Current Science

Arindam Guha ¹, K. Vinod Kumar ¹, E. N. Dhananjaya Rao ², Reshma Parveen ³

Affiliations
1 National Remote Sensing Centre, Balanagar, Hyderabad 500 625, IN
2 Andhra University, Visakhapatnam 530 003, IN
3 Jharkhand Space Application Centre, Ranchi 834 004, IN

Abstract

In the present study, we have attempted the delineation of limestone using different spectral mapping algorithms in ASTER data. Each spectral mapping algorithm derives limestone exposure map independently. Although these spectral maps are broadly similar to each other, they are also different at places in terms of spatial disposition of limestone pixels. Therefore, an attempt is made to integrate the results of these spectral maps to derive an integrated map using minimum noise fraction (MNF) method. The first MNF image is the result of two cascaded principal component methods suitable for preserving complementary information derived from each spectral map. While implementing MNF, noise or non-coherent pixels occurring within a homogeneous patch of limestone are removed first using shift difference method, before attempting principal component analysis on input spectral maps for deriving composite spectral map of limestone exposures. The limestone exposure map is further validated based on spectral data and ancillary geological data.

Keywords

Limestone, Minimum Noise Fraction, Spectral Mapping, Image Processing.

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Arindam Guha ¹, Biswajit Ghosh ², Sukanya Chaudhury ², Komal Rani ¹, K. Vinod Kumar ¹

Affiliations
1 Geosciences Group, National Remote Sensing Centre, Indian Space Research Organization, Balanagar, Hyderabad 500 625, IN
2 Department of Geology, University of Calcutta, 35 Ballygunge Circular Road, Kolkata 700 019, IN

Abstract

We have collected, processed and analysed the reflectance spectra of representative chromitite samples of spot type, clot type and disseminated type textural variants to understand the diagnostic spectral features of each of these samples. We have found that the reflectance spectrum of each textural variant is distinct from the spectra of other variants despite having few common absorption features. Spectral features of chromitite samples are governed by the spectra of two dominant minerals, chromite and chlorite. Spectral features of chromitite at 550 nm and 1100 nm are governed by electronic transition process in Fe³⁺ and crystal field effect in Fe²⁺ ions present in chromite structure respectively. On the other hand, spectral features at 1400 nm, 1900 nm and 2300 nm are related to the vibration of O–H, H–OH and metal hydroxide bonds in chlorite. Amongst these features, the spectral feature at 1100 nm (due to Fe²⁺ in chromite grains) is common to all three major textural varieties of chromitite samples studied here. Electron probe micro analysis (EPMA) data of chromite and chlorite grains of each texture are used to relate the presence and abundance of Fe₂₊ (in chromite grains) with absorption feature. Width of the 1100 nm feature has a correlation value 0.95, while depth of the same feature has a correlation value 0.94 with the abundance of chromite mineral estimated using modal analysis of chromite samples. Therefore, spectrometric parameter of 1100 nm spectral feature of chromitite can be used as proxy for estimating modal abundance of chromite in chromitite samples after estimating deposit specific correlation coefficient.

Keywords

Chromitite, Electronic Processes, Modal Analysis, Spectral Feature, Texture, Vibrational Processes.

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Satadru Bhattacharya ¹, Hrishikesh Kumar ¹, Arindam Guha ², Aditya K. Dagar ¹, Sumit Pathak ¹, Komal Rani (Pasricha) ², S. Mondal ³, K. Vinod Kumar ², William Farrand ⁴, Snehamoy Chatterjee ⁵, S. Ravi ⁶, A. K. Sharma ¹, A. S. Rajawat ¹

Affiliations
1 Space Applications Centre, Indian Space Research Organisation, Ahmedabad 380 015, IN
2 National Remote Sensing Centre, Indian Space Research Organisation, Hyderabad 500 042, IN
3 Department of Geophysics, Indian Institute of Technology (ISM), Dhanbad 826 004, IN
4 Space Science Institute, Boulder, Colorado 80301, US
5 Department of Geological and Mining Engineering and Sciences, Michigan Technological University, Houghton, Michigan 49931, US
6 Geological Survey of India Training Institute, Bandlaguda, Hyderabad 500 068, US

Abstract

In this article, we discuss the potential of airborne hyperspectral data in mapping host rocks of mineral deposits and surface signatures of mineralization using AVIRIS-NG data of a few important geological provinces in India. We present the initial results from the study sites covering parts of northwest India, as well as the Sittampundi Layered Complex (SLC) of Tamil Nadu and the Wajrakarur Kimberlite Field (WKF) of Andhra Pradesh from southern India. Modified spectral summary parameters, originally designed for MRO-CRISM data analysis, have been implemented on AVIRIS-NG mosaic of Jahazpur, Rajasthan for the automatic detection of phyllosilicates, carbonates and Fe–Mg-silicates. Spectral analysis over Ambaji and the surrounding areas indicates the presence of calcite across much of the study area with kaolinite occurring as well in the north and east of the study area. The deepest absorption features at around 2.20 and 2.32 μm and integrated band depth were used to identify and map the spatial distribution of phyllosilicates and carbonates. Suitable thresholds of band depths were applied to map prospective zones for marble exploration. The data over SLC showed potential of AVIRIS-NG hyperspectral data in detecting mafic cumulates and chromitites. We also have demonstrated the potential of AVIRIS-NG data in detecting kimberlite pipe exposures in parts of WKF.

Keywords

Data, Geological Provinces, Host Rocks, Hyperspectral, Mineral Deposits.

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