United European Leveling Net
The United European Leveling Net ( UELN ; German " United European Leveling Network "), alternative spelling: United European Leveling Network , is a superordinate network of European precision leveling and the future height reference of all state height networks in Europe. It serves less as a utility network than for scientific purposes. It was formed from around 1985 from the most precise leveling lines of the first order and is updated and expanded from time to time.
The first attempt to standardize heights in Europe took place in the middle of the 19th century. As part of the activities of the European level measurement , a parent of 48 loops of the leveling of Bavaria, France, Italy, the Netherlands, Austria, Prussia and Switzerland existing Nivellementsnetz evaluated. At that time, however, the participating countries could not agree on a common zero point for the network.
Recordings of 42 sea levels were also included in the evaluation of the measurements . One result was that the mean water of the Amsterdam Gauge was about 15 cm higher than the mean water of the Genoa Gauge . At that time, the view was still widespread that the sea level coincides exactly with the geoid and therefore no height differences should occur between the various levels. Therefore, the 15 cm difference was assumed to be the result of measurement errors in leveling. Today we know that at least the sign of the height difference was correct, even if the amount was determined to be about half too small. The differences between the sea level and the geoid are known as ocean surface topography and are characterized by currents, wind, temperature differences, different salinity and the like. caused.
In 1954 the IUGG decided to set up a uniform European leveling network called the United European Leveling Network (UELN) or Réseau Européen Unifiéde Nivellement (REUN). The reference point is the Amsterdam level. The measurements are adjusted in geopotential heights in order to strictly take into account the influence of the gravitational field. The UELN is connected to numerous coast gauges and thus allows precise monitoring of the sea level around Europe.
The first network and its evaluation were designated as UELN-55. The lines were still 100 to 200 km apart, because for reasons of computing capacity, not the complete first-order networks of the federal states, but only large, superordinate loops were included in the analysis. The power supply with Finland, Norway and Sweden had to be disconnected from the main network due to insufficient connection measurements and problems in taking into account the postglacial land elevation .
In the 1970s, the UELN-55 data was out of date. In the meantime, new leveling data with greater accuracy were available in many countries. That is why the IUGG General Assembly decided in 1971 to resume the UELN project. Many participating countries provided their complete, current leveling data of the 1st order, other countries continued to supply only thinned-out versions of their leveling networks. Work began in 1973 and the final adjustment took place in 1986. The results were therefore designated as UELN-73/86.
But neither in the 1950s nor in the 1970s it was possible to include the networks of Eastern Europe in the UELN. Instead, in Eastern Europe it was
UPLN / EPNN
Uniform Precise Leveling Network of Central and Eastern Europe (UPLN), also known in German as “Uniform Precision Leveling Network” (EPNN). In the 1950s and 1970s, jointly coordinated leveling campaigns took place in Eastern Europe, which were then evaluated by the Geodetic Service of the USSR in Moscow. The results were transferred to the individual countries as normal heights , based on the Kronstadt gauge , and formed the basis for the national height systems of these countries.
In the 1990s, it was possible for the first time to expand the UELN to Eastern Europe and to create a truly uniform European leveling network. After a resolution of the symposium of the European sub-commission of the International Association of Geodesy (EUREF) in Warsaw in 1994, the work started in 1995 with the same data that were also contained in UELN-73/86. In the following years the network was gradually expanded to the east. At the same time, obsolete measurement data from Western Europe were replaced by current data. The UELN-95 contains the complete first-order level nets of the respective countries. The first results were given to the participating countries in 1999 under the name UELN-95/98.
The work on the UELN-95 prompted EUREF to define the European Height Reference System (EVRS) in 2000 . Since then, the UELN has formed the basis for the implementation of the EVRS, which is known as the European Vertical Reference Frame (EVRF). So far the EVRF2000, the EVRF2007 and the EVRF2019 have been calculated at the Federal Agency for Cartography and Geodesy .
More recent edits aim at a pan-European solution whose reference system is the European quasigeoid instead of the geoid . Gradually, all states with their different height references are to switch to this uniform system.
- Wolfgang Torge: Geodesy , chap. 7.2 Vertical Control Networks . De Gruyter, Berlin / New York 2001
- Heribert Kahmen: Applied Geodesy; Surveying , 20th edition, de Gruyter, Berlin 2006, ISBN 978-3-11-018464-8
- Kneißl, M .: The formation of a uniform European leveling network, Zeitschrift für Vermessungswesen No. 9/1955, pp. 278–295
- Sea topography . Website Spektrum.de. Retrieved March 24, 2020
- Klug, A .: Investigations in the Western European mountain network. Diploma thesis, Geodetic Institute of the TU Dresden. 1994
- Augath, W., Ihde, J .: Definition and Realization of Vertical Reference System The European Solution EVRS / EVRF 2000. Proceedings of the "XXII FIG International Congress", April 19 to 26, 2002, Washington, DC
- Lang, H., Steinberg, J .: On the development of the height networks on the territory of the new federal states. General survey news. 8-9 / 1993
- Results of the Adjustment of the United European Leveling Network 1995 (UELN-95/98) - Report by the UELN data center website Federal Agency for Cartography and Geodesy. Retrieved March 24, 2020