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Sample records for altimeter system glas

  1. 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

  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. 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).

  4. 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.

  5. 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,...

  6. 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...

  7. 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 (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.

  8. 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

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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

  19. 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...

  20. 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.

  1. 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.

  2. Accelerated GLAS exposure station

    International Nuclear Information System (INIS)

    The Geoscience Laser Altimeter System (GLAS) is being developed by NASA/GSFC to measure the dynamics of the ice sheet mass balance, land, and cloud and atmospheric properties. An instrument altimetric resolution of 10 cm per shot is required. The laser transmitter will be a diode pumped, Q-switched, Nd:YAG laser producing 1064 nm, 100 mJ, 4 ns pulses at 40 Hz repetition rate in a TEM∞ mode. A minimum lifetime goal of 2 billion shots is required per laser transmitter. The performance of the GLAS laser can be limited by physical damage to the optical components caused by the interaction of intense laser energy with the optical coatings and substrates. Very little data exists describing the effects of long duration laser exposure, of 4 ns pulses, on an optical component. An Accelerated GLAS Exposure Station (AGES) is being developed which will autonomously operate and monitor the GLAS laser at an accelerated rate of 500 Hz. The effects of a large number of laser shots will be recorded. Parameters to be monitored include: laser power, pulsewidth, beam size, laser diode drive current and power, Q-switch drive voltage, temperature, and humidity. For comparison, one set of AGES-sister optical components will be used in the non-accelerated GLAS laser and another will be evaluated by a commercial optical damage test facility

  3. 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, ...

  4. 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.

  5. 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

  6. 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

  7. 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.

  8. 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.

  9. 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...

  10. Slope Estimation from ICESat/GLAS

    OpenAIRE

    Craig Mahoney; Natascha Kljun; Sietse O. Los; Laura Chasmer; Jorg M. Hacker; Christopher Hopkinson; North, Peter R.J.; Jacqueline A. B. Rosette; Eva van Gorsel

    2014-01-01

    We present a novel technique to infer ground slope angle from waveform LiDAR, known as the independent slope method (ISM). The technique is applied to large footprint waveforms (\\(\\sim\\) mean diameter) from the Ice, Cloud and Land Elevation Satellite (ICESat) Geoscience Laser Altimeter System (GLAS) to produce a slope dataset of near-global coverage at \\(0.5^{\\circ} \\times 0.5^{\\circ}\\) resolution. ISM slope estimates are compared against high resolution airborne LiDAR slope measurements for ...

  11. 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...

  12. ACCURACY AND RELIABILITY ASSESSMENT OF GLAS MEASUREMENTS OVER ISRAEL

    OpenAIRE

    Z. Shtain; S. Filin

    2012-01-01

    Availability of spaceborne laser data on a global scale motivates evaluation of their quality as a means to improve large scale terrain models or to identify changes over time. One prominent spaceborne system is the Geoscience Laser Altimeter System (GLAS) mounted on board the Ice Cloud and land Elevation Satellite (ICESat) whose objectives were to track elevation changes of the Greenland and Antarctica's glaciers, but topographic information on other regions has been acquired as well. As the...

  13. 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...

  14. 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.

  15. 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.

  16. Forest above Ground Biomass Inversion by Fusing GLAS with Optical Remote Sensing Data

    Directory of Open Access Journals (Sweden)

    Xiaohuan Xi

    2016-03-01

    Full Text Available Forest biomass is an important parameter for quantifying and understanding biological and physical processes on the Earth’s surface. Rapid, reliable, and objective estimations of forest biomass are essential to terrestrial ecosystem research. The Geoscience Laser Altimeter System (GLAS produced substantial scientific data for detecting the vegetation structure at the footprint level. This study combined GLAS data with MODIS/BRDF (Bidirectional Reflectance Distribution Function and ASTER GDEM data to estimate forest aboveground biomass (AGB in Xishuangbanna, Yunnan Province, China. The GLAS waveform characteristic parameters were extracted using the wavelet method. The ASTER DEM was used to compute the terrain index for reducing the topographic influence on the GLAS canopy height estimation. A neural network method was applied to assimilate the MODIS BRDF data with the canopy heights for estimating continuous forest heights. Forest leaf area indices (LAIs were derived from Landsat TM imagery. A series of biomass estimation models were developed and validated using regression analyses between field-estimated biomass, canopy height, and LAI. The GLAS-derived canopy heights in Xishuangbanna correlated well with the field-estimated AGB (R2 = 0.61, RMSE = 52.79 Mg/ha. Combining the GLAS estimated canopy heights and LAI yielded a stronger correlation with the field-estimated AGB (R2 = 0.73, RMSE = 38.20 Mg/ha, which indicates that the accuracy of the estimated biomass in complex terrains can be improved significantly by integrating GLAS and optical remote sensing data.

  17. 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.

  18. National Forest Aboveground Biomass Mapping from ICESat/GLAS Data and MODIS Imagery in China

    Directory of Open Access Journals (Sweden)

    Hong Chi

    2015-05-01

    Full Text Available Forest aboveground biomass (AGB was mapped throughout China using large footprint LiDAR waveform data from the Geoscience Laser Altimeter System (GLAS onboard NASA’s Ice, Cloud, and land Elevation Satellite (ICESat, Moderate Resolution Imaging Spectro-radiometer (MODIS imagery and forest inventory data. The entire land of China was divided into seven zones according to the geographic characteristics of the forests. The forest AGB prediction models were separately developed for different forest types in each of the seven forest zones at GLAS footprint level from GLAS waveform parameters and biomass derived from height and diameter at breast height (DBH field observation. Some waveform parameters used in the prediction models were able to reduce the effects of slope on biomass estimation. The models of GLAS-based biomass estimates were developed by using GLAS footprints with slopes less than 20° and slopes ≥ 20°, respectively. Then, all GLAS footprint biomass and MODIS data were used to establish Random Forest regression models for extrapolating footprint AGB to a nationwide scale. The total amount of estimated AGB in Chinese forests around 2006 was about 12,622 Mt vs. 12,617 Mt derived from the seventh national forest resource inventory data. Nearly half of all provinces showed a relative error (% of less than 20%, and 80% of total provinces had relative errors less than 50%.

  19. The ICESat/GLAS Instrument Operations Report. Volume 4

    Science.gov (United States)

    Jester, Peggy L.

    2012-01-01

    The Geoscience Laser Altimeter System (GLAS) was the primary instrument aboard the first ICESat spacecraft. ICESat's primary objectives are to determine the mass balance of the polar ice sheets and their contributions to global sea level change, and to obtain essential data for prediction of future changes in ice volume and sea-level. ICESat launched successfully from Vandenberg Air Force Base on January 12, 2003 23:45 UT. The ICESat science mission began in February 2003 and ended on October 11, 2009. De-orbit of the spacecraft occurred on August 30, 2010. This document focusses on the GLAS instrument operations during the ICESat mission. This document will not discuss science results.

  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. 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.

  2. Vegetation height products between 60° S and 60° N from ICESat GLAS data

    Directory of Open Access Journals (Sweden)

    E. van Gorsel

    2011-09-01

    Full Text Available We present a new method to obtain coarse resolution (0.5° × 0.5° vegetation height and vegetation-cover fraction data sets between 60° S and 60° N for use in climate models and ecological models. The data sets are derived from the Geoscience Laser Altimeter System (GLAS on the Ice, Cloud and land Elevation Satellite (ICESat, which is the only LiDAR instrument that provides close to global coverage when all data collected for 2003–2009 are combined. Filters are applied to the GLAS data to identify and eliminate spurious observations, e.g. data that are affected by clouds, atmosphere and terrain and as such result in erroneous estimates of vegetation height or vegetation cover. GLAS vegetation height estimates are aggregated in histograms from 0 to 70 m in 0.5 m intervals. The GLAS vegetation height product is evaluated in four ways. First, unfiltered and filtered individual GLAS vegetation height measurements are compared with aircraft LiDAR measurements of the same from seven sites in the Americas, Europe, and Australia. Application of filters increases the correlation with aircraft data from r = 0.36 to r = 0.67 and decreases the root-mean-square error by a factor 3. Second, the global aggregated GLAS vegetation height product is tested for sensitivity towards the choice of data quality filters; areas with frequent cloud cover and areas with steep terrain are the most sensitive to the choice of thresholds for the filters. Thirdly, the GLAS global vegetation height product is compared with two other global vegetation height products and is believed to produce more realistic characteristics: dominant vegetation height for tropical forests between 30 and 60 m versus 20 and 40 m in existing products. Finally, the GLAS bare soil cover fraction is compared globally with the MODIS bare soil fraction (r = 0.55 and with the FASIR bare soil cover fraction estimates (r = 0.58; the correlation between GLAS and MODIS tree-cover fraction was (r = 0

  3. The GLAS Standard Data Products Specification-Level 1, Version 9

    Science.gov (United States)

    Lee, Jeffrey E.

    2013-01-01

    The Geoscience Laser Altimeter System (GLAS) is the primary instrument for the ICESat (Ice, Cloud and Land Elevation Satellite) laser altimetry mission. ICESat was the benchmark Earth Observing System (EOS) mission for measuring ice sheet mass balance, cloud and aerosol heights, as well as land topography and vegetation characteristics. From 2003 to 2009, the ICESat mission provided multi-year elevation data needed to determine ice sheet mass balance as well as cloud property information, especially for stratospheric clouds common over polar areas. It also provided topography and vegetation data around the globe, in addition to the polar-specific coverage over the Greenland and Antarctic ice sheets.This document defines the Level-1 GLAS standard data products. This document addresses the data flow, interfaces, record and data formats associated with the GLAS Level 1 standard data products. GLAS Level 1 standard data products are composed of Level 1A and Level 1B data products. The term standard data products refers to those EOS instrument data that are routinely generated for public distribution. The National Snow and Ice Data Center (NSDIC) distribute these products. Each data product has a unique Product Identification code assigned by the Senior Project Scientist. GLAS Level 1A and Level 1B Data Products are composed from those Level 0 data that have been reformatted or transformed to corrected and calibrated data in physical units at the full instrument rate and resolution.

  4. 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.

  5. Insights Into GLAS Waveforms Using Google Earth

    Science.gov (United States)

    Fowler, D.; Khalsa, S. S.; Swick, R.; Haran, T.; Scambos, T.; Korn, D.

    2008-12-01

    The Geoscience Laser Altimeter System (GLAS) instrument aboard the Ice, Cloud, and land Elevation (ICESat) satellite was launched on 12 January 2003. The primary objective of the ICESat mission is to provide global measurements of polar ice sheet elevation to discern changes in ice volume and ice sheet mass balance over time. Secondary objectives of the mission are to measure sea ice thickness, cloud and atmospheric properties, land topography, vegetation canopy heights, ocean surface topography, and surface reflectivity. The GLAS instrument has three lasers, each of which has a 1064 nm laser channel for surface altimetry and dense cloud heights, and a 532 nm lidar channel for the vertical distribution of clouds and aerosols. The laser emits a pulse every 0.02 seconds, and receives a return signal. Laser footprints are roughly 70 meters in diameter and spaced 170 meters apart and are assigned terrestrial positions at the 10s of meters level of accuracy. As an aid to data selection we demonstrate how GLAS footprints, waveforms and quality information can be displayed in Google Earth. We represent the approximate spatial coverage of each laser shot on the Earth's surface, allowing users to assess the shot in the context of the surface characteristics gleaned from the underlying image and topography in Google Earth. Each footprint can be expanded to show the associated waveform, summarizing the detected return signal, along with numerical values for latitude and longitude, elevation, and date/time. Surface characteristics such as tree canopy, low- level dust or clouds, snow or ice cover, extreme surface roughness, have significant, easily-visible effects on the waveform. This application will provide extremely useful information, and will facilitate a detailed data preview before ordering or processing.

  6. Slope Estimation from ICESat/GLAS

    Directory of Open Access Journals (Sweden)

    Craig Mahoney

    2014-10-01

    Full Text Available We present a novel technique to infer ground slope angle from waveform LiDAR, known as the independent slope method (ISM. The technique is applied to large footprint waveforms (\\(\\sim\\ mean diameter from the Ice, Cloud and Land Elevation Satellite (ICESat Geoscience Laser Altimeter System (GLAS to produce a slope dataset of near-global coverage at \\(0.5^{\\circ} \\times 0.5^{\\circ}\\ resolution. ISM slope estimates are compared against high resolution airborne LiDAR slope measurements for nine sites across three continents. ISM slope estimates compare better with the aircraft data (R\\(^{2}=0.87\\ and RMSE\\(=5.16^{\\circ}\\ than the Shuttle Radar Topography Mission Digital Elevation Model (SRTM DEM inferred slopes (R\\(^{2}=0.71\\ and RMSE\\(=8.69^{\\circ}\\ ISM slope estimates are concurrent with GLAS waveforms and can be used to correct biophysical parameters, such as tree height and biomass. They can also be fused with other DEMs, such as SRTM, to improve slope estimates.

  7. 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...

  8. COMPARING ICESAT/GLAS BASED ELEVATION HEIGHTS WITH PHOTOGRAMMETRIC TERRAIN HEIGHTS FROM UAV-IMAGERY ON THE EAST TIBETAN PLATEAU

    OpenAIRE

    F. Enßle; Fritz, A.; B. Koch

    2015-01-01

    Digital elevation models (DEMs) and height measurements are broadly used in environmental studies. Two common elevation sources are the Ice Cloud and land elevation Satellite (ICESat), which acquired laser range measurements with the Geoscience Laser Altimeter System (GLAS) across the globe and elevation data from the Shuttle Radar Topography Mission (SRTM). Current developments of small unmanned aerial vehicles (UAV) provide the opportunity to collect aerial images of remote areas a...

  9. 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.

  10. 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.

  11. 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.

  12. Study on forest above-ground biomass synergy inversion from GLAS and HJ-1 data

    Science.gov (United States)

    Fang, Zhou; Cao, Chunxiang; Ji, Wei; Xu, Min; Chen, Wei

    2012-10-01

    The need exists to develop a systematic approach to inventory and monitor global forests, both for carbon stock evaluation and for land use change analysis. The use of freely available satellite-based data for carbon stock estimation mitigates both the cost and the spatial limitations of field-based techniques. Spaceborne lidar data have been demonstrated as useful for forest aboveground biomass (AGB) estimation over a wide range of biomass values and forest types. However, the application of these data is limited because of their spatially discrete nature. Spaceborne multispectral sensors have been used extensively to estimate AGB, but these methods have been demonstrated as inappropriate for forest structure characterization in high-biomass mature forests. This study uses an integration of ICESat Geospatial Laser Altimeter System (GLAS) lidar and HJ-1 satellites data to develop methods to estimate AGB in an area of Qilian Mountains, Northwest China. Considering the study area belongs to mountainous terrain, the difficulties of this article are how to extract canopy height from GLAS waveform metrics. Combining with HJ-1 data and ground survey data of the study area, we establish forest biomass estimation model for the GLAS data based on BP neural network model. In order to estimate AGB, the training sample data includes the canopy height extracted from GLAS, LAI, vegetation coverage and several kinds of vegetation indices from HJ-1 data. The results of forest aboveground biomass are very close to the fields measured results, and are consistent with land cover data in the spatial distribution.

  13. The GLAS Algorithm Theoretical Basis Document for Precision Attitude Determination (PAD)

    Science.gov (United States)

    Bae, Sungkoo; Smith, Noah; Schutz, Bob E.

    2013-01-01

    The Geoscience Laser Altimeter System (GLAS) was the sole instrument for NASAs Ice, Cloud and land Elevation Satellite (ICESat) laser altimetry mission. The primary purpose of the ICESat mission was to make ice sheet elevation measurements of the polar regions. Additional goals were to measure the global distribution of clouds and aerosols and to map sea ice, land topography and vegetation. ICESat was the benchmark Earth Observing System (EOS) mission to be used to determine the mass balance of the ice sheets, as well as for providing cloud property information, especially for stratospheric clouds common over polar areas.

  14. Validation of satellite altimeter range measurements over salar de Uyuni, Bolivia

    Science.gov (United States)

    Fricker, H. A.; Roca, M.; Laxon, S. W.; Carabajal, C. C.; Quinn, K.; Borsa, A. A.; Minster, J. B.

    2003-12-01

    The salar de Uyuni in the Bolivian altiplano covers approximately 9600 km2, and is the largest dry salt lake in the world. This vast, flat stable surface is ideal for estimation of the range bias on altimeter instruments such as GLAS on board ICESat (launched 12th January 2003), RA-2 on board ENVISAT (launched March 1st 2002) and the ERS-2 radar altimeter (RA, launched 1995), and to compare the measurements from these altimeters. Here we describe a kinematic GPS survey of the salar de Uyuni that was carried out in August/September 2002 and was designed to calibrate GLAS and RA-2. The eastern part of the salar was surveyed with 8 grids 22.5 km x 13.5 km at 2.25 km spacing, and with 2 grids which straddled one ascending and one descending ERS-2/ENVISAT orbit across this part of the salar, one 44.5 x 9 km, the other 18 x 13.5 km. Comparison of GPS heights from one GPS grid to the next and crossover analysis at intersections suggests that RMS accuracy of the GPS measurement is around 2 cm. We retracked the altimeter waveforms by fitting the system point target response to retrieve the altimeter surface elevation. We fitted a gaussian-smoothed surface to the GPS heights collected around the ERS-2/ENVISAT grids and interpolated these surfaces to the locations of altimeter footprints to obtain an estimate of the range bias for each instruments (GLAS, RA-2 and the ERS-2 RA). We also compare our results with data from one cycle of TOPEX data, which was collected during an orbit manoeuvre phase in September 2002. Ground tracks from this cycle serendipitously crossed our survey area at the same time we were on the ground.

  15. ACCURACY AND RELIABILITY ASSESSMENT OF GLAS MEASUREMENTS OVER ISRAEL

    Directory of Open Access Journals (Sweden)

    Z. Shtain

    2012-09-01

    Full Text Available Availability of spaceborne laser data on a global scale motivates evaluation of their quality as a means to improve large scale terrain models or to identify changes over time. One prominent spaceborne system is the Geoscience Laser Altimeter System (GLAS mounted on board the Ice Cloud and land Elevation Satellite (ICESat whose objectives were to track elevation changes of the Greenland and Antarctica's glaciers, but topographic information on other regions has been acquired as well. As the ICESat mission is the first to offer high-standard spaceborne laser derived topographic information, this paper evaluates its data quality. To that end, a large set of laser returns over Israel has been utilized and evaluated against a wide spectrum of data as a reference.

  16. 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.

  17. Comparing Icesat/glas Based Elevation Heights with Photogrammetric Terrain Heights from Uav-Imagery on the East Tibetan Plateau

    Science.gov (United States)

    Enßle, F.; Fritz, A.; Koch, B.

    2015-08-01

    Digital elevation models (DEMs) and height measurements are broadly used in environmental studies. Two common elevation sources are the Ice Cloud and land elevation Satellite (ICESat), which acquired laser range measurements with the Geoscience Laser Altimeter System (GLAS) across the globe and elevation data from the Shuttle Radar Topography Mission (SRTM). Current developments of small unmanned aerial vehicles (UAV) provide the opportunity to collect aerial images of remote areas at a high spatial resolution. These can be further processed to digital surface models by stereophotogrammetry and provide a reliable data source to evaluate coarse scale Digital Elevation Models (DEMs). This study compares ICESat/GLAS and SRTM90 elevation data against photogrammetric terrain heights within GLAS footprints on high altitudes on the East Tibetan Plateau. Without vegetation-bias, we were able to examine height differences under different topographic conditions and of different acquisition dates. Several resampling techniques were applied to SRTM90 data and averaged height within each footprint was calculated. ICESat/GLAS heights (n = 148) are most similar to UAV data based elevations with an averaged difference of -0.8m ±3.1m. Results furthermore indicate the validity of ICESat/GLAS heights, which are usually removed from analyses by applying different quality flags. Smallest difference of SRTM90 to UAV based heights could be observed by a natural neighbour resampling technique (averaged 3.6m ±14m), whereat other techniques achieved quite similar results. It can be confirmed that within a range of 3,800-4,200m above mean sea level the ICESat/GLAS heights are a precise source to determine elevation at footprint geolocation.

  18. The GLAS Standard Data Products Specification--Level 2, Version 9. Volume 14

    Science.gov (United States)

    Lee, Jeffrey E.

    2013-01-01

    The Geoscience Laser Altimeter System (GLAS) is the primary instrument for the ICESat (Ice, Cloud and Land Elevation Satellite) laser altimetry mission. ICESat was the benchmark Earth Observing System (EOS) mission for measuring ice sheet mass balance, cloud and aerosol heights, as well as land topography and vegetation characteristics. From 2003 to 2009, the ICESat mission provided multi-year elevation data needed to determine ice sheet mass balance as well as cloud property information, especially for stratospheric clouds common over polar areas. It also provided topography and vegetation data around the globe, in addition to the polar-specific coverage over the Greenland and Antarctic ice sheets.This document defines the Level-2 GLAS standard data products. This document addresses the data flow, interfaces, record and data formats associated with the GLAS Level 2 standard data products. The term standard data products refers to those EOS instrument data that are routinely generated for public distribution. The National Snow and Ice Data Center (NSDIC) distribute these products. Each data product has a unique Product Identification code assigned by the Senior Project Scientist. The Level 2 Standard Data Products specifically include those derived geophysical data values (i.e., ice sheet elevation, cloud height, vegetation height, etc.). Additionally, the appropriate correction elements used to transform the Level 1A and Level 1B Data Products into Level 2 Data Products are included. The data are packaged with time tags, precision orbit location coordinates, and data quality and usage flags.

  19. The GLAS Standard Data Products Specification-Data Dictionary, Version 1.0. Volume 15

    Science.gov (United States)

    Lee, Jeffrey E.

    2013-01-01

    The Geoscience Laser Altimeter System (GLAS) is the primary instrument for the ICESat (Ice, Cloud and Land Elevation Satellite) laser altimetry mission. ICESat was the benchmark Earth Observing System (EOS) mission for measuring ice sheet mass balance, cloud and aerosol heights, as well as land topography and vegetation characteristics. From 2003 to 2009, the ICESat mission provided multi-year elevation data needed to determine ice sheet mass balance as well as cloud property information, especially for stratospheric clouds common over polar areas. It also provided topography and vegetation data around the globe, in addition to the polar-specific coverage over the Greenland and Antarctic ice sheets.This document contains the data dictionary for the GLAS standard data products. It details the parameters present on GLAS standard data products. Each parameter is defined with a short name, a long name, units on product, type of variable, a long description and products that contain it. The term standard data products refers to those EOS instrument data that are routinely generated for public distribution. These products are distributed by the National Snow and Ice Data Center (NSDIC).

  20. Mapping Forest Height in Alaska Using GLAS, Landsat Composites, and Airborne LiDAR

    Directory of Open Access Journals (Sweden)

    Birgit Peterson

    2014-12-01

    Full Text Available Vegetation structure, including forest canopy height, is an important input variable to fire behavior modeling systems for simulating wildfire behavior. As such, forest canopy height is one of a nationwide suite of products generated by the LANDFIRE program. In the past, LANDFIRE has relied on a combination of field observations and Landsat imagery to develop existing vegetation structure products. The paucity of field data in the remote Alaskan forests has led to a very simple forest canopy height classification for the original LANDFIRE forest height map. To better meet the needs of data users and refine the map legend, LANDFIRE incorporated ICESat Geoscience Laser Altimeter System (GLAS data into the updating process when developing the LANDFIRE 2010 product. The high latitude of this region enabled dense coverage of discrete GLAS samples, from which forest height was calculated. Different methods for deriving height from the GLAS waveform data were applied, including an attempt to correct for slope. These methods were then evaluated and integrated into the final map according to predefined criteria. The resulting map of forest canopy height includes more height classes than the original map, thereby better depicting the heterogeneity of the landscape, and provides seamless data for fire behavior analysts and other users of LANDFIRE data.

  1. The GLAS Science Algorithm Software (GSAS) Detailed Design Document Version 6. Volume 16

    Science.gov (United States)

    Lee, Jeffrey E.

    2013-01-01

    The Geoscience Laser Altimeter System (GLAS) is the primary instrument for the ICESat (Ice, Cloud and Land Elevation Satellite) laser altimetry mission. ICESat was the benchmark Earth Observing System (EOS) mission for measuring ice sheet mass balance, cloud and aerosol heights, as well as land topography and vegetation characteristics. From 2003 to 2009, the ICESat mission provided multi-year elevation data needed to determine ice sheet mass balance as well as cloud property information, especially for stratospheric clouds common over polar areas. It also provided topography and vegetation data around the globe, in addition to the polar-specific coverage over the Greenland and Antarctic ice sheets.This document describes the detailed design of GLAS Science Algorithm Software (GSAS). The GSAS is used to create the ICESat GLAS standard data products. The National Snow and Ice Data Center (NSDIC) distribute these products. The document contains descriptions, flow charts, data flow diagrams, and structure charts for each major component of the GSAS. The purpose of this document is to present the detailed design of the GSAS. It is intended as a reference source to assist the maintenance programmer in making changes that fix or enhance the documented software.

  2. 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...

  3. Model Effects on GLAS-Based Regional Estimates of Forest Biomass and Carbon

    Science.gov (United States)

    Nelson, Ross F.

    2010-01-01

    Ice, Cloud, and land Elevation Satellite (ICESat) / Geosciences Laser Altimeter System (GLAS) waveform data are used to estimate biomass and carbon on a 1.27 X 10(exp 6) square km study area in the Province of Quebec, Canada, below the tree line. The same input datasets and sampling design are used in conjunction with four different predictive models to estimate total aboveground dry forest biomass and forest carbon. The four models include non-stratified and stratified versions of a multiple linear model where either biomass or (biomass)(exp 0.5) serves as the dependent variable. The use of different models in Quebec introduces differences in Provincial dry biomass estimates of up to 0.35 G, with a range of 4.94 +/- 0.28 Gt to 5.29 +/-0.36 Gt. The differences among model estimates are statistically non-significant, however, and the results demonstrate the degree to which carbon estimates vary strictly as a function of the model used to estimate regional biomass. Results also indicate that GLAS measurements become problematic with respect to height and biomass retrievals in the boreal forest when biomass values fall below 20 t/ha and when GLAS 75th percentile heights fall below 7 m.

  4. Vegetation height and cover fraction between 60° S and 60° N from ICESat GLAS data

    Directory of Open Access Journals (Sweden)

    S. O. Los

    2012-03-01

    Full Text Available We present new coarse resolution (0.5° × 0.5° vegetation height and vegetation-cover fraction data sets between 60° S and 60° N for use in climate models and ecological models. The data sets are derived from 2003–2009 measurements collected by the Geoscience Laser Altimeter System (GLAS on the Ice, Cloud and land Elevation Satellite (ICESat, the only LiDAR instrument that provides close to global coverage. Initial vegetation height is calculated from GLAS data using a development of the model of Rosette et al. (2008 with with further calibration on desert sites. Filters are developed to identify and eliminate spurious observations in the GLAS data, e.g. data that are affected by clouds, atmosphere and terrain and as such result in erroneous estimates of vegetation height or vegetation cover. Filtered GLAS vegetation height estimates are aggregated in histograms from 0 to 70 m in 0.5 m intervals for each 0.5° × 0.5°. The GLAS vegetation height product is evaluated in four ways. Firstly, the Vegetation height data and data filters are evaluated using aircraft LiDAR measurements of the same for ten sites in the Americas, Europe, and Australia. Application of filters to the GLAS vegetation height estimates increases the correlation with aircraft data from r = 0.33 to r = 0.78, decreases the root-mean-square error by a factor 3 to about 6 m (RMSE or 4.5 m (68% error distribution and decreases the bias from 5.7 m to −1.3 m. Secondly, the global aggregated GLAS vegetation height product is tested for sensitivity towards the choice of data quality filters; areas with frequent cloud cover and areas with steep terrain are the most sensitive to the choice of thresholds for the filters. The changes in height estimates by applying different filters are, for the main part, smaller than the overall uncertainty of 4.5–6 m established from the site measurements. Thirdly, the GLAS global vegetation height product is compared with a

  5. Estimating forest aboveground biomass using HJ-1 Satellite CCD and ICESat GLAS waveform data

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The ecosystem in northeastern China and the Russian Far East is a hotspot of scientific research into the global carbon balance.Forest aboveground biomass(AGB) is an important component in the land surface carbon cycle.In this study,using forest inventory data and forest distribution data,the AGB was estimated for forest in Daxinganlin in northeastern China by combining charge-coupled device(CCD) data from the Small Satellite for Disaster and Environment Monitoring and Forecast(HJ-1) and Geoscience Laser Altimeter System(GLAS) waveform data from the Ice,Cloud and land Elevation Satellite(ICESat).The forest AGB prediction models were separately developed for different forest types in the research area at GLAS footprint level from GLAS waveform parameters and field survey plot biomass in the Changqing(CQ) Forest Center,which was calculated from forest inventory data.The resulted statistical regression models have a R2=0.68 for conifer and R2=0.71 for broadleaf forests.These models were used to estimate biomass for all GLAS footprints of forest located in the study area.All GLAS footprint biomass coupled with various spectral reflectivity parameters and vegetation indices derived from HJ-1 satellite CCD data were used in multiple regression analyses to establish biomass prediction models(R2=0.55 and R2=0.52 for needle and broadleaf respectively).Then the models were used to produce a forest AGB map for the whole study area using the HJ-1 data.Biomass data obtained from forest inventory data of the Zhuanglin(ZL) Forest Center were used as independent field measurements to validate the AGB estimated from HJ-1 CCD data(R2=0.71).About 80% of biomass samples had an error less than 20 t ha-1,and the mean error of all validation samples is 5.74 t ha-1.The pixel-level biomass map was then stratified into different biomass levels to illustrate the AGB spatial distribution pattern in this area.It was found that HJ-1 wide-swath data and GLAS waveform data can be combined to

  6. Estimation of Regional Forest Aboveground Biomass Combining Icesat-Glas Waveforms and HJ-1A/HSI Hyperspectral Imageries

    Science.gov (United States)

    Xing, Yanqiu; Qiu, Sai; Ding, Jianhua; Tian, Jing

    2016-06-01

    Estimation of forest aboveground biomass (AGB) is a critical challenge for understanding the global carbon cycle because it dominates the dynamics of the terrestrial carbon cycle. Light Detection and Ranging (LiDAR) system has a unique capability for estimating accurately forest canopy height, which has a direct relationship and can provide better understanding to the forest AGB. The Geoscience Laser Altimeter System (GLAS) onboard the Ice, Cloud, and land Elevation Satellite (ICESat) is the first polarorbiting LiDAR instrument for global observations of Earth, and it has been widely used for extracting forest AGB with footprints of nominally 70 m in diameter on the earth's surface. However, the GLAS footprints are discrete geographically, and thus it has been restricted to produce the regional full coverage of forest AGB. To overcome the limit of discontinuity, the Hyper Spectral Imager (HSI) of HJ-1A with 115 bands was combined with GLAS waveforms to predict the regional forest AGB in the study. Corresponding with the field investigation in Wangqing of Changbai Mountain, China, the GLAS waveform metrics were derived and employed to establish the AGB model, which was used further for estimating the AGB within GLAS footprints. For HSI imagery, the Minimum Noise Fraction (MNF) method was used to decrease noise and reduce the dimensionality of spectral bands, and consequently the first three of MNF were able to offer almost 98% spectral information and qualified to regress with the GLAS estimated AGB. Afterwards, the support vector regression (SVR) method was employed in the study to establish the relationship between GLAS estimated AGB and three of HSI MNF (i.e. MNF1, MNF2 and MNF3), and accordingly the full covered regional forest AGB map was produced. The results showed that the adj.R2 and RMSE of SVR-AGB models were 0.75 and 4.68 t hm-2 for broadleaf forests, 0.73 and 5.39 t hm-2 for coniferous forests and 0.71 and 6.15 t hm-2 for mixed forests respectively. The

  7. 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

  8. 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.

  9. 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

  10. 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.

  11. Glumac i glas

    OpenAIRE

    Bertok-Zuoković, Tatjana

    2015-01-01

    Tekst je nastao kao prikaz sudjelovanja na osmom, međunarodnom znanstvenom pod nazivom Istraživanje govora koji se održao na Filozofskom fakultetu u Zagrebu, od 5. - 7.12. 2013. Na skupu su sudjelovali i asistenti s područja govora i glasa Umjetničke akademije u Osijeku: Selena Andrić i Ivan Ćaćić, koji su demonstrirali praktičnu primjenu vježbi za glas(govor): vježbe disanja i vježbe artikulacije to jest razgibanosti govornog aparata. Glas (govor) određuju uvjeti života, fizička spretnost, ...

  12. 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.

  13. Antarctica Cloud Cover for October 2003 from GLAS Satellite Lidar Profiling

    Science.gov (United States)

    Spinhirne, J. D.; Palm, S. P.; Hart, W. D.

