DORIS stands for Doppler Orbitography and Radiopositioning Integrated by Spacecraft. The antenna shown here is connected to the DORIS receiver inside the Instrument Module. The function of the receiver is to listen for signals from ground stations. By using the Doppler shift of these signals the satellite's position can be determined.
Currently, the CNES DORIS system has about fifty ground beacons distributed evenly around the globe. DORIS measurements are taken about every ten seconds.
Combining the DORIS information with that of the Laser Ranging System gives TOPEX/Poseidon an unprecedented precision orbit determination capability.
