Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) is a satellite tracking system designed by CNES as a new system to provide precise orbits on-board low Earth orbit satellites.
The relative motion of a satellite with respect to the beacon(s) in view induces a shift in the frequency due to the Doppler effect. This shift is directly proportional to the radial speed of the satellite with respect to the beacon. By combining this information with knowledge of the location of each beacon, it is then possible to derive the orbit of the satellite.
Sentinel-3 is equipped with a new-generation (multi-channel and digital) receiver developed by CNES, as a Customer Furnished Instrument (CFI) which is able to track up to seven beacons simultaneously. Real-time accuracy is 5 - 10 cm.
Figure 1: DORIS instrument (Credit: ESA)
Figure 2: DORIS antenna (Credit: ESA)