Re: Very small nuclear submarines?

In article <0VnMf.5381$Cp4.2237@edtnps90>, asandstrom@xxxxxxxxxxxxx
says...
"Brad Meyer" <bradm110@xxxxxxxxx> wrote in message
news:v9c302tqt8ctl02030q2oli78so9qt1tpr@xxxxxxxxxx
On 26 Feb 2006 12:25:25 GMT, Juergen Nieveler
<juergen.nieveler.nospam@xxxxxxxx> wrote:

BTW, wasn't there talk about the Ohio being TOO quiet, and people
trying to locate the area where there was not enough noise?

"Acoustic daylight" (that is, scattered ambient sound) imaging doesn't
require that the target be very quiet. Consider that everything you and I
see with our eyes is illuminated by diffuse scattered light, but also that
we will not stop seeing objects because they are themselves emitters of
light. Yes, in some circumstances the target's own radiation at optical
frequencies can cause us to lose it against the background (witness
counterlighting), but that's pretty tough to do.

So, in the acoustic realm, consider that the entire water column (containing
the sub) will be suffused with shipping noise, sea noise (sea state,
precipitation, surf, ice movement, turbulence) and biological noise. It will
"light up" a submersed object. Because of the wavelengths involved, a
working system would require a large real or synthetic aperture, but the
concept (in both seismics and underwater acoustics) is proven.

There is still a great deal of sense in the submarine trying to eradicate
self-noise: machinery, hydrodynamic, propeller, and internal other (dropping
a wrench). These are very distinctive noises, as ambient noise is not.
Acoustic daylight imaging will tell you that there's a relatively big thing
(sub, school of fish, amorous pair of whales etc) at such-and-such location,
but self-noise will tell the detector _what_ the big thing actually is.

So, having cut out as much self-noise as possible, and presupposing
effective acoustic daylight imaging being fielded, the sub now has the
option of counterlighting (adding ambient noise) or camouflage ("let's make
like a school of fish").

Just make sure you're imitating the right fish!



I don't know how far advanced acoustic daylight detection systems are; one
would have to imagine that various projects are well-advanced. Good
background from
http://extreme.ucsd.edu/papers/Book%20Chapters/ADHandbook(1999).pdf.

> I have not heard that one, but I have read something to the effect
that they are track via detecting wake distubances via special
sensors.

They have been using radar to detect ship wakes for a long time (although
since you can detect the ship at the same time....) For something (like a
sub) where you only have the wake, using SAR is a viable technique. It
obviously depends on sea state, depth and speed of the sub. For that matter,
submerged subs can also leave a surface IR disturbance.

I suspect that very sensitive thermal sensors could also detect changes
in turbulent heat distribution in the open ocean. But that would be
more a tracking tool than a detection tool. A large nuclear sub moving
at any speed above zero is adding many kilowatts of thermal energy to
an environment that is stable and stratified on scales much larger than
the sub.


Mark Borgerson


.

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