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A global vertical datum defined by the conventional geoid potential and the Earth ellipsoid parameters / Hadi Amin in Journal of geodesy, vol 93 n°10 (October 2019)  

Public [article]  inJournal of geodesy > vol 93 n°10 (October 2019) Titre : A global vertical datum defined by the conventional geoid potential and the Earth ellipsoid parameters Type de document : Article/Communication Auteurs : Hadi Amin, Auteur ; Lard Erik Sjöberg, Auteur ; Mohammad Bagherbandi, Auteur Année de publication : 2019 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] champ de pesanteur terrestre [Termes IGN] coordonnées cartésiennes géocentriques [Termes IGN] ellipsoïde de référence [Termes IGN] géoïde [Termes IGN] géoïde gravimétrique [Termes IGN] harmonique ellipsoïdale [Termes IGN] modèle de géopotentiel [Termes IGN] surface de la mer [Termes IGN] système de référence altimétrique [Termes IGN] système de référence géodésique Résumé : (auteur) The geoid, according to the classical Gauss–Listing definition, is, among infinite equipotential surfaces of the Earth’s gravity field, the equipotential surface that in a least squares sense best fits the undisturbed mean sea level. This equipotential surface, except for its zero-degree harmonic, can be characterized using the Earth’s global gravity models (GGM). Although, nowadays, satellite altimetry technique provides the absolute geoid height over oceans that can be used to calibrate the unknown zero-degree harmonic of the gravimetric geoid models, this technique cannot be utilized to estimate the geometric parameters of the mean Earth ellipsoid (MEE). The main objective of this study is to perform a joint estimation of W0, which defines the zero datum of vertical coordinates, and the MEE parameters relying on a new approach and on the newest gravity field, mean sea surface and mean dynamic topography models. As our approach utilizes both satellite altimetry observations and a GGM model, we consider different aspects of the input data to evaluate the sensitivity of our estimations to the input data. Unlike previous studies, our results show that it is not sufficient to use only the satellite-component of a quasi-stationary GGM to estimate W0. In addition, our results confirm a high sensitivity of the applied approach to the altimetry-based geoid heights, i.e., mean sea surface and mean dynamic topography models. Moreover, as W0 should be considered a quasi-stationary parameter, we quantify the effect of time-dependent Earth’s gravity field changes as well as the time-dependent sea level changes on the estimation of W0. Our computations resulted in the geoid potential W0 = 62636848.102 ± 0.004 m2 s−2 and the semi-major and minor axes of the MEE, a = 6378137.678 ± 0.0003 m and b = 6356752.964 ± 0.0005 m, which are 0.678 and 0.650 m larger than those axes of GRS80 reference ellipsoid, respectively. Moreover, a new estimation for the geocentric gravitational constant was obtained as GM = (398600460.55 ± 0.03) × 106 m3 s−2. Numéro de notice : A2019-608 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-019-01293-3 Date de publication en ligne : 12/09/2019 En ligne : https://doi.org/10.1007/s00190-019-01293-3 Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94791 [article]

Regional geoid computation by least squares modified Hotine’s formula with additive corrections / Silja Märdla in Journal of geodesy, vol 92 n° 3 (March 2018)  

Public [article]  inJournal of geodesy > vol 92 n° 3 (March 2018) . - pp 253 - 270 Titre : Regional geoid computation by least squares modified Hotine’s formula with additive corrections Type de document : Article/Communication Auteurs : Silja Märdla, Auteur ; Artu Ellmann, Auteur ; Jonas Ågren, Auteur ; Lard Erik Sjöberg, Auteur Année de publication : 2018 Article en page(s) : pp 253 - 270 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 local [Termes IGN] méthode des moindres carrés [Termes IGN] quasi-géoïde Résumé : (Auteur) Geoid and quasigeoid modelling from gravity anomalies by the method of least squares modification of Stokes’s formula with additive corrections is adapted for the usage with gravity disturbances and Hotine’s formula. The biased, unbiased and optimum versions of least squares modification are considered. Equations are presented for the four additive corrections that account for the combined (direct plus indirect) effect of downward continuation (DWC), topographic, atmospheric and ellipsoidal corrections in geoid or quasigeoid modelling. The geoid or quasigeoid modelling scheme by the least squares modified Hotine formula is numerically verified, analysed and compared to the Stokes counterpart in a heterogeneous study area. The resulting geoid models and the additive corrections computed both for use with Stokes’s or Hotine’s formula differ most in high topography areas. Over the study area (reaching almost 2 km in altitude), the approximate geoid models (before the additive corrections) differ by 7 mm on average with a 3 mm standard deviation (SD) and a maximum of 1.3 cm. The additive corrections, out of which only the DWC correction has a numerically significant difference, improve the agreement between respective geoid or quasigeoid models to an average difference of 5 mm with a 1 mm SD and a maximum of 8 mm. Numéro de notice : A2018-060 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-017-1061-7 Date de publication en ligne : 11/09/2017 En ligne : https://doi.org/10.1007/s00190-017-1061-7 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=89393 [article]

Fast GNSS ambiguity resolution as an ill-posed problem / Lard Erik Sjöberg in Journal of geodesy, vol 84 n° 11 (November 2010)  

