟偏差小于2cm,湿项延迟偏差小于1mm。

  9. Influence of atmospheric multiple scattering effects on the range bias for satellite laser altimeter%大气多次散射效应对星载激光测高仪测距偏差值的影响

    Institute of Scientific and Technical Information of China (English)

    陈舒杭; 李子乐; 陈梦竹; 胡磊; 周辉

    2012-01-01

    大气多次散射效应会使得星载激光测高仪脉冲回波信号发生拖尾现象,导致激光测高仪的测距值出现偏差.根据激光测高仪的工作原理并利用半解析型蒙特卡罗方法,建立了大气多次散射效应条件下的脉冲回波信号及距离偏差的数学模型,并基于GLAS系统参数,仿真分析了云和雾的多次散射效应对距离偏差值的影响规律.结果表明,随着大气参数的变化,距离偏差会呈现不规则的起伏变化.当云层粒子尺度大于150 μm或雾的消光系数小于1.68 km-1时,大气多次散射效应对测距偏差值的影响小于1 cm.所得的结论为星载激光测高仪测量天气的选取以及系统参数的优化提供了理论依据.%The atmospheric multiple scattering can produce a lag in the received pulse signal of satellite laser altimeter (SLA), which may introduce range bias for SLA. According to the operational principle of SLA and the semi—analytic Monte Carlo method, the mathematical models of the received pulse signal and range bias were built up in the condition of atmospheric multiple scattering. Based on the parameters of geoscience laser altimeter system (GLAS), the impacts of cloud and fog onto the range bias were simulated and analyzed. The results show that irregular fluctuation change appears in the range bias with varying atmospheric parameters. The range bias is less than 1 cm only if the effective radius of cloud particle size distribution is greater than 150 m or the extinction coefficient of fog is less than 1.68 km"1. The conclusions provide theoretical foundation for the choice of weather condition with measurements and parameters optimization for SLA.

  10. 基于“嫦娥一号”激光测高数据的月球极区光照条件研究%Lunar polar illumination based on Chang'E-1 laser altimeter

    Institute of Scientific and Technical Information of China (English)

    郝卫峰; 李斐; 鄢建国; 张杰; 苏晓莉

    2012-01-01

    The illumination condition of the lunar polar regions can be used to analyze the choice of ideal landing sites and to conduct the investigation of possible water ice deposits. The laser altimeter data obtained by 'Chang E-l' can provide high accuracy digital elevation models (DEM) for polar illumination model. In this study, we establish the mathematical model to study the polar illumination condition, by combining ' Chang' E-l' altimeter data and known parameters related to lunar orbit. The calculation period of illumination rate is 19 years, which is longer than the node precession period (18. 6 years). In this paper, the horizon method is used instead of the ray-tracing method, and the results show: (1) We don't find the areas that receive permanent illumination; (2) There are regions that are in constant darkness; (3) The edge of the craters can be found to be as continuous illumination region in the north summer or the south summer; (4) The Shackleton crater is one of the main targets as landing sites of the lunar rover.%月球极区光照模型为研究月球车着陆点选择和水冰存在的探测提供了依据.利用“嫦娥一号”探月卫星获取的激光测高数据,得到了全月面高精度的数字高程模型(DEM),特别是在月球两极地区,地形细节清晰可见,为极区光照模型的建立提供了精确的数据基础.本文通过由测高数据建立的DEM和月球轨道参数相结合,采用地形最大高度角法,对月球极区的光照条件及其应用进行了研究和分析.光照率的计算周期为19年,考虑了黄道和白道交点进动的影响(18.6年).计算结果表明:(1)未发现有持续光照区;(2)有长久阴影区存在;(3)在南极或北极的夏季,撞击坑边沿高地处可以享受到连续的光照;(4) Shackleton撞击坑可以作为月球车着陆的首选目标之一.

  11. Elevation error analysis of spaceborne laser altimeter for earth observation%对地观测星载激光测高系统高程误差分析

    Institute of Scientific and Technical Information of China (English)

    马跃; 阳凡林; 卢秀山; 冯成凯; 李松

    2015-01-01

    In space-borne laser altimeter system, the range between satellite and target was calculated by the weak received signal which was transmitted from laser device and reflected by earth surface, and the accurate location and elevation of laser footprint was acquired by combining satellite precise orbit with attitude data. The elevation error was mainly affected by the device noise, the environment and the target parameters, and there is no complete analyzing model of location and elevation error for spaceborne laser altimetry system. The error model of laser ranging for solid surface was simplified and improved. Meanwhile, the location and elevation error analysis model of laser footprint was established in this paper. Utilizing airborne lidar data with better spatial resolution and elevation accuracy, the elevation deviation of GLAS data were evaluated, and the result was consistent with the error model. It is proved that on the flat surface of ice sheets the elevation accuracy of GLAS system can meet its design value of approximate 15 cm. This research is instructive for elevation error assessment and system parameters designing of laser altimeter system.%星载激光测高系统通过接收卫星平台激光器发出的激光脉冲经地表反射的微弱回波,计算卫星与地表的距离;结合卫星轨道和姿态数据,生成激光脚点精确地理位置和高程结果。其高程误差主要受器件、环境和目标参数影响,目前还没有完整描述对地观测星载激光测高系统平面和高程误差的数学模型。简化并完善了针对固体地表的激光测距误差模型,建立了完整的激光脚点平面和高程误差模型。利用高程精度和空间分辨率更高的机载Lidar数据评估了星载激光测高系统GLAS实测数据的高程偏差,评估结果符合所建误差模型。在较平坦的冰盖表面,GLAS系统高程精度可以达到设计值约15 cm。研究内容对测高系统高程误差评估

  12. Calculation of elevation changing of Greenlandˊs ice sheet using GLAS laser altimeter%利用GLAS激光测高仪计算格陵兰冰盖高程变化

    Institute of Scientific and Technical Information of China (English)

    马跃; 阳凡林; 王明伟; 李松; 翁寅侃

    2015-01-01

    The spaceborne laser altimeter has the advantages of divergence angle of milli arc magnitude and no penetration effect on ice surface, which are suitable for monitoring the icesheet changing of polar region. Using elevation data of GLAS laser altimeter, the ice sheet changing of the region above 2 000 m of Greenland was obtained and analyzed through the crossing and repeat pairs over the time span of March 2003 to March 2009. The novel method was developed and applied to calculate crossing pairs in the entire Greenland where the latitudinal span was very large. After coarse error elimination and time series analysis, a positive elevation change rate of 3.80 cm/year, and a standard deviation of 0.91 cm were obtained, and change trends from the crossing and repeat pairs were agreed. The number of repeat pairs was much larger than that of cross pairs, approximately 4-15 times, while its spatial distribution was very non-uniform. The conclusion is that on elevation change monitoring in Greenlandˊs ice sheet,the crossing pairs is more fit for large zone, while the repeat ones suitable for small area.%星载激光测高系统亚毫弧量级的发散角和冰层表面几乎没有穿透效应的优势使其非常适于监测南北极冰盖变化.利用GLAS激光测高卫星的高程数据,通过交叉和重复点方法分析2003~2009年3月格陵兰2 000 m以上区域冰盖高程变化,并改进了交叉点计算方法,使其适合纬度跨度较大的格陵兰地区.经过粗差剔除和时序解算,研究结果表明,该区域7年间冰盖高程年均变化+3.80 cm/年,中误差0.91 cm,呈缓慢增长趋势;交叉点和重复点方法所得结果趋势一致,重复点数量为交叉点数量的4~15倍,但位置分布不均匀,使用星载激光测高数据分析极地冰盖变化时,较大区域适合使用交叉点方法,较小区域适合使用重复点方法.

  13. Parameter optimized design of satellite laser altimeter's receiving amplifier%星载激光测高仪接收放大器参数的优化设计

    Institute of Scientific and Technical Information of China (English)

    颜国强; 张鹏; 牛燕雄; 崔云霞; 冯丽爽

    2012-01-01

    In order to meet the demand of satellite laser altimeter (SLA) for high measurement accuracy, the design principles and requirements of receiving amplifier were analyzed. The parameters relationship and optimized parameters were given after some main performance parameters such as bandwidth, signal-noise ratio(SNR) , detection sensibility and amplifier gain were analyzed and researched in terms of theory. The results show that SLA could achieve the measurement accuracy of false alarm rate of about 1% with (he measuring range of 450 km~ 650km, pulse width of 8 ns~12 ns, working wavelength of 532 nm and,1064nm.%为使星载激光测高仪满足测量精度的需求,分析了接收放大器部分的设计原则与要求,对带宽、信噪比、探测灵敏度和放大倍数等主要性能参数进行了理论分析与研究,得到了性能参数的关系和优化的参量.理论结果表明,在激光测高仪测量范围为450 km~650 km,激光脉冲宽度为8 ns~12 ns,工作波长为532 nm与1064 nm的情况下,对放大器性能参数进行分析计算,可以满足虚警率为1%的星载激光测高仪的设计需求.

  14. Optimization of thermal control design for laser altimeter used during lunar landing%用于月球着陆的激光高度计热控设计探讨

    Institute of Scientific and Technical Information of China (English)

    宋馨; 张有为; 贾建军; 刘自军

    2014-01-01

    The Land-On-Moon Orbit has obvious transient characteristics. The optimization principle of the thermal control design plan for the laser equipment used on the Land-On-Moon Orbit is discussed through the thermal analysis. The best thermal control design plan is to use the heat capacity of the equipment, unless the laser equipment is required to operate for a long time. An application case is the thermal control design plan for the laser altimeter used on the Chang’e-3, which uses the heat capacity of the equipment. The remote measurement data show that the temperature restriction of the equipment is realized. The thermal control design method is shown to be practical.%文章对落月轨道的外热流进行了分析,比较了几种热控设计方案的优缺点,探讨了热控优化设计的原则,认为在落月轨道上激光设备的热控设计应首选热容热控方案,对于在其他飞行阶段有长期开机需求的情况再考虑散热面方案或热电致冷方案。“嫦娥三号”月面探测器激光高度计采用了热容热控设计,该设备热控设计能够满足不同阶段温度指标要求并且与热分析结果相一致,热控设计方案正确、优化原则合理可行。

  15. Study on Multipath Suppressing Algorithm of Phase-coded Modulation Radar Altimeter%伪码调相雷达高度表中多径信号抑制算法研究

    Institute of Scientific and Technical Information of China (English)

    郭通; 廉保旺; 赵恒斌

    2011-01-01

    Multipath error is one of the most important errors in phase - coded modulation radar altimeter. In order to improve the measurement accuracy of system, this paper presents a code tracking loop model based on strobe correlator, and it also provides the block diagram of this model. The correlation of multipath parameters and the pseudo - code tracking error is analyzed when considering single multi - path signals, and some simulations of the code tracking loop performance are given in the Matlab environment. Simulation results show that the strobe correlator can effectively reduce the tracking error caused by multipath, and the performance is better than narrow correlator. This method is propitious to implement in hardware, because it needs less correlators.%多径误差是伪码调相雷达高度表中重要的误差源之一,为了提高系统的测距精度,建立了采用strobe相关器的伪码跟踪环数学模型,给出了其实现的结构框图;在考虑单路多径信号的基础上分析了多径信号的参数对伪码跟踪环的跟踪误差的影响,并在Matlab环境下对伪码跟踪环的跟踪性能进行了仿真;仿真结果表明在相同的多径参数条件下,strobe相关器可以有效地减小多径引起的跟踪误差,性能优于窄相关器,运算量较多径估计延迟锁定环要小,易于在硬件上实时实现,具有实际应用价值.

  16. 高速铁路CPⅢ高程控制网测量方法研究%Methods to derive lunar DEM from Chang'E-1 laser altimeter data

    Institute of Scientific and Technical Information of China (English)

    李书亮; 刘成龙; 倪先桃; 徐小左

    2011-01-01

    本文分析高速铁路CPⅢ高程控制网建网时普遍采用的德国测量方法,指出其存在的不足,在此基础上提出了技术上更为合理又适合我国国情的矩形法测量方法.通过对矩形法相邻点高差相对中误差和最弱点高程中误差的估算以及实验验证,认为矩形法可以用于CPⅢ高程网的建网测量.研究结果对于目前高速铁路工程测量相关规范的制订和在建高速铁路CPⅢ高程网的测量具有重要的参照价值.%High-resolution digital elevation models (DEMs) based on data from Laser Altimeter (LAM) of Chinese Chang'E-1 mission provide geospatial characterizations of lunar topography. The primary LAM elevation data are two-dimensional topographic profiles. Developing three-dimensional DEMs from these profile data requires the elimination of gross errors and the interpolation of a confinuous surface. To detect and remove the error ( pseudo elevation) data from LAM observations the paper suggested an improved linear filter based on empirical formula which adapts the lunar surface feature. And the key parameters for this filter were discussed. In the second part, it tested eight different techniques of spatial interpolation with the filtered data. After comparing and analyzing these interpolation methods by their accuracies, shaded-relief visualizations and topographic profiles, it found the Kriging method worked better than other seven methods in deriving DEM grid. At last, an effective procedure for processing CE-1 elevation data was outlined, and the corresponding parameters were suggested.

  17. A Simulation Study on Waveform Model and Performance Evaluation for an Altimeter Transponder System%星载雷达高度计有源定标器回波模型及性能仿真研究

    Institute of Scientific and Technical Information of China (English)

    杜岳恒; 徐曦煜

    2012-01-01

    For the in-orbit calibration of HY-2 Satellite Radar Altimeter(ALT),three active transponders were developed by Mirslab,CSSAR,CAS,and the schemes and algorithms are designed for fulfilling the calibration requirements.Based on the system design and calibration rationales of HY-2 ALT and the transponders,the echo waveforms and trajectory's presented in the altimeter range window were simulated,and the calibration performance were also evaluated.Besides,the waveform features with multiple transponders are simulated to optimize their deployments.%为了对HY-2卫星雷达高度计进行定标,中国科学院空间科学与应用研究中心微波遥感重点实验室研制了3台有源定标器,并设计了利用有源定标器对高度计进行高度和散射系数定标的方案和算法。基于HY-2高度计和有源定标器的系统参数和定标方案,对高度计接收到的有源定标器回波波形和轨迹进行了仿真,研究了从中提取测量参数的方法,并对测量精度进行了分析。同时验证了3台有源定标器同时工作及其布设方案的可行性。

  18. Extraction of Significant Wave Height and Its Accuracy Analysis Based on HY-2 Altimeter Calibration Flight Data%基于HY-2卫星高度计机载校飞数据的有效波高信息提取及初步分析

    Institute of Scientific and Technical Information of China (English)

    李秀仲; 张有广; 孟俊敏

    2012-01-01

    利用HY-2卫星雷达高度计校飞数据,开展了有效波高信息提取及精度比对研究.首先对其进行波形筛选、1 s平均和去噪,然后基于Hayne海面回波模型进行波形拟合,提取出波高均方根并得到有效波高,并与浮标和同轨迹的Jason-1卫星高度计有效波高进行了比较.结果表明,本次校飞其高度计测波精度存在系统偏差,初步分析可能是其数据未经仪器校正等原因导致.%Based on the HY-2 calibration flight data, the significant wave height (SWH) is retrieved and its accuracy is compared with those from buoys and Jason-1 altimeter. For the extraction of the root mean square (RMS) of the wave heights and hence to obtain the SWH, first is to carry out waveform screening, averaging over 1 second and destriping, and then to make waveform fitting according to the Hayne echo model. The significant wave heights thus obtained are compared with those from the buoys and the Jason-1 altimeter which runs along the same track as that of the HY-2 calibration flight. The results indicate that a systematic bias is present for the accuracy of the SWH resulted from the HY-2 altimeter. This bias is mainly due to the absence of instrumental correction.

  19. The analysis of the characterstics of wind and wave fields over the surrounding waters of Taiwan Island using TOPEX satellite altimeter data%利用TOPEX卫星高度计资料分析台湾岛周边海域巨浪和大风特征

    Institute of Scientific and Technical Information of China (English)

    谢辛; 李燕初; 许德伟; 郑凌虹; 林明森

    2009-01-01

    卫星高度计实现了对全球性或区域性的海洋参量的实时监测,TOPEX卫星高度计提供了迄今为止时间序列最长、数据质量最高的全球海面风速和有效波高的同步观测资料.利用TOPEX卫星高度计资料,分析了有效波高4 m以上的巨浪在台湾岛周边海域的时空分布特征,结果表明台湾岛周边海域巨浪的分布具有明显的季节特征.每年平均有效波高最大值大多数出现在夏季,春季是1 a中有效波高最小的季节,而秋季和冬季是巨浪出现频率最高的季节.波高大干6 m的巨浪大都出现在台湾岛东部及东北部海域,在南部海域出现较少.%The satellite altimeter provides an efficient way for realtime monitoring global and regional oceanographic parameters.The TOPEX satellite altimeter has provided the synchronously observed data of the global sea surface wind speed and significant wave height(SWH), so far, these data have the longest time series and the best data quality. The data of the SWH and the wind speed over the surrounding waters of Taiwan Island are compared with the data from the TOPEX satellite altimeter,and the validity is analyzed from the TOPEX satellite altimeter data. Meanwhile, the characteristics of the SWH which is greater than or equal to 4 m over the surrounding waters of Taiwan Island is analyzed .It is shown that the large waves commonly appear in winter and autumn every year, and the maximum of the mean SWH often appears in summer, but it is opposite in spring. When the SWH is greater than or equal to 6 m, it appears in the surrounding waters of the east or northeast of Taiwan Island, and it less appears in the surrounding waters of the south of Taiwan Island.

  20. Prediction of Gravity Anomalies Over the South China and Philippine Seas from Multi-satellite Altimeter Sea Surface Heights%根据多卫星高度计海面高数据推算南中国海及菲律宾海域重力异常

    Institute of Scientific and Technical Information of China (English)

    Isaac Dadzie; 李建成; 褚永海

    2008-01-01

    Gravity anomalies on a 2.5×2.5 arc-minute grid in a non-tidal system were derived over the South China and Philippine Seas from multi-satellite altimetry data. North and east components of deflections of the vertical were computed from altimeter-derived sea surface heights at crossover locations, and gridded onto a 2.5×2.5 arc-minute resolution grid. EGM96-derived components of deflections of the vertical and gravity anomalies gridded into 2.5×2.5 arc-minute resolutions were then used as reference global geopotential model quantities in a remove-restore procedure to implement the Inverse Vening Meinesz formula via the 1D-FFT technique to predict the gravity anomalies over the South China and Philippine Seas from the gridded altimeter-derived Components of deflections of the vertical. Statistical comparisons between the altime-ter-derived and the shipboard gravity anomalies showed that there is a root-mean-square agreement of 5.7 mgals between them.

  1. Sea test development of laser altimeter

    OpenAIRE

    Crittenden, Eugene Casson; Rodeback, George Wayne; Milne, Edmund Alexander; Cooper, Alfred William

    1991-01-01

    Low altitude (81 m.) narrow-beam laser reflectance measurements were made from the nearly ocean-like water surface under the Golden Gate bridge. This site allowed precise measurements not possible from flying platforms. For short wavelength water waves superimposed on swell, the signal amplitude probability distribution showed periods of zero return signal, even for vertical incidence, apparently due to tipping of the average water surface. The nonzero signals show an antilog-n...

  2. Progress in georeferencing airborne laser altimeter measurements

    Energy Technology Data Exchange (ETDEWEB)

    Vaughn, C.R. [NASA/GSFC Wallops Flight Facility, Wallops Island, VA (United States); Bufton, J.L. [NASA/Goddard Space Flight Facility, Greenbelt, MD (United States)

    1996-10-01

    The NASA/Goddard Space Flight Center, including its Wallops Flight Facility, has conducted a series of airborne missions to collect transacts of pulsed-laser measured distances to the Earth`s surface. The primary purpose of these missions was to geolocate the points where the laser hit the earth. We present how we make these measurements with sufficient accuracy that a point on the earth can be geolocated in height to about 10 cm with-respect-to the WGS-84 ellipsoid. We give particular attention to determining the instantaneous spatial orientation of the laser beam and its transit time to the earth and back to the receiver. We also discuss the difficulty in assessing the accuracy of the ellipsoidal latitude and longitude of the point. From 1991 through 1994 we flew a nadir-pointing system in either a P3-B Orion or a T-39 Sabreline aircraft owned and operated by the Wallops Flight Facility. Flights in 1993 at an altitude of 500 to 600 meters over Lake Crowley, California (the Long Valley reservoir) gave a mean lake height that agreed to better than 10 cm with an accurate tide gage at the dam - after the local geoid undulation was removed from the laser data. In 1995 we built a new pulsed-laser ranger that raster-scans at 60 times per second, operates at a 523 run wavelength, fires 5000 pulses per second, and produces a 12 degrees wide scan line. We present preliminary results from this system. 5 refs., 5 figs.

