Doppler Orbitography and Radiopositioning Integrated by Satellite
The Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) is a French satellite system designed by Centre National d'etudes Spatiales (CNES), in partnership with France's mapping and survey agency Institut Geographique National (IGN). The system was designed primarily as a means of determining a satellite's orbit, but has been used for a wider range of applications such as precise positioning and measuring the flow of glaciers.
How it works
A DORIS beacon is installed on the ground, the beacon then transmits a radio signal which is received by a passing satellite. The observed frequency shift of the signal due to the satellite's motion can then be used to calculate the satellites orbit, ground positions of the DORIS beacon and numerous other geophysical parameters.
There are approximately 50-60 stations distributed around the world. Geoscience Australia has two installations located at Mount Stromlo , Canberra, Australian Capital Territory, and Yarragadee of Western Australia. A typical DORIS ground station is composed of a beacon (there are three different generations), an omni directional antenna and a set of optional meteorological sensors for the measurement of pressure, temperature and humidity. The beacons transmit on two different frequencies 2036.25 MHz and 401.25 MHz which are modulated to send messages containing ID number, timing information, data from meteorological sensors and engineering data.
The orbit produced from the DORIS system is at the centimetre level, making it ideal for satellite missions that observe the ocean's topography.
DORIS has been used to determine the orbit of satellite missions such as Spot 2, Spot 3, Spot 4, Topex/Poseidon, Spot 5, Jason-1, Jason-2 and Envisat. DORIS is also planned to be used on Pleides, Cryosat, Saral, and HY-2 missions.