ACOUSTIC LOCATION OF GUNSHOTS USING COMBINED ANGLE OF ARRIVAL AND TIME OF ARRIVAL MEASUREMENTS

• US 20080279046A1
• Filed: 07/11/2008
• Published: 11/13/2008
• Est. Priority Date: 10/10/2006
• Status: Active Grant

• Current Assignee: Shotspotter Incorporated
• Original Assignee: Shotspotter Incorporated
• Inventors: Calhoun, Robert B., Showen, Robert L., Dunham, Jason W.
• Granted Patent: US 7,599,252 B2
• Time in Patent Office: Days
• US Class Current: 367/127
• CPC Class Codes: G01S 5/18 using ultrasonic, sonic, or infrasonic waves
• CPC Class Codes: G01S 5/28 by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial

Abstract

A gunshot location system computes candidate gunshot locations [314] from angle-of-arrival information [304, 308] and time-of-arrival information [312] provided by acoustic sensors [300, 302]. In addition to an angle, each sensor calculates an angular uncertainty [306, 310] from impulses received at four or more microphones having rotational symmetry. An intersection of one or more time-of-arrival hyperbolas with one or more angle-of-arrival beams [322] is used to determine a candidate gunshot location. In simple environments, a location can be confirmed with just two sensors allowing sensor density to be significantly reduced, while in complex environments including reflections, blocking, and interfering acoustic events, the additional angle-of-arrival information improves location accuracy and confidence, allowing elimination of candidate locations inconsistent with the combined time-of-arrival and angle-of-arrival information.

Claims

1. A gunshot location system comprising a collection of acoustic sensors, a computer for computing gunshot locations using information communicated from the acoustic sensors, and communication links connecting the acoustic sensors to the computer,

wherein the collection of acoustic sensors comprises a first acoustic sensor and a second acoustic sensor,

wherein the first acoustic sensor communicates to the computer time-of-arrival information derived from acoustic impulses sensed at the first acoustic sensor and angle-of-arrival information derived from the acoustic impulses sensed at the first acoustic sensor,

wherein the second acoustic sensor communicates to the computer time-of-arrival information derived from acoustic impulses sensed at the second acoustic sensor;

and

wherein the computer for computing gunshot locations computes a hyperbola from the time-of-arrival information communicated from the first and second acoustic sensors, computes an angular beam from the angle-of-arrival information communicated from the first acoustic sensor, and computes a candidate gunshot location from an intersection of the hyperbola and the angular beam.

2. The system of claim 1

wherein the second acoustic sensor communicates to the computer angle-of-arrival information derived from the acoustic impulses sensed at the second acoustic sensor, and

wherein the computer for computing gunshot locations computes a hyperbola from the time-of-arrival information communicated from the first and second acoustic sensors, computes a first angular beam from the angle-of-arrival information communicated from the first acoustic sensor, computes a second angular beam from the angle-of-arrival information communicated from the second acoustic sensor, and computes a confirmed gunshot location from an intersection of the hyperbola, the first angular beam, and the second angular beam.

3. The system of claim 2

wherein the collection of acoustic sensors further comprises a third acoustic sensor;

wherein the third acoustic sensor communicates to the computer time-of-arrival information derived from acoustic impulses sensed at the third acoustic sensor and angle-of-arrival information derived from the acoustic impulses sensed at the third acoustic sensor;

wherein the computer for computing gunshot locations i) computes a candidate location from the time-of-arrival communicated from the first, second and third acoustic sensors, and ii) discards time-of-arrival information from a sensor if the computed candidate location is not consistent with angle-of-arrival information derived from the sensor.

4. The system of claim 2

wherein the collection of acoustic sensors further comprises a third acoustic sensor;

wherein the first, second, and third acoustic sensors are separated by a distance of 75% to 100% of a maximum range of sensor detectability and are arranged in a substantially linear geometry.

5. The system of claim 1 wherein the first acoustic sensor comprises three or more microphones equally spaced on a circumference of a circle.

6. The system of claim 1 wherein the first acoustic sensor comprises three or more microphones and a signal processor connected to the microphones, and wherein the signal processor calculates an azimuth from time-of-arrival information of the acoustic impulses arriving at the microphones.

7. The system of claim 1 wherein the first acoustic sensor comprises four or more microphones and a signal processor connected to the microphones, wherein the signal processor calculates an azimuth and an angular uncertainty from the time-of-arrival information of the acoustic impulses arriving at the microphones.

8. The system of claim 1 wherein the first acoustic sensor comprises three or more microphones, and wherein the computer calculates an azimuth from time-of-arrival information of the acoustic impulses arriving at the microphones.

9. A gunshot location system comprising a collection of acoustic sensors, a computer for computing gunshot locations using information communicated from the acoustic sensors, and communication links connecting the acoustic sensors to the computer,

wherein the collection of acoustic sensors comprises a first acoustic sensor, a second acoustic sensor, and a third acoustic sensor;

wherein the first acoustic sensor communicates to the computer time-of-arrival information derived from acoustic impulses sensed at the first acoustic sensor and angle-of-arrival information derived from the acoustic impulses sensed at the first acoustic sensor,

wherein the second acoustic sensor communicates to the computer time-of-arrival information derived from acoustic impulses sensed at the second acoustic sensor,

wherein the third acoustic sensor communicates to the computer time-of-arrival information derived from acoustic impulses sensed at the third acoustic sensor,

wherein the computer for computing gunshot locations computes two mathematically plausible candidate locations from the time-of-arrival information communicated from the first, second, and third acoustic sensors, and selects an actual location from among the two candidate locations using the angle-of-arrival information communicated from the first acoustic sensor.

