Improvement of GPS Positioning Availability using Ground Elevation Information

This paper presents the initial results of research suggesting a concept of taking an advantage of known GIS information, primarily the ground elevation contour, to enhance the performance of satellite positioning systems in terms of improved availability and positioning accuracy. Recent advances of laser telemetry allow nowadays very accurate measurements of the Earth’s elevation down to sub-meter accuracy. Having such accurate information allows the Earth contour to be incorporated into the pseudorange solution equations by providing an additional relation between the horizontal position of the receiver and its height. This allows the removal of one unknown from the calculations of and hence requires one less satellite fix in order to provide a unique solution of the receiver position. This is especially important in shaded areas and urban canyons where it is difficult to ensure the visibility of at least four satellites (three in case of having already resolved the clock inaccuracy). The papers further various functions that may be used to approximate the ground elevation contours. Impact on expected position accuracy is also discussed. The research has been sponsored by the European Commission through the Integrated Project LIAISON under the Framework 6 programme (contract number: FP6-2003-IST-2-511766) [1].