Real-Time Ionospheric Monitoring System Using GPS

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Abstract
Using data acquired from a GPS receiver, a real-time synoptic ionospheric monitoring system has been developed. The system is used at the Millstone Hill satellite tracking radar. Each GPS satellite transmits signals at two different L-band frequencies, L1 (1575.42 MHz) and L2 (1227.6 MHz). The total electron content (TEC) along the path to each satellite can be determined by combining both frequencies using the pseudorange and the phase data. The GPS data is input into a Kalman filter, which is used to predict the coefficients of a simple TEC model with azimuth and elevation dependence. This model takes advantage of the real-time knowledge of the variations in TEC around the radar site provided by the GPS data. The coefficients for this model are then sent to the satellite tracking computer, and the model is applied in real time to account for the ionospheric path delay to whatever satellite is currently in track. The preliminary results of using this ionospheric monitoring system are discussed.