Near-field and timing effects in simulation of focused array radar signals from a mine in subsurface clutter

In a previous paper (Raemer, Rappaport and Miller, Proc. SPIE 3392, Orlando, FL, April 1998) we discussed a frequency-domain simulation of GPR returns from buried mines in clutter due to random permittivity inhomogeneities, using a focused array radar system (Rappaport and Reidy, SPIE 2747, Orlando, FL, April 1996, pp. 202-213). 3-D image plots of the illuminated volume resulting from this simulation were presented and showed that a mine buried a few inches deep in clay loam or sandy soil appears distinguisable from the clutter if the rms deviation of the permittivity from its mean is less than ten percent of the mean permittivity. The simulation is designed to be a forward model for signal processing algorithms for mine detection and location. Hence, both accuracy and running speed are important considerations. The code discussed in our previous paper is very fast, but contains approximations that compromise the accuracy of the electromagnetic modeling. The recent work on which the present paper is based addresses improvements in accuracy, emphasizing inclusion of near-field effects and more accurate depiction of the timing algorithm that is the basis of the focused array system. The results obtained from the more accurate algorithms require more running time to obtain but are still sufficiently fast for use as a forward model for signal processing.