DORIS is a French satellite system used for the determination of satellite orbits (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 satellite. ...

) and for positioning. 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 ...

). 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 The (CNES; French: ''Centre national d'études spatiales'') is the French government space agency (administratively, a "public administration with industrial and commercial purpose"). Its headquarters are located in central Paris and it is und ...

). It is operated from

Toulouse Toulouse ( , ; oc, Tolosa ) is the prefecture of the French department of Haute-Garonne and of the larger region of Occitania. The city is on the banks of the River Garonne, from the Mediterranean Sea, from the Atlantic Ocean and fr ...

Ground segment

The

ground segment A ground segment consists of all the ground-based elements of a space system used by operators and support personnel, as opposed to the space segment and user segment. The ground segment enables management of a spacecraft, and distribution of pay ...

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 f ...

s, equally distributed over the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...

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 Yatharagga is an area associated with a homestead in the mid west of Western Australia (WA) near Yarragadee Station. It is located about north-west of Mingenew and about south-east of Geraldton. The area is also associated with two Aust ...

- active *

Orroral Valley Tracking Station The Orroral Valley tracking station, was Earth station in Australia, supported Earth-orbiting satellites, as part of NASA's Spacecraft Tracking and Data Acquisition Network (STADAN). It was located approximately 50 km south of Canberra, ...

- no longer active *

Mount Stromlo Observatory Mount Stromlo Observatory located just outside Canberra, Australia, is part of the Research School of Astronomy and Astrophysics at the Australian National University (ANU). History The observatory was established in 1924 as The Commonweal ...

- 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 altimeter joint mission for sea surface height measurements between NASA and CNES. It was the third satellite in a serie ...

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 mi ...

, and

Sentinel-6 Michael Freilich The Sentinel-6 Michael Freilich (S6MF) is a radar altimeter satellite developed in partnership between several European and American organizations. It is part of the Jason satellite series and is named after Michael Freilich. S6MF includes ...

. 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 Spot or SPOT may refer to: Places * Spot, North Carolina, a community in the United States * The Spot, New South Wales, a locality in Sydney, Australia * South Pole Traverse, sometimes called the South Pole Overland Traverse People * Spot (produ ...

, 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 satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite sy ...

, 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