Several oil slicks occurred on Lake Maracaibo in
northwestern Venezuela between December 2002 and
January 2003, and were observed by various satellite
instruments. These images from the Multi-angle Imaging
SpectroRadiometer (MISR) provide new information relating to
one such event near the center of Lake Maracaibo on
December 26, 2002.
In unpolluted areas, the water surface is "ruffled"
by wind and the resulting wave facets divert reflected rays
into many directions. An oil film dampens the presence of
small wind-driven "capillary" waves, resulting in a
smoother, more mirror-like surface. Also, oil is more strongly
absorbing than the surrounding water. Therefore, at most
viewing angles, a surface slick will appear darker than the
surrounding unpolluted areas, whereas near the specular
angle (the angle at which a perfect mirror reflects light) it
will appear brighter. Simultaneous observation at multiple
view angles therefore enhances the reliability of oil-slick
detection using optical imaging.
An example of how the optical contrast of an oil film on
a water surface changes as a function of viewing angle is
illustrated by these false-color MISR images, comprised of
near-infrared, red and blue spectral data at three different
angles, using the vertical-viewing camera (left), the
26°-forward-viewing camera (center) and the 46°-forward-viewing
camera (right). A swirly area in the middle of the lake
appears darker than the surrounding waters at both the
nadir and 46° views, but brighter than the surrounding waters
at the 26° view. Of the three images, only the 26° camera
observes close to specular reflection angle.
Lake Maracaibo is the largest lake in South America. The
lake is somewhat saline, since it is connected to the Gulf of
Venezuela by a narrow strait in the north. Venezuela is the
largest oil producing nation in the Western Hemisphere, and
the Lake Maracaibo basin includes the largest oil fields and
almost a quarter of this nation's population.
The Multi-angle Imaging SpectroRadiometer observes the
daylit Earth continuously from pole to pole, 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
16081. The panels cover an area of 72 kilometers x 225
kilometers, and utilize data from blocks 81 to 83 within
World Reference System-2 path 8.
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.
Image credit: NASA/GSFC/LaRC/JPL, MISR Team
Text acknowledgment: Clare Averill (Acro Service Corporation/Jet Propulsion Laboratory).
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