A New Band Ratio Approach for Discriminating Calcite and Dolomite by ASTER Imagery in Arid and Semiarid Regions

In this article, a new approach is developed for discrimination of calcite (limestone) and dolomite (dolostone) by utilizing data of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). The study area is located at the Zagros Mountains, SW Iran, in which outcrops of sedimentary carbonate rocks are abundant. The approach exploits short-wave infrared spectral features of dolomite and calcite and is based on the spectral variations of these minerals in bands 7 and 8 of ASTER imagery. In order to evaluate the efficacy of the method, spectral analysis was carried out on the spectra of dolomite, dolostone, calcite, and limestone, available in ASTER spectral library. The statistical analysis of the spectra showed that dolomite and calcite have distinguishable b 8 / b 7 band ratios. Spectral measurements of rock samples and knowledge of the mineral composition of rock samples attained by staining carbonate rocks in Alizarin red-S solution were used to evaluate the method used in this study. The applied imagery was normalized by the internal average relative reflectance (IARR) method due to the arid and semiarid climate of the region. The results showed that combined with spectral measurements of rock samples, the (( b 5 + b 9 )/ b 7 )/(( b 6 + b 9 )/ b 8 ), and b 8 / b 7 band ratios can be used to effectively discriminate limestone and dolostone. This approach is completely independent of variations in illumination conditions of image pixels; therefore, topographic correction of the image is not needed. The approach performs better in areas where weathering of rock surfaces and vegetation cover are minimal.