U.S. patent number 5,570,324 [Application Number 08/523,968] was granted by the patent office on 1996-10-29 for underwater sound localization system.
This patent grant is currently assigned to Northrop Grumman Corporation. Invention is credited to Frederick G. Geil.
United States Patent |
5,570,324 |
Geil |
October 29, 1996 |
Underwater sound localization system
Abstract
A control system connected to a passive underwater transducer
array is located remotely from the array, e.g. above the surface of
the water, to localize an underwater source of acoustic energy in a
relatively simple manner by introducing listener-motion, such as
head turning or body motion of a listener, into the sound
localization process and does so without any underwater mechanical
linkage of any kind. This is achieved by a pair of listener-motion
coupled potentiometers, referred to as mixing-pots, located at the
site of the listener, being connected to the outputs of an array of
passive acoustic transducers, with the two outputs of the
mixing-pots being coupled to a pair of headphones worn by the
listener.
Inventors: |
Geil; Frederick G. (Annapolis,
MD) |
Assignee: |
Northrop Grumman Corporation
(Los Angeles, CA)
|
Family
ID: |
24087175 |
Appl.
No.: |
08/523,968 |
Filed: |
September 6, 1995 |
Current U.S.
Class: |
367/124; 367/118;
367/120; 367/129 |
Current CPC
Class: |
G01S
3/28 (20130101) |
Current International
Class: |
G01S
3/14 (20060101); G01S 3/28 (20060101); G01S
003/80 () |
Field of
Search: |
;367/118,120,124,127,131 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Hydrophone Techniques for Underwater Sound Pickup", Audio
Engineering Society, 60 East 42nd St., NY, NY 10165, presented at
91st Convention 1991 Oct. 4-8, New York by Fred G. Geil,
Westinghouse Oceanic Division, Annapolis, MD..
|
Primary Examiner: Lobo; Ian J.
Attorney, Agent or Firm: Florenzo; Philip A.
Claims
I claim:
1. Apparatus for localizing a source of acoustic signals,
comprising:
an array of first type transducer means for converting acoustic
signals to corresponding electrical signals, said array of first
type transducer means comprising two sets of at least two
transducers each and mutually separated laterally by a first fixed
distance, each set of said first type transducers comprising at
least a front transducer and a rear transducer and separated by a
second fixed distance, said front and rear transducers of both sets
of first type transducers having relatively low impedance output
terminals and generating electrical output signals corresponding to
the acoustic signals sensed thereby and emanating from said
source;
first potentiometer means coupled across the output terminals of
one set of said first type transducers and having a first movable
output terminal;
second potentiometer means coupled across the output terminals of
the other set of said first type transducers and having a second
movable output terminal;
means responsive to the motion of an acoustic sensor remote from
said array of first type transducers and being coupled to and
moving said first and second movable output terminals of said first
and second potentiometer means in mutually opposite directions;
and
second type transducer means coupled to the output terminals of
said first and second potentiometer means for converting electrical
signals to corresponding acoustic signals located in proximity to
said acoustic sensor;
whereby the motion of the acoustic sensor varies the settings of
said potentiometer means, causing phase mixing of the respective
output signals from the front and rear transducers of both sets of
said first type transducers to provide an indication of the
location of the source of the sounds relative to the array by
utilizing the time difference between the arrival of said acoustic
signals at both sets of said first type transducer means.
2. The apparatus according to claim 1 wherein said array of first
type transducer means are located in a first environment and the
acoustic sensor as well as the second type transducer means are
located in a second environment.
3. The apparatus according to claim 2 wherein said first
environment comprises water and the second type environment
comprises air.
4. The apparatus according to claim 3 wherein said first type
transducer means are comprised of relatively low output impedance
acoustic transducers and said second type transducer means are
comprised of a pair of speaker elements.
5. The apparatus according to claim 3 wherein said first type
transducer means comprises underwater hydrophones and said second
type transducer means comprises speaker means.
6. The apparatus according to claim 5 wherein said acoustic sensor
comprises the head of a listener and said speaker means comprises a
pair of headphones located on the head of the listener.
