Some very old optical communications forums discussed cloud reflections and clear sky scattering as options for extending range without line-of-sight. Some tests were run bouncing light off high clouds similar to the way we do rain scatter but much shorter range. They also used it to find cloud height by measuring bounce time. The old experimenters also found plenty of volume scattering from clear air and assumed it was due to dust in the air. I assume most of these options would work better with less metro light pollution. Once in a while I think it would be interesting to setup an optical beacon on a tower or tall building to see how far it could be seen. We could even go back to our 10GHz FM roots and bounce optical comms off downtown Mpls? I tend to prefer 850nm near-infrared to get out of the visible spectrum, fewer questions to answer.... But I haven't done any testing....

73, Doug Reed, N0NAS.