Les satellites guident les personnels humanitaires pour le forage des puits destinés aux réfugiés africains   Sudanese refugee's gather outside their tents, Sunday, July 4, 2004, in the Koumouangou refugee camp in Chad near the Sudan border. An estimated 1 million Sudanese have been displaced during the conflict with Arab militias, with at least 200,000 fleeing into neighbouring Chad. Tents are from UNHCR (United Nations High Commission for Refugees).   Underground water is not visible in optical imagery   Underground water can be detected in radar imagery and water storage in alluvial deposits can be revealed down to 20 meters sub-surface.   Map of satellite and DEM derived drainage network, watersheds, underground water reserves in wadis, dams and water storage and proposed locations for drilling new wells. Release date: 7 septembre 2004