Subsurface imaging with low frequency SAR Field validation in Egypt using a Ground-Penetrating Radar

We study the capabilities of low frequency radar systems to sound the subsurface in arid countries. This approach is based on the coupling between two complementary radar techniques: the airborne Synthetic Aperture Radar (SAR) used in L-band (1.2 GHz) for imaging large scale subsurface structures, and the Ground-Penetrating Radar (GPR) used between 500 and 900 MHz for sounding soils at a local scale, from the surface down to several meters. In this paper, we first recall the results obtained on the well-known site of Bir Safsaf (southern Egypt). The comparison between L-band SAR and GPR sections shows that penetration effects occur in many places, revealing rich subsurface structures. A numerical model is then proposed for quantitatively interpreting the SAR/GPR data. This model is based on electric field extrapolation in the frequency domain, taking into account the looking specificities of both the SAR and GPR systems. Simulated signals from given realistic geological cross sections can then be analyzed in order to understand the contribution of volume backscattering on both of radar systems. These results suggest that airborne radar systems in a lower frequency range (P-L band) should be able to detect soil structures down to several meters, leading to innovative Earth observation systems for geological and hydrogeological mapping in arid regions.