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From: malloy@nprdc.navy.mil (Sean Malloy)
Newsgroups: sci.military
Subject: Re: Measuring range with passive sonar
Message-ID: <27156@amdcad.AMD.COM>
Date: 8 Sep 89 06:26:25 GMT
References: <27129@amdcad.AMD.COM> <27140@amdcad.AMD.COM>
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Organization: Navy Personnel R&D Center, San Diego
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From: malloy@nprdc.navy.mil (Sean Malloy)

In article <27140@amdcad.AMD.COM> broman@schroeder.nosc.mil (Vincent Broman) writes:
>Can the frequency dependence of sound speed in water enable passive
>sonar ranging?  

Under the right conditions (basically, deep enough water for the
effect to work) you can get rough ranging data from picking up a
passive sonar contact in the convergent zones. 

Convergence zones are rings around the listening ship where the noise
emitted downward by a vessel is refracted back up by the pressure
differential at increasing depth to the surface some miles away. The 
sound can then be reflected from the surface and make another 'hop'; 
several such hops may be made under ideal conditions.

In water over 12,000 feet deep, convergence zone information can be
approximated as follows (the actual distances and widths depend on
water conditions, but these numbers can be used for rough examples):

	Convergence Zone	Zone Distance	Zone Width
	First			30 nm.		3 nm.
	Second			60 nm.		6 nm.
	Third			90 nm.		9 nm.

You're not going to get _good_ range information from a CZ contact,
but you can get a good enough track to lob a missile out to take a
look if your sonarman IDs the contact as hostile.


 Sean Malloy					| "The proton absorbs a photon
 Navy Personnel Research & Development Center	| and emits two morons, a
 San Diego, CA 92152-6800			| lepton, a boson, and a
 malloy@nprdc.navy.mil				| boson's mate. Why did I ever
						| take high-energy physics?"