7. The apparatus according to claim 6 wherein said means responsive
to the motion of said acoustic sensor comprises means responsive to
head motion of the listener.
8. The apparatus according to claim 6 wherein said means responsive
to the motion of said acoustic sensor comprises means responsive to
a turning motion of the listener.
9. The apparatus according to claim 8 wherein said first and second
fixed distances of said first type transducers simulate hearing
response of a human head.
10. The apparatus according to claim 9 and additionally including a
baffle between said two sets of first type transducers to simulate
the delay caused by the bone of the skull of acoustic signals from
said source arriving at the ears of a listener.
11. The apparatus according to claim 9 wherein the second fixed
distance is equal to or less than 1/2.lambda. where .lambda. is the
wavelength of the highest frequency of interest emanating from said
source.
12. The apparatus according to claim 11 wherein the first fixed
distance is also equal to or less than 1/2.lambda..
13. The apparatus according to claim 12 where .lambda. is about 4.5
ft. and corresponds to a highest frequency of interest of 1
KHz.
14. The apparatus according to claim 9 wherein said array is
located on an underwater vehicle.
15. The apparatus according to claim 14 wherein the listener is
located on a vehicle on or above the surface of the water.
16. The apparatus according to claim 1 wherein said array comprises
two aligned sets of first type transducers.
17. The apparatus according to claim 16 wherein each said set of
first type transducers comprises a number of transducers greater
than two.
18. The apparatus according to claim 1 wherein said array comprises
two arcuate sets of first type transducers numbering greater than
two transducers each.
19. Apparatus for localizing a source of underwater acoustic
signals from a remote location, comprising:
a passive array of hydrophones located on an underwater vehicle for
converting acoustic signals to corresponding electrical signals,
said array of hydrophones comprising two sets of hydrophones
separated laterally by a first fixed distance, each said set of
hydrophones further comprising at least a front hydrophone and a
rear hydrophone separated by a second fixed distance, said front
and rear hydrophones of both sets of hydrophones having respective
outputs and generating electrical output signals corresponding to
the acoustic signals sensed thereby and emanating from said
source;
a first potentiometer coupled across the outputs of one set of said
hydrophones and having a first movable output signal tap;
a second potentiometer coupled across the outputs of the other set
of said hydrophones and having a second movable output signal
tap;
means responsive to at least the turning motion of a listener's
ahead remote from said underwater vehicle and being coupled to and
moving said first and second movable output signal taps of said
potentiometers in mutually opposite directions; and
a pair of headphones adapted to be worn by the listener and being
coupled to the output signal taps of said first and second
potentiometers for converting electrical signals to corresponding
acoustic signals emanating from said source and coupling said
acoustic signals to the ears of the listener;
whereby the direction from which acoustic signals impinge on the
array of hydrophones is resolved by the turning motion of at least
the listener's head varying the position of the output signal taps
of said first and second potentiometers.
20. The apparatus according to claim 19 wherein the listener is
located on a surface vehicle.
21. The apparatus according to claim 20 wherein the underwater
vehicle comprises a remotely controlled underwater vehicle.
22. The apparatus according to claim 21 wherein the remotely
controlled underwater vehicle is controlled in response to the
turning motion of the listener on said surface vehicle.
23. The apparatus according to claim 22 wherein the remotely
controlled underwater vehicle is controlled in response to the head
turning motion of the listener.
24. The apparatus according to claim 22 wherein the remotely
controlled underwater vehicle is controlled in response to a
rotatable seat assembly on said surface vehicle, said seat assembly
being coupled to and actuating the first and second movable output
signal taps of said potentiometers as a seat of said assembly is
turned in azimuth by a listener on said seat.
25. The apparatus according to claim 22 wherein said two sets of
hydrophones are spaced apart so as to replicate the hearing
response of the head of a listener.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to underwater detection of
acoustic signals and more particularly to a system for determining
the direction from which the acoustic signals emanate.
