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Developed in the 1980s by CNES in partnership with the French space geodesy research centre GRGS and the French mapping and survey agency IGN, the DORIS system performs two functions. First, it determines satellite orbits with centimetre accuracy thanks to a network of 60 ground stations around the globe. Second, it is able to calculate the position of any point on Earth’s surface with the same degree of precision. Such pinpoint accuracy serves many applications, like for example the ability to measure variations in sea level or ice sheet height, to monitor ground displacement, to gauge continental drift or precisely locate orbiting satellites.
The DORIS system relies on the well-known Doppler effect, a phenomenon we perceive when the pitch of a siren on a vehicle gets higher as it approaches and then lower as it moves away. DORIS employs the same principle to locate the position of an object emitting radio waves. Data collected by DORIS are processed by the SSALTO multimission ground segment in Toulouse, developed by CNES. DORIS was tested for the first time on the SPOT 2 satellite launched on 22 January 1990. Since then, the system has flown on many more satellites, including Envisat and the Jason and Pleiades series.