(a) PALSAR radar observation of the coastal part of the Mauritania. The scale of grey corresponds to the back-scattering power. (b) Coastal part of the Tamanrasett paleodrainage (black) identified in the PALSAR image. Isohypse map of the bedrock roof showing the presence of paleovalleys (arrows) of the Arguin Basin
Japan: A Japanese Advanced Land Observing Satellite remote-sensing instrument, called Phased Array type L-band Synthetic Aperture Radar (PALSAR), has detected an ancient river network along a 320-mile stretch of the Sahara Desert. PALSAR is an active microwave sensor using L-band frequency to achieve day-and-night and all-weather land observation. The L-band (1.2 GHz) radar has the capability to penetrate meters of low electrical loss material such as Aeolian sand, and thus to probe the first meters of subsurface geological features in arid areas.
The radar observations of the coastal Mauritania area (Fig. 'a' above) provide geomorphological evidence for the existence of a paleodrainage system located in the Arguin Bay, between Cap Blanc and Cap Timiris. This newly identified paleoriver bed is about 520 km long. The reconstruction of the complete paleodrainage was not possible using the PALSAR because of the presence of thick sand dunes, which severely limits the radar detection of underlying sediment structures.
The radar data also revealed that the course of the paleoriver is perfectly aligned with paleovalleys identified in the Arguin Basin (Fig. 'b' above), as well as with the proximal tributaries of the submarine Cap Timiris Canyon system.