Acoustic tracking system

• US 5,410,519 A
• Filed: 11/19/1993
• Issued: 04/25/1995
• Est. Priority Date: 11/19/1993
• Status: Expired due to Fees

• Current Assignee: Coastal & Offshore Pacific Corporation
• Original Assignee: Coastal & Offshore Pacific Corporation
• Inventors: Hall, John D., Gordon, Bruce, Miller, Clarence E.
• Primary Examiner(s): Pihulic, Daniel T.
• Application Number:
  US08/155,950
• Time in Patent Office: 522 Days
• Field of Search: 367/118, 367/127, 367/124, 367/125, 367/126, 367/129
• US Class Current: 367/127
• CPC Class Codes: G01S 11/14 using ultrasonic, sonic, or infrasonic waves
• CPC Class Codes: G01S 3/8083 determining direction of source
• CPC Class Codes: G01S 5/28 by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial

Abstract

An acoustic tracking system designed to allow scientists and fishermen to follow dolphins and whales without harming or harassing them. The system utilizes six flow shielded hydrophones mounted on the bottom of a vessel in two arrays of three hydrophones in each array. Acoustic signals of interest (dolphin calls) which strike the hydrophone piezo-electric elements are transmitted to a receiver-display device which determines and displays both the bearing to the signal of interest and the relative range from the vessel to that signal. The receiver-display device utilizes digital microprocessors to determine the difference in signal arrival time of an incoming signal at pairs of hydrophones. The resulting computed bearing to the dolphin call is displayed as a lighted indicator on an electronic heading display. In addition, the digital microprocessors compare the received sound pressure level of incoming signals of interest and display the relative range as a series of lighted LED'"'"'s on the electronic heading indicator.

Claims

1. An acoustic tracking system mounted on an ocean-going vessel having a keel and a chine on either side of the keel, the system being employed for locating and tracking sound emitting cetaceans remote from the vessel, the sounds emitted by the cetaceans having known characteristics and acoustic parameters, said system comprising:

a non-linear array of a plurality of sound sensitive units mounted on the bottom of the vessel and receiving the cetacean originated acoustic signal sounds through the water and converting the sounds to electrical signals;

receiving means mounted on the vessel;

means for transmitting the electrical signals from said sound sensitive units to said receiver means;

means included in said receiver means pursuant to the signals received from a plurality of said sound sensitive units for calculating relative range and bearing from the vessel to the acoustic signal producing cetacean; and

means connected to said receiver means for indicating said bearing and range.

2. The tracking system recited in claim 1, wherein said sound sensitive units are hydrophones.

3. The tracking system recited in claim 2, wherein the array comprises a plurality of said hydrophones mounted on either side of the keel and inboard of the chines of the vessel in fixed relationship to the vessel and to each other.

4. The tracking system recited in claim 2, wherein said receiver means comprises signal comparing and processing means for comparing time difference of arrival of the acoustic signals at a plurality of pairs of hydrophones and calculating the bearing to the acoustic signal source.

5. The tracking system recited in claim 4, wherein the hydrophones in each said pair are spaced by at least one half the wavelength of the received signals to thereby enable rapid and unambiguous determination of the bearing from the vessel to the acoustic signal source.

6. The tracking system recited in claim 2, wherein said receiver means comprises signal comparing and processing means for comparing the amplitude of a received acoustic signal with a known originating source acoustic amplitude level and calculating the range to the acoustic signal source.

7. The tracking system recited in claim 2, wherein said receiver means comprises signal comparing and processing means for comparing arrival times of the acoustic signals at a plurality of pairs of hydrophones and calculating the bearing to the acoustic signal source, and for comparing the amplitude of a received acoustic signal with a known originating source acoustic amplitude level and calculating the range to the acoustic signal source.

8. The tracking system recited in claim 7, wherein said signal comparing and processing means operates repetitively on successive received acoustic signals to refine bearing and range indications.

9. The tracking system recited in claim 6, said receiver means further comprising memory means storing a signal representative of the known originating source acoustic amplitude level.

10. The tracking system recited in claim 7, said receiver means further comprising memory means storing a signal representative of the known originating source acoustic amplitude level.

