The influence of anomalous solar activity on mid-latitude global positioning system performance

As ranging signals from the GPS satellites pass from space to earth, their propagation speed is altered by the presence of free electrons in the ionosphere. Anomalous solar activity such as solar flares, coronal mass ejections, and sunspots as they are transported to earth via the solar wind can cause perturbations in the electron densities in the ionosphere. The effects of these perturbations on the GPS ranging signals as well as the effects on the performance of the dual-frequency GPS system were investigated.; Solar data from the Advanced Composition Explorer (ACE) satellite were used to designate periods of anomalous solar activity as well as quiet solar periods. These solar data were used in conjunction with GPS data from eight mid-latitude sites in the eastern United States. The GPS data were obtained from the Continuously Operating Reference Station (CORS) network as well as the International GPS Service (IGS). Specifically, the influence of solar activity on the total positioning error for a dual-frequency GPS receiver was analyzed.; The key results of this research were a time of day comparison of the average performance of the GPS system during times of anomalous solar activity to its performance during solar quiet times. During most of the day, anomalous solar activity was found to have little average effect on the performance of the dual-frequency GPS system. One exception is the time between local sunset and midnight when anomalous solar activity was shown to cause GPS positioning errors to increase on average by 1--2 meters. This increase is primarily due to the inability of GPS receivers to maintain signal lock on one or more satellites due to the scintillation induced amplitude fading. Certain times of moderate performance improvement during anomalous solar activity were also identified.