steele@grove.crsfld.com (10/05/89)
From: <steele@grove.crsfld.com>
In regards an earlier discussion on passive sonar and
how you might get range data from it:
Yes, it can be done. Yes, it is done as we speak
(so to speak). The technique involves getting a time
delta on the same sound wave at different places,
and a pair of angles towards the source. The accuracy
of this depends on the distance between the sensors, among
other things.
If you have a series of sensors along the hull of
a big sub, (say, a Seawolf maybe...) and you know the
distance between them (really accurately), and you know
the angle to the source (your primary sonar suite provides
this to you), you now can figure the curvature of the sound
wave, and thus arrive at a working distance.
The Navy stole the idea (so I'm informed) from carnivorous
fish, who have been doing it for few millions of years.
The system that utilizes this is (I believe) the BQS-5
and is an intregal part of the Seawolf's tactical systems.
Certain sci.mil posters at official sounding places, were probably
not aware this information is now public knowledge. They may
have been forced to conveniently not mention it when they happened
to be (rightly) refuting other proposed schemes posted here.
As I have seen various descriptions in several
industry periodicals, and in at least one wargame update, I must
conclude that it not classified any longer.
I would think that while the initial calculation would be in the
right ballpark, it could not be extremely accurate. After all,
every water molecule between you and the source gets to add it's
two cents to the data. BUT: do this calculation to several distinctive
sounds or a transient dataset, and it firms up REAL fast. Especially
when your doing this a few dozen times a second.
The Navy must have tested this under a variety of conditions,
and had pretty fair results to have included it in the base design of
a complicated platform like the Seawolf.
-Tamooj
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