Near-field modeling of radar antennas for wave propagation in layered media: When models represent reality

Characterization of the electrical properties of a medium using ground-penetrating radar (GPR) appeals to inverse modeling, which has remained a major challenge in applied geophysics in particular due to antenna modeling limitations. In this paper, we propose a new near-field radar modeling approach for wave propagation in layered media. Radar antennas are modeled using an equivalent set of infinitesimal electric dipoles and characteristic, frequency-dependent, global reflection and transmission coefficients. These coefficients determine, through a plane wave decomposition, wave propagation between the radar reference plane, point sources, and field points. The interactions between the antenna and the medium are thereby inherently accounted for. The fields are calculated using three-dimensional Green´s functions. We validated the model using both time and frequency domain radars. The antennas were calibrated using measurements at different heights above a copper plane. The proposed model provided unprecedented results for describing near-field radar data collected over water, whose frequency-dependent electrical properties were described using the Debye model. Very good agreements were also obtained for measurements collected over water as validating medium for the inversions. The proposed modeling approach is fast and shows great promise for digital soil mapping or non-destructive material characterization.