The termfundamental station is used for special observatories which combine severalspace positioning techniques likeVLBI,satellite laser ranging,GPS,Glonass, etc. They are the basis ofplate tectonic analysis, allowing the monitoring ofcontinental drift rates with millimetre accuracies. Afundamental point is the geometric origin of ageodetic network and defines thegeodetic datum of anational survey.[1]
Some fundamental stations are an astronomical or satellite geodeticobservatory. Thegeographic latitude andlongitude of the station is precisely determined by methods ofastrogeodesy and is chosen asellipsoidal latitude and longitude at theEarth ellipsoid which is used to calculate the coordinates of the whole network.
Also, preciseazimuths to one or two network points are observed, and are taken over as orientateddirections of these network lines. By these procedures, the polar axis of the reference ellipsoid becomes parallel to theEarth rotation axis, and therefore thevertical deflection of the fundamental point is zero.
Important fundamental stations include:
Worldwide about 30 fundamental stations are in existence: about 5 in the United States and inCommonwealth of Independent States countries, and 2–3 in South America, Africa, Eastern Asia, Australia and Antarctica.[citation needed]
The basiccoordinate system is theITRF reference frame, which is related to theICRS celestialinertial system by means of very preciseEarth Orientation Parameters (EOPs), containingpolar coordinates,Earth rotation andnutation 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 500quasars in the far universe, and on some 3000fundamental stars of ourgalaxy. The actual coordinates of the latter (FK6) were published in 2000 by theAstronomisches Rechen-Institut (ARI) inHeidelberg.
