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GPS meteorology : with focus on climate applications / Tong Ning (2012)    

Public Titre : GPS meteorology : with focus on climate applications Type de document : Thèse/HDR Auteurs : Tong Ning, Auteur Editeur : Göteborg [Suède] : Chalmers University of Technology Année de publication : 2012 Importance : 82 p. Format : 21 x 30 cm ISBN/ISSN/EAN : 978-91-7385-675-1 Note générale : Thesis for the degree of doctor of philosophy, Department of Earth and Space Sciences, Chalmers University of Technology, Gothenburg, Sweden Langues : Anglais (eng) Descripteur : [Termes IGN] données GPS [Termes IGN] modèle atmosphérique [Termes IGN] retard troposphérique zénithal [Termes IGN] teneur en vapeur d'eau [Termes IGN] teneur intégrée en vapeur d'eau Résumé : (auteur) The vital role of water vapour in the Earth’s climate system requires measurements of the atmospheric Integrated Water Vapour (IWV) with a long-term stability and a high accuracy. This work focuses on using the Global Positioning System (GPS) to provide IWV estimates for climate applications. The advantages of the GPS measurements are that they can be performed independently on the weather and have a high temporal resolution (a few minutes) as well as a continuously improving spatial resolution (a few km for some local networks). The uncertainty of the GPS-derived IWV highly depends on the accuracy of the estimated Zenith Total Delay (ZTD), which is determined by many parameters, i.e. satellite orbit errors, ionospheric delay, signal multipath, antenna related errors (e.g. phase centre variations), and mapping functions. We demonstrated that the uncertainty of the GPS-derived IWV below 1 kg/m2 is achievable. The long-term change of the IWV can be an independent data source to detect climate changes. Using a global GPS IWV data set covering a 15-year-long time period, we found estimated IWV trends in a range from ¡1.65 to +2.32 kg/(m2¢decade) which, however, are comparable to the trend uncertainties varying from 0.21 to 1.52 kg/(m2¢decade). The trend uncertainty is mainly caused by the short-term variations of the IWV which cannot be modelled accurately. The uncertainty is also due to the errors in IWV estimates, which are random and/or elevation-dependent systematic errors. A higher elevation cutoff angle used in the GPS data analysis (a 25± was revealed for the time period investigated and for the region of Fennoscandia) can be an advantage to reduce the impact of such systematic errors. The GPS-derived IWV can also be used for the evaluation of climate models. The IWV derived from the GPS measurements acquired at 99 European sites, each with a maximum time series of 14 years, were compared to the IWV simulated by a regional climate model. Overall, a monthly mean difference of »0.5 kg/m2 (model¡GPS) is obtained where a significant seasonal variation is seen in the difference. The model is too dry in the summer. Study of the diurnal cycle of the IWV using both the GPS data and the model simulation shows a good agreement for the phase while a smaller amplitude is seen in the results from the model. Note de contenu : 1 Introduction 1.1 The role of water vapour in the climate system 1.2 Measurements of the atmospheric water vapour 1.3 Thesis structure 2 Measurement Techniques 2.1 Radiosonde 2.2 Radio techniques . 2.3 Summery of Paper A 3 Uncertainty Analysis of the IWV from GPS 3.1 Statistical analysis 3.2 Theoretical analysis 3.3 Summary of Paper B 4 GPS Meteorology for Climate Applications 4.1 Detection of climate changes using GPS data 4.2 Summary of Paper C 4.3 Evaluation of climate models using GPS data 4.4 Summary of Paper D 5 Conclusions Numéro de notice : 14899 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Thèse étrangère Note de thèse : PhD : Earth and Space Sciences : Chalmers University of Technology, Sweden : 2012 DOI : sans En ligne : https://core.ac.uk/download/pdf/70594409.pdf Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=76783

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Space geodesy techniques / R.T.K. Jaldehag (1995)

