A Volume Scattering Model for Coupled Interpretation of Ground-Penetrating Radar (GPR) and Synthetic Aperture Radar (SAR)

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/spaceborne Synthetic Aperture Radar (SAR) used in L-band (1.2 GHz) for imaging large scale subsurface structures, and the Ground-Penetrating Radar (GPR) used at 900 MHz for sounding soils from the surface down to several meters. Recent results obtained on the well-known site in southern Egypt (Bir Safsaf) are recalled and constrain a numerical model for quantitatively interpreting the SAR/GPR data. This model is based on electric field extrapolation in the frequency domain, taking into account the aperture and the incidence angle of the antenna for both the SAR and GPR systems. Simulated signals from given realistic geological cross sections can then be analysed in order to understand the contribution of volume backscattering on both of radar systems. The model is tested on the Bir Safsaf site, and gives a good description of the dielectric behaviour, since observed and simulated backscattered signals are quite comparable. Discussion on the domain of validity for the model is presented as well as the perspectives that it could offer in the future missions of quantitative mapping of the subsurface in arid deserts.