NASA / SCIENCE PHOTO LIBRARY NASA / SCIENCE PHOTO LIBRARY
Great Wall of China. Satellite radar images of the Great Wall of China. At left is a coloured image obtained using 4 radar channels. The Great Wall is the orange line running from top to bottom. Vegetation appears red and water is black. The area within the white rectangle, as recorded by each individual channel, appears in the mono- chrome images at right. These images show that the wall is comprised of two segments (shown best in the uppermost image). Sections of wall built 600 years ago in the Ming dynasty appear as a bright, continuous line running from top to bottom. Older, Sui Dynasty, sections of wall appear as a broken line immediately to the right of the Ming wall.
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