The term fundamental station is used for special observatories which combine several space positioning techniques like VLBI, satellite laser ranging, GPS, Glonass, etc. They are the basis of plate tectonic analysis, allowing the monitoring of continental drift rates with millimetre accuracies. A fundamental point is the geometric origin of a geodetic network and defines the geodetic datum of a national survey.Gupta, Harsh (ed) (2021) Encyclopedia of Solid Earth Geophysics Springer p329
Some fundamental stations are an astronomical or satellite geodetic observatory. The geographic latitude and longitude of the station is precisely determined by methods of astrogeodesy and is chosen as ellipsoidal latitude and longitude at the Earth ellipsoid which is used to calculate the coordinates of the whole network.
Also, precise azimuths to one or two network points are observed, and are taken over as orientated directions of these network lines. By these procedures, the polar axis of the reference ellipsoid becomes parallel to the Earth rotation axis, and therefore the vertical deflection of the fundamental point is zero.
Important fundamental stations include:
Grasse Métrologie Optique (MéO) observatory, France Graz-Lustbühel, Austria Herstmonceux Geodetic Observatory, EnglandNERC Herstmonceux Science and Technology Facilities Council Onsala Space Observatory, Sweden Metsähovi Radio Observatory, FinlandDrewes, Hermann (2009) Geodetic Reference Frames IAG p101 Geodetic Observatory Wettzell, GermanyGeodetic reference system enables highly accurate positioning Technical University of Munich, 2016 Zimmerwald Observatory, Switzerland Goddard Geophysical and Astronomical Observatory, U.S.Goddard Geophysical and Astronomical Observatory NASA Hartebeesthoek Radio Astronomy Observatory, South Africa Yarragadee Geodetic Observatory, Australia.Yarragadee: the ‘geodetic supersite’ in the West Australian desert Geoscience Australia, 2023
Worldwide about 30 fundamental stations are in existence: about 5 in the United States and in Commonwealth of Independent States countries, and 2–3 in South America, Africa, Eastern Asia, Australia and Antarctica.
The basic coordinate system is the ITRF reference frame, which is related to the ICRS celestial inertial system by means of very precise Earth Orientation Parameters (EOPs), containing polar coordinates, Earth rotation and nutation parameters. The ITRF data set is revised every 3–5 years, the actual accuracy is in the millimeter area. The ICRS is based on about 500 quasars in the far universe, and on some 3000 fundamental stars of our galaxy. The actual coordinates of the latter (FK6) were published in 2000 by the Astronomisches Rechen-Institut (ARI) in Heidelberg.
References
External links Fundamentalstation Wettzell, Bavaria Two Fundamental stations at the southern hemisphere (german website) Fundamental system FK6, Astronomisches Rechen-Institut (ARI), 1999