2. Description of the Prior Art
It is often useful to detect acoustic energy, such as sounds,
underwater and determine by ear the direction from which they
emanate. For example, it would be advantageous when capturing
biological pictures and sounds to be able to guide a vehicle
silently towards the sound's source. Moreover, it would be
desirable to localize these sounds without trial and error
meandering. Another example where the localization of sounds
underwater would be useful is the guidance of a rescue vehicle or
camera to a second vessel in murky water by homing in or the sound
of a distress beacon located on the vessel.
For a human, such as a diver, localizing the sounds underwater is
difficult, if not impossible, because unaided humans do not hear
accurately at all in water. This is due to the fact that
wavelengths are longer since sound travels faster in water than in
air and as a result reduces the effective separation or aperture of
the listener's ears. Furthermore, the ears are reduced in
sensitivity and sound via bone conduction in water forces sounds to
be monaural unless the sound is very close to one ear.
On the other hand, for a listener in an air environment, e.g. on a
vessel on the surface of the water, using a stationary array of
standard omnidirectional hydrophones results in a front to rear
ambiguity of direction. Also, a listener's pinnae in the ears are
not utilized to determine direction, and thus the underwater sound
field must be recreated locally, for example, at the site of the
listener.
For airborne sound, as opposed to sound in water, the most accurate
localization is achieved by the human brain, utilizing the slight
time difference or phase between the signals received by the two
ears of the listener and the smearing-in-time processing done by
the pinnae of the ears. This time processing is a function of the
azimuth angle to the source. It is important to note that there is
also a difference between front and rear sounds. Thus when sounds
are picked up by microphone pairs, it is important to apply the
separate acoustic signals to the ears separately, normally by means
of a pair of headphones. Such an arrangement avoids acoustic
crosstalk. Accordingly, phase matching between the microphones is
important as well as for the earphone pair. If the microphone pair
comprises omnidirectional microphones, there is no signal
difference between front and rear sounds and the front-rear
ambiguity immediately becomes evident to the listener. In absence
of any additional cues, such as sight or head motion, all sounds
will be localized to the rear hemisphere of the listener's
head.
Some types of microphone arrays can alleviate this problem, such as
the Office de Radio Diffusion-Television Francaise (ORTF) cardioid
array or a Stereo Ambient Sampling System (SASS) configuration,
both well known, which can at least favor, because of microphone
directivity, forward sounds. However, the arrangement which comes
closest to eliminating the front-rear ambiguity would be a "dummy
head" with microphones in its ears, which are replicas of the
listener's own pinnae. It is also necessary to include part of the
torso with the dummy head and to provide electronic filtering
tailored to each listener.
Thus for airborne sound localization accuracy, it is seldom
achieved without sight cues or head motion. In any event, a dummy
head with replica pinnae is not a practical solution for underwater
applications. Even if it were, the head size would have to be 4.5
times larger inasmuch as all dimensions must be scaled up by a
factor of 4.5 due to the increased speed of sound in water, which
is approximately 5000 ft./sec. as opposed to 1087 ft./sec. in
air.
SUMMARY
Accordingly, it is an object of the present invention to provide a
means for localizing the source of underwater acoustic signals.
It is a further object of the invention to utilize motion of the
listener in an underwater sound localization system.
It is yet a further object of the invention to resolve the
direction from which underwater acoustic signals are coming from by
electronically implementing the motion, such as head turning, of
the listener to an underwater hydrophone array without mechanically
coupling the head of the listener to the hydrophone array.
These and other objects are achieved by an underwater transducer
array which enables "virtual reality" to be realized underwater in
a relatively simple manner while introducing the important factor
of listener-motion, which is head turning, into the underwater
sound localization process and does so without any underwater
linkage of hydrophone motion of any kind. This is achieved by
listener-motion coupled potentiometers connected to the outputs of
an array of passive acoustic transducers and whose output terminals
are coupled to the headphones of a listener located remotely from
the transducer array.
