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C.l. Purdy – One of the best experts on this subject based on the ideXlab platform.

  • Prelaunch performance of the NASA Altimeter for the TOPEX/Poseidon project
    IEEE Transactions on Geoscience and Remote Sensing, 1993
    Co-Authors: P.c. Marth, G.s. Hayne, C.l. Purdy, D.w. Hancock, J.r. Jensen, C. C. Kilgus, J.a. Perschy, J.l. Macarthur, L. C. Rossi, C.j. Koblinsky
    Abstract:

    The TOPEX/Poseidon radar Altimeter satellite applies advances in remote sensing instrumentation to reduce long wavelength measurement errors to dramatically lower levels. The TOPEX Altimeter measures the range to the ocean surface with 2-cm precision and accuracy through the use of both Ku- and C-band radars, a high pulse repetition frequency, an agile tracker, and absolute internal height calibration. Dual pulse bandwidths for both frequencies make it possible to quickly acquire the surface and begin tracking after crossing the land/ocean boundary. The Altimeter requirements and the elements of the Altimeter design that have resulted in meeting these requirements are presented. Prelaunch test data, based on the use of a radar Altimeter system evaluator to simulate the backscatter from the ocean surface, are presented to demonstrate that the TOPEX Altimeter will meet these requirements and provide the data necessary to the understanding of basin scale mean circulation. >

  • NASA radar Altimeter for the TOPEX/POSEIDON Project
    Proceedings of the IEEE, 1991
    Co-Authors: A.r. Zieger, G.s. Hayne, D.w. Hancock, C.l. Purdy
    Abstract:

    The TOPEX/POSEIDON Project is a joint US and French mission to develop and operate an Earth-orbiting satellite with sensors capable of making accurate measurements of sea level. The NASA radar Altimeter (NRA), a fifth-generation US Altimeter, will provide the primary measurement for the TOPEX/POSEIDON Project altimetric mission. The authors present the requirements, Altimeter fundamentals, design description, integration and test program, primary elements of ground processing, and assessment for the dual-frequency NASA radar Altimeter. >

  • Engineering performance analysis of the TOPEX radar Altimeter
    Proceedings of IGARSS '94 – 1994 IEEE International Geoscience and Remote Sensing Symposium, 1
    Co-Authors: G.s. Hayne, D.w. Hancock, C.l. Purdy
    Abstract:

    Describes the Wallops Flight Facility continuing work in engineering performance analysis for the NASA radar Altimeter of the TOPEX/POSEIDON mission (referred to simply as the TOPEX Altimeter). Because an Altimeter measuring range at two frequencies allows the ionosphere-caused error to be corrected, the TOPEX Altimeter comprises a primary radar Altimeter at Ku-band (13.6 GHz) and a secondary radar Altimeter at C-band (5.3 GHz). For the TOPEX Ku and C Altimeters the authors report performance and calibration results for range and for the radar surface backscattering cross-section /spl sigma//sup 0/. Except for the antenna the TOPEX Altimeter has two redundant systems, sides A and B. Only side A has been operated since launch, and this paper discusses only side A. >

D.w. Hancock – One of the best experts on this subject based on the ideXlab platform.

  • On the Evaluation of the GEOSAT Follow On (GFO) Altimeter
    , 1998
    Co-Authors: D.w. Hancock, G.s. Hayne
    Abstract:

    The NAVY GFO satellite was launched on February 10, 1998. The spacecraft system and the GPS instrument have experienced a number of problems that have prevented the mission from entering normal operations. However the GFO radar Altimeter has been turned on a number of times and does appear to be performing well. We have been approved to help monitor the long term trends in the Altimeter similar to the functions we have been performing for the Ocean Topography Experiment POSEIDON (TOPEX) radar Altimeter. We will present some analysis of the pre-launch test data from the GFO Altimeter to indicate the characteristics of the instrument. We will also present analysis of in-flight data indicating that the Altimeter performance appears to be nominal. The current in-flight trends based on the calibration mode will be discussed.

  • Prelaunch performance of the NASA Altimeter for the TOPEX/Poseidon project
    IEEE Transactions on Geoscience and Remote Sensing, 1993
    Co-Authors: P.c. Marth, G.s. Hayne, C.l. Purdy, D.w. Hancock, J.r. Jensen, C. C. Kilgus, J.a. Perschy, J.l. Macarthur, L. C. Rossi, C.j. Koblinsky
    Abstract:

