Estimation of Water Content in Partially Saturated Soil Horizons with Ground-penetrating Radar

Abstract

Ground-penetrating radar (GPR) measurements have been used to map the absolute water content of water retentive layers found within the vadose zone of the superficial aquifer at the Gnangara Mound near Perth, Western Australia. The lateral water content distribution was derived from a pseudo 3D GPR dataset acquired over a podzolic soil profile. The water content of the bulk vadose zone was estimated from travel times. We discuss the parameters that influence the quantification of water content within a water retentive layer. By constraining key variables as layer thickness, porosity, Lichteneker-Rother model parameters, background permittivity and point of reflection, we can make a reasonable quantification of water content in the water retentive soil horizon. Calculated water content is shown to lie within reported values. The horizons were mapped laterally and reveal large variations throughout the test site. Our GPR derived hydrogeologic model is confirmed by time-lapse neutron logs and a high-resolution electrical resistivity image. Finally we compare results with total reflected energy from the interval above the regional water table and obtain a good correlation with the water content map.