Reflectance of pigmented polymer coatings: comparisons between measurements and radiative transfer calculations

Solar reflectance spectra of pigmented coatings have been obtained from spectroscopic measurements involving integrating sphere attachments. We demonstrate that measured and computed reflectances of an extended four-flux model [Appl. Opt. 37, 2615 (1998)] whose average path-length parameters (APP's) and forward-scattering ratios (FSR's) are explicitly evaluated from a multiple-scattering approach at the front or back interface of the particulate coatings display fairly good agreement. The agreement of these properties in a standard four-flux model [Appl. Opt. 23, 3353 (1984)], which neglects the spectral dependence of the APP and FSR, is found in the near infrared. Good agreement between these two four-flux approaches over the solar spectral range is obtained when the mean values of the APP's and FSR's are used in the standard model.