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Comparison of ray-tracing packages for troposphere delays / V. Nafisi in IEEE Transactions on geoscience and remote sensing, vol 50 n° 2 (February 2012)  

Public [article]  inIEEE Transactions on geoscience and remote sensing > vol 50 n° 2 (February 2012) . - pp 469 - 481 Titre : Comparison of ray-tracing packages for troposphere delays Type de document : Article/Communication Auteurs : V. Nafisi, Auteur ; L. Urquhart, Auteur ; M.C. Santos, Auteur ; et al., Auteur Année de publication : 2012 Article en page(s) : pp 469 - 481 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement du signal [Termes IGN] erreur systématique [Termes IGN] lancer de rayons [Termes IGN] modèle atmosphérique [Termes IGN] propagation troposphérique [Termes IGN] réfraction atmosphérique Résumé : (Auteur) A comparison campaign to evaluate and compare troposphere delays from different ray-tracing software was carried out under the umbrella of the International Association of Geodesy Working Group 4.3.3 in the first half of 2010 with five institutions participating: the GFZ German Research Centre for Geosciences (GFZ), the Groupe de Recherche de Geodesie Spatiale, the National Institute of Information and Communications Technology (NICT), the University of New Brunswick, and the Institute of Geodesy and Geophysics of the Vienna University of Technology. High-resolution data from the operational analysis of the European Centre for Medium-Range Weather Forecasts (ECMWF) for stations Tsukuba (Japan) and Wettzell (Germany) were provided to the participants of the comparison campaign. The data consisted of geopotential differences with respect to mean sea level, temperature, and specific humidity, all at isobaric levels. Additionally, information about the geoid undulations was provided, and the participants computed the ray-traced total delays for 5° elevation angle and every degree in azimuth. In general, we find good agreement between the ray-traced slant factors from the different solutions at 5° elevation if determined from the same pressure level data of the ECMWF. Standard deviations and biases are at the 1-cm level (or significantly better for some combinations). Some of these discrepancies are due to differences in the algorithms and the interpolation approaches. If compared with slant factors determined from ECMWF native model level data, the biases can be significantly larger. Numéro de notice : A2012-045 Affiliation des auteurs : non IGN Thématique : IMAGERIE/POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1109/TGRS.2011.2160952 Date de publication en ligne : 12/08/2011 En ligne : https://doi.org/10.1109/TGRS.2011.2160952 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=31493 [article]

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Ray-traced slant factors for mitigating the tropospheric delay at the observation level / L. Urquhart in Journal of geodesy, vol 86 n° 2 (February 2012)  

Public [article]  inJournal of geodesy > vol 86 n° 2 (February 2012) . - pp 149 - 160 Titre : Ray-traced slant factors for mitigating the tropospheric delay at the observation level Type de document : Article/Communication Auteurs : L. Urquhart, Auteur ; F. Nievinski, Auteur ; Marcelo C. Santos, Auteur Année de publication : 2012 Article en page(s) : pp 149 - 160 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] gradient de pente [Termes IGN] lancer de rayons [Termes IGN] modèle météorologique [Termes IGN] positionnement ponctuel précis [Termes IGN] propagation troposphérique [Termes IGN] signal GPS Résumé : (Auteur) Three-dimensional ray tracing through a numerical weather model has been applied to a global precise point positioning (PPP) campaign for modeling both the elevation angle- and azimuth-dependence of the tropospheric delay. Rather than applying the ray-traced slant delays directly, the delay has been parameterized in terms of slant factors, which are applied in a similar manner to traditional mapping functions, but which can account for the azimuthal asymmetry of the delay. Five strategies are considered: (1) Vienna Mapping Functions 1 (VMF1) and estimation of a residual zenith delay parameter; (2) VMF1, estimation of a residual zenith delay and estimation of two tropospheric gradient parameters; (3) three-dimensional ray-traced slant factors and estimation of a residual zenith delay; (4) using only ray-traced slant factors and no estimation of any tropospheric parameters and; (5) using both ray-traced slant factors and estimating a residual zenith delay and two tropospheric gradient parameters. The use of the ray-traced slant factors (solution 3) showed a 3.8% improvement in the repeatability of the up component when compared to the assumption of a symmetric atmosphere (solution 1), while the estimation of two tropospheric gradient parameters gave the best results showing an 7.6% improvement over solution 1 in the up component. Solution 4 performed well in the horizontal domain, allowing for sub-centimeter repeatability but the up component was degraded due to deficiencies in the modeling of the zenith delay, particularly for stations located at equatorial latitudes. The magnitude of the differences in the mean coordinates between solution 2 and solution 3, and the strong correlation with the differences between the north component and the ray-traced gradients (coefficient of correlation of 0.83), as well as the impact of observation geometry on the gradient solution indicate that the use of the ray-traced slant factors could have an implication on the realization of reference frames. The estimated tropospheric products from the PPP solutions were compared to those derived from ray tracing. For the zenith delay, a root mean square (RMS) of 5.4 mm was found, while for the gradient terms, a correlation coefficient of 0.46 for the N–S and 0.42 for the E–W was found for the north–south and east–west components, suggesting that there are still important differences in the gradient parameters which could be due to either errors in the NWM or to non-tropospheric error sources leaking into the PPP-estimated gradients. Numéro de notice : A2012-143 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-011-0503-x Date de publication en ligne : 04/09/2011 En ligne : https://doi.org/10.1007/s00190-011-0503-x Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=31590 [article]

