NIU meteorologist uses NASA satellite to track storm damage to Illinois crops

by Tom Parisi

NIU Professor Mace Bentley has devised a new technique to help farmers assess crop damage from storms and other natural disasters. Bentley led a team of researchers that used data produced by a NASA satellite orbiting more than 400 miles above the earth to estimate the cost of crop damage from hail and wind storms that swept through west-central Illinois.

Mace Bentley

"This could become the preferred method for assessing crop destruction from any natural or man-made disaster," said Bentley, a meteorology professor in the Department of Geography.

His study on the satellite technique is published as the cover story in the current Bulletin of the American Meteorological Society. The study also caught the attention of WTVO-TV in Rockford and the Peoria Journal Star newspaper.

Bentley said imagery produced from the satellite data found significant damage that went undetected by traditional means of assessment. He and two University of Georgia researchers used data produced by the U.S. satellite known as Landsat 7, which acquires high-resolution images of the earth's land surface.

Each year thousands of thunderstorms erupt in the United States, causing as much as $3 billion in property and agricultural losses. Many of the most damaging thunderstorms are concentrated in the central plains and Corn Belt regions.

"Spatial mapping of agricultural damage could be used by farmers, insurance companies and even meteorologists examining storm formation and downburst potential," Bentley said. "Combining this technology with radar would help meteorologists identify and be able to recognize storm features that produce the greatest amounts of damage. As advances in satellite remote sensing continue, there also is evidence that these techniques could prove useful for damage assessment in urban and suburban areas as well."

The satellite-produced imagery has distinct advantages over standard methods of storm-damage assessment, which typically consist of drive-by observations or occasional aerial photography. Those methods are particularly inadequate when trying to estimate the number of acres damaged. "Using data from the Landsat 7 represents a superior method of identifying actual acres that sustain damage," Bentley said.

Landsat 7 data can be used to measure differences in ground reflectance among different land-surface types. The satellite can detect chlorophyll absorption in vegetation and will identify changes in ground reflectance once crops have been destroyed—or within a week to 10 days after a storm. With the launch of Landsat 7 in 1999, the cost of acquiring data has dropped significantly, Bentley said.

For the study, he and his colleagues examined two wind and hail storms that rolled through a total of 14 counties in the corn- and soybean-rich region of west-central Illinois on Aug. 12 and Aug. 18 of 1999. The researchers compared data from July 12 (before the storms) and Aug. 28 (after the storms) to determine damage extent.

The major storm on Aug. 12, destroyed thousands of acres of corn across the area, causing more than $53 million in crop damage in eight counties, according to estimates published in Storm Data, a monthly publication produced by the National Climatic Data Center. A second series of storms six days later caused an additional $4 million in hail damage to corn and soybeans.

In comparison, Landsat 7 data detected more than $100 million in damage from the two storms. However, actual losses were not that high because of prevailing soft-soil conditions and the ability of farmers to modify harvesting equipment to salvage blown-down crops.

"Conditions were just right to make the crops salvageable, something we couldn't determine from the satellite imagery alone," Bentley said.

"It's much easier to determine hail damage than wind damage," he added. "That's not real surprising because large hail pulverizes crops. Wind, on the other hand, may simply blow the crops over. Sometimes portions remain rooted and still survive, though less productive and more difficult to harvest.

"By combining the old-fashioned methods of storm-damage assessment with the high-tech imagery, we can get more accurate readings of crop damage," Bentley said. "And when we're talking about millions of dollars in potential losses, that's good news for farmers and insurance companies."