Estimation of soil electromagnetic parameters using frequency domain techniques

In this paper two frequency domain methods for characterization of the dielectric properties of dry sand over a broad microwave frequency range will be presented. The investigated electromagnetic parameters of the soil relevant for most GPR applications are dielectric permittivity and loss tangent. Although the majority of GPR applications concentrate on frequencies below 1 GHz, this work will investigate the constitutive parameters of soil with very low water content in three microwave bands (X, Ku and part of K) ranging from 7 to 20 GHz. In particular, this study will focus on the evaluation of the complex permittivity by means of a numerically robust evaluation rather than the well-known Nicolson-Ross-Weir (NRW) method. The proposed procedure yields the apparent real part of the permittivity and the loss tangent without the inaccuracy in the vicinity of λ_m/2 resonances known from the NRW method. The second approach utilizes a free space measurement, in which the soil is confined by a polystyrene probe holder in a mono-static GPR setup. The measurement result of the backscattered excitation will be compared with a commercial time-domain solver based on Finite-Integration-Technique (FIT). The material parameters of the electromagnetic model are adapted iteratively in the way that measurement and simulation results coincide. The measurement results of both frequency domain methods demonstrate the validity of the estimated dielectric parameters.