Sniper Localization System

Marko Gasic Sandeep Brar

Ehsan Dallalzadeh Balraj Mattu

Overview Introduction Vision System Description Test Results Obstacles Encountered Project Finances Production Cost Conclusion Questions?

Introduction Snipers are a serious threat in urban warfare

environment. Civilian threat in cases such as Washington DC

sniper. Snipers are very effective at harassing and

impeding military operations. AcousticShield Designs system enables identification of

direction of origin of a sniper shot within seconds of the event.

System Overview

Vision

Existing Products• Above $15,000 US• Available only to elite military divisions and

not standard equipment to regular units or police forces

Acoustic Shield System• System cost around $2000• Low cost enables local police departments

and regular military units to purchase system

System Description

Functional Breakdown• Signal Acquisition• Gunshot Recognition• Delay Detection• 3-D Triangulation• Human-Machine Interface (H.M.I)

Principle of Operation• Sound waves reach 4 speakers at different times• Using these delays we can calculate the origin of

sound

Sound Acquisition

PC Hardware• M-Audio Delta 44 PCI audio card• 4/4 mono analog input/output channels• 24bit, 8kHz – 96kHz independent channel sampling• Winsound interface drivers

Sound Acquisition

Microphones• Electret Omni-directional condenser microphones.• -45dB sensitivity• 20Hz – 16kHz Frequency Response• 60 dB S/N ratio

Sound Acquisition

Microphone Preamplifier• Supplies minimum voltage required for microphone

operation• Amplifies signal to 500mV swing, compatible for PC

soundcard input.

Sound Acquisition Software

Sample at 44kHz

Continuously sample microphone inputs

When sample exceeds 0.2V, record next 1.0 seconds and place in memory

Recognition Algorithm

Understanding the characteristic of a gun shot

Time Domain Representation

Recognition Algorithm

Frequency Domain Representation

Recognition Algorithm

Algorithm is based on comparison of average power between two bins:

228 Hz (±150 Hz) 1 kHz – 1.5 kHz

Average Power

Average Power

11Bin1 average powerBin2 average power

Recognition Algorithm

Refinement after experimentation Needed to consider all 4 input at the

same time

Microphone

Sound Wave

Back

Distortion in frequency spectrum is introduced

Recognition Algorithm

Simple Solution

Analyze all four microphones

Accuracy is demonstrated in Test Results section

Δt Extraction 4 similar signals, out of phase Use Cross Correlation to determine phase difference

Δt14

Δt13Δt12

3-D Triangulation Extrapolate origin of sound using the 3 Δt’s and speed of

sound as input Use Gauss-Newton method to

solve 4 non linear equations

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tcazzyyxx

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Recover the X Y and Z coordinates of signal origin

Normalize vector to give azimuth and elevation angles

Easy to Use/Navigate Targeted towards Army Personnel Displays Azimuth and Elevation No installation Required

User Interface

Testing The testing was done in 2 phases:

• Testing for the detection in 2-D (X,Y)• Testing for detection of the elevation

Procedure A:• The system was setup• The software was running• Located the tripod at the center of a large circle • Drew a 2-D coordinate system about the center of the tripod • Marked the imaginary circle around the center of the tripod with points each about 30 degrees apart• Ran the sound sample of the gunshot twice at each point

Testing

• Recorded the Average, Trigger, X and Y values• Took a string from the sound source(speaker) to the

center of the tripod• Chose a point on the string and recorded its X and Y

components.• At the end, had pairs of vectors in 2-D

• Comparison Stage……• Wrote a C++ code to input each pair of vectors to

calculate the angle between the actual vector and the result vector from the system in Degrees

Observations

On average, the angle difference was about

2.78 Degrees

The accuracy was almost the same for all the

points in the surrounding

Testing cntd. Procedure B (Elevation):

• The system was setup• The software was running• Located the tripod at the center of a large circle • From points 90 Degrees apart, got samples • At each point, tried 3 different elevations: 1) above the center plane 2) at the same plane 3) below the center plane • Recorded the elevation that the program gave for each

trial• For each point, measured the elevation angle compared

to the center of the tripod (+ if above the center, (-) if below the center)

Observations

On average, elevation difference was 3.15

Degrees

Functional Specifications stated maximum

allowable error of 10 degrees

Obstacles Encountered

Initially used Texas Instruments DSP• Insufficient inputs: unable to sample both stereo

codecs simultaneously• Insufficient resolution: TMSC320 C6711 main audio

codec samples at only 11kHz, we need a minimum of 44kHz

• Extremely poor user interface and non-existent (yet advertised) compatibility with MATLAB

Obstacles Encountered

Initial Algorithm Divide sampled input into smaller intervals Analyze smaller intervals in frequency domain

Power Spectrum of t0 – t1 Power Spectrum of t2 – t3

Input Signal

Obstacles Encounterd

Initial Algorithm Determine if it’s gun shot or not by comparing

with known spectrum

Known SpectrumPower Spectrum of t0 – t1

Positive Match

Obstacles Encountered

Algorithm was implemented in Matlab and Simulink

Main Recognition BlockRecognition Subsystem 1

Obstacle Encountered

Problems Unable to achieve desired speed Didn’t do well when tried with real input

(instead of a wave file)

Financial Aspects

Prototype Development Cost:

• TMSC320 Daughter Board $120.00• MATLAB RTW Documentation $ 35.00• Microphones and Pre-Amps $ 60.00• Miscellaneous Audio Cables $ 30.00• M-Audio Delta44 $220.00• Other $ 25.00

• TOTAL $490.00

Budget Estimate Initial cost estimate $2260.00 Actual cost $490.00 Significantly lower cost due to change in

platform Savings with no loss in performance We were able to borrow the tripod, saving

~$100

Manufacturing Costs Assuming 50 units/month Based on Digi-Key bulk pricing where available

ITEM COSTMicrophone $ 1.20Pre-Amp $ 6.00Tripod $ 80.00M-Audio Card $ 130.00Cables $ 20.00PC $ 600.00Total $ 837.20

Conclusion

Successfully Demonstrated Functional Concept

Demonstrated market value and ability to produce at reduced cost

Encountered problems and chose alternate solutions

Stayed within budget and timeline considerations

Thank You

Questions?