Spotting danger from on high

Airborne sensors can identify mineral outcrops and soil that may contain natural asbestos

Airborne instruments can scan the ground to quickly and efficiently detect rocks and soil that may contain naturally occurring asbestos, researchers report.

HIGH SPY Airborne images confirm the presence of potentially asbestos-bearing serpentine minerals (red, orange) in California’s El Dorado County, north of the river (black) that bisects the image. White lines surround areas known to host such minerals. Previously unknown outcrops that might contain asbestiform minerals lie south of the river in Amador County (arrows at lower left). U.S. Geological Survey

In many regions, particularly in the West, rock outcrops can host several types of fibrous minerals known as asbestos. Though generally known for its past use as insulation in building construction, asbestos can also be a health concern for people who live on or near land that contains the minerals (SN: 7/8/06, p. 26). Field geologists in California have been mapping outcrops that could potentially contain asbestos for more than a century, says Gregg Swayze, a research geophysicist with the U.S. Geological Survey in Denver. Now, a technique developed by Swayze and his colleagues and described in the August Geology may make mapping remote areas quicker and easier.

Minerals have distinct chemical compositions and crystalline structures. The amount of each wavelength of light that is absorbed or reflected from a mineral’s surface often has a distinct fingerprint as well, Swayze says. Many minerals in the asbestos family — and the minerals from which they’re derived, such as the nonhazardous serpentine — absorb much of the 2.3-micrometer-wavelength light that falls on them. So, viewed in near-infrared light near that wavelength, such minerals appear darker than those around them.

Using airborne sensors tuned to wavelengths ranging from ultraviolet through the near-infrared, the researchers scanned areas of El Dorado County and Plumas County in California that are known to host asbestos-bearing rocks and soil. Data suggest that the instruments can spot rocks that may contain asbestos even in areas that are 80 percent covered by dry grass, Swayze says. Because water also absorbs some of the key wavelengths used to identify potentially asbestos-bearing minerals, airborne scans for such minerals would need to take place when vegetation is dry or absent, he notes.

The team’s flight tests, which took place in August 2001, spotted many areas already known to host naturally occurring asbestos but also identified a few new ones, including an area about 1 kilometer long and several hundred meters wide in a pasture in northern Amador County, just across the border from El Dorado County. The technique could help scientists to quickly and easily fill in gaps on current maps of asbestos-bearing minerals, the researchers contend. 

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