University of California Water Resources Center

Monitoring of soil water content is a vital component for agricultural and ecological programs, and the key component for rational water resources management. The information obtained from monitoring is critical for optimizing crop yields, achieving high irrigation efficiencies, planning irrigation scheduling, and minimizing lost yield due to waterlogging and salinization. Such water content monitoring is also important for addressing issues of water quantity and quality, both relevant for managing the environmental impacts of irrigated agriculture and for protecting functional ecosystems. Water content information is also needed for a variety of other scientific investigations, such as climate change, environmental remediation, and engineering investigations.

There are currently no techniques available to yield information about soil heterogeneities and water content at both the resolution and spatial coverage needed to assist in many subsurface problems, and in particular, vineyard management. We investigated the applicability of a surface based geophysical tool, Ground-Penetrating Radar (GPR), for estimating soil water content under both controlled and natural field conditions. Our studies focused on use of travel time data obtained from both the ground wave and from the reflected wave of the GPR signal. Our research shows that GPR groundwave techniques offer an accurate, quick, and reliable approach for estimating shallow (top 20 cm of soil surface) soil water content in very high resolution and in a non-invasive manner, and we recommend further development of this approach for use as a field tool (i.e., technology transfer). Investigations using the reflected component of the GPR signal suggests that accurate estimates of water content can be obtained using this approach when the depth to the reflector is known. More work is necessary to assess the accuracy and feasibility of the GPR reflection approach under natural field conditions.