A so-called beacon is installed on the ground and emits a radio signal, which is received by the satellite. A frequency shift of the signal occurs that is caused by the movement of the satellite (Doppler effect). From this observation satellite orbits, ground positions, as well as other parameters can be derived.
There are about 50-60 stations equally distributed over the earth and ensure a good coverage for orbit determination. For the installation of a beacon only electricity is required because the station only emits a signal but does not receive any information. Therefore it is possible to install beacons in remote areas such as the Mount Everest base camp.
The best known satellites equipped with DORIS are the altimetry satellites TOPEX/Poseidon, Jason 1 and Jason 2. They are used to observe the ocean surface as well as currents or wave heights. DORIS contributes to their orbit accuracy of about 2 cm.
Apart from orbit determination, the DORIS observations are used for positioning of ground stations. The accuracy is a bit lower than with GPS, but it still contributes to the International Terrestrial Reference Frame (ITRF).
- G. Seeber: Satellite Geodesy. De Gruyter-Verlag, 2. Auflage (590p.), Berlin 2003