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Global height system unification with GOCE: a simulation study on the indirect bias term in the GBVP approach / C. Gerlach in Journal of geodesy, vol 87 n° 1 (January 2013)
[article]
Titre : Global height system unification with GOCE: a simulation study on the indirect bias term in the GBVP approach Type de document : Article/Communication Auteurs : C. Gerlach, Auteur ; Reiner Rummel, Auteur Année de publication : 2013 Article en page(s) : pp 57 - 67 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique
[Termes IGN] altitude
[Termes IGN] anomalie de pesanteur
[Termes IGN] données GOCE
[Termes IGN] erreur systématique
[Termes IGN] géoïde gravimétrique
[Termes IGN] géoïde terrestre
[Termes IGN] harmonique sphérique
[Termes IGN] hauteur ellipsoïdale
[Termes IGN] modèle de géopotentiel
[Termes IGN] problème des valeurs limites
[Termes IGN] résidu
[Termes IGN] système de référence altimétriqueRésumé : (Auteur) One of the main objectives of ESA’s Gravity Field and Steady-State Ocean Circulation mission GOCE (Gravity field and steady-state ocean circulation mission, 1999) is to allow global unification of height systems by directly providing potential differences between benchmarks in different height datum zones. In other words, GOCE provides a globally consistent and unbiased geoid. If this information is combined with ellipsoidal (derived from geodetic space techniques) and physical heights (derived from leveling/gravimetry) at the same benchmarks, datum offsets between the datum zones can be determined and all zones unified. The expected accuracy of GOCE is around 2–3 cm up to spherical harmonic degree nmax ~ 200. The omission error above this degree amounts to about 30 cm which cannot be neglected. Therefore, terrestrial residual gravity anomalies are necessary to evaluate the medium and short wavelengths of the geoid, i.e. one has to solve the Geodetic Boundary Value Problem (GBVP). The theory of height unification by the GBVP approach is well developed, see e.g. Colombo (A World Vertical Network. Report 296, Department of Geodetic Science and Surveying, 1980) or Rummel and Teunissen (Bull Geod 62:477–498, 1988). Thereby, it must be considered that terrestrial gravity anomalies referring to different datum zones are biased due to the respective datum offsets. Consequently, the height reference surface of a specific datum zone deviates from the unbiased geoid not only due to its own datum offset (direct bias term) but is also indirectly affected by the integration of biased gravity anomalies. The latter effect is called the indirect bias term and it considerably complicates the adjustment model for global height unification. If no satellite based gravity model is employed, this error amounts to about the same size as the datum offsets, i.e. 1–2 m globally. We show that this value decreases if a satellite-only gravity model is used. Specifically for GOCE with nmax ~ 200, the error can be expected not to exceed the level of 1 cm, allowing the effect to be neglected in practical height unification. The results are supported by recent findings by Gatti et al. (J Geod, 2012). Numéro de notice : A2013-074 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-012-0579-y En ligne : https://doi.org/10.1007/s00190-012-0579-y Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32212
in Journal of geodesy > vol 87 n° 1 (January 2013) . - pp 57 - 67[article]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 266-2013011 SL Revue Centre de documentation Revues en salle Disponible Zur Höhensystemumstellung und Geoidberechnung in Bayern / C. Gerlach (2003)
Titre : Zur Höhensystemumstellung und Geoidberechnung in Bayern Titre original : [Sur le changement de système d'altitudes et l'estimation du géoïde en Bavière] Type de document : Thèse/HDR Auteurs : C. Gerlach, Auteur Editeur : Munich : Bayerische Akademie der Wissenschaften Année de publication : 2003 Collection : DGK - C Sous-collection : Dissertationen num. 571 Importance : 129 p. Format : 21 x 30 cm ISBN/ISSN/EAN : 978-3-7696-5010-5 Note générale : Bibliographie Langues : Allemand (ger) Descripteur : [Vedettes matières IGN] Géodésie physique
[Termes IGN] altitude normale
[Termes IGN] Bavière (Allemagne)
[Termes IGN] covariance
[Termes IGN] formule de Stokes
[Termes IGN] géoïde local
[Termes IGN] nivellement par GPS
[Termes IGN] précision décimétrique
[Termes IGN] problème des valeurs limites
[Termes IGN] réseau de premier ordre
[Termes IGN] système de référence altimétriqueIndex. décimale : 30.41 Géoïde Résumé : (Auteur) Topographic heights are determined for various purposes and using different measurement techniques. This work gives a contribution to an accurate national height system for the federal state of Bavaria, Germany. One aspect is the determination of physical heights by means of geometric levelling combined with gravity measurements. The other aspect is to derive an accurate geoid in order to make use of the efficient method of levelling by GPS. Of course the definitions of the heights must be consistent with the used geoid. For both quantities (heights and geoid) there are different definitions and the differences between those cannot be neglected when in comes to the cm-level.
For historic reasons, the former West-German national height system was computed in normal- orthometric heights and connected to the tide gauge Amsterdam. In the former German Democratic Republic normal heights were introduced, connected to a tide gauge in the Baltic sea. Thus, the reunification of Germany resulted in an inhomogeneous height system. The working group of the federal surveying authorities decided to set up a new consistent system, based on normal heights and connected to the level of Amsterdam. The first order network was computed in one step for the whole of Germany. It is the task of each federal state to compute the lower order networks for its own area.
The first part of this work deals with height computations in the area of Bavaria. Transformation algorithms from the old spheroidal heights into normal heights are investigated under the precondition, that the use of the original measurement records should be avoided because not all of them are available in digital form. It is shown that in most parts of Bavaria a relatively simple procedure can be used, while in mountainous regions, like the Alps, gravity interpolation becomes the critical point. The accuracy requirements can still be met by using Bouguer anomalies (including topographic reductions) or by a proper distribution of data and interpolation points. The quality descriptions are based on a comprehensive error budget of all relevant error sources and make use of empirical covariance functions.
As the new height system will be given in normal heights, the proper geoid is the quasi-geoid, based on the theory of Molodensky. The second part of this work deals with the computation of an accurate quasi-geoid in Bavaria. It is based on a combination of the global potential model EGM96 and terrestrial gravity anomalies within a 4° cap around Bavaria. A high resolution digital terrain model with a grid spacing of 50 m is used in Bavaria to compute topographic reductions. Molodensky's series is computed up to third order and different kinds of modifications of Stokes' function are tested. Comparison to GPS/Ievelling heights shows, that the best results are achieved using the original Stokes-kernel. Still there are long and medium wavelength errors of some decimeters in all solutions. This holds true for the European quasi-geoid EGG97, too. Error simulations indicate that those are due to errors in the global potential model. In order to allow the use of the derived quasi-geoid for the determination of physical heights, it is fitted to a set of GPS/Ievelling points. This way an accuracy of 2-3 cm is achieved, which is at the accuracy level of geodetic GPS measurements.Numéro de notice : 13201 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Thèse étrangère Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=54911 Réservation
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Code-barres Cote Support Localisation Section Disponibilité 13201-01 30.41 Livre Centre de documentation Géodésie Disponible 13201-02 30.41 Livre Centre de documentation Géodésie Disponible