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 Principle of Operation • Sound waves reach 4 speakers at different times • Using these delays we can calculate the origin of sound Functional Breakdown • Signal Acquisition • Gunshot Recognition • Delay Detection • 3-D Triangulation • Human-Machine Interface (H.M.I) 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 Continuously sample 44kHz 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: Average Power Bin1 average power 11 Bin2 average power Average Power 228 Hz (±150 Hz) 1 kHz – 1.5 kHz Recognition Algorithm Refinement after experimentation Needed to consider all 4 input at the same time Back Microphone Sound Wave 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 Δt1 4 Δt1 Δt1 2 3 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 x xa 2 y y a 2 z z a 2 a 2 x xb 2 y yb 2 z z a 2 a ct ab 2 x xc 2 y yc 2 z z c 2 a ct ac 2 x xd 2 y y d 2 z z d 2 a ct ad 2 Recover the X Y and Z coordinates of signal origin Normalize vector to give azimuth and elevation angles User Interface Easy to Use/Navigate Targeted towards Army Personnel Displays Azimuth and Elevation No installation Required 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 Input Signal Divide sampled input into smaller intervals Analyze smaller intervals in frequency domain Power Spectrum of t0 – t1 Power Spectrum of t2 – t3 Obstacles Encounterd Initial Algorithm Determine if it’s gun shot or not by comparing with known spectrum Positive Match Power Spectrum of t0 – t1 Known Spectrum Obstacles Encountered Algorithm was implemented in Matlab and Simulink Main Recognition Block Recognition 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 COST Microphone $ 1.20 Pre-Amp $ 6.00 Tripod $ 80.00 M-Audio Card $ 130.00 Cables $ 20.00 PC $ 600.00 Total $ 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?