Austrian Geodetic Commission

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The Austrian Geodetic Commission ( ÖGK ), until the 1990s Austrian Commission for International Geometric Surveying (ÖKIE), is a specialist commission for higher geodesy and neighboring geosciences in Vienna .

Since around 2000 it has also acted as the Austrian National Committee (ÖNK) for the International Union for Geodesy and Geophysics .

Field of activity

The field of activity of the commission was above all a scientifically based land survey , the determination of the best adjacent ellipsoid and the theoretical earth figure (see also geoid determination ), the further development of mathematical cartography and the compensation calculation , questions of the earth's rotation, polar movement and geodynamics , as well as relevant cross-connections to geophysics and astronomy.

history

The Austrian Commission for International Earth Measurement (ÖKIE) was founded in 1863 under the name Gradmessungskommission . It was the first expert commission of a state for higher geodesy worldwide .

It was founded at a time when geodesy was increasingly becoming detached from astronomy, which had dominated "geo-metry" (earth measurement), and the purely geometric to intuitive methods of geosciences were enriched by strictly physical analyzes of the earth's gravity field .

Nevertheless, some astronomers (as well as geophysicists ) can be found among the chairmen of the ÖKIE . The commission was - together with German geodesists - the initiator of the "International Earth Measurement", which shortly after the publication of the famous Bessel ellipsoid was looking for ways to derive not only an ellipsoid suitable for Eurasia from the surveying networks that meanwhile cover all continents , but also an "earth ellipsoid" averaged over the entire globe.

Based on a worldwide data collection to which Austria-Hungary made a decisive contribution, FR Helmert in Berlin succeeded for the first time in 1906, but this earth ellipsoid did not prevail against the Hayford ellipsoid determined in the USA in 1908 . In 1965 the satellite geodesy showed that it was too big by 220 m. The ellipsoid dimensions, which were better adapted to Central Europe, were used as the reference system for the then most precise meridian arc in the world, the approximately 500 km long Grossenhain- Kremsmünster - Pola geotraverse .

The long-term most important project of the Austrian and German geothermal measurements was the beginning merger of the land surveys of Central Europe , which in view of the many thousands of trigonometric points to be calculated together and two world wars did not lead to the first version of a " European network " until 1950 . Another world premiere was the geoid from 1951/53, which covers all of Austria and which Josef Litschauer calculated over many years. The surveying and gravity field data, which are essential for this and for the European network, largely originate from the period 1870–1915, when the Military Geography Institute (MGI) of the then 50 million state was able to fall back on many top staff and a large budget. During the German occupation from 1938 to 1945, the ÖKIE was dissolved.

At the turn of the century and since the end of World War II , the commission had an average of about 20 members: 7-10 professors from the geodetic institutes, civil engineers , representatives of geophysics , astronomy and the academy , as well as 2-3 senior officials from the Federal Surveying Service (today Federal Office for Metrology and Surveying ).

President was mostly a geodesist, but some came from neighboring disciplines. To mark its centenary in 1963, ÖKIE and IAG organized a one-week international symposium in the Vienna Hofburg , in which 500 scientists took part.

To mark its centenary, the ÖKIE published not only the usual conference reports, but also its 24th special issue of the ÖZV , the main content of which was the state of scientific geography from the point of view of Karl Ledersteger . He called his 95-page long contribution " The re-establishment of the theory of spheroidal equilibrium figures and the normal spheroid of the earth ". The discrepancies that emerged at the time between the methods of geometric and physical satellite geodesy were clarified 20–25 years later with the first altimetric geoid determination and the Global Positioning System .

Satellite network and geoid

These space-based techniques and the associated theories , to which the later ÖKIE President Helmut Moritz (Graz University of Technology) made a significant contribution, brought the entire geodesy onto the “international track” sketched out by Ledersteger in 1964. In 1973/74 the world network of satellite triangulation was completed, to which the small Austria (0.1% of the world population) contributed about 1% of the measurements, among other things in the trans-European geotraverse Tromsø-Hohenpeißenberg-Catania. Around 1980 members of the ÖKIE under the leadership of Hans Sünkel developed the method of geodetic collocation , which revolutionized geoid determination worldwide. In 1982/83 the commission headed by Karl Rinner was once again good for a world first: for the first time an astrogeoid achieved an average accuracy of ± 5 cm (state of the art in the western industrialized countries was ± 10–15 cm).

