Acoustic counter-sniper system

• US 6,178,141 B1
• Filed: 05/28/1999
• Issued: 01/23/2001
• Est. Priority Date: 11/20/1996
• Status: Expired due to Term

• Current Assignee: Raytheon BBN Technologies Corp. (Rtx Corporation)
• Original Assignee: GTE Internetworking Incorporated (Lumen Technologies, Inc.)
• Inventors: Barger, James E., Duckworth, Gregory L., Gilbert, Douglas C.
• Primary Examiner(s): Lobo, Ian J.
• Application Number:
  US09/322,359
• Time in Patent Office: 606 Days
• Field of Search: 367/908, 367/906, 367/118, 367/124, 367/127
• 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: G01S 3/8083 determining direction of source
• CPC Class Codes: G01S 5/20 Position of source determined by a plurality of spaced direction-finders
• CPC Class Codes: Y10S 367/906 Airborne shock-wave detection

Abstract

A low cost and highly accurate sniper detection and localization system uses observations of the shock wave from supersonic bullets to estimate the bullet trajectory, Mach number, and caliber. If available, muzzle blast observations from an unsilenced firearm is used to estimate the exact sniper location along the trajectory. The system may be fixed or portable and may be wearable on a user'"'"'s body. The system utilizes a distributed array of acoustic sensors to detect the projectile'"'"'s shock wave and the muzzle blast from a firearm. The detection of the shock wave and muzzle blast is used to measure the wave arrival times of each waveform type at the sensors. This time of arrival (TOA) information for the shock wave and blast wave are used to determine the projectile'"'"'s trajectory and a line of bearing to the origin of the projectile. A very accurate model of the bullet ballistics and acoustic radiation is used which includes bullet deceleration. This allows the use of very flexible acoustic sensor types and placements, since the system can model the bullet'"'"'s flight, and hence the acoustic observations, over a wide area very accurately. System sensor configurations can be as simple as two small three element tetrahedral microphone arrays on either side of the area to be protected or six omnidirectional microphones spread over the area to be monitored. Sensors may also be monitored to a helmet as used with the wearable system. Sensor nodes provide information to a command node via wireless network telemetry or hardwired cables for the command node comprising a computer to effect processing and display.

Claims

1. A system for determining the trajectory of a supersonic projectile comprising:

at least two spaced apart sensor nodes each in a known location encountering pressure waves generated by said supersonic projectile passing proximate to said sensor nodes, said sensor nodes each comprising a transducer collecting pressure wave information and generating pressure wave information signals in response to said pressure waves, the pressure wave information signals having a time series information signal;

a main processor processing said time series information signal to provide parameter information for determining said trajectory of said supersonic projectile;

said processor comprising,

a shock threshold detector receiving said time series information and recording arrival times of shock wave components of said pressure waves at each transducer for each of said at least two spaced apart sensor nodes,

a cross correlation processor receiving said arrival times of shock wave components of said pressure waves at each transducer and determining relative shock wave arrival times,

a blast threshold detector receiving said time series information and recording arrival times and amplitude information of potential blast wave components of said pressure waves at each transducer for each of said at least two spaced apart sensor nodes;

a discrimination processor discriminating said potential blast wave components to classify each of said potential blast wave components as blast wave, shock wave, or neither, and storing arrival times of each of said potential blast wave components classified as blast wave, a ballistic coefficient processor estimating a ballistic coefficient of said supersonic projectile as a function of peak voltage (Vp) and N-wave slope (V/T) of said time series information, and

a trajectory estimation processor calculating an estimated trajectory of said projectile based on said ballistic coefficient and said relative shock wave arrival times.

2. The system of claim 1, wherein said discrimination processor calculates an instantaneous signal to noise ratio, which is compared to a potentially data dependent threshold.

3. The system of claim 2, wherein said instantaneous signal to noise ratio is calculated from the following equation:

${\mathrm{snr}}_s<br><br>\left(i\right)=\frac{X_s^2<br><br>\left(i\right)}{N_s<br><br>\left(i\right)+{\mathrm{\sigma <br><br>}}_s}$

where N_s is the average noise power, X_s is high pass filtered time series data, and σ

_s is the minimum allowed standard deviation.

4. The system of claim 1, wherein said trajectory estimation processor further estimates a range value for said supersonic projectile using a variant of the Levenberg-Marquardt method of non-linear least squares, wherein residuals are weighed with weights calculated from:

${\mathrm{\xi <br><br>}}_{i,k}={\mathrm{\sigma <br><br>}}_i<br><br>\sqrt{q_{i,k}<br><br>\underset{m}{\sum <br><br>}<br><br>q_{m,k}^{-1}}$

for each element i on iteration k.

5. The system of claim 1, further including an anti-aliasing filter receiving said pressure wave information signal and suppressing unwanted harmonics in said pressure wave information signals to provide a filtered pressure wave information signal.

6. The system of claim 5, further including an analog to digital (A/D) converter receiving said filtered pressure wave information signal and transforming said filtered pressure wave information signal into the time series information signal.

7. The system of claim 1, wherein said trajectory estimation processor has an initial state comprising initialization values for trajectory parameters.

8. The system of claim 7, wherein said initialization values are calculated from peak voltage from the output of said anti-aliasing filter.

9. The system of claim 7, wherein said initialization values are calculated from the slant range S determined from said peak voltage and said N-wave slope values and fixing two points between which defines a line representing a preliminary trajectory.

10. The system of claim 7, wherein said initialization values are calculated from a global search of a quantized, ranked representation of the entire parameter space.

11. The system of claim 7, wherein said initialization values are calculated from a trajectory estimation determined from the time difference between the arrival of the shock wave at two of said sensors plus the ratio of the amplitudes of the peak voltages for the outputs of their anti-aliasing filters.

12. A method for estimating the trajectory of a supersonic projectile, said projectile producing a pressure wave, said pressure wave having a shock wave, said method comprising the steps of:

providing at least two spaced apart sensor nodes in known locations;

generating a pressure wave information signal at said sensor nodes in response to said pressure wave;

filtering unwanted harmonics in said pressure wave information signal;

converting said filtered pressure information signal into a time series signal;

recording arrival times of shock wave components of said pressure wave at said sensor nodes;

determining relative arrival times of said shock wave components at each of said sensor nodes;

estimating a ballistic coefficient for said supersonic particle based on a function of peak voltage (Vp) and N-wave slope (V/T) of said time series data; and

calculating an estimated trajectory of said projectile based on said ballistic coefficient and said relative shock wave arrival times.

13. The method of claim 12, further comprising the step of calculating slant ranges for said projectile as a function of the caliber of said projectile.

14. The method of claim 13, wherein said supersonic projectile is 50 caliber, and said slant range is computed from the equation:

15. The method of claim 13, wherein said supersonic projectile is 30 caliber, and said slant range is computed from the equation:

16. The method of claim 13, wherein said supersonic projectile is 22 caliber, and said slant range is computed from the equation:

17. The method of claim 13, wherein said supersonic projectile is 50 caliber, and said slant range is computed from the equation:

18. The method of claim 13, wherein said supersonic projectile is 30 caliber, and said slant range is computed from the equation:

19. The method of claim 13, wherein said supersonic projectile is 22 caliber, and said slant range is computed from the equation: