Discrimination of low-grade magnetite ores using remote sensing techniques |
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| Authors: | S Rajendran A Thirunavukkaraasu B Poovalingaganesh K Vinod Kumar G Bhaskaran |
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| Institution: | 1.Annamalai University,Annamalai Nagar, Chidambaram,India;2.National Remote Sensing Agency,Balanagar, Hyderabad;3.Department of Geography,Madras University,Chennai |
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| Abstract: | The remote sensing community in geology is widely using the Multispectral Landsat Thematic Mapper (TM) data which has a wider
choice of spectral bands (six between 0.45 and 2.35 μm, plus a thermal infrared channel 10.4-12.5 urn). These were evaluated for low-grade magnetite ores mapping over the high-grade
granulite region of Kanjamalai area of Tamil Nadu state, India. The Fourier Transform Infrared (FTIR) spectroscopy data (0.4-4.0
μm) for powders of the magnetite ores exposed with granulite rock and published spectral reflectance data were used as guides
in selecting TM band reflectance ratios, which maximize discrimination of magnetite ores on the basis of their respective
mineralogies. The study shows that the weathering mineralogy of magnetite ores causes absorption features in their reflectance
spectra which are particularly characteristic of the near infrared. Comparison of TM data with field and petrographic observations
shows the presence of magnetite and aluminosilicate minerals & show strong absorption at 0.7-1 μ.m wavelength spectral region
& increase in the product of two TM band ratios: band 5 (1.55-1.75 μm) to band 4 (0.76-0.9 μm) and band 3 (0.63-0.69 μm) to
band 4 (0.76-0.9 μm). Various computer image enhancement and data extraction techniques such as interactive digital image
classification techniques using color compositing stretched ratio, maximum likelihood and thresholding statistical approaches
using Landsat TM data are used to map the low-grade magnetite ores of the granulite region. The field traverses and local
verification enhanced to map the other rock types namely granulites and gneisses of the study area. |
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