Seasat Altimeter Calibration: Initial Results

Tapley, Byron D; Born, George H.; Hagar, H.; Lorell, J.; Parke, Michael; Diamante, J. M.; Douglas, Bruce C.; Goad, Clyde C.; Kolenkiewicz, R.; Marsh, J. G.; Martin, C. F.; Smith, Samuel; Townsend, W. F.; Whitehead, J. A.; Byrne, H. Michael; Fedor, L. S.; Hammond, D. C.; Mognard, N. M.

doi:10.1126/science.204.4400.1410

Cited by 31 publications

(4 citation statements)

References 2 publications

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“…Although the operational lifetime of the SEASATsatellite was only a few weeks, it confirmed the accuracy and usefulness of satellite-mounted radar altimeters for measuring ocean waveheights (Tapley et al 1979, Webb 1981. Errors of less than 5 per cent were achieved with world-wide coverage and without any tendency to undersample regions of extreme waves as occurs, for example, with ship observations.…”

Section: Introductionsupporting

confidence: 50%

Seasonal changes in the global wave climate measured by the Geosat altimeter

Challenor

Foale

Webb

1990

International Journal of Remote Sensing

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Wave height measurements made during the year November 1986 to November 1987 by the radar altimeter on the US Geosat satelliteare used to map the seasonal variations in the global wave climate. The largest significant wave heights are found in winter in the Southern Ocean with only a slight reduction during the southern summer. In the North Atlantic and North Pacific the significant wave heights are lowerand there is a larger variation between summer and winter.

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Section: Introductionsupporting

confidence: 50%

Seasonal changes in the global wave climate measured by the Geosat altimeter

Challenor

Foale

Webb

1990

International Journal of Remote Sensing

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“…The calibration activity [Tapley et al, 1979; Kolenkiewicz and Martin, this issue] modeled the error due to lack of precise geoid elevations as (1) an error source due to smoothing the altimeter data across the ground track over Bermuda, and (2) a geoidal slope error between the laser site and the closest approach of the altimeter ground tracks based on G EOS 3 mean sea surface data. As noted, this approach may not be entirely adequate.…”

Section: Discussionmentioning

confidence: 99%

Tidal and geodetic observations for the SEASAT altimeter calibration experiment

Diamante¹,

Douglas²,

Porter³

et al. 1982

J. Geophys. Res.

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A calibration experiment for the SEASAT radar altimeter was conducted in the Bermuda calibration area during September and.October of 1978 by a group of Federal Government agencies, universities, and research organizations. As part of the SEASAT calibration activities, a tide gage was installed by the National Ocean Survey at an open coastal location on Bermuda to provide a determination of the instantaneous sea surface height during the SEASAT overflights of the island. The tide gage was geodetically tied to the laser tracking station on Bermuda, so that SEASAT's position relative to the sea surface could be determined independently and compared with the value provided by the altimeter measurements. The root sum square error in the determination of the vertical position of the laser, relative to the sea surface, has been estimated to be 4.0 cm exclusive of possible errors arising from the present lack of precise information on the elevation of the geoid at Bermuda.

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“…The activities conducted by the team to evaluate and improve the accuracy of the altimeter measurement are discussed by Born et al [1979], Tapley et al [1979a, b], Barrick et al [1979], Businger et al [1980] and in the altimeter-related papers in this issue.…”

Section: Requirementsmentioning

confidence: 99%

The SEASAT altimeter data and its accuracy assessment

Tapley¹,

Born²,

Parke³

1982

J. Geophys. Res.

157

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The SEASAT satellite, launched on June 27, 1978, carried a radar altimeter designed to measure the altitude of the satellite above the ocean surface, the surface wave height, and the ocean-surface backscatter coetficient from which wind speed can be inferred. Postlaunch engineering assessment indicated that the SEASAT altimeter met the performance specification for 10-cm precision (noise) in the altitude measurements. However, to determine the accuracy of this measurement as well as the accuracy of the wave height and wind speed measurements a significant calibration, validation, and model development effort was required. This summary describes the instrument, atmospheric, and geophysical effects which influence the radar altimeter measurement accuracies and the attendant correction models adopted for the altimeter geophysical data record. Also summarized are the activities of the SEASAT Altimeter/Precision Orbit Determination Experiment Team directed towards the validation and improvement of these models, as well as the investigations required to assess the accuracy of the altimeter measurement and the computed satellite altitude ephemeris. Finally, an accuracy assessment is made for the various altimeter measurement corrections which are included on the altimeter geophysical data record. INTRODUCTIONThe development of satellite altimetry techniques for the remote sensing of ocean surface topography is one of the fundamental objectives of the NASA Ocean Processes Program. The requirements for NASA's satellite altimetry program were formulated at the 1969 Williamstown Conference on Solid Earth and Ocean Physics [Kaula et al., 1970]. Since this conference, satellite altimetry has evolved through the Skylab [McGoogan et al., 1974], GEeS 3 [Stanley, 1979], and SEASAT missions to the extent that it can dramatically improve the way we perform many future oceanographic measurements. Characteristics unique to satellite altimetry are (1) the high accuracy with which surface topography, wave height, and wind speed can be measured and (2) the ability to collect these measurements globally over the time interval of a few days [Apel, 1980]. The satellite served as a stable platform from which the altimeter measured the distance from the antenna feed point to the instantaneous electromagnetic mean sea level. The SEASAT altimeter tracked the position of the sea surface by using a closed loop microprocessor range tracker and an automatic gain control feedback loop. For a description of the altimeter design, see MacArthur [1978]. The geophysical measurements obtained from the returned altimeter pulse are (1) altitude above the ocean surface, which is related to ocean surface topography, (2) ocean surface significant wave height, and (3) ocean surface backscatter coefficient, which is related to the wind speed. Given an independent determination of the satellite position from the orbit determination system, the ocean surface topography can be inferred from the altimeter height measurement. The oceanographic phenomena which influe...

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Seasat Altimeter Calibration: Initial Results

Cited by 31 publications

References 2 publications

Seasonal changes in the global wave climate measured by the Geosat altimeter

Seasonal changes in the global wave climate measured by the Geosat altimeter

Tidal and geodetic observations for the SEASAT altimeter calibration experiment

The SEASAT altimeter data and its accuracy assessment

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