LIMITATIONS IN GPS POSITIONING ACCURACIES AND RECEIVER TRACKING PERFORMANCE DURING SOLAR MAXIMUM

GPS signals are refracted by the dispersive ionosphere, resulting in ranging errors dependent on both the given signal frequency and ionospheric total electron content (TEC). Such range errors translate into a degradation of positioning accuracy. While it is possible to mitigate the impact of ionospheric effects on GPS positioning applications, through differential techniques (DGPS) and/or ionosphere modelling, residual errors may persist in regions where steep gradients or localised irregularities in electron density exist – particularly during periods of high geomagnetic activity. In addition, loss of GPS signal availability can occur in regions where small-scale irregularities in electron density cause amplitude fading and phase scintillations. Such effects are increased with enhanced ionospheric activity and are an issue for the reliable implementation of safety-critical GPS systems. A solar maximum was observed mid-late 2000, with associated degradations in GPS positioning accuracies and receiver tracking performance, while geomagnetic storm activity is expected to expected to peak in the following years (2001-2003). In this paper, the impact of solar maximum and storm activity on GPS applications is investigated, with a focus on the high latitude auroral region and the low latitude anomaly region. Long-term trends are studied using data from permanent GPS reference networks in Canada, the United States and Brazil. Degradations in GPS performance are quantified in terms of receiver tracking performance and enhanced differential and single point positioning errors.

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