International Journal of Geosciences, 2013, 4, 371-379 http://dx.doi.org/10.4236/ijg.2013.42035 Published Online March 2013 (http://www.scirp.org/journal/ijg) Issues and Limitations of Broad Band Remote Sensing of Kimberlite—A Case Example from Kimberlites of Dharwar Craton, India Arindam Guha 1* , S. Ravi 2 , D. Ananth Rao 1 , K. Vinod Kumar 1 , E. N. Dhananjaya Rao 3 1 Geosciences Division, National Remote Sensing Centre, Indian Space Research Organization, Hyderabad, India 2 Geological Survey of India, Hyderabad, India 3 Department of Geology, Andhra University, Visakhapatnam, India Email: * arindamisro@gmail.com Received October 26, 2012; revised December 1, 2012; accepted January 2, 2013 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-granodio- rite gneiss based on processing of the ASTER data as ASTER’s spectral channels can detect some of the diagnostic ab- sorption 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 granodio- rite-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 de- veloped 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. Keywords: ASTER; Short-Wave-Infrared Channel; Per-Pixel; Sub Pixel Mapping; False Positives; Calcretes 1. Introduction Reflectance spectroscopy is a branch of spectroscopy mainly study the change in reflectance across the elec- tromagnetic wavelength region of spectral data collection [1]. Absorption dip or absorption feature imprinted in the reflectance spectra is indicative of atomic process related to atomic structure of minerals [1,2]. Therefore reflec- tance spectroscopy has become a potentially important tool for spatial mapping of the minerals. Another impor- tant advantage of reflectance spectra is that it can record mineralogy irrespective of the distance between target and sensor [1]. Therefore space borne/airborne sensors are often used to map mineralogy from space [3-12]. Delineation of kimberlite pipe is an important step for diamond exploration. In general, conventional explora- tion methods, such as indicator minerals survey, field based systematic mapping, are used for discovering kimberlite pipes [13-15]. Satellite data are also 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. Some research initia- tives were made earlier to map kimberlite based on spec- tral feature of its constituent minerals like antigorite etc. [16]. ASTER data has appropriate band for detecting spectral features of mineral like serpentine and calcite. Serpentine minerals and calcite have spectral feature at 2.32 and 2.34 micrometer respectively [17,18]. Launch of ASTER sensor in the NASA’s Terra satellite in 1999 has provided the remote sensing community multispec- tral data in SWIR domain capable of mapping minerals [19]. Different alteration minerals associated with hydro- thermal deposits and rocks like limestone and bauxites * Corresponding author. Copyright © 2013 SciRes. IJG