WEST
WEST (acronym for Western European Satellite Triangulation ) was a geodetic cooperation established in the 1960s between Western European universities and surveying administrations in the field of applied satellite geodesy . It served the goal of making the national surveys of the individual states comparable by means of a superordinate coordinate system. In technical language, this means the determination of transformation parameters for the geodetic datum of each of the participating states.
Earth surveying using satellite triangulation
The measurements were carried out according to the principle of satellite triangulation , in which several satellite stations equipped with special cameras simultaneously (within 0.001 seconds) photograph the same earth satellites against the night star background. The satellites only act as a high target for the formation of precisely measurable triangles, their orbits are not taken into account. After initial test runs with up to 20 ground stations, the majority of the observations took place between 1966 and 1972 at a total of 40 stations in Central and Western Europe.
Above all, bright satellites were measured so that less well-equipped ground stations could also be included in the WEST network. Of the five satellites used, the balloon satellites Echo 1 and Echo 2 were therefore particularly important, with an orbit height of around 1000 km corresponding to the average distances of the satellite cameras . From 1967 the newly launched PAGEOS was also included, although it circled at an altitude of over 4000 km.
The exact measurement of the approximately 1000 successfully simultaneous photo plates with the traces of the satellites and reference stars took place in the participating states, the entire network balancing at the earth measurement institute of Prof. Sigl at the Technical University of Munich . The most important person in charge of the project was Walter Ehrnsperger .
Comparison of terrestrial and satellite networks
By 1975 it was possible to increase the continental accuracy of the European network from 10 to 20 m to a few meters. To determine the exact scale factor, a baseline over 2000 kilometers long was measured in the first-order network of the participating states, which stretched from Norway to Sicily . This was later followed by a transverse baseline from southern England ( Malvern ) to the Graz University of Technology satellite station in Austria. Around 1980, meter accuracy was achieved across the whole of Western Europe.
The technical development of the following period made it possible to further increase the accuracy from the 1990s, which is based primarily on CCD technology for directional measurements. Even higher precision can be achieved today with radio processes (especially GPS ) and laser satellites , namely even a few centimeters intercontinental.
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Remarks
- ↑ The state surveying networks have internal accuracies in the cm to dm range, but they gape at the state borders by several meters, which u. a. is due to the position of their fundamental points (see absolute deviation from the perpendicular ) and different data for the earth ellipsoid .
literature
- W. Ehrnsperger, R.Sigl et al .: Status Report on WEST Satellite Triangulation, EUREF 1968
- Günter Seeber, Satellite Geodesy (590 p., Chapters 5.1 and 5.2). De Gruyter-Verlag, Berlin and New York 1989