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The effect on the geoid of lateral topographic density variations / Lard Erik Sjöberg in Journal of geodesy, vol 78 n° 1-2 (September 2004)  

Public [article]  inJournal of geodesy > vol 78 n° 1-2 (September 2004) . - pp 34 - 39 Titre : The effect on the geoid of lateral topographic density variations Type de document : Article/Communication Auteurs : Lard Erik Sjöberg, Auteur Année de publication : 2004 Article en page(s) : pp 34 - 39 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] anomalie de pesanteur [Termes IGN] formule de Stokes [Termes IGN] géoïde gravimétrique [Termes IGN] levé gravimétrique [Termes IGN] masse de la Terre [Termes IGN] précision centimétrique [Termes IGN] surface topographique [Termes IGN] variation de densité Résumé : (Auteur) Gravimetric geoid determination by Stokes' formula requires that the effects of topographic masses be removed prior to Stokes integration. This step includes the direct topographic and the downward continuation (DWC) effects on gravity anomaly, and the computations yield the co-geoid height. By adding the effect of restoration of the topography, the indirect effect on the geoid, the geoid height is obtained. Unfortunately, the computations of all these topographic effects are hampered by the uncertainty of the density distribution of the topography. Usually the computations are limited to a constant topographic density, but recently the effects of lateral density variations have been studied for their direct and indirect effects on the geoid. It is emphasised that the DWC effect might also be significantly affected by a lateral density variation. However, instead of computing separate effects of lateral density variation for direct, DWC and indirect effects, it is shown in two independent ways that the total geoid effect due to the lateral density anomaly can be represented as a simple correction proportional to the lateral density anomaly and the elevation squared of the computation point. This simple formula stems from the fact that the significant long-wavelength contributions to the various topographic effects cancel in their sum. Assuming that the lateral density anomaly is within 20% of the standard topographic density, the derived formula implies that the total effect on the geoid is significant at the centimetre level for topographic elevations above 0.66km. For elevations of 1000, 2000 and 5000 m the effect is within +2.2, +8.8 and +56.8 cm, respectively. For the elevation of Mt. Everest the effect is within + 1.78 m. Numéro de notice : A2004-381 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-003-0363-0 En ligne : https://doi.org/10.1007/s00190-003-0363-0 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=26908 [article]

Exemplaires(2)

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266-04032	RAB	Revue	Centre de documentation	En réserve L003	Disponible
266-04031	RAB	Revue	Centre de documentation	En réserve L003	Disponible

Two-step procedures for hybrid geoid modelling / Lard Erik Sjöberg in Journal of geodesy, vol 78 n° 1-2 (September 2004)  

Public [article]  inJournal of geodesy > vol 78 n° 1-2 (September 2004) . - pp 66 - 75 Titre : Two-step procedures for hybrid geoid modelling Type de document : Article/Communication Auteurs : Lard Erik Sjöberg, Auteur ; Will E. Featherstone, Auteur Année de publication : 2004 Article en page(s) : pp 66 - 75 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] covariance [Termes IGN] estimateur [Termes IGN] formule de Stokes [Termes IGN] géoïde [Termes IGN] géoïde gravimétrique [Termes IGN] méthode des moindres carrés [Termes IGN] pesanteur terrestre [Termes IGN] variance Résumé : (Auteur) A variety of mathematical models exist with which to combine long-wavelength geoid information from an Earth gravity model (EGM) with terrestrial gravity data. As new data become available, such as an extended or refined EGM and/or some variance-covariance information from terrestrial gravity data, this new information can be combined with a previous geoid model through a so-called hybrid estimator. The hybrid estimator is defined as a two-step estimator, which provides a solution that is a compromise between computational labour and matching of the entire data set. Some commonly used geoid modifications are compared, and several hybrid estimators are introduced. It is concluded that, in general, hybrid estimators linking the new information to old data by the least squares principle should be preferred to deterministic combinations. Numéro de notice : A2004-382 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-003-0367-9 En ligne : https://doi.org/10.1007/s00190-003-0367-9 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=26909 [article]

Exemplaires(2)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
266-04032	RAB	Revue	Centre de documentation	En réserve L003	Disponible
266-04031	RAB	Revue	Centre de documentation	En réserve L003	Disponible