Geodetic Reference System 1980
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| Geodetic Reference System 1980 | |
|---|---|
 U.S. Government · Public domain · source | |
| Name | Geodetic Reference System 1980 |
| Acronym | GRS 80 |
| Developed | 1979–1980 |
| Authority | International Association of Geodesy |
| Type | reference ellipsoid |
| A | 6378137.0 m |
| F | 1/298.257222101 |
Geodetic Reference System 1980 is a reference ellipsoid and associated set of geodetic constants developed to provide a consistent global framework for Earth measurement and mapping. It supplies numerical values for the Earth's equatorial radius, flattening, and gravitational constants that underlie modern International Terrestrial Reference Frame realizations, satellite geodesy, and hydrographic surveying. GRS 80 informed standards adopted by bodies such as the International Association of Geodesy, International Union of Geodesy and Geophysics, and national agencies including the National Geospatial-Intelligence Agency, United States Geological Survey, and Ordnance Survey.
Overview
GRS 80 was produced to harmonize values used in high-precision tasks across organizations such as the International Civil Aviation Organization, International Hydrographic Organization, North Atlantic Treaty Organization, and national mapping agencies like Institut Géographique National and Bundesamt für Kartographie und Geodäsie. It complements contemporary reference frames like the World Geodetic System and informed work by research institutions including Jet Propulsion Laboratory, National Aeronautics and Space Administration, and the European Space Agency. GRS 80's constants are integral to models used by global programs such as Global Navigation Satellite System constellations including Global Positioning System, GLONASS, Galileo, and BeiDou.
Definition and parameters
GRS 80 defines the Earth's shape as an oblate spheroid with specific parameters: the semi-major axis a = 6378137.0 metres and the reciprocal flattening 1/f = 298.257222101. It also provides the geocentric gravitational constant GM, the dynamical form factor J2, and the normal gravity formula parameters used by agencies like International Hydrographic Organization and survey organizations including Geoscience Australia. These parameters were chosen to be compatible with satellite tracking results from programs such as Lageos and missions supported by National Oceanic and Atmospheric Administration and Scripps Institution of Oceanography.
Mathematical formulation and constants
The principal GRS 80 constants include the semi-major axis a, flattening f, geocentric gravitational constant GM = 3986005×10^8 m^3 s^−2 (nominal value), and angular velocity of rotation ω. The ellipsoid's eccentricity e is derived from f by e^2 = 2f − f^2, a relation used in potential theory applied in work at Institut des Sciences de la Mer, Helsinki University of Technology, and University of Bern. The normal gravity formula on the ellipsoid is expressed using constants chosen for consistency with observations from Very Long Baseline Interferometry, Satellite Laser Ranging, and Doppler missions like Transit satellite system.
Realizations and reference frames
Realizations of GRS 80 have been implemented within terrestrial reference frames such as International Terrestrial Reference Frame (ITRF) and regional frames like European Terrestrial Reference System 1989 (ETRS89), North American Datum 1983 (NAD83), and national datums maintained by institutions including Geoscience Australia and Natural Resources Canada. Techniques employed in these realizations include Very Long Baseline Interferometry, Global Navigation Satellite System observations, Satellite Laser Ranging, and gravimetry campaigns performed by groups like Bureau Gravimétrique International and National Geodetic Survey.
Applications in geodesy and navigation
GRS 80 underpins transformations and projection systems used by mapping agencies such as Ordnance Survey, Institut Cartogràfic de Catalunya, and Instituto Geográfico Nacional (Spain), and supports navigation services operated by Federal Aviation Administration, Maritime and Coastguard Agency, and commercial providers including TomTom and Esri. It is used in geoid modeling efforts by research centers including University of Texas at Austin and German Research Centre for Geosciences for precise orthometric height determination applied in coastal engineering, surveying for Panama Canal works, and infrastructure projects coordinated with agencies like World Bank and Asian Development Bank.
Comparison with other geodetic systems
GRS 80 is closely related to but distinct from the World Geodetic System 1984 ellipsoid parameters used by Global Positioning System operational products; both share the same semi-major axis but differ slightly in derived constants and usage in datums such as NAD83 and WGS 84. Other historical ellipsoids include the Clarke ellipsoid, Hayford ellipsoid, and International 1924 ellipsoid, which were adopted by national mapping authorities like Survey of India and Geodetic Survey of Canada before global satellite techniques motivated adoption of GRS 80 and WGS 84.
History and development
Development of GRS 80 was a collaborative effort in the late 1970s and formalized in 1980 by committees of the International Association of Geodesy, drawing on data from satellite missions overseen by National Aeronautics and Space Administration, earth tide studies from Bureau International des Poids et Mesures, and oceanographic contributions from Scripps Institution of Oceanography and Woods Hole Oceanographic Institution. Its adoption by standards bodies such as International Organization for Standardization and operational institutions like United States Coast and Geodetic Survey marked a transition from regional classical geodesy to a global, satellite-era framework used by contemporary projects including GEOSAT altimetry and TOPEX/Poseidon.