11. The tracking system recited in claim 2, and further comprising a plurality of audio speakers, one for each hydrophone, to enable a system operator to binaurally monitor the signals received by said hydrophones.

12. The tracking system recited in claim 1, wherein said receiver means comprises a plurality of high pass frequency filters to enable a system operator to selectively eliminate ambient and vessel associated sounds.

13. The tracking system recited in claim 1, wherein said receiver means comprises a low pass filter for preventing aliasing of acoustic signals above a predetermined frequency.

33. The tracking system recited in claim 1, wherein:

the electrical signals representing the received sounds comprise an individual digital data stream from each said sound sensitive unit;

said means for calculating bearing comprises a microprocessor comprising;

means for converting the digital data streams from individual amplitude points to amplitude/frequency points using an 8 to 1 decimation ratio;

means for cross correlating the amplitude/frequency points to determine differential times of arrival of the acoustic signal sounds at the sound sensitive units; and

means for accurately calculating range and relative bearing to the source of the cetacean originated sounds.

37. The tracking system recited in claim 6, wherein the known originating source acoustic amplitude level is that emitted by the cetaceans being tracked at one meter distance from the cetaceans.

38. The tracking system recited in claim 37, wherein the source cetacean amplitudes are about 160 dB source level re 1 Pa at 1 m with substantial acoustic energy at frequencies ranging between 4 kHz and 20 kHz.

39. The tracking system recited in claim 7, wherein the known originating source acoustic amplitude level is that emitted by the cetaceans being tracked at one meter distance from the cetaceans.

40. The tracking system recited in claim 9, wherein the signal stored in said memory means is representative of the amplitude of sound emitted by the cetaceans being tracked at one meter distance from the cetaceans.

41. The tracking system recited in claim 10, wherein the signal stored in said memory means is representative of the amplitude of sound emitted by the cetaceans being tracked at one meter distance from the cetaceans.

46. The tracking system recited in claim 1, wherein said range indication means comprises an array of light emitting diodes (LED'"'"'s) arranged to provide relative range indication depending on the number of said LED'"'"'s which are lit.

47. The tracking system recited in claim 46, wherein:

said sound sensitive units are hydrophones having predetermined calibrated sensitivity;

the relative range determination is based on the calibrated sensitivity of said hydrophones, the known electrical outputs of said hydrophones based on received sound level input, and known attenuation equations of sound signals underwater.

48. The tracking system recited in claim 1, wherein said range and bearing indication means comprises an integrated visual display.

49. The tracking system recited in claim 1, wherein said bearing indication means comprises a digital display.

50. The tracking system recited in claim 12, wherein the ambient and vessel associated sounds are eliminated prior to the received signals being processed by said calculating means.

51. The tracking system recited in claim 13, wherein said low pass filter eliminates all incoming signals to said system which are higher than 20 kHz.

55. The tracking system recited in claim 11, and further comprising:

means in said receiver mans for storing the electrical signals representing the received acoustic signals;

means in said receiver means for playing back the stored signals; and

means in said receiver means for selective reduction of the playback speed of the stored signals below the recording speed, thereby downshifting the frequency of the signals projected from said audio speakers to facilitate directional detection by the operator.

56. The tracking system recited in claim 55, wherein the playback speed ranges between 10% and 100% of the recording speed, thereby proportionally reducing the signal frequency projected from said audio speakers.

14. An acoustic tracking system for a remote signal source emitting acoustic signals of predetermined frequencies, said system comprising:

an array of a plurality of individual, spaced sound sensitive units mounted on a body in the medium in which the acoustic signals are being propagated, said units receiving and converting the acoustic signals to electrical signals, the spacing between each adjacent said units being greater than one-half the wavelength of the acoustic signals;

receiver means mounted on said body;

means for transmitting the electrical signals from said sound sensitive units to said receiver means; and

signal processing means in said receiver means to unambiguously determine the time difference of arrival of a predetermined frequency signal at each said unit of each pair of adjacent pairs of said units and thereby determine the bearing from the body to the remote acoustic signal source.

