Robust altitude estimation for over-the-horizon radar using a state-space model for multipath fading

In previous work, a matched-field estimate of aircraft altitude from multiple over-the-horizon radar dwells was presented. This approach exploits the altitude dependence of direct and surface reflected returns off the aircraft and the relative phase changes of these micro-multipath arrivals across radar dwells. Since this previous approach assumed high dwell-to-dwell predictability, it is sensitive to mismatch between modeled versus observed micro-multipath phase and amplitude changes from dwell-to-dwell. A generalized matched-field altitude estimate is presented based on a state-space model that accounts for random ionospheric and target-motion effects which degrade the dwell-to-dwell predictability of target returns. The new formulation results in an efficient, robust recursive maximum likelihood altitude estimate. Simulation and real data results suggest that the proposed technique can achieve an accuracy within 5000 ft. using 10-20 dwells, even with relatively high levels of uncertainty in modeling of dwell-to-dwell changes in the target return.