Public Titre : Space geodesy techniques : an experimental and theoretical study of antenna sources Type de document : Monographie Auteurs : R.T.K. Jaldehag, Auteur Editeur : Göteborg [Suède] : Chalmers University of Technology Année de publication : 1995 Collection : Technical report num. 276 Importance : 100 p. Format : 21 x 30 cm ISBN/ISSN/EAN : 978-91-7197-168-5 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] antenne [Termes IGN] coin réflecteur [Termes IGN] diffusion du rayonnement [Termes IGN] Global Positioning System [Termes IGN] interférométrie à très grande base [Termes IGN] mesure de précision [Termes IGN] positionnement par GPS [Termes IGN] positionnement par ITGB [Termes IGN] rebond post-glaciaire [Termes IGN] réseau géodésique permanent [Termes IGN] Suède [Termes IGN] SWEPOS [Termes IGN] système de positionnement par satellites [Termes IGN] trajet multiple Index. décimale : 30.00 Géodésie - généralités Résumé : (Auteur) This thesis presents work associated with antenna related error sources, as well as antenna design, in space geodesy utilizing the techniques of Very-Long-Baseline Interferometry (VLBI) and the Global Positioning System (GPS). Geodetic VLBI uses large ra-dio telescopes, often in global networks observing at least a few times per year. As the number of dedicated antennas for this purpose is limited, also antennas designed for radio astronomical research are used. However, new feed systems are needed to handle the si-multaneous dual-frequency observations and the large bandwidth in geodetic VLBI. This thesis describes and numerically evaluates such a feed system. The design has the advan-tage of not interfering with existing front-end receivers of traditional Cassegrain antennas. In contrast to VLBI antenna systems, GPS antennas have low directivity in order to receive signals from the satellites in different directions simultaneously. The disadvantage with such antennas is the relatively high susceptibility to scattering from structures close to the antenna. Two studies presented in this thesis show that signal scattering from structures associated with the mounting of the antenna to the pillar and with the pillar itself, might be a significant source of error. As nearby structures are in general located below the antenna, scattering from these structures may be minimized using antennas with reduced side- and back-lobe levels. This thesis presents results from a preliminary study of two new designs of such antennas. The Swedish permanent GPS network, SWEPOS, consists of 20 stations distributed across Sweden. One of the scientific motivations for this network is to monitor crustal motions associated with postglacial rebound. This thesis describes SWEPOS, and results from almost 18 months of daily observations are presented and compared to models of postglacial rebound. The results from SWEPOS have also uncovered two major error sources. One of them is the scattering effect mentioned above. The other, which also is investigated in this thesis, is related to snow accumulated on the top of the pillars and on the radomes that covers the antennas. This accumulation appears to refract and delay the GPS signals, and thus degrade the positioning accuracy. Note de contenu : Preface PART 1 Chapter 1 Introduction 1.1 Space Geodesy Techniques 1.2 Global Geodynamics Chapter 2 Geodetic Very-Long-Baseline Interferometry 2.1 Background 2.2 The Main Principles 2.3 Antennas and Feeds Chapter 3 The Global Positioning System 3.1 Background 3.2 The Main Principles 3.3 Relative Positioning Using the Carrier Phase Observables 3.4 Error Sources 3.4.1 Satellite and Receiver Clocks 3.4.2 Satellite Orbits 3.4.3 Atmospheric Delay 3.4.4 Antenna Related Effects Chapter 4 Summary and Main Points of Thesis Papers 4.1 Main Points of Paper A 4.2 Main Points of Paper B 4.3 Main Points of Paper C 4.4 Main Points of Paper D 4.5 Main Points of Paper E 4.6 Main Points of Paper F References PART 2 Paper A Paper B Paper C Paper D Paper E Paper F Numéro de notice : 18238 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Monographie Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=55358

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Satellite-Earth range measurements : Correction of the excess path length due to atmospheric water vapour by ground based microwave radiometry / Gunnar Elgered (1985)