    2005-01-01

    Seeing clouds in polar regions has been a problem for the imagers used on satellites. Both clouds and snow and ice are white, which makes clouds over snow hard to see. And for thermal infrared imaging both the surface and the clouds cold. The Geoscience Laser Altimeter System (GLAS) launched in 2003 gives an entirely new way to see clouds from space. Pulses of laser light scatter from clouds giving a signal that is separated in time from the signal from the surface. The scattering from clouds is thus a sensitive and direct measure of the presence and height of clouds. The GLAS instrument orbits over Antarctica 16 times a day. All of the cloud observations for October 2003 were summarized and compared to the results from the MODIS imager for the same month. There are two basic cloud types that are observed, low stratus with tops below 3 km and high cirrus form clouds with cloud top altitude and thickness tending at 12 km and 1.3 km respectively. The average cloud cover varies from over 93 % for ocean and coastal regions to an average of 40% over the East Antarctic plateau and 60-90% over West Antarctica. When the GLAS monthly average cloud fractions are compared to the MODIS cloud fraction data product, differences in the amount of cloud cover are as much as 40% over the continent. The results will be used to improve the way clouds are detected from the imager observations. These measurements give a much improved understanding of distribution of clouds over Antarctica and may show how they are changing as a result of global warming.

  14. The Relevance of GLAS/ICESat Elevation Data for the Monitoring of River Networks

    Directory of Open Access Journals (Sweden)

    Jean Stéphane Bailly

    2011-04-01

    Full Text Available The Ice, Cloud and Land Elevation Satellite (ICESat laser altimetry mission from 2003 to 2008 provided an important dataset for elevation measurements. The quality of GLAS/ICESat (Geoscience Laser Altimeter System data was investigated for Lake Leman in Switzerland and France by comparing laser data to hydrological gauge water levels. The correction of GLAS/ICESat waveform saturation successfully improved the quality of water elevation data. First, the ICESat elevations and waveforms corresponding to water footprints across the transition from the land to water were analyzed. Water elevations (2 to 10 measurements following the land-water transition are often of lesser quality. The computed accuracy for the ICESat elevation measurements is approximately 5 cm, excluding transitions footprints, and 15 cm, including these footprints. Second, the accuracy of ICESat elevation was studied using data acquired on French rivers with a width greater than the size of the ICESat footprint. The obtained root mean square error (RMSE for ICESat elevations in regard to French rivers was 1.14 m (bias = 0.07 m; standard deviation = 1.15 m, which indicates that small rivers could not be monitored using ICESat with acceptable accuracy due to land-water transition sensor inertia.

  15. 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。

  16. Application of glas laser altimetry to detect elevation changes in East Antarctica

    OpenAIRE

    M. Scaioni; X. Tong; Li, R.

    2013-01-01

    In this paper the use of ICESat/GLAS laser altimeter for estimating multi-temporal elevation changes on polar ice sheets is afforded. Due to non-overlapping laser spots during repeat passes, interpolation methods are required to make comparisons. After reviewing the main methods described in the literature (crossover point analysis, cross-track DEM projection, space-temporal regressions), the last one has been chosen for its capability of providing more elevation change rate measurem...

  17. 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

  18. 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.

  19. 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

  20. Height and Biomass of Mangroves in Africa from ICEsat/GLAS and SRTM

    Science.gov (United States)

    Fatoyinbo, Temilola E.; Simard, Marc

    2012-01-01

    The accurate quantification of forest 3-D structure is of great importance for studies of the global carbon cycle and biodiversity. These studies are especially relevant in Africa, where deforestation rates are high and the lack of background data is great. Mangrove forests are ecologically significant and it is important to measure mangrove canopy heights and biomass. The objectives of this study are to estimate: 1. The total area, 2. Canopy height distributions and 3. Aboveground biomass of mangrove forests in Africa. To derive mangrove 3-D structure and biomass maps, we used a combination of mangrove maps derived from Landsat ETM+, LiDAR canopy height estimates from ICEsat/GLAS (Ice, Cloud, and land Elevation Satellite/Geoscience Laser Altimeter System) and elevation data from SRTM (Shuttle Radar Topography Mission) for the African continent. More specifically, we extracted mangrove forest areas on the SRTM DEM using Landsat based landcover maps. The LiDAR (Light Detection and Ranging) measurements from the large footprint GLAS sensor were used to derive local estimates of canopy height and calibrate the Interferometric Synthetic Aperture Radar (InSAR) data from SRTM. We then applied allometric equations relating canopy height to biomass in order to estimate above ground biomass (AGB) from the canopy height product. The total mangrove area of Africa was estimated to be 25 960 square kilometers with 83% accuracy. The largest mangrove areas and greatest total biomass was 29 found in Nigeria covering 8 573 km2 with 132 x10(exp 6) Mg AGB. Canopy height across Africa was estimated with an overall root mean square error of 3.55 m. This error also includes the impact of using sensors with different resolutions and geolocation error which make comparison between measurements sensitive to canopy heterogeneities. This study provides the first systematic estimates of mangrove area, height and biomass in Africa. Our results showed that the combination of ICEsat/GLAS and

  1. Application of Physically-Based Slope Correction for Maximum Forest Canopy Height Estimation Using Waveform Lidar across Different Footprint Sizes and Locations: Tests on LVIS and GLAS

    Directory of Open Access Journals (Sweden)

    Taejin Park

    2014-07-01

    Full Text Available Forest canopy height is an important biophysical variable for quantifying carbon storage in terrestrial ecosystems. Active light detection and ranging (lidar sensors with discrete-return or waveform lidar have produced reliable measures of forest canopy height. However, rigorous procedures are required for an accurate estimation, especially when using waveform lidar, since backscattered signals are likely distorted by topographic conditions within the footprint. Based on extracted waveform parameters, we explore how well a physical slope correction approach performs across different footprint sizes and study sites. The data are derived from airborne (Laser Vegetation Imaging Sensor; LVIS and spaceborne (Geoscience Laser Altimeter System; GLAS lidar campaigns. Comparisons against field measurements show that LVIS data can satisfactorily provide a proxy for maximum forest canopy heights (n = 705, RMSE = 4.99 m, and R2 = 0.78, and the simple slope correction grants slight accuracy advancement in the LVIS canopy height retrieval (RMSE of 0.39 m improved. In the same vein of the LVIS with relatively smaller footprint size (~20 m, substantial progress resulted from the physically-based correction for the GLAS (footprint size = ~50 m. When compared against reference LVIS data, RMSE and R2 for the GLAS metrics (n = 527 are improved from 12.74–7.83 m and from 0.54–0.63, respectively. RMSE of 5.32 m and R2 of 0.80 are finally achieved without 38 outliers (n = 489. From this study, we found that both LVIS and GLAS lidar campaigns could be benefited from the physical correction approach, and the magnitude of accuracy improvement was determined by footprint size and terrain slope.

  2. ICESat GLAS Elevation Changes and ALOS PALSAR InSAR Line-Of-Sight Changes on the Continuous Permafrost Zone of the North Slope, Alaska

    Science.gov (United States)

    Muskett, Reginald

    2016-04-01

    Measuring centimeter-scale and smaller surface changes by satellite-based systems on the periglacial terrains and permafrost zones of the northern hemisphere is an ongoing challenge. We are investigating this challenge by using data from the NASA Ice, Cloud, and land Elevation Satellite Geoscience Laser Altimeter System (ICESat GLAS) and the JAXA Advanced Land Observing Satellite Phased Array type L-band Synthetic Aperture Radar (ALOS PALSAR) on the continuous permafrost zone of the North Slope, Alaska. Using the ICESat GLAS exact-repeat profiles in the analysis of ALOS PALSAR InSAR Line-Of-Sight (LOS) changes we find evidence of volume scattering over much of the tundra vegetation covered active-layer and surface scattering from river channel/banks (deposition and erosion), from rock outcropping bluffs and ridges. Pingos, ice-cored mounds common to permafrost terrains can be used as benchmarks for assessment of LOS changes. For successful InSAR processing, topographic and tropospheric phase cannot be assumed negligible and must be removed. The presence of significant troposphere phase in short-period repeat interferograms renders stacking ill suited for the task of deriving verifiable centimeter-scale surface deformation phase and reliable LOS changes. Ref.: Muskett, R.R. (2015), ICESat GLAS Elevation Changes and ALOS PALSAR InSAR Line-Of-Sight Changes on the Continuous Permafrost Zone of the North Slope, Alaska. International Journal of Geosciences, 6 (10), 1101-1115. doi:10.4236/ijg.2015.610086 http://www.scirp.org/Journal/PaperDownload.aspx?paperID=60406

  3. A revised terrain correction method for forest canopy height estimation using ICESat/GLAS data

    Science.gov (United States)

    Nie, Sheng; Wang, Cheng; Zeng, Hongcheng; Xi, Xiaohuan; Xia, Shaobo

    2015-10-01

    Although spaceborne Geoscience Laser Altimeter System (GLAS) can measure forest canopy height directly, the measurement accuracy is often affected by footprint size, shape and orientation, and terrain slope. Previous terrain correction methods only took into account the effect of terrain slope and footprint size when estimating forest canopy height. In this study, an improved terrain correction method was proposed to remove the effect of all aforementioned factors when estimating canopy height over sloped terrains. The revised method was found significantly better than the traditional ones according to the canopy height tested using small footprint LiDAR data in China. It reduced the RMSE of the canopy height estimates by up to 1.2 m. The effect of slope on canopy height estimation is almost eliminated by the proposed method since the slope had little correlation with the canopy heights estimated by revised method. When the footprint eccentricity is small, the canopy height error due to the footprint shape and orientation is small. However, when the footprint eccentricity is large enough, the height estimation error due to footprint shape and orientation is large. Therefore, it is necessary to take into account the influence of footprint shape and orientation on forest canopy estimation.

  4. 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.

  5. 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

  6. Photon-counting multikilohertz microlaser altimeters for airborne and spaceborne topographic measurements

    Science.gov (United States)

    Degnan, John J.

    2002-11-01

    We consider the optimum design of photon-counting microlaser altimeters operating from airborne and spaceborne platforms under both day and night conditions. Extremely compact, passively Q-switched microlaser transmitters produce trains of low energy pulses at multi-kHz rates and can easily generate subnanosecond pulsewidths for precise ranging. To guide the design, we have modeled the solar noise background and developed simple algorithms, based on post-detection Poisson filtering (PDPF), to optimally extract the weak altimeter signal from a high noise background during daytime operations. The advantages of photon-counting detector arrays followed by multichannel timing receivers for high resolution topographic mapping are discussed. Practical technology issues, such as detector and/or receiver dead times and their impact on signal detection and ranging accuracy and resolution, have also been considered in the analysis. The theoretical results are reinforced by data from an airborne microlaser altimeter, developed under NASA's Instrument Incubator Program. The latter instrument has operated at several kHz rates from aircraft cruise altitudes up to 6.7 km with laser pulse energies on the order of a few microjoules. The instrument has successfully recorded decimeter accuracy or better single photon returns from man-made structures, tree canopies and underlying terrain and has demonstrated shallow water bathymetry at depths to a few meters. We conclude the discussion by analyzing a photon counting instrument designed to produce, over a mission life of 3 years, a globally contiguous map of the Martian surface, with 5 m horizontal resolution and decimeter vertical accuracy, from an altitude of 300 km. The transmitter power-receive aperture product required is comparable to the Geoscience Laser Altimeter System (GLAS) but the number of individual range measurements to the surface is increased by three to four orders of magnitude. For more modest scientific goals, on a

  7. 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.

  8. 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.

  9. 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.

  10. Canopy Height Estimation in French Guiana with LiDAR ICESat/GLAS Data Using Principal Component Analysis and Random Forest Regressions

    Directory of Open Access Journals (Sweden)

    Ibrahim Fayad

    2014-11-01

    Full Text Available Estimating forest canopy height from large-footprint satellite LiDAR waveforms is challenging given the complex interaction between LiDAR waveforms, terrain, and vegetation, especially in dense tropical and equatorial forests. In this study, canopy height in French Guiana was estimated using multiple linear regression models and the Random Forest technique (RF. This analysis was either based on LiDAR waveform metrics extracted from the GLAS (Geoscience Laser Altimeter System spaceborne LiDAR data and terrain information derived from the SRTM (Shuttle Radar Topography Mission DEM (Digital Elevation Model or on Principal Component Analysis (PCA of GLAS waveforms. Results show that the best statistical model for estimating forest height based on waveform metrics and digital elevation data is a linear regression of waveform extent, trailing edge extent, and terrain index (RMSE of 3.7 m. For the PCA based models, better canopy height estimation results were observed using a regression model that incorporated both the first 13 principal components (PCs and the waveform extent (RMSE = 3.8 m. Random Forest regressions revealed that the best configuration for canopy height estimation used all the following metrics: waveform extent, leading edge, trailing edge, and terrain index (RMSE = 3.4 m. Waveform extent was the variable that best explained canopy height, with an importance factor almost three times higher than those for the other three metrics (leading edge, trailing edge, and terrain index. Furthermore, the Random Forest regression incorporating the first 13 PCs and the waveform extent had a slightly-improved canopy height estimation in comparison to the linear model, with an RMSE of 3.6 m. In conclusion, multiple linear regressions and RF regressions provided canopy height estimations with similar precision using either LiDAR metrics or PCs. However, a regression model (linear regression or RF based on the PCA of waveform samples with waveform

  11. Concept selection and design considerations for compression facilities for FPSO Glas Dowr

    NARCIS (Netherlands)

    Roos, J. de; Eijk, A.; Gillis, J.

    2005-01-01

    As part of the modification of the Floating Production Storage and Offloading Unit (FPSO) Glas Dowr for operation on the Sable Field (offshore South Africa), a new gas compression system was installed. Associated gas is compressed for use as lift gas and re-injection back into the reservoir for pres

  12. 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

  13. 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

  14. Dimensionering af glas i klimaskærmen

    DEFF Research Database (Denmark)

    Munch-Andersen, Jørgen

    Denne anvisning berhandler dimensionering af glas som udfyldende element i klimaskærmen, det vil sige vinduer, facader og tage. Den indeholder de informationer, man normalt vil finde i en norm, men også andre oplysninger, der kan være nyttige ved dimensionering af glas. Anvisningen er udarbejdet i...

  15. 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...

  16. 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.

  17. Lovende folie/glas dækkemateriale

    DEFF Research Database (Denmark)

    Skou, Philip Thonning; Reisinger, Gerhard

    2006-01-01

    Folie har været et alternativ til glas i væksthuse i mange år, men har i Danmark været klart sekundært dækkemateriale. I de senere år har nye folietyper gjort dette til et nyt innovativt dækkemateriale. Denne artikel beskriver et lovende tysk forskningsprojekt med en kombination af glas og folie...

  18. Assessment Of ASTER GDEM And SRTM Performance By Comparing With Survey Control Points And Icesat/GLAS Data

    Science.gov (United States)

    Jarihani, A. A.; Callow, J. N.

    2011-12-01

    Topographic data plays a critical role in water resources modeling with determining watershed hydrologic characteristics from raster-based digital elevation models (DEM). Raster-based DEMs have been widely used to derive topographic attributes used in hydraulic and hydrologic modeling such as slope, stream network, basins boundary and area. Accurate models of floodplain topography are essential for having accurate output of hydrologic models. The Shuttle Radar Topography Mission (SRTM) provides near-global topographic coverage of the Earth's surface with unprecedented consistency and accuracy with the resolution of 1-3 arc sec. A new Global Digital Elevation Model (GDEM) from optical stereo data acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) was recently released with the resolution of 1 arc sec. This study the performance of the ASTER GDEM and SRTM DEMs is assessed by comparing with ground-based survey control points and point data from ICESat/GLAS (Ice, Cloud, and land Elevation Satellite/Geoscience Laser Altimeter System) for a 7x7degree area in Queensland Australia. This area contains large and remote river basins, where these datasets provide an invaluable resource from which river floodplain inundation can be measured and modelled. Our study focuses on both data and datum issues, which are required to provide a realistic assessment of the achievable relative and absolute ground topographic accuracies. We assessed ground-based survey control points' with ICESat satellite altimetry points and in turn assessed accuracy of the ASTER GDEM and SRTM DEMs over the study area. ICESat provides globally-distributed elevation data of high accuracy (2.47.3 m horizontal error and 0.040.13 m (per degree of incidence angle) vertical error)We applied the GLA14 elevation products (Land/Canopy elevations) for the Laser 3a observation period and Release 31 to compare with 5000 ground survey control points in study area.Our ICESat

  19. 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)

  20. Future Applications Using Return-Pulse Correlation from Imaging Laser Altimeters

    Science.gov (United States)

    Blair, J. Bryan; Hofton, Michelle A.; Rabine, David L.

    2000-01-01

    The Laser Vegetation Imaging Sensor (LVIS) is an airborne, wide-swath, digitization-only laser altimeter capable of collecting full return waveforms (i.e. echoes) from laser footprints ranging in diameter from 1 to 80 m across up to a 1 km wide data swath. The return waveform can be used to enhance the accuracy of laser ranging and to provide information about the vertical structure of vegetation and topography within each laser footprint. Although extremely small laser footprints (laser altimeters record the return echo or return pulse that is reflected from the Earth's surface (i.e. NASA's LVIS, SLA, VCL, and GLAS laser altimeters). Waveforms are currently interpreted to extract a timing or ranging point or points to represent the mean ground elevation or the vertical height of vegetation. But, recent progress using pulse shape correlation techniques shows promise for a variety of science applications involving change detection of surface topography and vegetation as well as potential for improving data processing by correlating images or crossovers to solve systematic biases. We show example correlation images from LVIS and discuss instrument design implications and potential science applications.

  1. 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.

  2. 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.

  3. Forest leaf area index estimation using combined ICESat/GLAS and optical remote sensing image%星载激光雷达GLAS与TM光学遥感联合反演森林叶面积指数

    Institute of Scientific and Technical Information of China (English)

    骆社周; 王成; 习晓环; 聂胜; 夏少波; 万怡平

    2015-01-01

    通过对地球科学激光测高系统(Geoscience Laser Altimeter System,GLAS)波形数据进行高斯分解,提取精确的波形特征信息,计算出GLAS波形数据激光穿透指数(LPI),基于LPI提出GLAS数据反演叶面积指数(LAI)的新方法,建立了GLAS数据反演森林LAI的模型(R2=0.84,RMSE=0.64),并用留一交叉验证法(LOOCV)对反演模型的可靠性进行了验证,结果表明,该模型没有过度拟合,具有很好的泛化能力,最后通过人工神经网络融合GLAS与TM(Thematic Mapper,专题制图仪)遥感数据实现区域尺度森林LAI反演,用25个实测LAI对反演精度进行了验证,研究表明反演LAI与实测值较为接近,精度较高(R2 =0.76,RMSE=0.69),为生态环境研究提供精确的输入参数,为GLAS数据大区域高精度LAI反演提供新的方法和思路.

  4. 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

  5. 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

  6. Comparison of cloud statistics from spaceborne lidar systems

    Directory of Open Access Journals (Sweden)

    S. Berthier

    2008-12-01

    Full Text Available The distribution of clouds in a vertical column is assessed on the global scale through analysis of lidar measurements obtained from three spaceborne lidar systems: LITE (Lidar In-space Technology Experiment, NASA, GLAS (Geoscience Laser Altimeter System, NASA, and CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization. Cloud top height (CTH is obtained from the LITE profiles based on a simple algorithm that accounts for multilayer cloud structures. The resulting CTH results are compared to those obtained by the operational algorithms of the GLAS and CALIOP instruments. Based on our method, spaceborne lidar data are analyzed to establish statistics on the cloud top height. The resulting columnar results are used to investigate the inter-annual variability in the lidar cloud top heights. Statistical analyses are performed for a range of CTH (high, middle, low and latitudes (polar, middle latitude and tropical. Probability density functions of CTH are developed. Comparisons of CTH developed from LITE, for 2 weeks of data in 1994, with ISCCP (International Satellite Cloud Climatology Project cloud products show that the cloud fraction observed from spaceborne lidar is much higher than that from ISCCP. Another key result is that ISCCP products tend to underestimate the CTH of optically thin cirrus clouds. Significant differences are observed between LITE-derived cirrus CTH and both GLAS and CALIOP-derived cirrus CTH. Such a difference is due primarily to the lidar signal-to-noise ratio that is approximately a factor of 3 larger for the LITE system than for the other lidars. A statistical analysis for a full year of data highlights the influence of both the Inter-Tropical Convergence Zone and polar stratospheric clouds.

  7. Comparison of cloud statistics from spaceborne lidar systems

    Directory of Open Access Journals (Sweden)

    S. Berthier

    2008-03-01

    Full Text Available The distribution of clouds in a vertical column is assessed on the global scale through analysis of lidar measurements obtained from three spaceborne lidar systems: LITE (Lidar In-space Technology Experiment, NASA, GLAS (Geoscience Laser Altimeter System, NASA, and CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization. Cloud top height (CTH is obtained from the LITE profiles based on a simple algorithm that accounts for multilayer cloud structures. The resulting CTH results are compared to those obtained by the operational algorithms of the GLAS and CALIOP instruments. Based on our method, spaceborne lidar data are analyzed to establish statistics on the cloud top height. The resulting columnar results are used to investigate the inter-annual variability in the lidar cloud top heights. Statistical analyses are performed for a range of CTH (high, middle, low and latitudes (polar, middle latitude and tropical. Probability density functions of CTH are developed. Comparisons of CTH developed from LITE, for 2 weeks of data in 1994, with ISCCP (International Satellite Cloud Climatology Project cloud products show that the cloud fraction observed from spaceborne lidar is much higher than that from ISCCP. Another key result is that ISCCP products tend to underestimate the CTH of optically thin cirrus clouds. Significant differences are observed between LITE-derived cirrus CTH and both GLAS and CALIOP-derived cirrus CTH. Such a difference is due primarily to the lidar signal ratio that is larger than a factor of approximately 3 for the LITE system. A statistical analysis for a full year of data highlights the influence of both the Inter-Tropical Convergence Zone and polar stratospheric clouds.

  8. 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.

  9. 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 ...

  10. 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.

  11. A Stochastic Approach to Noise Modeling for Barometric Altimeters

    Directory of Open Access Journals (Sweden)

    Angelo Maria Sabatini

    2013-11-01

    Full Text Available 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.

  12. O delírio de negação de Cotard a Séglas The negative delusion from Cotard to Séglas

    Directory of Open Access Journals (Sweden)

    Olivier Douville

    2007-01-01

    Full Text Available Vamos apresentar ao leitor, muito rapidamente, quem foi Séglas, a partir das distintas etapas que permitem destacar o delírio de negação, insistindo nas abordagens clínicas de Séglas e no modo pelo qual este organiza o seu texto, como um jardim à francesa, a fim de pôr em prática a discussão clínica em torno da melancolia delirante. Para encerrar, daremos algumas referências provenientes da clínica psicanalítica, na esperança de que tragam esclarecimento a respeito do significado atual do delírio de negação.We will present the reader, very briefly, who was Séglas, through the different stages that highlight the negative delusion, insisting in Séglas´ clinical approach and the way in which he organizes his text, such as a French garden, in order to clinically discuss delusional melancholy. To conclude, we will provide some references from the psychoanalytic clinic, in the hope that they bring clarification regarding negative delusion's current meaning.

  13. 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

  14. A comparison and evaluation between ICESat/GLAS altimetry and mean sea level in Thailand

    Science.gov (United States)

    Naksen, Didsaphan; Yang, Dong Kai

    2015-10-01

    Surface elevation is one of the importance information for GIS. Usually surface elevation can acquired from many sources such as satellite imageries, aerial photograph, SAR data or LiDAR by photogrammetry, remote sensing methodology. However the most trust information describe the actual surface elevation is Leveling from terrestrial survey. Leveling is giving the highest accuracy but in the other hand is also long period process spending a lot of budget and resources, moreover the LiDAR technology is new era to measure surface elevation. ICESat/GLAS is spaceborne LiDAR platform, a scientific satellite lunched by NASA in 2003. The study area was located at the middle part of Thailand between 12. ° - 14° North and 98° -100° East Latitude and Longitude. The main idea is to compare and evaluate about elevation between ICESat/GLAS Altimetry and mean sea level of Thailand. Data are collected from various sources, including the ICESat/GLAS altimetry data product from NASA, mean sea level from Royal Thai Survey Department (RTSD). For methodology, is to transform ICESat GLA14 from TOPX/Poseidon-Jason ellipsoid to WGS84 ellipsoid. In addition, ICESat/GLAS altimetry that extracted form centroid of laser footprint and mean sea level were compared and evaluated by 1st Layer National Vertical Reference Network. The result is shown that generally the range of elevation between ICESat/GLAS and mean sea level is wildly from 0. 8 to 25 meters in study area.

  15. Estimation of regional-scale forest resources using ICESat/GLAS spaceborne lidar

    Science.gov (United States)

    Hayashi, Masato; Saigusa, Nobuko; Borjigin, Habura; Sawada, Yoshito; Yamagata, Yoshiki; Hirano, Takashi; Ichii, Kazuhito

    2015-10-01

    Recently, the demand of forest resources monitoring technology on a large scale is growing, and spaceborne LiDAR is expected to provide a means for accurate monitoring. This study aims to clarify the potential of ICESat/GLAS spaceborne LiDAR for forest resources monitoring on a regional scale. The study areas were Hokkaido Island in Japan (cool-temperate forest), Borneo Island (tropical forest), and Siberia (boreal forest). Firstly, we conducted field measurements in Hokkaido and Borneo, and calculated the average canopy height (Lorey's height) and the above-ground biomass (AGB) for each GLAS-footprint. Then, we developed some models to estimate canopy height and AGB from the GLAS waveform parameters based on the field measurement data. Next, we applied the developed models to the GLAS data in Hokkaido and Borneo. The average canopy height and AGB were 17.8 m and 119.4 Mg ha-1, respectively, in Hokkaido, and 16.2 m and 190.2 Mg ha-1, respectively, in Borneo. These results suggest that the tropical forest in Borneo has a higher biomass than the cool-temperate forest in Hokkaido. Furthermore, we applied the estimation model to the GLAS data acquired in Siberia. The average AGB was 86.2 Mg ha-1, and it has decreased especially in Southern area of Western Siberia. This study showed that spaceborne LiDAR had an ability of forest resources monitoring on a regional scale, for each of boreal, cool-temperate, and tropical forests.

  16. 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.

  17. 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

  18. Hoe hoger de haze bij diffuus glas, hoe hoger de meerproductie (interview met Jan Janse en Sonny Moerenhout)

    NARCIS (Netherlands)

    Kierkels, T.; Janse, J.; Moerenhout, S.

    2012-01-01

    Een vroege komkommerteelt onder diffuus glas gaf vanaf het begin een grotere opbrengst dan onder gewoon glas. Jan Janse van Wageningen UR Glastuinbouw durft na de reeks proeven in de afgelopen jaren de conclusie te trekken: hoe hoger de haze, hoe hoger de meerproductie. Dus ook in een vroege teelt.

  19. Towards integration of GLAS data into a national fuels mapping program

    Science.gov (United States)

    Peterson, Birgit; Nelson, Kurtis; Wylie, Bruce

    2013-01-01

    Comprehensive canopy structure and fuel data are critical for understanding and modeling wildland fire. The LANDFIRE project produces such data nationwide based on a collection of field observations, Landsat imagery, and other geospatial data. Where field data are not available, alternate strategies are being investigated. In this study, vegetation structure data available from GLAS were used to fill this data gap for the Yukon Flats Ecoregion of interior Alaska. The GLAS-derived structure and fuel layers and the original LANDFIRE layers were subsequently used as inputs into a fire behavior model to determine what effect the revised inputs would have on the model outputs. The outputs showed that inclusion of the GLAS data enabled better landscape-level characterization of

  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. 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.

  2. 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.

  3. The GLAS Algorithm Theoretical Basis Document for Laser Footprint Location (Geolocation) and Surface Profiles

    Science.gov (United States)

    Shutz, Bob E.; Urban, Timothy J.

    2014-01-01

    This ATBD summarizes (and links with other ATBDs) the elements used to obtain the geolocated GLAS laser spot location, with respect to the Earth Center of Mass. Because of the approach used, the reference frame used to express the geolocation is linked to the reference frame used for POD and PAD, which are related to the ITRF. The geolocated spot coordinates (which includes the elevation or height, with respect to an adopted reference ellipsoid) is the inferred position of the laser spot, since the spot location is not directly measured. This document also summarizes the GLAS operation time periods.

  4. 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...

  5. 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.

  6. 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....

  7. 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.

  8. Using ICESat/GLAS Data Produced in a Self-Describing Format

    Science.gov (United States)

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

    2015-12-01

    For the life of the ICESat mission and beyond, GLAS data have been distributed in binary format by NASA's National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC) at the University of Colorado in Boulder. These data have been extremely useful but, depending on the users, not always the easiest to use. Recently, with release 33 and 34, GLAS data have been produced in an HDF5 format. The NSIDC User Services Office has found that most users find this HDF5 format to be more user friendly than the original binary format. Some of the advantages include being able to view the actual data using HDFView or any of a number of open source tools freely available for users to view and work with the data. Also with this format NSIDC DAAC has been able to provide more selective and specific services which include spatial subsetting, file stitching, and the much sought after parameter subsetting through the use of Reverb, the next generation Earth science discovery tool. The final release of GLAS data in 2014 and the ongoing user questions not just about the data, but about the mission, satellite platform, and instrument have also spurred NSIDC DAAC efforts to make all of the mission documents and information available to the public in one location. Thus was born the ICESat/GLAS Long Term Archive now available online. The data and specifics from this mission are archived and made available to the public at NASA's NSIDC DAAC.

  9. A comparison of GLAS SAT and NMC high resolution NOSAT forecasts from 19 and 11 February 1976

    Science.gov (United States)

    Atlas, R.

    1979-01-01

    A subjective comparison of the Goddard Laboratory for Atmospheric Sciences (GLAS) and the National Meteorological Center (NMC) high resolution model forecasts is presented. Two cases where NMC's operational model in 1976 had serious difficulties in forecasting for the United States were examined. For each of the cases, the GLAS model forecasts from initial conditions which included satellite sounding data were compared directly to the NMC higher resolution model forecasts, from initial conditions which excluded the satellite data. The comparison showed that the GLAS satellite forecasts significantly improved upon the current NMC operational model's predictions in both cases.

  10. 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.

  11. A Stochastic Approach to Noise Modeling for Barometric Altimeters

    OpenAIRE

    Angelo Maria Sabatini; Vincenzo Genovese

    2013-01-01

    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 w...

  12. 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.

  13. 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

  14. Energy-related renovation in the world heritage. Retrofitting 'Glas-Hoffmann' buildings, Berlin; Energetische Sanierung im Weltkulturerbe. Sanierung 'Glas-Hoffmann'-Bauten, Berlin

    Energy Technology Data Exchange (ETDEWEB)

    Brensing, Christian

    2012-11-01

    Between 1955 and 1959, the housing estate at the Schiller park in Berlin-Wedding (Federal Republic in Germany) established in the 1920ies was expanded by four-storey house lines, the so-called Glas-Hoffmann buildings. Since 2008, this ensemble belongs to the Unesco World Heritage. In improving the thermal insulation of the building envelope and the adaptation of the building services to today's standards, therefore the architectural aesthetics of these buildings should not be endangered. The retrofitting was a pilot project of the research project ''Monument and energy - Postwar Modernism''.

  15. 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.

  16. Materialverhalten von AR-Glas- und Carbonfilamentgarnen unter Dauerlast- sowie unter Hochtemperatureinwirkung

    OpenAIRE

    Younes, Ayham; Seidel, André; Engler, Thomas; Cherif, Chokri

    2009-01-01

    In vielen technischen Anwendungen werden Faserverbundwerkstoffe mit Hochleistungsfasern aus Carbon und AR-Glas eingesetzt, die aufgrund ihrer physikalischen und chemischen Eigenschaften ein hohes Festigkeitspotential aufweisen. Damit eröffnen sich neue Anwendungsgebiete, z. B. als textile Bewehrungen für Betonbauteile. Die Garnmaterialien müssen hohe sicherheitstechnische Anforderungen erfüllen. Dazu gehören u. a. eine ausreichende Tragfähigkeit unter Dauerlastbeanspruchung und eine hohe Temp...

  17. Ground truth data requirements for altimeter performance verification

    Science.gov (United States)

    Walsh, E. J.

    1972-01-01

    The amount and type of ground truth required for an altimeter experiment is a function of the uncertainty in the satellite orbit, the altimeter error budget and the type of operation being performed. Ground truth requirements will be discussed with reference to three areas of operation: the global mode, the high intensity mode and calibration.

  18. Surface slope and roughness measurement using ICESat/GLAS elevation and laser waveform

    Science.gov (United States)

    Li, Xiaolu; Xu, Kai; Xu, Lijun

    2016-09-01

    Surface slope and roughness are important geomorphological variables which have been used in the Earth and planetary sciences to infer material properties. For the ICESat/GLAS measurement, roughness and slope are two surface properties for broadening the width of the returned pulse. Based on this, a new method (GLAS waveform-derived roughness, GWR in short) is investigated to invert roughness from waveform broadening after excluding slope effect. Surface slope is estimated from the repeat tracks elevation of ICESat/GLAS, which is verified to be coincidence with geography facts (Landsat-7 images). Extensive experiments are performed using the proposed methods to evaluate the performance of surface properties (roughness, slope and elevation) in the Jakobshavn area. The experimental results demonstrate that, compared with the elevation-derived roughness method (GER in short), GWR is more sensitive to local surface properties in the gentle slope zone because it is a small-scale estimation. Additionally, GWR is a more stable roughness estimation which is immune to a strong elevation change.

