Effects of Ground Cover and Leaf Area on the Spectral Reflectance of Vegetation-Soil Target

Abstract

Abstract : The relations between spectral reflectance, percent ground cover, and leaf area index (LAI) for vegetation-soil targets were evaluated for green vegetation against either a light-toned sand and a dark-toned organic loam soil. The percent ground cover and LAI were calculated for the ground area in the radiometer's field of view. The special reflectances of the different targets were measured in the 400 to 1100 nm region. For the vegetation-organic loam targets, the present cover and LAI varied directly with the target reflectance in the green (520-600 nm) and the infrared (700-1100 nm) regions, but varied inversely with reflectance in the red region (650-700 nm). For the vegetation- sand targets, the percent cover and LAI varied inversely with reflectance in the visible region and directly in the IR region. Results show that the major change in reflectance of vegetation-soils was related more to the change in percent cover. For less than 100 percent cover, the LAI varied directly with percent ground cover. A change in LAI produced less change in target reflectance than did a change in percent cover. Once the canopy is closed, i.e., 100 percent cover, variation in LAI had little effect.