Powder River basin, Wyoming. Color ratio composite image, red-altered areas. Spectral reflectance studies indicate that a shift in the absorption band edge from 0.52 mu m (for goethitic sandstone) to 0.58 mu m (for hematitic sandstone) and an intensification of an absorption band at 0.85 mu m (for hematitic sandstone) are the bases for identifying the red-altered sandstone as green anomalous areas on the color ratio composite image. At high densities (>65%), vegetation masks the sandstones on the color ratio composite image.--Modified journal abstract.

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