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The RTM harmonic correction revisited / R. Klees in Journal of geodesy, vol 96 n° 6 (June 2022)  

Public [article]  inJournal of geodesy > vol 96 n° 6 (June 2022) . - n° 39 Titre : The RTM harmonic correction revisited Type de document : Article/Communication Auteurs : R. Klees, Auteur ; Kurt Seitz, Auteur ; D.C. Slobbe, Auteur Année de publication : 2022 Article en page(s) : n° 39 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] analyse harmonique [Termes IGN] anomalie de pesanteur [Termes IGN] Auvergne [Termes IGN] correction des altitudes [Termes IGN] géoïde local [Termes IGN] harmonique sphérique [Termes IGN] hauteur ellipsoïdale [Termes IGN] méthode des moindres carrés [Termes IGN] modèle de géopotentiel local [Termes IGN] modèle numérique de terrain [Termes IGN] Norvège [Termes IGN] quasi-géoïde [Termes IGN] résidu Résumé : (auteur) In this paper, we derive improved expressions for the harmonic correction to gravity and, for the first time, expressions for the harmonic correction to potential and height anomaly. They need to be applied at stations buried inside the masses to transform internal values into harmonically downward continued values, which are then input to local quasi-geoid modelling using least-squares collocation or least-squares techniques in combination with the remove-compute-restore approach. Harmonic corrections to potential and height anomaly were assumed to be negligible so far resulting in yet unknown quasi-geoid model errors. The improved expressions for the harmonic correction to gravity, and the new expressions for the harmonic correction to potential and height anomaly are used to quantify the approximation errors of the commonly used harmonic correction to gravity and to quantify the magnitude of the harmonic correction to potential and height anomaly. This is done for two test areas with different topographic regimes. One comprises parts of Norway and the North Atlantic where the presence of deep, long, and narrow fjords suggest extreme values for the harmonic correction to potential and height anomaly and corresponding large errors of the commonly used approximation of the harmonic correction to gravity. The other one is located in the Auvergne test area with a moderate topography comprising both flat and hilly areas and therefore may be representative for many areas around the world. For both test areas, two RTM surfaces with different smoothness are computed simulating the use of a medium-resolution and an ultra-high-resolution reference gravity field, respectively. We show that the errors of the commonly used harmonic correction to gravity may be as large as the harmonic correction itself and attain peak values in areas of strong topographic variations of about 100 mGal. Moreover, we show that this correction may introduce long-wavelength biases in the computed quasi-geoid model. Furthermore, we show that the harmonic correction to height anomaly can attain values on the order of a decimetre at some points. Overall, however, the harmonic correction to height anomaly needs to be applied only in areas of strong topographic variations. In flat or hilly areas, it is mostly smaller than one centimetre. Finally, we show that the harmonic corrections increase with increasing smoothness of the RTM surface, which suggests to use a RTM surface with a spatial resolution comparable to the finest scales which can be resolved by the data rather than depending on the resolution of the global geopotential model used to reduce the data. Numéro de notice : A2022-414 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article DOI : 10.1007/s00190-022-01625-w Date de publication en ligne : 30/05/2022 En ligne : https://doi.org/10.1007/s00190-022-01625-w Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=100769 [article]

Empirical comparison between stochastic and deterministic modifiers over the French Auvergne geoid computation test-bed / Ropesh Goyal in Survey review, vol 54 n° 382 (January 2022)  