  19. Glas Journal: Deep Mappings of a Harbour or the Charting of Fragments, Traces and Possibilities

    Directory of Open Access Journals (Sweden)

    Silvia Loeffler

    2015-09-01

    Full Text Available With reference to a hybrid ethnographic project entitled Glas Journal (2014–2016, this article invites readers to reflect on the cultural mapping of spaces we intimately inhabit. Developed with the participation of local inhabitants of Dún Laoghaire Harbour, Ireland, Glas Journal seeks to explore the maritime environment as a liminal space, whereby the character of buildings and an area’s economic implications determine our relationship to space as much as our daily spatial rhythms and feelings of safety. Deep mapping provides the methodological blueprint for Glas Journal. In order to create a heteroglossic narrative of place and belonging, I will contextualise the project with references to seminal works in the visual arts, literature, film and geography that emotionally map spaces. Chronotopes of the threshold will be used to elaborate on spatial and cultural phenomena that occur when crossings from public to private and interior to exterior take place. Touching upon questions such as “What is a space of protection?”, “Who am I in it?”, and “Who is the Other?”, this article traces forms of liquid mapping that do not strive to conquer but rather to gain insight into the inner landscapes that are reflected in outer space.

  20. 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...

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. ICESat—GLAS测高数据在长江中下游湖泊水位变化监测中的应用%Monitoring Lake Water Level Changes in the Middle and Lower Yangtze River Basin Based on ICESat-GLAS Altimetry Data

    Institute of Scientific and Technical Information of China (English)

    吴红波; 郭忠明; 毛瑞娟

    2012-01-01

    Changes in lakes because of global climate change has become a national and international issue. We selected six typical lakes in China and analysed ICESat-GLAS data (ice, cloud, and land elevation satellite-geoscience laser altimeter system) to extract lake water elevations for 2003-2009. ICESat-GLAS altimeter waveform data were denoised by a Gaussian filter and used to distinguish between water and land. Lake boundaries were extracted from pre-processed Landsat TM imageries using a Fusion algorithm. Water level values within lake boundaries were used to construct inter-annual and annual water level time-variation curves. We found that the spatial accuracy of lake boundary data extracted from Landsat TM imageries is 10 m. The mean accuracy of measured ICESat altimeter data in the vicinity of Jiangba station at Hongze Lake, Chenglingji station at Dongting Lake, Xingzi and Changdu stations at Poyang Lake, Xishan station at Tai Lake, Zha station at Chao Lake and Gaoyou station at Gaoyou Lake are validated and assessed by observation data, and mean accuracy was -3.9 cm, -8.3 cm, -9.0 cm, -2.5 cm,-3.1 cm and-4.1 cm, respectively. Lake water levels in the middle and lower reaches of the Yangtze River basin show periodic fluctuation, and compared with historical observation data, the mean water level has decreased slightly. Lake water levels have been affected by regulation of the Three Gorges Project since October 2006. The relationship between lake water levels in the middle and lower Yangtze River basin and annual precipitation was correlated. Average water level changes for Hongze and Tai Lakes in 2006 fluctuated significantly. The average water level of Dongting, Poyang, Chaohu and Gaoyou Lakes peaked from June to October 2006.%在全球气候变暖的背景下湖泊变化已是国内外地学界关注的环境问题,并日益受到各国政府和研究机构的重视。本文以长江中下游的6个典型湖泊为研究对象,基于2003年-2009

  11. 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

  12. 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.

  13. 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...

  14. 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.

  15. 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.

  16. 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.

  17. Los delirios de negación según Cotard y Séglas.

    Directory of Open Access Journals (Sweden)

    José María Álvarez Martínez

    2009-01-01

    Full Text Available Como señalan Haustgen y Bourgeois, hace algo más de un siglo el joven alienista parisino J. Séglas (1856-1939 publicó a lo largo de pocos años una serie de obras magistrales, destinadas a establecer de forma perdurable en Francia los cuadros de la clínica psiquiátrica. A los Trastornos del lenguaje en los alienados sucedieron tres años más tarde las Lecciones clínicas sobre las enfermedades mentales y nerviosas. Sólo dos años después apareció la famosa monografía sobre El delirio de negación. El colofón de toda esta obra fue el capítulo «Semiología de las afecciones mentales» del Tratado de Gilbert Ballet. En el intervalo, un número impresionante de artículos (se ha estimado que totalizan ciento treinta fue publicado por Séglas, tocando los más diversos terrenos de la clínica. Sin embargo, a pesar de que su nombre es muy frecuentemente citado por sus contemporáneos, esos trabajos y monografías no han sido reeditados, y hasta 1950 no comienzan a aparecer artículos un poco consecuentes sobre

  18. 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.

  19. 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.

  20. Analysis of laser altimeter waveforms for forested ecosystems of Central Florida

    Science.gov (United States)

    Weishampel, John F.; Harding, David J.; Boutet, Jeffry C., Jr.; Drake, Jason B.

    1997-07-01

    An experimental profiling airborne laser altimeter system developed at NASA's Goddard Space Flight Center was used to acquire vertical canopy data from several ecosystem types from The Nature Conservancy's Disney Wilderness Preserve, near Kissimmee, Florida. This laser altimeter, besides providing submeter accuracy of tree height, captures a profile of data which relates to the magnitude of reflectivity of the laser pulse as it penetrates different elevations of the forest canopy. This complete time varying amplitude of the return signal of the laser pulse, between the first (i.e., the canopy top) and last (i.e., the ground) returns, yields a waveform which is related to canopy architecture, specifically the nadir-projected vertical distribution of the surface of canopy components (i.e., foliage, twigs, and branches). Selected profile returns from representative covertypes (e.g., pine flatwoods, bayhead, and cypress wetland) were compared with ground truthed forest composition (i.e., species and size class distribution) and structural (i.e., canopy height, canopy closure, crown depth) measures to help understand how these properties contribute to variation in the altimeter waveform.

  1. 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

  2. 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).

  3. 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...

  4. 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.

  5. 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.

  6. 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

  7. Diagnostic analysis and spectral energetics of a blocking event in the GLAS climate model simulation

    Science.gov (United States)

    Chen, T.-C.; Shukla, J.

    1983-01-01

    A synoptic and spectral analysis of a blocking event is presented, with attention given to the temporal evolution, maintenance, and decay of the block. The GLAS numerical climate model was used to generate a blocking event by the introduction of SST anomalies. Wavenumbers 2 and 3 became stationary around their climatological locations, and their constructive interference produced persistent blocking ridges over the west coast of North America and the other over western Europe. Time variations of the kinetic and potential energies and energy conversions during the blocking were performed. Spectrally filtered Hovmoller diagrams were developed for the winter of 1976-77, and showed that long waves were stationary over most of the interval, which featured severe weather conditions.

  8. GlasKon `99 - 7th Innovation Forum for Glass, Architecture, and Technology from January 18 to 23, 1999; GlasKon `99: 7. Innovations-Forum Glas, Architektur, Technik - Kongress und Ausstellung in Verbindung mit der Bau `99; GlasKon `99 - 7th Innovation Forum for Glass, Architecture, and Technology from January 18 to 23, 1999

    Energy Technology Data Exchange (ETDEWEB)

    Krewinkel, H.W.; Seger, P.E.; Achenbach, J. [comps.

    1999-10-01

    Thanks to its basic properties, i.e. transparency, weather resistance, and easy recyclability, glass is very well suited as a ``solar radiation-trapping`` building material. This congress and exhibition report presents, amongst other things, a solar glass of variable light and energy transmission, possibilities of passivsolar energy recovery in non-transparent facades, glazing for intelligent daylight utilisation, and innovative facades with photovoltaics. Four contributions have been abstracted individually for the Energy Database. [Deutsch] Der Baustoff Glas mit seinen grundlegenden Eigenschaften - Transparenz, Wetterbestaendigkeit sowie problemlose Recyclebarkeit dient auch als `` solare Strahlenfalle``. Im Folgenden werden ein Sonnenschutzglas mit veraenderbarer Licht-und Energietransmission, Moeglichkeiten der passiven solaren Energiegewinnung im nicht-transparentern Fassadenbereich, Verglasungen fuer die intelligente Tageslichtnutzung sowie innovative Fassaden mit Photovoltaik vorgestellt. Fuer die Datenbank Energy wurden vier Beitraege einzeln aufgenommen.

  9. Antjie Krog se vertaling van Henk van Woerden se roman Een mond vol glas

    Directory of Open Access Journals (Sweden)

    H.P. van Coller

    2002-08-01

    Full Text Available Antjie Krog’s translation of Henk van Woerden’s novel Een mond vol glas (A mouth full of glass Against a historical backdrop several critical approaches to translational theory are explicated. Traditional criticism seems to imply positioning between the Source Text (ST and the Target Text (TT. A functionalist approach (as propagated among others by Snell-Hornby, Nord and Naaijkens is a descriptive rather than a normative approach that focuses almost exclusively on the ST. This approach is consequently adopted in the evaluation of Krog’s translation; yet even within this more relativistic paradigm, a comparison between ST and TT should not be evaded. In the case of Krog’s translation, this comparison leads to the identification of scores of lexical, grammatical and stylistic errors.

  10. 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.

  11. 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.

  12. Accuracy assessment of SRTM v4 and ASTER GDEM v2 over the Altiplano watershed using ICESat/GLAS data

    OpenAIRE

    Satge, F.; Bonnet, Marie-Paule; Timouk, Franck; Calmant, Stéphane; Pillco, R.; Molina, J; Lavado-Casimiro, W.; Arsen, A.; Cretaux, J. F.; J. Garnier

    2015-01-01

    The new Global Digital Elevation Model (GDEM v2) has been available since 17 October 2011. With a resolution of approximately 30 m, this model should provide more accurate information than the latest version of Shuttle Radar Topographic Mission (SRTM v4) with a resolution of 90 m outside of the USA. The accuracies of these two recently released digital elevation models (DEMs) were assessed over the Altiplano watershed in South America using ICESat/GLAS data (Ice, Cloud and Land Elevation Sate...

  13. 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.

  14. Elevation Change of the Southern Greenland Ice Sheet from Satellite Radar Altimeter Data

    Science.gov (United States)

    Haines, Bruce J.

    1999-01-01

    Long-term changes in the thickness of the polar ice sheets are important indicators of climate change. Understanding the contributions to the global water mass balance from the accumulation or ablation of grounded ice in Greenland and Antarctica is considered crucial for determining the source of the about 2 mm/yr sea-level rise in the last century. Though the Antarctic ice sheet is much larger than its northern counterpart, the Greenland ice sheet is more likely to undergo dramatic changes in response to a warming trend. This can be attributed to the warmer Greenland climate, as well as a potential for amplification of a global warming trend in the polar regions of the Northern Hemisphere. In collaboration with Drs. Curt Davis and Craig Kluever of the University of Missouri, we are using data from satellite radar altimeters to measure changes in the elevation of the Southern Greenland ice sheet from 1978 to the present. Difficulties with systematic altimeter measurement errors, particularly in intersatellite comparisons, beset earlier studies of the Greenland ice sheet thickness. We use altimeter data collected contemporaneously over the global ocean to establish a reference for correcting ice-sheet data. In addition, the waveform data from the ice-sheet radar returns are reprocessed to better determine the range from the satellite to the ice surface. At JPL, we are focusing our efforts principally on the reduction of orbit errors and range biases in the measurement systems on the various altimeter missions. Our approach emphasizes global characterization and reduction of the long-period orbit errors and range biases using altimeter data from NASA's Ocean Pathfinder program. Along-track sea-height residuals are sequentially filtered and backwards smoothed, and the radial orbit errors are modeled as sinusoids with a wavelength equal to one revolution of the satellite. The amplitudes of the sinusoids are treated as exponentially-correlated noise processes with a

  15. 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)

  16. 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

  17. 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...

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  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. Improvement of Europa's Gravity and Body Tides and Shape with a Laser Altimeter during a Flyby Tour

    Science.gov (United States)

    Mazarico, E.; Genova, A.; Smith, D. E.; Zuber, M. T.

    2014-12-01

    Laser altimeters have been primarily utilized with orbiter spacecraft. Recently, the Mercury Laser Altimeter on MESSENGER successfully operated at Mercury during two flybys and thousands of highly-elliptical orbits, and contributed greatly towards improved understanding of the innermost planet. We show that a laser altimeter instrument on a flyby tour mission such as the planned NASA Europa Clipper can constrain key geophysical parameters when supported by variable-frequency altimetric measurements over repeated ~145°-long arcs across the surface. Previous work by Park et al. (2011, GRL) showed through covariance analysis that a similar trajectory could yield the gravity tidal Love number k2 to good accuracy (0.05). Here, we conduct a full simulation of a 45-flyby trajectory in the Jupiter system with Europa as primary target. We consider reasonable tracking coverage and noise level (dominated by plasma noise), as well as gravity (degree 50) and topography (200m resolution supplemented by realistic fractal noise at shorter wavelengths), informed by relevant existing data (Galileo, Cassini). The simulation is initialized at pessimistic values, with C20, C22, k2, and h2 in error of 90%, 90%, 50%, and 50%, respectively. All other gravity coefficients up to degree 3 have zero a priori values. Assumed altimetric data sampling and noise are derived from the tour trajectory and the instrument performance described by Smith et al. (this meeting). This variable-frequency laser altimeter can greatly improve the surface coverage (for shape recovery) and the number of altimetric crossovers, the best measurement type to constrain the tidal surface deformation. We find from our simulation that the addition of altimetry data significantly improves the determination of the gravity tidal Love number k2 and enables the recovery of the body tidal Love number h2. Low-degree gravity and topography are most important to constrain the interior structure of Europa. Scientific objectives

  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. 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.

  14. Mapping lake level changes using ICESat/GLAS satellite laser altimetry data: a case study in arid regions of central Asia

    Science.gov (United States)

    Li, JunLi; Fang, Hui; Yang, Liao

    2011-12-01

    Lakes in arid regions of Central Asia act as essential components of regional water cycles, providing sparse but valuable water resource for the fragile ecological environments and human lives. Lakes in Central Asia are sensitive to climate change and human activities, and great changes have been found since 1960s. Mapping and monitoring these inland lakes would improve our understanding of mechanism of lake dynamics and climatic impacts. ICESat/GLAS satellite laser altimetry provides an efficient tool of continuously measuring lake levels in these poorly surveyed remote areas. An automated mapping scheme of lake level changes is developed based on GLAS altimetry products, and the spatial and temporal characteristics of 9 typical lakes in Central Asia are analyzed to validate the level accuracies. The results show that ICESat/GLAS has a good performance of lake level monitoring, whose patterns of level changes are the same as those of field observation, and the max differences between GLAS and field data is 3cm. Based on the results, it is obvious that alpine lakes are increasing greatly in lake levels during 2003-2009 due to climate change, while open lakes with dams and plain endorheic lakes decrease dramatically in water levels due to human activities, which reveals the overexploitation of water resource in Central Asia.

  15. 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.

  16. 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.

  17. 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.

  18. Geodetic Mobil Solar Spectrometer for JASON Altimeter Satellite Calibration

    Science.gov (United States)

    Somieski, A.; Buerki, B.; Geiger, A.; Kahle, H.-G.; Becker-Ross, H.; Florek, S.; Okruss, M.

    Atmospheric water vapor is a crucial factor in achieving highest accuracies for space geodetic measurements. Water vapor causes a delay of the propagation time of the altimeter satellite signal, which propagates into errors for the determination of surface heights. Knowledge of the precipitable water vapor (PW) enables a tropospheric correction of the satellite signal. Therefore, different remote sensing techniques have been pursued to measure the PW continuously. The prototype Geodetic Mobil Solar Spectrometer (GEMOSS) was developed at the Geodesy and Geodynamics Laboratory (GGL, ETH Zurich) in cooperation with the Institute of Spectrochemistry and Applied Spectroscopy (ISAS) (Berlin, Germany). A new optical approach allows the simultaneous measurement of numerous single absorption lines of water vapor in the wide range between 728 nm and 915 nm. The large number of available absorption lines increases the accuracy of the absolute PW retrievals considerably. GEMOSS has been deployed during two campaigns in Greece in the framework of the EU-project GAVDOS, which deals with the calibration of the altimeter satellite JASON. During the overfly of JASON, the ground-based determination of PW enables the correction of the satellite measurements due to tropospheric water vapor. Comparisons with radiometer and radiosondes data allow to assess the accuracy and reliability of GEMOSS. The instrumental advancement of GEMOSS is presented together with the results of the campaigns carried out.

  19. 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.

  20. User's guide: Programs for processing altimeter data over inland seas

    Science.gov (United States)

    Au, A. Y.; Brown, R. D.; Welker, J. E.

    1989-01-01

    The programs described were developed to process GEODYN-formatted satellite altimeter data, and to apply the processed results to predict geoid undulations and gravity anomalies of inland sea areas. These programs are written in standard FORTRAN 77 and are designed to run on the NSESCC IBM 3081(MVS) computer. Because of the experimental nature of these programs they are tailored to the geographical area analyzed. The attached program listings are customized for processing the altimeter data over the Black Sea. Users interested in the Caspian Sea data are expected to modify each program, although the required modifications are generally minor. Program control parameters are defined in the programs via PARAMETER statements and/or DATA statements. Other auxiliary parameters, such as labels, are hard-wired into the programs. Large data files are read in or written out through different input or output units. The program listings of these programs are accompanied by sample IBM job control language (JCL) images. Familiarity with IBM JCL and the TEMPLATE graphic package is assumed.

  1. Crossover Analysis of CHANG'E-1 Laser Altimeter Data

    Science.gov (United States)

    Hu, W.; Yue, Z.; Di, K.

    2011-08-01

    This paper presents a preliminary result of crossover analysis and adjustment of Chang'E-1(CE-1) Laser Altimeter (LAM) data of the Moon for global and regional mapping applications. During the operation of Chang'E-1 from November 28, 2007 to December 4, 2008, the laser altimeter acquired 1400 orbital profiles with about 9.12 million altimetric points. In our experiment, we derived more than 1.38 million crossovers from 1395 ground tracks covering the entire lunar surface after eliminating outliers of orbits and altimetric points. A method of least-squares crossover adjustment with a series of basis functions of time (trigonometric functions and polynomials) is developed to reconcile the LAM data by minimizing the crossover residuals globally. The normal equations are very large but sparse; therefore they are stored and solved using sparse matrix technique. In a test area (0°N~60°N, 50°W~0°W), the crossover residuals are reduced from 62.1m to 32.8m, and the quality of the DEM generated from the adjusted LAM data is improved accordingly. We will optimize the method for the global adjustment to generate a high precision consistent global DEM, which can be used as absolute control for lunar mapping with orbital images.

  2. Building with green and glass. Innovations in the horticulture for living and working; Bouwen met groen en glas. Innovaties uit de glastuinbouw voor wonen en werken

    Energy Technology Data Exchange (ETDEWEB)

    Bergs, J.; Ter Haar, H.; Huisman, S.; Kristinsson, J.; Kruseman, I.; Oei, P.

    2007-07-01

    New technologies and insights from greenhouses, space technology and psychology are used for innovative applications in the building sector. Use is made of daylight, solar heat and vegetation. Architects can thus realize a clean, healthy and comfortable indoor climate in houses, school buildings, offices, health care centers, and also reduce the consumption of energy for cooling and heating. In particular attention is paid to the use of glass. [Dutch] Glastuinbouw, ruimtevaart en psychologie. Drie boeiende vakgebieden die op het eerste gezicht weinig met elkaar te maken hebben. Bouwen met groen en glas bewijst het tegendeel door gebruik te maken van nieuwe technieken en inzichten uit deze vakgebieden. Het concept maakt optimaal gebruik van daglicht, zonnewarmte en de weldaad van groen. Het toont de vele mogelijkheden die architecten met groen en glas kunnen aanboren. Waarom zou een architect dat doen? Omdat Bouwen met groen en glas de kern raakt van een uiterst actueel en tevens tijdloos thema: een schoon, gezond en prettig binnenklimaat in woningen, scholen, kantoren en zorginstellingen, gecombineerd met een substantieel lager energieverbruik voor koelen en verwarmen. Nieuwe technieken uit de glastuinbouw bieden nieuwe oplossingen. Bijvoorbeeld, in de zomer warmte oogsten en opslaan om die in de winter weer aan te boren. Veel glas stimuleert ook de toepassing van groen. Planten zijn meer dan versiering. Ze reinigen de lucht, zorgen voor bevochtiging en bieden mensen aangename omstandigheden om in te leren en te werken. Bouwen met groen en glas pleit dan ook voor gebouwen met een eigen ecosysteem, met planten als integraal onderdeel van het gebouw en de technische installaties.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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...

  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. 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.

  12. 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...

  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. 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 ...

  15. 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.

  16. Seasonal, interannual, and mesoscale variability of the Black Sea upper layer circulation derived from altimeter data

    Science.gov (United States)

    Korotaev, Gennady; Oguz, T.; Nikiforov, A.; Koblinsky, C.

    2003-04-01

    TOPEX/Poseidon and ERS altimeter data comprising the period from May 1992 to May 1999 are assimilated into a shallow water model for providing a dynamically consistent interpretation of the sea surface height variations and estimation of the temporal and spatial characteristics of the upper layer circulation in the Black Sea. These 7-year-long observations offer a new capability for interpretation of major transient and quasi-permanent features of the upper layer circulation. The instantaneous flow fields involve a complex, eddy-dominated system with different types of structural organizations in which the eddies and the gyres of the interior cyclonic cell interact continuously among themselves and with meanders, and filaments of the Rim Current. The circulation possesses a distinct seasonal cycle whose major characteristic features repeat every year with some year-to-year variability. An organized two-gyre winter circulation system disintegrates gradually into a series of interconnecting eddies in the summer and autumn months, which are also characterized by more pronounced and complex mesoscale activity in the peripheral flow system. Our analyses suggest a revised schematic circulation picture of the major quasi-permanent and recurrent elements of the Black Sea.

  17. 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.

  18. 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.

  19. 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.

  20. The Slope Imaging Multi-polarization Photon-counting Lidar: an Advanced Technology Airborne Laser Altimeter

    Science.gov (United States)

    Dabney, P.; Harding, D. J.; Huss, T.; Valett, S.; Yu, A. W.; Zheng, Y.

    2009-12-01

    The Slope Imaging Multi-polarization Photon-counting Lidar (SIMPL) is an airborne laser altimeter developed through the NASA Earth Science Technology Office Instrument Incubator Program with a focus on cryopshere remote sensing. The SIMPL instrument incorporates a variety of advanced technologies in order to demonstrate measurement approaches of potential benefit for improved airborne laser swath mapping and spaceflight laser altimeter missions. SIMPL incorporates beam splitting, single-photon ranging and polarimetry technologies at green and near-infrared wavelengths in order to achieve simultaneous sampling of surface elevation, slope, roughness and scattering properties, the latter used to differentiate surface types. The transmitter is a 1 nsec pulse width, 11 kHz, 1064 nm microchip laser, frequency doubled to 532 nm and split into four plane-polarized beams using birefringent calcite crystal in order to maintain co-alignment of the two colors. The 16 channel receiver splits the received energy for each beam into the two colors and each color is split into energy parallel and perpendicular to the transmit polarization plane thereby proving a measure of backscatter depolarization. The depolarization ratio is sensitive to the proportions of specular reflection and surface and volume scattering, and is a function of wavelength. The ratio can differentiate, for example, water, young translucent ice, older granular ice and snow. The solar background count rate is controlled by spatial filtering using a pinhole array and by spectral filtering using temperature-controlled narrow bandwidth filters. The receiver is fiber coupled to 16 Single Photon Counting Modules (SPCMs). To avoid range biases due to the long dead time of these detectors the probability of detection per laser fire on each channel is controlled to be below 30%, using mechanical irises and flight altitude. Event timers with 0.1 nsec resolution in combination the narrow transmit pulse yields single

  1. Development of Software for a Lidar-Altimeter Processor

    Science.gov (United States)

    Rosenberg, Jacob S.; Trujillo, Carlos

    2005-01-01

    A report describes the development of software for a digital processor that operates in conjunction with a finite-impulse-response (FIR) chip in a spaceborne lidar altimeter. Processing is started by a laser-fire interrupt signal that is repeated at intervals of 25 ms. For the purpose of discriminating between returns from the ground and returns from such things as trees, buildings, and clouds, the software is required to scan digitized lidar-return data in reverse of the acquisition sequence in order to distinguish the last return pulse from within a commanded ground-return range window. The digitized waveform information within this range window is filtered through 6 matched filters, in the hardware electronics, in order to maximize the probability of finding echoes from sloped or rough terrain and minimize the probability of selecting cloud returns. From the data falling past the end of the range window, there is obtained a noise baseline that is used to calculate a threshold value for each filter. The data from each filter is analyzed by a complex weighting scheme and the filter with the greatest weight is selected. A region around the peak of the ground return pulse associated with the selected filter is placed in telemetry, as well as information on its location, height, and other characteristics. The software requires many uplinked parameters as input. Included in the report is a discussion of major software-development problems posed by the design of the FIR chip and the need for the software to complete its process within 20 ms to fit within the overall 25-ms cycle.

  2. 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.

  3. Modal recovery of sea-level variability in the South China Sea using merged altimeter data

    Science.gov (United States)

    Jiang, Haoyu; Chen, Ge

    2015-09-01

    Using 20 years (1993-2012) of merged data recorded by contemporary multi-altimeter missions, a variety of sea-level variability modes are recovered in the South China Sea employing three-dimensional harmonic extraction. In terms of the long-term variation, the South China Sea is estimated to have a rising sea-level linear trend of 5.39 mm/a over these 20 years. Among the modes extracted, the seven most statistically significant periodic or quasi-periodic modes are identified as principal modes. The geographical distributions of the magnitudes and phases of the modes are displayed. In terms of intraannual and annual regimes, two principal modes with strict semiannual and annual periods are found, with the annual variability having the largest amplitudes among the seven modes. For interannual and decadal regimes, five principal modes at approximately 18, 21, 23, 28, and 112 months are found with the most mode-active region being to the east of Vietnam. For the phase distributions, a series of amphidromes are observed as twins, termed "amphidrome twins", comprising rotating dipole systems. The stability of periodic modes is investigated employing joint spatiotemporal analysis of latitude/longitude sections. Results show that all periodic modes are robust, revealing the richness and complexity of sea-level modes in the South China Sea.

  4. 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.

  5. 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)

  6. 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.

  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

    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...... laser altimeters have relatively low errors but are spatially limited to the ground tracks, while DEMs have larger errors but provide spatially continuous surfaces. The principle of our method is to fit the DEM surface to the altimeter point clouds in time and space to minimize the DEM errors and use...... 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) and...

  8. 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.

  9. Aboveground forest biomass estimation using ICESat GLAS in Yunnan, China%基于ICESat GLAS的云南省森林地上生物量反演

    Institute of Scientific and Technical Information of China (English)

    黄克标; 庞勇; 舒清态; 付甜

    2013-01-01

    结合机载、星载激光雷达对GLAS(地球科学激光测高系统)光斑范围内的森林地上生物量进行估测,并利用MODIS植被产品以及MERIS土地覆盖产品进行了云南省森林地上生物量的连续制图.机载LiDAR扫描的260个训练样本用于构建星载GLAS的森林地上生物量估测模型,模型的决定系数(R2)为0.52,均方根误差(RMSE)为31 Mg/ha.研究结果显示,云南省总森林地上生物量为12.72亿t,平均森林地上生物量为94 Mg/ha.估测的森林地上生物量空间分布情况与实际情况相符,森林地上生物量总量与基于森林资源清查数据的估测结果相符,表明了利用机载LiDAR与星载ICESatGLAS结合进行大区域森林地上生物量估测的可靠性.%Accurate estimates of forest aboveground biomass (AGB) could reduce uncertainties in the characterization of terrestrial carbon fluxes. Light Detection and Ranging (LiDAR) provides an accurate measure of canopy height and vertical structure and information for the estimation of aboveground biomass of vegetation. Spaceborne large footprint LiDAR (ICESat GLAS) acquires over 250 million observations over forest regions globally and has been used successfully for forest height and biomass estimation in various sites. In this paper, airborne LiDAR and ICESat GLAS data were used to estimate aboveground biomass of forest at footprint level in Yunnan, China. Vegetation products from EOS MODIS and ENVISAT MERIS were used to expand these discrete estimations from GLAS data to a wall-to-wall map. The R2 between ICESat GLAS waveform parameters and airborne LiDAR estimated forest AGB is 0.52 after training with 260 footprints. Results showed that the total forest AGB in Yunnan Province was 1272 million ton and the average was 94 Mg/ha. The amount and distribution of predicted aboveground biomass were in good agreement with the reference data. The results showed that the predict model using GLAS data could be used to estimate

  10. Le livre : réflexions/réfractions dans Glas de Derrida et Rhizome de Deleuze et Guattari

    OpenAIRE

    Campaignolle-Catel, Hélène

    2012-01-01

    Poches par leur publication, Glas (1974) et Rhizome (1976) participent du double discours philosophique et littéraire et partagent tous deux une écriture transgressive : ces textes remettent en question les conventions discursives et matérielles de l’écriture livresque (la double lecture en colonnes chez Derrida, la lecture en « plateaux » chez Deleuze et Guattari rompent avec les normes de la présentation du livre, les conventions rhétoriques du discours philosophique (son « nappé », ses mod...

  11. Estimates of M2 Tidal Energy Dissipation from TOPEX/Poseidon Altimeter Data

    Science.gov (United States)

    Egbert, Gary D.; Ray, Richard D.

    2001-01-01

    Most of the tidal energy dissipation in the ocean occurs in shallow seas, as has long been recognized. However, recent work has suggested that a significant fraction of the dissipation, perhaps 1 TW or more, occurs in the deep ocean. This paper builds further evidence for that conclusion. More than 6 years of data from the TOPEX/Poseidon satellite altimeter are used to map the tidal dissipation rate throughout the world ocean. The dissipation rate is estimated as a balance between the rate of working by tidal forces and the energy flux divergence, computed using currents derived by least squares fitting of the altimeter data and the shallow water equations. Such calculations require dynamical assumptions, in particular about the nature of dissipation. To assess sensitivity of dissipation estimates to input assumptions, a large suite of tidal inversions based on a wide range of drag parameterizations and employing both real and synthetic altimeter data are compared. These experiments and Monte Carlo error fields from a generalized inverse model are used to establish error uncertainties for the dissipation estimates. Owing to the tight constraints on tidal elevation fields provided by the altimeter, area integrals of the energy balance are remarkably insensitive to required dynamical assumptions. Tidal energy dissipation is estimated for all major shallow seas (excluding individual polar seas) and compared with previous model and data-based estimates. Dissipation in the open ocean is significantly tnhanced around major bathymetric features, in a manner consistent with simple theories the generation of baroclinic tides.

  12. Validation of the geostrophic method for estimating zonal currents at the equator from Geosat altimeter data

    Science.gov (United States)

    Picaut, Joel; Camusat, Bruno; Busalacchi, Antonio J.; Mcphaden, Michael J.

    1990-01-01

    The applicability of satellite altimeter data for estimating zonal current variability at the equator is assessed using the meriodionally differenced form of the geostrophic balance. Estimates of geostrophic zonal flow anomalies in the equatorial Pacific have been deduced from 17-day collinear altimeter data during the first year of the Geosat Exact Repeat Mission. Altimeter-derived geostrophic estimates agree well with in situ zonal current variability. Comparison of flow-frequency near-surface zonal current observed from equatorial moorings at 165 deg E, 140 deg W, and 110 deg W yield correlations of 0.83, 0.85, and 0.51, respectively, with a mean rms difference of 23 cm/sec. The inclusion of up to 11 ascending and descending Geosat tracks within the 9-deg band for every 17-day repeat effectively reduced the temporal sampling interval to 1.5 days at 165 deg E and 140 deg W. The 6.8-km along track spacing of the altimeter measurements provides sufficient resolution for the effective filtering of small-scale meridional noise, both instrumental and oceanic.

  13. 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.

  14. 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...

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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

  20. Unabated global mean sea-level rise over the satellite altimeter era

    Science.gov (United States)

    Watson, Christopher S.; White, Neil J.; Church, John A.; King, Matt A.; Burgette, Reed J.; Legresy, Benoit

    2015-06-01

    The rate of global mean sea-level (GMSL) rise has been suggested to be lower for the past decade compared with the preceding decade as a result of natural variability, with an average rate of rise since 1993 of +3.2 +/- 0.4 mm yr-1 (refs , ). However, satellite-based GMSL estimates do not include an allowance for potential instrumental drifts (bias drift). Here, we report improved bias drift estimates for individual altimeter missions from a refined estimation approach that incorporates new Global Positioning System (GPS) estimates of vertical land movement (VLM). In contrast to previous results (for example, refs , ), we identify significant non-zero systematic drifts that are satellite-specific, most notably affecting the first 6 years of the GMSL record. Applying the bias drift corrections has two implications. First, the GMSL rate (1993 to mid-2014) is systematically reduced to between +2.6 +/- 0.4 mm yr-1 and +2.9 +/- 0.4 mm yr-1, depending on the choice of VLM applied. These rates are in closer agreement with the rate derived from the sum of the observed contributions, GMSL estimated from a comprehensive network of tide gauges with GPS-based VLM applied (updated from ref. ) and reprocessed ERS-2/Envisat altimetry. Second, in contrast to the previously reported slowing in the rate during the past two decades, our corrected GMSL data set indicates an acceleration in sea-level rise (independent of the VLM used), which is of opposite sign to previous estimates and comparable to the accelerated loss of ice from Greenland and to recent projections, and larger than the twentieth-century acceleration.

