Large abundances of aerosols, or airborne particulates, over the
low-lying plains of northeastern India appear in dramatic contrast
with the relatively pristine air of the high-altitude Tibetan Plateau.
This contrast is illustrated in these Multi-angle Imaging
SpectroRadiometer images from October 15, 2001. These data represent an area of about 400 kilometers wide by 1600 kilometers long. The aerosols that
contribute to poor air quality over much of the Indian subcontinent
are believed to originate from industrial smoke, vehicle emissions,
and biomass burning.
The two images at left show the scene from MISR's 26-degree and
70-degree forward viewing angles, respectively. The high levels of
aerosols are accentuated in the 70-degree forward image, due to the
longer atmospheric path length associated with the more oblique
viewing angle. The abundance of aerosols is derived from the variation
of scene brightness and contrast as a function of observation angle,
and is displayed in the third panel from the left as optical depth.
This quantity is logarithmically related to the atmosphere's ability
to transmit light, and is one of several variables used to characterize
the climatic and environmental influence of aerosols. Areas where
retrievals were not obtained, such as the topographically complex
Himalayas in Nepal, and cloudy or very turbid areas, are shown in
Surface calculations for the 26-degree view direction are shown in the
rightmost panel. These calculations use the optical depth field to
estimate surface reflectances as if the intervening atmosphere
were not present. Making corrections for atmospheric scattering is
important when using reflectances measured from space in surface
classification and physical process studies. Note that the algorithms
used to produce these results are still being refined, and future
product versions may show some differences from the preliminary values
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