  3. 基于ICESat/GLAS高度计数据的SRTM数据精度评估--以青藏高原地区为例%Accuracy evaluation of SRTM data based on ICESat/GLAS altimeter data:A case study in the Tibetan Plateau

    Institute of Scientific and Technical Information of China (English)

    万杰; 廖静娟; 许涛; 沈国状

    2015-01-01

    为全面了解航天飞机雷达测图计划( shuttle Radar topography mission,SRTM)高程数据的精度及误差特征,利用精度更高的ICESat/GLAS 激光高度计数据(简称ICESat高度计数据)为参照数据,以具有多种地貌类型的中国青藏高原地区为实验区,采用双线性插值算法分析了SRTM在中国青藏高原地区的高程精度,以及SRTM高程数据与地形因子(坡度和坡向)间的关系。实验结果表明:在青藏高原地区,ICESat高度计数据与相对应的SRTM高程数据高度相关,相关系数高达0.9998;SRTM的系统误差为2.36±16.48 m,中误差(RMSE)为16.65 m;当坡度低于25°时,SRTM高程数据精度随坡度增大而显著降低。此外,相对于ICESat高度计数据,SRTM在青藏高原地区N,NW和NE方向的测量值偏高,在S,SE和SW方向的测量值偏低。%To understand the accuracy and error characteristics of the shuttle Radar topography mission ( SRTM ) elevation data,the authors used the more precise ICESat/GLAS laser altimeter data as reference data in the Tibetan Plateau covering various landscape types so as to assess the accuracy of SRTM and explore the relationship between SRTM and terrain factors ( slope and aspect ) through bilinear interpolation algorithm. The experimental results show that ICESat altimeter data are highly correlated with SRTM data, with a correlation coefficient of 0. 999 8. The system error of SRTM is 2. 36 ± 16. 48 m,with a RMSE of 16. 65 m. The accuracy of SRTM data decreases obviously as the slope increases when the slope is lower than 25°. In addition, compared with ICESat altimeter data, the measurements of SRTM elevation are higher in the north, northwest and northeast directions, and lower in the south, southeast and southwest directions in the Tibetan Plateau.

  4. Errors Analysis on Lunar Surface On-orbit Elevation Data Measurement with the Laser Altimeter on Chang'e-1 Satellite%嫦娥一号激光高度计在轨测量数据误差分析研究

    Institute of Scientific and Technical Information of China (English)

    王东霞; 宋爱国; 温秀兰; 汪凤林

    2012-01-01

    利用嫦娥一号卫星(CE -1)激光高度计在轨探测科学数据,研究激光高度计月球高程探测误差.对月球南北极纬度60°~90°范围进行月球表面区域划分,进行高程测量重复点的搜索、区域高程粗差的剔除、残差和标准差的计算,并给出处理后区域残差与标准差的分布,对月球南北极区的处理结果作出对比分析,得出南极区纬度60°~90°内区域平均标准差较北极区域偏大.该处理结果为进一步分析激光高度计测量误差的来源提供科学依据,为探月卫星携带的各种有效载荷的设计在精度要求上提供理论指导和参考数据.%To study the detecting errors of lunar elevation of Laser Altimeter, the on-orbit measurement data obtained from Laser Altimeter of Chinese Chang' e-1 is investigated. Firstly, the elevation data from latitude 60°to 90°in the South and North Polar Regions are divided into different small sectors along latitude directions. Secondly, a series of process were developed in each small sector, such as searching the elevation repeated data, rejecting the gross error (pseudo elevation) data, calculating the residual error and standard deviation and presenting the results. Finally, the processing results from the South and North Polar Regions were compared and analyzed. And it turned out that the average standard deviation of the South Polar Regions which latitude is between 60°and 90° is larger than that of the North Polar Region. The research results will provide the scientific basis for further analyzing error sources of Laser Altimeter. And they also offer theory guidance and reference data to the design of effective loading which exploring satellites carry.

  5. Optimizational Design Method for Receiver Filter Bandwidth of Satellite Laser Altimeter%星载激光测高仪系统接收滤波器的带宽优化设计

    Institute of Scientific and Technical Information of China (English)

    周辉; 李松; 郑国兴; 涂兰芬; 张强

    2012-01-01

    Receiver filter bandwidth (RFB) of satellite laser altimeter (SLA) resolves the key performances of SLA. According to the operational principle of SLA, the theoretical models of received signal and receiver signal-to-noise ratio (SNR) are established, and the mathematical expressions about range error, probability of detection and false alarm are deduced. Under the condition that probability of detection and false alarm can satisfy the threshold, an optimizational design method for RFB on the basis of minimizing the range error is put forward. As an example of MOLA-2, the distributions of RFB and range error related with different target slope angles are simulated. The results show that the optimizational design values of RFB are larger than values given by conventional method within 40° target slope angle, whose difference limits the scope from 0. 7 MHz to 58. 7 MHz. However, corresponding range errors are less than them obtained by conventional method, the extent of their difference is 0. 2~16.2 m. With the restrictions of target variety and complexity, it is difficult to make every target correspond with a receiver filter during its manufacture, so multiple receiver filter channels are set up to piecewise fit the distribution curve of range errors, the RFB and corresponding scope of target slope angle for each channel are achieved. The optimizational method of designing the RFB provides a superior and practicable scheme for manufacturing receiver filter.%星载激光测高仪(SLA)接收滤波器带宽(RFB)直接决定系统的使用性能.根据星载激光测高仪的工作原理,建立了激光测高仪回波信号及输出信噪比(SNR)的简化模型,并推导了测距误差、探测概率和虚警概率的数学表达式.在探测概率和虚警概率满足阈值要求的前提下,提出了一种以测距误差最小化为依据的滤波器带宽优化设计方法.以MOLA-2星载激光测高仪系统为例,仿真计算出不同目标倾角对应的滤

  6. Methods to derive lunar DEM from Chang'E-1 laser altimeter data%利用嫦娥一号激光高度计数据制作月球DEM的方法研究

    Institute of Scientific and Technical Information of China (English)

    邹小端; 刘建军; 任鑫; 王文睿; 牟伶俐; 李春来

    2011-01-01

    High-resolution digital elevation models (DEMs) based on data from Laser Altimeter (LAM) of Chinese Chang'E-1 mission provide geospatial characterizations of lunar topography. The primary LAM elevation data are two-dimensional topographic profiles. Developing three-dimensional DEMs from these profile data requires the elimination of gross errors and the interpolation of a continuous surface. To detect and remove the error ( pseudo elevation) data from LAM observations the paper suggested an improved linear filter based on empirical formula which adapts the lunar surface feature. And the key parameters for this filter were discussed. In the second part, it tested eight different techniques of spatial interpolation with the filtered data. After comparing and analyzing these interpolation methods by their accuracies, shaded-relief visualizations and topographic profiles, it found the Kriging method worked better than other seven methods in deriving DEM grid. At last, an effective procedure for processing CE-1 elevation data was outlined, and the corresponding parameters were suggested.%本文结合嫦娥一号卫星(CE-1)激光高度计产品数据,研究卫星激光测距数据处理和数字高程模型(DEM)制作的方法.通过滤波实验分析,构造了符合月球地形特征的经验滤波器,并确定了适合LAM数据的滤波窗口大小和地形滤波参数.结合实验结果改进了滤波流程,并对实验区滤波.利用滤波后的数据对八种基本的插值方法进行实验,通过计算插值精度、比较地形晕渲图以及地形剖面细节,评价和比较各方法的插值结果,由此得到结论,克里金插值方法较其他七种方法更适用于月球地形规则格网的生成.最后结合月海和高地两个典型区数据,验证了该套DEM提取方案对不同地形特征区域的适用性.从而,为利用CE-1激光高度计数据开展月球科学研究的科研人员.提供一套行之有效的地形数据处理参考方案.

  7. High Precision Vertical Deflection Over China Marginal Sea and Global Sea Derived from Multi-Satellite Altimeter%联合多种测高数据确定中国边缘海及全球海域的垂线偏差

    Institute of Scientific and Technical Information of China (English)

    王虎彪; 王勇; 陆洋

    2008-01-01

    On the basis of gravity field model (EIGEN_CG01C),together with multi-altimeter data,the improved deflection of the vertical gridded in 2'×2' in China marginal sea and gridded in 5'×5' in the global sea was determined by using the weighted method of along-track least squares,and the accuracy is better than 1.2" in China marginal sea.As for the qual-ity of the deflection of the vertical,it meets the challenge for the gravity field of high resolution and accuracy.It shows that,compared with the shipboard gravimetry in the sea,the accuracy of the gravity anomalies computed with the marine deflec-tion of the vertical by inverse Vening-Meinesz formula is 7.75 m·s-2.

  8. 一个适用于大误指向角的雷达高度计回波模型及其在HY-2A卫星雷达高度计数据处理中的应用%An Echo Model for Big Antenna Mispointing Angle and Its Application in HY-2A Satellite Radar Altimeter

    Institute of Scientific and Technical Information of China (English)

    王磊; 许可; 刘鹏; 徐曦煜

    2013-01-01

    The main problem of the conventional radar altimeter echo model for big antenna mispointing angle is analyzed , and then an echo model containing the sea surface skewness coefficient is derived .This echo model can be used for retracking the e-cho wave when the antenna mispointing angle is big .Finally ,the model is used to process the data of the HY-2A radar altimeter during the stage of adjusting satellite attitude ,and the results are compared with the measurements of the buoys of NDBC (National Data Buoy Center ) .It shows that the model can give more accurate results .%本文分析了雷达高度计在天线误指向角较大的情况下,目前常用的回波模型存在的主要问题。提出了一个带有偏斜度系数的雷达高度计二阶回波模型,该模型适用于大误指向角情况下的回波重跟踪处理。本文利用该模型对HY-2A卫星雷达高度计的回波数据进行了处理,并将处理结果与NDBC (National Data Buoy Center )的海洋浮标观测数据做了比较,获得了比现有模型更好的结果。

  9. 基于多卫星融合数据的海平面特征分析%Global sea level change characteristics based on multi-altimeter data

    Institute of Scientific and Technical Information of China (English)

    陈美香; 王蕾; 左军成; 张国胜

    2012-01-01

    利用1993-2008年法国空间局的AVISO多卫星融合高度计资料,采用随机动态、EOF等方法分析全球海平面变化的长期趋势、变化幅度以及季节变化的空间分布特征.结果表明:(a) 1993-2008年间太平洋海平面呈西升东降的形态,印度洋绝大部分海区海平面呈上升趋势,大西洋除湾流流域外的其他海区海平面的长期趋势以上升为主;(b)全球海平面变化存在显著的年变化和半年变化等季节信号,无论是半球平均还是洋盆平均,北半球海平面季节变化的振幅明显大于南半球,中纬度海区季节变化的振幅最大;(c)北印度洋海平面季节变化的振幅高于同纬度带的北太平洋和北大西洋;(d)太平洋、印度洋、大西洋三大洋受西边界流、赤道流系等强流影响的海域海平面变化幅度大于周围海域;(e)赤道海域各大洋东、西边界和大洋内区海平面变化不同步,可能受赤道海洋波动的影响较大;(f)厄尔尼诺年,西太平洋暖池和赤道太平洋中部海平面明显降低,赤道东太平洋海域海平面明显升高,赤道印度洋海域东、西边界的海平面变化与其相反.%Based on the AVISO multi-altimeter data obtained by the Centre National d' Etudes Spatiales of France during the period from 1993 to 2008, the spatial distributions of long-term change and seasonal change of the global sea level were studied using the stochastic dynamic and EOF methods. The results show the following: (a) From 1993 to 2008, the Pacific sea level rose in the west and dropped in the east; the sea level of the Indian Ocean basically rose; and the Atlantic Ocean had a sea level rise in most areas except the Gulf Stream, (b) The global sea level change was characterized by significant seasonal (annual and semi-annual) variation, which was more significant in the Northern Hemisphere than in the Southern Hemisphere. The most significant seasonal variation occurred in the mid

  10. 对地观测星载激光测高仪在轨姿态系统误差检校方法%Calibration method of on-orbit attitude systematic error for space-borne laser altimeter of earth observation

    Institute of Scientific and Technical Information of China (English)

    马跃; 阳凡林; 易洪; 李松

    2015-01-01

    星载激光测高仪通过接收经地表反射的微弱激光脉冲回波,计算卫星与地表的距离;结合卫星位置和姿态数据,生成激光脚点精确地理位置和高程结果。对于高程精度10 cm量级的对地观测激光测高仪,必须对影响严重的姿态角系统误差进行标定和校正。文中推导得出星载激光测高仪姿态角误差与已知地表先验信息相关联的数学模型,设计了利用大洋表面作为地表标定场,通过卫星姿态机动方式,最小二乘估计算法校正卫星在轨系统误差的具体方法。仿真结果表明,所设计的方法能够准确估计存在的姿态系统误差,即使大规模观测值丢失,估计偏差也小于5%。这种在轨运行系统误差的标定方法对于对地观测星载激光测高仪的姿态误差检校具有参考意义。%The range between satellite and surface target was acquired by processing the weak received waveform which was transmitted from the space-borne laser altimeter and reflected by earth surface. Combined with the precise orbit and attitude data, the accurate location and elevation of laser footprint were calculated. As for the altimeter with elevation accuracy of 10 cm magnitude, the systematic error on attitude angles influencing the accuracy severely should be calibrated effectively. The analytic model of attitude angle error associated with priori knowledge of earth surface was deduced, and the calibration method used to eliminate the attitude error was designed, which utilized the ocean surface as calibration field, was by way of satellite attitude maneuver and based on least squares estimation algorithm. The results of simulation show that the designed method can estimate the systematic error precisely and effectively, even if the mass observed data were lost, the estimated bias is less than 5%. This on-orbit calibration method is beneficial to the systematic error correction for the space-borne laser altimeter

  11. 卫星姿态控制误差及飞行速度对星载激光测高仪测量精度的影响%Effects of satellite attitude control error and flying velocity on satellite laser altimeter measurement precision

    Institute of Scientific and Technical Information of China (English)

    崔云霞; 牛燕雄; 冯丽爽; 孙世君; 张慧

    2012-01-01

    A geometry model were established to analyse the effects on measurement precision by satellite attitude control error and flying velocity for both normal incidence of single pulse and non-normal incidence of multi-beam, the mathematical expression of distance measurement error was deduced, at the same time, numerical calculation was made here. In this study, the requirement for satellite control error was obtained to meet the measurement precision of 1m when the flight time is 1/300 s. Moreover, qualitative discussion was made about the flying velocity's effect on measurement precision. The results show that attitude control error has a direct impact on the distance measurement precision of spaceborne laser altimeter, but with the different azimuth of non-normal incidence beam, the effects on distance measurement precision by pitching error and rolling error will vary a lot; if velocity direction has common component with the propagation direction of laser pulses, the flying velocity must be taken into consideration when high precision measurement results is wanted.%建立了数学物理模型,理论分析了单光束垂直入射和多光束“品”字形入射时,卫星姿态控制误差及飞行速度对星载激光测高仪测量精度的影响,推导了测距误差的数学表达式,并进行数值模拟研究.文中以光束往返时间1/300 s为例,研究了为达到1m测距精度,卫星姿态控制误差需满足的误差区间,并定性讨论了卫星飞行速度对测量精度的影响.研究结果说明:卫星姿态控制误差直接影响星载激光测高仪的测量精度,但随着斜入射光束方位的不同,俯仰误差与滚转误差对测距精度的影响程度会发生变化;若测距光束传播方向与卫星飞行速度有相同方向分量,则卫星飞行速度的影响必须加以考虑.

  12. Geodynamics of the Earth according to the altimeter measurements

    Science.gov (United States)

    Uchytel, Igor; Jaroshenko, Victor; Mituchenko, Vadim; Kapochkin, Borys; Kucherenko, Nataliya

    2010-05-01

    We performed a comprehensive analysis of observations of the Black Sea level variations by different methods. The first method is a coastal monitoring by sea-level tide gauges which measures sea level changes relative to a moving reference frame - the state geodetic network. The second one is the satellite altimetry which results are performed in the fixed global reference frame. At the first stage we studied the mean monthly data smoothed over three points for the period 1993-2009. We found that during years 1994-1995, 1999-2001, and 2006, changes of the sea level registered by two different methods were almost identical. Hence both methods have high accuracy. Difference between results of the two methods is an indicator of errors. Changes in the shape of the geoid result in the satellite data errors. Systematic errors of this method have period of 10.3 months. Errors in the coastal sea level measurements are associated with vertical movements of the gauge instruments. Systematic errors of this method has 14.6 months period which coincides with the Chandler one. We performed cross-spectral analysis of the errors caused by global changes of the geoid shape and regional geodeformations in the Black Sea region. We found that results of the sea level measurements by two different methods are the same during short periods of phase overlapping of these incoherent cyclic errors. At the second stage we studied the sea level changes averaged over 24 hours for the period May - July 2009. We concluded that the Earth' geomagnetic field variations during 10-15 May generated changes of the geoid. Main ruptures of the high-pressure gas pipe-lines which occurred at 9, 10, 16, 28 May could be related to corresponding geodeformations. We found that rapid changes of the distance from the satellite to the sea surface during May 2009 were preceded by geodeformations. During July 2009 we registered maximal geodeformations caused by increase of the amplitude of the solid Earth tides. In July, the sea level rose up to 12 cm during 20 days. In this period measurement errors associated with vertical movements of the tide gauges reached 21 cm. Their period is 7 days. Recorded ruptures of the gas pipeline networks during July occurred almost every 7 days also. The phase shift between periodic component of the vertical movements and ruptures of the gas pipelines was 180 degrees.

  13. The Lunar Orbiter Laser Altimeter (LOLA) Laser Transmitter

    Science.gov (United States)

    Yu, Anthony W.; Novo-Gradac, Anne Marie; Shaw, George B.; Unger, Glenn; Lukemire, Alan

    2008-01-01

    We present the final configuration of the space flight laser transmitter as delivered to the LOLA instrument. The laser consists of two oscillators with co-aligned outputs on a single bench, each capable of providing one billion plus shots.

  14. Laser Transmitter for the Lunar Orbit Laser Altimeter (LOLA) Instrument

    Science.gov (United States)

    Yu, Anthony W.; Novo-Gradac, Anne-Marie; Shaw, George B.; Li, Steven X.; Krebs, Danny C.; Ramos-Izquierdo, Luis A.; Unger, Glenn; Lukemire, Alan

    2008-01-01

    We present the final configuration of the space flight laser transmitter as delivered to the LOLA instrument. The laser consists of two oscillators on a single bench, each capable of providing one billion plus shots.

  15. Video Altimeter and Obstruction Detector for an Aircraft

    Science.gov (United States)

    Delgado, Frank J.; Abernathy, Michael F.; White, Janis; Dolson, William R.

    2013-01-01

    Video-based altimetric and obstruction detection systems for aircraft have been partially developed. The hardware of a system of this type includes a downward-looking video camera, a video digitizer, a Global Positioning System receiver or other means of measuring the aircraft velocity relative to the ground, a gyroscope based or other attitude-determination subsystem, and a computer running altimetric and/or obstruction-detection software. From the digitized video data, the altimetric software computes the pixel velocity in an appropriate part of the video image and the corresponding angular relative motion of the ground within the field of view of the camera. Then by use of trigonometric relationships among the aircraft velocity, the attitude of the camera, the angular relative motion, and the altitude, the software computes the altitude. The obstruction-detection software performs somewhat similar calculations as part of a larger task in which it uses the pixel velocity data from the entire video image to compute a depth map, which can be correlated with a terrain map, showing locations of potential obstructions. The depth map can be used as real-time hazard display and/or to update an obstruction database.

  16. GEOSAT Follow-On (GFO) Altimeter Document Series. Volume 5; Version 1; GFO Radar Altimeter Processing at Wallops Flight Facility

    Science.gov (United States)

    Lockwood, Dennis W.; Conger, A. M.

    2003-01-01

    This document is a compendium of the WFF GFO Software Development Team's knowledge regarding of GDO CAL/VAL Data. It includes many elements of a requirements document, a software specification document, a software design document, and a user's guide. In the more technical sections, this document assumes the reader is familiar with GFO and its CAL/VAL Data.

  17. Assessment of wave modeling results with buoy and altimeter deep water waves for a summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Sudheesh, K.; Vethamony, P.; Babu, M.T.; Jayakumar, S.

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  18. Utilisation of CryoSat-2 SAR altimeter in operational ice charting

    OpenAIRE

    E. Rinne; Similä, M.

    2016-01-01

    We present methods to utilise CryoSat-2 (CS-2) synthetic aperture radar (SAR) mode data in operational ice charting. We compare CS-2 data qualitatively to SAR mosaics over the Barents and Kara seas. Furthermore, we compare the CS-2 to archived operational ice charts. We present distributions of four CS-2 waveform parameters for different ice types as presented in the ice charts. We go on to present an automatic classification method for CS-2 data which, after training wit...

  19. The turnstile mechanism across the Kuroshio current: analysis of dynamics in altimeter velocity fields

    Science.gov (United States)

    Mendoza, C.; Mancho, A. M.; Rio, M.-H.

    2010-03-01

    In this article we explore the utility of dynamical systems tools for visualizing transport in oceanic flows described by data sets measured from satellites. In particular we have found the geometrical skeleton of some transport processes in the Kuroshio region. To this end we have computed the special hyperbolic trajectories, and identified them as distinguished hyperbolic trajectories, that act as organizing centres of the flow. We have computed their stable and unstable manifolds, and they reveal that the turnstile mechanism is at work during several spring months in the year 2003 across the Kuroshio current. We have found that near the hyperbolic trajectories takes place a filamentous transport front-cross the current that mixes waters from both sides.

