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International Earth Rotation and Reference Systems Service
Glossary
The following terms are related to the IERS and to Earth rotation and reference systems in general.
Additions will follow, proposals are welcome.
datum
(plural datums) A geodetic reference frame. In surveying and geodesy, a datum is a set of reference points on the Earth's surface, and (often) an associated model of the shape of the Earth (reference ellipsoid) used to dene a geographic coordinate system. Horizontal datums are used to describe the location of a point on the Earth's surface, in latitude and longitude or other appropriate coordinates. Vertical datums are used to describe site elevations or depths.
DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite), a dual-frequency Doppler system, is used to determine geodetic positions from analyses of data transmitted from the sites of articial satellites. Receivers are on board specialized satellites while the transmitters are on the ground. The complete set of observations is downloaded from the satellite to the ground centre for analysis.
