These views of the Louisiana and Mississippi regions were acquired before
and one day after Katrina made landfall along the Gulf of Mexico coast,
and highlight many of the changes to the rivers and vegetation that
occurred between the two views. The images were acquired by NASA's
Multi-angle Imaging SpectroRadiometer (MISR) on August 14 and August 30,
2005. These multiangular, multispectral false-color composites were
created using red band data from MISR's 46° backward and forward-viewing
cameras, and near-infrared data from MISR's nadir camera. Such a display
causes water bodies and inundated soil to appear in blue and purple hues,
and highly vegetated areas to appear bright green. The scene
differentiation is a result of both spectral effects (living vegetation
is highly reflective at near-infrared wavelengths whereas water is
absorbing) and of angular effects (wet surfaces preferentially forward
scatter sunlight). The two images were processed identically and extend
from the regions of Greenville, Mississippi (upper left) to Mobile Bay,
Alabama (lower right).
There are numerous rivers along the Mississippi coast that were not
apparent in the pre-Katrina image; the most dramatic of these is a new
inlet in the Pascagoula River that was not apparent before Katrina. The
post-Katrina flooding along the edges of Lake Pontchartrain and the city
of New Orleans is also apparent. In addition, the agricultural lands along
the Mississippi floodplain in the upper left exhibit stronger
near-infrared brightness before Katrina. After Katrina, many of these
agricultural areas exhibit a stronger signal to MISR's oblique cameras,
indicating the presence of inundated soil throughout the floodplain. Note
that clouds appear in a different spot for each view angle due to a
parallax effect resulting from their height above the surface.
The Multi-angle Imaging SpectroRadiometer observes the daylit Earth
continuously, viewing the entire globe between 82° north and 82° south
latitude every nine days. Each image covers an area of about 380
kilometers by 410 kilometers. The data products were generated from a
portion of the imagery acquired during Terra orbits 30091 and 30324 and
utilize data from blocks 64-67 within World Reference System-2 path 22.
MISR was built and is managed by NASA's Jet Propulsion Laboratory,
Pasadena, CA, for NASA's Science Mission Directorate, Washington, DC. The
Terra satellite is managed by NASA's Goddard Space Flight Center,
Greenbelt, MD. JPL is managed for NASA by the California Institute of
Technology.