System and method for identifying and locating an acoustic event

• US 6,847,587 B2
• Filed: 01/24/2003
• Issued: 01/25/2005
• Est. Priority Date: 08/07/2002
• Status: Expired due to Term

• Current Assignee: GWACS Defense, Inc., Shotspotter Incorporated
• Original Assignee: Century Systems, Inc.
• Inventors: Holmes, Fred H., Patterson, Frank K., Baxter, Kevin C.
• Primary Examiner(s): PIHULIC, DANIEL T
• Application Number:
  US10/248,511
• Publication Number:
  US 20040100868A1
• Time in Patent Office: 732 Days
• Field of Search: 367/906, 367/127, 367/124
• US Class Current: 367/127
• CPC Class Codes: F41H 11/00 Defence installations; Defence devices constructional aspects see Section E, e.g. air-raid shelters E04H9/04; protective arrangements for buildings E04B1/92; extinguishing or preventing the spread of fire from, incendiary bombs A62C3/06; dynamic armour F41H5/007; ballistically deployed systems for restraining persons or animals F41H13/0006; electronic countermeasures G01S
• CPC Class Codes: G01R 31/085 in power transmission or distribution lines, e.g. overhead
• CPC Class Codes: G01S 19/18 Military applications
• CPC Class Codes: G01S 5/0036 of measured values, i.e. measurement on mobile and position calculation on base station
• CPC Class Codes: G01S 5/18 using ultrasonic, sonic, or infrasonic waves
• CPC Class Codes: G01S 5/30 Determining absolute distances from a plurality of spaced points of known location
• CPC Class Codes: G01S 7/539 using analysis of echo signal for target characterisation; Target signature; Target cross-section
• CPC Class Codes: G01V 1/001 Acoustic presence detection
• CPC Class Codes: H02J 3/40 Synchronising a generator for connection to a network or to another generator
• CPC Class Codes: Y10S 367/906 Airborne shock-wave detection

Abstract

A system and method for detecting, identifying, and fixing the location of the source of an acoustic event. The inventive system includes: a plurality of sensors dispersed at somewhat regular intervals throughout a monitored area; a communication network adapted to deliver information from the sensors to a host processor; and a process within the host processor for determining, from the absolute times of arrival of an event at two or more sensors, a position of the source of the event. Acoustic events are detected and analyzed at each sensor so that the sensor transmits over the network: an identifier for the sensor; an identifier for the type of event; and a precise absolute time of arrival of the event at the sensor. In a preferred embodiment, the system also identifies the type of weapon firing a gunshot.

Claims

1. A sensor for detecting and providing a time of arrival of an acoustic event produced in the environment comprising:

a microphone acoustically coupled to the environment, such that said microphone provides a signal representative of acoustic waves received at said sensor;

a microprocessor, said microprocessor being in electrical communication with said microphone such that a digital representation of said signal is present in said microprocessor;

an absolute time clock in digital communication with said microprocessor such that said microprocessor can obtain synchronized time from said absolute time clock;

a network interface in digital communication with said microprocessor such that said microprocessor can communicate over a computer network,

wherein when a predetermined event is received at said microphone, said microprocessor obtains a time of arrival from said absolute time clock and transmits said time of arrival over said communication network.

2. The sensor of claim 1 wherein said absolute time clock comprises a GPS receiver.

3. The sensor of claim 2 wherein said GPS receiver also communicates a position of said sensor to said microprocessor.

4. The sensor of claim 1 further comprising a power supply for supplying electrical power to said sensor.

5. The sensor of claim 4 wherein said power supply comprises a solar cell and a battery.

6. The sensor of claim 4 wherein said power supply comprises:

a current sensing coil having an aperture for receiving a power line therethrough;

a rectifier in communication with said current sensing coil, said rectifier providing a DC output;

a voltage regulator having an input for receiving said DC output and a regulated output,

wherein, when a power line is received through said aperture, electrical current flowing through the power line will induce a voltage in said current sensing coil which is rectified by said rectifier to produce said DC output.

7. The sensor of claim 1 wherein said network interface comprises a radio frequency transceiver.

8. The sensor of claim 1 wherein said network interface is configured to connect to an ethernet network.

9. The sensor of claim 1 wherein said network interface is configured to communicate over a cellular telephone network.

10. A system for locating and identifying an acoustic event comprising:

a plurality of sensors for reporting a time of arrival of a known acoustic event, each of said sensors comprising;

a microphone, said microphone producing a signal indicative of acoustic waves received at the sensor;

a microprocessor in communication with said microphone such that information produced by said signal in response to said acoustic waves can be processed by said microprocessor to detect said known acoustic event;

an absolute time clock in digital communication with said microprocessor such that said microprocessor can obtain synchronized time from said absolute time clock; and

a network interface in digital communication with said microprocessor such that said microprocessor can communicate over a network;

a network, each network interface of said plurality of sensors being connected to said network; and

a host processor connected to said network,

wherein, upon the occurrence of said known acoustic event, at least one sensor will detect said known acoustic event and, in response to said known acoustic event, report the identity of said acoustic event and the time of arrival of said known acoustic event to said host processor over said network.

11. The system for locating and identifying an acoustic event of claim 10 wherein said plurality of sensors includes at least three sensors and said known acoustic event is received by said at least three sensors and, upon receiving said time of arrival from said at least three sensors, said host processor will calculate a location for the source of said known acoustic event.

12. The system for locating and identifying an acoustic event of claim 11 wherein said host processor calculates a location and an initial time of said event by solving six equations in six unknown variables.

13. A method for locating the source of an acoustic event comprising the steps of:

providing at least three sensors dispersed over an area to be monitored at known locations, each sensor having a microphone for receiving an acoustic event and a synchronized clock;

providing a network, each of said at least three sensors being configured for communication over said network;

receiving a known acoustic event at said at least three sensors;

at each of said sensors, transmitting a time of arrival of said known acoustic event over said network, said time of arrival being obtained from said synchronized clock;

receiving said time of arrival from each sensor of said at least three sensors at a processor; and

at said processor, triangulating the location of the source of said known acoustic event from said received times of arrival and said known locations.

14. A method for identifying the source of a known acoustic event comprising the steps of:

storing envelope and spectral characteristics of a particular acoustic event;

receiving acoustic waves at a sensor;

storing said acoustic waves in memory;

processing the received acoustic waves to derive an envelope of the acoustic waves;

performing a first correlation between points along the derived envelope and points along the stored envelope of said particular acoustic event;

if said first correlation indicates that said derived envelope correlates with the stored envelope of said particular acoustic event, transforming the stored acoustic wave into the frequency domain to create spectral information of said received acoustic wave;

performing a second correlation between said spectral information of said stored acoustic wave and said spectral characteristics of said particular acoustic event; and

if a predetermined number of points of said spectral information correlate with points of said spectral characteristics, providing an identification that said acoustic waves were produced by an event matching said particular acoustic event.