USE OF AVIRIS TO ASSIST MAPPING OF AREAS IN CALIFORNIA THAT MAY CONTAIN NATURALLY OCCURRING ASBESTOS

Reconnaissance maps of areas that may contain Naturally Occurring Asbestos (NOA) are increasingly in demand to assist in the protection of public health. This has prompted on-going research to find new tools that can aid the mapping process. The U.S. Geological Survey and the California Geological Survey are jointly testing the capability of the Airborne Visible/InfraRed Imaging Spectrometer (AVIRIS) as a mapping tool to help identify areas of ultramafic rock, serpentinite, and tremolite-actinolite-bearing rock in California. These geologic materials are those most commonly associated with NOA in the state.

Sixteen AVIRIS lines were flown over known locations of ultramafic rock and serpentinite in El Dorado and Plumas counties in 2001. Four have been processed to produce mineral maps using the USGS Tetracorder algorithm. The maps display colored pixels that represent locations of serpentine, serpentine plus vegetation, and tremolite-actinolite/talc; the pixels are superimposed on black-and-white back-images of the ground surface along the flight lines. The spectral signatures of tremolite-actinolite and talc are very similar and are not easily distinguished by AVIRIS, thus these minerals are displayed as one map unit. There is good agreement between the mineral maps and previously mapped boundaries of areas in El Dorado County that are more likely to contain asbestos.

Detection of minerals by AVIRIS is influenced by the amount of vegetation present. In less-vegetated areas, serpentine and tremolite-actinolite/talc can be identified, while in other areas, dense vegetation can completely obscure these minerals. AVIRIS may also have the capability to map vegetation types that help identify areas and degrees of serpentinization. At this time, determination of whether a mineral is fibrous or non-fibrous is not possible from the AVIRIS data alone. Identification of asbestos minerals in any given area still requires appropriate field sampling and analysis.

For delineation of areas more likely to contain NOA, AVIRIS serves as a complement to, rather than a replacement for, field mapping. Because of the costs of acquisition and processing of the AVIRIS data, lines must be chosen carefully to maximize information gained.