At NASA's Goddard Space Flight Center (GSFC), Bi-Directional Reflectance Distribution Function (BRDF) is applied to characterize the scattering properties of optical and thermal surfaces. In addition, the Particle Fall Out (PFO) instrument (currently under evaluation) is used to determine the particulate contamination on surfaces. This paper describes both instruments and correlates the results from their empirical measurements. Both the BRDF and PFO instruments are located in a Class 1,000 cleanroom to minimize contamination. The BRDF instrument is completely automated and controlled by a personal computer. The FF0 is a scattering measurement instrument developed by SAAB and updated by Uramec (Bilthoven/The Netherlands) . The PFO is used to determine the surface cleanliness level on a contaminated plate by measuring the scattered light due to particles on the plate. For this paper, black glass is used as the contaminated sample for both the optical measurements. The PFO and BRDF instruments are then utilized to measure the scattering of the contaminated sample. Results are compared and related to the surface cleanliness level as well as obscuration factor.
Philip T.C. Chen,
Randy J. Hedgeland,
"Cleanliness Correlation By BRDF And PFO Instruments", Proc. SPIE 1165, Scatter from Optical Components, (2 January 1990); doi: 10.1117/12.962860; https://doi.org/10.1117/12.962860