The Global Positioning System (GPS) has been used for more than a decade for the accurate determination of position on the earth's surface, as well as navigation. The system consists of approximately thirty satellites, managed by the US Department of Defense, orbiting at an altitude of 20 200 kilometres, as well as thousands of stationary ground-based and mobile receivers. It has become apparent from numerous studies that the delay of GPS signals in the atmosphere can also be used to study the amosphere, particularly to determine the precipitable water vapour (PWV) content of the troposphere and the total electron content (TEC) of the ionosphere. This dissertation gives an overview of the mechanisms that contribute to the delay of radio signals between satellites and receivers. The dissertation then focuses on software developed at the Hartebeesthoek Radio Astronomy Observatory's (HartRAO's) Space Geodesy Programme to estimate tropospheric delays (from which PWV is calculated) in near real-time. In addition an application of this technique, namely the improvement of tropospheric delay models used to process satellite laser ranging (SLR) data, is investigated. The dissertation concludes with a discussion of opportunities for future work. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2004.

The Global Positioning System (GPS) has been used for more than a decade for the accurate determination of position on the earth's surface, as well as navigation. The system consists of approximately thirty satellites, managed by the US Department of Defense, orbiting at an altitude of 20 200 kilometres, as well as thousands of stationary ground-based and mobile receivers. It has become apparent from numerous studies that the delay of GPS signals in the atmosphere can also be used to study the amosphere, particularly to determine the precipitable water vapour (PWV) content of the troposphere and the total electron content (TEC) of the ionosphere. This dissertation gives an overview of the mechanisms that contribute to the delay of radio signals between satellites and receivers. The dissertation then focuses on software developed at the Hartebeesthoek Radio Astronomy Observatory's (HartRAO's) Space Geodesy Programme to estimate tropospheric delays (from which PWV is calculated) in near real-time. In addition an application of this technique, namely the improvement of tropospheric delay models used to process satellite laser ranging (SLR) data, is investigated. The dissertation concludes with a discussion of opportunities for future work. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2004.