In March 2005, Planning Systems, Inc. (PSI), Advanced Acoustic Concepts (AAC) and the U.S. Army Research
Development and Engineering Center (ARDEC) tested the PSI Acoustic Counter Battery System (ACBS) at the Yuma
Proving Ground (YPG). ACBS was designed to acoustically detect and locate mortar fire, and to detect and locate
heavy artillery fire out to ranges beyond 12 km. During analysis of the test data, we discovered that long-range sensors
were receiving multiple pulses in doublets and triplets from a single shot. Additionally, we observed that the leading
pulses were arriving earlier than anticipated by surface speed of sound calculations. The analysis team modeled the
atmosphere recorded during the test and identified the possible causes of multiple arrivals by modeling the supersonic
projectile trajectory and by using Green's Function Parabolic Equation numerical techniques to propagate recorded
pulses from the source to receivers. The lessons learned will be applied to adjust the signal processing algorithms in the
ACBS. This paper describes the test setup and reports the results of the analysis.
Planning Systems Incorporated (PSI) has been working with the National Institute of Justice, Center for Society Law and Justice (CSLJ) at the University of New Orleans, and law enforcement agencies in five highly varied United States locations to evaluate the use of an automated, wireless acoustic gun fire detection and localization system. Multiple SECURES(r) systems have been deployed and are in operation around the county. The most recent SECURES(r) implementation has been with the Newport News VA Police Department (NNPD) and East Orange NJ Police Department (EOPD). This paper will discuss successes and specific examples of its use by law enforcement to solve crimes and reduce community gunfire.
Planning Systems Incorporated has developed a System for the Effective Control of URban Environment Security, (SECURES) which detects and localizes gunshots acoustically. This is achieved by deploying a grid of acoustic sensors mounted to utility poles or buildings in the area plagued by gunfire. Localization is determined by a central processing unit which receives information about acoustic events via radio. One key question faced in the deployment of the sensors is whether all the desired area is going to be covered effectively. Until recently the required location and density of the sensors was determined through educated estimation by experienced staff. The role of the Acoustic Urban Evaluator (AUE 1.0) is to aid with determining the optimal geometry of the sensor grid, reduce coverage uncertainty and minimize the number of necessary sensors for effective coverage. AUE is a physics-based acoustic propagation model that takes into account the propagation of a pulse above a finite impedance plane as well as diffraction around obstacles. Assuming a source (shooter) situated anywhere in the monitored area, AUE computes the transfer function and the peak Sound Pressure Level (SPL) for all possible source-sensor pairs. Based on the peak SPL it is determined whether the shooters can be localized. The paper describes the model as well as the implementation details.
Landmines buried in the ground can be found acoustically by insonifying the ground and detecting a contrast between the vibratory motion of the ground surface directly above the mine and away from the mine. A technique for the numerical computation of the scattered velocity field is presented here. The mine is assumed to be a rigid cylinder with a compliant top. The ground (soil) is modeled both as an effective fluid and as an elastic effective solid. To discretize the full space model, the computational domain is taken to be a cylindrical waveguide of sufficiently large radius. It is shown that the method converges for the effective fluid case providing qualitative understanding of the field data. However, in the case of an elastic solid, a surface wave propagates radially out from the mine limiting the applicability of the method in its current form. Comparisons with actual field velocity data will also be presented.
The resonant behavior of landmines has been exploited by an acoustic detection technique to find buried mines. The resonance of the buried mine is induced by broadcasting an acoustic wave, which couples into the ground. The resonating mine causes the soil above it to vibrate and this vibration is measured with either a laser Doppler vibrometer (LDV) or a geophone. A set of resonance frequencies, which can be attributed to the design, material, and dimensions of the mine, is exhibited when the mine, sitting on a rigid surface above the ground, is excited by an acoustic wave. These resonance frequencies shift when the mine is buried. Acoustic models have been developed to predict these burial effects on mine resonant frequency behavior. This paper will discuss measurements made of several mines of the same type buried at various depths and will compare these measurements to predictions made by a lumped element model.
Land mines buried a few inches below the surface of the ground can be found by acoustic excitation of the porous ground surface and measuring the particle velocity at the surface. There are various theoretical models describing the ground: from a rigid porous frame model to a compete layered poroelastic description. The goal of this paper is to use the approach of Berry et al. to calculate the acoustic field at points on the ground surface in the vicinity of an object buried in a rigid, porous soil. The excitation is point sound source placed in the air above the ground, which is modeled a rigid, porous frame. A boundary element method is used for numerical integration to calculate the scattered acoustic field due to the presence of the object. This study represents the first step towards developing a complete model of acoustic scattering from near-surface objects embedded in a layered poroelastic material. The predicted disturbance associated with the buried object is much smaller than observed in field measurements.