  1. 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.

  2. 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...

  3. 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...

  4. 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.

  5. 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.

  6. 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 ...

  7. 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.

  8. 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...

  9. 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...

  10. 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...

  11. 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...

  12. 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...

  13. 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...

  14. 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...

  15. 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...

  16. Variability in Solomon Sea circulation derived from altimeter sea level data

    OpenAIRE

    A. Melet; Gourdeau, Lionel; J. Verron

    2010-01-01

    The Solomon Sea is a key region in the Pacific Ocean where equatorial and subtropical circulations are connected. The region exhibits the highest levels in sea level variability in the entire south tropical Pacific Ocean. Altimeter data was utilized to explore sea level and western boundary currents in this poorly understood portion of the ocean. Since the geography of the region is extremely intricate, with numerous islands and complex bathymetry, specifically reprocessed along-track data in...

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Active gust load alleviation system for flexible aircraft: Mixed feedforward/feedback approach

    DEFF Research Database (Denmark)

    Alam, Mushfiqul; Hromcik, Martin; Hanis, Tomas

    2015-01-01

    Lightweight flexible blended-wing-body (BWB) aircraft concept seems as a highly promising configuration for future high capacity airliners which suffers from reduced stiffness for disturbance loads such as gusts. A robust feedforward gust load alleviation system (GLAS) was developed to alleviate ...

  2. Mikrostrukturierte Metallschichten auf Glas

    OpenAIRE

    Meier, Martin

    2007-01-01

    Moderne Wärmeschutzverglasungen erreichen ihren niedrigen Wärmedurchgangskoeffizienten, den U-Wert, im Wesentlichen durch Low-e-Beschichtungen, also Schichten mit einem Emissionsgrad von unter 0.05 im infraroten Spektralbereich. Verantwortlich für die Low-e-Eigenschaften sind bei diesen Beschichtungen häufig eine oder zwei dünne Silberschichten. Im Schichtsystem kommen dazu etliche Schichten zur Entspiegelung, als Diffusionsblocker und zur Haftvermittlung. Sichtbare Strahlung wird durch diese...

  3. 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

  4. A High-altitude, Advanced-technology Scanning Laser Altimeter for the Elevation for the Nation Program

    Science.gov (United States)

    Harding, D. J.

    2007-12-01

    In January of this year the National Research Council's Committee on Floodplain Mapping Technologies recommended to Congress that an Elevation for the Nation program be initiated to enable modernization of the nation's floodplain maps and to support the many other nationwide programs reliant on high-accuracy elevation data. Their recommendation is to acquire a national, high-resolution, seamless, consistent, public-domain, elevation data set created using airborne laser swath mapping (ALSM). Although existing commercial ALSM assets can acquire elevation data of sufficient accuracy, achieving nationwide consistency in a cost-effective manner will be a challenge employing multiple low-flying commercial systems conducting local to regional mapping. This will be particularly true in vegetated terrain where reproducible measurements of ground topography and vegetation structure are required for change-detection purposes. An alternative approach using an advanced technology, wide-swath, high-altitude laser altimeter is described here, based on the Swath Imaging Multi-polarization Photon-counting Lidar (SIMPL) under development via funding from NASA's Instrument Incubator Program. The approach envisions a commercial, federal agency and state partnership, with the USGS providing program coordination, NASA implementing the advanced technology instrumentation, the commercial sector conducting data collection and processing and states defining map product requirements meeting their specific needs. An Instrument Synthesis and Analysis (ISAL) study conducted at Goddard Space Flight Center evaluated an instrument compliment deployed on a long-range Gulfstream G550 platform operating at 12 km altitude. The English Electric Canberra is an alternative platform also under consideration. Instrumentation includes a scanning, multi-beam laser altimeter that maps a 10 km wide swath, IMU and Star Trackers for attitude determination, JPL's Global Differential GPS implementation for

  5. Maintaining the Accuracy of a Sea Surface Height Climate Data Record from Multi-mission Altimeter Data

    Science.gov (United States)

    Ray, R. D.; Beckley, B. D.; Lemoine, F. G.; Zelensky, N. P.; Yang, X.; Mitchum, G. T.; Ricko, M.; Desai, S.; Brown, S. T.

    2014-12-01

    The determination of the rate of change of mean sea level (MSL) has undeniable societal significance. The measurement of geocentric sea level change from satellite altimetry requires an extreme stability of the altimeter measurement system since the signal being measured is at the level of a few mm/yr. Many of the obstacles previously impeding the measurement and validation of estimates of GMSL from satellite altimetry have been overcome (Fu and Haines, 2012). Nonetheless, measuring sea level rates at the precision required for climate science continues to be challenging for at least two reasons: (1) the Terrestrial Reference Frame (TRF) realizations are determined using space geodetic data over finite time spans, and must be periodically updated; (2) the dynamic nature of the Earth engenders global and regional variations in the geopotential which if not properly modeled ultimately cause errors in the computed sea level. Recent developments in Precise Orbit Determinations (POD) due to in particular to revisions to the terrestrial reference frame (i.e. updates to ITRF2008, and the expected availability of ITRF2013) and the development of improved time variable gravity (TVG) models continue to provide improvements to the accuracy and stability of the POD that directly affect mean sea level estimates. Long-term and reliable MSL estimates that rely on data from multiple altimeter missions require the highest possible orbit accuracy and consistency in the use of applied geophysical models in POD computations. The stringent GMSL accuracy requirements are particularly essential for closure of the mass budget over the relative short time period where measurements from Jason-1&2, GRACE, and Argo are coincident. In this presentation we describe the development, utility, and the accuracy maintenance of the MEaSURE's TPJAOS V3.0 sea surface height Climate Data Record (http://podaac.jpl.nasa.gov/dataset/MERGED_TP_J1_OSTM_OST_ALL). We provide an assessment of recent

  6. The Laser Vegetation Imaging Sensor: a medium-altitude, digitisation-only, airborne laser altimeter for mapping vegetation and topography

    Science.gov (United States)

    Blair, J. Bryan; Rabine, David L.; Hofton, Michelle A.

    The Laser Vegetation Imaging Sensor (LVIS) is an airborne, scanning laser altimeter, designed and developed at NASA's Goddard Space Flight Center (GSFC). LVIS operates at altitudes up to 10 km above ground, and is capable of producing a data swath up to 1000 m wide nominally with 25-m wide footprints. The entire time history of the outgoing and return pulses is digitised, allowing unambiguous determination of range and return pulse structure. Combined with aircraft position and attitude knowledge, this instrument produces topographic maps with dm accuracy and vertical height and structure measurements of vegetation. The laser transmitter is a diode-pumped Nd:YAG oscillator producing 1064 nm, 10 ns, 5 mJ pulses at repetition rates up to 500 Hz. LVIS has recently demonstrated its ability to determine topography (including sub-canopy) and vegetation height and structure on flight missions to various forested regions in the US and Central America. The LVIS system is the airborne simulator for the Vegetation Canopy Lidar (VCL) mission (a NASA Earth remote sensing satellite due for launch in year 2000), providing simulated data sets and a platform for instrument proof-of-concept studies. The topography maps and return waveforms produced by LVIS provide Earth scientists with a unique data set allowing studies of topography, hydrology, and vegetation with unmatched accuracy and coverage.

  7. The Distribution of Bigeye Tuna, Thunnus Obesus, and Three-Dimensional Thermal Structures Estimated from Satellite Altimeter

    Science.gov (United States)

    Takano, A.; Yamazaki, H.

    2006-07-01

    In order to improve the accuracy of estimation of fish distribution, one needs to know real-time oceanographic conditions where fish concentrate. In this contribution, we propose an empirical approach to estimate three-dimensional thermal structure in near real time using satellite altimeter data. Making use of a two-layer system model (Goni et al, 1996), an empirical regression model for three-dimensional thermal structure is derived combining absolute dynamic topography (ADT) by AVISO, in-situ data of temperature and salinity measured by Argo profiling floats, and monthly mean objective analysis data of temperature and salinity. We have applied the proposed technique to estimate three-dimensional thermal structure of the western part of the North Pacific subtropical gyre. We show a good agreement between the model result and observed temperature profiles taken from XBT. We also demonstrate that the location of bigeye tuna (Tunnus obesus) fishing ground appears where deep thermocline shallows. This procedure makes it possible to improve the accuracy of estimation for the distribution of bigeye tuna.

  8. 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.

  9. Determination of ocean tides from the first year of TOPEX/POSEIDON altimeter measurements

    Science.gov (United States)

    Ma, X. C.; Shum, C. K.; Eanes, R. J.; Tapley, B. D.

    1994-01-01

    An improved geocentric global ocean tide model has been determined using 1 year of TOPEX/POSEIDON altimeter measurements to provide corrections to the Cartwright and Ray (1991) model (CR91). The corrections were determined on a 3 deg x 3 deg grid using both the harmonic analysis method and the response method. The two approaches produce similar solutions. The effect on the tide solution of simultaneously adjusting radial orbit correction parameters using altimeter measurements was examined. Four semidiurnal (N(sub 2), M(sub 2), S(sub 2) and K(sub 2)), four diurnal (Q(sdub 1), O(sub 1), P(sub 1), and K(sub 1)), and three long-period (S(sub sa), M(sub m), and M(sub f)) constituents, along with the variations at the annual frequency, were included in the harmomnic analysis solution. The observed annual variations represents the first global measurement describing accurate seasonal changes of the ocean during an El Nino year. The corrections to the M(sub 2) constituent have an root mean square (RMS) of 3.6 cm and display a clear banding pattern with regional highs and lows reaching 8 cm. The improved tide model reduces the weighted altimeter crossover residual from 9.8 cm RMS, when the CR91 tide model is used, to 8.2 cm on RMS. Comparison of the improved model to pelagic tidal constants determined from 80 tide gauges gives RMS differences of 2.7 cm for M(sub 2) and 1.7 cm for K(sub 1). Comparable values when the CR91 model is used are 3.9 cm and 2.0 cm, respectively. Examination of TOPEX/POSEIDON sea level anomaly variations using the new tide model further confirms that the tide model has been improved.

  10. 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)

  11. 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......The 336 days of the geodetic phase of ERS-1 provides dense coverage, by satellite radar altimetry, of the whole of the Greenland ice sheet. These data have been used to produce a digital elevation model of the ice sheet. The errors present in the altimeter data were investigated via a comparison.......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....

  12. 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.

  13. 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.

  14. The Application of Identification Method of Ground Surfacesusing Fractal Dimension to Millimeter Wave Radar Altimeter

    Science.gov (United States)

    Araki, Kan

    Data of scattering coefficient on vertical incidence against ground surface at U-band are obtained by Millimeter Wave Radar Altimeter using FM-CW ranging. Noise suppression by wavelet shrinkage can be utilized to extract feature parameter in high spatial frequency band, in which level of fractal noise is dominated by that of white noise. We propose approximate algorithm for estimation of local fractal dimension in high spatial frequency band which is the most effective parameter for identification for classification of ground surfaces such as vegetation, town area and rice field.

  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. 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

  17. 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

    A number of geophysical phenomena in the open ocean are still unresolved by conventional 1 Hz altimetry, but could be observed through the potential improvements offered by SAR, or Delay-Doppler (DD), altimetry. The DD altimeter offers the following benefits with respect to conventional satellite...... wavelength geophysical signal related to mainly bathymetric features. The combination of upward continuation from the sea bottom and smoothing the altimeter observations resulted in the best recovery of geophysical signal for simulated 5-Hz DD observations. Simulations carried out in this investigation...

  18. 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...

  19. Efficient Swath mapping Laser Altimeter Instrument Incubator Program

    Science.gov (United States)

    Yu, A. W.; Harding, D. J.; Krainak, M.; Abshire, J. B.; Sun, X.; Cavanaugh, J. F.; Valett, S. R.; Ramos-Izquierdo, L.; Instrument Development Team Of Swath Mapping Iip

    2010-12-01

    In this paper we will discuss our progress in a three-year Instrument Incubator Program (IIP) funded by NASA Earth Science Technology Office (ESTO) on swath mapping laser altimetry system. The IIP began in 2009 and we are at the end of the second year. This paper will discuss the system approach, instrument development and enabling technologies for swath mapping laser altimetry. The IIP instrument development is to realize the mission goals and objectives of the Lidar Surface Topography (LIST) mission to simultaneous measure 5-m spatial resolution topography and vegetation vertical structure with decimeter vertical precision in an elevation-imaging swath several km wide from a 400 km altitude Earth orbit. To achieve the IIP goals, we are using a single laser to generate sixteen beams for mapping purpose. Backscatter from the surface is collected with a telescope and the spots from the swath are imaged onto a sensitive detector array. The output from each detector element is histogrammed and analyzed to determine ranges to the surface and derive echo waveforms that characterize the vertical structure of the surface. Multi-threshold signal processing technique allows for through-foliage interrogation in order to observe ground surface beneath vegetation cover and vegetation vertical structure. The approach is flexible and scalable in swath width, pixel width, laser power and telescope size. This work has considerable similarities and challenges as those faced by 3-D imaging laser radar (ladar) systems. In the 3rd year of this IIP, we plan to perform airborne demonstrations of the swath-mapping concept. We will leverage our recent experience on a micropulse lidar airplane demonstration, which was previously demonstrated on an ESTO funded IIP with a 1 µJ per beam, a 10 KHz laser, and a single-photon-threshold detector (Geiger-mode APD) based receiver. Our new lidar using micropulse photon-counting approach will demonstrate a laser with 100 µJ per beam, a 10 kHz pulse

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Glacier mass change evaluation in Lambert-Amery Area from 2002 to 2012 using ASTER stereo images and ICESat GLAS laser altimetry

    International Nuclear Information System (INIS)

    Currently, one of the major issues is to transform different remote sensing observations into a global reference for sustainable global-scale glacier change monitoring. In order to put glacier changes into a broader temporal context, it is desirable to extend the glacier observation time as far back as possible. In this paper, we present a case study of registering ASTER satellite stereo images to ICESat GLAS laser altimetry data, by matching terrain features identified from the ICESat measurements to those corresponding in the ASTER images. Features like ridges and nunatak can be extracted from ICESat data, and these features can also be measured in ASTER stereo images. A rigid body transformation (3 translations, 3 rotations) is applied for an optimal fit of these two sets of feature points. After transforming the ASTER photogrammetry measurements into the ICESat reference frame, we compute elevation change rates at each ICESat point by using a linear interpolation to obtain an estimate of surface elevation from ASTER. The surface firn/ice density model is used in converting the elevation changes to mass changes. Our study indicates that Lambert Glacier is close to being in mass balance between 2002 and 2012

  7. 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...

  8. An Ultra Wide-Band Radar Altimeter for Ice Sheet Surface Elevation and Snow Cover Over Sea Ice Measurement

    Science.gov (United States)

    Patel, A. E.; Gogineni, P. S.; Leuschen, C.; Rodriguez-Morales, F.; Panzer, B.

    2010-12-01

    The Ice sheets of Greenland and Antarctica are losing mass at a rapid rate and there has been significant decrease in sea ice volume over the last few years. CryoSat-II with optimized radar altimeter for ice-sheet and sea ice surface elevation measurements is launched. We developed ultra wide-band FM-CW radar that operates over the frequency range from 13-17 GHz for airborne measurements. The radar is designed to provide high-resolution surface-elevation data and also map near surface layers in polar firn with high precision. It is designed to generate an ultra linear transmit chirp using a fast settling PLL with a reference signal from Direct Digital Synthesizer (DDS). The pulse length of the transmit chirp is 240-us and pulse repetition frequency is 2-KHz. The peak transmit power of the system is 100-mW, radiated using horn antennas. The radar was deployed in Greenland and Antarctica in 2009-10 as a part of Operation Ice Bridge campaign to collect data in conjunction with other instruments including Airborne Topographic Mapper (ATM) and Digital Mapping System Camera (DMS). The radar also collected data under the Cryosat-II path. This paper will provide an overview of the Ku-Band radar design along with results from the 2009-2010 field campaigns. The data collected over polar firn shows near surface internal layers down to a depth of about 15-m with a resolution of 15-cm. When flying over sea ice the radar provides snow cover thickness data to a depth of about 0.5-m. Even over highly crevassed areas, such as outlet glaciers, the radar is able to detect large surface elevation changes of a few tens of meters with high resolution.

  9. Algorithm for Detection of Ground and Canopy Cover in Micropulse Photon-Counting Lidar Altimeter Data in Preparation for the ICESat-2 Mission

    Science.gov (United States)

    Herzfeld, Ute Christina; McDonald, Brian W.; Neumann, Thomas Allen; Wallin, Bruce F.; Neumann, Thomas A.; Markus, Thorsten; Brenner, Anita; Field, Christopher

    2014-01-01

    NASA's Ice, Cloud and Land Elevation Satellite-II (ICESat-2) mission is a decadal survey mission (2016 launch). The mission objectives are to measure land ice elevation, sea ice freeboard, and changes in these variables, as well as to collect measurements over vegetation to facilitate canopy height determination. Two innovative components will characterize the ICESat-2 lidar: 1) collection of elevation data by a multibeam system and 2) application of micropulse lidar (photon-counting) technology. A photon-counting altimeter yields clouds of discrete points, resulting from returns of individual photons, and hence new data analysis techniques are required for elevation determination and association of the returned points to reflectors of interest. The objective of this paper is to derive an algorithm that allows detection of ground under dense canopy and identification of ground and canopy levels in simulated ICESat-2 data, based on airborne observations with a Sigma Space micropulse lidar. The mathematical algorithm uses spatial statistical and discrete mathematical concepts, including radial basis functions, density measures, geometrical anisotropy, eigenvectors, and geostatistical classification parameters and hyperparameters. Validation shows that ground and canopy elevation, and hence canopy height, can be expected to be observable with high accuracy by ICESat-2 for all expected beam energies considered for instrument design (93.01%-99.57% correctly selected points for a beam with expected return of 0.93 mean signals per shot (msp), and 72.85%-98.68% for 0.48 msp). The algorithm derived here is generally applicable for elevation determination from photoncounting lidar altimeter data collected over forested areas, land ice, sea ice, and land surfaces, as well as for cloud detection.

  10. Estimates of forest canopy height and aboveground biomass using ICESat

    OpenAIRE

    Lefsky, Michael A; Harding, David J.; Keller, Michael; Cohen, Warren B.; Carabajal, Claudia C.; Espirito-Santo, Fernando Del Bom; Hunter, Maria O.; de Oliveira, Raimundo

    2005-01-01

    Exchange of carbon between forests and the atmosphere is a vital component of the global carbon cycle. Satellite laser altimetry has a unique capability for estimating forest canopy height, which has a direct and increasingly well understood relationship to aboveground carbon storage. While the Geoscience Laser Altimeter System (GLAS) onboard the Ice, Cloud and land Elevation Satellite (ICESat) has collected an unparalleled dataset of lidar waveforms over terrestrial targets, processing of IC...

  11. Allometric Scaling and Resource Limitations Model of Tree Heights: Part 1. Model Optimization and Testing over Continental USA

    OpenAIRE

    Nemani, Ramakrishna R.; Chunxiang Cao; Shilong Piao; Shihyan Lee; Wenge Ni-Meister; Saatchi, Sassan S; Marc Simard; Lefsky, Michael A; Hieu V. Duong; Gong Zhang; Sangram Ganguly; Xiliang Ni; Sungho Choi; Yuli Shi; Ranga B. Myneni

    2013-01-01

    A methodology to generate spatially continuous fields of tree heights with an optimized Allometric Scaling and Resource Limitations (ASRL) model is reported in this first of a multi-part series of articles. Model optimization is performed with the Geoscience Laser Altimeter System (GLAS) waveform data. This methodology is demonstrated by mapping tree heights over forested lands in the continental USA (CONUS) at 1 km spatial resolution. The study area is divided into 841 eco-climatic zones bas...

  12. SIMPL Laser Altimeter Measurements of Lake Erie Ice Cover: a Pathfinder for ICESat-2

    Science.gov (United States)

    Harding, D. J.; Dabney, P.; Valett, S. R.; Kelly, A.

    2010-12-01

    NASA’s ICESat-2 missions, scheduled for launch in 2015, will make measurements of ice sheet elevation change, sea ice thickness change and vegetation height using a micro-pulse, multi-beam laser altimeter employing single photon ranging at 532 nm (green). Lake Erie ice and snow cover data acquired in February 2009 by the Slope Imaging Multi-polarization Photon-counting Lidar (SIMPL) provides pathfinder information enabling improved understanding of this next-generation altimeter measurement approach. SIMPL is an airborne, multi-beam laser altimeter developed through the NASA Earth Science Technology Office Instrument Incubator Program with a focus on cryopshere remote sensing. SIMPL operates at 532 nm and 1064 nm using a micropulse laser, achieving a ranging precision of 8 cm per single photon, and acquires reflected energy parallel and perpendicular to the transmit pulse polarization plane. Approximately 30,000 single photon returns per second are acquired from snow and ice at the nominal flight altitude of 8,000 ft. The resulting two-color information on surface and volume scattering properties enables differentiation of open water and ice types with varying optical properties. For open water, SIMPL data documents laser pulse penetration at 532 nm in the water column, relative to the surface defined by the 1064 nm data. And increasing amount of perpendicularly polarized light with depth relative to the parallel polarization, indicating an increasing fraction of multiply scattered photons, provides a measure of water column optical depth. The observed ice cover types (skim, nias, new grey ice, new grey-white ice) represent the early stages of sea ice formation. Differences in surface roughness and transparency of the ice types are indicated by the 532 nm and 1064 nm perpendicular/parallel depolarization ratio measures of the degree of multiple scattering. The understanding of laser pulse interactions with water, ice and snow using this first-of-its-kind data set

  13. Survivability demonstration and characterization of a multi-billion shot, Q-switched, Nd:YAG laser

    Energy Technology Data Exchange (ETDEWEB)

    Dallas, J.L.; Stephen, M.A.; Afzal, R.S. [NASA, Greenbelt, MD (United States)

    1996-12-31

    As part of NASA`s suite of Earth Observing Satellites, Goddard Space Flight Center is developing a laser altimeter for measuring the polar ice sheet mass balance. The Geoscience Laser Altimeter System (GLAS) requires a diode pumped, Q-switched, Nd:YAG laser transmitter producing 150 mJ, 4 ns pulses at a 40 Hz repetition rate in a single transverse mode. The mission lifetime goal is five years (6.3 billion shots). The projected performance of the GLAS laser can be limited by a number of failure sources including optical damage to the components and degradation of the pump laser diodes. To the authors` knowledge, no data exists describing the multi-billion shot accumulative exposure effect Q-switched, 4 ns pulses have on intracavity optical components. To obtain multi-billion shot results in a reasonable time, an accelerated repetition rate (500 Hz) version of the GLAS oscillator was built with modifications for thermal management. An Accelerated GLAS Exposure Station (AGES) was developed to autonomously monitor the laser`s vital signs. Upon analysis of the stored data, the system dynamics were decoupled to identify the sources of degradation. Over 7 billion shots were accumulated during AGES` non-stop 5.5 month operation.

  14. 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.

  15. 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.

  16. Application of the Shuttle Laser Altimeter in an Accuracy Assessment of Global 1-Kilometer Digital Elevation Data

    Science.gov (United States)

    Harding, David J.; Carabajal, Claudia C.; Luthcke, Scott B.; Gesch, Dean B.

    1998-01-01

    Shuttle Laser Altimeter (SLA) data have been used to evaluate the accuracy of GTOPO30, the first comprehensive, 1 km resolution, global topographic data set. GTOPO30 was developed by the USGS Eros Data Center (EDC), in part, to address NASA's needs for a global topographic model in support of remote sensing instruments aboard the Earth Observing System AM-1 spacecraft. SLA flew as a part of the STS-72 mission in January, 1996 observing the latitude band from +/- 28.5 deg, and on STS-85 in August, 1997 extending the observations to +/- 57 deg. Combining the SLA ranging data with shuttle position and pointing knowledge yields surface elevation data of very high vertical accuracy in an Earth-centered, absolute reference frame (2.8 m rms difference for SLA-01 with respect to ocean reference surface). Use of the well-determined mean sea surface reference for calibration allows propagation of high accuracy altimetry onto the continents. 436,635 SLA-01 land elevations were compared to the GTOPO30 grid after conversion to a mean sea level vertical datum using the Earth Geoid Model 96, jointly developed by Goddard and NIMA. The comparison reveals systematic elevation biases in southern Asia, Africa, Australia, and south America on the order 10's to 100 meters in the GTOPO30 compilation on spatial scales of 100's to 1000's of kilometers. These biases are likely due to vertical datum errors in the topographic source materials used to compile GTOPO30, which primarily consist of Defense Mapping Agency (DMA) digital elevation and topographic map products. These biases imply that elevation corrections applied to land gravity measurements using these DMA source materials will be biased, leading to errors in geoid models incorporating these land gravity data.

  17. 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.

  18. 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.

  19. 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

  20. 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

  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. Nonlinear features of equatorial baroclinic Rossby waves detected in Topex altimeter observations

    Directory of Open Access Journals (Sweden)

    R. E. Glazman

    1996-01-01

    Full Text Available Using a recently proposed technique for statistical analysis of non-gridded satellite altimeter data, regime of long equatorially-trapped baroclinic Rossby waves is studied. One-dimensional spatial and spatiotemporal autocorrelation functions of sea surface height (SSH variations yield a broad spectrum of baroclinic Rossby waves and permit determination of their propagation speed. The 1-d wavenumber spectrum of zonal variations is given by a power-law k-2 on scales from about 103 km to 104 km. We demonstrate that the observed wave regime exhibits features of soliton turbulence developing in the long baroclinic Rossby waves. However, being limited to second statistical moments, the present analysis does not allow us to rule out a possibility of weak wave turbulence.

  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. 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.

  5. 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.

  6. 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.

  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. 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.

  9. Significant Dissipation of Tidal Energy in the Deep Ocean Inferred from Satellite Altimeter Data

    Science.gov (United States)

    Egbert, G. D.; Ray, R. D.

    2000-01-01

    How and where the ocean tides dissipate their energy are longstanding questions that have consequences ranging from the history of the Moon to the mixing of the oceans. Historically, the principal sink of tidal energy has been thought to be bottom friction in shallow seas. There has long been suggestive however, that tidal dissipation also occurs in the open ocean through the scattering by ocean-bottom topography of surface tides into internal waves, but estimates of the magnitude of this possible sink have varied widely. Here we use satellite altimeter data from Topex/Poseidon to map empirically the tidal energy dissipation. We show that approximately 10(exp 12) watts-that is, 1 TW, representing 25-30% of the total dissipation-occurs in the deep ocean, generally near areas of rough topography. Of the estimated 2 TW of mixing energy required to maintain the large-scale thermohaline circulation of the ocean, one-half could therefore be provided by the tides, with the other half coming from action on the surface of the ocean.

  10. 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

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. Multi-kilohertz Microlaser Altimeter(MMLA)Real-time Scan Footprint Mapping Software

    Science.gov (United States)

    Sanovia, J.

    2003-12-01

    It is expected that this near Real-time Scan Footprint Mapping Software (R-T Scan) display will alert us to any missed areas that we can re-fly to obtain more complete coverage. The value-added custom software is the Visual Basic Data conversion package. This software captures the GPS NEMA string(s) from the 2nd serial port, reads the attitude data form (the shared file of "most recent" attitude data), and performs a geometric projection of 10 (user adjustable) hypothetical laser scan angles to ground based latitude and longitude coordinates. The Lat/Long data are then converted back into the NEMA string format used by Street Atlas. The Multi-kilohertz Micro Laser Altimeter (MMLA) acquires high spatial resolution digital topographic databases and can observe geographical terrains such as hydrological runoff, measure ice sheet thickness, and the changes in lakes and reservoirs. The MMLA is ideal for making topographical (digital) maps of forest settings and cities. (NASA/GSFC 920.3) In order to maximize flight time efficiency and to avoid the potential disastrous situation of missing a target of prime importance, we have developed the MMLA R-T Scan.

  18. 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.

  19. 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.

  20. 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.

  1. 基于窗函数的林区ICESat-GLAS波形数据消噪研究%Denoising of Forest ICESat-GLAS Waveform Data Based on Window Function

    Institute of Scientific and Technical Information of China (English)

    王爱娟; 邢艳秋; 邱赛; 王蕊

    2016-01-01

    在利用对地学激光测高系统(the Ice,Cloud and land Elevation-Geoscience Laser Altimeter System)数据估测森林结构参数时,需对原始波形进行去噪处理,以提高估测精度.以吉林汪清林区为例,提出了基于窗函数的林区GLAS数据消噪方法,选取了5种窗函数对GLAS数据进行消噪并比较其消噪精度.结果表明:窗函数对林区波形数据消噪具有较好的效果,窗函数消噪法的信噪比SNR最高为40.488 679,均方根误差RMSE最低为0.000 335;GLAS数据经窗函数消噪后能够合理地预测林区冠层高度,预测冠层高度与实测冠层高度的回归精度r从0.725增至0.820;本研究所选的几种窗函数中布拉克曼窗函数的消噪效果较好.结果说明了窗函数在对IC-ESat-GLAS波形数据消噪中具有很大的应用潜力.

  2. 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.

  3. Experiences on Altimeter Calibration at Ibiza Island and Cape of Begur (Spain)

    Science.gov (United States)

    Martinez Benjamin, J. J.; Martinez Harcia, M.; Ortiz Castello, M. A.; Talaya, J.; Baron, A.; Rodriguez Velasco, G.; Martín Davila, J.; Garate, J.; Bonnefond, P.; Garcia, C.

    2006-07-01

    Three preliminary camp aigns for TOPEX /POSEIDON (T/P) wer e made in March 1999 and July 2000 and for JASON-1 in August 2002, in the NW Mediterran ean Sea at th e Begur Cape area. Dir ect abso lute altimeter calibration , and mapping of the sea surface, w ere made in these camp aigns from dir ect overflights using GPS buoys with a toroidal design performed at the I CC based in the orig inal design of the Univ ersity of Colorado at Boulder and a estimation of the TOPEX A lt- B bias w as made. A Spanish JASON-1 geoid gradien t campaign with Fench support has been made in June 2003 at the Ibiza island in the NW Mediterr anean Sea. Th e main objectiv e has b een to map w ith a new d esign ed, builded and calibrated GPS catamar an, the lo cal geoid gradien t in three ar eas around Ibiza island under the ascending (187) and descending (248) Jason-1ground tracks. The catamaran equ ipped with two GPS antennas to perform continuous sea lev el measur ements was towed by the Patro l Dev a from th e Span ish N avy. Five GPS reference stations were dep loyed on Ibiza island: one in Portinatx, two in San Anton io and two in Ibiza. The marin e geo id has been used to relate the coastal tide gauge data from Ibiza and San An tonio h arbours to off- shore altimetric data. In th e framework of the campaign, the levelling of the Ibiza and San Anton io tide gauges to the r espective GPS mark ers w as p erformed. We present synth esis of the resu lts obtained from Topex/Poseidon and th e first r esults on Jason-1 altimeter calibration using the direct measurements from GPS buoys and the derived marin e geoid. Th e Ibiza results agree relativ ely w ell with resu lts ob tained at Corsica, Harvest and Bass Strait calibration permanen t sites. Moreov er, the geod etic activities (e.g., GPS, levelling) has p ermitted to build a very accurate (few mm) local n etwork link ed to th e European one, w ith a reference frame compatible with th e satellite altimetry missions (ITRF2000). The GPS

  4. 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.

  5. Two-color, Polarimetric Laser Altimeter Measurements of Forest Canopy Structure and Composition

    Science.gov (United States)

    Dabney, P.; Yu, A. W.; Harding, D. J.; Valett, S. R.; Hicks, E.; Shuman, C. A.; Vasilyev, A. A.

    2010-12-01

    Over the past decade lidar remote sensing has proven to be a highly effective method for characterization of forest canopy structure and estimation of biomass stocks. However, traditional measurements only provide information on the vertical distribution of surfaces without ability to differentiate surface types. Also, an unresolved aspect of traditional measurements is the contribution of within-canopy multiple scattering to the lidar profiles of canopy structure. Slope Imaging Multi-polarization Photon-counting Lidar (SIMPL) data was acquired in July and August, 2010 for three sites with well-characterized forest structure in order to address these issues. SIMPL is an airborne, four-beam laser altimeter developed through the NASA Earth Science Technology Office Instrument Incubator Program. It acquires single-photon laser ranging data at 532 and 1064 nm, recording range-resolved measurements of reflected energy parallel and perpendicular to the transmit pulse polarization plane. Prior work with a non-ranging, multi-wavelength laser polarimetry demonstrated differentiation of tree species types based on depolarization differences related to surface and volume multiple scattering at the leaf scale. By adding the ranging component, SIMPL provides a means to investigate the vertical and horizontal distribution of optical scattering properties to better understand the interaction of pulsed laser energy with the foliage, stem and branch components of forest canopies. Data were acquired for the deciduous forest cover at the Smithsonian Environmental Research Center in Maryland and mixed deciduous and pine cover in the New Jersey Pine Barrens, two sites being used by the ICESat-2 project to assess micropulse, single-photon measurements of forest canopies. A third site, in the Huron National Forest in Michigan, has had diverse forest silviculture management practices applied to pine stands. The contrasts in forest stands between these sites will be used to illustrate

  6. 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.