Public [article]  inSurvey review > vol 54 n° 382 (January 2022) . - pp 57 - 69 Titre : Empirical comparison between stochastic and deterministic modifiers over the French Auvergne geoid computation test-bed Type de document : Article/Communication Auteurs : Ropesh Goyal, Auteur ; Jonas Ågren, Auteur ; Will E. Featherstone, Auteur Année de publication : 2022 Article en page(s) : pp 57 - 69 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] analyse comparative [Termes IGN] Auvergne [Termes IGN] géoïde local [Termes IGN] harmonique sphérique [Termes IGN] méthode déterministe [Termes IGN] NGF-IGN69 [Termes IGN] nivellement par GPS [Termes IGN] processus stochastique [Termes IGN] quasi-géoïde Résumé : (auteur) Since 2006, several different groups have computed geoid and/or quasigeoid (quasi/geoid) models for the Auvergne test area in central France using various approaches. In this contribution, we compute and compare quasigeoid models for Auvergne using Curtin University of Technology’s and the Swedish Royal Institute of Technology’s approaches. These approaches differ in many ways, such as their treatment of the input data, choice of type of spherical harmonic model (combined or satellite-only), form and sequence of correction terms applied, and different modified Stokes’s kernels (deterministic or stochastic). We have also compared our results with most of the previously reported studies over Auvergne in order to seek any improvements with respect to time [exceptions are when different subsets of data have been used]. All studies considered here compare the computed quasigeoid models with the same 75 GPS-levelling heights over Auvergne. The standard deviation for almost all of the computations (without any fitting) is of the order of 30–40 mm, so there is not yet any clear indication whether any approach is necessarily better than any other nor improving over time. We also recommend more standardisation on the presentation of quasi/geoid comparisons with GPS-levelling data so that results from different approaches over the same areas can be compared more objectively. Numéro de notice : A2022-111 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1080/00396265.2021.1871821 En ligne : https://doi.org/10.1080/00396265.2021.1871821 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=99628 [article]

Descriptif technique du quasi-géoïde gravimétrique QGF16 et de la surface de conversion altimétrique RAF18b / François L'écu (2021)

Public Titre : Descriptif technique du quasi-géoïde gravimétrique QGF16 et de la surface de conversion altimétrique RAF18b Type de document : Rapport Auteurs : François L'écu, Auteur Editeur : Saint-Mandé : Institut national de l'information géographique et forestière - IGN Année de publication : 2021 Collection : Publications techniques en géodésie num. 600 82 8671 Importance : 22 p. Format : 21 x 30 cm Langues : Français (fre) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] conversion altimétrique [Termes IGN] hauteur ellipsoïdale [Termes IGN] point GNSS nivelé [Termes IGN] Quasi-Géoïde Français 2016 [Termes IGN] Référence d'Altitudes Françaises 2018 Résumé : (auteur) Le document présente les caractéristiques techniques du quasi-géoïde gravimétrique QGF16 et de la surface de conversion altimétrique RAF18b. Note de contenu : 1- Introduction 2- Processus de calcul de quasi-géoïde utilisé au SGM 3- Données utilisées pour le calcul de QGF16 4- Le quasi-géoïde gravimétrique QGF16 5- La surface de conversion altimétrique RAF18b Numéro de notice : 28382 Affiliation des auteurs : IGN (2020- ) Thématique : POSITIONNEMENT Nature : Rapport d'étude technique nature-HAL : Rapport DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=98603

Exemplaires (1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
28382-01	7D	Livre	SGM	K001	Exclu du prêt

Height system unification and estimation of the lithospheric structure beneath Vietnam through high-resolution gravity field and quasigeoid modeling / Dinh Toan Vu (2021)  

