Alteration mapping by using ETM+ and ASTER data in Dehaj area, southeast of Iran

Abstract

The study area is about 2650 sq. kms that is located in the southern part of Central Iranian volcanic-sedimentary belt. This belt runs parallel with the Zagros mountain ranges. The main aim of this study is to differentiate between the altered rocks with the carbonates and calcareous shales. Both ASTER and ETM+ data are used here for hydrothermal alteration mapping. This study compares these two data for hydrothermal alteration mapping. Different image processing techniques such as band ratio, principal component analysis and band combinations are used here aiming at enhancing the altered areas. The band ratio has shown that band7/band9 and b4/b5 ratios of ASTER data are better than band5/band7 ratio of ETM+ data for mapping the clay minerals. Principal component analysis has shown that PC4 of ASTER data is better than PC5 of ETM+ data for enhancing phyllic and argillic alterations. Color combination of PC4 (Red), PC5 (green), and PC6 (Blue) for the ASTER data is enhancing the altered areas and, at the same time, suppressing the effects of carbonates, flysch and calcareous sediments. ASTER data was used for image classification using spectral angle mapper algorithm. Through this analysis it was found that clay minerals such as kaolinite and montmorilonite can be differentiated. Comparison of the above image processing techniques have shown that except the enhancement of the iron oxide bearing rocks, the ASTER data is more useful for alteration mapping than ETM+ data.