Effects of the ground surface on polarimetric features of broadband radar scattering from subsurface metallic objects

Throughout the world, the problem of buried unexploded ordnance (UXO) poses an enormous, persistent, and expensive problem. While UXO generally consist of sizable bodies of ferrous metal and can therefore be detected, with current technology it is extremely difficult to distinguish them reliably from typically widespread pieces of clutter. Thus the problem is one of subsurface discrimination. Our previous modeling work on scattering of ground penetrating radar (GPR) from metallic objects surrounded by an infinite soil-like medium has suggested the utility of a number of key discriminants, in broadband fully polarimetric sensing. In particular, resonance structure, induced field rotatation and ellipticity, and bistatic observation of scattered signals were shown to offer key information about target shape and size. Here we investigate the effects on signature features of the proximity of a ground surface to the target, for the common case of shallow burial (< 1 m). Overall our analyses suggest that the key discriminants seen in scattering in an infinite medium survive the complex interactions with the ground surface. In some instances these revealing signatures appear to be strengthened by the presence of a nearby surface. Multi-position backscatter also allows fundamental inferences about target elongation and symmetry when those cannot be obtained from single position viewing.