The DORIS system
In the early 1990s, CNES developed the DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) space system. Its initial mission was to carry out high-precision orbitography of altimetry satellites, primarily Topex/Poseidon. DORIS quickly made its mark as a new space geodesy technique for precise positioning as well as measuring the horizontal (tectonic plates) and vertical motions of the Earth's crust, for measuring polar motion and motion of the Earth's center of mass.
The DORIS system comprises a permanent network of about fifty emitting beacons evenly distributed on the Earth's surface, and a satellite-borne receiver. The radioelectric signals constantly emitted by the ground beacons, are received by the satellite with a frequency shift compared to the emission frequency (Doppler effect).
The first DORIS instrument was placed aboard the Spot-2 satellite launched in January 1990 as an experimental payload. It is still operating nominally. Several other DORIS instruments were developed for the Spot-3 (1993-1996), Topex/Poseidon (1992-2006) and Spot-4 (1998-), Jason-1 (2001-), Envisat (2002-) and Spot-5 satellites.
The space positioning results achieved prompted IERS (International Earth Reference Service) to start using DORIS in 1996 in conjunction with Laser, GPS and VLBI techniques to determine and maintain the terrestrial reference system. The GOHS team has been the IERS analysis centre for the DORIS system since that date, in collaboration with CLS (Collecte Localisation Satellite).
See "Recent results".".