Suppression of vegetation in multispectral remote sensing images

Vegetation cover is an impediment to the interpretation of multispectral remote sensing images for geological applications, especially in densely vegetated terrains. In order to enhance the underlying geological information in such terrains, it is desirable to suppress the reflectance component of vegetation. This article adapts the forced invariance technique proposed by Crippen and Blom (2001 Crippen, R.E. and Blom, R.G. 2001. Unveiling the lithology of vegetated terrains in remotely sensed imagery. Photogrammetric Engineering and Remote Sensing, 67: 935–943. [Web of Science ®] , [Google Scholar]) for the suppression of the vegetation reflectance component in a densely vegetated study area in northern Zhejiang province, eastern China. The approach uses a three-step process that comprises: (i) masking of barren or sparsely vegetated areas using a normalized difference vegetation index (NDVI) mask in order to retain their original spectral information through the subsequent processing; (ii) applying a forced invariance technique to subtract the spectral response of vegetation only in vegetated areas; and (iii) combining the processed vegetated areas with the masked barren or sparsely vegetated areas followed by a histogram equalization to eliminate the differences in colour scales between these two types of area. An evaluation based on comparison with the geological map shows that the forced invariance technique results in significant enhancement of the geological information in the processed image.