    The TOPEX/Poseidon radar Altimeter satellite applies advances in remote sensing instrumentation to reduce long wavelength measurement errors to dramatically lower levels. The TOPEX Altimeter measures the range to the ocean surface with 2-cm precision and accuracy through the use of both Ku- and C-band radars, a high pulse repetition frequency, an agile tracker, and absolute internal height calibration. Dual pulse bandwidths for both frequencies make it possible to quickly acquire the surface and begin tracking after crossing the land/ocean boundary. The Altimeter requirements and the elements of the Altimeter design that have resulted in meeting these requirements are presented. Prelaunch test data, based on the use of a radar Altimeter system evaluator to simulate the backscatter from the ocean surface, are presented to demonstrate that the TOPEX Altimeter will meet these requirements and provide the data necessary to the understanding of basin scale mean circulation. >

  • NASA radar Altimeter for the TOPEX/POSEIDON Project
    Proceedings of the IEEE, 1991
    Co-Authors: A.r. Zieger, G.s. Hayne, D.w. Hancock, C.l. Purdy
    Abstract:

    The TOPEX/POSEIDON Project is a joint US and French mission to develop and operate an Earth-orbiting satellite with sensors capable of making accurate measurements of sea level. The NASA radar Altimeter (NRA), a fifth-generation US Altimeter, will provide the primary measurement for the TOPEX/POSEIDON Project altimetric mission. The authors present the requirements, Altimeter fundamentals, design description, integration and test program, primary elements of ground processing, and assessment for the dual-frequency NASA radar Altimeter. >

Ian R Young – One of the best experts on this subject based on the ideXlab platform.

  • 33 years of globally calibrated wave height and wind speed data based on Altimeter observations
    Scientific Data, 2019
    Co-Authors: Agustinus Ribal, Ian R Young
    Abstract:

    This dataset consists of 33 years (1985 to 2018), of global significant wave height and wind speed obtained from 13 Altimeters, namely: GEOSAT, ERS-1, TOPEX, ERS-2, GFO, JASON-1, ENVISAT, JASON-2, CRYOSAT-2, HY-2A, SARAL, JASON-3 and SENTINEL-3A. The Altimeter data have been calibrated and validated against National Oceanographic Data Center (NODC) buoy data. Differences between Altimeter and buoy data as a function of time are investigated for long-term stability. A cross validation between Altimeters is also carried out in order to check the stability and consistency of the calibrations developed. Quantilequantile comparisons between Altimeter and buoy data as well as between Altimeters are undertaken to test consistency of probability distributions and extreme value performance. The data were binned into 1° by 1° bins globally, to provide convenient access for users to download only the regions of interest. All data are quality controlled. This globally calibrated and cross-validated dataset provides a single point of storage for all Altimeter missions in a consistent format.

  • joint calibration of multiplatform Altimeter measurements of wind speed and wave height over the past 20 years
    Journal of Atmospheric and Oceanic Technology, 2009
    Co-Authors: Stefan Zieger, J Vinoth, Ian R Young
    Abstract:

    Since 1985, for a period of more than 23 yr, seven Altimeter missions have provided global coverage of significant wave height and wind speed. This study undertakes a long-term analysis of the accuracy and stability of Altimeter-derived values of significant wave height and wind speed from the following satellites: European Remote Sensing-1 (ERS-1), ERS-2, Environmental Satellite (Envisat), Geosat, Geosat Follow-On (GFO), Jason-1, and the Ocean Topography Experiment (TOPEX). This study is a necessary step in developing a quality-controlled and fully calibrated and validated dataset from the combined satellites. Calibration of all Altimeters is performed against National Oceanographic Data Center (NODC) buoy data over the extended period. These calibrations are validated using intercomparisons between satellite missions at crossover ground points. This analysis shows that, for a number of the satellites, small ‘‘step like’’ changes occur during the missions. These inconsistencies are removed by subdividing these missions and undertaking a partial calibration for each section of the mission. The analysis also highlights that care is necessary when attempting to apply relationships between radar cross section and wind speed derived for one Altimeter to other platforms. Before undertaking such steps, it is first necessary to apply a platform-specific radar crosssectional offset to the data.

G.s. Hayne – One of the best experts on this subject based on the ideXlab platform.

  • On the Evaluation of the GEOSAT Follow On (GFO) Altimeter
    , 1998
    Co-Authors: D.w. Hancock, G.s. Hayne
    Abstract:

    The NAVY GFO satellite was launched on February 10, 1998. The spacecraft system and the GPS instrument have experienced a number of problems that have prevented the mission from entering normal operations. However the GFO radar Altimeter has been turned on a number of times and does appear to be performing well. We have been approved to help monitor the long term trends in the Altimeter similar to the functions we have been performing for the Ocean Topography Experiment POSEIDON (TOPEX) radar Altimeter. We will present some analysis of the pre-launch test data from the GFO Altimeter to indicate the characteristics of the instrument. We will also present analysis of in-flight data indicating that the Altimeter performance appears to be nominal. The current in-flight trends based on the calibration mode will be discussed.

