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 http://www.jpl.nasa.gov/earth/features/houston.cfm). 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 qualtiy. 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.
Image credit: NASA/GSFC/LaRC/JPL, MISR Team.
Text acknowledgment: Clare Averill (Acro Service Corporation/Jet Propulsion
Laboratory), Ralph Kahn (Jet Propulsion Laboratory).
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