  7. Variability in Solomon Sea circulation derived from altimeter sea level data

    Science.gov (United States)

    Melet, Angélique; Gourdeau, Lionel; Verron, Jacques

    2010-08-01

    The Solomon Sea is a key region in the Pacific Ocean where equatorial and subtropical circulations are connected. The region exhibits the highest levels in sea level variability in the entire south tropical Pacific Ocean. Altimeter data was utilized to explore sea level and western boundary currents in this poorly understood portion of the ocean. Since the geography of the region is extremely intricate, with numerous islands and complex bathymetry, specifically reprocessed along-track data in addition to standard gridded data were utilized in this study. Sea level anomalies (SLA) in the Solomon Sea principally evolve at seasonal and interannual time scales. The annual cycle is phased by Rossby waves arriving in the Solomon Strait, whereas the interannual signature corresponds to the basin-scale ENSO mode. The highest SLA variability are concentrated in the eastern Solomon Sea, particularly at the mouth of the Solomon Strait, where they are associated with a high eddy kinetic energy signal that was particularly active during the phase transition during the 1997-1998 ENSO event. Track data appear especially helpful for documenting the fine structure of surface coastal currents. The annual variability of the boundary currents that emerged from altimetry compared quite well with the variability seen at the thermocline level, as based on numerical simulations. At interannual time scales, western boundary current transport anomalies counterbalance changes in western equatorial Pacific warm water volume, confirming the phasing of South Pacific western boundary currents to ENSO. Altimetry appears to be a valuable source of information for variability in low latitude western boundary currents and their associated transport in the South Pacific.

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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

    coverage existed. The data were interpolated onto a regular grid with a spacing of similar to1 km. The accuracy of the resultant digital elevation model over the ice sheet was assessed using independent and spatially extensive measurements from an airborne laser altimeter that had an accuracy of between 10...... 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...... and 12 cm. In a comparison with the laser altimetry the digital elevation model was found to have a slope-dependent accuracy ranging from -1.04 +/-1.98 m to -0.06 +/- 14.33 m over the ice sheet for a slope range of 0.0-1.0 degrees. The mean accuracy over the whole ice sheet was -0.33 +/-6.97 m. Over...

  14. 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

  15. 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

  16. 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

  17. 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.

  18. Height variability from the MIROC IPCC model for the 20th century compared to that of the TOPEX/POSEIDON altimeter

    Science.gov (United States)

    Polito, P. S.; Sato, O. T.; Wainer, I.

    Planetary waves are key to large-scale dynamical adjustment in the global ocean as they transfer energy from the east to the west side of oceanic basins; they connect the forcing in the ocean interior with the variability at its boundaries; and they change the local heat content, thus coupling oceanic, atmospheric, and biological processes. Planetary waves, mostly of the first baroclinic mode, are observed as distinctive patterns in global time series of sea surface height anomaly (SSHA) and heat storage. The goal of this study is to compare and validate large-scale SSHA signals from coupled ocean-atmosphere general circulation Model for Interdisciplinary Research on Climate (MIROC) with TOPEX/POSEIDON satellite altimeter observations. The last decade of the models' time series is selected for comparison with the altimeter data. The wave patterns are separated from the meso- and large-scale SSHA signals by digital filters calibrated to select the same spectral bands in both model and altimeter data. The band-wise comparison allows for an assessment of the model skill to simulate the dynamical components of the observed wave field. Comparisons regarding both the seasonal cycle and the Rossby wave field differ significantly among basins. When carried within the same basin, differences can occur between equal latitudes in opposite hemispheres. Furthermore, at some latitudes the MIROC reproduces biannual, annual and semiannual planetary waves with phase speeds and average amplitudes similar to those observed by the altimeter, but with significant differences in phase.

  19. 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,...

  20. 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

  1. 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

  2. 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.

  3. A new assessment of global mean sea level from altimeters highlights a reduction of global trend from 2005 to 2008

    Directory of Open Access Journals (Sweden)

    M. Ablain

    2009-01-01

    Full Text Available A new error budget assessment of the global Mean Sea Level (MSL determined by TOPEX/Poseidon and Jason-1 altimeter satellites between January 1993 and June 2008 is presented. We discuss all potential errors affecting the calculation of the global MSL rate. We also compare altimetry-based sea level with tide gauge measurements over the altimetric period. This allows us to provide a realistic error budget of the MSL rise measured by satellite altimetry. These new calculations highlight a reduction in the rate of sea level rise since 2005, by ~2 mm/yr. This represents a 60% reduction compared to the 3.3 mm/yr sea level rise (glacial isostatic adjustment correction applied measured between 1993 and 2005. Since November 2005, MSL is accurately measured by a single satellite, Jason-1. However the error analysis performed here indicates that the recent reduction in MSL rate is real.

  4. 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.

  5. 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...

  6. 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

  7. 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....

  8. ICESat Laser Altimetry: Calibration/Validation

    Science.gov (United States)

    Schutz, B. E.

    2003-12-01

    The Geoscience Laser Altimeter System (GLAS) was launched on ICESat in January 2003 into a 600 km altitude, near polar orbit from Vandenberg, California. The GLAS instrument has been developed by NASA Goddard and it was mated to the spacecraft bus, built by Ball Aerospace, in June 2003. GLAS laser-1 was activated in orbit on February 20, 2003 and elevation profiles of the Greenland and Antarctic ice sheets, as well as land and ocean profiles, have been produced using the 1064 nm wavelength. The laser pulse has a divergence of about 0.11 mrad, which illuminates a spot on the surface with a 66 m diameter. The 170 m spot separation on the surface is determined by the ICESat orbital motion and the 40 Hz laser pulse repetition rate. Unlike wide pulse radar altimeters, accurate knowledge of the laser beam direction is required for the laser altimeter to produce accurate surface profiles. The laser pointing direction is determined with the assistance of an innovative system of CCD cameras plus calibration/validation methodologies. The combination of the laser pulse round trip time of flight and the pointing determination system provides an altitude vector. Determination of the direction of the altitude vector has an accuracy requirement of about 1.5 arcsec (or about 4.5 m on surface). In addition to the instrumentation required to produce the altitude vector, the position of a GLAS reference point with respect to the center of mass of the Earth is required. The ICESat BlackJack GPS receiver from NASA JPL has enabled determination of the radial component of the orbit to a few centimeter accuracy level. Laser-1 operated in orbit with a ground track that was controlled to within 800 m of an 8-day repeat reference track. During laser-1 operation and after the laser ceased firing on March 29, experiments were conducted to assess and improve the accuracy of off-nadir pointing, a unique capability to enhance the science return. This paper will provide an assessment of the

  9. 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

  10. Regional scale rain-forest height mapping using regression-kriging of spaceborne and airborne LiDAR data: application on French Guiana

    OpenAIRE

    Fayad, I.; Baghdadi, N.; Bailly, J.S.; Barbier, N.; Gond, V.; Hérault, B; El Hajj, M.; Fabre, F.; Perrin, J.

    2016-01-01

    LiDAR (Light Detection And Ranging) remote sensing has been shown to be a good technique for the estimation of forest parameters such as canopy heights and above ground biomass. Whilst airborne LiDAR data are in general very dense but only available over small areas due to the cost of their acquisition, spaceborne LiDAR data acquired from the Geoscience Laser Altimeter System (GLAS) have a coarser acquisition density associated with a global cover. It is therefore valuable to analyze the inte...

  11. MONITORING OF GLACIER VOLUME VARIATION FROM MULTI-SOURCE DATA OVER GELADANDONG AREA

    OpenAIRE

    Y. Zhang; Wu, H; Jin, S.; Wang, H.

    2013-01-01

    This paper presents a research on monitoring of glacier volume variation over the Geladandong area in Qinghai-Tibet plateau between 2000 and 2007 by integrating Landsat5 TM images, multi-source Digital Elevation Models (DEM) and the Geoscience Laser Altimeter System (GLAS) data from NASA Ice, Cloud, and land Elevation Satellite (ICESat). Landsat TM images acquired in 2000 and 2007 respectively are used to extract glacial area of the two dates. SRTM DEM and the national 1:50 000 DEM a...

  12. 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.

  13. 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

  14. Characterizing leaf area index (LAI) and vertical foliage profile (VFP) over the United States

    Science.gov (United States)

    Tang, H.; Ganguly, S.; Zhang, G.; Hofton, M. A.; Nelson, R. F.; Dubayah, R.

    2016-01-01

    Leaf area index (LAI) and vertical foliage profile (VFP) are among the important canopy structural variables. Recent advances in lidar remote sensing technology have demonstrated the capability of accurately mapping LAI and VFP over large areas. The primary objective of this study was to derive and validate a LAI and VFP product over the contiguous United States (CONUS) using spaceborne waveform lidar data. This product was derived at the footprint level from the Geoscience Laser Altimeter System (GLAS) using a biophysical model. We validated GLAS-derived LAI and VFP across major forest biomes using airborne waveform lidar. The comparison results showed that GLAS retrievals of total LAI were generally accurate with little bias (r2 = 0.67, bias = -0.13, RMSE = 0.75). The derivations of GLAS retrievals of VFP within layers were not as accurate overall (r2 = 0.36, bias = -0.04, RMSE = 0.26), and these varied as a function of height, increasing from understory to overstory - 0 to 5 m layer: r2 = 0.04, bias = 0.09, RMSE = 0.31; 10 to 15 m layer: r2 = 0.53, bias = -0.08, RMSE = 0.22; and 15 to 20 m layer: r2 = 0.66, bias = -0.05, RMSE = 0.20. Significant relationships were also found between GLAS LAI products and different environmental factors, in particular elevation and annual precipitation. In summary, our results provide a unique insight into vertical canopy structure distribution across North American ecosystems. This data set is a first step towards a baseline of canopy structure needed for evaluating climate and land use induced forest changes at the continental scale in the future, and should help deepen our understanding of the role of vertical canopy structure in terrestrial ecosystem processes across varying scales.

  15. Characterizing Leaf Area Index (LAI and Vertical Foliage Profile (VFP over the United States

    Directory of Open Access Journals (Sweden)

    H. Tang

    2015-08-01

    Full Text Available Leaf area index (LAI and vertical foliage profile (VFP are among the important canopy structural variables. Recent advances in lidar remote sensing technology have demonstrated the capability of accurately mapping LAI and VFP over large areas. The primary objective of this study was to derive and validate a LAI and VFP product over the contiguous United States using spaceborne waveform lidar data. This product was derived at the footprint level from the Geoscience Laser Altimeter System (GLAS using a biophysical model. We validated GLAS derived LAI and VFP across major forest biomes using airborne waveform lidar. The comparison results showed that GLAS retrievals of total LAI were generally accurate with little bias (r2 = 0.67, bias = −0.13, RMSE = 0.75. The derivations of GLAS retrievals of VFP within layers was not as accurate overall (r2 = 0.36, bias = −0.04, RMSE = 0.26, and these varied as a function of height, increasing from understory to overstory −0 to 5 m layer: r2 = 0.04, bias = 0.09, RMSE = 0.31; 10 to 15 m layer: r2 = 0.53, bias = −0.08, RMSE = 0.22; and 15 to 20 m layer: r2 = 0.66, bias =−0.05, RMSE = 0.20. Significant relationships were also found between GLAS LAI products and different environmental factors, in particular elevation and annual precipitation. In summary, our results provide a unique insight into vertical canopy structure distribution across North American ecosystems. This data set is a first step towards a baseline of canopy structure needed for evaluating climate and land use induced forest changes at continental scale in the future and should help deepen our understanding of the role of vertical canopy structure on terrestrial ecosystem processes across varying scales.

  16. 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.

  17. A Sensor Fusion Method for Tracking Vertical Velocity and Height Based on Inertial and Barometric Altimeter Measurements

    Directory of Open Access Journals (Sweden)

    Angelo Maria Sabatini

    2014-07-01

    Full Text Available A sensor fusion method was developed for vertical channel stabilization by fusing inertial measurements from an Inertial Measurement Unit (IMU and pressure altitude measurements from a barometric altimeter integrated in the same device (baro-IMU. An Extended Kalman Filter (EKF estimated the quaternion from the sensor frame to the navigation frame; the sensed specific force was rotated into the navigation frame and compensated for gravity, yielding the vertical linear acceleration; finally, a complementary filter driven by the vertical linear acceleration and the measured pressure altitude produced estimates of height and vertical velocity. A method was also developed to condition the measured pressure altitude using a whitening filter, which helped to remove the short-term correlation due to environment-dependent pressure changes from raw pressure altitude. The sensor fusion method was implemented to work on-line using data from a wireless baro-IMU and tested for the capability of tracking low-frequency small-amplitude vertical human-like motions that can be critical for stand-alone inertial sensor measurements. Validation tests were performed in different experimental conditions, namely no motion, free-fall motion, forced circular motion and squatting. Accurate on-line tracking of height and vertical velocity was achieved, giving confidence to the use of the sensor fusion method for tracking typical vertical human motions: velocity Root Mean Square Error (RMSE was in the range 0.04–0.24 m/s; height RMSE was in the range 5–68 cm, with statistically significant performance gains when the whitening filter was used by the sensor fusion method to track relatively high-frequency vertical motions.

  18. 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.

  19. 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...

  20. 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...

  1. Regional Scale Rain-Forest Height Mapping Using Regression-Kriging of Spaceborne and Airborne LiDAR Data: Application on French Guiana

    Directory of Open Access Journals (Sweden)

    Ibrahim Fayad

    2016-03-01

    Full Text Available LiDAR data has been successfully used to estimate forest parameters such as canopy heights and biomass. Major limitation of LiDAR systems (airborne and spaceborne arises from their limited spatial coverage. In this study, we present a technique for canopy height mapping using airborne and spaceborne LiDAR data (from the Geoscience Laser Altimeter System (GLAS. First, canopy heights extracted from both airborne and spaceborne LiDAR were extrapolated from available environmental data. The estimated canopy height maps using Random Forest (RF regression from airborne or GLAS calibration datasets showed similar precisions (~6 m. To improve the precision of canopy height estimates, regression-kriging was used. Results indicated an improvement in terms of root mean square error (RMSE, from 6.5 to 4.2 m using the GLAS dataset, and from 5.8 to 1.8 m using the airborne LiDAR dataset. Finally, in order to investigate the impact of the spatial sampling of future LiDAR missions on canopy height estimates precision, six subsets were derived from the initial airborne LiDAR dataset. Results indicated that using the regression-kriging approach a precision of 1.8 m on the canopy height map was achievable with a flight line spacing of 5 km. This precision decreased to 4.8 m for flight line spacing of 50 km.

  2. Sealing of ceramic SOFC-components with glass seals; Fuegen von keramischen Komponenten der Hochtemperatur-Brennstoffzellen mittels Glas- und Glaskeramikloten

    Energy Technology Data Exchange (ETDEWEB)

    Schillig, Cora

    2012-07-10

    The solid oxide fuel cell (SOFC) converts chemical energy of a fuel directly into electrical energy. However, for the implementation of SOFC-technology in competition to conventional power plants costs have to be reduced. The use of an alternative tubular cell design without closed end would allow reducing costs during cell manufacturing. However, this change in design makes a gastight sealing inside the generator near the gas inlet necessary. Different ceramic materials with varying coefficients of thermal expansion have to be sealed gastight and electrical insulating at temperatures between 850 C and 1000 C to prevent the gases from mixing and an electrical shortcut between the cells. This work comprises analysis of commercially available glass and glass-ceramic systems manufactured by Schott Electronic Packaging, Areva T and D and Ferro Corporation. Additionally new developed sealing glass and glass-ceramic systems were investigated and all systems were characterized fundamentally for the use as sealing material in SOFC generators. Therefore different test assemblies and series were conducted. Essential characteristics of a suitable sealing system are a thermal expansion coefficient between 9,5 and 12 . 10{sup -6}K{sup -1}, a viscosity in the range between 10{sup 4} to 10{sup 6} dPa{sup *}s and a wetting angle smaller than 90 during the sealing process. Also unwanted chemical side reactions between the sealing partners must be prevented, because a change in the phase composition or the creation of new phases in the sealing material could endanger the stability of the seal. Heat cycles, particularly those during generator operation, cause deterioration of the sealing material and subsequent reduction in its ability to prevent mixing of the gases. Sealant leaks can drastically impact efficiency of the generator. In order to ensure optimum operation low leak rates around 2,3 . 10{sup -4} mbar l/sec/cm{sup 2} must be maintained. Especially glass and glass

  3. 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.

  4. Single-photon, Dual-color, Polarimetric Laser Altimeter Measurements of Lake Ice Freeboard, Roughness and Scattering Properties

    Science.gov (United States)

    Harding, D. J.; Dabney, P.; Valett, S.; Shuman, C. A.

    2009-12-01

    The Slope Imaging Multi-polarization Photon-counting Lidar (SIMPL) is an advanced technology airborne laser altimeter developed with a focus on remote sensing of ice sheets and sea ice including their melt state. Its development was sponsored by the NASA Earth Science Technology Office Instrument Incubator Program. SIMPL utilizes micropulse single photon laser ranging at 532 nm (green) and 1064 nm (near-infrared) wavelengths in a four-beam push-broom configuration. Currently, the instrument is capable of flight altitudes of up to 5000 m; this spreads the 4 profiles over a cross-track distance of 30 m providing an estimate of both along-track and cross-track slope magnitudes and directions. For both wavelengths on each beam, depolarization is measured as the ratio of received energy perpendicular and parallel to the plane-polarized transmit beams. The precision of the single photon ranges is 8 cm and a range observation is acquired every 5 to 10 cm at airborne flight speeds. This performance enables measurement of ice freeboard and surface roughness at 5 m length scales based on the height dispersion of single photon ranges aggregated along the profiles. The depolarization ratio is a function of the scattering properties of the target, specifically the proportions of specular reflection and surface and volume scattering. The relationship between surface roughness and depolarization at green and near-IR wavelengths will be illustrated using data acquired during flights over Lake Erie ice cover in February 2009, an analog for sea ice. Observed in simultaneously acquired digital video frames, the ice cover appears to be a heterogeneous amalgamation of ice types, thicknesses and ages. The lake ice is covered by snow in places and contains numerous open water leads to enable ice freeboard detection relative to the water surface. The depolarization ratio differentiates open water, young clear ice, older granular ice and snow cover. The variability of the ratio along a

  5. 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.

  6. 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。

  7. 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.

  8. Global trends and vulnerabilities of mangrove forests

    Science.gov (United States)

    Simard, M.; Fatoyinbo, T. E.; Rivera-Monroy, V. H.; Castaneda, E.; Roy Chowdhury, R.

    2015-12-01

    Mangrove forests are located along Earth's coastlines and estuaries within tropical and subtropical latitudes. They provide numerous services functioning as an extraordinary carbon sequestration system and serving as habitat and nursery for fish, crustaceans and amphibians. To coastal populations, they provide livelihood, food, lumber and act as an effective protection against tsunamis, storm surges and hurricanes. Their vulnerability to sea level rise is strongly related to their extraordinary ability to accumulate soils, which is in part related to their productivity and therefore canopy structure. As a first step to understand their vulnerability, we seek to understand mangrove dependencies on environmental and geophysical setting. To achieve this, we mapped mangrove canopy height and above ground biomass (AGB) at the Global scale. To identify mangrove forests, existing maps derived from a collection of Landsat data around the 2000 era were used. Using the Shuttle Radar Topography Mission elevation data collected in February of 2000, we produced a Global map of mangrove canopy height. The estimated heights were validated with the ICESat/Geoscience Altimeter System (GLAS) and in situ field data. Most importantly, field data were also used to derive relationships between canopy height and AGB. While the geographical coverage of in situ data is limited, ICESat/GLAS data provided extensive geographical coverage with independent estimates of maximum canopy height. These estimates were used to calibrate SRTM-estimates of height at the Global scale. We found the difference between GLAS RH100 and SRTM resulted from several sources of uncertainty that are difficult to isolate. These include natural variations of canopy structure with time, system errors from GLAS and SRTM, geo-location errors and discrepancies in spatial resolution. The Global canopy height map was trnasormed into AGB using the field-derived allometry. Depending on the scale of analysis and geographical

  9. 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.

  10. 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.

  11. 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.

  12. Allometric Scaling and Resource Limitations Model of Tree Heights: Part 2. Site Based Testing of the Model

    Directory of Open Access Journals (Sweden)

    Ramakrishna R. Nemani

    2013-01-01

    Full Text Available The ultimate goal of this multi-article series is to develop a methodology to generate continuous fields of tree height and biomass. The first paper demonstrated the need for Allometric Scaling and Resource Limitation (ASRL model optimization and its ability to generate spatially continuous fields of tree heights over the continental USA at coarse (1 km spatial resolution. The objective of this second paper is to provide an assessment of that approach at site scale, specifically at 12 FLUXNET sites where more accurate data are available. Estimates of tree heights from the Geoscience Laser Altimeter System (GLAS waveform data are used for model optimization. Amongst the five possible GLAS metrics that are representative of tree heights, the best metric is selected based on how closely the metric resembles field-measured and Laser Vegetation Imaging Sensor tree heights. In the optimization process, three parameters of the ASRL model (area of single leaf, α; exponent for canopy radius, η; and root absorption efficiency, γ are simultaneously adjusted to minimize the difference between model predictions and observations at the study sites (distances to valid GLAS footprints ≤ 10 km. Performance of the optimized ASRL model was evaluated through comparisons to the best GLAS metric of tree height using a two-fold cross validation approach (R2 = 0.85; RMSE = 1.81 m and a bootstrapping approach (R2 = 0.66; RMSE = 2.60 m. The optimized model satisfactorily performed at the site scale, thus corroborating results presented in part one of this series. Future investigations will focus on generalizing these results and extending the model formulation using similar allometric concepts for the estimation of woody biomass.

  13. Allometric Scaling and Resource Limitations Model of Tree Heights: Part 3. Model Optimization and Testing over Continental China

    Directory of Open Access Journals (Sweden)

    Xiliang Ni

    2014-04-01

    Full Text Available The ultimate goal of our multi-article series is to demonstrate the Allometric Scaling and Resource Limitation (ASRL approach for mapping tree heights and biomass. This third article tests the feasibility of the optimized ASRL model over China at both site (14 meteorological stations and continental scales. Tree heights from the Geoscience Laser Altimeter System (GLAS waveform data are used for the model optimizations. Three selected ASRL parameters (area of single leaf, α; exponent for canopy radius, η; and root absorption efficiency, γ are iteratively adjusted to minimize differences between the references and predicted tree heights. Key climatic variables (e.g., temperature, precipitation, and solar radiation are needed for the model simulations. We also exploit the independent GLAS and in situ tree heights to examine the model performance. The predicted tree heights at the site scale are evaluated against the GLAS tree heights using a two-fold cross validation (RMSE = 1.72 m; R2 = 0.97 and bootstrapping (RMSE = 4.39 m; R2 = 0.81. The modeled tree heights at the continental scale (1 km spatial resolution are compared to both GLAS (RMSE = 6.63 m; R2 = 0.63 and in situ (RMSE = 6.70 m; R2 = 0.52 measurements. Further, inter-comparisons against the existing satellite-based forest height maps have resulted in a moderate degree of agreements. Our results show that the optimized ASRL model is capable of satisfactorily retrieving tree heights over continental China at both scales. Subsequent studies will focus on the estimation of woody biomass after alleviating the discussed limitations.

  14. Using satellite and airborne LiDAR to model woodpecker habitat occupancy at the landscape scale.

    Directory of Open Access Journals (Sweden)

    Lee A Vierling

    Full Text Available Incorporating vertical vegetation structure into models of animal distributions can improve understanding of the patterns and processes governing habitat selection. LiDAR can provide such structural information, but these data are typically collected via aircraft and thus are limited in spatial extent. Our objective was to explore the utility of satellite-based LiDAR data from the Geoscience Laser Altimeter System (GLAS relative to airborne-based LiDAR to model the north Idaho breeding distribution of a forest-dependent ecosystem engineer, the Red-naped sapsucker (Sphyrapicus nuchalis. GLAS data occurred within ca. 64 m diameter ellipses spaced a minimum of 172 m apart, and all occupancy analyses were confined to this grain scale. Using a hierarchical approach, we modeled Red-naped sapsucker occupancy as a function of LiDAR metrics derived from both platforms. Occupancy models based on satellite data were weak, possibly because the data within the GLAS ellipse did not fully represent habitat characteristics important for this species. The most important structural variables influencing Red-naped Sapsucker breeding site selection based on airborne LiDAR data included foliage height diversity, the distance between major strata in the canopy vertical profile, and the vegetation density near the ground. These characteristics are consistent with the diversity of foraging activities exhibited by this species. To our knowledge, this study represents the first to examine the utility of satellite-based LiDAR to model animal distributions. The large area of each GLAS ellipse and the non-contiguous nature of GLAS data may pose significant challenges for wildlife distribution modeling; nevertheless these data can provide useful information on ecosystem vertical structure, particularly in areas of gentle terrain. Additional work is thus warranted to utilize LiDAR datasets collected from both airborne and past and future satellite platforms (e.g. GLAS, and

  15. 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.

  16. 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 .

  17. 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.

  18. Combination of Radar Altimeter and In-Situ Measurements to deduce Rating-Curves at Some Virtual Stations in the Ungauged Amazon and Orinoco Basins

    Science.gov (United States)

    Leon, J.; Seyler, F.; Calmant, S.; Bonnet, M.

    2008-12-01

    In the last two years, virtual gauged stations have been proposed to increase the density of hydrological network in ungauged or very poorly monitored basins (Leon, 2006). In spatial hydrology a virtual station is considered as any crossing of water body surface (i.e., large rivers) by radar altimeter satellite tracks. The main objective of this study is to review the usefulness of altimetric data presenting rating curves obtained for some virtual stations at the poorly gauged basins of Caqueta (Colombian Amazon basin), Uaupes and Upper Negro (Brazilian Amazon basin) and Upper Orinoco. Rating curve parameters at virtual stations are estimated by fitting with a power law distribution the temporal series of water surface altitude derived from ENVISAT satellite measurements and modeled discharges. The applied methodology (Leon et al. 2006a) 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 river bed slope can be computed. These quantities combined with rating-curve parameters are highly valuable for understanding hydrological behaviour, especially at ungauged basins where hydrodynamical studies had always been prevented by the lack of in-situ data. The results obtained allow to propose a new insight into the hydrological behaviour of the region shared by Colombia, Brazil and Venezuela, which is very difficult to access, and then very poorly known.

  19. 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.

  20. 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.

  1. 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.

  2. Instruments and Methods: A Low-Cost Glacier-Mapping System

    DEFF Research Database (Denmark)

    Christensen, Erik Lintz; Reeh, Niels; Forsberg, René; Jørgensen, Jørn Hjelm; Skou, Niels; Woelders, Kim

    2000-01-01

    An old portable 60 MHz radar has been upgraded with a new digital data-processing and acquisition system and a new antenna construction enabling a fast and low-cost installation on a Twin Otter aircraft. Augmented by a laser altimeter and kinematic global positioning system (GPS), the system has...... the capability of acquiring accurate data on location and ice-surface elevation, and adequate-quality data on ice thickness. The system has been applied successfully in mapping the Nioghalvfjerdsfjorden glacier, northeast Greenland, in spite of the difficult conditions with melting water on the...... glacier surface. The measurements from the floating part of the glacier have been evaluated by comparison of radar data with laser-altimeter and in situ measurements....

  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

  4. 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.

  5. Spaceborne Laser Altimetry On Icesat

    Science.gov (United States)

    Schutz, B.

    The Geoscience Laser Altimeter System (GLAS) is planned for launch on ICESat in 2002, into a 600 km altitude, near polar orbit from Vandenberg, California. The sys- tem is designed to operate up to five years in orbit. GLAS is under development by NASA Goddard and it will be delivered to the spacecraft contractor, Ball Aerospace, for mating and testing with the spacecraft bus. The GLAS instrument will transmit both near infrared (1064 nm) and green (532 nm) pulses using a diode-pumped, Q- switched Nd:YAG laser. The 1064 wavelength will be used for surface altimetry, in- cluding dense clouds, and the 532 wavelength will be used for atmospheric backscat- ter measurements. The altitude measurement will produce elevation time series of the Greenland and Antarctic ice sheets, which will enable determination of present-day elevation change and mass balance. Other applications of the altimetry channel in- clude precise measurements of land topography and vegetation canopy heights, sea ice roughness and thickness, and ocean surface elevations. The atmospheric channel will provide information on the vertical distribution of clouds and aerosols. The laser pulse energy at 1064 nm is about 75 mJ with a width of about 5 ns and the pulse has a divergence of about 0.11 mrad, which illuminates a spot on the surface with a 66 m diameter. Three lasers are available (two are required for lifetime requirements and the third provides redundancy). The pulse echo is captured with a 1 m telescope mounted on the rigid GLAS optical bench. A Si analog detector receives the return pulse and an A/D converter digitizes the pulse with a 1 GHz sampling rate. Two detectors and two digitizers are available for redundancy. Unlike wide pulse radar altimeters, accurate knowledge of the laser beam direction is required for the laser altimeter. The pointing will be determined with the assistance of an innovative system of CCD cameras that will measure the direction of each laser pulse with respect to

  6. 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.

    HD model and its parameterization schemes can be found on http://www.dhimike.com. 7 Fig. 2: Time series of daily in-situ river discharge recorded at Dowlaiswaram dam along Godavari river during 2007 – 2012. Fig. 3: Time series of daily in...: The Godavari River System flows towards Bay of Bengal. (a) Catchment area (in grey color) and the rivulets/ tributaries (in blue color) connecting the river, black lines are the political borders of the states, (b) Detailed study area with the locations...

  7. Precise GPS/GNSS Positioning Solution for Airborne Data Acquisition Systems

    Institute of Scientific and Technical Information of China (English)

    B. G. Gerlach; D. Gondy

    2003-01-01

    The precise positioning of aircrafts during flights belongs to the great challenges with respect to the development of airborne data acquisition systems. Satellite positioning systems like GPS offers a unique capability for precise positioning but requires in depth knowledge of GPS in airborne applications, e.g.GPS for high dynamic application, integration of GPS with other sensors, dynamic behaviour of aircrafts or antenna location. For its positioning reference system of Flight Inspection systems Aerodata AG has developed a robust GPS carrier phase ambiguity solution P-DGPS, Precise Differential GPS combined with complementary sensors like INS, barometers, radio altimeters or laser altimeters as well as laser trackers. Using recorded data during the flight the algorithm offers also the capability to calculate more accurate positions in post-processing. The presented sensor fusion algorithm using GPS without differential corrections (SGPS, standalone GPS) offers a precise height reference solution for approach calibration based only on aircraft-based sensors. SGPS data are combined in post-processing with inertial, pressure, radio and laser altimeter data. Flight trials with a Bombardier "Global Express" at Braunschweig Airport on May 2002 shows the achieved accuracies of the height reference solution calculated by SGPS in comparison to P-DGPS. The SGPS solution for precise height calculation of special mission aircrafts provides accuracies in the order of 5 m and at the runway's threshold in the order of 30 cm.

  8. Instruments and Methods: A Low-Cost Glacier-Mapping System

    DEFF Research Database (Denmark)

    Christensen, Erik Lintz; Reeh, Niels; Forsberg, René;

    2000-01-01

    the capability of acquiring accurate data on location and ice-surface elevation, and adequate-quality data on ice thickness. The system has been applied successfully in mapping the Nioghalvfjerdsfjorden glacier, northeast Greenland, in spite of the difficult conditions with melting water on the...... glacier surface. The measurements from the floating part of the glacier have been evaluated by comparison of radar data with laser-altimeter and in situ measurements....

  9. ASPIS, A Flexible Multispectral System for Airborne Remote Sensing Environmental Applications

    Directory of Open Access Journals (Sweden)

    Riccardo Valentini

    2008-05-01

    Full Text Available 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.

  10. 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

  11. Allometric Scaling and Resource Limitations Model of Tree Heights: Part 1. Model Optimization and Testing over Continental USA

    Directory of Open Access Journals (Sweden)

    Ramakrishna R. Nemani

    2013-01-01

    Full Text Available A methodology to generate spatially continuous fields of tree heights with an optimized Allometric Scaling and Resource Limitations (ASRL model is reported in this first of a multi-part series of articles. Model optimization is performed with the Geoscience Laser Altimeter System (GLAS waveform data. This methodology is demonstrated by mapping tree heights over forested lands in the continental USA (CONUS at 1 km spatial resolution. The study area is divided into 841 eco-climatic zones based on three forest types, annual total precipitation classes (30 mm intervals and annual average temperature classes (2 °C intervals. Three model parameters (area of single leaf, α, exponent for canopy radius, η, and root absorption efficiency, γ were selected for optimization, that is, to minimize the difference between actual and potential tree heights in each of the eco-climatic zones over the CONUS. Tree heights predicted by the optimized model were evaluated against GLAS heights using a two-fold cross validation approach (R2 = 0.59; RMSE = 3.31 m. Comparison at the pixel level between GLAS heights (mean = 30.6 m; standard deviation = 10.7 and model predictions (mean = 30.8 m; std. = 8.4 were also performed. Further, the model predictions were compared to existing satellite-based forest height maps. The optimized ASRL model satisfactorily reproduced the pattern of tree heights over the CONUS. Subsequent articles in this series will document further improvements with the ultimate goal of mapping tree heights and forest biomass globally.

