I'm trying to put together a layer representing horizontal visibility at ground level. I'm thinking of using the EVC (vegetation cover) layer from the landfire project (see http://www.landfire.gov/vegetation.php). However, I know that, for instance, 70% cover does not correspond directly to 30% horizontal visibility...I imagine there is a threshold at which the cover saturates any visibility, with visibility increasing in a non-linear way as percent cover decreases - probably calculated over some neighborhood (100 meters, maybe?). I'm thinking of cooking something up myself along these lines.
However, I'm wondering if there hasn't been work done in this realm, or some theory to exploit that anyone may be aware of. A lit/google search hasn't turned up much of interest.