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For a given material, a fully characterized bidirectional reflectance distribution function (BRDF) describes how light from any given incident direction reflects into all possible observed directions in space. For simplification, many BRDF measurement and modeling techniques assume isotropic material surface characteristics, focusing primarily on in-plane reflection along individual azimuthal directions. An augmented Complete Angle Scatter Instrument® (CASI®) with a scientific-grade charge-coupled device (CCD) provides the ability to simultaneously capture both in-plane and out-of-plane BRDF data with high spatial resolution, particularly surrounding the specular peak. For any individual CCD frame, each pixel measures the portion of total flux reflected into a unique scatter direction. To properly calculate, analyze, and annotate BRDF readings from raw measurements, each pixel must be mapped to its corresponding scatter direction. This work describes a methodology for mapping pixel location to scatter coordinates based on the geometry of the augmented CASI® system, assuming both the CCD and material surfaces are at. For now, material sample and CCD misalignments are neglected. A broadband metallic laboratory mirror, circularly polished aluminum, and unwrinkled Kapton® samples are then each measured at three incident angles. Measurement results and pixel scatter coordinate mapping are demonstrated for each incident angle, using the beam signature as a proxy for normal incidence. The mirror produces a symmetric specular peak, matching the beam signature, while the polished aluminum and Kapton® produce qualitatively asymmetric specular peaks. Ultimately, this work hopes to foster improvements in BRDF measurement and modeling of materials with anisotropic properties for a range of radiometric simulation, hyperspectral sensing, and scene generation applications.
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