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Space-borne remote sensing imaging allows precise coverage of vast regions with basic data for geological exploration while significantly reducing exploration costs. These data provide valuable information for geological mapping and mineral exploration through highlighting geological structures such as lineaments, faults, and lithological contacts. The use of radar constitutes a very useful complement to optical remote sensing data, especially as regards to the surface but also the subsurface detection of structures. Specifically in and desert areas, radar waves penetrate the dry surface sand sheet and highlight concealed geological structures or fossil river systems. We present a synthesis of two experiments designed to compare the contribution of radar and optical images to geological exploration using the Akjoujt region in Mauritania and the Bir Safsaf region in Egypt as study sites. Ground-Penetrating Radar (GPR) is used to evaluate volume scattering coming from subsurface dielectric heterogeneities in cases of radar penetration of the dry sand. This evaluation is based on correlating the reflectivity of the GPR section with backscattering coefficients extracted from radar images. Radar clearly demonstrates superior capability for precise detection of surface structures associated with dikes, lithological variation, or paleo-hydrogeological features. The effectiveness of radar for mapping in arid environments lies in the fact that geological features can be distinguished on the basis of their morphological expression and surface roughness. We also confirm that low frequency radar (L-band) can retrieve information about subsurface structures down to a few meters' depth, where optical images cannot. (c) 2005 Elsevier Ltd. All rights reserved.