15. The tracking system recited in claim 14, wherein:

said signal processing meads is further sensitive to the amplitude of the received electrical signals, which are proportional to the received acoustic signals;

said receiver means further comprises computation and memory means, said memory means including amplitude characteristics of the signals of interest at the signal source, said computation means including the distance attenuation equations of the predetermined frequencies in the medium;

whereby said signal processing means determines the range from said body to the signal source.

52. The tracking system recited in claim 14, wherein said receiver means comprises a low pass anti-aliasing filter which eliminates all incoming signals to said system which are higher then 20 kHz.

16. An acoustic tracking system for a remote signal source emitting acoustic signals of predetermined frequencies, said system comprising:

an array of sound sensitive units mounted on a body in the medium in which the acoustic signals are being propagated, said units receiving and converting the acoustic signals to electrical signals, the spacing between adjacent said units being greater than one-half the wavelength of the acoustic signals;

receiver means mounted on said body;

means for transmitting the electrical signals from said sound sensitive units to said receiver means; and

signal processing means in said receiver means to unambiguously determine the time difference of arrival of an acoustic signal at each adjacent pair of said units and thereby determine the bearing from the body to the acoustic signal sources, said signal processing means being further sensitive to the amplitude of the received electrical signals, which are proportional to the received acoustic signals;

said receiver means further comprising computation and memory means, said memory means including amplitude characteristics of the predetermined frequency acoustic signals at the acoustic signal source, said computation means including the distance attenuation equations of the predetermined frequencies in the medium;

whereby said signal processing means determines the range from said body to the acoustic signal source, and said computation and memory means resolves bearing and range ambiguities by employing many time difference and amplitude calculations and correlating the results.

17. The tracking system recited in claim 16, and further comprising means connected to said receiver means for indicating said bearing and range results.

18. A method for acoustically tracking sound emitting cetaceans, said method comprising the steps of:

mounting a non-linear array of a plurality of sound sensitive units on an ocean-going vessel having a keel and a chine on either side of the keel;

moving the vessel and array to the vicinity of acoustic signal producing cetaceans;

receiving such acoustic signals by the plurality of sound sensitive units;

converting the acoustic signals to electrical signals;

transferring such electrical signals to a receiver;

calculating the relative range and bearing from the vessel to the acoustic signal producing cetaceans; and

providing indications of the calculated range and bearing.

19. The method recited in claim 18, wherein the sound sensitive units are hydrophones and the acoustic signals are converted to electrical signals by means of piezo-electrical elements in the hydrophones.

20. The method recited in claim 18, wherein the bearing is determined by comparing acoustic signal arrival times at each sound sensitive unit in each of a plurality of pairs of such units and calculating the bearing to the acoustic signal source.

21. The method recited in claim 20, wherein the hydrophones in each pair are spaced by at least one half the wavelength the acoustic signals to thereby enable rapid and unambiguous determination of the bearing.

22. The method recited in claim 18, wherein said calculating step is conducted repetitively on successive received acoustic signals to refine bearing and range indications.

23. The method recited in claim 18, wherein the range is determined by the steps of:

measuring the acoustic amplitude of a received signal;

comparing that received amplitude with a known originating source acoustic amplitude and determining a difference signal;

applying to that difference signal a propagation loss factor for ocean waters; and

calculating the range to the acoustic signal source.

24. The method reflected in claim 18, wherein the range is determined by the steps of:

measuring the acoustic amplitude of a received signal;

comparing that received amplitude with a known originating source acoustic amplitude and determining a difference signal;

applying to that difference signal a propagation loss factor for ocean waters;

calculating the range to the acoustic signal source; and

wherein the bearing is determined by comparing acoustic signal arrival times at each sound sensitive unit in each of a plurality of pairs of such units and calculating the bearing to the acoustic signal source.

25. The method recited in claim 18, wherein the mounting step comprises mounting an array of hydrophones on either side of the keel inboard of the respective chine of the vessel in fixed relationship to each other in non-linear arrangements.

26. The method recited in claim 18, said indications being visible.

27. The method recited in claim 18, said indications being audible.

28. The method recited in claim 26, said indications being also audible.

35. The method recited in claim 18, wherein:

the electrical signals representing the received acoustic signals comprise an individual digital data stream from each sound sensitive unit;

the calculating step includes the steps of;

converting the digital data streams from individual amplitude points to amplitude/frequency points by employing an 8 to 1 decimation ratio;

cross correlating the amplitude/frequency points to determine the differential times of arrival of the acoustic signals at the sound sensitive units; and

accurately calculating range and relative bearing to the source of the cetacean originated sounds.

