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Radar imagery recovers lost links in the Great Wall of China


China's famed Great Wall stretches some 3,000 kilometers (1,850 miles) between eastern China and the Himalayas. Built and rebuilt over hundreds of years, it served as the military frontier for a series of ancient Chinese dynasties. The color radar image at left shows a 50 km (30 mile) segment of the Great Wall in a desert region of north-central China (37.7 N, 107.5 E), about 700 km west of Beijing. The bright vertical orange line (passing through the box) is a portion of the Wall built during the Ming Dynasty (about 1350-1500 AD), which stands some 5-8 meters high.

[Fig.1: False color SIR-C image of Great Wall. (NASA/JPL image P-45924 ).]

Just right of the Ming wall is a much older remnant of the Great Wall dating from the Sui Dynasty at about 500 AD. Finding remains of the Sui Dynasty wall by spaceborne radar imagery is helping archaeologists to map a major cultural feature that has been buried by desert sands for generations.

Black and white enlarged NASA/JPL images at  right, each about 3 by 2 km. in area, show two L-band views of the same square in the color image. The L-band (one of two, along with C-band, used by the Spaceborne Imaging Radar) provides relatively clear images of the two wall segments. Parallel to the wall are trees and orchards which appear as bright rectangles.These images, taken from the space shuttle Endeavour on April 10, 1994,  also show towns and two shallow lakes used for salt extraction.

 Fig.2 (right): Enlarged b/w views (NASA/JPL image P-45924 ).]


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