Abstract/Summary

SubSAR is a new scheme for mapping subsurface features with synthetic aperture radar (SAR) at large stand-off distances applicable to airborne and satellite measurements. This is in sharp contrast to current techniques, where discrimination relies on close-proximity measurement of the scene, usually with a ground-based system. The scheme discriminates between surface and subsurface returns using a novel application of differential SAR interferometry (DInSAR). It is based on the differing phase histories of surface and subsurface features. Whereas the latter experiences phase delays in sympathy with variations in soil moisture, these are absent from the surface feature's phase history. To assess the predictions and performance of the model against measurements, a laboratory investigation was carried out at the GB-SAR Microwave Measurement Facility. C-band VV tomographic profiling (TP) was collected of a trihedral and a pile of cobble stones, buried in a sandy soil. The TP imagery displayed the vertical backscattering pattern through the soil, allowing separation of returns from the soil and buried features. Known amounts of water were added incrementally to the soil to precisely quantify DInSAR phase and backscatter behaviours of the soil and buried features. The measurements confirmed the two central tenets of the model: (i) a linear relationship between soil moisture and DInSAR phase, and (ii) that this is independent of incidence angle. Application and performance of the scheme applied to mapping subsurface archaeology is discussed. A low-level product would deliver a basic distinction between surface and subsurface features in SAR imagery. The high-level product, with supporting ground-truth data, could additionally deliver the depth of a feature.