The apparatus employed is comprised of an array of at least four
first type transducer means for converting acoustic signals to
corresponding electrical signals, the first type transducers being
utilized in sets of at least two transducers each and being
mutually separated laterally by a first fixed distance, each set of
the first type transducers comprising at least a front transducer
and a rear transducer and separated by a second fixed distance, the
front and rear transducers of both sets of first type transducers
having respective amplifiers with low output impedances connected
to the output terminals thereof and generating electrical output
signals corresponding to the acoustic signal sensed thereby and
emanating from the source being sensed; first potentiometer means
coupled across the output terminals of one set of the first type
transducers and having a first movable output terminal; second
potentiometer means coupled across the output terminals of the
other set of the first type transducers and having a second movable
output terminal; means responsive to the motion of an acoustic
sensor, typically a human listener, remote from the array of first
type transducers and being coupled to and moving the first and
second movable output terminals of the potentiometer means in
mutually opposite directions; and second type transducer means
coupled to the output terminals of the first and second
potentiometer means for converting electrical signals to
corresponding acoustic signals located in proximity to the acoustic
sensor, whereby the motion of the acoustic sensor varies the
settings of the potentiometer means, causing phase mixing of the
respective output signals from the front and rear transducers for
both sets of the first type transducers to provide an indication of
the location of the source of the sound relative to the array by
utilizing the time difference between arrival of the acoustic
signals at both sets of first type transducers.
In a specific embodiment of the invention, apparatus for localizing
a source of underwater acoustic signals from a remote location
comprises: a passive array of hydrophones for converting acoustic
signals to corresponding electrical signals, the array of
hydrophones consisting of two sets of low output impedance
hydrophones separated laterally by a first fixed distance, each set
of hydrophones further comprising at least a front hydrophone and a
rear hydrophone separated by a second fixed distance, the front and
rear hydrophones of both sets of hydrophones having respective
output signal taps and generating electrical output signal
corresponding to the acoustic signal sensed thereby and emanating
from the source; a first potentiometer coupled across the outputs
of one set of said hydrophones and having a first movable output
signal tap; a second potentiometer coupled across the outputs of
the other set of the hydrophones and having a second movable output
signal tap; means responsive to the turning motion e.g. head of a
listener remote from the source and being coupled to and moving the
first and second output signal taps of the potentiometers in
mutually opposite directions; and a pair of hydrophones adapted to
be worn by the listener and being coupled to the output signal taps
of the first and second potentiometers for converting electrical
signals to corresponding acoustic signals emanating from the source
and coupling the acoustic signals to the ears of the listener;
whereby the direction from which acoustic signals impinge on the
array of hydrophones is resolved by the turning motion of the
listener varying the position of the output signal taps of the
first and second potentiometers.
BRIEF DESCRIPTION OF THE DRAWINGS
The following detailed description of the invention will be more
readily understood when considered together with the accompanying
drawings wherein:
FIG. 1 is an electrical schematic diagram of a first embodiment of
the invention;
FIG. 2 is an electro-mechanical schematic diagram illustrative of
an application for the embodiment shown in FIG. 1;
FIG. 3 is an electrical schematic diagram illustrative of a second
embodiment of the subject invention and comprised of more than two
hydrophones in the two sets of hydrophones shown in FIG. 1;
FIG. 4 is an electrical schematic diagram of a third embodiment of
the invention and being a variation of the embodiment shown in FIG.
2 wherein the hydrophones are arranged in two arcuate sets of
hydrophones;
FIG. 5A is a partial perspective view of a first type of continuous
line hydrophone array; and
FIG. 5B is a perspective view of another type of continuous line
hydrophone array.
DETAILED OF THE PREFERRED EMBODIMENTS
Referring now to the drawings wherein like reference numerals refer
to like parts throughout, and more particularly to FIG. 1, shown
thereat is a passive acoustic transducer array for sensing an
underwater source 6 of acoustic energy 8 (FIG. 2) and comprised of
two pairs of hydrophones 10 and 12, along with their associated
amplifiers 20.sub.1, 20.sub.2 and 22.sub.1, 22.sub.2 and more
particularly a left-front (LF) hydrophone 10.sub.1 and a left-rear
(LR) hydrophone 10.sub.2 separated by a distance L.sub.1 and a
right-front (RF) hydrophone 12.sub.1 and a right-rear (RR)
hydrophone 122 also separated by the distance L.sub.1. The right
and left pairs of hydrophones 10 and 12, moreover, are separated by
a distance L.sub.2. A typical hydrophone is shown and described in
U.S. Pat. No. 4,933,919 issued to F. G. Geil et al on Jun. 12,
1990.
