Vegetation index variability as a function of viewing geometry

Combinations of red and near infrared reflectance and radiance measurements commonly called vegetation indices (VI) have been successfully correlated with certain vegetation canopy characteristics. However, little is known about the dependence of these indices on viewing geometry. In this paper reflectance data acquired under laboratory conditions at various viewing geometries are used to evaluate the variability of five vegetation indices as a function of the changing viewing combinations. The results indicate that ratioed indices are less affected by viewing geometry changes than non-ratioed indices, but it has yet to be determined which of the indices are most successful at estimating vegetation canopy characteristics and least affected by changing viewing geometry. The results have implications for the use of vegetation indices with airborne scanner and pointable sensor data.