10. A gunshot location system comprising a collection of at least four acoustic sensors, a computer for computing gunshot locations using information communicated from the acoustic sensors, and communication links connecting the acoustic sensors to the computer,

wherein the acoustic sensors communicate to the computer time-of-arrival information and angle-of-arrival information derived from acoustic impulses sensed at the acoustic sensors,

wherein the computer for computing gunshot locations computes multiple candidate locations from the time-of-arrival and angle-of-arrival information communicated from the acoustic sensors, and selects a best candidate location from among the computed candidate locations, wherein the selected candidate location has a largest number of time-of-arrival impulses and angle-of-arrival directions received from the acoustic sensors.

11. A method for computing gunshot locations, the method comprising:

communicating from a first acoustic sensor to a computer i) time-of-arrival information derived from acoustic impulses sensed at the first acoustic sensor and ii) angle-of-arrival information derived from the acoustic impulses sensed at the first acoustic sensor,

communicating from a second acoustic sensor to the computer time-of-arrival information derived from acoustic impulses sensed at the second acoustic sensor;

computing a hyperbola from the time-of-arrival information communicated from the first and second acoustic sensors;

computing an angular beam from the angle-of-arrival information communicated from the first acoustic sensor, and

computing a candidate gunshot location from an intersection of the hyperbola and the angular beam.

12. The method of claim 11 further comprising:

communicating from the second acoustic sensor to the computer angle-of-arrival information derived from the acoustic impulses sensed at the second acoustic sensor,

computing a hyperbola from the time-of-arrival information communicated from the first and second acoustic sensors,

computing a first angular beam from the angle-of-arrival information communicated from the first acoustic sensor,

computing a second angular beam from the angle-of-arrival information communicated from the second acoustic sensor, and

computing a confirmed gunshot location from an intersection of the hyperbola, the first angular beam, and the second angular beam.

13. The method of claim 12, further comprising:

communicating from a third acoustic sensor to the computer time-of-arrival information derived from acoustic impulses sensed at the third acoustic sensor and angle-of-arrival information derived from the acoustic impulses sensed at the third acoustic sensor;

computing a candidate location from the time-of-arrival information communicated from the first, second and third acoustic sensors, and

discarding time-of-arrival information from a sensor if an angular beam derived from angle-of-arrival information from a sensor is inconsistent with the candidate location.

14. The method of claim 11 further comprising calculating an azimuth from time-of-arrival information of acoustic impulses arriving at three or more microphones of an acoustic sensor.

15. The method of claim 11 further comprising calculating an azimuth and an angular uncertainty from time-of-arrival information of acoustic impulses arriving at four or more microphones of the first acoustic sensor.

16. The method of claim 15 wherein calculating the azimuth and the angular uncertainty comprises calculating azimuths from different triads of the acoustic impulses and calculating a mean and standard deviation from the calculated azimuths.

17. A method for computing gunshot locations, the method comprising:

communicating from a first acoustic sensor to a computer time-of-arrival information derived from acoustic impulses sensed at the first acoustic sensor and angle-of-arrival information derived from the acoustic impulses sensed at the first acoustic sensor,

communicating from a second acoustic sensor to the computer time-of-arrival information derived from acoustic impulses sensed at the second acoustic sensor,

communicating from a third acoustic sensor to the computer time-of-arrival information derived from acoustic impulses sensed at the third acoustic sensor,

computing two candidate locations from the time-of-arrival information communicated from the first, second, and third acoustic sensors, and

selecting a candidate location from among the two candidate locations using the angle-of-arrival information communicated from the first acoustic sensor.

18. A method for computing gunshot locations, the method comprising:

communicating to a computer time-of-arrival information and angle-of-arrival information derived from acoustic impulses sensed at a collection of at least four acoustic sensors;

computing multiple candidate locations from the time-of-arrival and angle-of-arrival information; and

selecting a candidate location from among the computed candidate locations, wherein the selected candidate location has a largest number of time-of-arrival impulses and angle-of-arrival directions received from the acoustic sensors.

19. A method for computing gunshot locations, the method comprising:

communicating from a first acoustic sensor to a computer i) time-of-arrival information derived from acoustic impulses sensed at the first acoustic sensor and ii) angle-of-arrival information derived from the acoustic impulses sensed at the first acoustic sensor,

communicating from a second acoustic sensor to the computer time-of-arrival information derived from acoustic impulses sensed at the second acoustic sensor;

computing time-of-arrival information for a pseudosensor from the angle-of-arrival information and time-of-arrival information communicated from the first acoustic sensor;

computing a candidate gunshot location from the time-of-arrival information from the first and second acoustic sensors and the pseudosensor.