Global Positioning System Reference
In-Depth Information
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C HAPTER 2
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G EODETIC REFERENCE SYSTEMS
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——
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It becomes increasingly important to focus on the definition of reference frames as
accuracy of geodetic space techniques increases. There are three types of frames we
are concerned with—the earth-fixed (international terrestrial reference frame, ITRF)
frame, the space-fixed (international celestial reference frame, ICRF) frame, and the
geodetic datum. Of course, we also need to be able to transform between the frames.
To satisfy the needs of scientists for a clear definition of coordinates, as well as to
explore fully the phenomenal increase in accuracy of geodetic space techniques,
the definition and maintenance of these reference frames in connection with the
deformable earth has become a science in itself. Current solutions have evolved over
many years, with contributions from the best scientific minds. The literature is rich
in contributions that document the interdisciplinary spectrum and depth needed to
arrive at solutions.
The International Earth Rotation Service (IERS) is responsible for establishing and
maintaining the ITRF and ICRF frames, whereas typically a national geodetic agency
is responsible for establishing and maintaining the datum. The IERS relies on the
cooperation of many research groups and national agencies to accomplish its tasks.
The International Astronomical Union (IAU) and the International Union of Geodesy
and Geophysics (IUGG) established the service in 1988. The IERS maintains a central
bureau that is responsible for the general management of the IERS and is governed by
a directing board. The conventions underlying the ITRF and the ICRF are published in
McCarthy (1996). They are currently completing revision and will become available
as IERS Conventions 2000. The old and new conventions are posted at the IERS
(2002). McCarthy (1996) is the principal reference for this chapter. For additional
details, please consult the many references listed in that publication.
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