43. The method recited in claim 23, wherein the known originating source acoustic amplitude level is that emitted by the cetaceans being tracked at one meter distance from the cetaceans.

44. The method recited in claim 24, wherein the known originating source acoustic amplitude level is that emitted by the cetaceans being tracked at one meter distance from the cetaceans.

53. The method recited in claim 18, and comprising the further step of filtering out all received signals above 20 kHz.

57. The method recited in claim 19, and comprising the further steps of:

storing the electrical signals representing the received acoustic signals;

selectively playing back the stored electrical signals over audio speakers; and

selectively reducing the playback speed of the stored electrical signals below the recording speed, thereby downshifting the frequency of the signals projected from the audio speakers to facilitate directional detection by the operator.

58. The method recited in claim 57, wherein the playback speed ranges between 10% and 100% of the recording speed, thereby proportionally reducing the signal frequency projected from said audio speakers.

29. A method for acoustically tracking a remote signal source emitting acoustic signals of predetermined frequencies, said method comprising the steps of:

mounting an array of a plurality of individual, spaced sound sensitive units, each sound sensitive unit being related to more than one such unit in a plurality of pairs of such units, the units being mounted in mutual fixed relationship on a body in the medium in which the acoustic signals are being propagated;

receiving the acoustic signals by the sound sensitive units, the spacing between the units in each pair being greater than one-half the wavelength of the acoustic signals;

converting the received acoustic signals to electrical signals;

transmitting the electrical signals to a receiver; and

determining in an unambiguous manner the time difference of arrival of a predetermined frequency acoustic signal at each unit of each pair of adjacent pairs of units and thereby determining the bearing from the body to the remote signal source.

30. The method recited in claim 29, and comprising the further step of:

determining the amplitude of the received electrical signals which are proportional to the received signals;

applying known amplitude characteristics of the signals at the signal source, add applying distance attenuation equations of the predetermined frequencies in the medium; and

calculating the range from the body to the signal source.

31. A method for acoustically tracking a remote signal source emitting acoustic signals of predetermined frequencies, said method comprising the steps of:

mounting an array of pairs of sound sensitive units in mutual fixed relationship on a body in the medium in which the acoustic signals are being propagated;

receiving the acoustic signals by the sound sensitive units, the spacing between the units in each pair being greater than one-half the wavelength of the predetermined frequency acoustic signals;

converting the received acoustic signals to electrical signals;

transmitting the electrical signals to a receiver;

determining in an unambiguous manner the time difference of arrival of an acoustic signal at each unit in each pair of units and thereby determining the bearing from the body to the acoustic signal source;

determining the amplitude of the received electrical signals which are proportional to the received acoustic signals;

applying known amplitude characteristics of the acoustic signals at the acoustic signal source, and applying distance attenuation equations of the predetermined frequencies in the medium;

calculating the range from the body to the acoustic signal source; and

repetitively calculating the bearing and range from successive received acoustic signals and correlating the results to refine the bearing and range results.

32. The method recited in claim 31, and comprising the further step of providing perceivable indications of the bearing and range calculations.

34. An acoustic tracking system for a remote signal source emitting acoustic signals of predetermined frequencies, said system comprising:

an array of sound sensitive units mounted on a body in the medium in which the acoustic signals are being propagated, said units receiving and converting the acoustic signals to electrical signals, the spacing between adjacent said units being greater than one-half the wavelength of the acoustic signals;

receiver means mounted on said body;

means for transmitting the electrical signals from said sound sensitive units to said receiver means; and

signal processing means in said receiver means to unambiguously determine the time difference of arrival of an acoustic signal at each adjacent pair of said units and thereby determine the bearing from the body to the acoustic signal source;

wherein

the electrical signals representing the received sounds comprise an individual digital data stream from each said sound sensitive unit;

said means for calculating bearing comprises a microprocessor comprising;

means for converting the digital data streams from individual amplitude points to amplitude/frequency points using an 8 to 1 decimation ratio;

means for cross correlating the amplitude/frequency points to determine differential times of arrival of the acoustic signal sounds at the sound sensitive units; and

means for accurately calculating range and relative bearing to the source of the acoustic signals.

