USING GROUND-PENETRATING RADAR TO DETECT LAYERS OF DISCONTINUOUS DIELECTRIC-CONSTANT

Many sandy soil materials consist of layers with different textures. Water in an unsaturated sandy soil can be funneled and start to flow expeditiously and preferentially as it encounters inclined coarse sand lenses. Along these funnel-type preferential-flow pathways, soil moisture is close to saturation, while the coarse sand lenses underneath the pathways are very dry. To nondestructively detect the existence of a coarse sand lenses is important in order to predict and estimate the influence of funnel-type preferential flow. The objective of this study was to demonstrate that ground-penetrating radar (GPR) can detect layers with a sharp discontinuity in dielectric constant from their surroundings. A GPR with a 450-MHz antenna was towed on the surface of a diving pool to detect a 2.4-m-long polyvinyl chloride (PVC) plate submerged in the pool at different depths and inclinations. The scenario would be similar to detecting a dry coarse layer embedded in a uniform saturated sandy soil. Results showed that GPR could accurately detect the depth, dimensions, and inclination of the plate from the 25- to 150-cm depth. Because sandy soils generally have an electrical conductivity of 10 to 1000 times less than the water in the pool, we expect that a 450-MHz GPR has the potential to accurately detect depth, dimensions, and inclination of an embedded coarse sand layer up to the 3-m depth.