Re: Visibility and wavelength

[shawl@torchlake.com (Jonathan Shawl)]

Another kind of remote viewing. Many years ago I saw a Cousteau video or
another video about Harold Edgerton, a friend of Cousteau's and the inventor
of the strobe flash we all have on our cameras now. In it Edgerton and
Cousteau was working on a under water vision system that would allow much
better visibility in silty waters. It was to work something like this. A
very bright, very short flash of light would be generated at the sub then
using a very high speed electronic shutter system it would capture only the
returning light that bounced of the object you are trying to see, and not
the back scattered light that was bouncing off all the silt between the sub
and the bottom.  In theory at least I can see how it could work. It would be
like having the lights mounted up close to the object you wanted to see
while you sat off in the dark back ground. In effect you are seeing around
or between the silt in the water as the silt would be back lit, it just
doesn't show up as much that way. Ever been to a Omnimax theater? It is a
perforated screen, when it is front lit during the movie you can't see the
small holes or the sound system behind the screen,  but when they turn out
the theater lights and back light the sound system behind the screen then
the screen becomes almost transparent and you see all the speakers. Cool
huh!
A strobe flash even back then could put out flashes of light in the
millionth of a second in duration but the tricky part then was to catch the
right part of the returning flash of light.  They didn't have high speed
liquid crystal shutters or very fast and sensitive CCD sensors like we have
today. So I have always wondered if our technology has reached the point
that we can make this work now. Is it true that the speed of light is about
60% slower in water? If true this would help with the timing of things. Any
body in the group up on this subject?
How about you John Brownlee, it sounds like this might be right up your
alley.

Jonathan Shawl

Michael B Holt wrote:

> On Mon, 05 Jul 1999 15:43:06 GMT hylands@ibm.net (Jon Hylands) writes:
> >I am not aware of *any* visible wavelength that will penetrate water
> >to any extent.
>
> If the water is clear, how far can we see?    In some places, the Secchi
> disk is visible for a long way.
>
> I asked about the exact frequency of lights, seeking a color that would
> permit me to illuminate "around" particulate matter.   (I wish I'd saved
> my notes.)   As I recall, the best was a blue-green light that had
> thallium
> in it.
>
> Mike Holt
>