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A GPS-based study to improve the accuracy of local geodetic ties at co-located sites that exploits small-scale atmospheric structure / Dhiman Mondal (2018)    

Public Titre : A GPS-based study to improve the accuracy of local geodetic ties at co-located sites that exploits small-scale atmospheric structure Type de document : Article/Communication Auteurs : Dhiman Mondal, Auteur ; Pedro Elosegui, Auteur ; James Davis, Auteur ; Zuheir Altamimi , Auteur ; Virgilio de Brito Mendes, Auteur Editeur : Washington : National Aeronautics and Space Administration NASA Année de publication : 2018 Conférence : IVS 2018, 10th general meeting of International VLBI Service for Geodesy and Astrometry 03/06/2018 09/06/2018 Longyearbyen Norvège Open Access Proceedings Importance : pp 279 - 282 Note générale : bibliographie This work is supported under NASA Space Geodesy Research Program award 16-SGR16-0002. Langues : Anglais (eng) Résumé : (auteur) The development of the next-generation of very long baseline interferometry (VLBI) systems, known as VLBI Global Observing System (VGOS), is well underway. Co-location of VGOS stations with instruments from the other space geodetic techniques (i.e., GPS, SLR, and DORIS) is essential for synergistic, robust global reference frame realization. The localties between reference points of geodetic instrumentsat co-location sites effectively connect the various techniques together. Precise ties are required for a multi-technique reference frame that is suitable for high-accuracy geophysical applications such as global sea-level change. Unfortunately, the uncertainties of local tie vectors remain above 3 mm. We are investigating approaches that could improve the accuracy of relative positions estimates of the co-location sites. These approaches use external constraints based on local atmospheric structure at core geodetic sites where multi-techniques are co-located. The challenge is to add information to the geodetic solution based on our knowledge of atmospheric structure without biasing the estimates of the intersite vectors. Here, we present preliminary results from tests wherein atmospheric structure is used to enhance the strength of geodetic solutions and combinations. In this study, we use data from existing small-scale GPS networks as a proxy for co-location sites instrumented with next-generation geodetic systems. Numéro de notice : C2018-099 Affiliation des auteurs : Géodésie+Ext (mi2018-2019) Thématique : POSITIONNEMENT Nature : Communication nature-HAL : ComAvecCL&ActesPubliésIntl DOI : sans En ligne : https://ivscc.gsfc.nasa.gov/publications/gm2018/IVS-2018-General-Meeting-Proceed [...] Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=97035

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Modeling the neutral-atmospheric propagation delay in radiometric space techniques / Virgilio de Brito Mendes (1999)    

Public Titre : Modeling the neutral-atmospheric propagation delay in radiometric space techniques Type de document : Thèse/HDR Auteurs : Virgilio de Brito Mendes, Auteur ; Richard B. Langley, Directeur de thèse Editeur : Fredericton [Canada] : University of New Brunswick Année de publication : 1999 Collection : Technical report num. 199 Importance : 353 p. Format : 21 x 30 cm Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] atmosphère terrestre [Termes IGN] lancer de rayons [Termes IGN] modèle numérique [Termes IGN] réfraction atmosphérique [Termes IGN] retard troposphérique Résumé : (auteur) The propagation delay induced by the electrically-neutral atmosphere has been recognized as the most problematic modeling error for radiometric space geodetic techniques. A mismodeling of this propagation delay affects significantly the height component of position and constitutes therefore a matter of concern in space-geodesy applications, such as sea-level monitoring, postglacial rebound measurement, earthquake-hazard mitigation, and tectonic-plate-margin deformation studies. The neutral-atmosphere propagation delay is commonly considered as composed of two components: a "hydrostatic" component, due essentially to the dry gases of the atmosphere, and a "non-hydrostatic" component, due to water vapor. Each one can be described as the product of the delay at the zenith and a mapping function, which models the elevation angle dependence of the propagation delay. This dissertation discusses primarily the accuracy of zenith delay prediction models and mapping functions found in the scientific literature. This performance evaluation is based on a comparison against 32,467 benchmark values, obtained by ray tracing one-year's worth of radiosonde profiles from 50 stations distributed worldwide, and comprised different phases: ray-tracing accuracy assessment, model development, and model accuracy assessment. We have studied the sensitivity of the ray-tracing technique to the choice of physical models, processing strategies, and radiosonde instrumentation accuracy. We have concluded that errors in ray tracing can amount to a few centimetres, under special circumstances, but they largely average out for each station's time series of profiles. In order to optimize the performance of the models, we have established databases of the temperature-profile parameters using 50 additional sites, for a total of 100 radiosonde stations. Based on these large databases, we have developed models for lapse rate and tropopause height determination, which have improved significantly the performance of models using the information. From our model assessment we have concluded that the hydrostatic component of the zenith delay can be predicted with sub-millimeter accuracy, using the Saastamoinen model, provided accurate measurements of surface total pressure are available. The zenith non-hydrostatic component is much more difficult to predict from surface meteorological data or site dependent parameters, and the best models show values of root-mean-square (rms) scatter about the mean of a few centimetres in the zenith direction. Notwithstanding the large number of mapping functions we have analyzed, only a small group meet the high standards of modern space geodetic data analysis: Ifadis, Lanyi, MTT, and NMF. For the total number of radiosonde stations analyzed, none of the mapping functions revealed themselves to be superior for all elevation angles. For elevation angles above 15 degrees, Lanyi, MTT, and NMF yield identical mean biases and the best total error performances. At lower elevation angles, Ifadis and NMF are clearly superior. As regards the rms scatter about the mean, Ifadis performs the best for all elevation angles, followed closely by Lanyi. Note de contenu : 1- Introduction 2- The Earth's atmosphere 3- Neutral-atmosphere refraction 4- Data description and analysis 5- Ray tracing 6- Model assessment 7- Conclusions and recommendations Numéro de notice : 14876 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Thèse étrangère Note de thèse : PhD : Geodesy and geomatics : University of New-Brunswick : 1998 DOI : sans En ligne : https://gge.ext.unb.ca/Pubs/TR199.pdf Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=75930

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peut être téléchargé 14876 these 1998 Mendes Adobe Acrobat PDF