Inversion of a soil bidirectional reflectance model for use with vegetation reflectance models

The need for anisotropic soil reflectance in canopy reflectance modeling is assessed for different sampling and canopy conditions. Based on the results for grasslands, a soil model is inverted with ground-based radiometer data from the First international Satellite Land Surface Climatology Project (ISLSCP) Field Experiment(FIFE). A general solution applicable over different spectral bands, solar angles, and soil moisture levels is determined using a diverse data set. With this solution, the model can be used as a lower boundary condition in FIFE canopy modeling. Despite the previously reported independence of retrieved model parameters to data sampling conditions, solutions determined with more limited data sets vary significantly. Moreover, the semiphysically based model may not accurately predict reflectance in angular regions where data are absent in the inversion process. These findings are important for the Earth Observing System multiangle imaging spectroradiometer (MISR), which will gather data in essentially one azimuthal plane per pass like the instrument used in this study did.