  20. Sensitivity, uncertainty analyses and algorithm selection for Sea Ice Thickness retrieval from Radar Altimeter

    CERN Document Server

    Djepa, Vera

    2013-01-01

    For accurate forecast of climate change, sea ice mass balance, ocean circulation and sea- atmosphere interactions is required to have long term records of Sea Ice Thickness (SIT). Different approaches have been applied to retrieve SIT and only satellite altimetry, radar or laser, have been proven to provide hemispheric estimates of SIT distribution over a sufficient thickness range. To simplify the algorithm for SIT retrieval from RA, constant ice density has been applied until now, which lead to different results for derived SIT and SID, in dependence on input information for sea ice density and snow depth. The purpose of this paper is to select algorithm for SID and SIT retrieval from RA, using statistical, sensitivity analyses and independent observations of SID from moored ULS, or on Submarine. The impact of ice density and snow depth on accuracy of the retrieved SIT has been examined, applying sensitivity analyses, and the propagated uncertainties have been summarised. Accuracy of algorithms for snow dep...

  1. Validation of the multi-mission altimeter data for the Baltic Sea region

    CERN Document Server

    Kudryavtseva, N A

    2016-01-01

    We present a complete cross-validation of Significant Wave Heights (SWH) extracted from altimetry data from all ten existing satellites with available in situ (buoy and echosounder) wave measurements for the Baltic Sea basin. The main purpose is to select an adequate altimetry data subset for a subsequent evaluation of the wave climate. The satellite measurements with the backscatter coefficients >13.5, errors in the SWH normalized standard deviation >0.5 m and snapshots with centroids closer than 0.2 degrees to the land are not reliable. The ice flag usually denotes the ice concentration of >50%. The presence of ice affects the SWH data starting from concentrations 10%, but substantial effects are only evident for concentrations >30%. The altimetry data selected based on these criteria have very good correspondence with in situ data, except for GEOSAT Phase 1 data (1985-1989) that could not be validated. The root-mean-square difference and bias of altimetry and in situ data are in the range of 0.23-0.37 and ...

  2. Impacts of altimeter corrections on local linear sea level trends around Taiwan

    DEFF Research Database (Denmark)

    Cheng, Yongcun; Andersen, Ole Baltazar

    2013-01-01

    .e. the inverted barometer correction, wet tropospheric correction, and sea state bias correction, have significant impacts on the determination of local LSLT. The trend of default corrections contribute more than 1.4 mm year-1 along the coastline of China mainland and 2.1 mm year-1 to local LSLT in the Taiwan...

  3. An Overview of the Bathymetry and Composition of Titan's Hydrocarbon Seas from the Cassini RADAR Altimeter

    Science.gov (United States)

    Mastrogiuseppe, M.; Hayes, A.; Lunine, J. I.; Poggiali, V.; Seu, R.; Hofgartner, J. D.; Lorenz, R. D.; Le Gall, A. A.

    2015-12-01

    The Cassini RADAR's altimetry mode has been successfully used for probing the depth and composition of Titan's hydrocarbons seas. In May 2013, during the spacecraft's 91stflyby of Titan (T91), the instrument demonstrates its capabilities as a radar sounder, presenting a unique opportunity to constrain direct measurements of the depth and composition of Titan's second largest sea, Ligeia Mare. Later, observations of Kraken Mare and Punga Mare were planned and executed in August 2014 (T104) and January 2015 (T108), respectively. While most of the seafloor was not detected at Kraken, suggesting the sea was either too deep or too absorptive in these areas to observe a return from the seafloor, shallow areas near Moray Sinus did return subsurface detections. At Punga Mare, a clear detection of the subsurface was observed with a maximum depth of 120 m along the interrogated track of the sea. We will present an analysis of all three altimetric observations of Titan's mare, as well a re-analysis of altimetry data acquired over southern Ontario Lacus. Depths measurements and liquid composition are obtained using a novel technique which makes use of radar simulations and Monte Carlo based inversions. Finally, we will show that the estimates obtained from the direct measurements described above can be used along with the RADAR's active (i.e. Synthetic Aperture Radar) and passive (Radiometry) modes to generate bathymetry maps of areas not observed by altimetry.

  4. Bathymetry and Composition of Titan's Hydrocarbon Seas from the Cassini RADAR Altimeter

    Science.gov (United States)

    Mastrogiuseppe, Marco; Hayes, Alex; Poggiali, Valerio; Lunine, Jonathan; Seu, Roberto; Hofgartner, Jason; Le Gall, Alice; Lorenz, Ralph

    2016-04-01

    The Cassini RADAR's altimetry mode has been successfully used for probing the depth and composition of Titan's hydrocarbons seas. In May 2013, during the spacecraft's T91 flyby of Titan, the instrument demonstrated its capabilities as a radar sounder, presenting a unique opportunity to constraint the depth and composition of Titan's second largest sea, Ligeia Mare. Later, observations of Kraken Mare and Punga Mare were planned and executed in August 2014 (T104) and January 2015 (T108), respectively. While most of the seafloor was not detected at Kraken, suggesting the sea was either too deep or too absorptive in these areas to observe a return from the seafloor, shallow areas near Moray Sinus did show subsurface reflections. At Punga Mare, a clear detection of the subsurface was observed with a maximum depth of 120 m along the radar altimetry transect. Herein we present a re-analysis of altimetry data acquired over Ligeia Mare and, earlier in the Cassini mission (in December 2008 during T49), over the southern Ontario Lacus. Depths measurements and liquid composition are obtained using a novel technique which makes use of radar simulations and Monte Carlo-based inversions. Simulation is based on a two-layer model, where the surface is represented by a specular reflection and the seafloor is modeled using a facet-based synthetic surface, including thermal noise, speckle effects, analog to digital conversion (ADC), block adaptive quantization (BAQ), and allows for possible receiver saturation. This new analysis provides an update to the Ku-band attenuation (the Cassini RADAR operates at a wavelength of 2 cm) and results in a new estimate for loss tangent and composition. We found a value of specific attenuation of the liquid equal to 0.14±0.02 dB/m and 0.2±0.1 dB/m, which is equivalent to a loss tangent of 4.4±0.9x10^-5 and 7±3x10^-5 for Ligeia Mare and Ontario Lacus, respectively. Assuming that Titan's liquid bodies are composed by a ternary mixture of methane, ethane, and nitrogen, these values of loss tangent are consistent with a composition of 69% of methane (CH4), 14% of ethane (C2H6) and 17% nitrogen (N2) for Ligeia Mare and 47% of methane (CH4), 40% of ethane (C2H6) and 13% nitrogen (N2) for Ontario Lacus.

  5. Observations of Antarctic Polar Stratospheric Clouds by Geoscience Laser Altimeter System (GLAS)

    Science.gov (United States)

    Palm, Stephen P.; Fromm, Michael; Spinhirne, James

    2005-01-01

    Polar Stratospheric Clouds (PSCs) frequently occur in the polar regions during winter and are important because they play a role in the destruction of stratospheric ozone. During late September and early October 2003, GLAS frequently observed PSCs over western Antarctica. At the peak of this activity on September 29 and 30 we investigate the vertical structure and extent, horizontal coverage and backscatter characteristics of the PSCs using the GLAS data. The PSCs were found to cover an area approximately 10 to 15 % of the size of Antarctica in a region where enhanced PSC frequency has been noted by previous PSC climatology studies. The area of PSC formation was found to coincide with the coldest temperatures in the lower stratosphere. In addition, extensive cloudiness was seen within the troposphere below the PSCs indicating that tropospheric disturbances might have played a role in their formation.

  6. Seasonal global mean sea level change from satellite altimeter, GRACE, and geophysical models

    OpenAIRE

    Chen, JL; Wilson, CR; Tapley, BD; Famiglietti, JS; Rodell, M.

    2005-01-01

    We estimate seasonal global mean sea level changes using different data resources, including sea level anomalies from satellite radar altimetry, ocean temperature and salinity from the World Ocean Atlas 2001, time-variable gravity observations from the Gravity Recovery and Climate Experiment (GRACE) mission, and terrestrial water storage and atmospheric water vapor changes from the NASA global land data assimilation system and National Centers for Environmental Prediction reanalysis atmospher...

  7. Effective aerodynamic roughness estimated from airborne laser altimeter measurements of surface features

    OpenAIRE

    de Vries, AC; Kustas, WP; Ritchie, JC; Klaassen, W.; M. Menenti; Rango, A; Prueger, JH

    2003-01-01

    Aerodynamic roughness length (z(0)) and displacement height (d(0)) are important surface parameters for estimating surface fluxes in numerical models. These parameters are generally determined from wind flow characteristics using logarithmic wind profiles measured at a meteorological tower or by balloon release. It would be an advantage to use measurements of land surface characteristics instead of wind flow characteristics to estimate the z(0), and d(0) for large areas. Important land surfac...

  8. Possible ancient oceans on Mars: evidence from Mars Orbiter Laser Altimeter data.

    Science.gov (United States)

    Head, J W; Hiesinger, H; Ivanov, M A; Kreslavsky, M A; Pratt, S; Thomson, B J

    1999-12-10

    High-resolution altimetric data define the detailed topography of the northern lowlands of Mars, and a range of data is consistent with the hypothesis that a lowland-encircling geologic contact represents the ancient shoreline of a large standing body of water present in middle Mars history. The contact altitude is close to an equipotential line, the topography is smoother at all scales below the contact than above it, the volume enclosed by this contact is within the range of estimates of available water on Mars, and a series of extensive terraces parallel the contact in many places. PMID:10591640

  9. Space-qualified laser system for the BepiColombo Laser Altimeter

    OpenAIRE

    Kallenbach, Reinald; Murphy, Eamonn; Gramkow, Bodo; Rech, Markus; Weidlich, Kai; Leikert, Thomas; Henkelmann, Reiner; Trefzger, Boris; Metz, Bodo; Michaelis, Harald; Lingenauber, Kay; DelTogno, Simone; Behnke, Thomas; Thomas, Nicolas; Piazza, Daniele

    2013-01-01

    The space-qualified design of a miniaturized laser for pulsed operation at a wavelength of 1064 nm and at repetition rates up to 10 Hz is presented. This laser consists of a pair of diode-laser pumped, actively q-switched Nd:YAG rod oscillators hermetically sealed and encapsulated in an environment of dry synthetic air. The system delivers at least 300 million laser pulses with 50 mJ energy and 5 ns pulse width (FWHM). It will be launched in 2017 aboard European Space Agency’s Mercury Planeta...

  10. Karakteristikk og anvendelser av ICESat/GLAS laser-altimeter i fjellterreng.

    OpenAIRE

    2011-01-01

    Denne oppgaven simulererer et fullstendig retursignal fra laseraltimeteret GLAS på satellitten ICESat ved å bruke en digital høydemodell med høy oppløsning og inkludere nær-infrarøde satelittbilder fra Landsat 7 for å kompensere for ulike refleksjonsegenskaper på bakken. Målet er å undersøke om Landsat-data kan forbedre simuleringsmodellen i studieområdet. For den type terreng det er sett på i studien, hovedsaklig furuskog innefor den subalpine sonen i Yosemite nasjonalpark i California, ...

  11. Space-based Swath Imaging Laser Altimeter for Cryospheric Topographic and Surface Property Mapping

    Science.gov (United States)

    Abshire, James; Harding, David; Shuman, Chris; Sun, Xiaoli; Dabney, Phil; Krainak, Michael; Scambos, Ted

    2005-01-01

    Uncertainties in the response of the Greenland and Antarctic polar ice sheets to global climatic change inspired the development of ICESat/GLAS as part of NASA's Earth Observing System. ICESat's primary purpose is the measurement of ice sheet surface elevation profiles with sufficient accuracy, spatial density, and temporal coverage so that elevation changes can be derived with an accuracy of <1.5 cm/year for averages of measurements over the ice sheets with areas of 100 x 100 km. The primary means to achieve this elevation change detection is spatial averaging of elevation differences at cross-overs between ascending and descending profiles in areas of low ice surface slope. Additional information is included in the original extended abstract.

  12. IMPROVE THE ZY-3 HEIGHT ACCURACY USING ICESAT/GLAS LASER ALTIMETER DATA

    OpenAIRE

    LI, GUOYUAN; Tang, Xinming; Gao, Xiaoming; Zhang, Chongyang; Li, Tao

    2016-01-01

    ZY-3 is the first civilian high resolution stereo mapping satellite, which has been launched on 9th, Jan, 2012. The aim of ZY-3 satellite is to obtain high resolution stereo images and support the 1:50000 scale national surveying and mapping. Although ZY-3 has very high accuracy for direct geo-locations without GCPs (Ground Control Points), use of some GCPs is still indispensible for high precise stereo mapping. The GLAS (Geo-science Laser Altimetry System) loaded on the ICESat (Ice Cloud and...

  13. WFF TOPEX Software Documentation Altimeter Instrument File (AIF) Processing, October 1998. Volume 3

    Science.gov (United States)

    Lee, Jeffrey; Lockwood, Dennis

    2003-01-01

    This document is a compendium of the WFF TOPEX Software Development Team's knowledge regarding Sensor Data Record (SDR) Processing. It includes many elements of a requirements document, a software specification document, a software design document, and a user's manual. In the more technical sections, this document assumes the reader is familiar with TOPEX and instrument files.

  14. Utilisation of CryoSat-2 SAR altimeter in operational ice charting

    Directory of Open Access Journals (Sweden)

    E. Rinne

    2015-08-01

    Full Text Available We present methods to utilise Cryosat-2 (CS-2 Synthetic Aperture (SAR mode data in operational ice charting. We compare CS-2 data qualitatively to Synthetic Aperture Radar (SAR mosaics over Barents and Kara seas. Furthermore, we compare the CS-2 to archived operational ice charts. We present distributions of four CS-2 waveform parameters for different ice types as presented in the ice charts. We go on to present an automatic classification method for CS-2 data which, after training with operational ice charts, is capable of determining open water from ice with a hit rate of > 90 %. The training data is dynamically updated every five days using the most recent 15 days CS-2 data and operative ice charts. This helps the adaption of the classifier to the evolving ice/snow conditions throughout winter. The classifier is also capable of detecting three different ice classes (thin and thick first year ice as well as old ice with success rates good enough for the output to be usable to support operational ice charting. Finally, we present a near real time CS-2 product just plotting the waveform characteristics and conclude that even such a simple product is usable for some of the needs of ice charting.

  15. Spectral characteristics of time-dependent orbit errors in altimeter height measurements

    Science.gov (United States)

    Chelton, Dudley B.; Schlax, Michael G.

    1993-01-01

    A mean reference surface and time-dependent orbit errors are estimated simultaneously for each exact-repeat ground track from the first two years of Geosat sea level estimates based on the Goddard Earth model (GEM)-T2 orbits. Motivated by orbit theory and empirical analysis of Geosat data, the time-dependent orbit errors are modeled as 1 cycle per revolution (cpr) sinusoids with slowly varying amplitude and phase. The method recovers the known 'bow tie effect' introduced by the existence of force model errors within the precision orbit determination (POD) procedure used to generate the GEM-T2 orbits. The bow tie pattern of 1-cpr orbit errors is characterized by small amplitudes near the middle and larger amplitudes (up to 160 cm in the 2 yr of data considered here) near the ends of each 5- to 6-day orbit arc over which the POD force model is integrated. A detailed examination of these bow tie patterns reveals the existence of daily modulations of the amplitudes of the 1-cpr sinusoid orbit errors with typical and maximum peak-to-peak ranges of about 14 cm and 30 cm, respectively. The method also identifies a daily variation in the mean orbit error with typical and maximum peak-to-peak ranges of about 6 and 30 cm, respectively, that is unrelated to the predominant 1-cpr orbit error. Application of the simultaneous solution method to the much less accurate Geosat height estimates based on the Naval Astronautics Group orbits concludes that the accuracy of POD is not important for collinear altimetric studies of time-dependent mesoscale variability (wavelengths shorter than 1000 km), as long as the time-dependent orbit errors are dominated by 1-cpr variability and a long-arc (several orbital periods) orbit error estimation scheme such as that presented here is used.

  16. An improved wind speed algorithm for“Jason-1”altimeter under tropical cyclone conditions

    Institute of Scientific and Technical Information of China (English)

    QIN Bangyong; ZHOU Xuan; ZHANG Honglei; YANG Xiaofeng; LU Rong; YU Yang; SHI Lijian

    2014-01-01

    Rain effect and lack of in situ validation data are two main causes of tropical cyclone wind retrieval errors. The National Oceanic and Atmospheric Administration’s Climate Prediction Center Morphing technique (CMORPH) rain rate is introduced to a match-up dataset and then put into a rain correction model to re-move rain effects on“Jason-1”normalized radar cross section (NRCS);Hurricane Research Division (HRD) wind speed, which integrates all available surface weather observations, is used to substitute in situ data for establishing this relationship with“Jason-1”NRCS. Then, an improved“Jason-1”wind retrieval algorithm under tropical cyclone conditions is proposed. Seven tropical cyclones from 2003 to 2010 are studied to validate the new algorithm. The experimental results indicate that the standard deviation of this algorithm at C-band and Ku-band is 1.99 and 2.75 m/s respectively, which is better than the existing algorithms. In addition, the C-band algorithm is more suitable for sea surface wind retrieval than Ku-band under tropical cyclone conditions.

  17. Global Topography of Mars with the MGS Laser Altimeter (MOLA): Latest Results

    Science.gov (United States)

    Smith, David E.; Zuber, Maria T.

    1999-01-01

    After acquiring topographic measurements of the northern hemisphere of Mars last Spring and Summer the Mars Global Surveyor (MGS) spacecraft will begin to observe the rest of Mars from its planned mapping orbit in early March of this this year. After successfully completing the aerobraking phase of the mission in February, the spacecraft will be finally placed into the near circular, 400 km polar, mapping orbit for almost continuous observation of the planet for one Mars year. Of particular interest in the early phases will be the structure of the southern ice cap, the cratered southern highlands and the topography in the region of the landing sites of the Mars 98 and the Mars 01 missions.

  18. Martian Polar Impact Craters: A Preliminary Assessment Using Mars Orbiter Laser Altimeter (MOLA)

    Science.gov (United States)

    Sakimoto, S. E. H.; Garvin, J. B.

    1999-01-01

    Our knowledge of the age of the layered polar deposits and their activity in the volatile cycling and climate history of Mars is based to a large extent on their apparent ages as determined from crater counts. Interpretation of the polar stratigraphy (in terms of climate change) is complicated by reported differences in the ages of the northern and southern layered deposits. The north polar residual ice deposits are thought to be relatively young, based on the reported lack of any fresh impact craters in Viking Orbiter Images. Herkenhoff et al., report no craters at all on the North polar layered deposits or ice cap, and placed an upper bound on the surface age (or, alternatively, the vertical resurfacing rate) of 100 thousand years to 10 million years, suggesting that the north polar region is an active resurfacing site. In contrast, the southern polar region was found to have at least 15 impact craters in the layered deposits and cap. Plaut et al, concluded that the surface was less than or = 120 million years old. This reported age difference factor of 100 to 1000 increases complexity in climate and volatile modeling. Recent MOLA results for the topography of the northern polar cap document a handful or more of possible craters, which could result in revised age or resurfacing estimates for the northern cap. This study is a preliminary look at putative craters in both polar caps. Additional information is contained in the original extended abstract.

  19. Reflected Signal Analysis and Surface Albedo in the Mars Orbiter Laser Altimeter (MOLA) Investigation

    Science.gov (United States)

    Ivanov, Anton B.; Muhleman, Duane O.

    2001-01-01

    This work presents results from the analysis of the reflectivity data from the MOLA investigation. We will discuss calculation of the surface albedo using the MGS TES 9 micron opacity. We will also overview reflectivity data collected to date. Additional information is contained in the original extended abstract.

  20. Constraints on Gusev Basin Infill from the Mars Orbiter Laser Altimeter (MOLA) Topography

    Science.gov (United States)

    Carter, B. L.; Frey, H.; Sakimoto, S. E. H.; Roark, J.

    2001-01-01

    MOLA topography provides volume estimates for Gusev crater based on higher resolution. Revisiting work previously done by Grin and Cabrol (1997), we find a substantial increase in original sedimentation estimates. Additional information is contained in the original extended abstract.

  1. Comparing the steric height in the Nordic Seas with satellite altimeter sea surface height

    Institute of Scientific and Technical Information of China (English)

    SHAO Qiuli; ZHAO Jinping

    2015-01-01

    In this study the steric height anomaly which is calculated from the hydrological data (EN3) is compared with the sea level anomaly derived from satellite altimetry in the Nordic Seas. The overall pattern of steric height is that it is higher in the margin area and lower in the middle area. The extreme values of steric height linear change from 1993 to 2010 occur in the Lofoten Basin and off the Norwegian coast, respectively. Such a distribution may be partly attributed to the freshening trend of the Nordic Seas. The correlation between SLA (sea level anomaly) and SHA (steric height anomaly) is not uniform over the Nordic Seas. The time series of SLA and SHA agree well in the Lofoten Basin and northern Norwegian Basin, and worse in the northern Norwegian Sea, implying that the baroclinic effect plays a dominant role in most areas in the Norwegian Sea and the barotropic effect plays a dominant role in the northern Norwegian Sea. The weaker correlations between SLA and SHA in the Greenland and Iceland Seas lead a conclusion that the barotropic contribution is significant in these areas. The area-mean SHA over the entire Nordic Seas has similar amplitudes compared with the SLA during 1996–2002, but SHA has become lower than SLA, being less than half of SLA since 2006.

