Acoustic location of gunshots using combined angle of arrival and time of arrival measurements
View Patent ↗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.
1. 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 three acoustic sensors, wherein at least one of the three acoustic sensors 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;
computing multiple candidate locations of a detected gunshot from the time-of-arrival and angle-of-arrival information; and
selecting a best candidate location as an actual gunshot location from among the computed candidate locations, wherein the best candidate location has a larger quantity of compatible time-of-arrival impulses and angle-of-arrival directions events from the acoustic sensors, than comparable quantities of compatible events associated with one or more false candidate gunshot locations.
2. The method of claim 1 further comprising computing a candidate location using time-of-arrival information computed for a pseudosensor from the angle-of-arrival information and time-of-arrival information communicated from an acoustic sensor.
3. The method of claim 1 , wherein the pseudosensor is positioned along a line determined by a sensor position and a direction to a gunshot source.
4. The method of claim 1 further comprising computing a hyperbola from the time-of-arrival information, computing an angular beam from the angle-of-arrival information, and computing a candidate gunshot location from an intersection of the hyperbola and the angular beam.
5. The method of claim 1 wherein at least one of the acoustic sensors 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.
6. 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 three acoustic sensors;
computing multiple candidate locations of a detected gunshot from the time-of-arrival and angle-of-arrival information; and
selecting a best candidate location as an actual gunshot location from among the computed candidate locations, wherein the best candidate location is determined as a function of having a larger quantity of votes corresponding to compatible time-of-arrival impulses and angle-of-arrival directions events from the acoustic sensors, than comparable quantities of compatible events associated with one or more false candidate gunshot locations, wherein votes accorded to one or more events are weighted based upon reliability of measurements regarding the one or more events.
7. The method of claim 6 further comprising computing a candidate location using a time-of-arrival information computed for a pseudosensor from the angle-of-arrival information and time-of-arrival information communicated from an acoustic sensor.
8. The method of claim 6 , wherein the pseudosensor is positioned along a line determined by a sensor position and a direction to a gunshot source.
9. The method of claim 6 further comprising computing a hyperbola from the time-of-arrival information, computing an angular beam from the angle-of-arrival information, and computing a candidate gunshot location from an intersection of the hyperbola and the angular beam.
10. The method of claim 6 wherein at least one of the acoustic sensors 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.
11. A method for processing gunshot location information, the method comprising:
communicating to a computer time-of-arrival information and angle-of-arrival information derived from acoustic impulses arriving at acoustic sensors placed in substantially linear manner characterized in that a triangle formed by connecting a sequence of 3 adjacent sensors has a smallest angle no larger than about 30 degrees; and
using a hyperbolic solution from only two sensors and crossing of beams from the directions of the same two sensors, and determining a source location of the gunshot;
wherein the sensor spacing can be increased over sensor arrays wherein only omnidirectional sensors are used, as only 2 sensors are needed to detect and confirm a location.
12. The method of claim 11 wherein normal impulsive events of moderate strength are prevented from being interpreted as gunfire as a result of the increase in spacing between the sensors.
13. The method of claim 11 wherein spacing between sensors can be increased by a factor of up to about 2 times greater than spacing in sensor arrays wherein only omnidirectional sensors are used.
14. The method of claim 11 wherein spacing between sensors can be increased by a factor of about 2 times greater than spacing in sensor arrays wherein only omnidirectional sensors are used.
15. The method of claim 11 wherein spacing between sensors can be increased by about 75% to about 100% of an expected maximum range of a sensor to the gunshots being detected.
16. The method of claim 11 wherein spacing between sensors can be increased to between about 2500 feet to about 5000 feet in applications where subject gunshots can be detected at a range of about 1 mile.
17. The method of claim 11 the source of the gunshot location is determined using a time-of-arrival information computed for a pseudosensor from the angle-of-arrival information and time-of-arrival information communicated from an acoustic sensor.
18. A method 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 widened hyperbola from uncertain time-of-arrival information communicated from the first and second acoustic sensors;
calculating an azimuth and a widened angular beam from time-of-arrival information of acoustic impulses arriving at three or more microphones of the first acoustic sensor; and
computing an approximate gunshot location region from an intersection of the widened hyperbola and the widened angular beam.
19. The method of claim 18 , where the approximate gunshot location region is calculated more accurately via processing as intersection of a second widened beam calculated from another sensor distinct from the sensor from which the widened angular beam was derived.
20. The method of claim 18 , wherein the intersection of the two widened beams overlap the widened hyperbola to form a more accurate location area, wherein a centroid of which is used to define an approximate location of the event.
21. The method of claim 18 wherein the widened angular beam is calculated from time-of-arrival information of acoustic impulses arriving at four or more microphones of the first acoustic sensor.