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Coordinate Systems

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Title Coordinate Systems
Author(s) J. Sanz Subirana, J.M. Juan Zornoza and M. Hernández-Pajares, Technical University of Catalonia, Spain.
Level Basic
Year of Publication 2011

To describe satellite motion, observables and models it is necessary to have a well-defined and reproducible reference coordinate system. Since the accuracy in satellite systems and the precision requirements are tight, these reference systems have to be accurate as well.

It is important to note the difference between Reference System and Reference Frame, two different concepts. The first one is understood as a theoretical definition, including models and standards for its implementation. The second one is its practical implementation through observations and a set of reference coordinates, e.g. a set of fundamental stars, for a Celestial Reference Frame, or fiducial stations, for a Terrestrial Reference Frame.

The International Celestial Reference System (ICRS) was proposed by the International Earth Rotation and Reference Systems Service (IERS) and formally accepted by the International Astronomical Union (IAU) in 1997. A realization of the ICRS is the International Celestial Reference Frame (ICRF). On the other hand, IERS is in charge of defining, realizing and promoting the International Terrestrial Reference System (ITRS). Realizations of ITRS are the International Terrestrial Reference Frames (ITRFs), being the ITRF2005 the current reference realization of ITRS.