Founder at Lab de Electro Acustica y Procesamiento de Señal
SPIE Involvement:
Author
Area of Expertise:
Algorithms for acoustic-based gunfire detection and localization ,
Acoustical signature model of small firearm ,
Microphone array techniques ,
Automatic pattern recognition ,
Acoustical design of theatres
Accurate modeling of small firearms muzzle blast wave propagation in the far field is critical to predict sound pressure
levels, impulse durations and rise times, as functions of propagation distance. Such a task being relevant to a number of
military applications including the determination of human response to blast noise, gunfire detection and localization,
and gun suppressor design. Herein, a time domain model to predict small arms fire muzzle blast wave propagation is
introduced. The model implements a Friedlander wave with finite rise time which diverges spherically from the gun
muzzle. Additionally, the effects in blast wave form of thermoviscous and molecular relaxational processes, which are
associated with atmospheric absorption of sound were also incorporated in the model. Atmospheric absorption of blast
waves is implemented using a time domain recursive formula obtained from numerical integration of corresponding
differential equations using a Crank-Nicholson finite difference scheme. Theoretical predictions from our model were
compared to previously recorded real world data of muzzle blast wave signatures obtained by shooting a set different
sniper weapons of varying calibers. Recordings containing gunfire acoustical signatures were taken at distances between
100 and 600 meters from the gun muzzle. Results shows that predicted blast wave slope and exponential decay agrees
well with measured data. Analysis also reveals the persistency of an oscillatory phenomenon after blast overpressure in
the recorded wave forms.
Most of modern automatic sniper localization systems are based on the utilization of the acoustical emissions produced
by the gun fire events. In order to estimate the spatial coordinates of the sniper location, these systems measures the time
delay of arrival of the acoustical shock wave fronts to a microphone array. In more advanced systems, model based
estimation of the nonlinear distortion parameters of the N-waves is used to make projectile trajectory and calibre
estimations. In this work we address the sniper localization problem using a model based search-matching approach. The
automatic sniper localization algorithm works searching for the acoustics model of ballistic shock waves which best
matches the measured data. For this purpose, we implement a previously released acoustics model of ballistic shock
waves. Further, the sniper location, the projectile trajectory and calibre, and the muzzle velocity are regarded as the
inputs variables of such a model. A search algorithm is implemented in order to found what combination of the input
variables minimize a fitness function defined as the distance between measured and simulated data. In such a way, the
sniper location, the projectile trajectory and calibre, and the muzzle velocity can be found. In order to evaluate the
performance of the algorithm, we conduct computer based experiments using simulated gunfire event data calculated at
the nodes of a virtual distributed sensor network. Preliminary simulation results are quite promising showing fast
convergence of the algorithm and good localization accuracy.
The phenomenon of ballistic shock wave emission by a small calibre projectile at supersonic speed is quite relevant in
automatic sniper localization applications. When available, ballistic shock wave analysis makes possible the estimation
of the main ballistic features of a gunfire event. The propagation of ballistic shock waves in air is a process which mainly
involves nonlinear distortion, or steepening, and atmospheric absorption. Current ballistic shock waves propagation
models used in automatic sniper localization systems only consider nonlinear distortion effects. This means that only the
rates of change of shock peak pressure and the N-wave duration with distance are considered in the determination of the
miss distance. In the present paper we present an improved acoustical model of small calibre ballistic shock wave
propagation in air, intended to be used in acoustics-based automatic sniper localization applications. In our approach, we
have considered nonlinear distortion, but additionally we have also introduced the effects of atmospheric sound
absorption. Atmospheric absorption is implemented in the time domain in order to get faster calculation times than those
computed in frequency domain. Furthermore, we take advantage of the fact that atmospheric absorption plays a
fundamental role in the rise times of the shocks, and introduce the rate of change of the rise time with distance as a third
parameter to be used in the determination of the miss distance. This lead us to a more accurate and robust estimation of
the miss distance, and consequently of the projectile trajectory, and the spatial coordinates of the gunshot origin.
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