Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!sun-barr!newstop!sun!amdahl!amdcad!military
From: broman@schroeder.nosc.mil (Vincent Broman)
Newsgroups: sci.military
Subject: Re: Measuring range with passive sonar
Message-ID: <27140@amdcad.AMD.COM>
Date: 7 Sep 89 07:18:30 GMT
References: <27129@amdcad.AMD.COM>
Sender: cdr@amdcad.AMD.COM
Organization: Naval Ocean Systems Center, San Diego
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Approved: military@amdcad.amd.com



From: broman@schroeder.nosc.mil (Vincent Broman)

Can the frequency dependence of sound speed in water enable passive
sonar ranging?  I doubt it.  It would be difficult to compute a
time-difference from signals found in two different frequency bins,
because you don't know that the two signals were identical and
simultaneous when they were emitted.  Sound speed depends on many
factors, e.g. temperature, pressure, and salinity.  The sound energy
measured in one incoming beam of sound may be a mixture of several
signals which travelled over different propagation paths, possibly
originating from several sources.  Ocean acoustics deals with some
very dirty data.

If one has prior intelligence on the strength of an emitted signal,
then the transmission loss in signal power might be compared to a
model of the attenuation and refraction expected in the current ocean
environment to produce information on the length of the signal
propagation path.  The resulting probability density on range can be
strange and multimodal.

If your array of hydrophones is in the near field of the sound source,
one may estimate range from the curvature of the sound wave fronts.
Generally, such towed array passive ranging methods produce
usable results only under limited conditions.


Vincent Broman,  code 632, Naval Ocean Systems Center, San Diego, CA 92152, USA
Phone: +1 619 553 1641    Internet: broman@nosc.mil   Uucp: sdcsvax!nosc!broman