36. A method for acoustically tracking a remote signal source emitting acoustic signals of predetermined frequencies, said method comprising the steps of:

mounting an array of pairs of sound sensitive units in mutual fixed relationship on a body in the medium in which the acoustic signals are being propagated;

receiving the acoustic signals by the sound sensitive units, the spacing between the units in each pair being greater than one-half the wavelength of the acoustic signals;

converting the received acoustic signals to electrical signals;

transmitting the electrical signals to a receiver; and

determining in an unambiguous manner the time difference of arrival of an acoustic signal at each unit in each pair of units and thereby determining the bearing from the body to the acoustic signal source;

wherein

the electrical signals representing the received acoustic signals comprise an individual digital data stream from each sound sensitive unit;

the calculating step includes the steps of;

converting the digital data streams from individual amplitude points to amplitude/frequency points by employing an 8 to 1 decimation ratio;

cross correlating the amplitude/frequency points to determine the differential times of arrival of the acoustic signals at the sound sensitive units; and

accurately calculating range and relative bearing to the source of the acoustic signals.

42. An acoustic tracking system for a remote signal source emitting acoustic signals of predetermined frequencies, said system comprising:

an array of sound sensitive units mounted on a body in the medium in which the acoustic signals are being propagated, said units receiving and converting the acoustic signals to electrical signals, the spacing between adjacent said units being greater than one-half the wavelength of the acoustic signals;

receiver means mounted on said body;

means for transmitting the electrical signals from said sound sensitive units to said receiver means; and

signal processing means in said receiver means to unambiguously determine the time difference of arrival of an acoustic signal at each adjacent pair of said units and thereby determine the bearing from the body to the acoustic signal sources, said signal processing means being further sensitive to the amplitude of the received electrical signals, which are proportional to the received acoustic signals;

said receiver means further comprising computation and memory means, said memory means including amplitude characteristics of the predetermined frequency acoustic signals at the acoustic signal source, said computation means including the distance attenuation equations of the predetermined frequencies in the medium;

whereby said signal processing means determines the range from said body to the acoustic signal source;

wherein

the signal stored in said memory means is representative of the amplitude of sound emitted by the acoustic signal source being tracked at one meter distance from the acoustic signal source.

45. A method for acoustically tracking a remote signal source emitting acoustic signals of predetermined frequencies, said method comprising the steps of:

mounting an array of pairs of sound sensitive units in mutual fixed relationship on a body in the medium in which the acoustic signals are being propagated;

receiving the acoustic signals by the sound sensitive units, the spacing between the units in each pair being greater than one-half the wavelength of the acoustic signals;

converting the received acoustic signals to electrical signals;

transmitting the electrical signals to a receiver;

determining in an unambiguous manner the time difference of arrival of an acoustic signal at each unit in each pair of units and thereby determining the bearing from the body to the acoustic signal source;

determining the amplitude of the received electrical signals which are proportional to the received acoustic signals;

applying known amplitude characteristics of the acoustic signals at the acoustic signal source, and applying distance attenuation equations of the predetermined frequencies in the medium; and

calculating the range from the body to the acoustic signal source;

wherein

the amplitude characteristics of the acoustic signals at the acoustic signal source are those emitted by the acoustic signal source being tracked at one meter distance from the acoustic signal source.

54. A method for acoustically tracking a remote signal source emitting acoustic signals of predetermined frequencies, said method comprising the steps of:

mounting an array of pairs of sound sensitive units in mutual fixed relationship on a body in the medium in which the acoustic signals are being propagated;

receiving the acoustic signals by the sound sensitive units, the spacing between the units in each pair being greater than one-half the wavelength of the predetermined frequency acoustic signals;

converting the received acoustic signals to electrical signals;

transmitting the electrical signals to a receiver;

determining in an unambiguous manner the time difference of arrival of an acoustic signal at each unit in each pair of units and thereby determining the bearing from the body to the acoustic signal source; and

filtering out all received acoustic signals above 20 kHz.