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Astronomical-topographic levelling using high-precision astrogeodetic vertical deflections and Digital Terrain Model data / C. Hirt in Journal of geodesy, vol 82 n° 4-5 (April - May 2008)

Public [article]  inJournal of geodesy > vol 82 n° 4-5 (April - May 2008) . - pp 231 - 248 Titre : Astronomical-topographic levelling using high-precision astrogeodetic vertical deflections and Digital Terrain Model data Type de document : Article/Communication Auteurs : C. Hirt, Auteur ; J. Flury, Auteur Année de publication : 2008 Article en page(s) : pp 231 - 248 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Nivellement [Termes descripteurs IGN] Alpes [Termes descripteurs IGN] champ de pesanteur local [Termes descripteurs IGN] collocation par moindres carrés [Termes descripteurs IGN] déviation de la verticale [Termes descripteurs IGN] modèle numérique de terrain [Termes descripteurs IGN] nivellement indirect Résumé : (Auteur) At the beginning of the twenty-first century, a technological change took place in geodetic astronomy by the development of Digital Zenith Camera Systems (DZCS). Such instruments provide vertical deflection data at an angular accuracy level of 0.?1 and better. Recently, DZCS have been employed for the collection of dense sets of astrogeodetic vertical deflection data in several test areas in Germany with high-resolution digital terrain model (DTM) data (10–50 m resolution) available. These considerable advancements motivate a new analysis of the method of astronomical-topographic levelling, which uses DTM data for the interpolation between the astrogeodetic stations. We present and analyse a least-squares collocation technique that uses DTM data for the accurate interpolation of vertical deflection data. The combination of both data sets allows a precise determination of the gravity field along profiles, even in regions with a rugged topography. The accuracy of the method is studied with particular attention on the density of astrogeodetic stations. The error propagation rule of astronomical levelling is empirically derived. It accounts for the signal omission that increases with the station spacing. In a test area located in the German Alps, the method was successfully applied to the determination of a quasigeoid profile of 23 km length. For a station spacing from a few 100 m to about 2 km, the accuracy of the quasigeoid was found to be about 1–2 mm, which corresponds to a relative accuracy of about 0.05-0.1 ppm. Application examples are given, such as the local and regional validation of gravity field models computed from gravimetric data and the economic gravity field determination in geodetically less covered regions. Copyright Springer Numéro de notice : A2008-168 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29163 [article]

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Transforming ellipsoidal heights and geoid undulations between different geodetic reference frames / C. Kotsakis in Journal of geodesy, vol 82 n° 4-5 (April - May 2008)

Public [article]  inJournal of geodesy > vol 82 n° 4-5 (April - May 2008) . - pp 249 - 260 Titre : Transforming ellipsoidal heights and geoid undulations between different geodetic reference frames Type de document : Article/Communication Auteurs : C. Kotsakis, Auteur Année de publication : 2008 Article en page(s) : pp 249 - 260 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux [Termes descripteurs IGN] coordonnées cartésiennes [Termes descripteurs IGN] coordonnées curvilignes [Termes descripteurs IGN] ellipsoïde de référence [Termes descripteurs IGN] géoïde gravimétrique [Termes descripteurs IGN] hauteur ellipsoïdale [Termes descripteurs IGN] repère de référence [Termes descripteurs IGN] similitude [Termes descripteurs IGN] transformation de Helmert Résumé : (Auteur) Transforming height information that refers to an ellipsoidal Earth reference model, such as the geometric heights determined from GPS measurements or the geoid undulations obtained by a gravimetric geoid solution, from one geodetic reference frame (GRF) to another is an important task whose proper implementation is crucial for many geodetic, surveying and mapping applications. This paper presents the required methodology to deal with the above problem when we are given the Helmert transformation parameters that link the underlying Cartesian coordinate systems to which an Earth reference ellipsoid is attached. The main emphasis is on the effect of GRF spatial scale differences in coordinate transformations involving reference ellipsoids, for the particular case of heights. Since every three-dimensional Cartesian coordinate system ‘gauges’ an attached ellipsoid according to its own accessible scale, there will exist a supplementary contribution from the scale variation between the involved GRFs on the relative size of their attached reference ellipsoids. Neglecting such a scale-induced indirect effect corrupts the values for the curvilinear geodetic coordinates obtained from a similarity transformation model, and meter-level apparent offsets can be introduced in the transformed heights. The paper explains the above issues in detail and presents the necessary mathematical framework for their treatment. Copyright Springer Numéro de notice : A2008-169 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29164 [article]

