As the summer 2012 drought continued to afflict the U.S. Midwest, water levels of the Mississippi River approached historic lows, halting barge and towboat traffic and seriously disrupting shipping traffic. Sand bars are exposed in this image (right) acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument on NASA's Terra spacecraft on Aug. 24, 2012, 13 miles (20 kilometers) north of Vicksburg, Miss. For comparison, the left image shows the same area in Sept. 2009. Vegetation is portrayed in red colors, and water as black or dark gray. The images cover an area of 12.1 by 17.2 miles (19.5 by 27.7 kilometers).

With its 14 spectral bands from the visible to the thermal infrared wavelength region and its high spatial resolution of 15 to 90 meters (about 50 to 300 feet), 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, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate, Washington, D.C.

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