Abstract
The mineralogical indices the Quartz Index (QI), Carbonate Index (CI) and Mafic Index (MI) for ASTER multispectral thermal infrared (TIR) data were applied to various geological materials for regional lithological mapping on the Tibetan Plateau. Many lithological and structural features are not currently well understood in the central Tibetan Plateau, including the distribution of mafic-ultramafic rocks related to the suture zones, the quartzose and carbonate sedimentary rocks accreted to the Eurasian continent, and sulfate layers related to the Tethys and neo-Tethys geological setting. These rock types can now be mapped with the interpretation of the processed ASTER TIR images described in this paper. A methodology is described for the processing of ASTER TIR data applied to a very wide region of the Tibetan Plateau. The geometrical and radiometric performance of the processed images is discussed, and the advantages of using ortho-rectified data are shown. The challenges of using ASTER data with a small footprint in addition to selecting an appropriate subset of scenes are also examined. ASTER scenes possess a narrow swath width when compared to LANDSAT data (60 km vs. 185 km, respectively). Furthermore, the ASTER data archive is vast, consisting of approximately three million images. These details can present an added level of complexity during an image processing workflow. Finally, geological interpretations made on the maps of the indices are compared with prior geological field studies. The results from the investigations suggest that the indices perform well in the classification of quartzose rocks based on the carbonate and mafic mineral content, in addition to the granitic rocks based on the feldspar content.
Highlights
Spectroscopic studies of inorganic materials in the thermal infrared (TIR) region (8–12 μm) [1,2] have demonstrated strong absorption features caused by the stretching vibrations of the Si–O bonds in silicate minerals, the major components of the terrestrial surface, whereas the Si–O bonds do not cause any prominent spectral features in the visible and near-infrared (VNIR) region of the spectrum (0.4–2.5 μm) [3]
The granule ID, observation date and location at the scene center of the ASTER data products consisting of the regional maps (Figures 4 and 5) are summarized in Table A1, which will be useful in reproducing the results sGheooswcienncehse2r0e1.6, 6, 39
Considering the geometrical and radiometric performances on the ASTER data and the indices discussed above, using the ortho-rectified radiance registered at the sensor data (e.g., Level-3A) is obviously advantageous in the mosaic lithological mapping of this study
Summary
Spectroscopic studies of inorganic materials in the thermal infrared (TIR) region (8–12 μm) [1,2] have demonstrated strong absorption features caused by the stretching vibrations of the Si–O bonds in silicate minerals, the major components of the terrestrial surface, whereas the Si–O bonds do not cause any prominent spectral features in the visible and near-infrared (VNIR) region of the spectrum (0.4–2.5 μm) [3]. The airborne and satellite remote sensing systems were developed after the results of the spectroscopic studies shown above. They demonstrated the capability of detecting rock composition, despite the radiometric, spectral and spatial resolutions being much worse when compared to a modern system such as ASTER. The infrared interferometric spectrometer onboard the Nimbus-4 satellite derived a global surface emissivity map at 9 μm, which discovered the significantly low emissivities over arid areas due to quartz, even with a quite low spatial resolution (~100 km) [8]
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