Improved inverse method for radiative characteristics of closed-cell absorbing porous media

Radiative characteristics such as the extinction coefficient, the scattering albedo, and the scattering phase function of fused quartz containing closed cells are determined by using an inverse method based on theoretical and experimental bidirectional transmittances. The theoretical transmittances are obtained by solving the radiative transfer equation with the discrete ordinate method. Improvements have been made over previously reported experimental determination of porous fused quartz radiative characteristics by using a more accurate phase function and an adaptive quadrature to compute more precisely the intensities in the measurement directions. In addition, a two-step inverse method to compute accurately and simultaneously the radiative parameters has been developed. The results are shown to be independent of samples thickness. Exhaustive comparison between experimental measurements of hemispherical transmittance and reflectance and computational results using the retrieved radiative characteristics shows good agreement. The retrieved absorption coefficient of porous fused quartz appears to be more realistic than that reported in our earlier publication.