Electromagnetic matched-field processing for target height finding with over-the-horizon radar

The refraction of over-the-horizon skywave radar signals by the ionosphere facilitates wide-area surveillance. While current systems measure target ground range, azimuth, and velocity they do not estimate target altitude, which is important for classification purposes. A method akin to matched-field processing in underwater acoustics is proposed for target height-finding. The approach exploits the delay-Doppler differences between direct and surface-reflected multipath returns from the target. In particular, the coherent sum of these multipath returns can be matched in the complex delay-Doppler space for a single dwell to estimate target altitude, ground range, and radial velocity. A maximum likelihood estimate (MLE) of these target coordinates is developed without requiring a knowledge of the target backscatter reflection coefficients. The performance of the MLE is evaluated through simulation for an uncertain quasi-parabolic ionosphere and compared to the Cramer-Rao lower bound (CRLB).