The effect of incident light polarization on spectralon BRDF measurements

Many satellite instruments operating in the reflective solar wavelength region between 400nm and 2500nm require accurate and precise determination of the Bidirectional Reflectance Distribution Function (BRDF) of Spectralon diffusers used in their pre-flight and on-orbit calibrations. Calibration measurements of the BRDF of a laboratory optical grade Spectralon diffuse target at different incident polarized light in ultraviolet and visible is presented. The Spectralon diffuser was measured using P and S incident polarized light and over a range of incident and scatter angles from 0 to 60 degrees. The experimental data were obtained using the out-of-plane optical scatterometer located in NASA's Goddard Space Flight Center's Diffuse Calibration Facility's. The typical measurement uncertainty of reported BRDF measurements is 0.7 % (k=1). It is shown how BRDF of Spectralon at P and S polarization of the incident light depends on the incident and scatter angles and on wavelengths. The difference is significant, depends strongly on the incident and scatter angles can be as high as 5.7% at 60 deg incident, 60 deg scatter zenith and 0 deg scatter azimuth angles.