  2. A Miniature FMCW Altimeter for imminet Fuse%小型FMCW近炸引信高度表

    Institute of Scientific and Technical Information of China (English)

    甘体国

    1993-01-01

    本文介绍用于导弹或炮弹近炸引信的小型C波段FMCW高度表.分析了影响测高精度的因素,提出了参数选择的原则,介绍了系统组成和试验结果.高度表装在高123mm锥底直径56mm的圆锥体内.

  3. Lessons Learned from Assimilating Altimeter Data into a Coupled General Circulation Model with the GMAO Augmented Ensemble Kalman Filter

    Science.gov (United States)

    Keppenne, Christian; Vernieres, Guillaume; Rienecker, Michele; Jacob, Jossy; Kovach, Robin

    2011-01-01

    Satellite altimetry measurements have provided global, evenly distributed observations of the ocean surface since 1993. However, the difficulties introduced by the presence of model biases and the requirement that data assimilation systems extrapolate the sea surface height (SSH) information to the subsurface in order to estimate the temperature, salinity and currents make it difficult to optimally exploit these measurements. This talk investigates the potential of the altimetry data assimilation once the biases are accounted for with an ad hoc bias estimation scheme. Either steady-state or state-dependent multivariate background-error covariances from an ensemble of model integrations are used to address the problem of extrapolating the information to the sub-surface. The GMAO ocean data assimilation system applied to an ensemble of coupled model instances using the GEOS-5 AGCM coupled to MOM4 is used in the investigation. To model the background error covariances, the system relies on a hybrid ensemble approach in which a small number of dynamically evolved model trajectories is augmented on the one hand with past instances of the state vector along each trajectory and, on the other, with a steady state ensemble of error estimates from a time series of short-term model forecasts. A state-dependent adaptive error-covariance localization and inflation algorithm controls how the SSH information is extrapolated to the sub-surface. A two-step predictor corrector approach is used to assimilate future information. Independent (not-assimilated) temperature and salinity observations from Argo floats are used to validate the assimilation. A two-step projection method in which the system first calculates a SSH increment and then projects this increment vertically onto the temperature, salt and current fields is found to be most effective in reconstructing the sub-surface information. The performance of the system in reconstructing the sub-surface fields is particularly impressive for temperature, but not as satisfactory for salt.

  4. A new, high-resolution digital elevation model of Greenland fully validated with airborne laser altimeter data

    OpenAIRE

    Bamber, JL; Ekholm, S; Krabill, WB

    2001-01-01

    A new digital elevation model of the Greenland ice sheet and surrounding rock outcrops has been produced at 1 km postings from a comprehensive suite of satellite remote sensing and cartographic data sets. Height data over the ice sheet were mainly from ERS-1 and Geosat radar altimetry. These data were corrected for a slope-dependent bias that had been identified in a previous study. The radar altimetry was supplemented with stereo photogrammetric data sets, synthetic aperture radar interferom...

  5. Effects of surface roughness on sea ice freeboard retrieval with an Airborne Ku-Band SAR radar altimeter

    OpenAIRE

    Hendricks, Stefan; Stenseng, Lars; Helm, Veit; Haas, Christian

    2010-01-01

    Results from two years of the CryoSat Validation Experiment (CryoVEx) over sea ice in the western Arctic Ocean are presented. The estimation of freeboard, the height of sea ice floating above the water level, is one the main goals of the CryoSat-2 mission of the European Space Agency (ESA) in order to investigate sea ice volume changes on an Arctic wide scale. Freeboard retrieval requires precise radar range measurements to the ice surface, therefore we investigate the penetration of the Ku-B...

  6. Laser Altimeter Technology and Its Applications%激光高度计技术及其应用

    Institute of Scientific and Technical Information of China (English)

    张翼飞; 杨辉

    2007-01-01

    我国的嫦娥1号月球卫生有一项很重要的工作,那就是绘制一张完整且精确的月球三维地形图,即测量卫星到星下点月球表面的距离,结合光学成像数据,生成月球表面三维影像。担任这项工作的是卫星上的“激光眼”——激光高度计。

  7. 激光测高仪回波分解算法%Decomposing Algorithm of Laser Altimeter Waveforms

    Institute of Scientific and Technical Information of China (English)

    杨庚; 黄春明

    2005-01-01

    开发了一种激光测高仪回波基本信息提取算法,对回波数据进行了高斯波分解,获取了高斯波分量的个数,及每个高斯波分量的波中心位置、宽度和幅度等参数.该算法首先根据回波拐点的数目和位置确定出高斯分量的个数及每个高斯分量的波中心位置和宽度初始值,随后利用线性最小二乘法计算出每个高斯分量的幅度,最后将经过选择和标记的高斯分量针对实际回波采用Levenberg-Marquardt方法进行拟合,得到优化后的高斯波基本参数.通过这些基本参数信息,能够进一步推导出激光测高仪光斑内各个反射表面的垂直分布、起伏程度和反射率等基本信息.

  8. High-Speed Radiation Tolerant Avalanche Photodiodes Based on InGaN for Space Altimeter Systems Project

    Data.gov (United States)

    National Aeronautics and Space Administration — High-performance, radiation-tolerant detectors are required for the time-of-flight laser based rangefinders. Avalanche photodiodes (APDs) are conventionally chosen...

  9. The Observation of SAR, Optical and Altimeter Data to Study the Generation of Internal Wave in Tsushima Strait

    Science.gov (United States)

    Arvelyna, Y.; Oshima, M.

    2006-07-01

    This study proposes D iscr eet Mey er wavelet tr ansform and spectr al reflectan ce analysis for internal w ave detection in ERS1/2 and ASTER imag es data over the Tsushima Strait, Jap an, during 1993-2004 period. The wavelet tr ansform of imag e w as successfully der ived the intern al wav e f eature with h igher w avelet coeff icien t than sea surf ace, i.e. between 2-4.59 times, on horizon tal and vertical d etail coefficient at level 2-5, incr eased the detection probability over 80%. The intern al w ave is modeled using Co mbined Korteweg the Vries (combKdV) model. Non linier speed of in ternal wave is calculated about 85 cm-1. Th e altimetry data products from Topex/Poseidon and Jason-1 data are used to predict th e internal wav e gener ation. Th e observation results show th e propagation of in ternal w aves wer e varied between N W-SW at eastern channel and N-SW at western channel of Tsush ima Strait, p arallel to the direction of the geostrophic curren t. A t NE coast off Tsushima Island, the direction is on S/SE dir ection. I t is suggested th at th e internal wav es w ere sourced from south co ast off Tsush ima Island and south coast off the Japan Sea. They w ere possib ly tid ally gen erated and formed due to bathymetr ic change.

  10. Multi-scale wavelet analysis of TOPEX/Poseidon altimeter significant wave height in eastern China seas

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The multi-scale characteristics of wave significant height (Hs) in eastern China seas were revealed by multi-scale wavelet analysis. In order to understand the relation between wave and wind, the TOPEX/Poseidon measurements of Hs and wind speed were analyzed. The result showed that Hs and wind speed change in multi-scale at one-, two-month, half-, one- and two-year cycles. But in a larger time scale, the variations in Hs and wind speed are different. Hs has a five-year cycle similar to the cycle of ENSO variation, while the wind speed has no such cycle. In the time domain, the correlation between Hs and ENSO is unclear.

  11. Altimeter-derived flow field over a newly identified coastal ocean boundary in the eastern Arabian Sea

    Digital Repository Service at National Institute of Oceanography (India)

    Antony, M.K.; Somayajulu, Y.K.; Swamy, G.N.

    part, tapers off towards north and bulges towards south. In the present communication, the T/P-derived flow pattern over this new boundary is presented. The derived flow pattern shows the general dominance of meso-scale eddies in the Arabian Sea...

  12. Global Geometric Properties of Martian Impact Craters: An Assessment from Mars Orbiter Laser Altimeter (MOLA) Digital Elevation Models

    Science.gov (United States)

    Garvin, J. B.; Frawley, J. J.; Sakimoto, S. E. H.; Schnetzler, C.

    2000-01-01

    Global geometric characteristics of topographically fresh impact craters have been assessed, for the first time, from gridded MOLA topography. Global trends of properties such as depth/diameter differ from previous estimates. Regional differences are observed.

  13. Participation of D.O. Muhleman as a Co-Investigator on the Mars Observer Laser Altimeter (MOLA) Team

    Science.gov (United States)

    Muhleman, Duane O.

    2004-01-01

    The Co-I has been a principle member of the MOLA Team since the beginning of the Mars Observer Project and the MOLA Team formation. The basic area of research for the Co-I involved the interactions of the MOLA laser beam with the Mars atmosphere, ice fields and surface in general. The Co-I was assisted by one graduate student, and later a research assistant, Anton Ivanov, throughout the reporting period. Dr. Ivanov received a PhD from Caltech in 2000 from research involving the MOLA project. Dr. Ivanov continued with the MOLA project after receiving his degree as a research assistant to Professor Muhleman. Most of the funding from this grant was used to support Dr. Ivanov during the later years. The primary results of these investigations included the measurement of Mars atmospheric opacity at the 1 micron wavelength of the laser, the effects of dust within the craters and canyons of Mars, and a detailed study of the North Polar Ice Cap in terms of ice sublimation and the current structure of that ice cap. We were able to show that the sublimation of the ice on the polar cap would create the current average shape of the norther cap. Extensive data collection and study were made of the Mars surface 1 micron reflectivity until the laser mechanically failed during the reporting period. Reflectivity maps of Mars were produced although there were serious problems of the laser echo signal strength calibration. After that event the efforts were mainly to complete the older investigations. All of the work supported by this grant was theoretical in nature and did not lead to any patents.

  14. Using Mars Orbiter Laser Altimeter (MOLA) Data to Assess Impact Crater Modification in the Arrhenius Region of Mars

    Science.gov (United States)

    Garvin, J. B.; Grosfils, E. B.; Sakimoto, S. E. H.

    2000-01-01

    This study combines MOLA altimetry with photographic imagery to begin assessing the extent to which sedimentary and volcanic processes have affected impact crater morphology in the Arrhenius region of Mars.

  15. Recovery Of Short Wavelength Geophysical Signals With Future Delay-Doppler Altimeters (Cryosat Ii And Sentinel Type)

    DEFF Research Database (Denmark)

    Andersen, Ole Baltazar

    2010-01-01

    altimetry: Factor of 20 improvements in along track resolution. An along-track footprint length that does not vary with wave height (sea state). Twice the precision in sea surface height measurements / sea surface slope measurements. These improvements are studied with respect to retrieval of short...

  16. Estimating discharge from the Godavari river using ENVISAT, Jason-2, and SARAL/AltiKa radar altimeters

    Digital Repository Service at National Institute of Oceanography (India)

    Sridevi, T.; Sharma, Rashmi; Mehra, P.; Prasad, K.V.S.R.

    ; Dubey et al. 2014). There are various databases that provide time series of water stages in the various basins of the world, Hydro web databases by LEGOS (Laboratoired'Etudes en GeodésieetOcéanographieSpatiales, (http...-term flooding) due to low temporal (35 days) coverage of SARAL mission (SARAL/AltiKa handbook 2013). Although Godavari River is considered as the second longest river in India and contributing fresh water flux next to Ganges, the usefulness of altimetry...

  17. LIC and LID considerations in the design and implementation of the MEMS laser pointing mechanism for the EUSO UV laser altimeter

    Science.gov (United States)

    Bozzo, Enrico; Burch, Thomas; Ciapponi, Alessandra; Heese, Clemens; Hoogerwerf, Arno; Lan, Nicholas; Neronov, Andrii; Revol, Vincent; Stanley, Ross

    2016-07-01

    The EUSO (Extreme Universe Space Observatory) project is developing a new mission concept for the scientific research of Ultra High Energy Cosmic Rays (UHECRs) from space. The EUSO wide-field telescope will look down from space onto the Earth night sky to detect UV photons emitted from air showers generated by UHECRs in our atmosphere. In this article we concentrate on the mitigation strategies agreed so far, and in particular on the implementation of a careful early selection and testing of subsystem materials (including optics), design and interfaces of the subsystem and an optimization of the instrument operational concept.

  18. 基于SystemVue的FMCW定高系统建模与仿真%FMCW Altimeter System Modeling and Simulation Based on SystemVue

    Institute of Scientific and Technical Information of China (English)

    2016-01-01

    FMCW是一种定高引信体制.为了实现FMCW定高系统性能评估和方案验证,利用SystemVue仿真软件进行系统建模与仿真.通过搭建系统模型和设置系统参数,仿真得到定高距离不大于100m时,FMCW定高系统测距精度优于10%的结论.仿真结果证明了系统方案的可行性及参数选择的正确性,为FMCW定高系统的工程实现提供了参考.

  19. Geoid undulations and gravity anomalies over the Aral Sea, the Black Sea and the Caspian Sea from a combined GEOS-3/SEASAT/GEOSAT altimeter data set

    Science.gov (United States)

    Au, Andrew Y.; Brown, Richard D.; Welker, Jean E.

    1991-01-01

    Satellite-based altimetric data taken by GOES-3, SEASAT, and GEOSAT over the Aral Sea, the Black Sea, and the Caspian Sea are analyzed and a least squares collocation technique is used to predict the geoid undulations on a 0.25x0.25 deg. grid and to transform these geoid undulations to free air gravity anomalies. Rapp's 180x180 geopotential model is used as the reference surface for the collocation procedure. The result of geoid to gravity transformation is, however, sensitive to the information content of the reference geopotential model used. For example, considerable detailed surface gravity data were incorporated into the reference model over the Black Sea, resulting in a reference model with significant information content at short wavelengths. Thus, estimation of short wavelength gravity anomalies from gridded geoid heights is generally reliable over regions such as the Black Sea, using the conventional collocation technique with local empirical covariance functions. Over regions such as the Caspian Sea, where detailed surface data are generally not incorporated into the reference model, unconventional techniques are needed to obtain reliable gravity anomalies. Based on the predicted gravity anomalies over these inland seas, speculative tectonic structures are identified and geophysical processes are inferred.

  20. Trends of wave height and period in the Central Arabian Sea from 1996 to 2012: A study based on satellite altimeter data

    Digital Repository Service at National Institute of Oceanography (India)

    Hithin, N.K.; SanilKumar, V.; Shanas, P.R.

    trend of 0.63 cm yr−1 in the annual mean SWH. In contrast, a negative trend of 2.66 cm yr−1 is found for the annual maximum SWH due to the decreasing trend of extreme tropical cyclone events. The annual mean and maximum wave period...

  1. LIC and LID considerations in the design and implementation of the MEMS laser pointing mechanism for the EUSO UV laser altimeter

    CERN Document Server

    Bozzo, Enrico; Ciapponi, Alessandra; Heese, Clemens; Hoogerwerf, Arno; Lan, Nicholas; Neronov, Andrii; Revol, Vincent; Stanley, Ross

    2016-01-01

    The EUSO (Extreme Universe Space Observatory) project is developing a new mission concept for the scientific research of Ultra High Energy Cosmic Rays (UHECRs) from space. The EUSO wide-field telescope will look down from space onto the Earth night sky to detect UV photons emitted from air showers generated by UHECRs in our atmosphere. In this article we concentrate on the mitigation strategies agreed so far, and in particular on the implementation of a careful early selection and testing of subsystem materials (including optics), design and interfaces of the subsystem and an optimization of the instrument operational concept.

  2. Assessment of an ensemble system that assimilates Jason-1/Envisat altimeter data in a probabilistic model of the North Atlantic ocean circulation

    Directory of Open Access Journals (Sweden)

    G. Candille

    2014-12-01

    Full Text Available A realistic circulation model of the North Atlantic ocean at 1/4° resolution (NATL025 NEMO configuration has been adapted to explicitly simulate model uncertainties. This is achieved by introducing stochastic perturbations in the equation of state to represent the effect of unresolved scales on the model dynamics. The main motivation for this work is to develop ensemble data assimilation methods, assimilating altimetric data from past missions JASON-1 and ENVISAT. The assimilation experiment is designed to better control the Gulf Stream circulation for years 2005/06, focusing on frontal regions which are predominantly affected by unresolved dynamical scales. An ensemble based on such stochastic perturbations is first produced and evaluated using along-track altimetry observations. The Incremental Analysis Update (IAU scheme is applied in order to obtain an ensemble of continuous trajectories all over the 2005/06 assimilation period. These three elements – stochastic parameterization, ensemble simulation and 4-D observation operator – are then used together to perform a 4-D analysis of along-track altimetry over 10 day windows. Finally, the results of this experiment are objectively evaluated using the standard probabilistic approach developed for meteorological applications (Toth et al., 2003; Candille et al., 2007. The results show that the free ensemble – before starting the assimilation process – correctly reproduces the statistical variability over the Gulf Stream area: the system is then pretty reliable but not informative (null probabilistic resolution. Updating the free ensemble with altimetric data leads to a better reliability with an information gain around 30% (for 10 day forecasts of the SSH variable. Diagnoses on fully independent data (i.e. data that are not assimilated, like temperature and salinity profiles provide more contrasted results when the free and updated ensembles are compared.

  3. Satellite altimeter-derived monthly discharge of the Ganga-Brahmaputra River and its seasonal to interannual variations from 1993 to 2008

    OpenAIRE

    Papa, Fabrice; Durand, Fabien; Rossow, William B.; Rahman, Altiqur; Bala, Sujit

    2010-01-01

    The Ganga-Brahmaputra accounts for similar to 25% of the total amount of freshwater received by the Bay of Bengal. Using daily in situ river discharge data along with altimetry-derived river heights, the present study aims to produce a monthly data set of altimetry-derived Ganga-Brahmaputra River discharge at the river mouths for 1993-2008. First, we estimate the standard error of ENVISAT-derived water levels over the Ganga to be 0.26 m, much smaller than the range of variability of similar t...

  4. Accuracy Analysis of ICESat Laser Altimeter Data Using TOPEX Data%卫星激光测高ICESat确定海面高精度分析

    Institute of Scientific and Technical Information of China (English)

    聂琳娟; 范春波; 超能芳

    2011-01-01

    讨论了ICESat卫星在大地测量学与海洋学中的应用,利用目前国际上公认的最高精度的测高数据TOPEX,分析了ICESat确定的海平面高以及中尺度的海面异常精度,给出了统计结果。%Application research on geodesy and oceanography of ICESat are discussed.We analyze the accuracy of ICESat data using TOPEX data as well as the statistic of the mean and standard deviation between them.A systematic deviation of 10 cm is foud.

  5. The determination of the Hermean gravity and topography from radio science and laser altimeter data of the mission BepiColombo

    OpenAIRE

    MARABUCCI, MANUELA

    2013-01-01

    The thesis is about the use of laser altimetric crossover observables in the orbit determination process, in the frame of the BepiColombo radio science experiment. Numerical simulations have been carried out with the JPL’s orbit determination program (ODP), in order to evaluate the crossover contribution in the trajectory reconstruction when accurate radio measurements are provided, and to device the best strategy to retrieve Mercury’s gravity field and topography. The software used was the J...

  6. Waveform Simulator of Return Signal for Laser Altimeter%激光测高仪接收信号波形模拟器

    Institute of Scientific and Technical Information of China (English)

    周辉; 李松

    2006-01-01

    分析了激光测高系统中接收信号的建立过程及其相关物理量;在忽略大气对激光脉冲的影响下,推导出接佑收信号和目标响应函数的理论模型,表明了接收信号可以看作是发射信号与目标响应函数的卷积.以现有的测高系统(GLAS)为例,采用网格划分的方法,将目标模型离散化,进而模拟出不同观测角及目标模型情况下的接收信号波形.同时将模拟波形的输出参数与测高仪理论计算得到的参数进行了比较,结果发现:模拟接收波形的脉宽与理论计算的脉宽吻合度达99.5%;模拟波形的总光子数与国际上GSFC模拟器得到的总光子数仅相差0.4%;脉冲重心对应的高度值与实际设定的高度值仅相差1%.从而验证了该方法的正确性和可靠性.

  7. 基于FPGA的星载激光测高仪飞行时间测量%Measurement of flight time for satellite laser altimeter based on FPGA

    Institute of Scientific and Technical Information of China (English)

    姚萍萍; 赵欣; 张毅; 涂碧海; 赵平建

    2008-01-01

    激光测高仪是通过测量激光脉冲的飞行时间来获得测高仪与测量目标之间的距离,因此激光飞行时间测量的准确性是衡量其系统能力的根本指标.研制了在星载激光测高系统中基于单芯片现场可编程门阵列(FPGA)的激光飞行时间测量模块.该模块采用高频计数法结合数字内插法的技术,且单片FPGA的使用提高了激光测高仪的距离分辨率、缩短了测量时间.同时大大简化了电路结构和系统体积,受外界环境干扰小,十分符合星载激光测高要求.最后通过地面检测,整个系统在500 km范围内一般条件下获得±50 cm的测高精度.

