Re: Navy releases photos of U.S.S. San Francisco

lou_at_cadence.com
Date: 01/31/05 

Date: 31 Jan 2005 09:19:38 -0800

Henry Spencer wrote:
> In article
<41fd703a$0$23777$5a62ac22@per-qv1-newsreader-01.iinet.net.au>,
> Neil Gerace <geracen@iinet.net.au> wrote:
> >...My question is why
> >didn't they see it? All that technology, and they can't detect
what's right
> >in front...
>
> Trouble is, all that technology doesn't change the fact that it's
pretty
> damn dark 500 feet down.

Clearly this is often true, but in daylight, and in the tropics where
the water tends to be clear, you should have quite a bit of light at
500 feet (150 meters or so). See for example:

http://oceanworld.tamu.edu/resources/ocng_textbook/chapter06/Images/Fig6-18.htm

which shows that in very pure tropical water, up to 1% of the
blue-green component of the sun gets to this depth. Considering that
moonight is only about a millionth as bright as sunlight, that should
be plenty of light.

Of course, this may still not help you navigate. In a car, for
example, the problem with driving during (daylight) fog is not lack of
light, it's lack of useful visibility. I suspect this is true of a sub
except for some specialized cases involving low speed approaches.
Lou Scheffer

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