Abstract
Present study attempts to understand the potential of multispectral ASTER (Advanced space borne thermal emission and reflection radiometer) data for spatial mapping of kimberlite. Kimberlite is an economic rock known for hosting diamond. Kimberlite also has petrogenetic importance for giving us clue on the composition of lower part of the mantle. Kimberlites often contain serpentine, carbonate minerals; which have their diagnostic spectral signatures in short wave infrared (SWIR) domain. In the present study, attempt is made to delineate kimberlite from adjacent granite-granodiorite gneiss based on processing of the ASTER data as ASTER’s spectral channels can detect some of the diagnostic absorption features of kimberlites. But it has been observed that the kimberlites are difficult to be delineated by processing the ASTER data using correlative information of both sub-pixel and per-pixel mapping. Moreover, smaller spatial size of kimberlites with respect to pixel size of ASTER SWIR channels further obscures the spectral feature of kimberlite. Therefore, an attempt is also made to understand how intra pixel spectral mixing of kimberlite and granite granodiorite-gneiss modifies the diagnostic spectral feature of kimberlite. It is observed that spectral feature of kimberlites would be obscured when it is has very small spatial size (one-tenth of pixel) with respect to pixel size. Moreover, calcrete developed in the adjacent soil has identical absorption feature similar to the spectral features of kimberlites imprinted in the respective ASTER convolved spectral profiles. This also has resulted false-positives in ASTER image when we use spectral feature as a tool for spatial mapping of kimberlite. Therefore hyperspectral data with high spatial and spectral resolution is required for targeting kimberlites instead of using broad band spectral feature of kimberlites.
Highlights
Reflectance spectroscopy is a branch of spectroscopy mainly study the change in reflectance across the electromagnetic wavelength region of spectral data collection [1]
Calcrete developed in the adjacent soil has identical absorption feature similar to the spectral features of kimberlites imprinted in the respective ASTER convolved spectral profiles
It has been observed that anomalous pixels characterizing kimberlites are widely spread in comparison to restricted spatial extent of known kimberlite pipes
Summary
Reflectance spectroscopy is a branch of spectroscopy mainly study the change in reflectance across the electromagnetic wavelength region of spectral data collection [1]. Reflectance spectroscopy has become a potentially important tool for spatial mapping of the minerals. Another important advantage of reflectance spectra is that it can record mineralogy irrespective of the distance between target and sensor [1]. Satellite data are used in narrowing down the search of pipe based on mapping of lineaments and their intersections suitable for kimberlite emplacement. Another way of getting the indication of kimberlites is to delineate the surface signature of pipes based on their spectral characters. Different alteration minerals associated with hydrothermal deposits and rocks like limestone and bauxites
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