Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS)
DORIS is a dual-frequency Doppler system that can be included as a host experiment on various space missions, Spot-2, -3, -4, -5, Topex/Poseidon, Jason, ENVISAT and Cryosat (planned for early 2005) in the future.
On contrary to most navigation systems, DORIS is based on an uplink device: the receiver is on board the satellite while the transmitters are on the ground. This creates a naturally centralized system, in which the complete set of observations is downloaded from the satellite to the ground centre, from where they are distributed after unified editing.
The system at the present time started operation in 1990. Its permanently tracked network includes 50 beacons evenly distributed on the earth, including stations on all major tectonic plates.
The station positioning results have a precision of 1-2 cm, and daily polar motion determinations have a precision of about 1-2 milliarcseconds. The geocenter location can also be precisely monitored at 1-2 cm.
In the IERS, DORIS is represented by the International DORIS Service (IDS).