  • Prelaunch performance of the NASA Altimeter for the TOPEX/Poseidon project
    IEEE Transactions on Geoscience and Remote Sensing, 1993
    Co-Authors: P.c. Marth, G.s. Hayne, C.l. Purdy, D.w. Hancock, J.r. Jensen, C. C. Kilgus, J.a. Perschy, J.l. Macarthur, L. C. Rossi, C.j. Koblinsky
    Abstract:

    The TOPEX/Poseidon radar Altimeter satellite applies advances in remote sensing instrumentation to reduce long wavelength measurement errors to dramatically lower levels. The TOPEX Altimeter measures the range to the ocean surface with 2-cm precision and accuracy through the use of both Ku- and C-band radars, a high pulse repetition frequency, an agile tracker, and absolute internal height calibration. Dual pulse bandwidths for both frequencies make it possible to quickly acquire the surface and begin tracking after crossing the land/ocean boundary. The Altimeter requirements and the elements of the Altimeter design that have resulted in meeting these requirements are presented. Prelaunch test data, based on the use of a radar Altimeter system evaluator to simulate the backscatter from the ocean surface, are presented to demonstrate that the TOPEX Altimeter will meet these requirements and provide the data necessary to the understanding of basin scale mean circulation. >

  • NASA radar Altimeter for the TOPEX/POSEIDON Project
    Proceedings of the IEEE, 1991
    Co-Authors: A.r. Zieger, G.s. Hayne, D.w. Hancock, C.l. Purdy
    Abstract:

    The TOPEX/POSEIDON Project is a joint US and French mission to develop and operate an Earth-orbiting satellite with sensors capable of making accurate measurements of sea level. The NASA radar Altimeter (NRA), a fifth-generation US Altimeter, will provide the primary measurement for the TOPEX/POSEIDON Project altimetric mission. The authors present the requirements, Altimeter fundamentals, design description, integration and test program, primary elements of ground processing, and assessment for the dual-frequency NASA radar Altimeter. >

R.k. Raney – One of the best experts on this subject based on the ideXlab platform.

  • The delay/Doppler radar Altimeter
    IEEE Transactions on Geoscience and Remote Sensing, 1998
    Co-Authors: R.k. Raney
    Abstract:

    The key innovation in the delay/Doppler radar Altimeter is delay compensation, analogous to range curvature correction in a burst-mode synthetic aperture radar (SAR). Following delay compensation, height estimates are sorted by Doppler frequency, and integrated in parallel. More equivalent looks are accumulated than in a conventional Altimeter. The relatively small along-track footprint size is a constant of the system, typically on the order of 250 m for a Ku-band Altimeter. The flat-surface response is an impulse rather than the more familiar step function produced by conventional satellite radar Altimeters. The radar equation for the delay/Doppler radar Altimeter has an h/sup -5/2/(CT)/sup 1/2/ dependence on height h and compressed pulse length /spl tau/, which is more efficient than the corresponding h/sup 3/CT factor for a pulse-limited Altimeter. The radiometric response obtained by the new approach would be 10 dB stronger than that of the TOPEX/Poseidon Altimeter, for example, if the same hardware were used in the delay/Doppler Altimeter mode. This new technique leads to a smaller instrument that requires less power, yet performs better than a conventional radar Altimeter. The concept represents a new generation of Altimeter for Earth observation, with particular suitability for coastal ocean regions and polar ice sheets as well as open oceans.

  • the delay doppler radar Altimeter
    International Geoscience and Remote Sensing Symposium, 1998
    Co-Authors: R.k. Raney
    Abstract:

    The key innovation in the delay/Doppler radar Altimeter is delay compensation, analogous to range curvature correction in a burst-mode synthetic aperture radar (SAR). Following delay compensation, height estimates are sorted by Doppler frequency, and integrated in parallel. More equivalent looks are accumulated than in a conventional Altimeter. The relatively small along-track footprint size is a constant of the system, typically on the order of 250 m for a Ku-band Altimeter. The flat-surface response is an impulse rather than the more familiar step function produced by conventional satellite radar Altimeters. The radar equation for the delay/Doppler radar Altimeter has an h -5/2 (cT) 1/2 dependence on height h and compressed pulse length T, which is more efficient than the corresponding h -3 cT factor for a pulse-limited Altimeter. The radiometric response obtained by the new approach would be 10 dB stronger than that of the TOPEX/Poseidon Altimeter, for example, if the same hardware were used in the delay/Doppler Altimeter mode. This new technique leads to a smaller instrument that requires less power, yet performs better than a conventional radar Altimeter. The concept represents a new generation of Altimeter for earth observation, with particular suitability for coastal ocean regions and polar ice sheets as well as open oceans.