  12. Combination of optical and LiDAR satellite imagery with forest inventory data to improve wall-to-wall assessment of growing stock in Italy

    Science.gov (United States)

    Maselli, F.; Chiesi, M.; Mura, M.; Marchetti, M.; Corona, P.; Chirici, G.

    2014-02-01

    The acquisition of information about growing stock is a fundamental step in the framework of forest management planning and scenario modeling, besides being essential for assessing the amount of carbon stored within forest ecosystems. Gallaun et al. (2010) produced a pan-European map of forest growing stock by the combination of ground and remotely sensed data. The first objective of the current paper is to assess the accuracy of this map versus the ground data collected during the latest Italian National Forest Inventory (INFC). Next, a new wall-to-wall estimation of growing stock is obtained by combining ground measurements of four regional forest inventories with the CORINE land cover map of Italy and the global canopy height map derived from Geoscience Laser Altimeter System (GLAS) and Moderate Resolution Imaging Spectroradiometer (MODIS) data. More particularly, the growing stock measurements of the four inventories are stratified by ecosystem type and extended over all Italian forest areas through the application of locally weighted regressions to the GLAS/MODIS canopy height map. When compared to the INFC measurements, the new map shows higher accuracy than that by Gallaun et al., particularly for high growing stock values. The coefficient of determination between estimated and INFC growing stocks is improved by about 0.5, whilst the mean square error is reduced from 90 to 48 m3 ha-1.

  13. Improvements in Near-Terminator and Nocturnal Cloud Masks using Satellite Imager Data over the Atmospheric Radiation Measurement Sites

    Energy Technology Data Exchange (ETDEWEB)

    Trepte, Q.Z.; Minnis, P.; Heck, P.W.; Palikonda, R.

    2005-03-18

    Cloud detection using satellite measurements presents a big challenge near the terminator where the visible (VIS; 0.65 {micro}m) channel becomes less reliable and the reflected solar component of the solar infrared 3.9-{micro}m channel reaches very low signal-to-noise ratio levels. As a result, clouds are underestimated near the terminator and at night over land and ocean in previous Atmospheric Radiation Measurement (ARM) Program cloud retrievals using Geostationary Operational Environmental Satellite (GOES) imager data. Cloud detection near the terminator has always been a challenge. For example, comparisons between the CLAVR-x (Clouds from Advanced Very High Resolution Radiometer [AVHRR]) cloud coverage and Geoscience Laser Altimeter System (GLAS) measurements north of 60{sup o}N indicate significant amounts of missing clouds from AVHRR because this part of the world was near the day/night terminator viewed by AVHRR. Comparisons between MODIS cloud products and GLAS at the same regions also shows the same difficulty in the MODIS cloud retrieval (Pavolonis and Heidinger 2005). Consistent detection of clouds at all times of day is needed to provide reliable cloud and radiation products for ARM and other research efforts involving the modeling of clouds and their interaction with the radiation budget. To minimize inconsistencies between daytime and nighttime retrievals, this paper develops an improved twilight and nighttime cloud mask using GOES-9, 10, and 12 imager data over the ARM sites and the continental United States (CONUS).

  14. ICESat Elevation Validation at the White Sands Missile Range

    Science.gov (United States)

    Webb, C. E.; Urban, T. J.; Neuenschwander, A. L.; Magruder, L. A.; Schutz, B. E.

    2005-12-01

    The Geoscience Laser Altimeter System (GLAS) on-board the Ice, Cloud and land Elevation Satellite (ICESat) has been shown to produce range measurements with a precision of 2-3 centimeters, depending on the surface characteristics within the illuminated laser footprint. These measurements are combined with knowledge of the position and orientation of the GLAS instrument, obtained through precision orbit and attitude determination, to yield geodetic elevations. These results are examined at the White Sands Missile Range, in New Mexico, which serves as a principal calibration/validation site for ICESat. In addition to hosting arrays of passive retro-reflectors and active detectors that provide horizontal position and timing information for the laser footprints, this site was surveyed early in the mission with the Airborne Laser Topographic Mapper (ALTM). ICESat-derived elevations from this area are compared to those that make up this independent, high-resolution topographic data set. Examples from several laser campaigns, at various off-nadir pointing angles, are shown, and the observed differences are discussed relative to the larger context of assessing ICESat elevation accuracy.

  15. 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.

  16. 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.

  17. 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.

  18. Utilization of low-temperature heat out of Philippsburg nuclear power plant and concepts for economical district heating systems

    International Nuclear Information System (INIS)

    The project had to develop technical and economical concepts of utilization of low temperature heat and waste heat out of the Philippsburg nuclear power plant. Three general techniques turned out to be feasible and economical: - District heating for the eastern part of the town by extraction of 18 MW (thermal output) out of the low pressure part of the condensing turbine (total load of the district heating system is 37 MW), - Supply of greenhouses (total area of 20.000 m2 under glas) close to the plant by waste heat out of the condensing - turbine and generator-cooling-circuit (8 MW, 300C), - Supply of low-temperature waste heat out of the condensing circuit (4 MW, 200C) for fish-growing-basins. (orig.)

  19. 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

  20. 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。

  1. Lidar Technology at the Goddard Laser and Electro-Optics Branch

    Science.gov (United States)

    Heaps, William S.; Obenschain, Arthur F. (Technical Monitor)

    2000-01-01

    The Laser and Electro-Optics Branch at Goddard Space flight Center was established about three years ago to provide a focused center of engineering support and technology development in these disciplines with an emphasis on spaced based instruments for Earth and Space Science. The Branch has approximately 15 engineers and technicians with backgrounds in physics, optics, and electrical engineering. Members of the Branch are currently supporting a number of space based lidar efforts as well as several technology efforts aimed at enabling future missions. The largest effort within the Branch is support of the Ice, Cloud, and land Elevation Satellite (ICESAT) carrying the Geoscience Laser Altimeter System (GLAS) instrument. The ICESAT/GLAS primary science objectives are: 1) To determine the mass balance of the polar ice sheets and their contributions to global sea level change; and 2) To obtain essential data for prediction of future changes in ice volume and sea-level. The secondary science objectives are: 1) To measure cloud heights and the vertical structure of clouds and aerosols in the atmosphere; 2) To map the topography of land surfaces; and 3) To measure roughness, reflectivity, vegetation heights, snow-cover, and sea-ice surface characteristics. Our efforts have concentrated on the GLAS receiver component development, the Laser Reference Sensor for the Stellar Reference System, the GLAS fiber optics subsystems, and the prelaunch calibration facilities. We will report on our efforts in the development of the space qualified interference filter [Allan], etalon filter, photon counting detectors, etalor/laser tracking system, and instrument fiber optics, as well as specification and selection of the star tracker and development of the calibration test bed. We are also engaged in development work on lidar sounders for chemical species. We are developing new lidar technology to enable a new class of miniature lidar instruments that are compatible with small

  2. Modeling the Height of Young Forests Regenerating from Recent Disturbances in Mississippi using Landsat and ICESat data

    Science.gov (United States)

    Li, Ainong; Huang, Chengquan; Sun, Guoqing; Shi, Hua; Toney, Chris; Zhu, Zhiliang; Rollins, Matthew G.; Goward, Samuel N.; Masek, Jeffrey G.

    2011-01-01

    Many forestry and earth science applications require spatially detailed forest height data sets. Among the various remote sensing technologies, lidar offers the most potential for obtaining reliable height measurement. However, existing and planned spaceborne lidar systems do not have the capability to produce spatially contiguous, fine resolution forest height maps over large areas. This paper describes a Landsat-lidar fusion approach for modeling the height of young forests by integrating historical Landsat observations with lidar data acquired by the Geoscience Laser Altimeter System (GLAS) instrument onboard the Ice, Cloud, and land Elevation (ICESat) satellite. In this approach, "young" forests refer to forests reestablished following recent disturbances mapped using Landsat time-series stacks (LTSS) and a vegetation change tracker (VCT) algorithm. The GLAS lidar data is used to retrieve forest height at sample locations represented by the footprints of the lidar data. These samples are used to establish relationships between lidar-based forest height measurements and LTSS-VCT disturbance products. The height of "young" forest is then mapped based on the derived relationships and the LTSS-VCT disturbance products. This approach was developed and tested over the state of Mississippi. Of the various models evaluated, a regression tree model predicting forest height from age since disturbance and three cumulative indices produced by the LTSS-VCT method yielded the lowest cross validation error. The R(exp 2) and root mean square difference (RMSD) between predicted and GLAS-based height measurements were 0.91 and 1.97 m, respectively. Predictions of this model had much higher errors than indicated by cross validation analysis when evaluated using field plot data collected through the Forest Inventory and Analysis Program of USDA Forest Service. Much of these errors were due to a lack of separation between stand clearing and non-stand clearing disturbances in

  3. 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.

  4. By og Byg Resultater 005.Facaderenovering med glas

    DEFF Research Database (Denmark)

    Wittchen, Kim Bjarne

    Målinger i et forsøgsbyggeri med glasinddækkede altaner viser, at det er muligt at opnå store energibesparelser. Dette er sikret ved glasinddækkede altaner, luftsolfanger til forvarmning af ventilationsluften, udskiftning af vinduerne og opsætning af energialarmer. Samtidig har det været muligt a...

  5. GLAS/ICESat L2 Ocean Altimetry Data V033

    Data.gov (United States)

    National Aeronautics and Space Administration — GLA15 contains the ocean elevation and small-scale roughness corrected for geodetic and atmospheric affects, calculated from algorithms fine-tuned for ocean...

  6. GLAS : framework to improve assesment in educational videogames

    OpenAIRE

    Serrano Laguna, Ángel

    2012-01-01

    El proceso de evaluación es fundamental para valorar los resultados de cualquier proceso educativo. Además es un elemento crucial en la aceptación de un nuevo proceso educativo por parte de los profesores. Esta evaluación se hace aún más complicada cuando se ha de realizar sobre juegos educativos. Learning Analytics es una nueva disciplina que aboga por colectar la información derivada de la interacción de los estudiantes con cualquier material educativo on-line, para por un la...

  7. Jamstec/deep tow camera system (on the manned submersible "SHINKAI 2000 vehicle")

    OpenAIRE

    Otsuka, K.

    1990-01-01

    The JAMSTEC/Deep Tow Camera System conducts pre-site-surveys for the manned submersible "SHINKAI 2000". The vehicle is towed by double armored coaxial cable (RG-8/U) of 4500 m length. The color composite video signal is converted to an FM signal with central frequency of 6.15 MHz because it is very difficult to compensate completely for the transmission loss of video frequency through the coaxial cable. The data from the CTD sensors and the altimeter are displayed with date and time on the mo...

  8. 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.

  9. 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.

  10. 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。

  11. 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.

  12. 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.

  13. The Uncertainty of Plot-Scale Forest Height Estimates from Complementary Spaceborne Observations in the Taiga-Tundra Ecotone

    Directory of Open Access Journals (Sweden)

    Paul M. Montesano

    2014-10-01

    Full Text Available Satellite-based estimates of vegetation structure capture broad-scale vegetation characteristics as well as differences in vegetation structure at plot-scales. Active remote sensing from laser altimetry and radar systems is regularly used to measure vegetation height and infer vegetation structural attributes, however, the current uncertainty of their spaceborne measurements is likely to mask actual plot-scale differences in vertical structures in sparse forests. In the taiga (boreal forest—tundra ecotone (TTE the accumulated effect of subtle plot-scale differences in vegetation height across broad-scales may be significant. This paper examines the uncertainty of plot-scale forest canopy height measurements in northern Siberia Larix stands by combining complementary canopy surface elevations derived from satellite photogrammetry and ground elevations derived from the Geosciences Laser Altimeter System (GLAS from the ICESat-1 satellite. With a linear model, spaceborne-derived canopy height measurements at the plot-scale predicted TTE stand height ~5 m–~10 m tall (R2 = 0.55, bootstrapped 95% confidence interval of R2 = 0.36–0.74 with an uncertainty ranging from ±0.86 m–1.37 m. A larger sample may mitigate the broad uncertainty of the model fit, however, the methodology provides a means for capturing plot-scale canopy height and its uncertainty from spaceborne data at GLAS footprints in sparse TTE forests and may serve as a basis for scaling up plot-level TTE vegetation height measurements to forest patches.

  14. Use of Orbital LIDAR in the Brazilian Cerrado Biome: Potential Applications and Data Availability

    Directory of Open Access Journals (Sweden)

    Laerte Guimarães Ferreira

    2011-10-01

    Full Text Available This paper focuses on the Ice, Cloud and land Elevation Satellite (ICESat Geoscience Laser Altimeter System (GLAS data availability over the 2 million km2 Cerrado, the Brazilian central savanna biome and one of the world’s biodiversity hotspots. Overall, about 2.5 million laser shots, distributed along the seven years of ICESat operation (2003–2009 and comprising three major seasonal domains, were acquired, from which, 206,026 and 176,035 screened footprints are coincident with the remnant vegetation and cultivated pasture areas (the dominant land-use form in the Cerrado. Although these points are well distributed over the entire Cerrado, the ICESat track data collection results in substantial data gaps. In relation to the 15,612 Cerrado watersheds (6th order Otto basin system, 8,369 and 4,415 watersheds are completely deprived of data points over their remnant vegetation and pasture covers, respectively. Light Detection and Ranging (LIDAR availability was also evaluated in relation to specific targets of interest, including both fully-protected conservation units as well as areas impacted by fire and deforestation. In spite of the very few occurrences, our assessments indicate that enough LIDAR data is available for retrieving structural and functional properties of a variety of Cerrado physiognomies, as well as to assess how these physiognomies respond to anthropogenic induced changes. In fact, the comprehensive data availability analysis conducted in this study corroborate the potential of GLAS LIDAR waveforms for the retrieval of biophysical properties at both local and regional scales, particularly concerning remnant carbon stocks and pasture conditions, key information for the conservation of the fast-changing and severely threatened Cerrado.

  15. A Multi-satellite Remote Sensing Product of Reservoir Storage, Elevation, and Surface Area in South Asia

    Science.gov (United States)

    Zhang, S.; Gao, H.; Naz, B. S.

    2014-12-01

    Reservoir storage information is essential for accurate flood monitoring and prediction. South Asia, however, is dominated by international river basins where communications among neighboring countries about reservoir storage and management are extremely limited. A suite of satellite observations were combined to create a high quality reservoir storage product in South Asia from 2000 to 2012. The approach used water surface area estimations from the Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation indices product and the area-elevation relationship to estimate reservoir storage. The surface elevation measurements were from the Geoscience Laser Altimeter System (GLAS) on board the Ice, Cloud and land Elevation Satellite (ICESat). In order to improve the accuracy of water surface area estimations for relatively small reservoirs, a novel classification algorithm was developed. This remotely sensed product contains time series of reservoir elevation, area, and storage for a total of 21 reservoirs, which represents 28% of the integrated reservoir capacity in South Asia. The remotely sensed results were validated comprehensively over five reservoirs through two steps. First, the MODIS surface water classification images were compared with Landsat high resolution (30 m) classifications. Second, the reservoir elevation and storage dataset from remote sensing was evaluated using gauge observations. . The storage estimates were highly correlated with observed values (i.e., the correlation coefficients were all larger than 0.9), with normalized root mean square error (NRMSE) ranging from 9.51% to 25.20%. Uncertainty analysis was also conducted for the remotely sensed storage estimations. For the parameterization uncertainty associated with surface area retrieval, the storage mean relative uncertainty was 3.90%. With regard to the uncertainty introduced by ICESat/GLAS elevation measurements, the storage mean absolute uncertainty was 0.67%.

  16. A high success rate full-waveform lidar echo decomposition method

    Science.gov (United States)

    Xu, Lijun; Li, Duan; Li, Xiaolu

    2016-01-01

    A full-waveform Light detection and ranging (LiDAR) echo decomposition method is proposed in this paper. In this method, the peak points are used to detect the separated echo components, while the inflection points are combined with corresponding peak points to detect the overlapping echo components. The detected echo components are then sorted according to their energies in a descending order. The sorted echo components are one by one added into the decomposition model according to their orders. For each addition, the parameters of all echo components already added into the decomposition model are iteratively renewed. After renewing, the amplitudes and full width at half maximums of the echo components are compared with pre-set thresholds to determine and remove the false echo components. Both simulation and experiment were carried out to evaluate the proposed method. In simulation, 4000 full-waveform echoes with different numbers and parameters of echo components were generated and decomposed using the proposed and three other commonly used methods. Results show that the proposed method is of the highest success rate, 91.43%. In experiment, 9549 Geoscience Laser Altimeter System (GLAS) echoes for Shennongjia forest district in south China were employed as test echoes. The test echoes were first decomposed using the four methods and the decomposition results were also compared with those provided by the National Snow and Ice Data Center. Comparison results show that the determination coefficient ({{R}2} ) of the proposed method is of the largest mean, 0.6838, and the smallest standard deviation, 0.3588, and the distribution of the number of the echo components decomposed from the GLAS echoes is the most satisfied with the situation of full-waveform echoes from the forest area, implying that the superposition of the echo components decomposed from a full-waveform echo by using the proposed method can best approximate the full-waveform echo.

  17. A Newly Adopted Helicopter Platform for Geophysical and Remote Sensing

    Science.gov (United States)

    Meyer, Uwe

    2014-05-01

    The Federal Institute for Geosciences and Natural Resources in Hannover owns a Sikorsky S-76B helicopter for geophysical and remote sensing airborne surveys. This platform has been completely refurbished and in parts newly designed to be fit for easy installations of complex geophysical instruments underneath, upon and within the helicopter. The airborne platform is equipped with a modern basic navigation equipment consisting of several GNSS antennae, state of the art inertial navigation systems, laser altimeter and video camera systems. Different other modules can be added to the helicopter as a state of the art gamma spectrometer, a laser scanner, airborne gravity meters etc. within the cabin. Moreover, external sensing systems as a photogrammetric camera, infraread camera or optional mulitspectral systems can be installed on the outer skin of the cabin. Different kinds of bird systems towed underneath the helicopter can be hooked up using standard cabling, glas fibres or wireless LAN. Available birds are equipped for frequency domain electromagnetics or gradient magnetics (IPHT Jena & Supracon, Jena). Besides, large georadar systems can be installed as well. The helicopter is able as well to carry TEM-gear or system in development. Main survey targets are groundwater systems, mineral deposits and natural hazards.

  18. Forest Vertical Parameters from Lidar and Multi-angle Imaging Spectrometer Data%利用激光雷达和多角度频谱成像仪数据估测森林垂直参数

    Institute of Scientific and Technical Information of China (English)

    孙国清; Ranson K J; 张钟军

    2006-01-01

    Vegetation spatial structure including plant height, biomass, vertical and horizontal heterogeneity, is an important factor influencing the exchanges of matter and energy between the landscape and atmosphere, and the biodiversity of ecosystems. Most remote sensing systems, although providing images of the horizontal organization of canopies, do not provide direct information on the vertical distribution of canopy elements. The lidar waveform signature from a large-footprint lidar instrument, such as the Laser Vegetation Imaging Sensor(LVIS) has been successfully used to estimate the tree height and forest above-ground biomass. But the most lidar instruments do not have the mapping capability, and provide only sample data in a region. Other remote sensing data, such as a multi-angle spectral, a hyper-spectral, a temporal spectral radiometer, or radar data, will be needed to extrapolate the GLAS sample measurements into continuous regional coverage for forest structure parameters.The ability to image the surface through various angles by the Multi-angle Imaging Spectrometer(MISR) instrument provides canopy structure information through the anisotropy of the BRDF. Combining the vertical sampling of lidar with MISR's mapping capability provides a possibility of mapping forest spatial parameters in regional, even global scales. The data from the Geoscience Laser Altimeter System(GLAS) on ICESat, and data from MISR on Terra are potential dataset for regional or global forest structure parameter mapping. The objectives of this study are to evaluate the GLAS data and to investigate the ability of MISR-like data for forest structural parameter estimation. The LVIS, AirMISR, and GLAS data were used in this study. The comparisons between GLAS tree height measurement and the average tree height from LVIS within the GLAS footprint show the high correlations. The study also shows the capability of multi-angle imaging spectrometer data to predict tree height information, which

  19. Mapping Forest Canopy Height over Continental China Using Multi-Source Remote Sensing Data

    Directory of Open Access Journals (Sweden)

    Xiliang Ni

    2015-06-01

    Full Text Available Spatially-detailed forest height data are useful to monitor local, regional and global carbon cycle. LiDAR remote sensing can measure three-dimensional forest features but generating spatially-contiguous forest height maps at a large scale (e.g., continental and global is problematic because existing LiDAR instruments are still data-limited and expensive. This paper proposes a new approach based on an artificial neural network (ANN for modeling of forest canopy heights over the China continent. Our model ingests spaceborne LiDAR metrics and multiple geospatial predictors including climatic variables (temperature and precipitation, forest type, tree cover percent and land surface reflectance. The spaceborne LiDAR instrument used in the study is the Geoscience Laser Altimeter System (GLAS, which can provide within-footprint forest canopy heights. The ANN was trained with pairs between spatially discrete LiDAR metrics and full gridded geo-predictors. This generates valid conjugations to predict heights over the China continent. The ANN modeled heights were evaluated with three different reference data. First, field measured tree heights from three experiment sites were used to validate the ANN model predictions. The observed tree heights at the site-scale agreed well with the modeled forest heights (R = 0.827, and RMSE = 4.15 m. Second, spatially discrete GLAS observations and a continuous map from the interpolation of GLAS-derived tree heights were separately used to evaluate the ANN model. We obtained R of 0.725 and RMSE of 7.86 m and R of 0.759 and RMSE of 8.85 m, respectively. Further, inter-comparisons were also performed with two existing forest height maps. Our model granted a moderate agreement with the existing satellite-based forest height maps (R = 0.738, and RMSE = 7.65 m (R2 = 0.52, and RMSE = 8.99 m. Our results showed that the ANN model developed in this paper is capable of estimating forest heights over the China continent with a

  20. A multi-sensor lidar, multi-spectral and multi-angular approach for mapping canopy height in boreal forest regions

    Science.gov (United States)

    Selkowitz, David J.; Green, Gordon; Peterson, Birgit; Wylie, Bruce

    2012-01-01

    Spatially explicit representations of vegetation canopy height over large regions are necessary for a wide variety of inventory, monitoring, and modeling activities. Although airborne lidar data has been successfully used to develop vegetation canopy height maps in many regions, for vast, sparsely populated regions such as the boreal forest biome, airborne lidar is not widely available. An alternative approach to canopy height mapping in areas where airborne lidar data is limited is to use spaceborne lidar measurements in combination with multi-angular and multi-spectral remote sensing data to produce comprehensive canopy height maps for the entire region. This study uses spaceborne lidar data from the Geosciences Laser Altimeter System (GLAS) as training data for regression tree models that incorporate multi-angular and multi-spectral data from the Multi-Angle Imaging Spectroradiometer (MISR) and the Moderate Resolution Imaging SpectroRadiometer (MODIS) to map vegetation canopy height across a 1,300,000 km2 swath of boreal forest in Interior Alaska. Results are compared to in situ height measurements as well as airborne lidar data. Although many of the GLAS-derived canopy height estimates are inaccurate, applying a series of filters incorporating both data associated with the GLAS shots as well as ancillary data such as land cover can identify the majority of height estimates with significant errors, resulting in a filtered dataset with much higher accuracy. Results from the regression tree models indicate that late winter MISR imagery acquired under snow-covered conditions is effective for mapping canopy heights ranging from 5 to 15 m, which includes the vast majority of forests in the region. It appears that neither MISR nor MODIS imagery acquired during the growing season is effective for canopy height mapping, although including summer multi-spectral MODIS data along with winter MISR imagery does appear to provide a slight increase in the accuracy of resulting

  1. CBSIT 2009: Airborne Validation of Envisat Radar Altimetry and In Situ Ice Camp Measurements Over Arctic Sea Ice

    Science.gov (United States)

    Connor, Laurence; Farrell, Sinead; McAdoo, David; Krabill, William; Laxon, Seymour; Richter-Menge, Jacqueline; Markus, Thorsten

    2010-01-01

    The past few years have seen the emergence of satellite altimetry as valuable tool for taking quantitative sea ice monitoring beyond the traditional surface extent measurements and into estimates of sea ice thickness and volume, parameters that arc fundamental to improved understanding of polar dynamics and climate modeling. Several studies have now demonstrated the use of both microwave (ERS, Envisat/RA-2) and laser (ICESat/GLAS) satellite altimeters for determining sea ice thickness. The complexity of polar environments, however, continues to make sea ice thickness determination a complicated remote sensing task and validation studies remain essential for successful monitoring of sea ice hy satellites. One such validation effort, the Arctic Aircraft Altimeter (AAA) campaign of2006. included underflights of Envisat and ICESat north of the Canadian Archipelago using NASA's P-3 aircraft. This campaign compared Envisat and ICESat sea ice elevation measurements with high-resolution airborne elevation measurements, revealing the impact of refrozen leads on radar altimetry and ice drift on laser altimetry. Continuing this research and validation effort, the Canada Basin Sea Ice Thickness (CBSIT) experiment was completed in April 2009. CBSIT was conducted by NOAA. and NASA as part of NASA's Operation Ice Bridge, a gap-filling mission intended to supplement sea and land ice monitoring until the launch of NASA's ICESat-2 mission. CBIST was flown on the NASA P-3, which was equipped with a scanning laser altimeter, a Ku-band snow radar, and un updated nadir looking photo-imaging system. The CB5IT campaign consisted of two flights: an under flight of Envisat along a 1000 km track similar to that flown in 2006, and a flight through the Nares Strait up to the Lincoln Sea that included an overflight of the Danish GreenArc Ice Camp off the coast of northern Greenland. We present an examination of data collected during this campaign, comparing airborne laser altimeter measurements

  2. 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...

  3. systems

    Directory of Open Access Journals (Sweden)

    Alexander Leonessa

    2000-01-01

    Full Text Available A nonlinear robust control-system design framework predicated on a hierarchical switching controller architecture parameterized over a set of moving nominal system equilibria is developed. Specifically, using equilibria-dependent Lyapunov functions, a hierarchical nonlinear robust control strategy is developed that robustly stabilizes a given nonlinear system over a prescribed range of system uncertainty by robustly stabilizing a collection of nonlinear controlled uncertain subsystems. The robust switching nonlinear controller architecture is designed based on a generalized (lower semicontinuous Lyapunov function obtained by minimizing a potential function over a given switching set induced by the parameterized nominal system equilibria. The proposed framework robustly stabilizes a compact positively invariant set of a given nonlinear uncertain dynamical system with structured parametric uncertainty. Finally, the efficacy of the proposed approach is demonstrated on a jet engine propulsion control problem with uncertain pressure-flow map data.

  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. 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.

  6. 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

  7. Shuttle STS-2 mission communication systems RF coverage and performance predictions. Volume 1: Ascent

    Science.gov (United States)

    Porter, J. A.; Gibson, J. S.; Kroll, Q. D.; Loh, Y. C.

    1981-10-01

    The RF communications capabilities and nominally expected performance for the ascent phase of the second orbital flight of the shuttle are provided. Predicted performance is given mainly in the form of plots of signal strength versus elapsed mission time for the STDN (downlink) and shuttle orbiter (uplink) receivers for the S-band PM and FM, and UHF systems. Performance of the NAV and landing RF systems is treated for RTLS abort, since in this case the spacecraft will loop around and return to the launch site. NAV and landing RF systems include TACAN, MSBLS, and C-band altimeter. Signal strength plots were produced by a computer program which combines the spacecraft trajectory, antenna patterns, transmit and receive performance characteristics, and system mathematical models. When available, measured spacecraft parameters were used in the predictions; otherwise, specified values were used. Specified ground station parameter values were also used. Thresholds and other criteria on the graphs are explained.

  8. Laser Systems For Use With Airborne Platforms

    Science.gov (United States)

    Jepsky, Joseph

    1984-10-01

    This paper describes a family of airborne laser systems in use for terrain profiling, surveying, mapping, altimetry, collision avoidance and shipboard landing systems using fixed and rotary wing aircraft as the platforms. The laser altimeter has also been used in systems compatible with the Army T-16 and. T-22 carrier missiles (platform). Both pulsed gallium arsenide and Nd:YAG (neodymium-doped, yttrium-aluminum-garnet) laser rangefinders have been used for these applications. All of these systems use ACCI's advanced measurement techniques that permit range accuracies of 8 cm, single shot, 1 cm averaged, to be achieved. Pulse rates up to 4 Khz are employed for airborne profiling. This high data density rate provides 1 data point every 2" along the aircraft flight line at aircraft speed of 500 knots. Scanning modes for some applications are employed. Systems have been integrated with all current inertial navigation systems (Litton, Ferranti and Honeywell), as well as a number of microwave positioning systems. Removal of aircraft motion from the laser range measurements by use of an accelerometer is described. Flight data from a number of program performed by U.S. and Canadian Federal Agencies, in addition to those of commercial surveying and mapping companies are described.

  9. 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。

  10. 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.

  11. AltiKa: a Ka-band Altimetry Payload and System for Operational Altimetry during the GMES Period

    Directory of Open Access Journals (Sweden)

    Jacques Verron

    2006-03-01

    Full Text Available This paper describes the Ka-band altimetry payload and system that has beenstudied for several years by CNES, ALCATEL SPACE and some science laboratories.Altimetry is one of the major elements of the ocean observing system to be madesustainable through the GEOSS (Global Earth Observation System of Systems and GMES(Global Monitoring of the Environment and Security programs. A short review of somemission objectives to be fulfilled in terms of mesoscale oceanography in the frame of theGEOSS and GMES programs is performed. To answer the corresponding requirements, theapproach consisting in a constellation of nadir altimeter is discussed. A coupled Ka-bandaltimeter-radiometer payload is then described; technical items are detailed to explain howthis payload shall meet the science and operational requirements, and expectedperformances are displayed. The current status of the payload development and flightperspectives are given.

  12. A psychologist's view of validating aviation systems

    Science.gov (United States)

    Stein, Earl S.; Wagner, Dan

    1994-01-01

    All systems, no matter what they are designed to do, have shortcomings that may make them less productive than was hoped during the initial development. Such shortcomings can arise at any stage of development: from conception to the end of the implementation life cycle. While systems failure and errors of a lesser magnitude can occur as a function of mechanical or software breakdown, the majority of such problems, in aviation are usually laid on the shoulders of the human operator and, to a lesser extent, on human factors. The operator bears the responsibility and blame even though, from a human factors perspective, error may have been designed into the system. Human factors is not a new concept in aviation. The name may be new, but the issues related to operators in the loop date back to the industrial revolution of the nineteenth century and certainly to the aviation build-up for World War I. During this first global confrontation, military services from all sides discovered rather quickly that poor selection and training led to drastically increased personnel losses. While hardware design became an issue later, the early efforts were primarily focused on increased care in pilot selection and on their training. This actually involved early labor-intensive simulation, using such devices as sticks and chairs mounted on rope networks which could be manually moved in response to control input. The use of selection criteria and improved training led to more viable person-machine systems. More pilots survived training and their first ten missions in the air, a rule of thumb arrived at by experience which predicted ultimate survival better than any other. This rule was to hold through World War II. At that time, personnel selection and training became very sophisticated based on previous standards. Also, many psychologists were drafted into Army Air Corps programs which were geared towards refining the human factor. However, despite the talent involved in these programs

  13. Changes in glacier extent and surface elevations in the Depuchangdake region of northwestern Tibet, China

    Science.gov (United States)

    Li, Zhiguo; Tian, Lide; Wu, Hongbo; Wang, Weicai; Zhang, Shuhong; Zhang, Jingjing; Li, Xuexin

    2016-01-01

    Remote sensing data, including those from Landsat Thematic Mapper/Enhanced Thematic Mapper Plus (TM/ETM +), the Shuttle Radar Topography Mission Digital Elevation Model (SRTM4.1 DEM), and the Geoscience Laser Altimeter System Ice, Cloud, and Land Elevation Satellite (Glas/ICESat), show that from 1991 to 2013 the glacier area in the Depuchangdake region of northwestern Tibet decreased from 409 to 393 km2, an overall loss of 16 km2, or 3.9% of the entire 1991 glacial area. The mean glacier-thinning rate was - 0.40 ± 0.16 m equivalent height of water per year (w.e./yr), equating to a glacier mass balance of - 0.16 ± 0.07 km3 w.e./yr. Total mass loss from 2003 to 2009 was - 1.13 ± 0.46 km3. Glacier retreat likely reflects increases in annual total radiation, annual positive degree days, and maximum temperature, with concurrent increases in precipitation insufficient to replenish glacial mass loss. The rate of glacier retreat in Depuchangdake is less than that for Himalayan glaciers in Indian monsoon-dominated areas, but greater than that for Karakoram glaciers in mid-latitude westerly-dominated areas. Glacier type, climate zone, and climate change all impact on the differing degrees of long-term regional glacial change rate; however, special glacier distribution forms can sometimes lead to exceptional circumstances.