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Troposphere delay modeling based on numerical weather models / Johannes Böhm (31/08/2011)    

Public Titre : Troposphere delay modeling based on numerical weather models Type de document : Article/Communication Auteurs : Johannes Böhm , Auteur ; Harald Schuh, Auteur ; L. Urquhart, Auteur ; et al., Auteur Editeur : Vienne [Autriche] : Vienna University of Technology Année de publication : 31/08/2011 Conférence : ESA 2011, 3rd International Colloquium, Scientific and fundamental aspects of the Galileo programme 31/08/2011 02/09/2011 Copenhague Danemark Importance : 4 p. Format : 21 x 30 cm Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] lancer de rayons [Termes IGN] modèle atmosphérique [Termes IGN] modèle météorologique [Termes IGN] propagation troposphérique [Termes IGN] traitement de données GNSS Résumé : (Auteur) Modern troposphere delay models like the Vienna Mapping Functions (VMF1) are based on data from Numerical Weather Models (NWM) with a time resolution of typically 6 hours. Different from purely analytical formulations like the Global Mapping Functions, the VMF1 can account for real weather phenomena like changing high and low pressure systems and are thus more accurate. Additionally, the zenith hydrostatic delays can also be derived from NWM if pressure values recorded at the sites are not available. We compare the VMF1 and zenith delays as derived from data of the European Centre for Medium-range Weather Forecasts (ECMWF) with those parameters derived from data of the National Centers for Environmental Prediction (NCEP), and we find a good agreement between those two realizations with station height differences at the few-millimeter level. Numéro de notice : 14255 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Communication DOI : sans En ligne : http://www2.unb.ca/gge/Personnel/Santos/Boehm2011_3rd-Galileo-Colloquium.pdf Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=64321

Documents numériques

en open access 14255_ctap_tropospheric_delay_boehm.pdf Adobe Acrobat PDF

Impact of a priori gradients on VLBI-derived terrestrial reference frames / Johannes Böhm (2011) 

Public Titre : Impact of a priori gradients on VLBI-derived terrestrial reference frames Type de document : Article/Communication Auteurs : Johannes Böhm , Auteur ; H. Spicakova, Auteur ; L. Urquhart, Auteur ; et al., Auteur Editeur : Bonn : Universität Bonn Année de publication : 2011 Collection : Schriftenreihe des Instituts für Geodäsie und Geoinformation, ISSN 2699-6685 num. 22 Conférence : EVGA 2011, 20th working meeting of the European VLBI Group for Geodesy and Astrometry 29/03/2011 30/03/2011 Bonn Allemagne OA proceedings Importance : pp 128 - 132 Format : 21 x 30 cm Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux [Termes IGN] analyse diachronique [Termes IGN] données ITGB [Termes IGN] gradient de troposphère [Termes IGN] International Terrestrial Reference Frame Résumé : (Auteur) We compare the influence of two different a priori gradient models on the terrestrial reference frame (TRF) as determined from Very Long Baseline Interferometry (VLBI) observations. One model has been determined by vertical integration over horizontal gradients of refractivity as derived from data of the Goddard Data Assimilation Office (DAO), whereas the second model (APG) has been determined by ray-tracing through monthly mean pressure level re-analysis data of the European Centre for Medium-Range Weather Forecasts. We compare VLBI solutions from 1990.0 to 2011.0 with fixed DAO and APG gradients to a solution with gradients being estimated, and we find better agreement of station coordinates when fixing DAO gradients compared to fixing APG gradients. As a consequence, we recommend that gradients are constrained to DAO gradients, in particular in the early years of VLBI observations (up to about 1990), when the number of stations per session is small and the sky distribution is far from uniform. Later than 1990, the gradients can be constrained loosely and the a priori model is of minor importance. Numéro de notice : C2011-052 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Communication DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=64322

Documents numériques

en open access 14256_evga2011_boehm.pdf Adobe Acrobat PDF