This precise gravity field determination is based on a network of 700 vertical deviations , which are only 10–15 km apart, even in high mountains ; the employees of several university institutes and the BEV carried out measurement campaigns with the Ni2 astrolabe and other instruments that lasted 4-6 years. Most of the measurements came from G. Gerstbach, K. Bretterbauer and T. Matausch (TU Vienna), from E. Erker (BEV), G. Chesi and H. Lichtenegger (TU Graz) and from employees of the University of Innsbruck. When the resulting geoid solution really turned out to be accurate to within 5–6 cm, the leading German geodesist Wolfgang Torge (Hanover) gave the motto to strive for a “ centimeter geoid ” for Central Europe over the next 25 years . To date, however, it has only come close to being achieved in the German-speaking countries.

These internationally recognized successes earned the then ÖKIE President K. Rinner the title of universal scholar of geosciences at an IAG congress . As a reminder of this, Rinner allowed the Festschrift published in 1983 to receive the title Geodaesia Universalis on his 70th birthday . It brought together a total of 40 scientific articles from international sources on 400 pages.

Global Positioning System

These interdisciplinary and transnational developments were crowned from around 1990 by the fact that GPS technology not only achieved centimeter accuracies locally in a short time, but also penetrated this area globally . At the Hamburg Congress of the International Association of Geodesy in 1983, there was still a heated discussion as to whether the new GRS world ellipsoid (large axis a = 6,378,137.0 meters) propagated by H. Moritz was 50 cm too big or too small. Almost no one believed in the rapid development of satellite geodesy at the time.

In the 1990s, the ÖKIE received its current name - based on the German Geodetic Commission , with which there has always been an intensive exchange. At the same time, the ÖKIE intensified specialist contacts to geophysics , which was a logical consequence of the final recognition of plate tectonics and the geophysical implications in the gravitational field . It finally merged with geophysics to form the National Committee for Geodesy and Geophysics in order to take into account the interdisciplinary orientation of the international Union for Geodesy and Geophysics .

Also in the 1990s, what is now the ÖGK set itself an ambitious goal: the next Austrian geoid determination , under the name Austrian Geoid 2002, was to achieve an accuracy range of 2 cm and thus come close to Torge's vision of 1983. At the Graz University of Technology , a group under Hans Sünkel and N. Kühtreiber began to work on a combination solution of astrogeoid and gravimetry , for which several data gaps in Styria as well as on some borders to the former Eastern Bloc and in western Austria had to be closed.

Some of the measurement campaigns proposed for this project fell victim to budget cuts, so the accuracy turned out to be a third less than hoped. It was possible to request the geoid solutions for Slovenia and parts of Hungary and Croatia , so that the central part of the former monarchy now has a 3 cm geoid. In the meantime, Switzerland had based itself on the example of Austria and even condensed its vertical deviation network to a 10 km grid. The current 2 cm geoid allows extensive use of GPS for an economic determination of heights in the mountains. In Austria, instead, an alternative route is being considered using geological data: if the rock density of the mountains is known precisely enough and has been entered into a database , then the often irregular vertical deviation between the astronomical measuring points can be integrated about 30–50% more precisely. What such a geodetic-geological cooperation could look like was discussed for the first time at the GeoLIS conference, but is still open to date.

Future projects of the Austrian earth survey are emerging: a further consolidation of the GPS basic network, the oe 3D database of geological density values ​​(Slovakia is pursuing a similar goal), and the use of GIS technology for interdisciplinary geoscientific topics.

See also

literature

  • K. Ledersteger: Astronomical and physical geodesy (earth measurement) . JEK Volume V, Metzler-Verlag, Stuttgart 1968.
  • ÖKIE: Centenary of the Austrian Commission for International Earth Surveying . Special issue 24 of the ÖZV , Vienna 1963/64

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