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Global height datum unification : a new approach in gravity potential space / Alireza A. Ardalan in Journal of geodesy, vol 79 n° 9 (December 2005)  

Public [article]  inJournal of geodesy > vol 79 n° 9 (December 2005) . - pp 512 - 523 Titre : Global height datum unification : a new approach in gravity potential space Type de document : Article/Communication Auteurs : Alireza A. Ardalan, Auteur ; A. Safari, Auteur Année de publication : 2005 Article en page(s) : pp 512 - 523 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] géoïde terrestre [Termes IGN] International Terrestrial Reference System [Termes IGN] Iran [Termes IGN] levé gravimétrique [Termes IGN] niveau moyen des mers [Termes IGN] ondelette d'Abel-Poisson [Termes IGN] positionnement par GNSS [Termes IGN] potentiel de pesanteur terrestre [Termes IGN] problème des valeurs limites [Termes IGN] système de référence altimétrique [Termes IGN] système de référence local Résumé : (Auteur) The problem of "global height datum unification" is solved in the gravity potential space based on: (1) high-resolution local gravity field modeling, (2) geocentric coordinates of the reference benchmark, and (3) a known value of the geoid's potential. The high-resolution local gravity field model is derived based on a solution of the fixed-free two-boundary-value problem of the Earth's gravity field using (a) potential difference values (from precise leveling), (b) modulus of the gravity vector (from gravimetry), (c) astronomical longitude and latitude (from geodetic astronomy and/or combination of (GNSS) Global Navigation Satellite System observations with total station measurements), (d) and satellite altimetry. Knowing the height of the reference benchmark in the national height system and its geocentric GNSS coordinates, and using the derived high-resolution local gravity field model, the gravity potential value of the zero point of the height system is computed. The difference between the derived gravity potential value of the zero point of the height system and the geoid's potential value is computed. This potential difference gives the offset of the zero point of the height system from geoid in the "potential space", which is transferred into "geometry space" using the transformation formula derived in this paper. The method was applied to the computation of the offset of the zero point of the Iranian height datum from the geoid's potential value W0=62636855.8 m 2/S2 . According to the geometry space computations, the height datum of Iran is 0.09 m below the geoid. Numéro de notice : A2005-518 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-005-0001-0 En ligne : https://doi.org/10.1007/s00190-005-0001-0 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=27654 [article]

Exemplaires(2)

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266-05091	RAB	Revue	Centre de documentation	En réserve L003	Disponible
266-05092	RAB	Revue	Centre de documentation	En réserve L003	Disponible

Analysis of long-range network RTK during a severe ionospheric storm / Pawel Wielgosz in Journal of geodesy, vol 79 n° 9 (December 2005)  

Public [article]  inJournal of geodesy > vol 79 n° 9 (December 2005) . - pp 524 - 531 Titre : Analysis of long-range network RTK during a severe ionospheric storm Type de document : Article/Communication Auteurs : Pawel Wielgosz, Auteur ; I. Kashani, Auteur ; Dorota A. Grejner-Brzezinska, Auteur Année de publication : 2005 Article en page(s) : pp 524 - 531 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] correction ionosphérique [Termes IGN] GPS en mode cinématique [Termes IGN] ionosphère [Termes IGN] Ohio (Etats-Unis) [Termes IGN] perturbation ionosphérique [Termes IGN] positionnement cinématique en temps réel [Termes IGN] résolution d'ambiguïté [Termes IGN] station GPS [Termes IGN] station permanente [Termes IGN] tempête [Termes IGN] temps réel Résumé : (Auteur) The network-based GPS technique provides a broad spectrum of corrections to support RTK (real-time kinematic) surveying and geodetic applications. The most important among them are the ionospheric corrections generated in the reference network. The accuracy of these corrections depends upon the ionospheric conditions and may not always be sufficient to support ambiguity resolution (AR), and hence accurate GPS positioning. This paper presents the analyses of the network-derived ionospheric correction accuracy under extremely varying quiet and stormy geomagnetic and ionospheric conditions. In addition, the influence of the correction accuracy on the instantaneous (single-epoch) and on-the-fly (OTF) AR in long-range RTK GPS positioning is investigated, and the results, based on post-processed GPS data, are provided. The network used here to generate the ionospheric corrections consists of three permanent stations selected from the Ohio Continuously Operating Reference Stations (CORS) network. The average separation between the reference stations was 200 km and the test baseline was 121 km long. The results show that, during the severe ionospheric storm, the correction accuracy deteriorates to the point when the instantaneous AR is no longer possible, and the OTF AR requires much more time to fix the integers. The analyses presented here also outline the importance of the correct selection of the stochastic constraints in the rover solution applied to the network derived ionospheric corrections. Numéro de notice : A2005-519 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-005-0003-y En ligne : https://doi.org/10.1007/s00190-005-0003-y Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=27655 [article]

Exemplaires(2)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
266-05091	RAB	Revue	Centre de documentation	En réserve L003	Disponible
266-05092	RAB	Revue	Centre de documentation	En réserve L003	Disponible

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)  

