Rough-surface effects on subsurface target detection

The generally rough interface between air and ground produces two adverse effects on the performance of a forward-looking ground-penetrating radar system. The first is that the rough surface scatters some of the transmitted radar energy back to the receiver, raising the effective noise level. The second is the reduction in the coherent signal level scattered by a buried target and received by the radar, owing to the passage of the electromagnetic field once through the rough surface as it propagates toward the target and once again as it propagates back to the receiver. We address the second of these effects in this paper. The interface is modeled as a random phase screen, and we specifically consider the problem of backscattering form a buried conducting disk. We quantify the coherent and incoherent components of the backscattering cross-section of this target, using the physical-optics approximation to address the scattering problem itself. It is assumed that the variance of the surface roughness is small over the frequency range of interest. Representative numerical results are shown over the frequency band 300-1900 MHz, derived from the assumption of a Gaussian autocorrelation function of the surface roughness.