Tuesday, January 03, 2006
The use of ASTER data has grown in recent years due to its relatively low cost, broad area of coverage and the fact that data from additional channels are available for critical parts of the spectrum. Bob Agar of Australian Geological and Remote Sensing Services needed a way to use ASTER data to detect areas of mining that would prove lucrative.
Agar used ASTER data and ENVI to discriminate between specific iron and clay species by means of their unique spectral signatures in Peru to aid in mining efforts. Using the ASTER data, Agar detected economic mineral deposits by mapping important indicator, or alteration, minerals – minerals that have unique spectral signatures and are known to surround target minerals. For example kaolinite is a mineral commonly found near deposits of gold, so targeting concentrations of kaolinite can indicate the presence of gold.
To provide field workers with useful information, Agar first calibrated the raw data and corrected it for atmospheric backscatter, which provided him with a cleaner, more reliable dataset. He then used ENVI’s built in routines to create mineral indices for a suite of alteration minerals, and used spectral variations to generate a phyllic index which provides a simple index for the probable wavelength position of maximum absorption. Finally, some 25 alteration minerals were mapped, showing regions of hydrothermal alteration that may indicate the presence of mineral deposits. Using ENVI, Agar was able to glean necessary crucial detail about the type and degree of alteration in the area.
Although geological field work cannot be completely replaced with the use of remotely sensed images, multispectral data, such as ASTER, can be used to determine regions of interest and to target field mining efforts. Using ASTER data and ENVI processing capabilities, Agar was able to discriminate between styles of mineral alteration that can reduce the costs involved in exploration, while at the same time increasing the chance of profitable returns.
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