Public Titre : Height system unification and estimation of the lithospheric structure beneath Vietnam through high-resolution gravity field and quasigeoid modeling Titre original : Unification du système de hauteur et estimation de la structure lithosphérique sous le Vietnam utilisant la modélisation du champ de gravité et du quasigéoïde à haute résolution Type de document : Thèse/HDR Auteurs : Dinh Toan Vu, Auteur ; Sylvain Bonvalot, Directeur de thèse ; Sean L. Bruinsma, Directeur de thèse Editeur : Toulouse : Université de Toulouse Année de publication : 2021 Importance : 234 p. Format : 21 x 30 cm Note générale : bibliographie Thèse en vue de l'obtention du Doctorat de l'Université de Toulouse délivrée par l'Université Toulouse 3 - Paul Sabatier Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] anomalie de pesanteur [Termes IGN] champ de pesanteur terrestre [Termes IGN] données GNSS [Termes IGN] données GOCE [Termes IGN] géoïde gravimétrique [Termes IGN] géoïde local [Termes IGN] lithosphère [Termes IGN] modèle de géopotentiel local [Termes IGN] nivellement [Termes IGN] quasi-géoïde [Termes IGN] Viet Nam Index. décimale : THESE Thèses et HDR Résumé : (auteur) The goal of this work was twofold. The first part was devoted to the research of the size and physical shape of the Earth in Vietnam through the determination of a local gravimetric quasigeoid model. The second part was to better constrain the Earth's interior structure beneath Vietnam by determining the Moho and Lithosphere-Asthenosphere Boundary (LAB) depth models. For the first objective, a high-resolution gravimetric quasigeoid model for Vietnam and its surrounding areas was determined based on new land gravity data in combination with fill-in data where no gravity data existed. The resulting quasigeoid model was evaluated using 812 GNSS/levelling points in the study region. This comparison indicates that the quasigeoid model has a standard deviation of 9.7 cm and 50 cm in mean bias. This new local quasigeoid model for Vietnam represents a significant improvement over the global models EIGEN-6C4 and EGM2008, which have standard deviations of 19.2 and 29.1 cm, respectively, when compared to the GNSS/levelling data. An essential societal and engineering application of the gravimetric quasigeoid is in GNSS levelling, and a vertical offset model for Vietnam and its surrounding areas was determined based on the GNSS/levelling points and gravimetric-only quasigeoid model for this purpose. The offset model was evaluated using cross-validation technique by comparing with GNSS/levelling data. Results indicate that the offset model has a standard deviation of 5.9 cm in the absolute sense. Thanks to this offset model, GNSS levelling can be carried out over most of Vietnam's territory complying to third-order levelling requirements, while the accuracy requirements for fourth-order levelling networks is met for the entire country. To unify the height system towards the International Height Reference Frame (IHRF), the zero-height geopotential value for the Vietnam Local Vertical Datum W_0^LVD was determined based on two approaches: 1) Using high-quality GNSS/levelling data and the estimated gravimetric quasigeoid model, 2) Using the Geodetic Boundary Value Problem (GBVP) approach based on the GOCE global gravity field model enhanced with terrestrial gravity data. This geopotential value can be used to connect the height system of Vietnam with the neighboring countries. Moreover, the GBVP approach was also used for direct determination of the gravity potential on the surface at three GNSS Continuously Operating Reference Station (CORS) stations at epoch 2018.0 in Vietnam. Based on time series of the vertical component derived from these GNSS observations as well as InSAR data, temporal variations in the geopotential were also estimated on these permanent GNSS stations. This enables monitoring of the vertical datum and detect possible deformation. These stations may thus contribute to increase the density of reference points in the IHRF for this region. For the second objective, the local quasigeoid model was first converted to the geoid. Then, high-resolution Moho and LAB depth models were determined beneath Vietnam based on the local isostatic hypothesis using the geoid height derived from the estimated geoid, elevation data and thermal analysis. From new land gravity data, a complete grid and map of gravity anomalies i.e., Free-air, Bouguer and Isostatic was determined for the whole of Vietnam. The Moho depth was also computed based on the gravity inversion using the Bouguer gravity anomaly grid. All new models are computed at 1' resolution. The resulting Moho and LAB depth models were evaluated using available seismic data as well as global and local lithospheric models available in the study region. [...] Note de contenu : 1- Introduction 2- Theoretical basis 3- Data and map of gravity anomalies 4- The gravimetric quasigeoid solution 5- Quasigeoïd application for GNSS levelling and height system unification 6- Quasigeoid application for determination of the lithospheric structure 7- Conclusion and perspectives Numéro de notice : 28495 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Thèse française Note de thèse : Thèse de Doctorat : Sciences de la Terre et des Planètes Solides : Toulouse : 2021 Organisme de stage : Geosciences Environnement Toulouse GET DOI : sans En ligne : http://www.theses.fr/2021TOU30050 Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=99240

