Journal of MMIJ (Jun 2016)
Recent Trends of Remote Sensing Technologies Applied to Metallic Mineral and Geothermal Resources Exploration
Abstract
This paper reviews recent technologies and applications of remote sensing of optical and microwave sensors to metallic mineral and geothermal resources explorations. The most useful indicator of the optical remote sensing is location and depth of the reflectance absorption bands in the visible to short-wavelength infrared region, because this feature is caused by chemical composition and crystal structure of minerals. This reflectance spectral feature and image processing techniques to enhance the absorption, such as band ratio, have served a basis of identifying index minerals specific to deposit types such as epithermal, porphyry copper, and banded iron formation deposits and hydrothermally altered minerals accompanying high temperature geothermal system. For the areas covered by thick vegetation, plant physiology is occasionally affected by metal contaminant soils originated from latent metal deposits. Therefore, vegetation index that discriminates metal-induced stress by the degree of reflectance absorption related to chlorophyll activity and water content in the above wavelength range is also useful. This approach can extend widely the applicable areas of remote sensing-based resource exploration to vegetated areas. Emissivity spectra and radiance in the thermal-infrared region are also effective to identify silicate and carbonate minerals and detect high surface temperature zones. In addition to the spectral analysis, lineament detection from topographic features has been useful common to both the sensor types images, because lineament distribution helps to clarify fracture sets and orientation (strike and dip) of the dominant fractures by a combination with digital elevation model data. As compared with optical images, applications of Synthetic Aperture Radar (SAR) images are indirect such as estimation of rock types, not to resource-related minerals, based on back-scattering intensity of microwaves which is mainly dependent upon the Earth surface roughness. However, SAR image has great advantages in that it is not affected by weather condition and it can provide information about surface physical property such as dielectric permittivity. Monitoring of crustal deformation with resource development of coal, geothermal, and petroleum is also feasible by a technique of differential interferometric SAR. This monitoring must be important to resource development co-existent with environment.
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