Broadband TDR permittivity spectra of lossy soils at medium to high water contents: Separation of electrode polarization from Maxwell-Wagner relaxation by modeling

Abstract

We discuss complex permittivity spectra of two lossy soils measured from 6 kHz to 6 GHz using time domain reflectometry, in which Maxwell-Wagner relaxation (MWR) is present but also unwanted electrode polarization EP, mainly below 1 MHz, is strong. The soils are mostly quartz, with one having lesser calcite and the other lesser gypsum. Volumetric water contents ranged from 8.5-30.9%. We use a simple model that adds an EP diffusion term to Debye-type terms for the MWR and free water relaxation centered near 19 GHz, and which allows us to separate the EP from the MWR. All samples show MWRs centered from 1-196 MHz, regardless of water content, and with small to significant Cole-Cole factors. The increasing water content diminishes the effect of MWR, likely by decreasing the conductive and dielectric contrasts between isolated inclusions and the soil matrix, but still can strongly contribute to attenuation rate across the 100-1000 MHz GPR bandwidth.