Modelling and model verification of the spectral reflectance of soils under varying moisture conditions

On the basis of theoretical considerations on the interaction of soil, water and radiation a model for the spectral response of soils with varying moisture conditions was developed. The concept of the model takes into account two processes. First, the total internal reflection of the reflected radiance in a water layer covering the soil, which leads to a general darkening of the soil. Second, the absorptions of the water contained in the soil in certain spectral regions. It is shown that the absorption coefficient of pure liquid water has to be adapted to the realistic case of soil-bound water. The aim of the reflectance modelling is to extract information on the water content of the surface as well as to eliminate the moisture influence on soil spectra. For airborne or spaceborne applications it is necessary to develop procedures which are considering atmospheric absorption features as well. The model is verified with laboratory and field reflectance measurements of different soils conducted with a GER-SIRIS spectrometer and applied to airborne data measured by AVIRIS during the MAC-Europe ´91 campaign