This thesis is concerned with the modelling of Global Positioning System (GPS) phase multipath. GPS is increasingly used for very high precision (centimetre level) engineering surveying applications such as setting out on construction sites and the control of major civil engineering plant (e.g. bulldozers, graders and pavement layers). In such applications the phase of the carrier signal is the basic observable and the dominant error source is multipath (electromagnetic reflections of the carrier waves from surfaces in the surroundings of the antennas). The work contained in the thesis has been carried out in collaboration with the LCPC (Laboratoire Central des Ponts et Chaussées) in Nantes, France, which made available its test facility and Leica Geosystems, Heerbrugg, Switzerland, a GPS manufacturer, which funded the work and which made available modified equipment for testing.The specific subject of the research is the assessment and improvement of the capabilities of a Phase Multipath Mitigation Window correlator (PMMW) to model GPS multipath phase errors. The phase window correlator is a new sampling technique dedicated to the estimation of multipath errors in phase measurements. The thesis contains background material on GPS multipath mitigation and on several existing patents related to

GPS applications that require precise phase solutions in difficult environments, where loss of lock is likely, would benefit from instantaneous (single-epoch) phase integer ambiguity resolution. Among these applications are aircraft positioning and attitude determination during a photogrammetric flight, engineering surveying, and large-scale mapping. This paper reviews current GPS on-the-fly (OTF) techniques; a single-epoch ambiguity resolution approach is discussed in detail. Test results from 48 h of static data and 105 min. of kinematic data are presented. Results are also provided to demonstrate the ability of the algorithm to determine the attitude of a platform. Comparison of the technique's performance with that of commercial software demonstrates subcentimeter precision results all of the time (100 percent success), provided that at least five satellites are available and multipath errors are small.

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