View angle eVects on canopy re ectance and spectral mixture analysis of coniferous forests using AVIRIS

The dependence of vegetation re ectance on sun and sensor geometry can potentially provide information on canopy properties, but also may be a source of unmodelled systematic error in single-angle remote sensing measurements. In this study, we investigated the angular variability of re ectance measurements from the NASA Airborne Visible/Infrared Imaging Spectrometer (AVIRIS), and the resulting impact on spectral mixture analysis (SMA) using both full-range (400–2500nm) and shortwave-infrared wavelengths (2080–2280 nm; AutoSWIR). The study was conducted in coniferous forests in Central Oregon using Ž ve AVIRIS overpasses to generate multiple view angle measurements. Canopy re ectance was highly anisotropic, with the strength of the angular signal controlled by species type, canopy cover and soil re ectance. Canopy cover estimates from full-range SMA averaged only slight decreases (~6% relative) toward the retro-solar direction for 16 Ž eld plots in the study region. AutoSWIR was even less in uenced by view angle, exhibiting changes only for large diVerences in view angle. In addition, AutoSWIR’s ability to accommodate endmember variability led to stronger agreement with Ž eld cover values than full-range SMA. The results suggest that while view angle can signiŽ cantly aVect re ectance measurements from AVIRIS, the consequent variability in vegetation cover estimates from SMA and AutoSWIR is low.