Characterization of ground-penetrating radar (GPR) response in a variety of Earth materials under different moisture conditions

As part of a study using GPR to quantitatively determine Volumetric Moisture Content (VMC) spatially for hillslope hydrology and water leak detection applications, a series of controlled laboratory experiments were conducted to investigate material-specific GPR response to different VMC conditions. Using a specially developed GPR-soil hydrology test facility, six materials were tested with incremented moisture from dry to saturation. A number of directly derived GPR trace parameters acquired using Reflection Profiling Mode were used to develop and test VMC-GPR relationships to enable GPR measurement of soil moisture and to determine the effect of different material properties on hydraulic characteristics and how this is manifested in GPR response. Data was analysed in both the time and frequency domains as a depth-average and at specific depths beneath the subsurface. The most consistent parameter investigated used was the mean instantaneous amplitude. A strong textural dependence related to how the water interacted with the host material suggests that individual models can be combined to form a moisture response model for GPR based on the particle size distribution of a material. This only works for well-structured materials and where there is a relatively simple subsurface structure and where other system interference is low.