Seasonal GPR Signal Changes in Two Soil-Hillslopes.

Experimental evidence has shown that soil layering can significantly affect water movement.  So detailed knowledge of the spatial distribution of soil layering structures are needed when estimating subsurface soil water movement. In this study, we used GPR combined with high resolution real time soil water content monitoring to compare the seasonal GPR signal changes at the interfaces of soil layers in two soils. The results indicate that in deep Rushtown soil, reflection in BC-C horizon became clearer as soil became wetter. High resolution real time soil water content monitoring and field observation indicate the increased reflection may be due to the lateral flow above and below BC horizon, which increase the contrast along interfaces. While in shallow Weikert soil, reflections in soil -bedrock interface and weathered-unweathered rock interface become intermittent as soil became wetter. The reason was likely to be non uniform distribution of water into bedrock fracture, which created locally strong contrast between soil and bedrock leading to point scatter of GPR reflection. The results also indicate optimal time to detect soil horizon in two soils.  In addition, the results also indicate seasonal GPR survey with high resolution real time soil water content monitoring provided a useful methodology for improved understanding of hydrologic processes in the subsurface, which facilitates the formulation and test of different conceptualizations of subsurface network modeling