June 1, 1995 Wadi Kufra, Libya
The ability of a sophisticd radar instrument to image large regions of the world from space, using different frequencies the can penetrate dry sand cover, produced the discovery in this image: a previously unknown branch of an ancient river, buried under thousands of years of windblown sand in a region of the Sahara Desert in North Africa. This area is near the Kufra Oasis in southeast Libya, centered 23.3 degrees north latitude, 22.9 degrees east longitude. The image was acquired by the Spaceborne Imaging Radar-C/X-band Synthetic Aperture (SIR-C/X-SAR) imaging radar when it flew aboard the space shuttle Endeavour on its 60th orbit on October 4, 1994. This SIR-C image reveals a system of old, now inactive stream valleys, called "paleodrainage systems," which, during periods of wetter clim, carried running Water northward across the Sahara. The region is now hyper-arid, receiving only a few millimeters of rainfall per year, and the valleys are now dry "wadis," or channels, mostly buried by windblown sand. Prior to the SIR-C mission, the west branch of this paleodrainage system, known as the Wadi Kufra (the dark channel along the left side of the image), was recognized and much of its course outlined. The broader east branch of Wadi Kufra, running from the upper center to the right edge of the image, was, however, unknown until the SIR-C imaging radar instrument was able to delineate its dimensions at least 5 kilometers wide and nearly100 kilometers long (3 miles by 62 miles). The two branches of Wadi Kufra converge at the Kufra Oasis, at the cluster of circular fields at the top of the image. The farms at Kufra depend on irrigation Water from the Nubian Aquifer System. The paleodrainage pern unveiled by SIR-C suggests that the location of productive wells at the confluence of the old river valleys is no accident. Quite likely, the Water supply for the Kufra Oasis has been recharged by episodic runoff and by groundWater that moved northward in the alluvial fill of the old stream channels.
Rainfall was more abundant in this region during parts of the Qurnary when Stone Age (Paleolithic and lr Neolithic) people left their implements along the riverbanks. The SIR-C image, which clearly shows river channels cut into the surrounding bedrock, provides a "road map" for geoarchaeologists to locate artifacts and to better interpret the history of early people and climatic conditions in this region. The area shown is approximatly 120 kilometers by 78 kilometers (74 miles by 48 miles). North is toward the upper left. The colors in this image were obtained using the following radar channels: red represents the L-band (horizontally transmitted and received); green represents the average of the C- and L-band (horizontally transmitted and received); blue represents the C-band (horizontally transmitted and received). -----
Spaceborne Imaging Radar-C and X-band Synthetic Aperture Radar (SIR-C/X-SAR) is part of NASA's Mission to Planet Earth. The radars illumin Earth with microwaves, allowing detailed observation any time, regardless of Weather or sunlight conditions. SIR-C/X-SAR uses three microwave wavelengths: L-band (24 cm), C-band (6 cm) and X-band (3 cm). The multi-frequency image will be used by the International scientific community to better understand the global environment and how it is changing. The SIR-C/X-SAR d, complemented by aircraft and ground studies, will give scientists clearer insights into those environmental changes which are caused by nature and those changes which are induced by human activity. SIR-C was developed by NASA's Jet Propulsion Laborry. X-SAR was developed by the Dornier and Alenia Spazio companies for the German space agency, Deutsche Agentur fuer Raumfahrtangelegenheiten (DARA), and the Italian space agency, Agenzia Spaziale Italiana (ASI), with the Deutsche Forschungsanstalt fuer Luft und Raumfahrt e.v.(DLR), the major partner in science, operations and data processing of X-SAR.
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