[Laser] Cloud Bounce, Comm or Distance

[n5gui at cox.net]

---- Mike <mikecouture at bellsouth.net> wrote: 
> 
> Do we have any interest in cloud bounce for either communications or
> distance measuring using low to medium power lasers or LED's?
> 


Your question got me to thinking ( which is usually dangerous ) about a couple of things.

The first is perhaps a subset of cloud bounce.  The classic idea of cloud bounce, to me at least, is that you see a cloud in the sky, you point your light beam at it, and then someone sees your "spot" and decides to reply.  I have frequently seen an advertising searchlight hit clouds so this does not take a lot of imagination.

There are atmospheric conditions other than puffy cotton ball clouds that might be used.  One such condition causes rainbows or fogbows.  I am thinking more of thin ice clouds.  Often in winter there are thin ice crystal clouds, usually observed with sun dogs or halos, or their equivalents from bright moonlight.  These ice crystal clouds are hard to see directly.  The ice crystals form different shaped prisms or flat hexagonal plates which reflect and / or refract light at predictable, but narrow angles.  ( That was a hint for the curious to investigate the atmospheric physics involved. )  A beam of light, whether from the sun, moon, or optical communication equipment, comes away in a cone defined by that angle.  

In order to use the reflections/refractions for communications you would need considerably more skill, or perhaps extraordinary luck, than the more typical cloud bounce.  I would not suggest anyone start on a project to use ice crystal reflections instead of, or before the puffy cloud bounce.  But maybe it is the next step ( or the next challenge after ).

The second thing was listening practice for cloud bounce, for either the puffy cloud version or the ice crystal reflection/refraction version.  In the densely populated areas, streetlights and other manmade lights pulsing at 60 Hertz and various harmonics, should be detectable on every cloud overhead.  I live in Kansas, so there are places with some pretty dark skys, so I should be able to find places where only limited sites can illuminate the clouds, puffy or icy.  Predicting and then confirming the cloud bounce, seems to be a useful practice before trying to communicate.  I am not currently working on such a project, but I thought I would pass the idea along in case someone else could use it.


James
 n5gui