The distances L.sub.1 and L.sub.2 are shown in FIG. 1 as being
substantially equal and comprises a distance which is less than
1/2.lambda. where .lambda. is the highest frequency of interest
which for a 1 kHz acoustic signal, is approximately 2 ft. or 24 in.
Such a separation corresponds to the dimensions of a typical human
head multiplied by a factor of 4.5 for water immersion. Also as
shown in FIG. 1, a baffle 14 is located between the left and right
pairs of hydrophones 10 and 12. The baffle 14 is intended to
simulate the bone portion of a listener's skull as it relates to
causing delays in sounds reaching the ears from opposite sides of
the head. The baffle 14, however, is not essential to this
invention and can be omitted when desirable.
A pair of potentiometers 16 and 18 are respectively coupled across
the outputs of the left and right pairs of hydrophones 10.sub.1,
10.sub.2, and 12.sub.1, 12.sub.2. The potentiometers 16 and 18
comprise "mixing pots" for establishing a virtual source 10'
located between the two hydrophones 10.sub.1 and 10.sub.2 on the
left and a vertical source 12' located between the two hydrophones
12.sub.1 and 12.sub.2 on the right, with the two vertical sources
10' and 12' being delivered to left and right ears, respectively,
of a listener 30. As shown, one end of the mixing-pot 16 is coupled
to the output of the left-front (LF) hydrophone 10.sub.1 by a low
output impedance pre-amplifier/amplifier or simply pre-amp
20.sub.1. The other end of the potentiometer 16 is coupled to the
output of the left-rear (LR) hydrophone 10.sub.2 by means of a
second low output impedance pre-amp 20.sub.2. In a like manner, the
output of a right-front (RF) hydrophone 12.sub.1 is connected to
one end of the mixing-pot 18 by means of a low output impedance
pre-amp 22.sub.1, while its opposite end is coupled to the output
of the right-rear hydrophone 12.sub.2 by means of low output
impedance pre-amp 22.sub.2.
The sliders i.e. output terminals 24 and 26 of the mixing-pots 16
and 18 are caused to move in mutually opposite directions in
response to movement of a listener 30, for example, rotation of the
listener's head. This is provided by a mechanical coupling, shown
schematically by reference numeral 28, to the listener 30. The
output terminals 24 and 26 of the mixing-pots 16 and 18 are
furthermore electrically connected to the left and right ear pieces
32.sub.1 and 32.sub.2 of a pair of headphones 32 by means of a pair
of amplifiers 34.sub.1 and 34.sub.2.
The output impedance of the hydrophones 101, 102 and 12.sub.1,
12.sub.2 , moreover, is low relative to the resistance of the
mixing pots 16 and 18 so that when a pot is directly coupled to one
hydrophone, the other hydrophone signal is effectively shorted out.
At less extreme positions, the percentage of each hydrophone's
signal contribution to the virtual hydrophone's phase-mixed signal
is determined by the voltage divider action of the mixing pots 16
and 18.
In the assembly shown in FIG. 1, only the hydrophones 10 and 12 are
located underwater. The remaining elements are located in the
listener's environment which may be, for example, in a craft or
vessel 36 (FIG. 2), remote from the hydrophone array.