The impact of terrestrial gravity data density on geoid accuracy: case study Bilogora in Croatia / Olga Bjelotomić Oršulić in Survey review, vol 52 n° 373 (July 2020)  

Public [article]  inSurvey review > vol 52 n° 373 (July 2020) . - pp 299 - 308 Titre : The impact of terrestrial gravity data density on geoid accuracy: case study Bilogora in Croatia Type de document : Article/Communication Auteurs : Olga Bjelotomić Oršulić, Auteur ; Danko Markovinović, Auteur ; Matej Varga, Auteur ; Tomislav Basic, Auteur Année de publication : 2020 Article en page(s) : pp 299 - 308 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] Croatie [Termes IGN] données CHAMP [Termes IGN] géoïde [Termes IGN] gravimétrie terrestre [Termes IGN] levé gravimétrique [Termes IGN] quasi-géoïde [Termes IGN] station d'observation Résumé : (auteur) One of the main challenges in physical geodesy today is achieving the 1-centimetre gravimetric quasi-geoid model, since a model of such accuracy could be used in the definition and realisation of the height reference frame. One of the main obstacles in this challenge is the lack of terrestrial gravity data or its uneven distribution. Therefore, the main question arises: what density of gravity points is necessary in order to obtain a gravimetric quasi-geoid model with an accuracy of 1 centimetre or even better? In this simulated study, the results show a trend of decreasing RMS related to the sparser dataset used in computation, leading to the conclusion that the determination of the sub-centimetre quasi-geoid model is no longer a theory, but can be achieved with the exact density of terrestrial gravity data: gravity observation stations have to be distributed no farther than 500 m from one another. When dealing with a very rough topography, the distance should be even shorter. Numéro de notice : A2020-456 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1080/00396265.2018.1562747 Date de publication en ligne : 13/01/2020 En ligne : https://doi.org/10.1080/00396265.2018.1562747 Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=95555 [article]

40 ans de géodésie à l'IGN (Institut Géographique National rebaptisé en 2012 Institut national de l'information géographique et forestière) : 2ème partie, la géodésie physique / Françoise Duquenne in XYZ, n° 162 (mars 2020)

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Precise local quasigeoid modelling using GNSS/levelling height anomalies and gravity data / Marek Trojanowicz in Survey review, Vol 52 n°370 (January 2020)  

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Error propagation for the Molodensky G1 term / Jack C. McCubbine in Journal of geodesy, vol 93 n°6 (June 2019)  

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AUSGeoid2020 combined gravimetric–geometric model : location-specific uncertainties and baseline-length-dependent error decorrelation / Nicholas J. Brown in Journal of geodesy, vol 92 n° 12 (December 2018)  

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The New Zealand gravimetric quasigeoid model 2017 that incorporates nationwide airborne gravimetry / Jack C. McCubbine in Journal of geodesy, vol 92 n° 8 (August 2018)  

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A methodology for least-squares local quasi-geoid modelling using a noisy satellite-only gravity field model / R. Klees in Journal of geodesy, vol 92 n° 4 (April 2018)  

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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)  

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The first Australian gravimetric quasigeoid model with location-specific uncertainty estimates / Will E. Featherstone in Journal of geodesy, vol 92 n° 2 (February 2018)  

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Applying the GOCE-based GGMs for the quasi-geoid modelling of Finland / Timo Saari in Journal of applied geodesy, vol 12 n° 1 (January 2018)  

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Assessing the quality of GEOID12B model through field surveys / Ahmed F. Elaksher in Journal of applied geodesy, vol 12 n° 1 (January 2018)  

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