VEGETATION IN DESERTS .1. A REGIONAL MEASURE OF ABUNDANCE FROM MULTISPECTRAL IMAGES

A method was tested in the semiarid Owens Valley, California for measuring sparse vegetation cover using Landsat Thematic Mapper (TM) multispectral images. Although green vegetation has a characteristic reflectance spectrum in the visible and near-infrared, using conventional image-processing methods, it has been difficult to quantify vegetation cover of less than about 40%, owing to the spectral dominance of the background soils and rocks. Thus multispectral images have been of limited use in mapping variations in vegetation cover in arid and semiarid regions. In this study fractions of vegetation, soils, and shading and shadow within the smallest resolution elements (30 × 30 m pixels) of the TM images were computed by applying a mixing model based on laboratory and field reference spectra. Fractions of vegetation were calculated for each pixel in TM images taken in December 1982 and May 1985, and the results were compared with ground transects. Despite spatial variations in background soil, temporal differences in satellite instrument response, and differences in atmospheric and lighting conditions, the fractions of vegetation computed from each image gave a spatially consistent measure of the projected vegetation cover. Results were obtained for a 150-km segment of Owens Valley; they indicate that the method can facilitate mapping and monitoring sparse vegetation cover over large regions covered by satellite images. © 1990.