  8. Processing of Satellite Laser Altimeter Forest Waveform%星载激光测高仪测量森林的回波信号处理

    Institute of Scientific and Technical Information of China (English)

    陈喜明; 黄春明

    2007-01-01

    星载激光测高仪的回波信号能够灵敏反映地面植被组成和地表高度的变化,因此能够用于探测森林地貌;首先对星载激光测高仪的森林回波信号及其处理方法进行了介绍,探讨了在不考虑植被聚集情况下,植被组成与回波信号之间的关系;由于植被的聚集效应,例如树叶群集成树冠,会导致植被组成参数与真实值之间存在差异,这需要建立关于三维的空间分布模型加以解决.

  9. Recent Progress of Spaceborne Laser Altimeter System%星载激光测高仪发展现状综述

    Institute of Scientific and Technical Information of China (English)

    李松

    2004-01-01

    介绍了作为天基系统重要遥感遥测手段的星载激光测高仪(或称为测距仪)的发展现状以及星载激光测高仪关键技术,比较了具有代表性的几个星载激光测高仪系统的主要技术参数.

  10. Application of Binary Optical Element in Satellite Laser Altimeters%二元光学元件在星载激光测高仪中的应用

    Institute of Scientific and Technical Information of China (English)

    刘博; 李松

    2003-01-01

    采用二元光学元件通过波面变换实现了对光束发散角的压缩,同时大大降低了系统的重量.计算和实验表明本系统可将出射光束的发散角压缩至小于20 μrad,完全满足了测高仪的要求,并且不会对其测程造成影响.

  11. Selection and Design of Filters for Laser Altimeters%激光测高系统中匹配滤波器的设计

    Institute of Scientific and Technical Information of China (English)

    李洋; 戚俊; 张毅; 赵欣; 陈结祥; 涂碧海; 王相京; 黄正英

    2006-01-01

    激光测高仪不仅可以精确测量目标的距离,还能够从回波信号中提取倾斜度、粗糙度等特征信息,应用十分广泛.通过对测高系统中信号检测单元分析,采用匹配滤波对回波信号进行处理,达到了理想的滤波效果,这对特征信号的提取和提高系统的探测精度起到了关键的作用.

  12. Correction of atmosphere delay for geoscience laser altimeter system%地球科学激光测高系统大气延迟修正算法

    Institute of Scientific and Technical Information of China (English)

    王欢; 李松; 周辉

    2007-01-01

    为了对大气传播延迟误差进行修正,达到精确测量的目的,推导了天顶延迟的理论计算公式;在大仰角情况下提出了一种简化的映射函数,并把它与连分式映射函数进行了比较.以地球科学激光测高系统在南极的观测数据为依据,分析得到该系统的平均大气延迟量为2.35m,修正误差控制在12mm以内.结果表明,在大仰角情况下,两者对总延迟的影响差异不超过0.1mm.总的延迟量可以通过天顶延迟和映射函数计算得出.

  13. Hydrological parameter estimation for ungauged basin based on satellite altimeter data and discharge modeling. A simulation for the Caqueta River (Amazonian Basin, Colombia

    Directory of Open Access Journals (Sweden)

    J. G. Leon

    2006-09-01

    Full Text Available The main objective of this paper is to review the usefulness of altimetric data in ungauged or very poorly monitored basin. It is shown that altimetric measurements can be combined with a single in-situ gauge to derive a reliable stage-discharge relationship upstream from the gauge. The Caqueta River in the Colombian Amazon Basin was selected to simulate a poorly monitored basin. Thus it was possible to derive the stage-discharge relationship for 13 "virtual gauge stations'' defined at river crossing with radar altimetric ground tracks. Stage measurements are derived from altimetric data following the methodology developed by Leon et al. (2006. Discharge is modeled using PROGUM – a flow routing model based on the Muskingum Cunge (M-C approach considering a diffusion-cum-dynamic wave propagation (Leon et al., 2006 using a single gauge located downstream from the basin under study. Rating curve parameters at virtual stations are estimated by fitting with a power law the temporal series of water surface altitude derived from satellite measurements and the modelled discharges. The methodology allows the ellipsoidal height of effective zero flow to be estimated. This parameter is a good proxy of the mean water depth from which the bottom slope of the reaches can be computed. Validation has been conducted by comparing the results with stages and discharges measured at five other gauges available on the Caqueta basin. Outflow errors range from 10% to 20% between the upper basin and the lower basin, respectively. Mean absolute differences less than 1.10 m between estimated equivalent water depth and measured water depth indicates the reliability of the proposed method. Finally, a 1.2×10−4 mm−1 mean bottom slope has been obtained for the 730 km long reach of the Caqueta main stream considered.

  14. 基于ATLAS语言的无线电高度表测试研究%Research of Radio Altimeter Test Based on ATLAS Language

    Institute of Scientific and Technical Information of China (English)

    吴凌燕

    2010-01-01

    文章以脉冲式无线电高度表为研究对象,用面向对象的ATLAS语言开发了自动测试程序,实现了对无线电高度表的自动检测.测试结果表明,可准确测出设备要求的项目数据,测试精度提高,且以ATLAS开发的程序,可移植性强,大大节约了研制的经费.

  15. Impact of model resolution on sea-level variability characteristics at various space and time scales: insights from four DRAKKAR global simulations and the AVISO altimeter data

    Directory of Open Access Journals (Sweden)

    T. Penduff

    2009-07-01

    Full Text Available Four global ocean/sea-ice simulations driven by the same realistic 46-year daily atmospheric forcing were performed within the DRAKKAR project at 2°, 1°, ½° and ¼° resolutions. Model sea-level anomalies are collocated over the period 1993–2004 onto the AVISO SLA dataset. These five collocated SLA datasets are then filtered and quantitatively compared over various time and space scales regarding three characteristics: SLA standard deviations, spatial correlations between SLA variability maps, and temporal correlations between observed and simulated band-passed filtered local SLA timeseries. Beyond the 2°–1° transition whose benefits are quite moderate, further increases in resolution and associated changes in subgrid scale parameterizations simultaneously induce (i strong increases in SLA standard deviations, (ii strong improvements in the spatial distribution of SLA variability, and (iii slight decreases in temporal correlations between observed and simulation SLA timeseries. These 3 effects are not only clear on mesoscale (14–180 days and quasi-annual (5–18 months fluctuations, but also on the slower (interannual, large-scale variability ultimately involved in ocean-atmosphere coupled processes. Most SLA characteristics are monotonically affected by successive resolution increases, but irregularly and with a strong dependance on frequency and latitude. Benefits of enhanced resolution are maximum in the ½°–¼° transition, in the 14–180 day range, and within eddy-active mid- and high-latitude regions. They are particularly clear in the Southern Ocean where mesoscale eddies probably sustain a substantial intrinsic interannual variability.

  16. Improving the wind and wave estimation of dual-frequency altimeter JASON1 in Typhoon Shanshan and considering the rain effects

    Institute of Scientific and Technical Information of China (English)

    YANG Le; LIN Mingsen; ZOU Juhong; LI Zhenghua; PAN Delu

    2008-01-01

    Altimetry data have been widely used in various fields of oceanography, including the extreme weather events such as tropical cyclones, typhoons, and hurricanes. The performance of JASONI in Typhoon Shanshan is assessed by examining the sensor geophysical data record and illustrates how the measured return waveform, significant wave height, and backscatter are all affected by various factors associated with the typhoon, with details by the rain are illustrated. The correction method to maintain accurate wave height and wind speed measurements in Typhoon Shanshan and the results are presented. Furthermore, the additional results of rain rate and typhoon eye diameter can be retrieved. Because of the lack of in-situ measurements of wind, wave, and rain rate at Typhoon Shanshan, results are compared with the forecasted typhoon data and a good agreement is found.

  17. Sea-level-rise trends off the Indian coasts during the last two decades

    Digital Repository Service at National Institute of Oceanography (India)

    Unnikrishnan, A.S.; Nidheesh, A.G.; Lengaigne, M.

    The present communication discusses sea-level-rise trends in the north Indian Ocean, particularly off the Indian coasts, based on estimates derived from satellite altimeter and tide-gauge data. Altimeter data analysis over the 1993–2012 period...

  18. Adaptive Fiter Algorithm of Ins/Sar Intergrated Navigation Based on Barometric Altimeter%大气高度辅助的惯导/SAR组合自适应算法研究

    Institute of Scientific and Technical Information of China (English)

    张旭; 熊智; 吴旋; 方峥

    2013-01-01

    Consider the shortcoming that SAR image matching navigation can only provide inertial navigation error level position correction, in order to improve the classical control theory design inertia/air damper height channel performance, fully reflect both the atmosphere and inertial navigation union performance advantage, we studied and put forward an integrated navigation scheme using atmospheric altitude auxiliary INS/SAR. The paper designed atmosphere combination model considering dynamic measurement error based on thorough analysis of the basic principle of the inertia/air altitude damping system. To enhance the combination system in transonic flight dynamic flight conditions navigation performance, the paper put forward the atmospheric height of auxiliary based on inertial navigation/ SAR combination adaptive Sage - Husa method. Integrated navigation system simulation results show that the proposed adaptive filter algorithm of INS/SAR can effectively improve transonic flight dynamic environment combination system performance, so as provides a good way to solve the inertial/SAR combination altitude channel stable performance.%在组合惯导系统优化问题的研究中,SAR图像匹配导航仅能提供对惯性导航误差水平位置修正,无法获得高度信息.为改善基于经典控制理论设计的惯性/大气阻尼高度通道性能,充分体现大气和惯性导航两者结合的优势,提出了利用大气高度辅助惯性/SAR的组合导航方案.在深入分析惯性/大气高度阻尼系统工作原理的基础上,设计了考虑大气动态测量误差的组合模型;为有效提升组合系统在跨音速等高动态飞行条件下的导航性能,提出了改进的采用大气高度辅助的惯导/SAR组合自适应Sage-Husa方法.最后仿真可行性结果表明,提出的大气高度辅助的惯导/SAR自适应组合滤波方法可以有效改善跨音速等高动态环境下的组合系统性能.

  19. Ground-based calibration and performance verification of the lunar observation laser altimeter%月球探测卫星激光高度计地面定标与性能验证技术

    Institute of Scientific and Technical Information of China (English)

    黄庚华; 王斌永; 舒嵘; 张海洪

    2006-01-01

    月球探测卫星激光高度计服务于月面三维影像获取的科学目标,在研制过程中需要对激光高度计的固定参数及系统性能进行定标与验证试验,为分析科学和应用目标实现及后期三维数据处理提供必要的参数.介绍了月球探测卫星激光高度计地面定标与性能验证技术,内容包括激光光束发散角、测距系统延迟常数、测距范围、最大测程、测距分辨率及测距不确定度,并对测试误差进行了分析.试验结果表明,激光高度计系统性能符合设计要求,可以保证月面三维影像获取的实现.

  20. Simulation and Realization of the fidelity of the signal of Laser Altimeter Based on Besse%基于贝塞尔滤波器的回波信号提取的仿真和实现

    Institute of Scientific and Technical Information of China (English)

    李洋; 刘元廷; 任萍; 张建秋

    2011-01-01

    激光测高仪的回波信号中包含着目标物的粗糙度、倾斜度、反射率等信息,对于复杂地物特征的回波信号,采用多通道匹配滤波技术不仅可以获得高的信嗓比,还可以保证信号的保真度.

  1. 激光测高仪中雪崩光电二极管的探测性能分析%Detection characteristics of avalanche photodiode in laser altimeter

    Institute of Scientific and Technical Information of China (English)

    姚萍萍; 赵欣; 张毅; 赵平建; 涂碧海

    2008-01-01

    光电探测器是影响激光测高仪探测性能的重要器件.为了使探测器性能保持最佳状态,采用了近似算法进行分析.该算法使用近似分布函数来模拟探测器的输出,推导出虚警率与阈值门限和倍增因子三者之间的函数关系,找出虚警率、阈值和增益之间的最佳结合点.实验表明,根据该方法设计的激光测高仪探测器接收电路,可使探测概率和回波信噪比有显著提高.这一结果对激光测高仪目标特性的回波分析和地形地貌3维轮廓重建有很大帮助.

  2. 基于植被表面的激光测高仪回波波形模型化分析%Modeling Raw Signals of Laser Altimeter Echo Waveform Based on Canopy Surface

    Institute of Scientific and Technical Information of China (English)

    赵欣; 张毅; 王相京; 涂碧海; 赵平建; 张黎明

    2011-01-01

    It has been demonstrated that decomposing the return waveforms into a mixture of Gaussian components was suitable to achieve the information of the target. But the laser impulse is slightly asymmetric, and approximating the waveforms by using a sum of Gaussians may not be an accurate representation depending on the application and target.This paper focus on the improvement of raw signal modeling and refine peak detection greatly increased the number of detected targets as well as their positional accuracy. More complex models than the Gaussian model, such as the Lognormal or generalized Gaussian functions, were introduced and fitted with backscatter waveform of canopy to improve the raw signal by LM algorithm. The results show, through introduction of new echo parameters, it is easy to extract the additional information on the target shape, and calculate reflectivity and roughness.%针对激光测高仪中发射的激光脉冲并不是高斯对称的,并且由于目标物的影响,使用一系列标准高斯函数的和来拟合回波脉冲并不精确,本文提出改变回波分解的取模模型,通过正确模型的选取来改善回波位置的精确度.该方法采用比高斯函数复杂的对数正态函数和广义高斯函数,采用LM非线性拟合算法拟合回波波形.实验结果表明,通过对植被等回波数据的拟合显示出针对不同的地形存在不同的改善效果,同时新参数的引入可获得波形的额外信息,使得对目标物表面几何形状、反射率和粗糙度等信息的解算变得更为容易.

  3. 基于IDL的激光测高雷达回波时域仿真算法研究%Time-domain Simulation Study of Laser Altimeter Waveform Based on IDL

    Institute of Scientific and Technical Information of China (English)

    李骥; 陈结祥; 张毅; 涂碧海; 戚俊; 王相京; 赵平建

    2007-01-01

    从激光测高雷达回波能量分布模型和地表模型入手,详细介绍了基于IDL的激光测高雷达回波的仿真过程及仿真程序各个模块的功能,用Pearson相关性方法将仿真所得波形与实测回波波形进行了分析比对,二者的相关性系数达到90%以上,并分析了回波脉冲波形随测高系统参数和地表参数的变化情况.该方法可以直观有效地对不同地表的回波进行仿真,为激光测高雷达的回波分析提供了重要的技术手段.

  4. Research on Simulation and Analysis of Spaceborne Full Waveform Laser Altimeter%星载全波形激光测高仪仿真分析技术研究

    Institute of Scientific and Technical Information of China (English)

    王春辉; 李旭; 彭欢

    2015-01-01

    全波形激光测高仪技术以其高精度和信息含量丰富成为星载激光测高仪发展的重要方向.为了实现星载激光测高仪完整链路的性能评估,对星载全波形激光测高仪仿真分析模型进行了研究,提出了仿真模型的模块组成.根据激光发射模型、地物模型和接收模型,采用空间细分思想,利用激光雷达方程,完成了星载激光测高仪全波形回波信号的仿真,并采用参数提取算法对回波信号的特征参数进行了提取,实现了星载激光测高仪完整链路的仿真与数据分析.在星载激光测高仪系统设计之初即可实现各环节激光回波信号的预估,在系统设计、产品研制和数据处理中可以发挥重要作用.

  5. 激光高度表与干涉雷达数据融合在高度测量中的应用%Data Fusion of Interferometric Radar and Laser Altimeter for Height Finding

    Institute of Scientific and Technical Information of China (English)

    鲍乐群; 付毓生; 黄顺吉

    2003-01-01

    雷达干涉仪和激光高度表广泛应用于地面高度测量,本文首先利用雷达干涉仪确定地面高度,然后再融合激光高度表数据改进雷达测量结果.数据测量结果表明,与仅使用雷达干涉仪测得的数据相比,数据融合获得的高度测量数据更为精确.

  6. Design and realization of electronics system of laser altimeter%基于匹配滤波技术的激光测高仪电子系学统的设计与实现

    Institute of Scientific and Technical Information of China (English)

    李洋; 汤永新; 任萍; 张建秋; 戚俊

    2010-01-01

    设计了一种基于主动遥感技术的激光测高仪的电子学系统.系统利用匹配滤波技术可自动获得不同目标物回波信号的最佳信噪比并保证了信号的保真度.还设计了一套基于延时线的方法测量距离作为测高系统测量距离的一个备份.实验结果表明,该电子学系统完全实现了测距精度和信号的保真度要求.

  7. 太阳辐照对近红外激光高度计接收系统的影响%EFFECTS OF SOLAR RADIATION ON THE RECEIVER OF NEAR INFRARED LASER ALTIMETER

    Institute of Scientific and Technical Information of China (English)

    张海洪; 王建宇; 舒嵘; 胡以华

    2006-01-01

    根据太阳辐射传输理论,对一星载近红外激光高度计样机在轨运行时,不同的姿态所受到的太阳辐照进行了分析.该激光高度计的工作波长为1064nm.结合激光高度计样机的系统灵敏度,分析得到在激光高度计正常工作时,系统所接收到的星球表面漫射的太阳辐照产生的背景噪声约是系统灵敏度的十分之一,对系统的影响可以忽略.根据雪崩二极管的损伤闻值以及太阳直接辐照时到达探测器的太阳辐照,得到在空间没有任何保护措施的情况下,雪崩二极管所能承受的太阳直接辐照持续为4s.根据分析所得结果,提出了改进措施,为系统的进一步完善提供了依据.

  8. Study of the Technology of Inspecting the Optical Calibration on Pulse Laser Altimeter%脉冲式激光主动遥感器光校实时检测系统研制

    Institute of Scientific and Technical Information of China (English)

    王岚; 舒嵘; 童鹏

    2007-01-01

    以CMOS图像传感器技术为核心,采用USB数据传输和可编程逻辑器件技术,针对脉冲式激光主动遥感器特点研制了光校检测系统.该系统可推广应用于脉冲武激光器的光束成像与研究.

  9. 大气传输介质引起的激光测高仪回波能量衰减分析%Analysis of laser altimeter echo energy attenuation in atmosphere transfer medium

    Institute of Scientific and Technical Information of China (English)

    毕云峰; 陈结祥; 张毅; 戚俊; 涂碧海; 赵平建

    2005-01-01

    阐述了大气传输介质引起激光测高仪回波能量衰减的机制;采用中纬度地区晴朗和霾雾天气下标准大气模式数据,计算了各衰减因素对1.064μm和0.86 μm激光的影响程度和大气斜程透射率随测高仪平台倾角的变化情况.为测高仪设计和对地观测应用提供了依据.

  10. 激光测高仪平顶高斯光束条件下的回波参数模型%Model of Waveform Parameters for Laser Altimeter System Under Flattened Gaussian Beams

    Institute of Scientific and Technical Information of China (English)

    马跃; 李松; 阳凡林; 周辉

    2015-01-01

    星载激光测高仪通过提取激光回波参数计算卫星与地表的距离,结合轨道和姿态信息生成激光脚点的三维坐标.普通高斯光束的空间能量分布随光斑半径增加迅速衰减,不利于探测复杂和分层的地表目标,而平顶高斯光束可以克服这一缺点.根据平顶高斯光束和激光测高回波的相关理论推导得出平顶高斯激光模式下回波波形主要参数的解析式,并使用波形模拟器、波形处理算法,以及地球科学激光测高系统(GLAS)真实回波对所得理论模型进行了验证,结果显示不同阶数激光脉冲的对比偏差都小于3%,且随着目标斜率或阶数的增加,回波宽度和距离误差也随之增加,4阶平顶高斯光束目标斜率0.05时对应的距离误差超过10 cm.

  11. Effect of natural terrain object on return signal of space based laser altimeter%自然地物对星载激光测高仪回波特性的影响

    Institute of Scientific and Technical Information of China (English)

    崔云霞; 牛燕雄; 颜国强; 冯丽爽; 王彩丽; 张鹏

    2012-01-01

    According to the theory of Fresnel diffraction, a continuous land model was established for natural terrain like desert and grass land, a method of gridding partition was developed to simulate the effect of average surficial height and height mean square error on the properties of return signal, including waveform, power and pulse width. The results show thai height mean square error determines the properties of return signal, while the change of terrain mean height cause no difference in return signal in the case of fixed height mean square error.%为了研究沙漠、草地等具有连续分布特点的自然地物对星载激光测高仪回波特性的影响,以菲涅耳衍射理论为基础,建立连续地面物理模型,采用网格划分的方法,对地面平均高度以及地面高度均方差对回波形状、功率和脉冲宽度等特性的影响进行了数值模拟研究.结果表明,若地面高度均方差一定,地面平均高度的变化不会引起脉冲回波信号的变化,而地面高度均方差的变化会直接导致回波信号的变化.

