A technique using Fourier transform analysis which is suitable for measuring the specularity of solar glass components in the mrad and sub-mrad is discussed and demonstrated. A brief mathematical background as well as illustrative examples are included. A number of methods for image analysis are discussed with particular emphasis given to electronic integrating detectors. Typical Fourier plane image distributions are given for a few common solar utilization materials and details of the instrument used to produce the images are considered. The limitations and capabilities of various instruments are outlined along with methods for further enhancing the utility and sensitivity of the technique.
M. A. Lind,
J. S. Hartman,
H. L. Hampton,
"Specularity Measurements For Solar Materials", Proc. SPIE 0161, Optics Applied to Solar Energy IV, (17 November 1978); doi: 10.1117/12.956878; https://doi.org/10.1117/12.956878