Author： Kenea N. H.
Publisher： Taylor & Francis Ltd
ISSN： 1366-5901
Source： International Journal of Remote Sensing, Vol.22, Iss.10, 2001-07, pp. : 1879-1894
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Abstract
Laboratory spectra have been used for studying the characteristics of desert varnish in the context of Landsat TM data in order to establish its influence on the reflectance of gossans and their discrimination. Supported by limited chemical analysis, reflectance values from selected rock samples have been processed using statistical methods, and spectral plots produced and visually interpreted.Spectral analysis shows that paucity and Mn/Fe proportion in desert varnish, lightness or darkness of the rock, its mineral composition, and the wavelength under consideration control the effect of desert varnish on Landsat TM data. In general, overall reflectance of rocks is reduced by up to 70% in the VIS parts and about 20% in the SWIR parts of the electromagnetic spectrum due to desert varnish. For acidic rocks this effect seems to be intense, whereas mafic rocks are less influenced. The latter generally display spectral crossovers partly due to Mn/Fe content. In the VIS region absorption bands turn to featureless spectra due to desert varnish, whereas in the SWIR spectra are generally subdued but preserved. This has apparently little consequence on the discrimination of gossans from other rock types on composites constituted by bands from the VIS, IR and SWIR parts.
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