I've been searching for an answer to this question in professional circles for a while; now I'd like to ask here, to find out why the answer is not there :)
In my optical modelling (computer simulation), I would like to take scattering on rough surfaces into account. Professional software (like Zemax) can do it, provided that I know the scattering model (e.g. in terms of Gaussian scattering). However I cannot find the model parameters anywhere. It is possible to derive the model parameters if one knows the BSDF of the surface, which in turn can be measured. But I cannot find any standard values, like for example scattering by aluminium surface with a roughness of Rz=5. Photopia seems to include the measured values for some surfaces, but the range is very limited, and it's the only such database I could find. Others, such as Disney's BRDF Explorer, seem to be less accurate and are probably not applicable for design optimization. At the same time, refractive indices of dozens of glasses are readily available.
Specialists gave me reasons why such information cannot be provided: one has to assume ergodicity of the manufacturing processes, which is not necessarily there. Then I wonder: from the general point of view, does an aluminium surface with a defined roughness really look very different depending on who made it?
Any comments or additional data on the topic would be highly appreciated. I was actually asked to suggest an optimal shape of some element for an experiment, and it turns out it should be scattering. However, while I can optimize scattering in simulation, I will not be able to convert it to roughness, i.e. tell the guys: "sand-blast it to Rz=x". This is what I am missing, and I cannot understand why the situation is as it is.