Computation of light scattered into a detector

To compare a the computed bidirectional reflectance distribution function (BRDF) or intensity distribution of a rough surface to a measured one we have to consider at least three issues beyond the computation of the intensity as a function of the scattering angle: the convolution with the instrument signature; averaging over intervals to take into account the specular peak and speckle; and the inclusion of a windowing function in the Kirchhoff approximation. Integration over the detector aperture can replace the convolution with the instrument signature.