Full-Wave Removal of Internal Antenna Effects and Antenna-Medium Interactions for Improved Ground-Penetrating Radar Imaging

Antenna effects alter the detection of buried objects during ground-penetrating radar (GPR) surveys. In this paper, we propose a novel approach based on full-wave inversion to filter out antenna effects from GPR data. The approach, which is exact for locally planar layered media, resorts to a recently developed electromagnetic model that takes advantage of an intrinsic, closed-form solution of Maxwell's equations to describe the antenna-medium system. As any multilayered medium can be reduced to a half-space medium with effective, frequency-dependent, global reflection coefficients, the method consists in inverting the radar data to retrieve a frequency-dependent, half-space complex conductivity. Converted into the time domain, this quantity represents the filtered radar image. We validated the approach through numerical simulations and laboratory experiments with pipes buried in a sandbox. The results demonstrated the validity of the concept and showed that the filtered radar images include only medium reflections, which means an easier interpretation in terms of medium structures. Antenna radiation pattern effects are, however, not removed. This physically based approach including the full-wave antenna model appears to be very promising for improved subsurface imaging and provides the basis for multifrequency GPR data fusion as the source is inherently normalized.