| Several canonical examples are considered as initial steps toward understanding wave physics associated with short-pulse scattering from buried targets. These examples include a buried, arbitrarily oriented thin wire as well as buried perfectly conducting bodies of revolution, such as cylinders and spheres. Further, prototype land mines are considered to demonstrate the ability of the algorithm to simulate realistic scenarios of ultra-wideband ground penetrating radar operation. The soil in all cases is modeled as a lossy, dispersive half space, with the electrical properties obtained from previously published results or from laboratory measurements. The scattering problem is solved in the frequency domain via the Method of Moments, with the time-domain fields synthesized via Fourier transform. A key aspect of this work is the use of the complex-image technique for the efficient computation of the half-space dyadic Green's function. The phenomenology associated with short-pulse scattering from buried targets is investigated in detail by examining both the time-domain scattered fields and the late-time resonant frequencies. With regard to the time-domain scattered fields, it is demonstrated that they are characterized by the single and multiple diffraction (and by creeping wave modes in the case of bodies of revolution), which characterizes time-domain scattering from the same targets in free space; additionally, the air-ground interface introduces target-interface reverberations which are not present in the free-space case. Contributions from the latter phenomenon complicate the scattered fields and can affect, for example, the buried-target late-time resonant frequencies. In particular, while the resonant frequencies of free-space targets are orientation independent, this is not true in general for buried targets: the contributions from target-interface reverberations are generally a function of the target depth and orientation. Additional factors in the buried-target problem are the effects of soil loss and dispersion. |
