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The Geodynamics and Earth Ocean Satellite 3 (GEOS 3) platform was part of a geodetic mission series in the 1970s. The spacecraft carried a radar altimeter for mapping of the oceans, as well as a laser retroflector and other tracking beacons.

The goals of GEOS-3 were to measure the gravitational field around the Earth, specifically to identify the irregularities and anomalies. Gravitational anomalies over the ocean also can be used to measure large mesoscale circulation.

Altimeter data from GEOS-3 became part of the GEM-T3, JGM-1, and JGM-2 gravity models. In addition, satellite laser ranging (SLR) data to GEOS-3 and satellite-to-satellite Doppler tracking data from the geostationary satellite ATS-6 were also included in these models. During the development of the prelaunch TOPEX gravity models, GEOS-3 was considered to be an important platform, since it was located near the mirror inclination of TOPEX/POSEIDON (66.6 deg).

The geopotential model EGM96 included GEOS-3 SLR data, as well as combined SLR and satellite-to-satellite tracking data from ATS-6.

Learn more about GEOS-3

Type

Earth Observation Satellite

Data Center

PO.DAAC

Launch

April 9, 1975

Objective

Measure Earth's gravitational field
Inclination115°
Perigee824 km
Apogee856 km
Period101.82 minutes
Eccentricity0.00115

The following instruments flew aboard GEOS 3:

  • Two C-band antenna – Used to determine what the accuracies would be for gravimetric and geometric measurements.
  • S-band tracking system – Consisted of an ATS and Earth viewing antennae, diplexer, and transponder. The transponder operated in three modes: satellite-to-satellite tracking, direct unified S-band, and Goddard Range and Range Rate ground-station tracking.
  • Radar altimeter – Ku band altimeter, it was the first altimeter to measure sea surface height.
  • Doppler beacon – Dual frequency (162 and 324 MHz) Doppler used to measure ionosphere.
  • Retroreflector array – Used to calculate the orbit by using ground laser ranging.

Instruments Aboard GEOS-3

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