Mapping of the silica-rich rocks and serpentinites using newly defined thermal indices from Advanced Spaceborne Thermal Emission and Reflection Radiometer thermal infrared data of Udaipur-Rakhabdev region, Rajasthan, India

Advanced Spaceborne Thermal Emission and Reflection Radiometer L1T data were used for the derivation of the new indices for the identification and mapping of the silica-rich and mafic-ultramafic rocks of the Udaipur-Rakhabdev region. The newly derived silica-rich rock index Ronak Jain (QI-RJ) was used in four bands except band 10 as [((band 13 - sqrt(band 11))/band 14)/band 12]. The mafic-rich rocks were also defined by a new index (MI-RJ), as (band 10 + band 14) / band 13. The new indices had advantages in accurate mapping compared with those given by Ninomiya (QI-N), Rockwell and Hofstra (QI-RH), and Guha and Vinod Kumar (QI-AV) for mapping of silica-rich rocks by removing striping noise. Similarly, mafic minerals were mapped by indices given by Ninomiya (MI-N) and Guha and Vinod Kumar (MI-AV) for ultramafics, but they have not mapped the discontinuous outcrops of serpentinites. The statistical regression analysis approach was used for the prediction of the goodness of fit between the new indices and already existing indices. The silica index (QI-RJ) is highly correlated with the QI-RH and QI-AV and represents low values for QI-N. In a similar way, MI-RJ shows a high correlation with the MI-N and MI-AV indices. The regression analyses for the QI-RJ with MI-RJ, MI-N, and MI-AV, show a negative trend but have high values of regression correlation. The generated maps from the newly defined index were also compared with the indices maps generated from the existing indices and were found to have better maps of litho-units. Field collected data and petrological studies also validated the presence of silica-rich rocks and ultramafics of the region mapped with the help of newly defined indices, and a better spatial accuracy of maps was obtained. The new mafic index was more suitable for mapping serpentinites and their alteration products exposed in the area. (C) 2022 Society of Photo-Optical Instrumentation Engineers (SPIE)