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A new method for three-carrier GNSS ambiguity resolution / U. Fernandez-Plazaola in Journal of geodesy, vol 82 n° 4-5 (April - May 2008)

Public [article]  inJournal of geodesy > vol 82 n° 4-5 (April - May 2008) . - pp 269 - 278 Titre : A new method for three-carrier GNSS ambiguity resolution Type de document : Article/Communication Auteurs : U. Fernandez-Plazaola, Auteur ; T. Martin-Guerrero, Auteur ; J. Entrambasaguas, Auteur Année de publication : 2008 Article en page(s) : pp 269 - 278 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement du signal [Termes descripteurs IGN] factorisation de Cholesky [Termes descripteurs IGN] phase GPS [Termes descripteurs IGN] résolution d'ambiguïté [Termes descripteurs IGN] signal GNSS Résumé : (Auteur) A new method for resolving the carrier-phase integer ambiguity in Global Navigation Satellite Systems (GNSS) is presented: the MOdified Cholesky factorization for Ambiguity (MOCA) resolution. The characteristics and features of this method are described and results obtained using a software simulator and an emulator are presented to validate its efficiency. The results are then compared to those obtained using another existing method and good performance of the MOCA method in new GNSS systems is shown. Furthermore, the proposed method yields accurate results even when short time spans are used or when there are poor estimations of measurement error, making it immune to non-ideal conditions and ultimately a practical solution for real applications. Copyright Springer Numéro de notice : A2008-170 Affiliation des auteurs : non IGN Thématique : IMAGERIE/POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29165 [article]

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Length-of-day and space-geodetic determination of the Earth's variable gravity field / G. Bourda in Journal of geodesy, vol 82 n° 4-5 (April - May 2008)

Public [article]  inJournal of geodesy > vol 82 n° 4-5 (April - May 2008) . - pp 295 - 305 Titre : Length-of-day and space-geodetic determination of the Earth's variable gravity field Type de document : Article/Communication Auteurs : G. Bourda, Auteur Année de publication : 2008 Article en page(s) : pp 295 - 305 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes descripteurs IGN] analyse comparative [Termes descripteurs IGN] champ de pesanteur terrestre [Termes descripteurs IGN] données GRACE [Termes descripteurs IGN] données TLS (télémétrie) [Termes descripteurs IGN] GRACE [Termes descripteurs IGN] télémétrie laser sur satellite [Termes descripteurs IGN] variation Résumé : (Auteur) The temporal variations of the Earth’s gravity field, nowadays routinely determined from satellite laser ranging (SLR) and GRACE (Gravity Recovery And Climate Experiment), are related to changes in the Earth’s rotation rate through the Earth’s inertia tensor. We study this connection from actual data by comparing the traditional length-of-day (LOD) measurements provided by the International Earth Rotation and Reference Systems Service (IERS) to the variations of the degree-2 and order-0 Stokes coefficient of the gravity field determined from fitting the orbits of the LAGEOS-1 and -2 satellites since 1985. The two series show a good correlation (0.62) and similar annual and semi-annual signals, indicating that the gravity-field-derived LOD is valuable. Our analysis also provides evidence for additional signals common to both series, especially at a period near 120 days, which could be due to hydrological effects. Copyright Springer Numéro de notice : A2008-171 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=29166 [article]

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