Target altitude estimation in OTHR via diffuse surface scatter

The operational value of aircraft target information obtained from HF skywave (over-the-horizon) radar is substantially reduced when the altitude of the target is undetermined. A number of techniques for estimating altitude have been proposed, relying in each case on the interference between direct and specularly ground-reflected rays, and the resulting echo amplitude distribution in delay-Doppler space. For idealised propagation models, a useful degree of accuracy is predicted, but existing techniques cannot be said to yield a reliable and robust capability. In this paper we examine the potential of inverting echoes received via diffuse surface scatter to provide such information.