  12. Pulse Laser Altimeter Applicable to Low-flying UAV%适用于无人机超低空飞行的脉冲激光测高系统

    Institute of Scientific and Technical Information of China (English)

    蒙文; 韩万鹏; 李云霞; 马丽华

    2010-01-01

    为了确保无人机超低空飞行时的精确定位和进入机场时的安全着陆,研制了一种重量轻、功耗低、快速精确的脉冲激光测高仪.系统基于脉冲激光测距原理,利用连续波脉冲测距方法精度高、测速快的特点,集成信号处理、计算机控制仿真、虚拟样机、精密机械、精密光学等先进技术,采用红外半导体激光器、专用激光测距传感器模块、高速A/D转换模块和高性能的单片机处理控制芯片等器件最终完成了样机的设计和研制.在实验阶段为了避免计算机建模仿真的复杂性和不准确性,灵活运用半实物仿真技术对整机进行模拟和测量,实验测试结果表明,样机的各项技术性能指标均符合无人机测高系统的使用要求,可以满足无人机在一般环境下超低空飞行的精确定位和安全着陆.

  13. 基于贝塞尔滤波器的回波信号提取的仿真和实现%Simulation and Realization of the fidelity of the signal of Laser Altimeter Based on Bessel filter

    Institute of Scientific and Technical Information of China (English)

    李洋; 刘元廷; 任萍; 张建秋

    2011-01-01

    激光测高仪的回波信号中包含着目标物的粗糙度、倾斜度、反射率等信息,对于复杂地物特征的回波信号,采用多通道匹配滤波技术不仅可以获得高的信噪比,还可以保证信号的保真度.

  14. Influence of single atmospheric scattering effect on received pulse waveform of satellite laser altimeter%单次大气散射效应对星载激光测高仪接收脉冲回波的影响

    Institute of Scientific and Technical Information of China (English)

    周辉; 李松; 王良训; 涂兰芬

    2016-01-01

    大气散射效应是影响星载激光测高仪接收脉冲回波的重要因素.根据星载激光测高仪接收脉冲回波信号与大气响应函数之间的关系式,在忽略大气多次散射效应的条件下,通过分析散射激光束的几何轨迹和散射概率,推导出单次大气散射激光脉冲和接收脉冲回波的特征参数的数学解析式.以地球科学激光测高仪系统参数为输入,采用数值仿真分析的方法,模拟了大气散射介质分布、激光指向角和目标倾斜角对接收脉冲回波信号特征参数的影响.结果表明,若散射介质的高度和粒子半径范围分别为0.2~6 km和0~120 μm,则其对接收脉冲回波的能量、重心和均方根脉宽的影响最大值分别超过15%、250 cm和800 cm.随着激光指向角或目标倾斜角的增加,接收脉冲回波的能量基本不产生影响,但是其重心和均方根脉宽近似呈线性增加趋势.同时,采用高斯拟合方法可以减小大气散射效应对接收脉冲回波的影响.所得结论对于接收脉冲回波的数据处理与分析以及激光测距精度的评估具有一定的指导意义.

  15. Study on Atmospheric Refraction Delay Correction for Satellite Laser Altimeter System%星载激光测高系统的大气折射延迟改正模型研究

    Institute of Scientific and Technical Information of China (English)

    李松; 肖建明; 马跃; 周辉; 郭想

    2013-01-01

    星载激光测高仪通过测量从卫星平台发射的激光脉冲在卫星与地面激光脚点之间的渡越时间计算两者之间的距离.由于光束经过大气层时发生的折射,导致卫星激光测高系统典型的与大气延迟相关的测距误差在数米量级.讨论了大气折射延迟修正的理论与方法,分析比较了各种大气折射率模型,以全球首个对地观测星载激光测高仪系统GLAS系统为例,给出了各种折射率模型的计算偏差,发现在常见温度和湿度范围内Owens375模型是一种精度较高的简化折射率模型;计算了GLAS系统高度角偏离天顶方向不超过10°的情况下,使用简单映射函数与CfA2.2映射函数模型的值,发现其差异不超过0.5 mm.%Satellite laser altimetry system(SLR) measures the distance between the satellite and the surface of the earth by figuring out the transit time of laser pulse. The characteristics ranging error is few meters for a SLR because of the atmospheric refraction delay. The theory and method of atmospheric refraction delay correction are discussed. The various models of atmospheric refraction are analyzed and compared. The atmospheric refraction delay based on different models by using GLAS's parameters is calculated. It shows that the model of Owens 375 is with great precise and simplified in most temperature and humidity conditions. The refraction delay corrections in the condition that altitude angle within 10?are calculated by using a simplified mapping function and CfA2. 2, and diffrences between them is only 0. 5 mm.

  16. Modeling and Simulation of Laser Altimeter Echo Signal Based on Monte Carlo Algorithm%激光测高仪回波建模与蒙特卡罗仿真实现

    Institute of Scientific and Technical Information of China (English)

    毕云峰

    2007-01-01

    对激光测高仪回波进行分析研究,可提高系统测距精度,获取目标信息.但单纯的实验方法条件苛刻代价高昂,且难以定量化评价各因素对回波的影响.而对测高仪回波信号的理论求解又极其复杂.通过仿真技术研究激光测高仪回波是一条可行之路.对测高仪回波信号进行了建模分析,应用Monte Carlo算法实现了激光测高仪回波波形的仿真,对典型情况的仿真证明了该算法和系统的有效性.基于Labview7.1软件平台的仿真系统为激光测高仪回波处理提供了研究平台和一种灵活、可行的方法,并可应用到测高仪设计、实验中去.

  17. GM 测高数据反演中国近海及邻域精细重力场%Refined marine gravity field of the China’s seas and its adjacent area derived from GM altimeter data

    Institute of Scientific and Technical Information of China (English)

    张胜军; 李建成; 王立伟; 孔祥雪

    2014-01-01

    The advanced threshold method was selected for processing the Jason-1 geodetic mission waveform data based on the comparative analysis of four waveform retracking methods.Combined with the retracked ERS-1 and Geosat geodetic mission data,the along-track data were resampled at 2Hz to improve the spatial resolution of coast-al areas.Considering the influence of sea surface topography after the data quality control process,a refined 1′×1′resolution gravity field of the China sea and its adjacent sea areas(0°~45°N,100°~140°E)was obtained by remove-restore method and Vening-Meinesz formula.The validation with shipborne data showed that the accuracy of in-version result is about 4 mGal and 10 mGal in open seas and shallow water areas,respectively.Moreover,the inver-sion result is better than both of the DTU10 model and the V21.1 model.%综合对比4种波形重跟踪算法,选择改进阈值法处理 Jason-1 GM 数据,联合波形重跟踪后的Geosat 和 ERS-1 GM 数据,沿轨2 Hz 重采样以提高数据空间分辨率。通过数据质量控制剔除粗差数据,考虑海表面地形的影响,基于移去-恢复法和维宁-曼齐兹公式反演了中国近海及邻近海域(0°~45° N,100°~140°E)1′×1′的精细重力场。船测数据检核表明反演结果在开阔海域精度约4 mGal,近岸浅水区约10 mGal,均优于 DTU10和 V21.1模型。

  18. MABEL photon-counting laser altimetry data in Alaska for ICESat-2 simulations and development

    OpenAIRE

    K. M. Brunt; T. A. Neumann; Amundson, J. M.; Kavanaugh, J. L.; Moussavi, M. S.; Walsh, K. M.; Cook, W. B.; Markus, T

    2016-01-01

    Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) is scheduled to launch in 2017 and will carry the Advanced Topographic Laser Altimeter System (ATLAS), which is a photon-counting laser altimeter and represents a new approach to satellite determination of surface elevation. Given the new technology of ATLAS, an airborne instrument, the Multiple Altimeter Beam Experimental Lidar (MABEL), was deployed in July 2014 to Alaska to provide data needed for satellite-algorithm development, sim...

  19. Performance of the GLAS Laser Transmitter in Space

    Science.gov (United States)

    Yu, Anthony W.; Afzal, Robert S.; Dallas, Joseph L.; Melak, Anthony; Mamakos, William

    2006-01-01

    The Geoscience Laser Altimeter System (GLAS), launched in January 2003, is a laser altimeter and lidar for the Earth Observing System's (EOS) ICESat mission. The laser transmitter requirements, design and qualification test results and in-flight performance for this space-based remote sensing instrument is summarized and presented.

  20. Initial results from retracking and reprocessing the ERS-1 geodetic mission altimetry for gravity field purposes

    DEFF Research Database (Denmark)

    Andersen, Ole Baltazar; Knudsen, Per; Berry, P.A.M.;

    2004-01-01

    All present global marine gravity fields are based on the lHz ERS-1 Geodetic Mission (GM) altimeter data combined with other altimetric datasets. Close to the coast (......All present global marine gravity fields are based on the lHz ERS-1 Geodetic Mission (GM) altimeter data combined with other altimetric datasets. Close to the coast (...

  1. Combining Envisat type and CryoSat-2 altimetry to inform hydrodynamic models

    DEFF Research Database (Denmark)

    Schneider, Raphael; Nygaard Godiksen, Peter; Villadsen, Heidi;

    2015-01-01

    . Satellite radar altimeters provide water level measurements of inland water bodies. So far, many studies making use of satellite altimeters have been based on data from repeat-orbit missions such as Envisat, ERS or Jason or on synthetic wide-swath altimetry data as expected from the SWOT mission. This work...

  2. Design and Implementation of Three-dimensional Visualization of the Moon Based on Chang'E-1 Data of CCD Camera and Laser Altimeter%基于嫦娥一号CCD相机和激光测距数据的月球三维可视化系统

    Institute of Scientific and Technical Information of China (English)

    左维; 刘阳; 任鑫; 李春来

    2012-01-01

    The high-resolution and high-definition terrain and image data of lunar surface were successfully collected by Chang'E-1, which provides a real and rich data source for establishing three-dimensional visualization of the whole Moon. By analyzing key techniques of large-scale three-dimensional visualization of spatial data, this paper introduces the design and implementation of functions, structure and work flow of the moon's three-dimensional visualization system, and describes the system's key techniques in detail. The moon's three-dimensional visualization system has some unique solutions for the visual modeling of spatial data, organization mode of raster data and vector data, three-dimensional presentation of the polar region data, dynamic scheduling of data and real-time three-dimensional scene rendering techniques. It realizes the seamless organization, efficient access and seamless browsing of the large-scale data of the whole moon.%嫦娥一号成功地获取了月球表面高分辨率和高清晰的地形和影像数据,为建立全月球三维场景的可视化提供了真实而丰富的数据源.通过分析大规模空间数据的三维可视化,介绍了所设计和实现的月球三维可视化系统的功能、体系结构和工作流程,并对系统的关键技术进行了重点讨论.实例结果表明,月球三维可视化系统在空间数据可视化建模、栅格数据和矢量数据的组织方式、极区数据的三维表现,以及数据的动态调度和三维场景的实时渲染技术等方面都有独特的解决方案,实现了全月球大规模数据的无缝组织、高效访问和无缝浏览.

  3. INFLUENCE OF BACKGROUND RADIANT POWER ON THE SIGNAL-TO-NOISE RATIO OF SPACE-BORNE LASER ALTIMETER%背景辐射功率对星载激光高度计信噪比的影响研究

    Institute of Scientific and Technical Information of China (English)

    黄庚华; 欧阳俊华; 舒嵘; 王建宇; 薛永祺

    2009-01-01

    "嫦娥一号"卫星的有效载荷激光高度计通过测量发射与接收信号之间的时间间隔,获得星-月距离数据.本文分析了背景辐射功率、倍增因子与激光高度计最佳信噪比之间的关系,并利用积分球进行了不同背景辐射功率下的信噪比试验,验证了背景辐射功率以及雪崩二极管倍增因子对接收系统信噪比的影响.结果表明,在不同的背景辐射功率条件下,存在不同的最佳倍增因子,使接收系统获得最大信噪比.

  4. 一种基于宽带低噪声THS4012运放的激光测高仪前置放大电路设计与实现%Design Method of Preamplifier Circuit with THS4012 in Laser Altimeter

    Institute of Scientific and Technical Information of China (English)

    伯广宇; 戚俊; 李季; 张毅; 赵平建; 赵欣; 涂碧海

    2007-01-01

    激光测高仪依靠回波信号包含的信息来反演地面目标的物理特性,因此必须保持回波信号的保真度和高信噪比.通过选择合适的探测器、设计与探测器匹配的放大电路、设计可以最大信噪比提取信号并保持滤波信号波形的滤波器来达到系统指标.讨论了激光测高仪前置放大电路的设计原则,分析了测高系统中对放大器选择的要求.实验表明,所设计的前置放大电路可以有效地满足设计要求.

  5. High-Resolution Measurement of Flight Time for Laser Altimeter Based on Field Programmable Gate Array%激光测高仪中基于现场可编程门阵列的高精度飞行时间测量

    Institute of Scientific and Technical Information of China (English)

    姚萍萍; 赵欣; 张毅; 赵平建; 涂碧海

    2008-01-01

    设计了在激光测高系统中基于单芯片现场可编程门阵列(FPGA)的高精度时间间隔测量模块.该模块采用高频计数器实现粗时间测量,差分延时线内插技术完成细时间测量,时间分辨率为300 ps.该芯片同时还集成了时序切割电路、回波脉宽测量和数据传输模块等.在环境温度20℃时对该测量模块进行精度测试,获得标准偏差为94.68 ps,转换成距离为1.42 cm.最后通过地面检测,整个系统在500 km范围内的一般条件下可获得测高精度±50 cm.

  6. NOAA Laboratory for Satellite Altimetry Sea Level Rise Products: Global and regional sea level time series and trend maps for the major ocean basins and marginal seas, based on measurements from satellite radar altimeters, from 1992-12-17 to 2016-09-15 (NCEI Accession 0125535)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This archival package contains global and regional mean sea level time series and trend maps calculated on a continual basis since December 1992 by Laboratory for...

  7. Analyses of altimetry errors using Argo and GRACE data

    Science.gov (United States)

    Legeais, Jean-François; Prandi, Pierre; Guinehut, Stéphanie

    2016-05-01

    This study presents the evaluation of the performances of satellite altimeter missions by comparing the altimeter sea surface heights with in situ dynamic heights derived from vertical temperature and salinity profiles measured by Argo floats. The two objectives of this approach are the detection of altimeter drift and the estimation of the impact of new altimeter standards that requires an independent reference. This external assessment method contributes to altimeter calibration-validation analyses that cover a wide range of activities. Among them, several examples are given to illustrate the usefulness of this approach, separating the analyses of the long-term evolution of the mean sea level and its variability, at global and regional scales and results obtained via relative and absolute comparisons. The latter requires the use of the ocean mass contribution to the sea level derived from Gravity Recovery and Climate Experiment (GRACE) measurements. Our analyses cover the estimation of the global mean sea level trend, the validation of multi-missions altimeter products as well as the assessment of orbit solutions.Even if this approach contributes to the altimeter quality assessment, the differences between two versions of altimeter standards are getting smaller and smaller and it is thus more difficult to detect their impact. It is therefore essential to characterize the errors of the method, which is illustrated with the results of sensitivity analyses to different parameters. This includes the format of the altimeter data, the method of collocation, the temporal reference period and the processing of the ocean mass solutions from GRACE. We also assess the impact of the temporal and spatial sampling of Argo floats, the choice of the reference depth of the in situ profiles and the importance of the deep steric contribution. These analyses provide an estimation of the robustness of the method and the characterization of associated errors. The results also allow us

  8. Differential GPS/inertial navigation approach/landing flight test results

    Science.gov (United States)

    Snyder, Scott; Schipper, Brian; Vallot, Larry; Parker, Nigel; Spitzer, Cary

    1992-01-01

    Results of a joint Honeywell/NASA-Langley differential GPS/inertial flight test conducted in November 1990 are discussed focusing on postflight data analysis. The test was aimed at acquiring a system performance database and demonstrating automatic landing based on an integrated differential GPS/INS with barometric and radar altimeters. Particular attention is given to characteristics of DGPS/inertial error and the magnitude of the differential corrections and vertical channel performance with and without altimeter augmentation. It is shown that DGPS/inertial integrated with a radar altimeter is capable of providing a precision approach and autoland guidance of manned return space vehicles within the Space Shuttle accuracy requirements.

  9. Airborne campaigns for CryoSat prelaunch calibration and validation

    DEFF Research Database (Denmark)

    Skourup, Henriette; Hanson, Susanne; Hvidegaard, Sine Munk;

    2011-01-01

    After the successful launch of CryoSat-2 in April 2010, the first direct validation campaign of the satellite is planned for spring 2011. DTU Space has been involved in ESA’s CryoSat Validation Experiment (CryoVEx) with airborne activities since 2003. To validate the prelaunch performance...... of the CryoSat radar altimeter (SIRAL), an airborne version of the SIRAL altimeter (ASIRAS) has been flown together with a laser scanner in 2006 and 2008. Of particular interest is to study the penetration depth of the radar altimeter over both land- and sea ice. This can be done by comparing the radar...

  10. Studies on thermal fields in the Bay of Bengal

    Digital Repository Service at National Institute of Oceanography (India)

    Gopalakrishna, V.V.; Rao, A.S.

    : (1) Renold's weekly SSTs, and (2) TOPEX altimeter sea-level anomalies. During the observational period a few events were captured to examine thermal response of the upper ocean to varying storm forcing. Special CTD cruises were conducted to supplement...

  11. GEOSAT Follow-On (GFO): Operational Orbit Determination Data for 1998-2008 (NODC Accession 0085961)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The GEOSAT Follow-On (GFO) program is the Navy's initiative to develop an operational series of radar altimeter satellites to maintain continuous ocean observation...

  12. Morphological changes at Godavari delta region due to waves, currents and the associated physical processes

    Digital Repository Service at National Institute of Oceanography (India)

    Sastry, J.S.; Vethamony, P.; Swamy, G.N.

    Wave conditions, the most important in coastal modification, prevailing in the region of Godavari Delta for different seasons are illustrated. The analysis of GEOSAT altimeter data for the period November 1986 to October 1987 shows that only during...

  13. GEOSAT Follow-On (GFO): Geophysical Data Record (NODC Accession 0085960)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The GEOSAT Follow-On (GFO) program is the Navy's initiative to develop an operational series of radar altimeter satellites to maintain continuous ocean observation...

  14. GEOSAT Follow-On (GFO): Precise Orbit Ephemeris (NODC Accession 0085958)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The GEOSAT Follow-On (GFO) program is the Navy's initiative to develop an operational series of radar altimeter satellites to maintain continuous ocean observation...

  15. Mars meter-scale roughness: Goldstone Solar System Radar delay-doppler database

    Science.gov (United States)

    Haldemann, A. F. C.; Jurgens, R. F.; Slade, M. A.

    2002-01-01

    The entire fourteen-year database of Goldstone Solar System Radar Mars near-nadir radar scattering model fits is being revised using the latest topography from the Mars Global Surveyor Mars Orbiter Laser Altimeter instrument.

  16. Physical forcing of biological productivity in the northern Arabian Sea during the northeast monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    PrasannaKumar, S.; Ramaiah, N.; Gauns, M.; Sarma, V.V.S.S.; Muraleedharan, P.M.; Raghukumar, S.; DileepKumar, M.; Madhupratap, M.

    to the inference that even a 1 degree C decrease in SST could lead to significantly higher primary productivity. Satellite data on sea surface temperature (advanced very high-resolution radiometer, AVHRR) and TOPEX/POSEIDON altimeter data suggest...

  17. GEOSAT Follow-On (GFO): Housekeeping Telemetry, Calibration and Waveform Data (NODC Accession 0085962)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The GEOSAT Follow-On (GFO) program is the Navy's initiative to develop an operational series of radar altimeter satellites to maintain continuous ocean observation...

  18. GEOSAT 44: High-Accuracy, High-Resolution Gravity

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This satellite altimeter data base contains precise geoid and gravity anomaly profiles which were constructed from the average of 44 repeat cycles of Geosat. The...

  19. GEOSAT44: High-Accuracy, High-Resolution Gravity

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This satellite altimeter data base contains precise geoid and gravity anomaly profiles which were constructed from the average of 44 repeat cycles of Geosat. The...

  20. Greenland Ice Surface Elevations from NASA ATM Airborne Lidar

    Data.gov (United States)

    National Aeronautics and Space Administration — Scanning laser altimeters were flown over the Greenland icesheet during late spring or early summer from 1993 to 1999. Flights spanned the entire icesheet, sampling...

  1. River Systems Classification- Towards Inland Water Height Retrieval from Sentinel3

    Science.gov (United States)

    Berry, P. A. M.; Smith, R. G.; Salloway, M. K.

    2015-12-01

    The advent of SAR altimeters presents both opportunities and challenges for retrieval of river surface heights. While lake levels have been well monitored by prior altimeter missions, these missions had varying success at capturing the more challenging river targets. This paper examines the global capability of prior altimeters over rivers and presents statistics showing that Envisat was the most successful altimeter to date for river monitoring. The requirement for one ‘clean’ echo is found to be the fundamental constraint on river height retrieval. A detailed Cryosat2 data analysis is performed over three river systems to provide a forward look towards Sentinel3 performance over inland water. Both SAR and LRM echoes are analysed. More than 70% of echoes are found to be complex multi-target responses, a far higher proportion than in previous missions; however, ‘clean’ water echoes are found throughout all three river systems and in both SAR and LRM modes.

