Bi-directional calibration results for the cleaning of Spectralon™ reference panels

The Remote Sensing Group at the University of Arizona uses Spectralon(TM) (a sintered polytetraflouroethylene-based material) as a white reference source for ground based measurements used in vicarious calibration. These Spectralon panels degrade spectrally and angularly over time due to use in harsh field conditions with their reflectance falling off at shorter wavelengths. This paper examines the effects of sanding on the bi-directional reflectance of Spectralon using measurements in the Remote Sensing Group's calibration lab. The objective is to determine whether the near-Lambertian and spectrally flat nature can be restored through wet sanding with wet/dry sandpaper and de-ionized water. The reference for this method is the hemispherical reflectance of pressed polytetrafluoroethylene (PTFE) powder prepared according to National Institute of Standards and Technology (NIST) directions. The panels and a radiometer are mounted on rotation stages to measure the reflectance factor at different incidence angles for a normal view angle. These measurements are repeated for different panel alignments. Sanding techniques are examined using several grit sizes and strokes.