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During its brief 110-day lifetime, the SEASAT-1 spacecraft, launched on June 28, 1978 by NASA's Jet Propulsion Laboratory, collected information on sea-surface winds, sea-surface temperatures, wave heights, internal waves, atmospheric water, sea ice features, ice sheet topography, and ocean topography. This was the first JPL mission to study Earth with the use of imaging radar.
Ocean Dynamics Satellite/SEASAT
SEASAT supported five sensors: ALT (radar altimeter), SMMR (Scanning Multichannel Microwave Radiometer), SAR (Synthetic Aperture Radar), SASS (SEASAT-A Scatterometer System), and VIRR (Visible and Infrared Radiometer). SEASAT was in a near-circular, polar orbit at an altitude of 805 kilometers and at an inclination of 108 degrees. The satellite orbited the Earth 14 times daily and covered 95 percent of the world's oceans every 36 hours. On October 10, 1978, the satellite suffered a massive short circuit in its electrical system and stopped functioning.
SEASAT was a NASA/Jet Propulsion Laboratory Earth observation mission.
SEASAT's five onboard sensors were individually managed by the following centers:
SEASAT was specifically designed to study oceanographic phenomena. The mission's purpose was to help determine the requirements for an operational ocean remote sensing satellite system.
SEASAT was launched on June 26, 1978 from the Vandenberg Air Force Base, California. The SEASAT launch vehicle, Atlas-Agena, provided attitude control, power, guidance, telemetry, and command functions. A sensor module was attached to the Agena and carried the payload of five microwave instruments and their antennas. Together, the two modules measured 21 meters long and 1.5 meters in diameter. Once in orbit and after burnout of the Agena stage, the SEASAT spacecraft weighed 2300 kilograms.
SEASAT was in a near-circular, polar orbit, at an altitude of 805 kilograms and an inclination of 108 degrees. The satellite completed 14 Earth orbits per day.
Atlas-Agena, the SEASAT launch vehicle, provided attitude control for the satellite. In orbit, SEASAT appeared to stand on end, with the sensor and communications antennas pointing toward Earth and the Agena rocket nozzle and solar panels pointing toward space. SEASAT was stabilized by a momentum wheel/horizon sensing system.
No information is available at this time.
For the SEASAT mission, the radar altimeter determined ocean topography with height measurements to within 10 centimeters. The SEASAT altimeter collected 90 days of data, specifically acquiring more than 600 thousand useful alimeter observations of the Greenland and Antarctic ice sheets. Parameters, which included satellite height, waveform data, wave height, and automatic gain control were telemetered to the ground processing system at a 10/second rate. The SEASAT altimeter carrier frequency was 13.5 GHz and operated in chirp pulse mode with a 3.2-microsecond uncompressed pulse width and 3.125-nanosecond compressed pulse width. The limited pulse footprint diameter was 1.2 kilometers for calm seas and up to 12 kilometers for rough seas. The data volume for this product is approximately 20.3 gigabytes.
SAR (Synthetic Aperture Radar)
The SAR onboard SEASAT monitored the global surface wave field and polar sea ice conditions, providing information on ice caps, snow coverage, and coastal regions. The experiment operated at L-band (1.275 Ghz) with a 100-km swath and provided 25-m vertical resolution. About 42 hours of data were recorded.
SASS (SEASAT-A Scatterometer System)
SASS measured wind speed and direction on the SEASAT mission. Global measurements of the surface wind velocity over the seas were obtained from SASS at least once every 36 hours; the high latitudes were more frequently covered. SASS collected data in two 500-km swaths. Pulse duration was 4.8 milliseconds, and the data stream was updated every 1.89 seconds. Resolution was 50 kilometers and the grid spacing of the output data product, 100 kilometers.
The SMMR instrument acquired sea surface temperatures for the SEASAT mission. SMMR measures dual polarized microwave radiation from the earth's surface and atmosphere in five frequencies: 6.63, 10.69, 18.0, 21.0, and 37.0 Gigahertz. SEASAT data from SMMR were obtained in swath widths of 600 kilometers. Output was in the form of calibrated sensor data records. Data product volume is 45.7 gigabytes. For SEASAT, coverage was within a +77/-72-degree latitude from July 7 to August 17, 1978, with a ground track equatorial spacing of 165 kilometers. From August 18 to October 10, 1978, the ground track equatorial spacing was 900 kilometers. From July 7 to August 26, 1978, the ground track was repeated every 17 days; from August 27 to October 10, 1978, once every three days. The temporal resolution was 10/second.
VIRR (Visible and Infrared Radiometer)
The VIRR identified cloud, land, and water features on the SEASAT mission. It operated in the visible band (0.49-0.94 micrometers) and in the infrared band (10.5-12.5 micrometers). The swath of the VIRR is approximately 2280 kilometers wide, centered on nadir. Spatial coverage for the mission was global, and temporal coverage spanned July 4, 1978 to August 27, 1978. The normal scan period was 1.25 seconds, and 48 scans were completed per minute.
Data were transmitted from the satellite in three separate streams: A 25-kbps real-time stream containing instrument data from ALT, SASS, SMMR, and VIRR and all engineering subsystem data, an 800-kbps playback stream of recorded real-time data, and a 20-MHz analog SAR instrument data stream.
Radar altimeter data, in the form of Geophysical Data Records (GDRs) and Sensor Data Records (SDRs) were produced by NASA's SEASAT project at the Jet Propulsion Laboratory.
SAR data from SEASAT were acquired digitally, and most of the data were optically processed into survey data products, available on 70-mm film. The SEASAT 100-km swath data were processed into four 25-km wide products at JPL. A small percentage of the data were digitally processed. These products contain the complete 100-km wide swath of data. (JPL's SEASAT digital processor operated from 1978 to 1982, converting approximately 10 percent of the total SEASAT data set to precision data. JPL currently has no capability to process additional SAR data from SEASAT.)
SASS data were produced by the NASA Goddard Space Flight Center, which processed the Wentz 100-km by 100-km scatterometer data using an objective ambiguity removal scheme.
SMMR output from SEASAT is in the form of calibrated SDRs. Data product volume is 45.7 gigabytes. SMMR data are archived at JPL.
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NASA/Jet Propulsion Laboratory. Seasat. Mission and Spacecraft Library, Internet page. http://spacepc.jpl.nasa.gov/msl/QuickLooks/seasatQL.html.
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NASA/Jet Propulsion Laboratory. Seasat 1978. JPL Imaging Radar, Internet page. http://southport.jpl.nasa.gov/gif/smap.gif.
NASA/Jet Propulsion Laboratory. Seasat altimeter geophysical record. Digital data available from http://podaac.jpl.nasa.gov. Jet Propulsion Laboratory (JPL) Physical Oceanography Distributed Active Archive Center (PO.DAAC), NASA, California Institute of Technology, Pasadena, CA.
NASA/Jet Propulsion Laboratory. Seasat (ocean monitor). Internet page. http://www.jpl.nasa.gov/mip/info/seasat.txt.
Zwally, H. Jay, Anita C. Brenner, Judith A. Major, Thomas V. Martin, and Robert A. Bindschadler. 1990. Satellite radar altimetry over ice. NASA Reference Publication 1233(1): 1.
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February 3, 1998
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