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Spotting erosion from space.

Spotting erosion from space

Billions of tons of dirt wash into the oceans each year, making soil one of the world's most endangered resources. Not only does topsoil erosion steal precious nutrients away from fields, it also increases the cost of farming and lowers food production. Now scientists are using satellite images to spot areas facing the greatest erosion danger.

Department of Agriculture researchers exploit the muddy side-effects of erosion in their search. As soil particles wash into lakes and rivers, they change water color by adding red hues, says Jerry C. Ritchie with the USDA in Beltsville, Md. The earthy tones allow Ritchie and his colleagues to find soil-filled lakes on images from the U.S. Landsat satellite, which carries several cameras, each recording a specific color of light.

The scientists start by subtracting all land areas from the satellite images, then examine the colors of the remaining lakes and reservoirs. By comparing the colors against a theoretical model they devised, the researchers can estimate with about 90 percent accuracy the total amount of suspended sediment in the water, Ritchie says. If used several times a year, this technique would quickly tell conservation officers which watersheds suffer the greatest erosion.

The model is based on over a decade's worth of comparisons between satellite images and water samples from a lake in Mississippi and another in nearby Arkansas. Since developing the system, the USDA scientists have tried it out on several more lakes and investigators in Oklahoma are currently testing it on a statewide basis, Ritchie says.
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Title Annotation:Geology
Author:Monastersky, Richard
Publication:Science News
Date:Jul 22, 1989
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