Tracking system and method

• US 5,481,505 A
• Filed: 05/15/1995
• Issued: 01/02/1996
• Est. Priority Date: 05/15/1995
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Nuttall, Albert H., Donald, James B., Wilson, James H.
• Primary Examiner(s): Pihulic, Daniel T.
• Application Number:
  US08/446,117
• Time in Patent Office: 232 Days
• Field of Search: 367/118, 367/119, 367/121, 367/124, 367/129, 367/130, 367/901, 364/516
• US Class Current: 367/130
• CPC Class Codes: G01S 3/8083 determining direction of source
• CPC Class Codes: G01S 5/20 Position of source determined by a plurality of spaced direction-finders

Abstract

A method and apparatus for detecting, processing and tracking sonar signalso provide bearing, range and depth information that locates an object in three-dimensional underwater space. An inverse beamformer utilizes signals from a towed horizontal array of hydrophones to estimate a bearing to a possible object. A matched field processor receives measured covariance matrix data based upon signals from the hydrophones and signals from a propagation model. An eight nearest neighbor peak picker provides plane wave peaks in response to output beam levels from the matched processor. A five-dimensional M of N tracker identifies peaks within the specified limit of frequency, bearing change over time, range and depth to specify an object as a target and to display its relative range and depth with respect to the array of hydrophones.

Claims

1. A method for locating, in three-dimensional underwater space and in relation to a predetermined location, an object emitting acoustic signals comprising the steps of:

receiving acoustic signals including the acoustic signals from the object at the predetermined location by means of a towed, horizontal array of acoustic transducers;

estimating a bearing to the object in response to the received acoustic signals;

generating beam values for signals received by said acoustic transducers from different incremental locations at incremental ranges and depths along the estimated bearing;

selecting an individual incremental location with a peak beam value; and

providing bearing, range and depth information from the predetermined location to the incremental location thereby locating the object in three-dimensional underwater space.

2. A method as recited in claim 1 wherein said step of generating beam values additionally includes generating beam values along bearings offset from the estimated bearing, and said step of selecting an incremental location includes determining the peak beam value from all beam values from the estimated and offset bearings.

3. A method as recited in claim 1 wherein each of said beam values is generated for each of a plurality of frequency bands and over time whereby said step of providing bearing, range and depth information additionally comprises providing frequency information of said received acoustic signal, and wherein the method additionally comprises the step of analyzing the provided frequency information for obtaining further information about object.

4. A method as recited in claim 3 wherein said step of generating beam values is repeated at regular intervals whereby the bearing, depth, range and frequency information is provided as a function of time.

5. A method as recited in claim 1 wherein said step of generating beam values is repeated at regular intervals whereby the bearing, depth and range information is provided as a function of time.

6. A method as recited in claim 5 further comprising the step of deploying an array of acoustic transducers before the step of receiving acoustic signals, said step of estimating a bearing includes inverse beamforming processing the signals from each transducers in the array.

7. A method as recited in claim 6 wherein said beamforming processing uses different frequencies and multipath analysis.

8. A method as recited in claim 7 wherein said step of generating beam values from an incremental location includes obtaining a correlation value for each frequency and for each incremental location.

9. A method as recited in claim 8 wherein said step of obtaining a correlation value includes the step of correlating the results of a propagation model for each measured frequency and each incremental location along the bearing and a measured covariance matrix for the signals from the transducer array.

10. A method as recited in claim 8 wherein said step of selecting an individual incremental location includes the step of determining peak values based upon an inverse beamformer eight nearest neighbor peak picker analysis.

11. A method as recited in claim 10 wherein said step of selecting an individual incremental location additionally includes analyzing the succession of peak values in an M of N tracker.

12. A method as recited in claim 11 wherein said M of N tracker is a five-dimensional tracker based upon correlation peak values versus bearing, frequency, range, depth and time.

13. Apparatus for locating, in three-dimensional underwater space and in relation to a predetermined location, an object emitting acoustic signals, said apparatus comprising:

a receiver means having a towed horizontal array of transducers for obtaining acoustic signals including the acoustic signals from the object at the predetermined location;

an estimating means connected to said receiver means and responsive to the processed acoustic signals for estimating the bearing to a possible object;

a beam value generating means for generating beam values for signals detected from different incremental locations at incremental ranges and depths along the estimated bearing;

a location selection means joined to said estimating means for selecting an individual incremental location with peak beam value;

a locating means for providing the bearing to, the predetermined location to, and the range and depth of the incremental location thereby the object in three-dimensional underwater space and designating the object as a target; and

a display means for displaying the location of the target joined to said locating means.

14. Apparatus as recited in claim 13 wherein said estimating means includes:

a Fast Fourier Transform processing means joined to each transducer;

an inverse plane wave beamforming means joined to process the output signals from said Fast Fourier Transform processing means; and

a covariance matrix data means using signal from said receiver means for generating measured covariance matrix data.

15. Apparatus as recited in claim 14 additionally comprising a weighting means joined to said covariance data means for weighting the values of the signals.

16. Apparatus as recited in claim 14 wherein said beam value generating means comprises:

a signal propagation model means for generating a model for the plurality of range-depth cells; and

an inverse beam forming matched field processing means responsive to said signal propagation means and said measured covariance matrix means for producing a beam value for each of the range-depth cells, said signal propagation model means being joined to said inverse beamforming matched field processing means.

17. Apparatus as recited in claim 16 wherein said inverse beamforming matched field processing means produces correlation values for each of a plurality of acoustic signal frequencies from data received from said signal propagation model means and said covariance data means.

18. Apparatus as recited in claim 17 wherein the beam value for each incremental location represents a correlation value and said location selection means includes a nearest neighbor peak picker circuit means for identifying each incremental location for which the correlation value exceeds the correlation value in each adjacent incremental location.

19. Apparatus as recited in claim 18 wherein said apparatus operates in an iterative fashion and said locating means includes an M of N tracker means for tracking the correlation values as a function of bearing, frequency, range, depth and time over a series of iterations.

20. Apparatus as recited in claim 19 wherein said display means includes means for displaying, as functions of time, the range to, the depth of and the bearing to the target.