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

Many sandy soil materials consist of layers with different textures. W ater in an unsaturated sandy soil can be funneled and start to flow ex peditiously and preferentially as it encounters inclined coarse sand l enses. Along these funnel-type preferential-flow pathways, soil moistu re 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 i nfluence of funnel-type preferential flow. The objective of this study was to demonstrate that ground-penetrating radar (GPR) can detect lay ers with a sharp discontinuity in dielectric constant from their surro undings. A GPR with a 450-MHz antenna was towed on the surface of a di ving pool to detect a 2.4-m-long polyvinyl chloride (PVC) plate submer ged in the pool at different depths and inclinations. The scenario wou ld be similar to detecting a dry coarse layer embedded in a uniform sa turated sandy soil. Results showed that GPR could accurately detect th e depth, dimensions, and inclination of the plate from the 25- to 150- cm depth. Because sandy soils generally have an electrical conductivit y 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 .