Encyclopedia > International Terrestrial Reference System
The International Terrestrial Reference System (ITRS) describes procedures for creating reference frames suitable for use with measurements on or near the Earth's surface. This is done in much the same way that a physical standard might be described as a set of procedures for creating a realization of that standard. The IERS defines a geocentric system of coordinates using the SI system of measurement.
An International Terrestrial Reference Frame (ITRF) is a realization of the IERS. New ITRF solutions are produced every few years, using the latest mathematical and surveying techniques to attempt to realize the IERS as precisely as possible. Due to experimental error, any given ITRF will differ very slightly from any other realization of the ITRF.
Practical navigation systems are in general referenced to a specific ITRF solution, or to their own coordinate systems which are then referenced to an ITRF solution.
The InternationalTerrestrialReferenceSystem (ITRS) constitutes a set of prescriptions and conventions together with the modelling required to define origin, scale, orientation and time evolution of a Conventional TerrestrialReferenceSystem (CTRS).
The ITRS is an ideal referencesystem, as defined by the IUGG resolution No. 2 adopted in Vienna, 1991.
The system is realised by the InternationalTerrestrialReference Frame (ITRF) based upon estimated coordinates and velocities of a set of stations observed by VLBI, LLR, GPS, SLR, and DORIS.
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