This Seasat synthetic aperture radar image from Aug. 27, 1978, shows the Massachusetts coast from Nantucket Island in the south past Cape Cod and Boston to Cape Ann in the north.

This Seasat synthetic aperture radar image from Aug. 27, 1978, shows the Massachusetts coast from Nantucket Island in the south past Cape Cod and Boston to Cape Ann in the north. The dark patch east and south of Nantucket is caused by the Nantucket Shoals, where a shallow ocean bottom creates surface waves and currents that appear as variations in brightness on the image. More subtle darker and lighter stripes to the east and north of Cape Cod are caused by internal waves, which are formed within the ocean by tides, rather than on the ocean surface by winds.

Seasat, which was managed by NASA's Jet Propulsion Laboratory in Pasadena, Calif., was the first satellite mission designed specifically to observe the ocean. Launched in 1978, it suffered a mission-ending power failure after 105 days of operation. But in that short time, Seasat collected more information about the ocean than had been acquired in the previous hundred years of shipboard research. The complete catalog of Seasat images has been processed digitally and is freely available from the Alaska Satellite Facility.

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