  2. Martian Wrinkle Ridge Topography: Evidence for Subsurface Faults from MOLA

    Science.gov (United States)

    Golombek, M. P.; Anderson, F. S.; Zuber, M. T.

    2000-01-01

    Mars Orbiter Laser Altimeter (MOLA) profiles across wrinkle ridges are characterized by plains surfaces at different elevations on either side that appear best explained by subsurface thrust faults that underlie the ridges and produce the offset.

  3. Interactive Graphics Tools for Analysis of MOLA and Other Data

    Science.gov (United States)

    Frey, H.; Roark, J.; Sakimoto, S.

    2000-01-01

    We have developed several interactive analysis tools based on the IDL programming language for the analysis of Mars Orbiting Laser Altimeter (MOLA) profile and gridded data which are available to the general community.

  4. Air Data Calibration Facility

    Data.gov (United States)

    Federal Laboratory Consortium — This facility is for low altitude subsonic altimeter system calibrations of air vehicles. Mission is a direct support of the AFFTC mission. Postflight data merge is...

  5. Assimilation of geodetic dynamic ocean topography with ensemble based Kalman filter

    OpenAIRE

    Janjic Pfander, Tijana; A. Albertella; Schröter, Jens; R. Savcenko; Rummel, R.; Bosch, W.

    2012-01-01

    We use the geodetic method to obtain the dynamical ocean topography (DOT). This method combines the multi-mission-altimeter sea surface height and the GRACE/GOCE gravity field. Using the new global filtering approach, the spectral consistency of both fields is achieved by filtering the sea surface height and the geoid. The new global filtering approach reduces the artificats near the coast lines. Further, results of assimilation of multi-mission-altimeter data and the GRACE/GOCE g...

  6. Apport du filtrage particulaire au recalage altimétrique dans un contexte de navigation hybridée

    OpenAIRE

    Flament, Mathieu

    2009-01-01

    A hybrid navigation system combines several positioning means so as to achieve a greater accuracy, availability, and reliability. This study focuses on the association of an inertial navigation system, an on-board radar-altimeter and a digital terrain elevation model. The target application is autonomous aircrafts (UAVs, long-range missiles). The problem consists in combining the inertial data and radio-altimeter measurements in an optimal way. The problem can be expressed as a non-linear fil...

  7. Cramér-Rao Bounds and Estimation Algorithms for Delay/Doppler and Conventional Altimetry

    OpenAIRE

    Halimi, Abderrahim; Mailhes, Corinne; Tourneret, J. -Y.

    2013-01-01

    International audience Delay/Doppler radar altimetry has been receiving an increasing interest, especially since the launch of the first altimeter in 2010. It aims at reducing the measurement noise and increasing the along-track resolution in comparison with conventional pulse limited altimetry. A semi-analytical model was recently introduced for this new generation of delay/Doppler altimeters. The first contribution of this paper is the derivation of the Cramér-Rao bounds (CRBs) associat...

  8. Ice-sheet elevations from across-track processing of airborne interferometric radar altimetry

    OpenAIRE

    R. L. Hawley; SHEPHERD, A; Cullen, R; V. Helm; Wingham, D. J.

    2009-01-01

    Interferometric Radar Altimeters (IRA's) use dual receive antennas to overcome one of the spatial limitations of pulse-limited altimeters. In a conventional IRA measurement, the range and across-track direction of a scatterer are determined using the phase difference between the antennas. We demonstrate a method of determining multiple elevation points across a swath orthogonal to the instrument ground track in regions of steep terrain, such as ice-sheet margins. We use data from an airborne ...

  9. Improved ice loss estimate of the northwestern Greenland ice sheet

    OpenAIRE

    Kjeldsen, K. K.; Khan, S. A.; van den Broeke, M.R.; van Angelen, J.H.

    2013-01-01

    We estimate ice volume change rates in the northwest Greenland drainage basin during 2003–2009 using Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter data. Elevation changes are often reported to be largest near the frontal portion of outlet glaciers. To improve the volume change estimate, we supplement the ICESat data with altimeter surveys from NASA’s Airborne Topographic Mapper from 2002 to 2010 and NASA’s Land, Vegetation and Ice Sensor from 2010. The Airborne data are mai...

  10. Depth, distribution, and density of CO2 deposition on Mars

    OpenAIRE

    Aharonson, Oded; Zuber, Maria T.; Smith, David E.; Neumann, Gregory A.; Feldman, William C.; Prettyman, Thomas H

    2004-01-01

    Observations by the Mars Orbiter Laser Altimeter have been used to detect subtle changes of the polar surface height during the course of seasonal cycles that correlate with the expected pattern of CO2 deposition and sublimation. Using altimetric crossover residuals from the Mars Orbiter Laser Altimeter, we show that while zonally averaged data capture the global behavior of CO2 exchange, there is a dependence of the pattern on longitude. At the highest latitudes the surface height change is ...

  11. Optical Performance Measurements of the BELA EQM and FM Transmitter Laser during AIV

    OpenAIRE

    Althaus, Christian; Lingenauber, Kay; Behnke, Thomas; Michaelis, Harald

    2014-01-01

    The BepiColombo Laser Altimeter (BELA) onboard the Mercury Planetary Orbiter is Europe’s first built Laser Altimeter for a planetary mission. Its main objectives are global mapping of Mercury’s topography as well as measuring its tidal deformations to learn about the internal structure of this small terrestrial planet [1]. Crucial part of the instrument for this task is the transmitter laser. It must withstand all mission phases till operation in orbit and work within tight parameter margins....

  12. Marginal thinning in Northwest Greenland during 2002-2011

    OpenAIRE

    Khan, Shfaqat Abbas; K. H. Kjær; J. M. Wahr; Bevis, M; Korsgaard, N; A. A. Bjørk; Kjeldsen, K. K.; Timm, L. M.; Dam, T. v.

    2012-01-01

    Many glaciers along the southeast and northwest coast of Greenland have accelerated, increasing the Greenland ice sheet's (GrIS) contribution to global sea-level rise. Here, we map elevation changes in northwest Greenland during 2003-2009 using high-resolution Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter data (Zwally, 2010) supplemented with altimeter surveys from NASA's Airborne Topographic Mapper (ATM) during 2002-2011 (Krabill, 2011). We use the measurements of elevatio...

  13. A new 1 km digital elevation model of the Antarctic derived from combined satellite radar and laser data - Part 1: Data and methods

    OpenAIRE

    J. L. Bamber; J. L. Gomez-Dans; Griggs, J. A.

    2009-01-01

    Digital elevation models (DEMs) of the whole of Antarctica have been derived, previously, from satellite radar altimetry (SRA) and limited terrestrial data. Near the ice sheet margins and in other areas of steep relief the SRA data tend to have relatively poor coverage and accuracy. To remedy this and to extend the coverage beyond the latitudinal limit of the SRA missions (81.5° S) we have combined laser altimeter measurements from the Geosciences Laser Altimeter System onboard ICESat...

  14. Satellite radar altimetry over ice. Volume 1: Processing and corrections of Seasat data over Greenland

    Science.gov (United States)

    Zwally, H. Jay; Brenner, Anita C.; Major, Judith A.; Martin, Thomas V.; Bindschadler, Robert A.

    1990-01-01

    The data-processing methods and ice data products derived from Seasat radar altimeter measurements over the Greenland ice sheet and surrounding sea ice are documented. The corrections derived and applied to the Seasat radar altimeter data over ice are described in detail, including the editing and retracking algorithm to correct for height errors caused by lags in the automatic range tracking circuit. The methods for radial adjustment of the orbits and estimation of the slope-induced errors are given.

  15. Combining Envisat type and CryoSat-2 altimetry to inform hydrodynamic models

    OpenAIRE

    Schneider, Raphael; Nygaard Godiksen, Peter; Villadsen, Heidi; Madsen, Henrik; Bauer-Gottwein, Peter

    2015-01-01

    Hydrological models are developed and used for flood forecasting and water resources management. Such models rely on a variety of input and calibration data. In general, and especially in data scarce areas, remote sensing provides valuable data for the parameterization and updating of such models. Satellite radar altimeters provide water level measurements of inland water bodies. So far, many studies making use of satellite altimeters have been based on data from repeat-orbit missions such as...

  16. 15 Years of Wave Height Data Assimilation

    Science.gov (United States)

    Janssen, P.

    2006-07-01

    Over the past fiffteen years there has been a continuous interplay between ocean wave forecasting and altimeter data resulting in improvemen ts in both. The prospect of global observations of wind and waves gave a significan t stimulus to wave model development, while the need to have reliab le wav e predictions stimu lated the d evelopment of altimeter wind and wave products. This p aper covers the following: - Altimeter W ave Height D ata Assimilation of altimeter wave height data is of vital importance for the quality of the wave analysis and ocean wave forecasting. In addition, these data are a great h elp in diagnosing wave model problems. Furthermore th ey have great value in ob taining a g lobal wave climato logy. -Altimeter W ind Sp eed D ata Wind speed data are important for mon itor ing the quality of modelled surface w ind. Recen tly, the 'classical' W itter and Ch elton (1991) retriev al algorithm for wind speed (σ0 = ƒ(U10))has been extended by includ ing sea state eff ects and has been in troduced for Jason. On the other hand, th e classical scheme was improved by Abdalla (2006) and introduced for ENVISAT. Th e Abdalla algorithm is shown to perform better, however . Altimeter w indspeed data h ave the potential to be of great value in hurricane conditions as w ell. -Tsunamis An altimeter can ind eed observe tsunami even ts, but there is doubt th at this may be of value for an early warning system.

  17. A multi-subwaveform parametric retracker of the radar satellite altimetric waveform and recovery of gravity anomalies over coastal oceans

    Institute of Scientific and Technical Information of China (English)

    HWANG; CheinWay

    2010-01-01

    The quality of satellite radar altimetric data is very important in studies of geodesy,geophysics,and oceanography.Over coastal oceans,altimeter waveforms are contaminated by the terrain and physical environments so that the accuracy of altimeter data is lower than that over open oceans.Here we develop a new multi-subwaveform parametric retracker(MSPR) to improve the quality of altimeter data for the recovery of gravity anomaly in coastal oceans.The least squares collocation method is used to recover the residual gravity anomaly over the coastal water from altimetric data.The waveform data records from Geosat/GM around Taiwan Island are practically retracked with MSPR.When compared with the Taiwan geoid height,the results retracked by MSPR are more accurate than those retracked by the well-known β-5-parmeter method and from the geophysical data records(GDRs).The gravity anomalies over Taiwan coastal waters are calculated from the retracked altimeter data with the least squares collocation.When we compared gravity anomalies computed using altimeter GDRs with the ship-borne gravity data over Taiwan coastal ocean,we found that the results from retracked data are more accurate than those from GDRs.

  18. Calibration of HY-2A satellite significant wave heights within situ observation

    Institute of Scientific and Technical Information of China (English)

    PENG Hailong; LIN Mingsen

    2016-01-01

    Significant wave height (SWH) can be computed from the returning waveform of radar altimeter, this parameter is only raw estimates if it does not calibrate. But accurate calibration is important for all applications, especially for climate studies. HY-2a altimeter has been operational since April 2012 and its products are available to the scientific community. In this work, SWH data from HY-2A altimeters are calibrated againstin situ buoy data from the National Data Buoy Center (NDBC), Distinguished from previous calibration studies which generally regarded buoy data as "truth", the work of calibration for HY-2A altimeter wave data againstin situ buoys was applied a more sophisticated statistical technique—the total least squares (TLS) method which can take into account errors in both variables. We present calibration results for HY-2A radar altimeter measurement of wave height against NDBC buoys. In addition, cross-calibration for HY-2A and Jason-2 wave data are talked over and the result is given.

  19. The GANDER constellation for maritime dissaster mitigation

    Science.gov (United States)

    da Silva Curiel, R. A.; Jolly, G.; Zheng, Y.

    1999-09-01

    The development of sea state monitoring from polar-orbiting satellites has recently moved away from the concept of single, multi-sensor platform such as ERS-2, Topex/Poseidon or ENVISAT towards the design of a system that would allow frequent updates from a constellation of small satellites equipped with special-purpose radar altimeters. This new system, called GANDER for Global Altimeter Network Designed to Evaluate Risk, has attracted significant support from a number of important customer segments including the military. This paper details the design of an altimeter for a Surrey small satellite, and illustrates the major system trade-offs that need to be made. Critical to the viability of the mission will be the development of a radar altimeter capable of operating successfully on a small satellite bus, within a limited volume and power budget. The mission design presents a number of key technological challenges, in order to permit a physically small antenna to be employed, and to minimise the pulse power. This can be achieved by advanced techniques, such as the delay Doppler altimeter concept, which emphasises the needs for high-speed on-board signal processing, phase linearity and pulse-to-pulse phase coherency. The system design for the GANDER constellation is also described, illustrating how it not only offers a means for maritime disaster mitigation, but also can reduce shipping cost and time.

  20. Blended sea level anomaly fields with enhanced coastal coverage along the U.S. West Coast.

    Science.gov (United States)

    Risien, C M; Strub, P T

    2016-01-01

    We form a new 'blended' data set of sea level anomaly (SLA) fields by combining gridded daily fields derived from altimeter data with coastal tide gauge data. Within approximately 55-70 km of the coast, the altimeter data are discarded and replaced by a linear interpolation between the tide gauge and remaining offshore altimeter data. To create a common reference height for altimeter and tide gauge data, a 20-year mean is subtracted from each time series (from each tide gauge and altimeter grid point) before combining the data sets to form a blended mean sea level anomaly (SLA) data set. Daily mean fields are produced for the 22-year period 1 January 1993-31 December 2014. The primary validation compares geostrophic velocities calculated from the height fields and velocities measured at four moorings covering the north-south range of the new data set. The blended data set improves the alongshore (meridional) component of the currents, indicating an improvement in the cross-shelf gradient of the mean SLA data set. PMID:26927667

  1. The influence of actual and apparent geoid error on ocean analysis and prediction

    Science.gov (United States)

    Thompson, J. D.

    1984-01-01

    The radar altimeter is the only satellite remote sensor with a proven capability for synoptically measuring an integral property of the dynamic ocean on a near global, all weather basis. Because acquisition of global, in situ ocean data with space/time resolution adequate to describe dynamically important ocean features is practically impossible, any attempt to develop a global ocean monitoring and forecasting system will rely heavily on altimetric data for initialization and updating. Maximizing useful information from the altimeter while minimizing error sources and developing methods for assimilating altimeter data into dynamical models are, therefore, vital areas for research and development. The limits imposed on ocean prediction by errors in the geoid or apparent errors associated with ground track variations near strong geopotential gradients are examined.

  2. Reconfigurable Computing As an Enabling Technology for Single-Photon-Counting Laser Altimetry

    Science.gov (United States)

    Powell, Wesley; Hicks, Edward; Pinchinat, Maxime; Dabney, Philip; McGarry, Jan; Murray, Paul

    2003-01-01

    Single-photon-counting laser altimetry is a new measurement technique offering significant advantages in vertical resolution, reducing instrument size, mass, and power, and reducing laser complexity as compared to analog or threshold detection laser altimetry techniques. However, these improvements come at the cost of a dramatically increased requirement for onboard real-time data processing. Reconfigurable computing has been shown to offer considerable performance advantages in performing this processing. These advantages have been demonstrated on the Multi-KiloHertz Micro-Laser Altimeter (MMLA), an aircraft based single-photon-counting laser altimeter developed by NASA Goddard Space Flight Center with several potential spaceflight applications. This paper describes how reconfigurable computing technology was employed to perform MMLA data processing in real-time under realistic operating constraints, along with the results observed. This paper also expands on these prior results to identify concepts for using reconfigurable computing to enable spaceflight single-photon-counting laser altimeter instruments.

  3. Is the detection of accelerated sea level rise imminent?

    Science.gov (United States)

    Fasullo, J T; Nerem, R S; Hamlington, B

    2016-01-01

    Global mean sea level rise estimated from satellite altimetry provides a strong constraint on climate variability and change and is expected to accelerate as the rates of both ocean warming and cryospheric mass loss increase over time. In stark contrast to this expectation however, current altimeter products show the rate of sea level rise to have decreased from the first to second decades of the altimeter era. Here, a combined analysis of altimeter data and specially designed climate model simulations shows the 1991 eruption of Mt Pinatubo to likely have masked the acceleration that would have otherwise occurred. This masking arose largely from a recovery in ocean heat content through the mid to late 1990 s subsequent to major heat content reductions in the years following the eruption. A consequence of this finding is that barring another major volcanic eruption, a detectable acceleration is likely to emerge from the noise of internal climate variability in the coming decade. PMID:27506974

  4. Instrument Design and In Orbit Performance of Planetary L1dars at NASA GSFC

    Science.gov (United States)

    Sun, Xiaoli; Cavanaugh, John F.; Smith, James C.; Abshire, James B.; Neumann, Gregory A.; Smith, David E.; Zuber, Maria T.

    2012-01-01

    Space lidars provides a unique and powerful tool in earth environment monitoring and planetary exploration. Lidars operate at a much shorter wavelength than radars and can have a much narrower beam and much smaller transmitter and receiver. Lidars carry their own light sources and can continue measurement day and night, and over polar regions, where the passive instruments cannot observe. NASA Goddard Space Flight Center (GSFC) has developed several space lidars, three of them on planetary missions. These were the Mars Orbiter Laser Altimeter (MOLA) on the Mars Observer and Mars Global Surveyor missions, the Mercury Laser Altimeter (MLA) on the MErcury Surface Space ENvironment, GEochemistry and Ranging (MESSENGER) mission and the Lunar Orbital Laser Altimeter (LOLA) on the Lunar Reconnaissance (LRO) mission. These lidars all use similar technologies but with major improvement from one instrument In the next in size, power, measurement capability and operating environment.

  5. Is the detection of accelerated sea level rise imminent?

    Science.gov (United States)

    Fasullo, J. T.; Nerem, R. S.; Hamlington, B.

    2016-08-01

    Global mean sea level rise estimated from satellite altimetry provides a strong constraint on climate variability and change and is expected to accelerate as the rates of both ocean warming and cryospheric mass loss increase over time. In stark contrast to this expectation however, current altimeter products show the rate of sea level rise to have decreased from the first to second decades of the altimeter era. Here, a combined analysis of altimeter data and specially designed climate model simulations shows the 1991 eruption of Mt Pinatubo to likely have masked the acceleration that would have otherwise occurred. This masking arose largely from a recovery in ocean heat content through the mid to late 1990 s subsequent to major heat content reductions in the years following the eruption. A consequence of this finding is that barring another major volcanic eruption, a detectable acceleration is likely to emerge from the noise of internal climate variability in the coming decade.

  6. Ocean dynamics in the Nordic Seas using satellite altimetry

    Science.gov (United States)

    Pettersson, Lasse H.; Johannessen, O. M.; Olaussen, T. I.

    1991-01-01

    The main objective of this TOPEX/POSEIDON project is to integrate the accurately measured sea surface topography, as resolved by both TOPEX/POSEIDON radar altimeters, into the above-mentioned quantitative studies of the short- and long-term variations in the mesoscale ocean dynamics of the Nordic Seas south of 66 deg N. This implies: (1) comparison and validation of the capability to resolve the general basin-scale circulation and the mesoscale variability by, respectively, radar altimeters and numerical ocean circulation models; (2) calibration and validation of the altimeter-derived sea surface topography against in situ measurements from research vessels and moorings, particularly under extreme wind and wave conditions; and (3) improved monitoring and understanding of the flux variations between the North Atlantic and the Nordic Seas, both on the short and seasonal time scales.

  7. Comparison of sea-ice freeboard and thickness distributions from aircraft data and cryosat-2

    DEFF Research Database (Denmark)

    The only remote sensing technique capable of obtaining sea-ice thickness on basin-scale are satellite altimeter missions, such as the 2010 launched CryoSat-2. It is equipped with a Ku-Band radar altimeter, which measures the height of the ice surface above the sea level. This method requires highly...... accurate range measurements. During the CryoSat Validation Experiment (CryoVEx) 2011 in the Lincoln Sea, Cryosat-2 underpasses were accomplished with two aircraft, which carried an airborne laser-scanner, a radar altimeter and an electromagnetic induction device for direct sea-ice thickness retrieval. Both...... aircraft flew in close formation at the same time of a CryoSat-2 overpass. This is a study about the comparison of the sea-ice freeboard and thickness distribution of airborne validation and CryoSat-2 measurements within the multi-year sea-ice region of the Lincoln Sea in spring, with respect...

  8. Validation of SARAL/AltiKa data in the Amazon basin

    Science.gov (United States)

    Santos da Silva, Joecila; Calmant, Stephane; Medeiros Moreira, Daniel; Oliveira, Robson; Conchy, Taina; Gennero, Marie-Claude; Seyler, Frederique

    2015-04-01

    SARAL/AltiKa is a link between past missions (since it flies on the ERS-ENVISAT orbit with Ku band nadir altimeters in LRM) and future missions such as SWOT's Ka band interferometry swaths. In the present study, we compare the capability of its altimeter AltiKa to that of previous missions working in the Ku band such as ENVISAT and Jason-2 in retrieving water levels over the Amazon basin. Same as for the aforementioned preceding missions, the best results were obtained with the ICE-1 retracking algorithm. We qualitatively analyze the impact of rainfalls in the loss of measurements. Since making long -multi mission- time series is of major importance either for hydro-climatic studies or for basin management, we also present an estimate of the altimeter bias in order that the SARAL series of water level can be appended to those of these previous missions.

