May 16, 2011

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.

Tornado Tracks (ground track, 550px)
An ASTER visible-IR image of tornado damage near Tuscaloosa, AL. []

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.

Tornado Tracks (damage, 200px)
Ground survey teams have a lot to contend with. [Youtube video]

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.

Tornado Tracks (three tracks, 550px)
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."

Author: Dauna Coulter | Editor: Dr. Tony Phillips | Credit: Science@NASA

More Information

ASTER Home Page

Terra Home Page

Gary Jedlovec heads up the SPoRT (Short-term Prediction and Research Transition) project at the Marshall Space Flight Center in Huntsville, Alabama, a city that was spared the worst of the damage, though an EF-5 tornado just missed it, destroying communities only a few miles away.

SPoRT personnel created the NASA images in this story using data provided courtesy of NASA Goddard Space Flight Center, the Land Processes Distributed Active Archive Center, Japan’s Earth Remote Sensing Data Analysis Center, the Ministry of Economy, Trade and Industry, along with the Japan Research Observation System Organization.

The ASTER image in this story came from an observation on May 4, 2011 at 11:45 A.M. local time (1645 UTC), and shows the tornado track was roughly 80.3 miles (129.2 kilometers) long and up to 1.5 miles (2.4 kilometers) wide.

For more information on using remote sensing to track tornado damage paths, see this paper by Jedlovec.