Subsurface valleys and geoarcheology of the eastern Sahara revealed by Shuttle radar

Previously unknown buried valleys, geologic structures, and possible Stone Age occupation sites have been revealed through the Shuttle Imaging Radar (SIR-A) penetration of the extremely dry Selima Sand Sheet, dunes and drift sand of the eastern Sahara. Radar penetration of dry sand and soils varies with the wavelength of the incident signals, which is 24 cm for the SIR-A system, as well as incidence angle and electrical properties of the material which are largely determined by moisture content. The calculated depth of radar penetration of dry sand and granules has been established to be 5 m on the basis of laboratory measurements of Selima Sand Sheet sample electrical properties. September 1982 field studies in Egypt have verified SIR-A signal penetration depths of at least 1 m in the Selima Sand Sheet and drift sand, and 2 m or more in sand dunes.