Biophysical parameter retrievals using bidirectional measurements

Measurements with oblique viewing angles can provide complementary information about land surfaces since these measurements reveal structural aspects while nadir measurements do not. Consequently, bidirectional measurements can be used to characterize surface biophysical properties. In this study, the authors developed an algorithm that combined bidirectional measurements with three existing bidirectional reflectance distribution function (BRDF) models to retrieve surface physical parameters such as leaf area index (LAI). The algorithm was applied to a multidirectional reflectance data set collected during an experiment at Maricopa Agricultural Center in 1991 over three different types of land surfaces (recently harvested alfalfa, pecan, and cotton). It was further validated with ground-based multitemporal reflectance measurements over a growing wheat canopy in 1983. Preliminary results showed that the algorithm was promising in retrieval of LAI and had potential to monitor vegetation growth on an operational basis