<title>Spectral discrimination of ignimbritic rocks of southern Argentina in Landsat Thematic Mapper imagery using GER SIRIS laboratory data</title>

Abstract

The article shows some basic approaches to discriminate ignimbrite type pyroclastic flow deposits in Landsat Thematic Mapper imagery of semi-arid areas. Beside certain topographical and tectonical fea- tures which already describe ignimbrites and associated pyroclastic flows in those environments, our interest is focused on the influence of specific mineralogical and depositional characteristics on the spectral reflectance response. Spectral signatures in the visible and near infrared region of various fresh and weathered samples as well as desert varnish and soil samples were recorded using a GER SIRIS laboratory spectroscope to determine the factors controlling their proper response in all Thematic Mapper bands. Whole rock geochemistry data, X-ray powder diffraction analysis and microscopical studies as well as surface interpretations of the samples documented certain properties which might cause different spectral signatures also of geochemically mostly equivalent rocks. According to the semi-arid conditions of the South Patagonian Massif which are the most important constituents with respect to rock weathering and mineral alteration a more effective discrimination of the mostly leucocratic rocks was obtained using TM bands 7-4-1 and 7-5-2 as RGB false colour com- posites. Three image processing techniques, contrast stretched ratio composites, decorrelation stretched false colour composites and relative channel colour composites were examined to distinguish the variable ignimbrite outcrops in the chosen test site.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.