  14. Concept study of a vegetation lidar on International Space Station

    Science.gov (United States)

    Kimura, T.; Imai, T.; Sakaizawa, D.; Kobayashi, T.; Murooka, J.

    2015-10-01

    IPCC Fifth Assessment Report says that there are still large uncertainties of carbon flux estimations in the interaction between ground and atmosphere. That is because of the uncertainties of "change of land use", in other words, "change of biomass" such as deforestation. Biomass estimation needs not only area of the forest but also its height information with topological features. In that sense, active sensors are highly expected for precise height measurement. Laser Altimeter or simply LIDAR is able to measure the height of dense forest, where SAR has salutation. ICESat / GLAS is firstly used to measure biomass as satellite LIDAR. However it was reported that there is uncertainty where terrain relief exists. To calibrate terrain relief using multi footprints, a Vegetation LIDAR named MOLI (Multi Observation LIDAR and Imager) was studied by JAXA. The unique points of MOLI are the dual beams with enough small and close footprints to determine terrain relief. Full wave analysis technique is also under development to distinguish canopy heights, crown depth and other forest features. Co-aligned imager will be used for determination of positions where LIDAR measured and observation of phonology. MOLI system design is about to finalize. Regarding Laser Transmitter, Bread Board Model with pressure vessel is being tested under vacuum condition. Target launch year of MOLI is around 2019.

  15. SRTM DEM Correction in Vegetated Mountain Areas through the Integration of Spaceborne LiDAR, Airborne LiDAR, and Optical Imagery

    Directory of Open Access Journals (Sweden)

    Yanjun Su

    2015-09-01

    Full Text Available The Shuttle Radar Topography Mission (SRTM digital elevation model (DEM is one of the most complete and frequently used global-scale DEM products in various applications. However, previous studies have shown that the SRTM DEM is systematically higher than the actual land surface in vegetated mountain areas. The objective of this study is to propose a procedure to calibrate the SRTM DEM over large vegetated mountain areas. Firstly, we developed methods to estimate canopy cover from aerial imagery and tree height from multi-source datasets (i.e., field observations, airborne light detection and ranging (LiDAR data, Geoscience Laser Altimeter System (GLAS data, Landsat TM imagery, climate surfaces, and topographic data. Then, the airborne LiDAR derived DEM, covering ~5% of the study area, was used to evaluate the accuracy of the SRTM DEM. Finally, a regression model of the SRTM DEM error depending on tree height, canopy cover, and terrain slope was developed to calibrate the SRTM DEM. Our results show that the proposed procedure can significantly improve the accuracy of the SRTM DEM over vegetated mountain areas. The mean difference between the SRTM DEM and the LiDAR DEM decreased from 12.15 m to −0.82 m, and the standard deviation dropped by 2 m.

  16. An Aerosol Extinction-to-Backscatter Ratio Database Derived from the NASA Micro-Pulse Lidar Network: Applications for Space-based Lidar Observations

    Science.gov (United States)

    Welton, Ellsworth J.; Campbell, James R.; Spinhime, James D.; Berkoff, Timothy A.; Holben, Brent; Tsay, Si-Chee; Bucholtz, Anthony

    2004-01-01

    Backscatter lidar signals are a function of both backscatter and extinction. Hence, these lidar observations alone cannot separate the two quantities. The aerosol extinction-to-backscatter ratio, S, is the key parameter required to accurately retrieve extinction and optical depth from backscatter lidar observations of aerosol layers. S is commonly defined as 4*pi divided by the product of the single scatter albedo and the phase function at 180-degree scattering angle. Values of S for different aerosol types are not well known, and are even more difficult to determine when aerosols become mixed. Here we present a new lidar-sunphotometer S database derived from Observations of the NASA Micro-Pulse Lidar Network (MPLNET). MPLNET is a growing worldwide network of eye-safe backscatter lidars co-located with sunphotometers in the NASA Aerosol Robotic Network (AERONET). Values of S for different aerosol species and geographic regions will be presented. A framework for constructing an S look-up table will be shown. Look-up tables of S are needed to calculate aerosol extinction and optical depth from space-based lidar observations in the absence of co-located AOD data. Applications for using the new S look-up table to reprocess aerosol products from NASA's Geoscience Laser Altimeter System (GLAS) will be discussed.

  17. Characterizing uncertainties of the national-scale forest gross aboveground biomass (AGB) loss estimate: a case study of the Democratic Republic of the Congo

    Science.gov (United States)

    Tyukavina, A.; Stehman, S.; Potapov, P.; Turubanova, S.; Baccini, A.; Goetz, S. J.; Laporte, N. T.; Houghton, R. A.; Hansen, M.

    2013-12-01

    Modern remote sensing techniques enable the mapping and monitoring of aboveground biomass (AGB) carbon stocks without relying on extensive in situ measurements. The Democratic Republic of the Congo (DRC) is among the countries where a national forest inventory (NFI) has yet to be established due to a lack of infrastructure and political instability. We demonstrate a method for producing national-scale gross AGB loss estimates and quantifying uncertainty of the estimates using remotely sensed-derived forest cover loss and biomass carbon density data. Forest cover type and loss were characterized using published Landsat-based data sets and related to LIDAR-derived biomass data from the Geoscience Laser Altimeter System (GLAS). We produced two gross AGB loss estimates for the DRC for the last decade (2000-2010): a conservative estimate accounting for classification errors in the 60-m resolution FACET forest cover change product, and a maximal estimate that also took into consideration omitted change at the 30m spatial resolution. Omitted disturbances were largely related to smallholder agriculture, the detection of which is scale-dependent. The use of LIDAR data as a substitute for NFI data to estimate AGB loss based on Landsat-derived activity data was demonstrated. Comparisons of our forest cover loss and AGB estimates with published studies raise the issue of scale in forest cover change mapping and its impact on carbon stock change estimation using remotely sensed data.

  18. 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

  19. Southwest PAVE PAWS radar system: Environmental assessment

    Science.gov (United States)

    Everett, S. J.; Edson, W. A.; Heynick, L. N.; Pierce, S. R.; Shepherd, R. A.; Wlaklet, T. H.

    1983-03-01

    This document describes the probable environmental impacts of constructing and operating a new surveillance and tracking radar that would operate between 420 and 450 MHz. Four candidate sites in the vicinity of Goodfellow Air Force Base were considered. The impact analysis found that chronic exposure of humans to the radiofrequency radiation levels outside the exclusion fence is not likely to be harmful. No hazards would be associated with fuel handling or cardiac pacemakers at ground level beyond the exclusion fence. Interference with TV reception and other home electronic systems and with UHF land mobile and amateur radios is possible, depending on the site. Handling and use of electro-explosive devices (EEDs) would be safe beyond about 1.2 miles for the basic system and about 2.4 miles for the optional, higher power system. Electromagnetic interference with radar altimeters, air navigation, and air-ground communication is not likely except at two candidate sites, where interference and EED and pacemaker hazards may exist for aircraft operating into or out of a nearby landing strip. No significant adverse biophysical impacts are expected in any location.

  20. Sea Ice Mapping using Unmanned Aerial Systems

    Science.gov (United States)

    Solbø, S.; Storvold, R.

    2011-12-01

    Mapping of sea ice extent and sea ice features is an important task in climate research. Since the arctic coastal and oceanic areas have a high probability of cloud coverage, aerial platforms are superior to satellite measurements for high-resolution optical measurements. However, routine observations of sea ice conditions present a variety of problems using conventional piloted aircrafts. Specially, the availability of suitable aircrafts for lease does not cover the demand in major parts of the arctic. With the recent advances in unmanned aerial systems (UAS), there is a high possibility of establishing routine, cost effective aerial observations of sea ice conditions in the near future. Unmanned aerial systems can carry a wide variety of sensors useful for characterizing sea-ice features. For instance, the CryoWing UAS, a system initially designed for measurements of the cryosphere, can be equipped with digital cameras, surface thermometers and laser altimeters for measuring freeboard of ice flows. In this work we will present results from recent CryoWing sea ice flights on Svalbard, Norway. The emphasis will be on data processing for stitching together images acquired with the non-stabilized camera payload, to form high-resolution mosaics covering large spatial areas. These data are being employed to map ice conditions; including ice and lead features and melt ponds. These high-resolution mosaics are also well suited for sea-ice mechanics, classification studies and for validation of satellite sea-ice products.

  1. Dynamical systems theory methods to study mixing and transport in the ocean

    International Nuclear Information System (INIS)

    We review the recently developed dynamical systems and chaos theory approach in oceanography that focuses on finding and specifying fundamental geometric structures in the ocean and their impact on large-scale transport and mixing of water masses. It is demonstrated that the methods of that theory in the framework of the Lagrangian approach work well with both kinematic and dynamic models and with real velocity fields derived from satellite altimeter measurements of anomalies of the sea height. We start with simple models of the eddy and jet flows and show how some underlying geometric structures arise and produce chaotic advection of passive particles even in time-periodic flows. Then we apply the Lagrangian methods for detecting Lagrangian fronts with favorable fishery conditions in the North Pacific Ocean and for modelling radionuclide propagation from the Fukushima–Daiichi nuclear plant. Finally, we discuss the perspectives on the Lagrangian approach in oceanography and its possible practical applications. (comment)

  2. Overview of the aerial radiological measuring system (ARMS) program

    International Nuclear Information System (INIS)

    Since 1960 EG and G, Inc. has developed and maintained for the U.S. Energy Research and Development Administration (ERDA) a state-of-the-art radiation surveillance program called the Aerial Radiological Measuring System (ARMS). Radiological surveys covering more than 300,000 square miles have been performed. In addition to the radiation detector gear, the system includes an inertial navigation system, radar altimeter, meteorological probes, air sampler, air sample analyzer, multispectral cameras, aerial mapping camera and infrared scanner. The recently improved data acquisition system, REDAR, records all inputs digitally on magnetic tape and is readily mounted in fixed-wing aircraft or helicopters. The data analysis system, REDAC, is mounted in a mobile processing laboratory which accompanies the aircraft on surveys. Radiation isopleth maps, both for gross counts and selected isotopes, can be prepared in the field. Special computer software enables the ARMS to detect changes of less than 1.0 μR/hr in exposure rates between successive surveys of a given site

  3. Analysis of different atmospheric physical parameterizations in COAWST modeling system for the Tropical Storm Nock-ten application

    DEFF Research Database (Denmark)

    Ren, Danqin; Du, Jianting; Hua, Feng;

    2016-01-01

    A coupled ocean–atmosphere–wave–sediment transport modeling system was applied to study the atmosphere and ocean dynamics during Tropical Storm Nock-ten. Different atmospheric physical parameterizations in WRF model were investigated through ten groups of numerical experiments. Results of...... atmosphere, ocean wave and current features were compared with storm observations, ERA-Interim data, NOAA sea surface temperature data, AVISO current data and HYCOM data, respectively. It was found that the storm track and intensity are sensitive to the cumulus and radiation schemes in WRF, especially around...... recommended for this study. Ocean parameters such as significant wave height, SST and current speed are more sensitive to Single-Moment 6-class microphysics scheme than to Eta microphysics scheme at the storm center. By analyzing modeled data with JASON-2 altimeter data, ERA-Interim data and HYCOM data in...

  4. Mapping and monitoring deforestation and forest degradation in Sumatra (Indonesia) using Landsat time series data sets from 1990 to 2010

    International Nuclear Information System (INIS)

    As reported by FAO (2005 State of the World’s Forests (Rome: UNFAO), 2010 Forest Resource Assessment (FRA) 2010/095 (Rome: UNFAO)), Indonesia experiences the second highest rate of deforestation among tropical countries. Hence, timely and accurate forest data are required to combat deforestation and forest degradation in support of climate change mitigation and biodiversity conservation policy initiatives. Within Indonesia, Sumatra Island stands out due to the intensive forest clearing that has resulted in the conversion of 70% of the island’s forested area through 2010. We present here a hybrid approach for quantifying the extent and change of primary forest in Sumatra in terms of primary intact and primary degraded classes using a per-pixel supervised classification mapping followed by a Geographic Information System (GIS)-based fragmentation analysis. Loss of Sumatra’s primary intact and primary degraded forests was estimated to provide suitable information for the objectives of the United Nations Framework on Climate Change (UNFCCC) Reducing Emission from Deforestation and Forest Degradation (REDD and REDD+) program. Results quantified 7.54 Mha of primary forest loss in Sumatra during the last two decades (1990–2010). An additional 2.31 Mha of primary forest was degraded. Of the 7.54 Mha cleared, 7.25 Mha was in a degraded state when cleared, and 0.28 Mha was in a primary state. The rate of primary forest cover change for both forest cover loss and forest degradation slowed over the study period, from 7.34 Mha from 1990 to 2000, to 2.51 Mha from 2000 to 2010. The Geoscience Laser Altimeter System (GLAS) data set was employed to evaluate results. GLAS-derived tree canopy height indicated a significant structural difference between primary intact and primary degraded forests (mean height 28 m ± 8.7 m and 19 m ± 8.2 m, respectively). The results demonstrate a method for quantifying primary forest cover stand-replacement disturbance and degradation that

  5. Flexible vision-based navigation system for unmanned aerial vehicles

    Science.gov (United States)

    Blasch, Erik P.

    1995-01-01

    A critical component of unmanned aerial vehicles in the navigation system which provides position and velocity feedback for autonomous control. The Georgia Tech Aerial Robotics navigational system (NavSys) consists of four DVTStinger70C Integrated Vision Units (IVUs) with CCD-based panning platforms, software, and a fiducial onboard the vehicle. The IVUs independently scan for the retro-reflective bar-code fiducial while the NavSys image processing software performs a gradient threshold followed by a image search localization of three vertical bar-code lines. Using the (x,y) image coordinate and CCD angle, the NavSys triangulates the fiducial's (x,y) position, differentiates for velocity, and relays the information to the helicopter controller, which independently determines the z direction with an onboard altimeter. System flexibility is demonstrated by recognition of different fiducial shapes, night and day time operation, and is being extended to on-board and off-board navigation of aerial and ground vehicles. The navigation design provides a real-time, inexpensive, and effective system for determining the (x,y) position of the aerial vehicle with updates generated every 51 ms (19.6 Hz) at an accuracy of approximately +/- 2.8 in.

  6. GLONASS-R: GNSS reflectometry with a Frequency Division Multiple Access-based satellite navigation system

    Science.gov (United States)

    Hobiger, T.; Haas, R.; Löfgren, J. S.

    2014-04-01

    The information from reflected Global Navigation Satellite System (GNSS) signals can become a valuable data source, from which geophysical properties can be deduced. This approach, called GNSS Reflectometry (GNSS-R), can be used to develop instruments that act like an altimeter when arrival times of direct and reflected signals are compared. Current GNSS-R systems usually entirely rely on signals from the Global Positioning Service (GPS), and field experiments could demonstrate that information from such systems can measure sea level with an accuracy of a few centimeters. However, the usage of the Russian GLONASS system has the potential to simplify the processing scheme and to allow handling of direct and reflected signals like a bistatic radar. Thus, such a system has been developed and deployed for test purposes at the Onsala Space Observatory, Sweden, that has an operational GPS-based GNSS-R system. Over a period of 2 weeks in October 2013, GPS-based GNSS-R sea level monitoring and measurements with the newly developed GLONASS-R system were carried out in parallel. In addition, data from colocated tide gauge measurements were available for comparison. It can be shown that precision and accuracy of the GLONASS-based GNSS-R system is comparable to, or even better than, conventional GPS-based GNSS-R solutions. Moreover, the simplicity of the newly developed GLONASS-R system allows to make it a cheap and valuable tool for various remote sensing applications.

  7. Abiotic Controls on Macroscale Variations of Humid Tropical Forest Height

    Directory of Open Access Journals (Sweden)

    Yan Yang

    2016-06-01

    Full Text Available Spatial variation of tropical forest tree height is a key indicator of ecological processes associated with forest growth and carbon dynamics. Here we examine the macroscale variations of tree height of humid tropical forests across three continents and quantify the climate and edaphic controls on these variations. Forest tree heights are systematically sampled across global humid tropical forests with more than 2.5 million measurements from Geoscience Laser Altimeter System (GLAS satellite observations (2004–2008. We used top canopy height (TCH of GLAS footprints to grid the statistical mean and variance and the 90 percentile height of samples at 0.5 degrees to capture the regional variability of average and large trees globally. We used the spatial regression method (spatial eigenvector mapping-SEVM to evaluate the contributions of climate, soil and topography in explaining and predicting the regional variations of forest height. Statistical models suggest that climate, soil, topography, and spatial contextual information together can explain more than 60% of the observed forest height variation, while climate and soil jointly explain 30% of the height variations. Soil basics, including physical compositions such as clay and sand contents, chemical properties such as PH values and cation-exchange capacity, as well as biological variables such as the depth of organic matter, all present independent but statistically significant relationships to forest height across three continents. We found significant relations between the precipitation and tree height with shorter trees on the average in areas of higher annual water stress, and large trees occurring in areas with low stress and higher annual precipitation but with significant differences across the continents. Our results confirm other landscape and regional studies by showing that soil fertility, topography and climate may jointly control a significant variation of forest height and

  8. GLAS/ICESat L1B Global Waveform-based Range Corrections Data V033

    Data.gov (United States)

    National Aeronautics and Space Administration — The level 1B waveform parameterization data will contain waveform-based range corrections and surface characteristics at the full 40 per second resolution. Data...

  9. GLAS/ICESat L1B Global Elevation Data (HDF5) V033

    Data.gov (United States)

    National Aeronautics and Space Administration — Data granules contain approximately 23 minutes (1/4 orbit) and include the surface elevation, surface roughness assuming no slope, surface slope assuming no...

  10. Mikrostrukturelle und mechanische Charakterisierung des Bondens von Silizium, Silizium und Silizium, Glas mit Laserstrahlung

    OpenAIRE

    Sari, Fahri

    2011-01-01

    This PhD-Thesis (dissertation) introduces the bonding of silicon and silicon with laser radiation applying an intermediate absorbing layer of platinum as well as the direct bonding of silicon and glass with laser radiation. Selective silicide bonding of silicon and silicon with laser radiation: This section introduces an Innovative selective bonding method called “silicide bonding” for bonding silicon and silicon with laser radiation. The achieved bonding results are based on the formation of...

  11. GLAS/ICESat L2 Global Antarctic and Greenland Ice Sheet Altimetry Data V033

    Data.gov (United States)

    National Aeronautics and Space Administration — GLA12 contains the ice sheet elevation and elevation distribution corrected for geodetic and atmospheric affects calculated from algorithms fine-tuned for ice sheet...

  12. GLAS/ICESat L2 Global Land Surface Altimetry Data (HDF5) V033

    Data.gov (United States)

    National Aeronautics and Space Administration — GLAH14 contains the land elevation and elevation distribution corrected for geodetic and atmospheric affects calculated from algorithms fine-tuned for over land...

  13. GLAS/ICESat L1B Global Elevation Data V033

    Data.gov (United States)

    National Aeronautics and Space Administration — Data granules contain approximately 23 minutes (1/4 orbit) and include the surface elevation, surface roughness assuming no slope, surface slope assuming no...

  14. Onderzoek naar de samenstelling van gescheiden ingezameld glas uit de glasbak

    NARCIS (Netherlands)

    Buijze A; Otte PF; LAE

    1994-01-01

    This report presents the results of sorting analyses of used glass derived from communal glass-waste containers. Analyses took place in January 1994 in the framework of activities defined in the Packaging Convention, an agreement between the Dutch Government and the packaging industry to reduce the

  15. GLAS/ICESat L2 Sea Ice Altimetry Data (HDF5) V033

    Data.gov (United States)

    National Aeronautics and Space Administration — GLAH13 contains sea ice and open ocean elevations corrected for geodetic and atmospheric affects, calculated from algorithms fine-tuned for sea ice returns....

  16. GLAS/ICESat L2 Ocean Altimetry Data (HDF5) V033

    Data.gov (United States)

    National Aeronautics and Space Administration — GLAH15 contains the ocean elevation and small-scale roughness corrected for geodetic and atmospheric affects, calculated from algorithms fine-tuned for ocean...

  17. GLAS/ICESat L2 Sea Ice Altimetry Data V033

    Data.gov (United States)

    National Aeronautics and Space Administration — GLA13 contains sea ice and open ocean elevations corrected for geodetic and atmospheric affects, calculated from algorithms fine-tuned for sea ice returns. Granules...

  18. GLAS/ICESat L2 Global Land Surface Altimetry Data V033

    Data.gov (United States)

    National Aeronautics and Space Administration — GLA14 contains the land elevation and elevation distribution corrected for geodetic and atmospheric affects calculated from algorithms fine-tuned for over land...

  19. Premixing hydrogen burners for surface refinement of glass; Vormischende Wasserstoffbrenner zur Oberflaechenbearbeitung von Glas

    Energy Technology Data Exchange (ETDEWEB)

    Goerisch, Matthias [Linde AG, Linde Gas Deutschland, Nuernberg (Germany)

    2013-02-15

    As a result, inter alia, of unceasing globalisation, European glass producers in practically all sectors - flat glass, container glass, crystal glass and special glasses - are faced with ever tougher competition from Asia. In the 2012 to 2015 period and beyond, the principal focuses in the manufacture of glass products will again be on reducing overall production costs and increasing process efficiency wherever possible, on greater productivity and on enhanced product (surface) quality. To meet these challenges in the field of surface refinement and flame polishing of glass products as efficiently as possible, Linde AG/Linde Gases Division has developed premixing Hydropox {sup registered} burner technology for hydrogen/oxygen fuels. (orig.)

  20. PerioGlasU acts on human stem cells isolated from peripheral blood

    Directory of Open Access Journals (Sweden)

    Vincenzo Sollazzo

    2010-01-01

    Conclusion : PG has a differentiation effect on mesenchymal stem cells derived from peripheral blood. The obtained results can be relevant to better understanding of the molecular mechanism of bone regeneration and as a model for comparing other materials with similar clinical effects.

  1. Der feine Griff zum Glas : Zur Anatomie einer frühneuzeitlichen Handgeste

    OpenAIRE

    Mohrmann, Ruth-E.

    2010-01-01

    Dass gerade das 16. und 17. Jahrhundert in der abendländischen Trinkkultur eine Zeit außerordentlich hohen Alkoholkonsums waren, ist hinlänglich bekannt. Die Berichte über große, oft tagelange Trinkgelage sind Legion und die „Tischzuchten“ des 15. und 16. Jahrhunderts wissen vom Zutrinken, vom Bescheid Geben, vom Weiterreichen des Bechers detaillierte Einzelheiten der Trinksitten zu berichten. Das Trinken mit einer Hand galt lange noch als verpönt, aber die Regularien waren oft re...

  2. Preparation and mass spectrometrical high temperature investigations on compounds of the quasi-ternary system Cs2O-Al2O3-SiO2

    International Nuclear Information System (INIS)

    Additions of aluminium oxide and silicen oxide to ceramic fuel for pyrocarbon-coated nuclear fuel paticles counteract a release of fission-cesium by compound formation. The vapourization tests carried out here using samples from the quasi-ternary system cesium-oxide-aluminium-oxide-silicon-oxide by means of high-temperature mass spectroscopy using a Knudsen cell served the optimization of this retention effect. The aim of the apparative changes on the knudsen cell were to shield heat radiation on the temperature measuring borehole through the tungsten wire cathode in order to be able to perform exact temperature measurements even below 1,0000C. A new method of preparation was developed to obtain defined cesium aluminium silicates whose composition was determined by Guinier and goniometer pictures as well as by microscopic investigations. According to the latter, 3 ternary compounds are present in the system investigated: CsAlSiO4, CsAlSi2O6 and CsAlSi5O12. Their lattice constants were determined from goniometric measurements; the vapour pressure equection were set up from the measured cesium vapour pressure values over each sample and the enthalpies of the vapourization reactions were found to be 84 kcal for CsAlSiO4 at 1,4000K, 100 kcal for CsAlSi2O6 at 1,5500K and 122 kcal for CsAlSi5O12 at 1,6500K. The cesium vapour pressures of the glas phases investigated of the system are above the Cs partial pressures of the solid crystalline phases of the same composition. The results of the work explain the causes of the reduction of the Cs release and show that the vapour pressure can be lowered by more than 10 orders of magnitude at reactor relevant temperatures by compound formation. (RB)

  3. Feasibility of Estimating Snow Depth in Complex Terrain Using Satellite Lidar Altimetry

    Science.gov (United States)

    Jasinski, Michael F.; Stoll, Jeremy

    2012-01-01

    Satellite retrievals of snow depth and water equivalent (SWE) are critical for monitoring watershed scale processes around the world. However, the problem is especially challenging in mountainous regions where complex heterogeneities limit the utility of low resolution satellite sensors. The Geoscience Laser Altimeter Sensor (GLAS) aboard the Ice, Cloud, and land Elevation Satellite (ICESat) collected surface elevation data along near-repeat reference transects over land areas from 2003-2009. Although intended for monitoring ice caps and sea ice, the seven year global GLAS data base has provided unprecedented opportunity to test the capability of satellite lidar technology for estimating snow depth over land. GLAS single track and low repeat frequency does not provide data sufficient for operational estimates. However, its comparatively small footprint size of -65 m and its database of seasonal repeat observations during both snow and no-snow conditions have been sufficient to evaluate the potential of spacebased lidar altimetry for estimating snow depth. Recent analysis of ICESat elevations in the Uinta Mountains in NE Utah provide encouraging results for watershed scale estimates of snow depth. Research reported here focuses on the sensitivity of several versions of an ICESat snow depth algorithm to a range of landscape types defined by vegetation cover, slope and roughness. Results are compared to available SNOTEL data.

  4. 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.

  5. Estimating Digital Terrain Model in forest areas from TanDEM-X and Stereo-photogrammetric technique by means of Random Volume over Ground model

    Science.gov (United States)

    Lee, S. K.; Fatoyinbo, T. E.; Lagomasino, D.; Osmanoglu, B.; Feliciano, E. A.

    2015-12-01

    The Digital Terrain Model (DTM) in forest areas is invaluable information for various environmental, hydrological and ecological studies, for example, watershed delineation, vegetation canopy height, water dynamic modeling, forest biomass and carbon estimations. There are few solutions to extract bare-earth Digital Elevation Model information. Airborne lidar systems are widely and successfully used for estimating bare-earth DEMs with centimeter-order accuracy and high spatial resolution. However, expensive cost of operation and small image coverage prevent the use of airborne lidar sensors for large- or global-scale. Although IceSAT/GLAS (Ice, Cloud, and Land Elevation Satellite/Geoscience Laser Altimeter System) lidar data sets have been available for global DTM estimate with relatively lower cost, the large footprint size of 70 m and the interval of 172 m are insufficient for various applications. In this study we propose to extract higher resolution bare-earth DEM over vegetated areas from the combination of interferometric complex coherence from single-pass TanDEM-X (TDX) data at HH polarization and Digital Surface Model (DSM) derived from high-resolution WorldView (WV) images by means of random volume over ground (RVoG) model. The RVoG model is a widely and successfully used model for polarimetric SAR interferometry (Pol-InSAR) forest canopy height inversion. The bare-earth DEM is obtained by complex volume decorrelation in the RVoG model with the DSM estimated by stereo-photogrammetric technique. Forest canopy height can be estimated by subtracting the estimated bare-earth model from the DSM. Finally, the DTM from airborne lidar system was used to validate the bare-earth DEM and forest canopy height estimates.

  6. 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.

  7. Laser Ranging in Solar System: Technology Developments and New Science Measurement Capabilities

    Science.gov (United States)

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

    2015-12-01

    Laser Ranging has played a major role in geodetic studies of the Earth over the past 40 years. The technique can potentially be used in between planets and spacecrafts within the solar system to advance planetary science. For example, a direct measurement of distances between planets, such as Mars and Venus would make significant improvements in understanding the dynamics of the whole solar system, including the masses of the planets and moons, asteroids and their perturbing interactions, and the gravity field of the Sun. Compared to the conventional radio frequency (RF) tracking systems, laser ranging is potentially more accurate because it is much less sensitive to the transmission media. It is also more efficient because the laser beams are much better focused onto the targets than RF beams. However, existing laser ranging systems are all Earth centric, that is, from ground stations on Earth to orbiting satellites in near Earth orbits or lunar orbit, and to the lunar retro-reflector arrays deployed by the astronauts in the early days of lunar explorations. Several long distance laser ranging experiments have been conducted with the lidar in space, including a two-way laser ranging demonstration between Earth and the Mercury Laser Altimeter (MLA) on the MESSENGER spacecraft over 24 million km, and a one way laser transmission and detection experiment over 80 million km between Earth and the Mars Orbiting Laser Altimeter (MOLA) on the MGS spacecraft in Mars orbit. A one-way laser ranging operation has been carried out continuously from 2009 to 2014 between multiple ground stations to LRO spacecraft in lunar orbit. The Lunar Laser Communication Demonstration (LLCD) on the LADEE mission has demonstrated that a two way laser ranging measurements, including both the Doppler frequency and the phase shift, can be obtained from the subcarrier or the data clocks of a high speed duplex laser communication system. Plans and concepts presently being studied suggest we may be

  8. National-scale estimation of gross forest aboveground carbon loss: a case study of the Democratic Republic of the Congo

    International Nuclear Information System (INIS)

    Recent advances in remote sensing enable the mapping and monitoring of carbon stocks without relying on extensive in situ measurements. The Democratic Republic of the Congo (DRC) is among the countries where national forest inventories (NFI) are either non-existent or out of date. Here we demonstrate a method for estimating national-scale gross forest aboveground carbon (AGC) loss and associated uncertainties using remotely sensed-derived forest cover loss and biomass carbon density data. Lidar data were used as a surrogate for NFI plot measurements to estimate carbon stocks and AGC loss based on forest type and activity data derived using time-series multispectral imagery. Specifically, DRC forest type and loss from the FACET (Forêts d’Afrique Centrale Evaluées par Télédétection) product, created using Landsat data, were related to carbon data derived from the Geoscience Laser Altimeter System (GLAS). Validation data for FACET forest area loss were created at a 30-m spatial resolution and compared to the 60-m spatial resolution FACET map. We produced two gross AGC loss estimates for the DRC for the last decade (2000–2010): a map-scale estimate (53.3 ± 9.8 Tg C yr−1) accounting for whole-pixel classification errors in the 60-m resolution FACET forest cover change product, and a sub-grid estimate (72.1 ± 12.7 Tg C yr−1) that took into account 60-m cells that experienced partial forest loss. Our sub-grid forest cover and AGC loss estimates, which included smaller-scale forest disturbances, exceed published assessments. Results raise the issue of scale in forest cover change mapping and validation, and subsequent impacts on remotely sensed carbon stock change estimation, particularly for smallholder dominated systems such as the DRC. (letter)

  9. Experience gained with the solar facade of 'Energy systems Aschauer'; Erfahrungen mit der Solarfassade der 'Energiesysteme Aschauer'

    Energy Technology Data Exchange (ETDEWEB)

    Aschauer, J. [Energie Inst., Linz (Austria)

    1998-07-01

    The solar facade is a translucent-outer wall-thermally insulated system that allows to use solar energy. In case of an optimal design equal energy balances (k-value effective= 0,0 W/m{sub 2}K) can be achieved at the facades directed to the South, East and West during the whole heating period and profits can be yielded as well. The construction consists of reusable material. Recycling paper, glass and wood profiles (perhaps metal profiles) were utilised. The core piece of the construction is a honeycomb that spares the use of shadowing devices. A simulation program has been developed for qualitative forecasts and optimised wall construction. Its results have been checked and validated with measurements at completed facades. Solar facades can also be used in light constructions, hence TTI solutions can be realised for the first time in light constructions and prove to be an ideal supplement for wooden constructions. (orig.) [German] Die Solarfassade ist ein transluzentes Aussenwand-Waermedaemmsystem, das es ermoeglicht, solare Eintraege zu nutzen. Bei optimaler Auslegung ist es damit moeglich, ueber die gesamte Heizperiode gesehen, an Sued-, Ost- und Westfassaden energetisch ausgeglichen zu bilanzieren (k-Wert{sub effektiv}=0,0 W/m{sup 2}K) und sogar Gewinne zu erzielen. Die Konstruktion besteht aus wiederverwendbaren Materialien. Es werden Recyclingpapier, Glas und Holzprofile (evtl. auch Metallprofile) verwendet. Das Kernstueck der Konstruktion, eine Wabe aus Zellulose, eruebrigt den Einsatz von Abschattungseinrichtungen. Fuer qualitative Voraussagen und Wandausbauoptimierungen wurde ein Simulationsprogramm entwickelt, dessen Ergebnisse messtechnisch bei fertiggestellten Fassaden ueberprueft und validiert wurden. Bemerkenswert erscheint, dass die Solarfassade auch im Leichtbau eingesetzt werden kann, womit erstmals TWD-Ansaetze im Leichtbau realisierbar sind und fuer den Holzbau eine ideale Ergaenzung darstellen. (orig.)

  10. How essential are Argo observations to constrain a global ocean data assimilation system?

    Science.gov (United States)

    Turpin, V.; Remy, E.; Le Traon, P. Y.

