MAP-PF multi-mode tracking for over-the-horizon radar

Detection, localization, and tracking in over-the-horizon radar (OTHR) systems is a challenging problem due to the existence of multiple propagation paths, or modes, between the transmitter, target, and receiver. Traditional OTHR multi-target tracking techniques use three isolated processes: slant azimuth/range/Doppler estimation (detection), followed by association of detections to targets and mode paths, followed by fusion of associated slant detections or tracks into a single track in Earth coordinates for each target. In this paper, we use the Maximum a Posteriori Penalty Function (MAP-PF) approach to formulate the tracking problem as a MAP estimation problem operating directly on the radar array data. The result is a two-step estimation process similar to traditional methods, except the processes are coupled via the penalty function and the data association step is eliminated. In the azimuth/range/Doppler estimation process, the penalty function guides the estimator to look for detections at slant coordinates of possible mode paths for the current target state. In the track estimation process, the penalty function adaptively determines the influence of mode path estimates on the final track estimates. Performance is demonstrated on simulated OTHR data in a scenario with two ionospheric layers and four propagation modes.