from: http://science.nasa.gov/science-news/science-at-nasa/2011/16may_groundtracks/
Unique Space Image of Alabama Tornado Tracks
May
16, 2011: NASA has released a unique satellite image tracing the damage
of a monster EF-4 tornado that tore through Tuscaloosa, Alabama, on
April 27th. It combines visible and infrared data to reveal damage
unseen in conventional photographs.
"This is the first time
we've used the ASTER instrument to track the wake of a super-outbreak
of tornadoes," says NASA meteorologist Gary Jedlovec of the Marshall
Space Flight Center in Huntsville, AL.
Click the Picture for a Larger Image
In
the picture, captured just days after the storm, pink represents
vegetation and aqua is the absence of vegetation. The tornado ripped up
everything in its path, scouring the Earth's surface with its terrible
force. The "tearing up" of vegetation makes the tornado's track stand
out as a wide swath of aqua.
"This image and others like it are
helping us study the torn landscape to determine just how huge and
powerful these twisters were and to assess the damage they inflicted,"
says Jedlovec.
ASTER, short for Advanced Spaceborne Thermal
Emission and Reflection Radiometer, orbits Earth onboard NASA's Terra
spacecraft. Its data products include digital elevation maps from
stereo images; surface temperatures; vegetation maps; cloud and sea ice
data; and more. Last spring the instrument helped track the movement of
the oil spill in the Gulf of Mexico...
To detect the scars left
by the twisters, ASTER senses the visible and infrared energy reflected
from the planet's surface. Destruction like crushed houses, torn and
snapped trees, and uprooted crops are evident in the multi-wavelength
images.
"A demolished house, debris and soil scattered on
vegetated surfaces, and damaged trees and crops all change the pattern
of reflected radiation measured by the satellite," explains Jedlovec.
"We can analyze these patterns to help storm survey teams evaluate the
damage."
Ground teams conducting field surveys of tornado damage
must try to pinpoint where the twisters touched down, how long they
stayed on the ground, and the force of their winds. But doing this from
ground level can be tricky. Some places are nearly impossible to reach
by foot or car. Also, in remote areas, damage often goes unreported, so
survey teams don't know to look there.
This is where satellites can help.
"To
get an accurate picture survey teams need to look everywhere that
sustained damage – even unreported areas. Satellite sensors detect
damage in rural areas, wilderness areas, and other unpopulated areas.
Only with that knowledge can surveyors determine the true track of a
tornado."
Otherwise, says Jedlovec, a twister could have
flattened a single dwelling in a remote location, killing everyone
inside, and no one would know.
Another sample of ASTER tornado data showing three nearly-parallel tracks of destruction.
Less
critical but still important are home owners' insurance issues. To
evaluate claims submitted by storm victims, insurance companies rely on
National Weather Service storm reports based on the field surveys.
"Let's
say you live in a remote area," says Jedlovec. "If there's no record of
a storm passing over your area, you could be out of luck."
Jedlovec
and colleagues are working now to produce satellite images of other
areas ravaged by the historic outbreak of tornadoes.
"We want to help the storm victims any way we can."
