GEOSAT data available soon


  • Robert Cheney


GEOSAT altimeter data collected after November 8, 1986, will be made available to the general research community by the National Oceanic and Atmospheric Administration (NOAA) beginning in early 1987. Although GEOSAT has been operating since April 1985, observations from the first 18 months are classified. In October 1986 the satellite was maneuvered into a 17-day exact repeat orbit whose ground track coincides with the previous Seasat altimeter tracks, allowing new GEOSAT data to be unclassified. Under agreement reached with the U.S. Navy and the Johns Hopkins University Applied Physics Laboratory (Laurel, Md.), NOAA will assume responsibility for generating the unclassified data sets from this Exact Repeat Mission (ERM). Doppler tracking data will first be evaluated by the Naval Astronautics Group (NAG) to ensure that the GEOSAT ground track has deviated by no more than 1 km (cross track) from the exactrepeat orbit. On-board thrusters will be fired when necessary (approximately monthly) to maintain colinearity. Raw data in, the form of sensor data records (SDRs) will then be transmitted to a NOAA processing facility in Rockville, Md., where they will be converted to finished geophysical data records (GDRs). SDR-to-GDR production consists of merging the altimeter data with an ephemeris provided by NAG and adding correctionfields for tides, troposphere (wet and dry components), and ionosphere. Completed GDRs will be sent to NOAA National Environmental Satellite Data and Information Service (NESDIS) in Washington, D.C., where they will be made avilable to the public. (GEOSAT data will initially be distributed to U.S. institutions only; foreign institutions are advised to seek access through formal embassy channels.)