Regional geoid

A regional geoid is a geoid determination or solution for an area (region) on the mainland based on measurement points on the earth's surface . The main difference to global geoid solutions is that individual regional geoid determinations cannot, or only with difficulty, be combined into a global, intercontinental geoid.

Methods

Four methods can be used for regional geoid determination:

the astrogeoid : for position-wise known surveying points their vertical deviations are calculated, which are connected as an astronomical leveling to a surface network.
a gravimetric geoid , which is calculated from grid-shaped gravity measurements on relatively closely adjacent measuring points. When evaluating the measurement data - in contrast to (1) - a topographical reduction must be applied in order to eliminate the disruptive influence of the terrain .
the combination of the two methods to form an "astro-gravimetric geoid". It has been technically possible since the mid-1970s because precise digital terrain models are available.
a global "Satellitengeoid" , the local by calculating geoid separations by means of digital terrain and density models , a regional satisfactory resolution is given.

For an accuracy of 5 cm, an astrogeoid manages with point spacings of around 10 km. In contrast, a gravimetric geoid with the same accuracy requires around 10 to 20 times more measurement points, i.e. a point grid of around 3 km; however, some of these gravity measurements are already available from operations in geodetic precision leveling or geophysical raw material research.

The combination solution (3) lies - depending on the measurement data - between these two cases.

Help from satellites

Such geoids can be spatially supported by gravitational field data from satellite geodesy . These supporting data are primarily models of the geopotential in the outer space of the earth. From the orbital disturbances of suitable satellites caused by the geoid and the interior of the earth , potential developments with spherical surface functions of high degree are calculated, which today already have resolutions down to 100 km or less.

In the future, satellite-to-satellite tracking (STS) and satellite gradiometry will contribute to regional geoid solutions; With the GRACE satellite pair, which was launched a few years ago , these methods are already used today for the temporal change of long-wave geoid undulations and in oceanography . Since the start of the GOCE gradiometer probe in 2009, this goal has come within reach and in about 10 years - with a combination solution according to method (4) - could almost lead to the centimeter geoid that has been aimed for since the 1990s .

literature

Erhard Erker: The austrian geoid - local geoid determination using modified conservative algorithms. In: The Gravity Field in Austria - Austria's Geodetic Works for International Earth Surveying Volume IV, 1987, pp. 19–46.

Individual evidence

↑ cf. for example Erhard Erker: Astro-geodetic measurements of the Federal Office for Metrology and Surveying for the determination of the geoid in Austria. In: The Geoid in Austria - Austria's Geodetic Work for International Earth Measurement Volume III, 1983, pp. 49–60.
Bernadette Wiesenhofer: Investigations into the astrogeodetic geoid solution in the south-east of Austria . Master's thesis Institute for Navigation and Satellite Geodesy, Graz University of Technology. June 2007 ( tugraz.at [PDF; accessed on February 20, 2018]).
↑ for example the geoid and quasigeoid model EGG97 (European Gravimetric Geoid 1997)
↑ cf. for example J. Brennecke, et al., German Geodetic Commission, Bavarian Academy of Sciences: A European Astro-gravimetric Geoid . (= German Geodetic Commission, Series B: Applied Geodesy , Issue 269), 1983
^ See G. Gerstbach, Astro or gravimetric geoid - that is the question , EGS-AGU-Symposium, Nice 2003, bibcode : 2003EAEJA .... 14539G
↑ PNAM Visser, R. Rummel, G. Balmino, H. Sünkel, J. Johannessen, M. Aguirre, PL Woodworth, C. Le Provost, CC Tscherning, R. Sabadini: The European Earth Explorer Mission GOCE: Impact for the geosciences . In: JX Mitrovica, LLA Vermeersen (Ed.): Ice Sheets, Sea Level and the Dynamic Earth (= Geodynamics Series . No. 29 ). American Geophysical Union, Washington DC 2002, p. 95-107 , doi : 10.1002 / 9781118670101.ch6 (English).

[1] . for example Erhard Erker: Astro-geodetic measurements of the Federal Office for Metrology and Surveying for the determination of the geoid in Austria. In: The Geoid in Austria - Austria's Geodetic Work for International Earth Measurement Volume III, 1983, pp. 49–60.
Bernadette Wiesenhofer: Investigations into the astrogeodetic geoid solution in the south-east of Austria . Master's thesis Institute for Navigation and Satellite Geodesy, Graz University of Technology. June 2007 ( tugraz.at [PDF; accessed on February 20, 2018]).

[2] r example the geoid and quasigeoid model EGG97 (European Gravimetric Geoid 1997)

[3] . for example J. Brennecke, et al., German Geodetic Commission, Bavarian Academy of Sciences: A European Astro-gravimetric Geoid . (= German Geodetic Commission, Series B: Applied Geodesy , Issue 269), 1983

[4] See G. Gerstbach, Astro or gravimetric geoid - that is the question , EGS-AGU-Symposium, Nice 2003, bibcode : 2003EAEJA .... 14539G

[5] PNAM Visser, R. Rummel, G. Balmino, H. Sünkel, J. Johannessen, M. Aguirre, PL Woodworth, C. Le Provost, CC Tscherning, R. Sabadini: The European Earth Explorer Mission GOCE: Impact for the geosciences . In: JX Mitrovica, LLA Vermeersen (Ed.): Ice Sheets, Sea Level and the Dynamic Earth (= Geodynamics Series . No. 29 ). American Geophysical Union, Washington DC 2002, p. 95-107 , doi : 10.1002 / 9781118670101.ch6 (English).