29 August 2008 Improved hyperspectral imagery using diffuse illumination or a polarizer
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Under a contract with the Air Force Phillips Laboratory, two proposed methods for enhancing spectral content of hyperspectral remote sensing data are discussed. The first method would use diffuse sky light in which specular solar reflection from the 1st surface is absent. Characteristic material emission spectra would be observed from a much wider range of view angles than for a sunlit scene. In diffuse light, the observed polarization is reduced in comparison to the sun lit case, because the non-polarized volume radiance is increased relative to the 1st surface scatter. Hence, diffraction grating artifacts due to polarized inputs are reduced. In a second method, a polarizer positioned in front of a hyperspectral imager, is shown to enhance spectral contrast by reducing polarized 1st surface reflections in forward scatter directions. A polarizer of known orientation improves diffraction grating performance because changes in the polarization dependent grating efficiency can be accounted for through calibration. In support of these methods, polarimetric bidirectional reflectance distribution function (BRDF) data from the visible grating spectral polarimeter (VGSP)1 with wavelength range (375nm to 900nm) is presented. This data indicates that angular scatter or the BRDF from many outdoor materials may be decomposed into a polarimetric 1st surface single scatter component with little spectral variation and a diffuse or multiple scattered component having a significant spectral dependence.
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David Wellems, David Wellems, David Bowers, David Bowers, "Improved hyperspectral imagery using diffuse illumination or a polarizer", Proc. SPIE 7065, Reflection, Scattering, and Diffraction from Surfaces, 706509 (29 August 2008); doi: 10.1117/12.791778; https://doi.org/10.1117/12.791778

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