In the configuration of FIG. 1, the mixing-pots 16 and 18 are
ganged together and controlled by the listener's 10 head movement
such that at one extreme the left-front (LF) and right-rear (RR)
hydrophones 10.sub.1 and 12.sub.2 are utilized 100%, while the
other two hydrophones (LR and RF) 10.sub.2 and 12.sub.1 is 0. This
condition corresponds to the listener's head being turned
45.degree. to the right. If the mixing-pots 16 and 18 are moved to
the opposite extreme, the left-rear (LR) and right-forward (RF)
hydrophones 10.sub.2 and 12.sub.1 are utilized 100.degree. and
corresponds to the listener's head being turned 45.degree. to the
left. As noted above, the mixing-pots 16 and 18 are located in the
listener's environment such that as the listener's head is turned,
the pots 16 and 18 are actuated, since their shafts are
mechanically attached to the listener's headphone assembly. If
standard 330 degree pots are employed, a rotational step-up is
employed, equivalent to a 3.7:1 gear ratio. When the listener's
head is centered (0.degree.), all four hydrophone signals are
utilized the same level of 50% each. In this condition, a "virtual"
hydrophone 10' and 12' appears midway between the hydrophone pairs
10.sub.1, 10.sub.2 and 12.sub.1, 12.sub.2. Each new head position
creates new positions for the virtual hydrophones 10' and 12'.
It should be pointed out that an important feature of the
embodiment shown in FIG. 1 is that outputs of the left and right
hydrophone pairs 10.sub.1, 10.sub.2 and 12.sub.1 and 12.sub.2 are
phase mixed and not amplitude mixed. However, phase mixing has its
limitations and the distance between the hydrophone pair being
mixed should be less than 1/2.lambda. as noted above. When the
spacing equals 1/2.lambda., the signal is equal and opposite in
each of the hydrophones and is cancelled. This requires that the
left-front (LF) and left-rear (LR) spacing L.sub.1 be, for example,
no greater than 2.5 feet for a pure 1 kHz signal. While a four
hydrophone geometry with 2 ft. separation as described violates the
1/2.lambda. principle in theory for higher frequencies, in practice
the spacing is satisfactory since real sounds are not pure tones
but a collection of may frequencies. Nevertheless, this theoratical
frequency limitation is addressed below in an alternate
embodiment.
Referring now to FIG. 2, shown thereat is an embodiment whereby the
listener 30 is located, for example, on a surface vehicle 36, such
as a ship, and there is a need to control a remotely operated
vehicle (ROV) 38 navigating in a self-propelled mode underwater as
shown by reference numeral 40. The two sets of hydrophones
10.sub.1, 10.sub.2 and 12.sub.1 and 12.sub.2 are located in a quad
pattern on the underside of the ROV 38 and are electrically coupled
to a pre-amp assembly 42 located in the ROV 38. The pre-amp
assembly 42 is coupled to a potentiometer assembly 46 in the
surface vehicle 36 by an umbilical cable 44. The pre-amp assembly
42 houses the pre-amps 20.sub.1, 20.sub.2, and 22.sub.1 and
22.sub.2 shown in FIG. 1 while the potentiometer assembly 46
contains the mixing pots 16 and 18.
In the embodiment shown in FIG. 2, the potentiometer assembly 46 is
located beneath a swivel type seat 48 whose post 50 and is integral
with and activates the potentiometer assembly 46 which also acts as
a base for the seat 48. In this embodiment, movement of the
listener 30 in azimuth causes the seat to rotate and thus actuate
the setting of the mixing-pots 16 and 18 instead of the listener 30
simply turning his head from left to right as taught in FIG. 1.
In operation, the operator or listener 30 would be facing straight
ahead in the swivel chair 48. This corresponds to the direction of
travel of the ROV 38 and where the virtual hydrophones 10' and 12'
(FIG. 1) would be midway between the left-front (LF) and left-rear
(LR) hydrophones 101 and 102 as well as the right-front (RF) and
right-rear (RR) hydrophones 12.sub.1 and 12.sub.2, since the seat's
0.degree. orientation provides a mixing-pot setting at
mid-position. Now assuming a sound 8 of interest from the source 6
impinges from the northeast (NE) at a 45.degree. angle. Before
swiveling, the operator 30 cannot tell whether the sound 8 is
coming from 45.degree. or 135.degree. which is to the southeast
(SE) because of the phase ambiguity. However, by swiveling, the
ambiguity can be resolved, since when the operator 30 rotates to
the right, the sound 8 will appear to be less offset. If the true
direction was 135.degree., it would have appeared even more offset.
If the operator completely swivels to 45.degree., the mixing-pots
are in the extreme position, but the sound 8 will be centered and
the ROV 38 can then be instructed to steer 45.degree. to the
starboard.