Public [article]  inJournal of geodesy > vol 79 n° 9 (December 2005) . - pp 540 - 551 Titre : Effect of the STRM global DEM on the determination of a high-resolution geoid model: A case study in Iran Type de document : Article/Communication Auteurs : R. Kiamehr, Auteur ; Lard Erik Sjöberg, Auteur Année de publication : 2005 Article en page(s) : pp 540 - 551 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] altitude [Termes IGN] anomalie de pesanteur [Termes IGN] géoïde gravimétrique [Termes IGN] géoïde local [Termes IGN] Iran [Termes IGN] MNS SRTM [Termes IGN] modèle numérique de surface [Termes IGN] modèle numérique de terrain [Termes IGN] nivellement [Termes IGN] positionnement par GPS [Termes IGN] propagation d'erreur Résumé : (Auteur) Any errors in digital elevation models (DEMs) will introduce errors directly in gravity anomalies and geoid models when used in interpolating Bouguer gravity anomalies. Errors are also propagated into the geoid model by the topographie and downward continuation (DWC) corrections in the application of Stokes's formula. The effects of those errors are assessed by the evaluation of the absolute accuracy of nine independent DEMs for the Iran region. It is shown that the improvement in using the high-resolution Shuttle Radar Topography Mission (SRTM) data versus previously available DEMs in gridding of gravity anomalies, terrain corrections and DWC effects for the geoid model are significant. Based on the Iranian GPS/levelling network data, we estimate the absolute vertical accuracy of the SRTM in Iran to be 6.5 m, which is much better than the estimated global accuracy of the SRTM (say 16 m). Hence, this DEM has a comparable accuracy to a current photogrammetric high-resolution DEM of Iran under development. We also found very large differences between the GLOBE and SRTM models on the range of -750 to 550 m. This difference causes an error in the range of -160 to 140mGal in interpolating surface gravity anomalies and -60 to 60 mGal in simple Bouguer anomaly correction terins. In the view of geoid heights, we found large differences between the use of GLOBE and SRTM DEMs, in the range of - 1.1 to 1 m for the study area. The terrain correction of the geoid model at selected GPS/levelling points only differs by 3 cm for these two DEMs. Numéro de notice : A2005-609 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-005-0006-8 En ligne : https://doi.org/10.1007/s00190-005-0006-8 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=27656 [article]

Exemplaires(2)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
266-05091	RAB	Revue	Centre de documentation	En réserve L003	Disponible
266-05092	RAB	Revue	Centre de documentation	En réserve L003	Disponible

Is there utility in rigorous combinations of VLBI and GPS Earth orientation parameters? / Jim Ray in Journal of geodesy, vol 79 n° 9 (December 2005)  

Public [article]  inJournal of geodesy > vol 79 n° 9 (December 2005) . - pp 505 - 511 Titre : Is there utility in rigorous combinations of VLBI and GPS Earth orientation parameters? Type de document : Article/Communication Auteurs : Jim Ray, Auteur ; Jan Kouba, Auteur ; Zuheir Altamimi , Auteur Année de publication : 2005 Article en page(s) : pp 505 - 511 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux [Termes IGN] données GPS [Termes IGN] données ITGB [Termes IGN] orientation de la Terre [Termes IGN] point de liaison (géodésie) [Termes IGN] positionnement par GPS [Termes IGN] positionnement par ITGB [Termes IGN] série temporelle [Termes IGN] système de référence mondial Résumé : (Auteur) Combinations of station coordinates and velocities from independent space-geodetic techniques have long been the standard method to realize robust global terrestrial reference frames (TRFs). In principle, the particular strengths of one observing method can compensate for weaknesses in others if the combination is properly constructed, suitable weights are found, and accurate co-location ties are available. More recently, the methodology has been extended to combine time-series of results at the normal equation level. This allows Earth orientation parameters (EOPs) to be included and aligned in a fully consistent way with the TRF. While the utility of such multi-technique combinations is generally recognized for the reference frame, the benefits for the EOPs are yet to be quantitatively assessed. In this contribution, which is a sequel to a recent paper on co-location ties (Ray and Altamimi in J Geod 79(4–5): 189–195, 2005), we have studied test combinations of very long baseline interferometry (VLBI) and Global Positioning System (GPS) time-series solutions to evaluate the effects on combined EOP measurements compared with geophysical excitations. One expects any effect to be small, considering that GPS dominates the polar motion estimates due to its relatively dense and uniform global network coverage, high precision, continuous daily sampling, and homogeneity, while VLBI alone observes UT1-UTC. Presently, although clearly desirable, we see no practical method to rigorously include the GPS estimates of length-of-day variations due to significant time-varying biases. Nevertheless, our results, which are the first of this type, indicate that more accurate polar motion from GPS contributes to improved UT1-UTC results from VLBI. The situation with combined polar motion is more complex. The VLBI data contribute directly only very slightly, if at all, with an impact that is probably affected by the weakness of the current VLBI networks (small size and sparseness) and the quality of local ties relating the VLBI and GPS frames. Instead, the VLBI polar motion information is used primarily in rotationally aligning the VLBI and GPS frames, thereby reducing the dependence on co-location tie information. Further research is needed to determine an optimal VLBI-GPS combination strategy that yields the highest quality EOP estimates. Improved local ties (including internal systematic effects within the techniques) will be critically important in such an effort. Copyright Springer Numéro de notice : A2005-596 Affiliation des auteurs : IGN (1940-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-005-0007-7 Date de publication en ligne : 10/11/2005 En ligne : http://dx.doi.org/10.1007/s00190-005-0007-7 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=27727 [article]

Exemplaires(2)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
266-05091	RAB	Revue	Centre de documentation	En réserve L003	Disponible
266-05092	RAB	Revue	Centre de documentation	En réserve L003	Disponible