A laboratory investigation into soil moisture estimation using DInSAR

The ability to plan and move resources in the battlespace is a vital role in any military operation. As such, it is important to have current and predicted knowledge of the surface conditions of roads and transport routes. One of the key parameters in this respect is soil moisture. As moisture can vary rapidly, knowledge of both its spatial and temporal distribution is needed at high resolution. However, as yet, its reliable measurement at spatial scales of less than a kilometre has remained elusive. This work investigates the feasibility of using differential interferometric synthetic aperture radar (DInSAR) to construct dynamic time-series of soil moisture maps at high spatial resolution with a volumetric resolution on the order of 1%. The technique appears particularly appealing for desert regions where soils are comprised chiefly of sand with little clay content, there is minimal vegetation cover, and there is often little topography. The paper reports on a laboratory-based experimental investigation under controlled conditions to accurately investigate the phase and amplitude behaviour of C-band SAR signals reflected from a sandy soil with varying moisture content. Simultaneous detailed optical measurements of the surface topography were made in conjunction with the radar measurements, to monitor any vertical shifts in the soil horizon. The results indicate that the DInSAR deformation phase arises from changing penetrations depths into the sample, rather than from physical movement of the surface horizon, offering the prospect that it may be utilised as a proxy for soil moisture.