  9. Comparison of sea-ice freeboard distributions from aircraft data and cryosat-2

    DEFF Research Database (Denmark)

    Ricker, Robert; Hendricks, Stefan; Helm, Veit;

    2012-01-01

    highly accurate range measurements. During the CryoSat Validation Experiment (CryoVEx) 2011 in the Lincoln Sea Cryosat-2 underpasses were accomplished with two aircraft which carried an airborne laser scanner, a radar altimeter and an electromagnetic induction device for direct sea ice thickness...... retrieval. Both aircraft flew in close formation at the same time of a CryoSat-2 overpass. This is a study about the comparison of the sea-ice freeboard distribution of laser scanner and radar altimeter measurements with the CryoSat-2 product within the multi-year sea ice region of the Lincoln Sea in spring...

  10. Spatially extensive estimates of annual accumulation in the dry snow zone of the Greenland Ice Sheet determined from radar altimetry

    OpenAIRE

    Peña, S.; Nienow, P.; SHEPHERD, A; V. Helm; D Mair; Hanna, E.; Huybrechts, P.; Guo, Q.; Cullen, R; Wingham, D.

    2010-01-01

    We present estimates of accumulation rate along a 200 km transect ranging in elevation from 2750 to 3150 m in the dry snow zone on the western slope of the Greenland Ice Sheet. An airborne radar altimeter is used to estimate the thickness of annual internal layers and, in conjunction with ground based snow/firn density profiles, annual accumulation rates between 1998 and 2003 are derived. A clear gradient in the thickness of each layer observed by the radar altimeter and in the associated est...

  11. Sensitivity of CryoSat-2 Arctic sea-ice freeboard and thickness on radar-waveform interpretation

    OpenAIRE

    Ricker, R.; Hendricks, S.; V. Helm; H. Skourup; M. Davidson

    2014-01-01

    In the context of quantifying Arctic ice-volume decrease at global scale, the CryoSat-2 satellite was launched in 2010 and is equipped with the Ku band synthetic aperture radar altimeter SIRAL (Synthetic Aperture Interferometric Radar Altimeter), which we use to derive sea-ice freeboard defined as the height of the ice surface above the sea level. Accurate CryoSat-2 range measurements over open water and the ice surface of the order of centimetres are necessary to achieve...

  12. Comparison of gridded multi-mission and along-track mono-mission satellite altimetry wave heights with in situ near-shore buoy data.

    Digital Repository Service at National Institute of Oceanography (India)

    Shanas, P.R.; SanilKumar, V.; Hithin, N.K.

    larger number of collocation points, an improvement that would make the comparison statistically stable. The Gaussian weight function is applied for averaging the along-track altimeter data to the exact buoy location. The collocated value of the SWH... location, and xn, yn, and tn are the respective spatial grid points in x, y and time of the satellite data. Additionally, X = 100 km, Y=100 km, and T=30 min. The statistical parameters used for comparison of the altimeter data with the measured data...

  13. Bathymetric Inversion of South China Sea from Satellite Altimetry Data

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    This paper focuses on the study of ocean bathymetric inversion from satellite altimeter data by using FFT technique.In this study,the free-air gravity anomalies over the South China Sea are determined by the satellite altimeter data of GEOSAT,ERS-1,ERS-2 and T/P.And the 2.5′×2.5′ bathymetry model in South China Sea is calculated from the gravity anomalies with the inversion model given.After the analysis of the inversion and the comparison between the results,some conclusions can be drawn.

  14. Marginal thinning in Northwest Greenland during 2002-2011

    DEFF Research Database (Denmark)

    Khan, Shfaqat Abbas; Kjær, Kurt H.; Wahr, John M;

    Greenland during 2003-2009 using high-resolution Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter data (Zwally, 2010) supplemented with altimeter surveys from NASA's Airborne Topographic Mapper (ATM) during 2002-2011 (Krabill, 2011). We use the measurements of elevation change to estimate...... catchment-wide ice volume loss (convert is to mass loss) and compare with independent measurements from GPS and the Gravity Recovery and Climate Experiment (GRACE) satellite gravity mission, launched in March, 2002. The GRACE results provide a direct measure of mass loss averaged over the entire northwest...

  15. Local Marine Geoid Variations and Jason-2 Bias Determination using the Gavdos Permanent Cal/Val Facility

    DEFF Research Database (Denmark)

    Mertikas, S. P.; Daskalakis, A.; Tziavos, I. N.;

    2012-01-01

    This work outlines how changes in steep bathymetry (from 200 m to 3500 m depth over a distance of 10 km) are reflected on the determined sea surface anomalies at the Gavdos site used for satellite altimeter calibration. After almost 4 years of Jason-2 calibration activities, it has been observed......, but others are related to under-sampling of the Earth's gravity field due to the resolution of the geoid model. New reference surfaces for calibration have thus emerged. Finally, new updated values for the Jason-2 altimeter bias have been determined as 191.81 ± 2.80 mm with the geoid model and as 181.51 ± 2...

  16. A new 1 km digital elevation model of Antarctica derived from combined radar and laser data – Part 2: Validation and error estimates

    OpenAIRE

    Griggs, J. A.; J. L. Bamber

    2009-01-01

    We have developed a new digital elevation model (DEM) of Antarctica from a combination of satellite radar and laser altimeter data. Here, we assess the accuracy of the DEM by comparison with airborne altimeter data from four campaigns covering a wide range of surface slopes and ice sheet regions. Root mean squared (RMS) differences varied from 4.75 m, when compared to a densely gridded airborne dataset over the Siple Coast region of West Antarctica to 33.78 m when compared to a more limited d...

  17. A new regional high-resolution map of basal and surface topography for the Greenland ice-sheet margin at Paakitsoq, West Greenland

    DEFF Research Database (Denmark)

    Mottram, R.; Nielsen, C.; Ahlstrøm, A. P.;

    2009-01-01

    In 2005 an airborne survey was carried out from a Twin Otter aircraft at Pâkitsup Akuliarusersua (Paakitsoq) near Ilulissat in West Greenland. The survey aimed to measure ice thickness with a 60 MHz cohrent radar and surface elevation with a scanning laser altimeter.......In 2005 an airborne survey was carried out from a Twin Otter aircraft at Pâkitsup Akuliarusersua (Paakitsoq) near Ilulissat in West Greenland. The survey aimed to measure ice thickness with a 60 MHz cohrent radar and surface elevation with a scanning laser altimeter....

  18. Comparison of sea-ice freeboard distributions from aircraft data and cryosat-2

    OpenAIRE

    Ricker, Robert; Hendricks, Stefan; Helm, Veit; Gerdes, Rudiger; Skourup, Henriette; Ouwehand, L.

    2012-01-01

    The only remote sensing technique capable of obtaining sea ice thickness on basin-scale are satellite altimeter missions, such as the 2010 launched CryoSat-2. It is equipped with a Ku-Band radar altimeter which measures the height of the ice surface above the water level. This method requires highly accurate range measurements. During the CryoSat Validation Experiment (CryoVEx) 2011 in the Lincoln Sea Cryosat-2 underpasses were accomplished with two aircraft which carried an airborne laser sc...

  19. A Comparison of Sea-Ice Freeboard Distributions from Aircraft Data and CryoSat-2

    OpenAIRE

    Ricker, Robert; Hendricks, Stefan; Helm, Veit; Gerdes, Rüdiger; Skourup, Henriette

    2012-01-01

    Sea ice thickness on basin-scale is an important variable in the polar climate system, however datasets are sparse. The only remote sensing technique capable of obtaining sea ice thickness on that scale are satellite altimeter missions, such as the ICESat and CryoSat-2. The CryoSat-2 satellite was launched in 2010 and is equipped with the Ku-Band radar altimeter SIRAL. CryoSat-2 is part of the ESA’s Living Planet Programme and was especially developed for the observation of changes in the cry...

  20. Arctic sea ice freeboard from AltiKa and comparison with CryoSat-2 and Operation IceBridge

    OpenAIRE

    Armitage, T. W. K.; Ridout, A. L.

    2015-01-01

    Satellite radar altimeters have improved our knowledge of Arctic sea ice thickness over the past decade. The main sources of uncertainty in sea ice thickness retrievals are associated with inadequate knowledge of the snow layer depth and the radar interaction with the snow pack. Here we adapt a method of deriving sea ice freeboard from CryoSat-2 to data from the AltiKa Ka band radar altimeter over the 2013–14 Arctic sea ice growth season. AltiKa measures basin-averaged freeboards between 4.4 ...

  1. CRUCIAL: Cryosat-2 Success over Inland Water and Land

    DEFF Research Database (Denmark)

    Moore, Philip; Berry, Philippa; Balmbra, Robert;

    2014-01-01

    of inland water, salar and ice surfaces has enabled Earth-orbiting satellite radar altimeters to be used for land surface applications including mapping and measurement of river and lake systems. Research with EnviSat Burst Echoes has shown that substantial high frequency information content is present...... at short spatial scales with a small bright reflecting patch at nadir, such as over inland water, able to dominate the returned echo. Onboard echo averaging of the previous generation of satellite radar altimeters therefore causes loss of significant amounts of information. The high along-track sampling...

  2. High Resolution Altimetry Reveals New Characteristics of the December 2004 Indian Ocean Tsunami

    OpenAIRE

    Ablain, Michaël; Dorandeu, Joël; Le Traon, Pierre-Yves; Sladen, Anthony

    2006-01-01

    The Indian Ocean tsunami, which occurred on December 26, 2004, was the first to be clearly observed using satellite altimeters. The wave amplitude observed in deep-ocean by TOPEX and Jason-1 was close to 60 cm about 2 hours after the earthquake. Envisat crossed the tsunami wave 3h15 after the earthquake and measured a 35 cm wave. Even though it flew over the tsunami 7h20 after the earthquake, GFO still observed a wave close to 20 cm. To better extract the tsunami signal from altimeter measure...

  3. In-situ calibration and validation of Cryosat-2 observations over arctic sea ice north of Svalbard

    DEFF Research Database (Denmark)

    Gerland, Sebastian; Renner, Angelika H. H.; Spreen, Gunnar;

    CryoSat-2's radar altimeter allows to observe the panArctic sea ice thickness up to 88°N on a monthly basis. However, calibration and validation are crucial to assess limitations and accuracy of the altimeter, and to better quantify the uncertainties involved in converting sea ice freeboard...... to thickness. We conducted four ship-based campaigns 2010-2012 to the pack ice north of Svalbard. Detailed in situ measurements of snow and ice thickness, freeboard, and snow stratigraphy and density were performed. The data were integrated with satellite data, airborne ice thickness observations, and aerial...

  4. Polar Remote Sensing by CryoSat-type Radar Altimetry

    DEFF Research Database (Denmark)

    Stenseng, Lars

    observations, but the thickness and thereby the mass of the sea-ice is subject to large uncertainties. Satellite observations of the icecaps are also affected by errors in the margin zones, where the largest changes takes place. The development of a new type of radar altimeter, named the SAR altimeter....... Furthermore, a method has been developed to separate radar signals returned by ice floes from radar signals returned from the sea between the ice floes. When heights measured over ice floes and heights measured over ocean can be separated, the height by which the ice floe is above the sea surface can...

  5. Esa Cryovex 2011 Airborne Campaign For Cryosat-2 Calibration And Validation

    OpenAIRE

    Skourup, Henriette; Einarsson, Indriði; Sørensen, Louise Sandberg; Forsberg, René; Stenseng, Lars; Hendricks, Stefan; Helm, Veit; Davidson, Malcolm

    2011-01-01

    After the successful launch of CryoSat-2 in April 2010, the first direct validation campaign of the satellite was carried out in the April-May 2011. DTU Space has been involved in ESA’s CryoSat Validation Experiment (CryoVEx) with airborne activities since 2003. To validate the performance of the CryoSat-2 radar altimeter (SIRAL), the aircraft is equipped with an airborne version of the SIRAL altimeter (ASIRAS) together with a laser scanner. Of particular interest is to study the penetration ...

  6. Altimetry, bathymetry and geoid variations at the Gavdos permanent Cal/Val facility

    DEFF Research Database (Denmark)

    Mertikas, Stelios P.; Daskalakis, Antonis; Tziavos, Ilias N.;

    2013-01-01

    The aim of this work has been to examine the relationship of steep bathymetry in the coastal areas around the permanent Cal/Val facility of Gavdos, and their influence on the produced calibration values for the Jason-2 satellite altimeter. The paper describes how changes in seafloor topography...... calibration data and careful data analysis, certain features and variations, with permanent signatures at some locations south of Gavdos, have been found in the altimeter bias values. Causes of these variations have been interpreted. Some of these features, for example, at 12km south of the Cal/Val site seem...

  7. Propagation of Atlantic Ocean swells in the north Indian Ocean: A case study

    Digital Repository Service at National Institute of Oceanography (India)

    Samiksha, S.V.; Vethamony, P.; Aboobacker, V.M.; Rashmi, R.

    An analysis of altimeter significant wave height data of May 2007 revealed the occurrence of an extreme weather event off southern tip of South Africa in the Atlantic Ocean, and generation of a series of very high swells at 40 degrees S...

  8. Interannual variability of the Equatorial Jets in the Indian Ocean from the merged altimetry data

    Digital Repository Service at National Institute of Oceanography (India)

    Somayajulu, Y.K.; Murty, V.S.N.; Neelima, C.; Jagadeesh, P.S.V.

    The merged ERS-1/2, TOPEX/Poseidon and Jason-1 altimeter weekly sea level anomalies (SLAs) for the period 1997- 2005 were analyzed to study the variability of sea level and computed geostrophic currents in relation to the equatorial jets...

  9. Mapping of aggregated floodplain plant communities using image fusion of CASI and LiDAR data

    NARCIS (Netherlands)

    Verrelst, J.; Geerling, G.W.; Sykora, K.V.; Clevers, J.G.P.W.

    2009-01-01

    Combined optical and laser altimeter data offer the potential to map and monitor plant communities based on their spectral and structural characteristics. A problem unresolved is, however, that narrowly defined plant communities, i.e. plant communities at a low hierarchical level of classification i

  10. Observing and studying extreme low pressure events with altimetry.

    Science.gov (United States)

    Carrère, Loren; Mertz, Françoise; Dorandeu, Joel; Quilfen, Yves; Patoux, Jerome

    2009-01-01

    The ability of altimetry to detect extreme low pressure events and the relationship between sea level pressure and sea level anomalies during extra-tropical depressions have been investigated. Specific altimeter treatments have been developed for tropical cyclones and applied to obtain a relevant along-track sea surface height (SSH) signal: the case of tropical cyclone Isabel is presented here. The S- and C-band measurements are used because they are less impacted by rain than the Ku-band, and new sea state bias (SSB) and wet troposphere corrections are proposed. More accurate strong altimeter wind speeds are computed thanks to the Young algorithm. Ocean signals not related to atmospheric pressure can be removed with accuracy, even within a Near Real Time context, by removing the maps of sea level anomaly (SLA) provided by SSALTO/Duacs. In the case of Extra-Tropical Depressions, the classical altimeter processing can be used. Ocean signal not related to atmospheric pressure is along-track filtered. The sea level pressure (SLP)-SLA relationship is investigated for the North Atlantic, North Pacific and Indian oceans; three regression models are proposed allowing restoring an altimeter SLP with a mean error of 5 hPa if compared to ECMWF or buoys SLP. The analysis of barotropic simulation outputs points out the regional variability of the SLP/Model Sea Level relationship and the wind effects. PMID:22573955

  11. Integrating Non-Tidal Sea Level data from altimetry and tide gauges for coastal sea level prediction

    DEFF Research Database (Denmark)

    Cheng, Yongcun; Andersen, Ole Baltazar; Knudsen, Per

    2012-01-01

    from the joint TOPEX/Jason-1/Jason-2 altimeters with that from eleven tide gauges. The model results give a maximum hindcast skill of 0.95, which means maximum 95% of NSL variance can be explained by the model. The minimum Root Mean Square Error (RMSe) between altimetric observations and model...

  12. Improved ice loss estimate of the northwestern Greenland ice sheet

    NARCIS (Netherlands)

    Kjeldsen, K.K.; Khan, S.A.; van den Broeke, M.R.; van Angelen, J.H.

    2013-01-01

    We estimate ice volume change rates in the northwest Greenland drainage basin during 2003–2009 using Ice, Cloud and land Elevation Satellite (ICESat) laser altimeter data. Elevation changes are often reported to be largest near the frontal portion of outlet glaciers. To improve the volume change est

  13. Validation of CryoSat-2 SAR mode based lake levels

    DEFF Research Database (Denmark)

    Nielsen, Karina; Stenseng, Lars; Andersen, Ole B.;

    2015-01-01

    of conventional altimetry, primarily been used for large lakes. CryoSat-2, which was launched in 2010, carries the first altimeter that is able to operate in SAR mode. The along-track resolution is approximately 300. m in SAR mode thus enabling us to accurately monitor substantially smaller lakes.Here we evaluate...

  14. The East Madagascar Current: Volume Transport and Variability Based on Long-Term Observations

    NARCIS (Netherlands)

    Ponsoni, L.; Aguiar-González, B.; Ridderinkhof, H.; Maas, L.

    2016-01-01

    This study provides a long-term description of the poleward East Madagascar Current (EMC) in terms of its observed velocities, estimated volume transport, and variability based on both ~2.5 yr of continuous in situ measurements and ~21 yr of satellite altimeter data. An array of five moorings was de

  15. Altimetry with GNSS-R interferometry: first proof of concept experiment

    NARCIS (Netherlands)

    Rius, A.; Nogués-Correig, O.; Ribó, S.; Cardellach, E.; Oliveras, S.; Valencia, E.; Park, H.; Tarongi, J.M.; Camps, A.; Van der Marel, H.; Van Bree, R.; Altena, B.; Martín-Neira, M.

    2011-01-01

    The Global Navigation Satellite System Reflectometry (GNSS-R) concept was conceived as a means to densify radar altimeter measurements of the sea surface. Until now, the GNSS-R concept relied on open access to GNSS transmitted codes. Recently, it has been proposed that the ranging capability of the

  16. Seasonal variation of the South Indian tropical gyre

    NARCIS (Netherlands)

    Aguiar-González, B.; Ponsoni, L.; Ridderinkhof, H.; van Aken, H.M; de Ruijter, W.P.M.; Maas, L

    2016-01-01

    Based on satellite altimeter data and global atlases of temperature, salinity, wind stress and wind-driven circulation we investigate the seasonal variation of the South Indian tropical gyre and its associated open-ocean upwelling system, known as the Seychelles–Chagos Thermocline Ridge (SCTR). Resu

  17. Minima of interannual sea-level variability in the Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Shankar, D.; Aparna, S.G.; McCreary, J.P.; Suresh, I.; Neetu, S.; Durand, F.; Shenoi, S.S.C.; Al Saafani, M.A.

    Wavelet analysis of altimeter sea level in the Indian Ocean shows regions of high variability (maxima) and low variability (minima) at all time scales. At interannual time scales, i.e., at periods of 17 months or more, minima are seen at several...

  18. A new regional high-resolution map of basal and surface topography for the Greenland ice-sheet margin at Paakitsoq, West Greenland

    OpenAIRE

    Mottram, R.; Nielsen, C.; Ahlstrøm, A. P.; Reeh, N.; Kristensen, Steen Savstrup; Christensen, Erik Lintz; Forsberg, René; Stenseng, Lars

    2009-01-01

    In 2005 an airborne survey was carried out from a Twin Otter aircraft at Pâkitsup Akuliarusersua (Paakitsoq) near Ilulissat in West Greenland. The survey aimed to measure ice thickness with a 60 MHz cohrent radar and surface elevation with a scanning laser altimeter.

  19. ASPIS, A Flexible Multispectral System for Airborne Remote Sensing Environmental Applications

    OpenAIRE

    Riccardo Valentini; Francesco Primo Vaccari; Cesare Ronchi; Franco Miglietta; Beniamino Gioli; Claudio Belli; Dario Papale

    2008-01-01

    Airborne multispectral and hyperspectral remote sensing is a powerful tool for environmental monitoring applications. In this paper we describe a new system (ASPIS) composed by a 4-CCD spectral sensor, a thermal IR camera and a laser altimeter that is mounted on a flexible Sky-Arrow airplane. A test application of the multispectral sensor to estimate durum wheat quality is also presented.

  20. MOLA Topography of Small Volcanoes in Tempe Terra and Ceraunius Fossae, Mars: Implications for Eruptive Styles

    Science.gov (United States)

    Wong, M. P.; Sakimoto, S. E. H.; Garvin, J. B.

    2001-01-01

    We use Mars Orbiter Laser Altimeter (MOLA) data to measure small volcanoes in the Tempe Terra and Ceraunius Fossae regions of Mars. We find that previous geometry estimates based on imagery alone are inaccurate, but MOLA data support image-based interpretations of eruptive style. Additional information is contained in the original extended abstract.