Potential of ASTER’s VNIR, SWIR, and TIR bands for phosphate exploration in central west Tunisia

Abstract

Owing to the inaccessibility of most of the mineral deposits as well as cost and time requirements for conventional ground-based methods, remote sensing techniques become very useful for the rapid detection, mapping, and multitemporal tracking of different mineralization surface states. In this context, a methodological approach based on hyperspectral spectroscopy and Advanced Spaceborne Thermal Emission and Reflection (ASTER) data is proposed for the phosphate exploration and mapping in a specific geological context in Tunisia. ASTER’s thermal infrared (TIR) portion has been particularly expedited in phosphate detection and mapping. Visible near-infrared (VNIR), shortwave infrared (SWIR), and TIR atmospherically and geometrically corrected data are thus processed using the matched filtering (MF) method and VNIR-SWIR reflectance spectra of the collected samples. Results revealed that different absorption features of carbonate minerals (calcite and dolomite) in the SWIR region have to be considered for an efficient identification of rock phosphate. Proposed band combinations using MF fraction maps have successfully discriminated phosphate mineralization and outcrops. Moreover, the surface temperature map derived from TIR bands using the emissivity normalization method reveals the usefulness of the proposed method for rock phosphate delineation. Both geological map and published prospects map as well as x-ray diffraction (XRD) analysis results are used for the validation purposes. A high kappa coefficient value of 0.92, 0.97, and 0.88, is thus calculated, respectively, for VNIR, SWIR, and TIR data-based maps. The high kappa coefficient values implicate the contribution of proposed methodological approach in exploration and mapping phosphates in the Chaketma mine site in central west Tunisia.