The impact of viewing geometry on material discriminability in hyperspectral images

An increase in the off-nadir viewing angle for an airborne visible/near-inf rared through short-wave infrared (VNIR/SWIR) imaging spectrometer leads to a decrease in upward atmospheric transmittance and an increase in line-of- sight scattered path radiance. These effects combine to reduce the spectral contrast between different materials in the sensed, signal. We analyze the impact of viewing angle on material discriminability for 237 materials ove r a wide range of conditions. Material discriminability is quantified using a statistical algorithm that employs a subspace model to represent the set of spectra for a material as conditions vary. We show that reliable materi al discrimination is possible over a range of conditions even for large off -nadir viewing angles. We illustrate the performance of material identifica tion over different viewing angles using simulated forest and desert hypers pectral digital imagery collection experiment (HYDICE) images.