System for effective control of urban environment security

• US 5,703,835 A
• Filed: 04/01/1996
• Issued: 12/30/1997
• Est. Priority Date: 05/27/1994
• Status: Expired due to Term

• Current Assignee: Foster-Miller Incorporated (Thermo Fisher Scientific Incorporated)
• Original Assignee: Alliant Techsystems Incorporated (Northrop Grumman Corporation)
• Inventors: Page, Edward A., Belt, Ronald A., Doblar, Randy A., Bothwell, Frank E., Sharkey, J. Brian
• Primary Examiner(s): Lobo, Ian J.
• Application Number:
  US08/627,323
• Time in Patent Office: 638 Days
• Field of Search: 367/118, 367/124, 367/129, 367/906
• US Class Current: 367/124
• CPC Class Codes: G01S 3/801 Details G01S3/82, G01S3/84, G01S3/86 take 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 3/8086 determining other position line of source
• CPC Class Codes: G01V 1/001 Acoustic presence detection
• CPC Class Codes: G08B 13/1672 using sonic detecting means, e.g. a microphone operating in the audio frequency range
• CPC Class Codes: Y10S 367/906 Airborne shock-wave detection

Abstract

A security system for detecting a gunshot event. A communication link, and a number of pole units are arranged in a dense grid. Each one of the pole units includes a microphone and a signal conditioning and thresholding unit coupled to the microphone. The signal conditioning and thresholding unit outputs a detection signal in response to an event when an output signal from the microphone exceeds a peak background average. A data acquisition and signal processing unit is coupled to the signal conditioning and thresholding unit for discriminating gunshot events. The data acquisition and signal processing unit remains in a powered down stand-by mode so as to conserve energy until a detection signal is received. The data acquisition and signal processing unit includes apparatus for identifying a gunshot event by measuring an initial pulse time duration and subsequent pulse pattern features, and a communication interface coupled at an input to the data acquisition and signal processing unit. A central processor is coupled to the communication link so as to receive data from the pole units where the central processor and the pole units operate so as to detect and locate gunshot events sensed by one or more of the pole units.

Claims

1. A security system for detecting a gunshot event, wherein a gunshot event produces an acoustic signature including an initial pulse and subsequent pulse pattern, the security system comprising:

(a) a communication link;

(b) a plurality of pole units arranged in a dense grid, wherein each one of the plurality of pole units includes,

(i) a microphone for providing an output signal in response to an acoustic event,

(ii) a signal conditioning and thresholding unit coupled to said microphone wherein the signal conditioning and thresholding unit outputs a detection signal when the output signal exceeds a peak background average signal, where the peak background average signal is dynamically determined,

(iii) a data acquisition and signal processing unit for discriminating gunshot events connected to receive the detection signal, wherein the data acquisition and signal processing unit remains in a powered down stand-by mode so as to conserve energy until the detection signal is received, and wherein the data acquisition and signal processing unit includes means for identifying a gunshot event by measuring an initial pulse time duration and a plurality of subsequent pulse pattern features in the detection signal, and,

(iv) a communication interface coupled at an input to the data acquisition and signal processing unit, the communication interface also being coupled to the communication link, where the communication interface transmits and receives data on the communication link; and

(c) a central processor coupled to the communication link so as to receive data from the plurality of pole units where the central processor and the plurality of pole units operate so as to detect and locate gunshot events sensed by one or more of the plurality of pole units.

2. The security system of claim 1 wherein the communication interface comprises a modem and a receiver/transmitter coupled to the communication link.

3. The security system of claim 1 wherein the signal conditioning and thresholding unit comprises:

(a) an amplifier coupled to the microphone for receiving an acoustic signal from the microphone, the amplifier having an amplified output for carrying an amplified acoustic signal;

(b) a first comparator having a first input coupled to the amplified output; and

(c) a reference signal coupled to a second input of the first comparator wherein the first comparator outputs a detection signal if the amplified detection signal exceeds the reference signal.

4. The security system of claim 1 wherein the data acquisition and signal processing unit further comprises a digital modem including means for filling the digital modem with a time tag and a pole unit identification number.

5. The security system of claim 1 wherein the data acquisition and signal processing unit further comprises means for detecting the presence of a transient above the background acoustic level, wherein the transient exceeds a predetermined energy level threshold.

6. The security system of claim 5 wherein the data acquisition and signal processing unit further comprises high speed digital signal processing hardware and software that is activated to differentiate gunshot acoustic characteristics from other noise sources.

7. The security system of claim 1 for detecting a gunshot event wherein the signal conditioning and thresholding unit includes a peak background level averager, where the peak background level averager applies a rise time constant and a decay time constant to acoustic signals where the averager rise time constant and averager decay time constant operate together with the peak background level averager in order to dynamically provide the peak background average signal so as to allow the signal conditioning and threshold unit to discriminate transient background events from candidate gunshot events.

8. A method for sensing a gunshot event comprising the steps of:

(a) sensing a transient acoustic event;

(b) producing a first signal representative of the transient acoustic event;

(c) dynamically producing a second signal representative of the average peak background level;

(d) responding to the first signal by powering on a means for determining whether the transient event exceeds the average peak background level by a specified ratio and whether the transient event exceeds a predetermined energy level threshold;

(e) if the conditions of step (d) are true, then determining whether the transient event exhibits an event duration less than a predetermined time period; and

(f) if condition of step (e) is true, then initiating RF transmission of a message from an RF transmitter that is in a powered off state unless transmitting.

9. The method of claim 8 wherein the step of dynamically producing a second signal representative of the average peak background level further comprises the steps of applying a rise time constant and a decay time constant to acoustic signals where the rise time constant and the decay time constant dynamically produce a peak background average signal.