Augmenting CASI® BRDF measurement device to measure out-of-plane scatter with CCD pixel array

Data-driven algorithm to classify the degree of isotropy in the bidirectional reflectance distribution function

“…The data collection set-up is described fully in Small's SPIE conference paper. 17,18 Overall, the relative uncertainty present in data collected via the modified Complete Angle Scatter Instrument (CASI) system was between 4% and 17%, with the highest uncertainty being present in the more diffuse samples due to the neutral density filter uncertainty, which affects the CCD uniformly. 19 The beam signature was a Helium-Neon laser source passing directly to the CCD detector.…”

Uncertainty analysis for CCD-augmented CASI® BRDF measurement system

“…The quantity δΦ i is the total incident flux on a small material surface area; δΦ s is the scattered flux measured by a small detector area, which subtends the solid angle δΩ d ; and θ s is the zenith angle between the material surface normal and the scattered direction. 4 For now, a single wavelength λ will be assumed, although f r , δΦ s , and δΦ i can all depend on wavelength as well. The δ symbols (denoting smallness of detector and sample illumination spot sizes) will be dropped for the rest of this work for clarity.…”

“…5 Augmenting the CASI ® with a charge-coupled device (CCD) pixel array provides the ability to simultaneously measure scatter directions outside the plane of incidence (out-of-plane) with high spatial resolution, particularly surrounding specular peaks. 4,6 The original uncertainty analysis for the CASI ®3 was built upon identifying uncertainties in various system parameters, and then quantifying how changes from nominal parameter values affect the overall BRDF calculation in Eq. (1).…”

“…The uncertainty analysis presented in this paper ultimately builds upon original CASI ® analysis methods 3 but also incorporates the fundamental differences of using a multi-pixel array detector. 4,6 Descriptions and definitions associated with the CCD-augmented CASI ® system (including setup, alignment, coordinate systems, etc.) are carried forward from previous work.…”

“…are carried forward from previous work. 4,6 This analysis will focus on CCD measurements centered on the specular peak, leaving considerations associated with off-specular measurements for future work. Polarizing elements are not incorporated, so polarization misalignment terms are ignored.…”