In the high plateau of southwestern Bolivia, two large salt deserts, or
playas, are located between the eastern and western Andes. The Salar de
Uyuni is the largest and highest playa in the world, encompassing an
area of more than 9000 square kilometers and situated more than 3600
meters above sea level. It is separated by a range of hills from its
smaller neighbor to the north, the Salar de Coipasa. During the
Pleistocene the climate of the region was wetter and the entire area
was covered by a massive lake. As the waters slowly dried, abundant
dissolved minerals were left behind to form the playas. The salt pans
are now excellent indicators of rainfall fluctuations within the
region and are also important sites for the study of paleoclimatology.
These two image pairs from the Multi-angle Imaging SpectroRadiometer (MISR)
depict the playas on January 16, 2002 and January 3, 2003. At this time
of year the wet season has already begun, and the Salar de Coipaso is usually
at least partially flooded. Data from these two dates were processed
identically to preserve relative variations in brightness between them.
Varying degrees of surface moisture around the two playas are illustrated by
the different display techniques of the right and left-hand panels.
At left are two false-color views acquired by MISR's nadir camera. Data from
the near-infrared, green and blue bands are displayed as red, green and blue.
This spectral display causes bright, wet surfaces to appear
blue-green because water selectively absorbs longer wavelengths such
as near-infrared. Significantly more standing water is present in the
Salar de Coipaso in 2002 than in 2003. However, a stronger signal at
the near-infrared band on the 2003 date, which causes the overall hue
in the 2003 image to be redder than 2002, suggests an increase in
photosynthetic activity (plant growth) at the 2003 date compared with
one year earlier.
The right-hand panels were created using only red band data, and are
multi-angle composites in which color variations serve as a proxy for changes
in angular reflectance. Data from the 46-degree forward, nadir and 46-degree
backward-viewing cameras are displayed here as red, green and blue. The
angular composites contain information relating to surface moisture and/or
texture characteristics that are not apparent with a single view. In the
southern hemisphere, the backward pointing cameras receive a stronger
signal from surfaces which predominantly forward scatter sunlight
(which generally tend to be smooth and/or wet surfaces). The salt
encrusted playas appear bright white and gray but the edges of the
playas and some smaller salt flats exhibit a purple-blue hue that
corresponds with enhanced forward scattering, possibly caused by
greater moisture content of these soils. If this interpretation is
correct, it indicates that the soil moisture content is greater
around the playa perimeters on the 2003 date.
Thin, wispy clouds that are almost invisible over the Salar de Uyuni in the
nadir 2003 image are also more easily identified using the composite views,
since geometric parallax associated with the clouds' elevation above
the surface causes the individual camera images to be spatially
separated.
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 orbits 11071 and 16197. The panels
cover an area of 199 kilometers x 174 kilometers, and utilize data from blocks 106 to 107 within
World Reference System-2 path 233.
Image credit: NASA/GSFC/LaRC/JPL, MISR Team.
Text acknowledgment: Clare Averill (Acro Service Corporation/Jet Propulsion
Laboratory), David J. Diner (Jet Propulsion Laboratory).
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