Hydrothermal Alteration Mapping at Bodie, California, Using AVIRIS Hyperspectral Data

AVIRIS data covering the Bodie and neighboring Paramount mining districts, eastern California, were used to map hydrothermal alteration minerals. Two spectral analysis algorithms were used: Spectral Angle Mapper (SAM) and Tricorder. The objective was to compare the performance of the two algorithms where no a priori ground or atmospheric information is available. AVIRIS data were calibrated to apparent surface reflectance using a modified MODTRAN radiative transfer model in conjunction with laboratory and in-flight calibration data. Both algorithms appear to produce satisfactory results for geologic reconnaissance and mapping applications, but Tricor- der generally classified more pixels and identified more mineral species than SAM. For some minerals, such as Na-montmorillonite, results from Tricorder and SAM matched reasonably well, but major differences appeared in how the two algorithms classified kaolinite group minerals and ferric oxides. Laboratory spectra of rock samples from five localities were compared to reference spectra of minerals identified by the classification algorithms for corresponding pixels, with the results matching to some extent.