Vegetation-soil spectral mixture analysis

This paper describes the measurement and analysis of laboratory reflectance of green leaf and soil mixtures. Various combinations of leaf area index and percent cover were generated by stacking leaf discs over a dry soil background. Reflectance spectra (400-2500 nm) of these miniature pixels were measured with a spectroradiometer (Fieldspec FR) under laboratory conditions. The measured spectra were then compared with linear combinations of the pure spectra of green leaves and soil. Several vegetation indices such as the red edge wavelength position, derivative peak areas, NDVI, DVI, and RVI were analysed for the effects of varying leaf area index and percent cover against the soil background. The results show that there is non-linear mixing between soil and green leaf components. New derivative indices such as the area of the second derivative peak (715-780 nm) were found to be better indicators of green vegetation amount than previously used indices such as NDVI. The second derivative transform removed most of the soil background effect from the composite spectra, especially in the red edge and near infrared region