Using ASTER TIR radiance and surface emissivity data to map lithology and silica abundance in a metamorphic terrain

Most of the important rock forming silicate minerals have their diagnostic spectral features in the thermal infrared (TIR, 8-14 mum) wavelength region. The variation in silicate mineralogy from felsic to mafic is represented as a shift of the main spectral feature (reststrahlen band) towards longer wavelengths. This characteristic is utilized in mapping silicate mineralogy using multispectral TIR data. We use some lithologic indices on ASTER TIR data (L1B and L2) of a metamorphic terrain in NW India to map surface lithologies. The test area represents metamorphosed rocks with almost pure silicates (quartzites) on one end, and impure carbonates and mafic rocks (amphibolites) on the other. The results demonstrate that atmospherically corrected surface radiance data lead to an overall improvement in remote lithology mapping. Surface emissivity data derived using temperature and emissivity separation (TES) algorithm are used to generate a silica abundance map of the study area in conjunction with an empirical model. Field and laboratory analyses of select rock samples collected from the study area are used to validate remote silica abundance estimates.