DORIS is a French satellite system used for the determination of

satellite orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

s (e.g.

TOPEX/Poseidon TOPEX/Poseidon was a joint satellite altimeter mission between NASA, the U.S. space agency; and CNES, the French space agency, to map ocean surface topography. Launched on August 10, 1992, it was the first major oceanographic research satelli ...

) and for

positioning Positioning may refer to: * Positioning (marketing), creating an identity in the minds of a target market * Positioning theory, a theory in social psychology * Positioning (critical literacy), reader context * Positioning (telecommunications), a t ...

. The name is an acronym of "Doppler Orbitography and Radiopositioning Integrated by Satellite" or, in French, ''Détermination d'Orbite et Radiopositionnement Intégré par Satellite''.

Principle

Ground-based radio beacons emit a signal which is picked up by receiving satellites. This is in reverse configuration to other GNSS, in which the transmitters are space-borne and receivers are in majority near the surface of the Earth. A frequency shift of the signal occurs that is caused by the movement of the satellite (

Doppler effect The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who d ...

). From this observation satellite orbits, ground positions, as well as other parameters can be derived.

Organization

DORIS is a French system which was initiated and is maintained by the French Space Agency ( CNES). It is operated from Toulouse.

Ground segment

The ground segment includes about 50-60

ground station A ground station, Earth station, or Earth terminal is a terrestrial radio station designed for extraplanetary telecommunication with spacecraft (constituting part of the ground segment of the spacecraft system), or reception of radio waves fro ...

s, 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. DORIS beacons transmit to the satellites on two UHF frequencies, 401.25 MHz and 2036.25 MHz.

Australian ground segments

There are two active DORIS stations in Australia: * Yatharagga - active * Orroral Valley Tracking Station - no longer active * Mount Stromlo Observatory - currently active, replaced Orroral Valley Tracking station installation

Space segment

The best known satellites equipped with DORIS receivers are the altimetry satellites

Jason-1 Jason-1 was a satellite altimeter oceanography mission. It sought to monitor global ocean circulation, study the ties between the ocean and the atmosphere, improve global climate forecasts and predictions, and monitor events such as El Niño ...

OSTM/Jason-2 OSTM/Jason-2, or Ocean Surface Topography Mission/Jason-2 satellite, was an international Earth observation satellite, Earth observation satellite altimeter joint mission for sea surface height measurements between NASA and CNES. It was the t ...

Jason-3 Jason-3 is a satellite altimeter created by a partnership of the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) and National Aeronautic and Space Administration (NASA), and is an international cooperative mis ...

, and Sentinel-6 Michael Freilich. 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. Other DORIS satellites are the

Envisat Envisat ("Environmental Satellite") is a large inactive Earth-observing satellite which is still in orbit and now considered space debris. Operated by the European Space Agency (ESA), it was the world's largest civilian Earth observation satell ...

, SPOT, HY-2A and

CryoSat-2 CryoSat-2 is a European Space Agency (ESA) Earth Explorer Mission that launched on April 8th 2010. CryoSat-2 is dedicated to measuring polar sea ice thickness and monitoring changes in ice sheets. Its primary objective is to measure the thinnin ...

satellites.

Positioning

Apart from orbit determination, the DORIS observations are used for positioning of ground stations. The accuracy is a bit lower than with

GPS The Global Positioning System (GPS), originally Navstar GPS, is a Radionavigation-satellite service, satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of t ...

, but it still contributes to the

International Terrestrial Reference Frame The International Terrestrial Reference System (ITRS) describes procedures for creating reference frames suitable for use with measurements on or near the Earth's surface. This is done in much the same way that a physical standard might be descri ...

(ITRF).

References

External links

DORIS presentation on AVISO
website which distributes satellite altimeter data
IDS
International DORIS Service
ESA page for Envisat DORIS
offering technical information and data {{Time signal stations Satellite navigation systems Spacecraft instruments