Nanjing, China City Walls

The largest city wall in the world is in Nanjing, China. It was built between 1366 and 1386 by the Ming Dynasty Emperor Zhu Yuangzhang to enclose and fortify his capital city. The wall is over 33 km long, is constructed from 350 million bricks, and is 14 meters wide, and 14-20 meters high. Its 13 massive gates today have been restored and house museums telling the story of the city of Nanjing. The ASTER image was acquired October 25, 2014, covers an area of 20.5 by 21.6 kilometers, and is located at 32.1 degrees north and 118.7 degrees east.

With its 14 spectral bands from the visible to the thermal infrared wavelength region and its high spatial resolution of about 50 to 300 feet (15 to 90 meters), ASTER images Earth to map and monitor the changing surface of our planet. ASTER is one of five Earth-observing instruments launched Dec. 18, 1999, on Terra. The instrument was built by Japan's Ministry of Economy, Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and data products.

The broad spectral coverage and high spectral resolution of ASTER provides scientists in numerous disciplines with critical information for surface mapping and monitoring of dynamic conditions and temporal change. Example applications are monitoring glacial advances and retreats; monitoring potentially active volcanoes; identifying crop stress; determining cloud morphology and physical properties; wetlands evaluation; thermal pollution monitoring; coral reef degradation; surface temperature mapping of soils and geology; and measuring surface heat balance.

The U.S. science team is located at NASA's Jet Propulsion Laboratory in Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate, Washington.

More information about ASTER is available at http://asterweb.jpl.nasa.gov/.