Public [article]  inJournal of geodesy > vol 84 n° 11 (November 2010) . - pp 699 - 702 Titre : Fast GNSS ambiguity resolution as an ill-posed problem Type de document : Article/Communication Auteurs : Lard Erik Sjöberg, Auteur Année de publication : 2010 Article en page(s) : pp 699 - 702 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] ambiguïté entière [Termes IGN] matrice de covariance [Termes IGN] mesurage de phase [Termes IGN] phase GNSS [Termes IGN] positionnement par GNSS [Termes IGN] problème inverse [Termes IGN] résolution d'ambiguïté Résumé : (Auteur) A linear observational equation system for real-time GNSS carrier phase ambiguity resolution (AR) is often severely ill-posed in the case of poor satellite geometry. An ill-posed system may result in unreliable or unsuccessful AR if no care is taken to mitigate this situation. In this paper, the GNSS AR model as an ill-posed problem is solved by regularizing its baseline and ambiguity parameters, respectively, with the threefold contributions: (i) The regularization parameter is reliably determined in context of minimizing mean square error of regularized solution where the covariance matrix of initial values of unknowns is used as an approximate smoothness term instead of the quadratic matrix of the true values of unknowns; (ii) The different models for computing initial values of unknowns are systematically discussed in order to address the potential schemes in real world applications; (iii) The superior performance of the regularized AR are demonstrated through the numerically random simulations as well as the real GPS experiments. The results show that the proposed regularization strategies can effectively mitigate the model’s ill-condition and improve the success AR probability of the observational system with a severely ill-posed problem. Numéro de notice : A2010-478 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-010-0403-5 Date de publication en ligne : 22/08/2010 En ligne : https://doi.org/10.1007/s00190-010-0403-5 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=30671 [article]

Exemplaires(1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
266-2010111	SL	Revue	Centre de documentation	Revues en salle	Disponible

On the topographic bias in geoid determination by the external gravity field / Lard Erik Sjöberg in Journal of geodesy, vol 83 n° 10 (October 2009)  

Public [article]  inJournal of geodesy > vol 83 n° 10 (October 2009) . - pp 967 - 972 Titre : On the topographic bias in geoid determination by the external gravity field Type de document : Article/Communication Auteurs : Lard Erik Sjöberg, Auteur Année de publication : 2009 Article en page(s) : pp 967 - 972 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] erreur systématique [Termes IGN] géoïde gravimétrique [Termes IGN] modèle numérique de terrain Résumé : (Auteur) The topographic bias is defined as the error/bias committed by continuing the external gravity field inside the topographic masses by a harmonic function. We study the topographic bias given by a digital terrain model defined by a spherical template, and we show that the topographic bias is given only by the potential of an inner-zone cap, and it equals the bias of the Bouguer shell, independent of the size of the cap. Then we study the effect on the real Earth by decomposing its topography into a template, and we show also in this case that the topographic bias is that of the Bouguer shell, independent of the shape of the terrain. Finally, we show that the topographic potential of the terrain at the geoid can be determined to any precision by a Taylor expansion outside the Earth’s surface. The last statement is demonstrated by a Taylor expansion to fourth order. Copyright Springer Numéro de notice : A2009-431 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-009-0314-5 En ligne : https://doi.org/10.1007/s00190-009-0314-5 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=30062 [article]

Exemplaires(1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
266-09091	SL	Revue	Centre de documentation	Revues en salle	Disponible

The topographic bias by analytical continuation in physical geodesy / Lard Erik Sjöberg in Journal of geodesy, vol 81 n° 5 (May 2007)  

Public [article]  inJournal of geodesy > vol 81 n° 5 (May 2007) . - pp 345 - 350 Titre : The topographic bias by analytical continuation in physical geodesy Type de document : Article/Communication Auteurs : Lard Erik Sjöberg, Auteur Année de publication : 2007 Article en page(s) : pp 345 - 350 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] erreur systématique [Termes IGN] formule de Stokes [Termes IGN] géoïde terrestre [Termes IGN] potentiel de pesanteur terrestre Résumé : (Auteur) This study emphasizes that the harmonic downward continuation of an external representation of the Earth’s gravity potential to sea level through the topographic masses implies a topographic bias. It is shown that the bias is only dependent on the topographic density along the geocentric radius at the computation point. The bias corresponds to the combined topographic geoid effect, i.e., the sum of the direct and indirect topographic effects. For a laterally variable topographic density function, the combined geoid effect is proportional to terms of powers two and three of the topographic height, while all higher order terms vanish. The result is useful in geoid determination by analytical continuation, e.g., from an Earth gravity model, Stokes’s formula or a combination thereof. Copyright Springer Numéro de notice : A2007-123 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-006-0112-2 En ligne : https://doi.org/10.1007/s00190-006-0112-2 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=28486 [article]

Exemplaires(2)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
266-07051	RAB	Revue	Centre de documentation	En réserve L003	Disponible
266-07052	RAB	Revue	Centre de documentation	En réserve L003	Disponible

A new technique to determine geoid and orthometric heights from satellite positioning and geopotential numbers / Lard Erik Sjöberg in Journal of geodesy, vol 80 n° 6 (September 2006)  

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The effects of Stokes's formula for an ellipsoidal layering of the Earth's atmosphere / Lard Erik Sjöberg in Journal of geodesy, vol 79 n° 12 (March 2006)  

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Effect of the STRM global DEM on the determination of a high-resolution geoid model: A case study in Iran / R. Kiamehr in Journal of geodesy, vol 79 n° 9 (December 2005)  

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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)  

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

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Adjustment and variance-covariance component estimation with a singular covariance matrix / Lard Erik Sjöberg in ZFV Zeitschrift für Vermessungswesen, vol 110 n° 4 (01/04/1985)

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A comparison of Bjerhammar's methods and collocation in physical geodesy / Lard Erik Sjöberg (1978)

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