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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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Code-barres	Cote	Support	Localisation	Section	Disponibilité
18238-01	30.00	Livre	Centre de documentation	Géodésie	Disponible