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 prototype system that processes phase and group delay time series from dual frequency GPS receivers and produces a dynamic ionospheric model over a fixed geographical area with dimensions of the order of several thousand kilometers that is consistent with all the input data. 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 the GPS measurement noise and receiver-transmitter biases. We propose to validate our algorithm using real and synthetic data, identify limitations in the approach as the number of GPS receivers is reduced from many to few or even a single GPS receiver (such limitations will be addressed in Phase II), and consider the incorporation of models for quasi-deterministic ionospheric features such as the subauroral trough/boundary blob and equatorial plumes to provide an alert function for anomalous ionospheric conditions.