- Fundamental station
A Fundamental point (in German "Fundamentalpunkt") is the geometric origin of a
geodetic network and defines the geodetic datum of anational survey .Some fundamental stations are an astronomical or satellite geodetic
observatory . In any case, thegeographic latitude andlongitude of the station is precisely determined by methods ofastrogeodesy and is chosen asellipsoid alö latitude and longitude at theEarth ellipsoid which is used to calculate the coordinates of the whole network.Also, precise
azimuth s to one or two nework points are observed, and are taken over as orientateddirection s of these network lines. By these procedure, the polar axis of the reference ellipsoid becomes parallel to theEarth rotation axis, and therefore thevertical deflection of the fundamental point is "zero".The term Fundamental station is used for special observatories which combine several
space positioning techniques likeVLBI ,Satellite Laser Ranging ,GPS ,Glonass etc. They are the basis ofPlate tectonic analyses which allow themonitoring ] ofcontinental drift rates with accuracies of mm/year.Important fundamental stations in
Europe are
*Grasse , centralFrance
*Graz -Lustbühel (Austria )
*Malvern , England (?)
*Onsala (largeRadio telescope ), Sweden
*Wettzell (20m Radio telescope) in the Bayerischer Wald,Germany
*Zimmerwald near Berne,Switzerland .Worldwide about 30 fundamental stations are existing - about 5 in the
USA and inGUS countries, 2-3 in South America, Africa, Eastern Asia, Australia and Antarctica.The basic
coordinate system is theITRF reference frame, which is related to theICRS celestialinertial system by means of very preciseEOP s (Earth orientation parameters, containingpolar coordinate s,Nutation - andEarth rotation parameters. The ITRF data set is revised every 3-5 years, the actual accuracy is in themillimeter area. The ITCS is based on about 500Quasar s in the far universe, and on some 3000fundamental star s of ourgalaxy . The actual coordinates of the latter (FK6 ) were published in 2000 by theAstronomisches Rechen-Institut (ARI) inHeidelberg .External links
* [http://www.wettzell.ifag.de/ Fundamentalstation Wettzell, Bavaria]
* [http://www.wettzell.ifag.de/publ/FGS/FGS_wettzell.html Two Fundamental stations at the southern hemisphere (german website)]
* [http://www.ari.uni-heidelberg.de/publikationen/vhd/vhd035/fulltext/gifframe.htm Fundamental system FK6, Astronomisches Rechen-Institut (ARI), 1999]
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