DORIS is a French satellite system used for the determination of satellite orbits (e.g. TOPEX/Poseidon) 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 A satellite navigation or satnav system is a system that uses satellites to provide autonomous geopositioning. A satellite navigation system with global coverage is termed global navigation satellite system (GNSS). , four global systems are op ...

, 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 (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. The ''Doppler effect'' is named after the physicist Christian Doppler, who described ...

). 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 CNES () is the French national space agency. Headquartered in central Paris, the agency is overseen by the ministries of the Armed Forces, Economy and Finance and Higher Education, Research and Innovation. It operates from the Toulouse Spac ...

). It is operated from

Toulouse Toulouse (, ; ; ) is a city in southern France, the Prefectures in France, prefecture of the Haute-Garonne department and of the Occitania (administrative region), Occitania region. The city is on the banks of the Garonne, River Garonne, from ...

Ground segment

The

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

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 fr ...

s, equally distributed over the

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

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 Aus ...

- active *

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

- 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 TOPEX/Poseidon, Jason-1, OSTM/Jason-2,

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. 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 Earth-observing satellite which has been inactive since 2012. It is still in orbit and considered space debris. Operated by the European Space Agency (ESA), it was the world's largest civilian Ear ...

, SPOT, HY-2A and CryoSat-2 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, 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 descr ...

(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