In the year 2000 Houston officially exceeded Los Angeles as the city with the worst air quality in the United States. Since then, major research has been underway to characterize the type, extent and sources of air pollutants in and around Houston. The Multi-angle Imaging SpectroRadiometer (MISR) is participating in work underway to study Houston's air quality (see JPL Space Images). These MISR views portray Houston and Galveston Bay on September 12, 2002, and display data from three of MISR's nine cameras along with a map of retrieved aerosol optical thickness.
The left-hand panel is a natural-color view from MISR's vertical-viewing (nadir) camera. The center images cover the same geographic area, from the perspectives of the 70-degree forward-viewing and 70-degree backward viewing cameras. The appearance of haze is enhanced in these oblique views, and the overall area appears significantly brighter in the oblique forward view because the atmospheric particles scatter more sunlight into the forward direction. Due to geometric parallax, clouds appear to move relative to the ground as the view angle changes.
At right is a map of aerosol optical depth, a measure of the amount of aerosol present in the atmosphere and one of several key variables used to characterize their climatic and environmental influence. The extent of haze across Galveston Bay can be identified by the presence of light blue and green pixels, and places where clouds or other factors precluded a retrieval are shown in dark grey. MISR uses the changes in the atmosphere's ability to transmit light and the variation in scene brightness at different viewing angles to retrieve aerosol optical depth, and to deduce some information about particle properties, such as size, shape and composition.
These data are being used as part of the Houston regional air quality study. Airborne pollution particles that contribute to the poor air quality come in part from upwind power plants and petrochemical manufacturing facilities. Over a dozen local observing stations are scattered across the area to monitor air quality. The MISR aerosol data help provide a context into which the particulate pollution sources, the monitoring site observations, and locations downwind, can all be placed.
The Multi-angle Imaging SpectroRadiometer observes the daylit Earth continuously and every 9 days views the entire globe between 82 degrees north and 82 degrees south latitude. These data products were generated from a portion of the imagery acquired during Terra orbit 14553. The panels cover an area of 380 kilometers x 704 kilometers, and utilize data from blocks 65 to 69 within World Reference System-2 path 25.
MISR was built and is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Office of Earth Science, Washington, DC. The Terra satellite is managed by NASA's Goddard Space Flight Center, Greenbelt, MD. JPL is a division of the California Institute of Technology.