While the embodiments shown in FIGS. 1 and 2 disclose a four
hydrophone array, another arrangement is disclosed whereby a
rotation range can be enhanced by the use of an array of a
hydrophone array comprised of more than just four hydrophones
10.sub.1, 10.sub.2 and 12.sub.1 and 12.sub.2. In the embodiment
shown in FIG. 3, a plurality n of hydrophones 10.sub.1, 10.sub.2,
10.sub.3 . . . 10.sub.n-1, 10.sub.n are utilized with multi-tapped
potentiometers 16' and 18'. All the hydrophone signals of the left
and right sets of hydrophones 20.sub.1 . . . 20.sub.n, and 12.sub.1
. . . 12.sub.n respectively couple to the multi-tapped mixing-pots
16' and 18'.
Each virtual hydrophone 10' and 12' is panned smoothly from
left-front (LF) to left-rear (LR) and right-front (RF) to
right-rear (RR) without 1/2, .lambda. cancellations because no more
than two hydrophones at a time, for example, hydrophones 20.sub.2
and 20.sub.3 can contribute to generating a "virtual" signal.
Contributions from the other hydrophones 20.sub.1, 20.sub.n-1,
20.sub.n are prevented by the low output impedance of each of its
respective preamplifiers 20.sub.1, 20.sub.2 . . . 20.sub.n.
Furthermore, the separation of L.sub.3 between the two sets of
hydrophones 10 and 12 can be much smaller than the distance L.sub.2
in FIG. 1.
A variation of the embodiment disclosed in FIG. 3 is shown in FIG.
4 and simply comprises arranging the two sets of headphones
10.sub.1, 10.sub.2 . . . 10.sub.n and 12.sub.1, 12.sub.2 . . .
12.sub.n in a circular configuration which would provide an even
more precise and accurate system of localization than in the linear
configurations described heretofore.
It is conceivable that the two sets of hydrophones 10.sub.1 . . .
10.sub.n and 12.sub.1 . . . 12.sub.n could be placed on the bottom
41 (FIG. 2) in a stationary array.
Referring now briefly to FIGS. 5A and 5B, shown thereat are two
different types of linear hydrophone arrays. In FIG. 5A, a linear
hydrophone array 52 is shown comprised of a plurality of discrete
cylindrical passive hydrophone elements 54.sub.1, 54.sub.2,
54.sub.3, 54.sub.4, which are housed in a cylindrical casing 56 and
which is adapted to conduct acoustic energy therethrough to the
individual hydrophone elements 54.sub.1, 54.sub.2, etc. Each of the
hydrophones 54.sub.1, 54.sub.2, 54.sub.3 and 54.sub.4 have
individual output leads 58.sub.1, 58.sub.2, 58.sub.3 and 58.sub.4
which can be arranged in a wiring harness, not shown, so as to be
fed out of one end of the casing 56 to respective signal amplifiers
such as shown in FIGS. 1-4.
The embodiment shown in FIG. 5B, on the other hand, discloses a
linear hydrophone array 60 comprised of a plurality of contiguous
passive hydrophone elements 62.sub.1, 62.sub.2 . . . 62.sub.4, etc.
comprised of segmented strips of piezo-rubber material. An example
of this type of device is shown and described in U.S. Pat. No.
4,833,659, which issued to F. G. Geil et al on May 23, 1989. As
before, each hydrophone 62.sub.1, 62.sub.2, etc. includes a
respective output lead 64.sub.1, 64.sub.2 . . . 64.sub.5, etc.
which is adapted to be coupled to a respective amplifier, not
shown.
Thus what has been shown and described is a passive hydrophone
arrangement whereby "virtual reality" may be implemented
effectively in an underwater environment for the localization of
sound sources remote from the listener and which permits the
localization of the source to control the movement of an underwater
vehicle.
Having thus disclosed what is at present considered to be the
preferred embodiments of the invention, it should be noted that the
same has been made by way of explanation and not limitation.
Therefore, all modifications, alterations and changes coming within
the spirit and scope of the invention as defined by the appended
claims are herein meant to be included.
* * * * *