[107654] in Cypherpunks
Re: CDR: Re: [Fwd: C-Subs, a very scary thought] (fwd)
daemon@ATHENA.MIT.EDU (Jim Choate)
Wed Jan 20 12:15:35 1999
From: Jim Choate <ravage@einstein.ssz.com>
To: cypherpunks@einstein.ssz.com
Date: Wed, 20 Jan 1999 10:55:55 -0600 (CST)
Reply-To: Jim Choate <ravage@einstein.ssz.com>
----- Forwarded message from Mark Hahn -----
Date: Wed, 20 Jan 1999 11:04:23 -0600
From: Mark Hahn <MHahn@TCBTech.com>
Subject: Re: CDR: Re: [Fwd: C-Subs, a very scary thought] (fwd)
At 07:10 AM 1/20/99 -0600, Jim Choate wrote:
> > Date: Wed, 20 Jan 1999 00:33:06 -0800
> > From: Tim May <tcmay@got.net>
> > ...
> > Not that steel vs. concrete has anything to do with showing up on sonar:
> > ...
> ...
>As to a new set of laws, of course not. But since concrete is basicaly sand
>and gypsum with a handful of other materials it makes sense that they will
>be harder to pull out of the grass since their basic constituents, and by
>extension their sonar reflective properties, will be similar.
>
>It's the same old physics: density, reflection, refraction, diffraction.
> ...
Sonar is mostly about reflection. Concrete or metal, it will reflect a sound
wave. As to whether or not you can tell if the reflected sound wave was
reflected off of metal or concrete (rock like stuff), I don't think it effects
the interpretation. I don't believe a USN sonar is going to disregard
a large "rock" floating 200 feet above the ocean floor.
Or, if the sonar is that sensitive, and the hiding submarine is sitting on
the floor, it will look like a suspiciously long, cylindrical "rock".
I would suspect disguising your vessel to sonar is more difficult than
disguising your self to radar.
But then we should be asking someone with a background in sonar
and not just guessing ;-)
----- End of forwarded message from Mark Hahn -----
I've used seismo for geological surveys years ago and I've played with
commercial sonar and SSS in the mid-80's when I was working on a fisheries
project. I've also used sonar for years on my robots.
The reflection comes from the difference in density, ie the difference in
the speed of sound in the material. If we're talking a thermal inversion
then we deal with diffraction, the waves are being bent out of line of
sight. If you had a material, say concrete, that had a change of density
(say the mixing process wasn't done well) then you would get a sonar
refraction off that boundary if the delta-density wasn't too abrupt.
Sonar is quite good at telling what is going on and what the materials are.
Examination of some of the feats of dolphins would be enlightening.
As to your rock in mid-column. Irrelevant. We're talking about a sub sitting
on the bottem. If it's in mid-column and it's concrete it needs to be under
power. The article I read said these are supposed to use bottem
mounted/gymbaled water jets. No way you're going to hide that on sonar
unless you've made some stunning breakthrough in MHD propulsion. (I wonder
if Alice will smoke from that catepillars pipe?
Considering the structure of the bottem and its broken nature a rock ridge
200-300ft long will look like all the other ridges it's sitting among. On
muddy bottem with a hard substrate would be the most difficult to hide in.
Not to mention the hundreds of thousands of wrecks that litter the bottem.
By the use of tiles (just like on real subs - their steel skin is NOT
exposed to the water) it shouldn't be any harder to hide than current subs.
You could of course use something like Prarie Masking if you're really
paranoid and don't mind the surface signature.
____________________________________________________________________
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The Armadillo Group ,::////;::-. James Choate
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