    2016-02-01

    Observing system experiments (OSEs) are carried out over a 1-year period to quantify the impact of Argo observations on the Mercator Ocean 0.25° global ocean analysis and forecasting system. The reference simulation assimilates sea surface temperature (SST), SSALTO/DUACS (Segment Sol multi-missions dALTimetrie, d'orbitographie et de localisation précise/Data unification and Altimeter combination system) altimeter data and Argo and other in situ observations from the Coriolis data center. Two other simulations are carried out where all Argo and half of the Argo data are withheld. Assimilating Argo observations has a significant impact on analyzed and forecast temperature and salinity fields at different depths. Without Argo data assimilation, large errors occur in analyzed fields as estimated from the differences when compared with in situ observations. For example, in the 0-300 m layer RMS (root mean square) differences between analyzed fields and observations reach 0.25 psu and 1.25 °C in the western boundary currents and 0.1 psu and 0.75 °C in the open ocean. The impact of the Argo data in reducing observation-model forecast differences is also significant from the surface down to a depth of 2000 m. Differences between in situ observations and forecast fields are thus reduced by 20 % in the upper layers and by up to 40 % at a depth of 2000 m when Argo data are assimilated. At depth, the most impacted regions in the global ocean are the Mediterranean outflow, the Gulf Stream region and the Labrador Sea. A significant degradation can be observed when only half of the data are assimilated. Therefore, Argo observations matter to constrain the model solution, even for an eddy-permitting model configuration. The impact of the Argo floats' data assimilation on other model variables is briefly assessed: the improvement of the fit to Argo profiles do not lead globally to unphysical corrections on the sea surface temperature and sea surface height. The main conclusion

  11. 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.

  12. 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.

  13. 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.

  14. Spatial distribution of forest aboveground biomass in China: estimation through combination of spaceborne lidar, optical imagery, and forest inventory data

    Science.gov (United States)

    Xue, B. L.; Su, Y.; Guo, Q.; Hu, T.; Alvarez, O.; Tao, S.; Fang, J.

    2015-12-01

    The global forest ecosystem, which acts as a large carbon sink, plays an important role in modeling the global carbon balance. An accurate estimation of the total forest carbon stock in the aboveground biomass (AGB) is therefore necessary to improve our understanding of carbon dynamics, especially against the background of global climate change. The forest area of China is among the top five globally. However, because of limitations in forest AGB mapping methods and the availability of ground inventory data, there is still a lack in nationwide wall-to-wall forest AGB estimation map for China. In this study, we collected over 8000 ground inventory data from the literature, and developed an AGB mapping method using a combination of these ground inventory data, Geoscience Laser Altimeter System (GLAS)/Ice, Cloud, and Land Elevation Satellite (ICESat) data, optical imagery, climate surfaces, and topographic data. An uncertainty field model was introduced into the forest AGB mapping model to minimize the influence of plot locality uncertainty. Our nationwide wall-to-wall forest AGB mapping results show that the forest AGB density in China is 120 Mg/ha on average, with a standard deviation of 61 Mg/ha. Evaluation with an independent ground inventory dataset showed that our proposed method can accurately map wall-to-wall forest AGB across a large landscape. The coefficient of determination (R2) and root-mean-square error between our predicted results and the validation dataset were 0.75 and 42.39 Mg/ha, respectively. This new method and the resulting nationwide wall-to-wall AGB map will help to improve the accuracy of carbon dynamic predictions in China.

  15. Sensitivity of L-Band SAR Backscatter to Aboveground Biomass of Global Forests

    Directory of Open Access Journals (Sweden)

    Yifan Yu

    2016-06-01

    Full Text Available Synthetic Aperture Radar (SAR backscatter measurements are sensitive to forest aboveground biomass (AGB, and the observations from space can be used for mapping AGB globally. However, the radar sensitivity saturates at higher AGB values depending on the wavelength and geometry of radar measurements, and is influenced by the structure of the forest and environmental conditions. Here, we examine the sensitivity of SAR at the L-band frequency (~25 cm wavelength to AGB in order to examine the performance of future joint National Aeronautics and Space Administration, Indian Space Research Organisation NASA-ISRO SAR mission in mapping the AGB of global forests. For SAR data, we use the Phased Array L-Band SAR (PALSAR backscatter from the Advanced Land Observing Satellite (ALOS aggregated at a 100-m spatial resolution; and for AGB data, we use more than three million AGB values derived from the Geoscience Laser Altimeter System (GLAS LiDAR height metrics at about 0.16–0.25 ha footprints across eleven different forest types globally. The results from statistical analysis show that, over all eleven forest types, saturation level of L-band radar at HV polarization on average remains ≥100 Mg·ha−1. Fresh water swamp forests have the lowest saturation with AGB at ~80 Mg·ha−1, while needleleaf forests have the highest saturation at ~250 Mg·ha−1. Swamp forests show a strong backscatter from the vegetation-surface specular reflection due to inundation that requires to be treated separately from those on terra firme. Our results demonstrate that L-Band backscatter relations to AGB can be significantly different depending on forest types and environmental effects, requiring multiple algorithms to map AGB from time series of satellite radar observations globally.

  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. The National Polar-orbiting Operational Environmental Satellite System

    Science.gov (United States)

    Hoffman, C. W.; Mango, S.; Schneider, S.; Duda, J.; Haas, J.; Bloom, H.

    2005-12-01

    Over the last decade, the tri-agency Integrated Program Office (IPO), comprised of the National Oceanic and Atmospheric Administration (NOAA), the Department of Defense (DoD), and the National Aeronautics and Space Administration (NASA), has been managing the development of the National Polar-orbiting Operational Environmental Satellite System (NPOESS). Once operational later this decade, NPOESS will replace NOAA's Polar-orbiting Operational Environmental Satellites (POES) and DoD's Defense Meteorological Satellite Program (DMSP) systems. The IPO, through its Acquisition and Operations contractor, Northrop Grumman, will launch NPOESS spacecraft into three orbital planes to provide a single, national system capable of satisfying both civil and national security requirements for space-based, remotely sensed environmental data. With the development of NPOESS, we are evolving the existing 'weather' satellites into integrated environmental observing systems by expanding our capabilities to observe, assess, and predict the total Earth system - ocean, atmosphere, land, and the space environment. NPOESS will transform today's short-term, space-based ocean research missions into a sustained, operational ocean remote sensing observation program. Ocean measurements comprise one-fourth of the 55 user-validated requirements for geophysical measurements that will be made by NPOESS sensors. In 1997, the IPO initiated a robust sensor risk reduction effort for early development of the critical sensor suites and algorithms necessary to support NPOESS. In 2001, preliminary design efforts were completed for the last of five critical imaging/sounding instruments for NPOESS. Ocean requirements have directly and substantially 'driven' the design of three NPOESS sensors: the Visible/Infrared Imager Radiometer Suite (VIIRS); the Conical-scanning Microwave Imager/Sounder (CMIS); and the Altimeter. With these instruments, NPOESS will deliver higher resolution (spatial and temporal) and more

  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. Characterizing Vegetation 3D structure Globally using Spaceborne Lidar and Radar.

    Science.gov (United States)

    Simard, M.; Pinto, N.; Riddick, S.

    2008-12-01

    We characterized global vegetation 3D structure using ICEsat-I/Geoscience Laser Altimeter (GLAS) and improved spatial resolution using ALOS/Phased Array L-band Synthetic Aperture radar (PALSAR) data over 3 sites in the United States. GLAS is a 70m footprint lidar altimeter sampling the ground along-track every 170m with a track separation near the equator around 30km. Forest type classes were initially defined according to the Global Land Cover 2000 map (GLC2000), and 5-degree latitude intervals. This strategy enabled analysis of canopy structure as a function of land cover type and latitude. This produced an irregular grid geographically consistant with GLC2000. To estimate canopy height we removed the ground component from the lidar waveform and computed the centroid of the component due to the forest canopy. Canopy height within a grid cell was produced by computing the weighted mean of the GLAS estimates contained within that cell. The weights were used to reduce the impact of slope on Lidar height estimation errors. Slope is the single most significant source of error when estimating height with a large footprint lidar. It stretches the waveform and causes false estimates of canopy height. The Shuttle Radar Topography Mission (SRTM) elevation data was used to derive slope and weights. Thus, data points located in flat areas were assigned a higher weight than points located in slopes. For each forest type, we modeled the relationship between Lidar-estimated canopy height and five environmental variables: temperature, precipitation, slope, elevation, and anthropogenic disturbance. This ecological model was constructed using the machine learning method Random Forest, due to its flexibility and non-parametric nature. Model accuracy was calculated by subsampling the Lidar data set: using 75% of the data set to produce the map previously described and the remaining 25% for validation. This approach was chosen to characterize individual forest canopy types and their

  20. Thirty-four years of Hawaii wave hindcast from downscaling of climate forecast system reanalysis

    Science.gov (United States)

    Li, Ning; Cheung, Kwok Fai; Stopa, Justin E.; Hsiao, Feng; Chen, Yi-Leng; Vega, Luis; Cross, Patrick

    2016-04-01

    The complex wave climate of Hawaii includes a mix of seasonal swells and wind waves from all directions across the Pacific. Numerical hindcasting from surface winds provides essential space-time information to complement buoy and satellite observations for studies of the marine environment. We utilize WAVEWATCH III and SWAN (Simulating WAves Nearshore) in a nested grid system to model basin-wide processes as well as high-resolution wave conditions around the Hawaiian Islands from 1979 to 2013. The wind forcing includes the Climate Forecast System Reanalysis (CFSR) for the globe and downscaled regional winds from the Weather Research and Forecasting (WRF) model. Long-term in-situ buoy measurements and remotely-sensed wind speeds and wave heights allow thorough assessment of the modeling approach and data products for practical application. The high-resolution WRF winds, which include orographic and land-surface effects, are validated with QuickSCAT observations from 2000 to 2009. The wave hindcast reproduces the spatial patterns of swell and wind wave events detected by altimeters on multiple platforms between 1991 and 2009 as well as the seasonal variations recorded at 16 offshore and nearshore buoys around the Hawaiian Islands from 1979 to 2013. The hindcast captures heightened seas in interisland channels and around prominent headlands, but tends to overestimate the heights of approaching northwest swells and give lower estimates in sheltered areas. The validated high-resolution hindcast sets a baseline for future improvement of spectral wave models.

  1. Rip current monitoring using GPS buoy system

    Science.gov (United States)

    Song, DongSeob; Kim, InHo; Kang, DongSoo

    2014-05-01

    The occurrence of rip current in the Haeundae beach, which is one of the most famous beaches in South Korea, has been threatening beach-goers security in summer season annually. Many coastal scientists have been investigating rip currents by using field observations and measurements, laboratory measurements and wave tank experiments, and computer and numerical modeling. Rip current velocity is intermittent and may rapidly increase within minutes due to larger incoming wave groups or nearshore circulation instabilities. It is important to understand that changes in rip current velocity occur in response to changes in incoming wave height and period as well as changes in water level. GPS buoys have been used to acquire sea level change data, atmospheric parameters and other oceanic variables in sea for the purposes of vertical datum determination, tide correction, radar altimeter calibration, ocean environment and marine pollution monitoring. Therefore, we adopted GPS buoy system for an experiment which is to investigate rip current velocity; it is sporadic and may quickly upsurge within minutes due to larger arriving wave groups or nearshore flow uncertainties. In this study, for high accurate positioning of buy equipment, a Satellite Based Argumentation System DGPS data logger was deployed to investigate within floating object, and it can be acquired three-dimensional coordinate or geodetic position of buoy with continuous NMEA-0183 protocol during 24 hours. The wave height measured by in-situ hydrometer in a cross-shore array clearly increased before and after occurrence of rip current, and wave period also was lengthened around an event. These results show that wave height and period correlate reasonably well with long-shore current interaction in the Haeundae beach. Additionally, current meter data and GPS buoy data showed that rip current velocities, about 0.2 m/s, may become dangerously strong under specific conditions. Acknowledgement This research was

  2. A system for generating multi-resolution Digital Terrain Models of Mars based on the ESA Mars Express and NASA Mars Reconnaissance Orbiter data

    Science.gov (United States)

    Yershov, V.

    2015-10-01

    We describe a processing system for generating multiresolution digital terrain models (DTM) of Mars within the the iMars project of the European Seventh Framework Programme. This system is based on a non-rigorous sensor model for processing highresolution stereoscopic images obtained fromthe High Resolution Imaging Science Experiment (HiRISE) camera and Context Camera (CTX) onboard the NASA Mars Reconnaissance Orbiter (MRO) spacecraft. The system includes geodetic control based on the polynomial fit of the input CTX images with respect to to a reference image obtained from the ESA Mars Express High Resolution Stereo Camera (HRSC). The input image processing is based on the Integrated Software for Images and Spectrometers (ISIS) and the NASA Ames stereo pipeline. The accuracy of the produced CTX DTM is improved by aligning it with the reference HRSC DTMand the altimetry data from the Mars Orbiter Laser Altimeter (MOLA) onboard the Mars Global Surveyor (MGS) spacecraft. The higher-resolution HiRISE imagery data are processed in the the same way, except that the reference images and DTMs are taken from the CTX results obtained during the first processing stage. A quality assessment of image photogrammetric registration is demonstrated by using data generated by the NASA Ames stereo pipeline and the BAE Socet system. Such DTMs will be produced for all available stereo-pairs and be displayed asWMS layers within the iMarsWeb GIS.

  3. GLAS/ICESat L1B Global Waveform-based Range Corrections Data (HDF5) V033

    Data.gov (United States)

    National Aeronautics and Space Administration — The level 1B waveform parameterization data will contain waveform-based range corrections and surface characteristics at the full 40 per second resolution. Data...

  4. GLAS/ICESat L2 Global Antarctic and Greenland Ice Sheet Altimetry Data (HDF5) V033

    Data.gov (United States)

    National Aeronautics and Space Administration — GLAH12 contains the ice sheet elevation and elevation distribution corrected for geodetic and atmospheric affects calculated from algorithms fine-tuned for ice...

  5. Microfluidics: Functionality Integration for Proteomic Applications

    DEFF Research Database (Denmark)

    Petersen, Daria

    2006-01-01

    Interessen for miniaturiserede kemiske og biologiske analyser er voksende. I denne rapport er der set på design, fabrikation, og karakterisering af miniaturiserede analytiske systemer. Fokus er lagt på mikrochips fabrikeret i glas til kemiske analyser. Rapporten består af tre dele: 1) design, fab...

  6. Operational System for Estimating Compaction of Arctic Glacial Firn and Surface Mass Balance

    Science.gov (United States)

    Crowell, J. M.; Behar, A.; Howat, I. M.; de la Peña, S.; Thanga, J.

    2015-12-01

    NASA and other agencies are invested in obtaining measurements of Greenland Ice Sheet surface elevation with the objective of constraining the ice sheet's contribution to present and future sea level rise. However, a major limitation of repeat altimetry measurements, such as air and space-based surveys, is that variations in the density of surface accumulation and the firn layer must be constrained in order to relate changes in ice thickness to the overall ice sheet mass imbalance. The temporal variability of accumulation thickness and firn compaction rate is poorly constrained, particularly in regions subject to surface melt and refreezing. Additionally, recent warming and extreme melt events may be substantially changing the density of the firn, affecting altimeter measurements. This knowledge gap about snow accumulation and firn density, therefore, is a critical challenge to the ICESat-2 mission objectives. Our in-situ sensor packages, dubbed the Compaction Reconnaissance of Arctic Glacial Snow (CRAGS), will aid the deconvolution of surface change observations, with the goal of providing an operational system in concert with the launch of ICESat-2. The CRAGS prototype was deployed in April 2014 at 69.0754N, -45.6603E, and two fully-equipped systems were deployed in April 2015 at 69.0952N, -46.4446E and 69.0527N, -44.4281E. CRAGS is a tower system equipped with three instruments for measuring snow accumulation: a strain sensor, a sonar, and a snow scale. These systems will be taking measurements for at least two more years, but they are designed to last longer with limited maintenance. The use of a modular tower design allows for them to be extended higher for many years of observations. This method will supplement air and space-based observations, providing the polar science community with valuable ground-truth data regarding the state of the interior of the Greenland ice sheet.

  7. Assimilating along-track SLA data using the EnOI in an eddy resolving model of the Agulhas system

    Science.gov (United States)

    Backeberg, Björn C.; Counillon, François; Johannessen, Johnny A.; Pujol, Marie-Isabelle

    2014-08-01

    The greater Agulhas Current is one of the most energetic current systems in the global ocean. It plays a fundamental role in determining the mean state and variability of the regional marine environment, affecting its resources and ecosystem, the regional weather and the global climate on a broad range of temporal and spatial scales. In the absence of a coherent in-situ and satellite-based observing system in the region, modelling and data assimilation techniques play a crucial role in both furthering the quantitative understanding and providing better forecasts of this complicated western boundary current system. In this study, we use a regional implementation of the Hybrid Coordinate Ocean Model and assimilate along-track satellite sea level anomaly (SLA) data using the Ensemble Optimal Interpolation (EnOI) data assimilation scheme. This study lays the foundation towards the development of a regional prediction system for the greater Agulhas Current system. Comparisons to independent in-situ drifter observations show that data assimilation reduces the error compared to a free model run over a 2-year period. Mesoscale features are placed in more consistent agreement with the drifter trajectories and surface velocity errors are reduced. While the model-based forecasts of surface velocities are not as accurate as persistence forecasts derived from satellite altimeter observations, the error calculated from the drifter measurements for eddy kinetic energy is significantly lower in the assimilation system compared to the persistence forecast. While the assimilation of along-track SLA data introduces a small bias in sea surface temperatures, the representation of water mass properties and deep current velocities in the Agulhas system is improved.

  8. Evaluation of real time and future global monitoring and forecasting systems at Mercator Océan

    Directory of Open Access Journals (Sweden)

    J.-M. Lellouche

    2012-03-01

    Full Text Available Since December 2010, the global analysis and forecast of the MyOcean system consists in the Mercator Océan NEMO global 1/4° configuration with a 1/12° "zoom" over the Atlantic and Mediterranean Sea. The zoom open boundaries come from the global 1/4° at 20° S and 80° N.

    The data assimilation uses a reduced order Kalman filter with a 3-D multivariate modal decomposition of the forecast error. It includes an adaptative error and a localization algorithm. A 3D-Var scheme corrects for the slowly evolving large-scale biases in temperature and salinity.

    Altimeter data, satellite temperature and in situ temperature and salinity vertical profiles are jointly assimilated to estimate the initial conditions for the numerical ocean forecasting.

    This paper gives a description of the recent systems. The validation procedure is introduced and applied to the current and future systems. This paper shows how the validation impacts on the quality of the systems. It is shown how quality check (in situ, drifters and data source (satellite temperature impacts as much as the systems design (model physics and assimilation parameters. The validation demonstrates the accuracy of the MyOcean global products. Their quality is stable in time. The future systems under development still suffer from a drift. This could only be detected with a 5 yr hindcast of the systems. This emphasizes the need for continuous research efforts in the process of building future versions of MyOcean2 forecasting capacities.

  9. Using X-band Weather Radar Measurements to Monitor the Integrity of Digital Elevation Models for Synthetic Vision Systems

    Science.gov (United States)

    Young, Steve; UijtdeHaag, Maarten; Sayre, Jonathon

    2003-01-01

    Synthetic Vision Systems (SVS) provide pilots with displays of stored geo-spatial data representing terrain, obstacles, and cultural features. As comprehensive validation is impractical, these databases typically have no quantifiable level of integrity. Further, updates to the databases may not be provided as changes occur. These issues limit the certification level and constrain the operational context of SVS for civil aviation. Previous work demonstrated the feasibility of using a realtime monitor to bound the integrity of Digital Elevation Models (DEMs) by using radar altimeter measurements during flight. This paper describes an extension of this concept to include X-band Weather Radar (WxR) measurements. This enables the monitor to detect additional classes of DEM errors and to reduce the exposure time associated with integrity threats. Feature extraction techniques are used along with a statistical assessment of similarity measures between the sensed and stored features that are detected. Recent flight-testing in the area around the Juneau, Alaska Airport (JNU) has resulted in a comprehensive set of sensor data that is being used to assess the feasibility of the proposed monitor technology. Initial results of this assessment are presented.

  10. Sea Ice Topography Profiling using Laser Altimetry from Small Unmanned Aircraft Systems

    Science.gov (United States)

    Crocker, Roger Ian

    Arctic sea ice is undergoing a dramatic transition from a perennial ice pack with a high prevalence of old multiyear ice, to a predominantly seasonal ice pack comprised primarily of young first-year and second-year ice. This transition has brought about changes in the sea ice thickness and topography characteristics, which will further affect the evolution and survivability of the ice pack. The varying ice conditions have substantial implications for commercial operations, international affairs, regional and global climate, our ability to model climate dynamics, and the livelihood of Arctic inhabitants. A number of satellite and airborne missions are dedicated to monitoring sea ice, but they are limited by their spatial and temporal resolution and coverage. Given the fast rate of sea ice change and its pervasive implications, enhanced observational capabilities are needed to augment the current strategies. The CU Laser Profilometer and Imaging System (CULPIS) is designed specifically for collecting fine-resolution elevation data and imagery from small unmanned aircraft systems (UAS), and has a great potential to compliment ongoing missions. This altimeter system has been integrated into four different UAS, and has been deployed during Arctic and Antarctic science campaigns. The CULPIS elevation measurement accuracy is shown to be 95±25 cm, and is limited primarily by GPS positioning error (<25 cm), aircraft attitude determination error (<20 cm), and sensor misalignment error (<20 cm). The relative error is considerably smaller over short flight distances, and the measurement precision is shown to be <10 cm over a distance of 200 m. Given its fine precision, the CULPIS is well suited for measuring sea ice topography, and observed ridge height and ridge separation distributions are found to agree with theoretical distributions to within 5%. Simulations demonstrate the inability of course-resolution measurements to accurately represent the theoretical distributions

  11. System Budgets

    DEFF Research Database (Denmark)

    Jeppesen, Palle

    1996-01-01

    The lecture note is aimed at introducing system budgets for optical communication systems. It treats optical fiber communication systems (six generations), system design, bandwidth effects, other system impairments and optical amplifiers.......The lecture note is aimed at introducing system budgets for optical communication systems. It treats optical fiber communication systems (six generations), system design, bandwidth effects, other system impairments and optical amplifiers....

  12. ICESat Observations of Topographic Change in the Northern Segment of the 2004 Sumatra-Andaman Islands Earthquake Rupture Zone

    Science.gov (United States)

    Harding, D.; Sauber, J.; Luthcke, S.; Carabajal, C.; Muller, J.

    2005-05-01

    The Andaman Islands are located 120 km east of the Sunda trench in the northern quarter of the 1300 km long rupture zone of the 2004 Sumatra-Andaman Islands earthquake inferred from the distribution of aftershocks. Initial field reports indicate that several meters of uplift and up to a meter of submergence occurred on the western and eastern shorelines of the Andaman Islands, respectively, associated with the earthquake (Bilham, 2005). Satellite images also document uplift of western shoreline coral reef platforms above sea level. Body-wave (Ji, 2005; Yamamaka, 2005) and tide-gauge (Ortiz, 2005) slip inversions only resolve coseismic slip in the southern one-third to one-half of the rupture zone. The amount of coseismic slip in the Andaman Islands region is poorly constrained by these inversions. The Ice, Cloud, and land Elevation Satellite (ICESat), a part of the NASA Earth Observing System, is being used to document the spatial pattern of Andaman Islands vertical displacements in order to constrain models of slip distribution in the northern part of the rupture zone. ICESat carries the Geoscience Laser Altimeter System (GLAS) that obtains elevation measurements from 80 m diameter footprints spaced 175 m apart along profiles. For surfaces of low slope, single-footprint absolute elevation and horizontal accuracies of 10 cm and 6 m (1 sigma), respectively, referenced to the ITRF 2002 TOPEX/Poseidon ellipsoid are being obtained. Laser pulse backscatter waveforms enable separation of ground topography and overlying vegetation cover. During each 33-day observing period ICESat acquires three profiles crossing the Andaman Islands. A NNE-SSW oriented track consists of 1600 laser footprints along the western side of North, Middle, and South Andaman Islands and 240 laser footprints across the center of Great Andaman Island. Two NNW-SSE tracks consist of 440 footprints across Middle Andaman Island and 25 footprints across the west side of Sentinel Island. Cloud

  13. System Identification

    NARCIS (Netherlands)

    Keesman, K.J.

    2011-01-01

    Summary System Identification Introduction.- Part I: Data-based Identification.- System Response Methods.- Frequency Response Methods.- Correlation Methods.- Part II: Time-invariant Systems Identification.- Static Systems Identification.- Dynamic Systems Identification.- Part III: Time-varying Syste

  14. Research on Large Spot Laser Altimetry Echo Simulation of General Terrain%一般地形大光斑激光测高回波模拟研究

    Institute of Scientific and Technical Information of China (English)

    潘浩; 李国元; 王华斌; 谭天亚; 王伶俐

    2015-01-01

    国内对基于陆地模型的地表回波仿真的研究较多,主要分析了三种特定的地表模型:平面、阶梯、斜坡地形,取得了不错的进展,但是却不具有一般性。针对这种情况,本文从一般性地表模型出发,根据实际的地形三维离散点,用Delaunay三角形剖分拟合出地表模型,用剖分后的三角面片返回的能量代表整个地表返回的能量,拟合出回波波形。通过和GLAS系统获取的相同区域的实际回波波形进行相关性比较,结果发现两者具有很好的相关性,验证了算法的正确性。文章结论为后续继续深入开展激光大光斑内精细地形信息分析、激光测高数据与光学影像复合处理提供了理论基础,为发展我国自主的星载激光测高卫星的有关指标论证提供参考。%Domestic research on ground echo simulation model based on three main surface model:flat, ladder, slope terrain, has made great progress, but it is not general. Method: to address this situation, this paper embarks from the general surface model, according to these three-dimensional discrete points of the actual terrain, fitting the surface model with Delaunay triangulations, and using the energy from these split triangulations returned to represent the entire surface returned energy, fitting out the echo waveform. Result: comparing simulated waveform with one obtained from geoscience laser altimeter system(GLAS)in the same region, the results showed that both of them have good correlation, which verifies the correctness of the algorithm. Conclusion: the results provided the theoretical foundation for information analysis of more-refined terrains and combined treatment of laser altimetry data with the optical image, and also provided a reference for the development of the domestic space-borne laser altimetry satellite on related indicators.

  15. Developing a global mixed-canopy, height-variable vegetation structure dataset for estimating global vegetation albedo and biomass in the NASA Ent Terrestrial Biosphere Model and GISS GCM

    Science.gov (United States)

    Montes, C.; Kiang, N. Y.; Yang, W.; Ni-Meister, W.; Schaaf, C.; Aleinov, I. D.; Jonas, J.; Zhao, F. A.; Yao, T.; Wang, Z.; Sun, Q.

    2015-12-01

    Processes determining biosphere-atmosphere coupling are strongly influenced by vegetation structure. Thus, ecosystem carbon sequestration and evapotranspiration affecting global carbon and water balances will depend upon the spatial extent of vegetation, its vertical structure, and its physiological variability. To represent this globally, Dynamic Global Vegetation Models (DGVMs) coupled to General Circulation Models (GCMs) make use of satellite and/or model-based vegetation classifications often composed by homogeneous communities. This work aims at developing a new Global Vegetation Structure Dataset (GVSD) by incorporating varying vegetation heights for mixed plant communities to be used as input to the Ent Terrestrial Biosphere Model (TBM), the DGVM coupled to the NASA Goddard Institute for Space Studies (GISS) GCM. Information sources include the Moderate Resolution Imaging Spectroradiometer (MODIS) land cover and plant functional types (PFTs) (Friedl et al., 2010), vegetation height from the Geoscience Laser Altimeter System (GLAS) on board ICESat (Ice, Cloud, and land Elevation Satellite) (Simard et al., 2011; Tang et al., 2014) along with the Global Data Sets of Vegetation Leaf Area Index (LAI)3g (Zhu et al. 2013). Further PFT partitioning is performed according to a climate classification utilizing the Climate Research Unit (CRU) and the NOAA Global Precipitation Climatology Centre (GPCC) data. Final products are a GVSD consisting of mixed plant communities (e.g. mixed forests, savannas, mixed PFTs) following the Ecosystem Demography model (Moorcroft et al., 2001) approach represented by multi-cohort community patches at the sub-grid level of the GCM, which are ensembles of identical individuals whose differences are represented by PFTs, canopy height, density and vegetation structure sensitivity to allometric parameters. To assess the sensitivity of the GISS GCM to vegetation structure, we produce a range of estimates of Ent TBM biomass and plant

  16. Developing a global mixed-canopy, height-variable vegetation structure dataset for estimating global vegetation albedo by a clumped canopy radiative transfer scheme in the NASA Ent Terrestrial Biosphere Model and GISS GCM

    Science.gov (United States)

    Montes, Carlo; Kiang, Nancy Y.; Ni-Meister, Wenge; Yang, Wenze; Schaaf, Crystal; Aleinov, Igor; Jonas, Jeffrey A.; Zhao, Feng; Yao, Tian; Wang, Zhuosen; Sun, Qingsong; Carrer, Dominique

    2016-04-01

    Processes determining biosphere-atmosphere coupling are strongly influenced by vegetation structure. Thus, ecosystem carbon sequestration and evapotranspiration affecting global carbon and water balances will depend upon the spatial extent of vegetation, its vertical structure, and its physiological variability. To represent this globally, Dynamic Global Vegetation Models (DGVMs) coupled to General Circulation Models (GCMs) make use of satellite and/or model-based vegetation classifications often composed by homogeneous communities. This work aims at developing a new Global Vegetation Structure Dataset (GVSD) by incorporating varying vegetation heights for mixed plant communities to be used as boundary conditions to the Analytical Clumped Two-Stream (ACTS) canopy radiative transfer scheme (Ni-Meister et al., 2010) incorporated into the NASA Ent Terrestrial Biosphere Model (TBM), the DGVM coupled to the NASA Goddard Institute for Space Studies (GISS) GCM. Information sources about land surface and vegetation characteristics obtained from a number of earth observation platforms and algorithms include the Moderate Resolution Imaging Spectroradiometer (MODIS) land cover and plant functional types (PFTs) (Friedl et al., 2010), soil albedo derived from MODIS (Carrer et al., 2014), along with vegetation height from the Geoscience Laser Altimeter System (GLAS) on board ICESat (Ice, Cloud, and land Elevation Satellite) (Simard et al., 2011; Tang et al., 2014). Three widely used Leaf Area Index (LAI) products are compared as input to the GVSD and ACTS forcing in terms of vegetation albedo: Global Data Sets of Vegetation (LAI)3g (Zhu et al. 2013), Beijing Normal University LAI (Yuan et al., 2011), and MODIS MOD15A2H product (Yang et al., 2006). Further PFT partitioning is performed according to a climate classification utilizing the Climate Research Unit (CRU; Harris et al., 2013) and the NOAA Global Precipitation Climatology Centre (GPCC; Scheider et al., 2014) data. Final

  17. Systems autonomy

    Science.gov (United States)

    Lum, Henry, Jr.

    1988-01-01

    Information on systems autonomy is given in viewgraph form. Information is given on space systems integration, intelligent autonomous systems, automated systems for in-flight mission operations, the Systems Autonomy Demonstration Project on the Space Station Thermal Control System, the architecture of an autonomous intelligent system, artificial intelligence research issues, machine learning, and real-time image processing.

  18. High-Rate Data-Capture for an Airborne Lidar System

    Science.gov (United States)

    Valett, Susan; Hicks, Edward; Dabney, Philip; Harding, David

    2012-01-01

    A high-rate data system was required to capture the data for an airborne lidar system. A data system was developed that achieved up to 22 million (64-bit) events per second sustained data rate (1408 million bits per second), as well as short bursts (less than 4 s) at higher rates. All hardware used for the system was off the shelf, but carefully selected to achieve these rates. The system was used to capture laser fire, single-photon detection, and GPS data for the Slope Imaging Multi-polarization Photo-counting Lidar (SIMPL). However, the system has applications for other laser altimeter systems (waveform-recording), mass spectroscopy, xray radiometry imaging, high-background- rate ranging lidar, and other similar areas where very high-speed data capture is needed. The data capture software was used for the SIMPL instrument that employs a micropulse, single-photon ranging measurement approach and has 16 data channels. The detected single photons are from two sources those reflected from the target and solar background photons. The instrument is non-gated, so background photons are acquired for a range window of 13 km and can comprise many times the number of target photons. The highest background rate occurs when the atmosphere is clear, the Sun is high, and the target is a highly reflective surface such as snow. Under these conditions, the total data rate for the 16 channels combined is expected to be approximately 22 million events per second. For each photon detection event, the data capture software reads the relative time of receipt, with respect to a one-per-second absolute time pulse from a GPS receiver, from an event timer card with 0.1-ns precision, and records that information to a RAID (Redundant Array of Independent Disks) storage device. The relative time of laser pulse firings must also be read and recorded with the same precision. Each of the four event timer cards handles the throughput from four of the channels. For each detection event, a flag is

  19. Immune System

    Science.gov (United States)

    ... Can I Help a Friend Who Cuts? Immune System KidsHealth > For Teens > Immune System Print A A ... put us out of commission. What the Immune System Does The immune (pronounced: ih-MYOON) system, which ...

  20. 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.