A simplified model of scatter from particulate-coated optical surfaces has been presented formerly. Results using it are compared with measured data and with a more rigorous model that uses integrated Mie and imaging techniques.
Paul R. Spyak,
William L. Wolfe,
"The Use Of A Simplified Model For Particulate Scatter", Proc. SPIE 1165, Scatter from Optical Components, (2 January 1990); doi: 10.1117/12.962859; https://doi.org/10.1117/12.962859