Mapping white micas and their absorption wavelengths using hyperspectral band ratios

Measuring the wavelength position of the absorption feature of white micas in the 2200 nm region is a useful tool in mapping the affects of hydrothermal alteration. However, this subtle wavelength shift is difficult to measure accurately using unmixing and matching algorithms that rely on spectral end members, because the wavelength position is uncorrelated to the general shape of the reflectance spectra of white micas. An alternative method is presented that uses pixel-dependent information only and that is based on extracting diagnostic spectral information of the mineral of interest through band ratios. Multiple regression analysis is then used to determine the relation between band ratios calculated from airborne imaging spectroscopy and the absorption wavelength of white micas measured in rock samples on the ground. The complicating effects of vegetation mixing with mineral signatures at the pixel level are addressed through a combination of band ratios that target the respective diagnostic absorptions.