Radar Ionospheric Impact Mitigation

Accurate real-time determination of the three-dimensional electron density distribution of the ionosphere is required to mitigate ionospheric delay and refraction effects on Air Force ground-based space-surveillance radars. We have developed a system for processing dual frequency GPS beacon data to produce a real-time dynamic ionospheric model. The core of the inversion technique is Tikhonov’s methodology for solving ill-posed problems extended to multidimensional nonlinear inverse problems and optimized for fast numerical solution. The resulting solution is guaranteed to be spatially and temporally smooth and to agree with input data within measurement error. The system automatically estimates GPS measurement noise and receiver-transmitter biases. We call this method GPSII, for GPS Ionospheric Inversion. In Phase I we validated GPSII using synthetic data and tested the performance of the method as the number of GPS receivers is reduced from many to few and even a single GPS receiver. In the Phase II effort we will refine this method and mature it for operational use and develop the capability to estimate and geographically display the validity/error bounds of its solutions. We will also consider methods of providing an alert function for anomalous ionospheric conditions for such features as the subauroral trough/boundary blob and equatorial plumes.