Public Titre : Satellite-Earth range measurements : Correction of the excess path length due to atmospheric water vapour by ground based microwave radiometry Type de document : Rapport Auteurs : Gunnar Elgered, Auteur ; B. Ronnang, Auteur ; E. Winberg, Auteur ; J. Askne, Auteur Editeur : Göteborg [Suède] : Chalmers University of Technology Année de publication : 1985 Collection : Research report num. 147 Importance : 112 p. Format : 21 x 30 cm Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Rayonnement électromagnétique [Termes IGN] hyperfréquence [Termes IGN] propagation ionosphérique [Termes IGN] propagation troposphérique [Termes IGN] radiomètre à hyperfréquence [Termes IGN] teneur en vapeur d'eau [Termes IGN] water vapour radiometer Index. décimale : 24.30 Rayonnement électromagnétique Résumé : (Auteur) This report deals with the excess delay of radio waves penetrating the neutral atmosphere of the earth, especially the delay due to water vapour, and reviews the state of the art of sounding techniques and instrumentation, in particular microwave radiometry. The physical background of the water vapour radiometer (WVR) method is presented and seven different types of WVR are described in detail. The expected accuracies of wet path delays vary with the local climate as well as with instrumental errors and the operating frequencies of the WVR. It is shown that errors in the wet path delay for zenith observations range from O.M to 0.9 cm rms for optimum WVR frequencies and instrumental errors of 0.5 K rms. Two different WVR designs - one with high accuracy and one with low cost (but less accurate) - are proposed for the ESA POPSAT system. Numéro de notice : 18239 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Rapport Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=41451

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Satellite Earth range measurements : correction of the excess path length due to atmospheric water vapour by ground based microwave radiometry / Gunnar Elgered (1985)

Public Titre : Satellite Earth range measurements : correction of the excess path length due to atmospheric water vapour by ground based microwave radiometry Type de document : Rapport Auteurs : Gunnar Elgered, Auteur ; E. Ronnang, Auteur ; E. Winberg, Auteur ; J. Askne, Auteur Editeur : Göteborg [Suède] : Chalmers University of Technology Année de publication : 1985 Collection : Research report num. 147 Importance : 112 p. Format : 21 x 30 cm Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement du signal [Termes IGN] atmosphère terrestre [Termes IGN] humidité de l'air [Termes IGN] hyperfréquence [Termes IGN] onde radioélectrique [Termes IGN] propagation troposphérique [Termes IGN] radiomètre à hyperfréquence [Termes IGN] vapeur d'eau Index. décimale : 24.20 Traitement du signal Résumé : (Auteur) This report deals with the excess delay of radio waves penetrating the neutral atmosphere of the earth, especially the delay due to water vapour, and reviews the state of the art of sounding techniques and instrumentation, in particular microwave radiometry. The physical background of the water vapour radiometer (WVR) method is presented and seven different types of WVR are described in detail. The expected accuracies of wet path delays vary with the local climate as well as with instrumental errors and the operating frequencies of the WVR. It is shown that errors in the wet path delay for zenith observations range from 0.4 to 0.9 cm rms for optimum WVR frequencies and instrumental errors of 0.5 K rms. Two different WVR designs - one with high accuracy and one with low cost (but less accurate) - are proposed for the ESA POPSAT system. Numéro de notice : 56389 Affiliation des auteurs : non IGN Thématique : IMAGERIE/POSITIONNEMENT Nature : Rapport Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=43781

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Radio interferometry as a probe of tectonic plate motion / G. Lundqvist (1984)

Public Titre : Radio interferometry as a probe of tectonic plate motion Type de document : Monographie Auteurs : G. Lundqvist, Auteur Editeur : Göteborg [Suède] : Chalmers University of Technology Année de publication : 1984 Collection : Technical report num. 150 Importance : 83 p. Format : 21 x 30 cm Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] interférométrie à très grande base [Termes IGN] positionnement par ITGB [Termes IGN] tectonique des plaques Index. décimale : 30.82 Applications géophysiques de géodésie spatiale Numéro de notice : 18246 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Monographie Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=55360

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