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- How DORIS works (figure curtsey of CNES)
- © CNES
The Doppler Orbitography and Radio positioning Integrated by Satellite (DORIS) was developed by the French CNES, Institut Géographique National (IGN) and Groupe de Recherche en Géodésie Spatiale (GRGS) to meet scientific and operational user requirementsin very precise orbit determination. Although the DORIS system was primarily designedfor the precise orbit computation required for observing the oceans by altimetry missions, the unique network of ground stations and its highly accurate positioning capability have also played a great role for geodesy and geophysical applications. This includes measuring continental drift, fitting the local geodetic network, monitoring the geophysical deformations, determining the rotation and the gravity parameters of the Earth, and contributing to the realization of an international terrestrial reference system. Due to the fact that the DORIS system uses two different frequencies for its measurement, it is capable of monitoring the ionosphere as well.
The basic principle of the DORIS system is based on the accurate measurement on board the Space craft of the Doppler shift of radio frequency signals emitted by ground beacons. Measurementsare made on two frequencies: ~2 GHz and 400 MHz. About 56 ground beacon stations transmit dual frequency signals from locations distributed all over the world. The satellites carrying the DORIS receivers include Jason, Topex, Envisat, SPOT 2, SPOT 4, and SPOT 5. These satellites are at the range of 800- 1,336 km altitude. The ionospheric products deduced from the Doppler measurements are recorded at each count interval of about 10 sec, and are used to derive the ionospheric TEC. The ionospheric corrections are available at the CDDIS website (CDDIS, 2011). For more details on DORIS mission refer to Fleuryet al. (1991) or Yin & Mitchell (2011), or the International DORIS Service (IDS) website (http://ids-doris.org/ ).
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