Water content and porosity estimated from ground-penetrating radar and resistivity

Abstract

Both ground-penetrating radar and the resistivity method have proven to be useful tools for exploring water content variations, since related parameters such as dielectric constant and the resistivity of rocks and sediments are highly dependent on moisture content. These methods were used independently to estimate volumetric water content in the unsaturated zone and porosity in the saturated zone in a 100-m sandy section. Two sample sites along the profile were also chosen for a shallow geophysical investigation and soil sampling, to enable the calibration and verification of the indirect geophysical methods. The grain distribution at these sites is dominated by medium-sized sand (0.25–0.5 mm). The water content was 6.9 vol.% and calculated porosities are 37% and 40% respectively. At each of these sites the mean water content values calculated from resistivity are within one percentage unit of measured water content while those calculated from ground-penetrating radar give higher values by as much as 2.9 percentage units. The water contents in the unsaturated zone in the section, estimated from resistivity and ground-penetrating radar, show very similar trends, although that deduced from ground-penetrating radar is generally somewhat larger, consistent with the results from the sample sites. The mean porosity values obtained from the two methods in the saturated zone are in good agreement.