System and method for disambiguating shooter locations

• US 20070030763A1
• Filed: 10/13/2006
• Published: 02/08/2007
• Est. Priority Date: 08/24/2004
• Status: Active Grant

• Current Assignee: Raytheon BBN Technologies Corp. (Rtx Corporation)
• Original Assignee: BBN Technologies (Rtx Corporation)
• Inventors: Brinn, Marshall, Barger, James, Milligan, Stephen
• Granted Patent: US 7,408,840 B2
• Time in Patent Office: Days
• US Class Current: 367/127
• CPC Class Codes: F41J 5/06 Acoustic hit-indicating systems, i.e. detecting of shock waves F41J5/056 takes precedence
• CPC Class Codes: G01S 3/808 using transducers spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems
• CPC Class Codes: G01S 5/22 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/28 takes precedence
• CPC Class Codes: Y10S 367/906 Airborne shock-wave detection

Abstract

Systems and methods for locating the shooter of supersonic projectiles based on shockwave-only measurements are described. Muzzle blast signals are neither sought nor required. The system uses at least five, preferably seven, acoustic sensors that are spaced apart at least 1 meter. The sensor signals are acquired with a time resolution in the order of microseconds and processed to find and disambiguate the shockwave arrival angle unit vector. Two different Time-Difference-Of-Arrival (TDOA) measurement techniques are described, with one technique using counters in each signal channel and the other technique using cross-correlation between signal channels. A genetic algorithm can be used to efficiently disambiguate the results.

Claims

1-24. -24. (canceled)

25. A method for disambiguating from shockwave-only signals a trajectory of a projectile producing a shockwave wavefront, comprising:

measuring at least an initial portion of the shockwave-only signals with a plurality of spaced acoustic sensors forming an antenna;

determining from the measured portion of the shockwave-only signals Time-Difference-Of-Arrival (TDOA) values for sensor pairs with an accuracy sufficient to determine a gradient of curvature of the shockwave wavefront across the antenna;

determining the gradient of curvature of the shockwave wavefront; and

determining from the determined gradient of curvature the disambiguated projectile trajectory.

26. The method of claim 25, wherein the accuracy sufficient to determine the gradient of curvature depends on a size of the antenna.

27. The method of claim 25, wherein the accuracy sufficient to determine the gradient of curvature depends on a spatial distribution of sensor locations.

28. The method of claim 25, wherein measuring the initial portion of the shockwave-only signals includes measuring acoustic energy of a received signal and excluding the received signal from being a shockwave-only signal if the acoustic energy of the received has less than a predetermined threshold value over a predetermined frequency band.

29. The method of claim 28, wherein the predetermined frequency band comprises frequencies between approximately 700 Hz and 10 kHz.

30. The method of claim 25, wherein measuring the initial portion of the shockwave-only signals includes measuring a time interval where a received signal has a positive value and excluding the received signal from being a shockwave-only signal if the time interval is less than a minimum time or greater than a maximum time.

31. The method of claim 30, wherein the minimum time is approximately 70 μ

s and the maximum time is approximately 300 μ

s.

32. The method of claim 25, wherein determining the Time-Differences-Of-Arrival (TDOA) values for sensor pairs comprises

designating a sensor of the plurality of sensors that first encounters the shockwave wavefront as a reference sensor;

setting a first latch of a timing circuit when an amplitude of the initial portion of the shockwave-only signal at the reference sensor crosses a threshold value, said first latch activating counters for each of the other sensors; and

stopping the counters in each of the other sensors when the respective other sensors encounter the shockwave wavefront;

wherein a count between start and stop of the counters represents the TDOA between the other sensors and the reference sensor.

33. The method of claim 25, wherein determining the Time-Differences-Of-Arrival (TDOA) values for sensor pairs comprises

measuring at least the initial portion of the shockwave-only signals at the acoustic sensors with a first clock rate;

correlating the measured portions between the acoustic sensors with a second clock rate greater than the first clock rate; and

determining a Time-Difference-Of-Arrival (TDOA) from a time shift producing a maximum value of the correlation.

34. The method of claim 33, and further computing from the correlated portions a residual for each sensor and selecting the smallest residual as producing optimum TDOA values.

35. A method for disambiguating a trajectory of a supersonic projectile from shockwave-only signals with an antenna having a plurality of acoustic sensors, comprising:

detecting shockwave-only signals at the plurality of acoustic sensors;

determining from a correlation between the shockwave-only signals detected at the plurality of sensors Time-Difference-Of-Arrival (TDOA) values for sensor pairs;

for an expected closest distance between a projectile trajectory and the antenna, determining if a precision of the Time-Difference-Of-Arrival (TDOA) values is adequate for determining a gradient of curvature of a shockwave wavefront across the antenna;

determining the gradient of curvature of the shockwave wavefront; and

determining the disambiguated projectile trajectory from the gradient of curvature.

36. The method of claim 35, wherein the correlation is performed with a timing resolution which is greater than a timing resolution used to measure the portion of the shockwave-only signals.

37. The method of claim 35, wherein detecting shockwave-only signals comprises measuring at least an initial portion of a received shockwave-only signals, measuring acoustic energy of the received signal, and excluding the received signal from being a shockwave-only signal if the acoustic energy of the received has less than a predetermined threshold value over a predetermined frequency band.

38. The method of claim 35, wherein detecting shockwave-only signals comprises measuring at least an initial portion of a received shockwave-only signals, measuring a time interval where a received signal has a positive value, and excluding the received signal from being a shockwave-only signal if the time interval is less than a minimum time or greater than a maximum time.

39. The method of claim 35, wherein detecting shockwave-only signals comprises eliminating detected signal not originating from a shockwave.

40. The method of claim 39, wherein a detected signal is deemed to be a shockwave-only signal if it satisfies all of the following criteria:

(a) the detected signal has a minimum and a maximum peak signal amplitude, with at least the minimum peak signal amplitude exceeding a predetermined threshold value;

(b) the detected signal has a sharp transient from zero to the maximum peak signal amplitude, without being preceded by another signal with a value that is not significantly smaller than the peak signal value;

(c) a time between the minimum and maximum peak signal amplitudes of the detected signal is greater than a predetermined time interval;

(d) a magnitude of the minimum peak signal amplitude is substantially identical to the maximum peak signal amplitude;

(e) the detected signal has a sharp transient from the minimum peak signal amplitude to zero; and

(f) a time between the maximum peak signal amplitude and a zero-crossing between the maximum peak signal amplitude and the minimum peak signal amplitude, and between the zero-crossing and the minimum peak signal amplitude are substantially identical.

41. A system for disambiguating a trajectory of a supersonic projectile from shockwave-only signals, comprising:

an antenna having a plurality of acoustic sensors; and

a processor configured to

receive signals at the acoustic sensors and determine if the received signals are shockwave-only signals;

perform a correlation between the shockwave-only signals;

determine from the correlation Time-Difference-Of-Arrival (TDOA) values for sensor pairs;

determine for an expected closest distance between a projectile trajectory and the antenna, if a precision of the Time-Difference-Of-Arrival (TDOA) values is adequate for determining a gradient of curvature of a shockwave wavefront across the antenna;

determine the gradient of curvature of the shockwave wavefront; and

determine the disambiguated projectile trajectory from the gradient of curvature.

42. The system of claim 41, wherein the antenna is mounted on a vehicle.

43. The system of claim 41, wherein the antenna comprises a frame and elastomeric couplings attached to the frame, with the elastomeric couplings holding the acoustic sensors.

44. The system of claim 43, wherein the acoustic sensors having a mechanical resonance frequency of less than approximately 1 Hz.