Centimeter geoid

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The centimeter geoid is the current objective of earth measurement , according to which the geoid - the most important height reference area in geodesy - is to be determined with an accuracy of 1–2 centimeters in the current decade  .

The term was coined around 1990 by the then IAG President Wolfgang Torge (TU Hannover) when it was foreseeable that the methods of satellite geodesy (especially GPS , but also GLONASS and satellite laser ranging ) as well as cosmic interferometry ( VLBI ) would soon achieve centimeter accuracy .


Behind this goal is a theoretical problem of height determination : the heights determined using space methods are of a purely geometric nature (i.e. they relate to a mean earth ellipsoid ), while all terrestrially measured heights ( orthometric heights ) have the geoid as a reference surface. For the transformations between these heights that will be necessary in the future, the geoid determination would therefore also have to advance into the cm range.

Possible paths to the cm geoid

When Prof. Torge postulated this objective, the geoid had an accuracy of 10 cm in most industrialized countries worldwide , in emerging countries about 20 cm and only in a few countries in Central Europe more accurate than about 5 cm. To date, the accuracy has increased by more than 50% worldwide, mainly thanks to the geodetic satellites GRACE (launched in 2002) and GOCE  (2009). Their main purpose, however, is geodynamics , and their measurements only provide regional geoid heights, averaged over areas of around 100 km.

The short-wave geoid undulations must still be determined by

  1. terrestrial measurements ( gravimetry and astro-geodetic vertical deviations ) or
  2. precise terrain and density models .

Both paths are currently limited to 2-3 cm at best. Modern gravimetry or gradiometry requires only short measurement times, but a very dense point grid of about 1 km, which is currently only available in small areas, e.g. B. in raw material exploration or in special test networks . The vertical deviation measurements (see Astrogeoid ) are more complex, but would be sufficient at 5 km point intervals. At intervals of 10–15 km they only exist in Austria, Switzerland and parts of Germany. a. in Croatia and Slovakia. Projects for further consolidation are partly in the planning stage, but would require many millions of euros. The terrain models are accurate enough for the computational methods (2), but not the models of the local rock density .


As a result, the best geoid models of the states mentioned reach ± ​​2–3 cm and around 5 cm across Europe, which is unlikely to change much in the next few years. GPS leveling (a combination of GPS and terrestrial leveling ) offers a possibility for a certain increase in accuracy , but here too the data density is still too low. It is therefore likely that the goal of the “centimeter geoid” will be delayed by a decade or reduced to a status of ± 2 cm.

Literature and web links

  • W. Torge: Geodesy , 3rd Edition, deGruyter-Verlag, Berlin 2001
  • IAG: Geodesy Beyond 2000 , conference proceedings Vol. 121, Springer-Verlag 2000
  • H.Denker, D.Behrend, W.Torge: European gravimetric geoid: Status report 1994 . In Gravity and Geoid , Springer-Verlag 1995, doi : 10.1007 / 978-3-642-79721-7_43
  • G.Gerstbach: Astro- or gravimetric geoid - that is the question , EGS-AGU-Symposium, Nice 2003, bibcode : 2003EAEJA .... 14539G
  • N. Kühtreiber: High Precision Geoid Determination of Austria using heterogeneous data . 3rd meeting of the Int. Gravity and Geoid Commission ( Gravity and Geoid ), Athens 2002 ( PDF ; 1.6 MB)
  • C.Voigt, H.Denker, C.Hirt: Regional astrogeodetic validation of GPS / leveling data and quasigeoid models . In Observing Our Changing Earth , Springer-Verlag 2008, doi : 10.1007 / 978-3-540-85426-5_49