Mapping Palaeorivers from Satellite Radar and Surface-wave Velocities

Satellite radar data have revealed the existence of extensive palaeodrainage patterns below sand dunes in the eastern Sahara. So far, studies have focused mainly on the lateral mapping of these so-called radar rivers. We use seismic surface-wave data to estimate the penetration of satellite radar into the ground on a regional scale. We developed a scheme for the classification of radar backscatter intensity that allows the discrimination of direct surface backscatter in areas with hard rock at the surface from areas where the radar data penetrate the surface and provide information about palaeorivers in the subsurface. The estimated radar penetration depth is calibrated with seismic surface-wave velocity profiles. Corendering both data sets in 3D shows the high degree of correlation. The method is demonstrated on an area of about 200 x 200 km in the hyperarid desert of southwest Egypt. A 200-km high-resolution seismic section provides the shallow seismic data. The seismic surface waves confirm the existence of two phases of palaeovalleys in the area: wide valleys of several km in width from the Tertiary and Pleistocene rivers, the channels of which are mapped by the satellite radar data.