Fast iterative shooter localization in urban terrain using ray casting.

This study presents a method for real-time capable localization of impulsive acoustic events in urban terrain, omitting the need for precomputation phases, such as in time matching or impulse response matching. Using ray casting, solutions of the wave equation are computed using a boundary discretization of intersected objects, forming a weighted graph using line of sight checks, and deploying an A* search graph traversal algorithm for the calculation of the propagation time. Subsequently, the wave amplitude along the identified eigenrays is computed. The study discusses the properties and suitability of cost functions based on time differences of arrival, amplitude differences of arrival, and a combined cost function for iterative ray-based localization. The method is validated using pressure data of the muzzle blasts of various firearms collected via unattended ground sensors during an experimental campaign at the military urban combat facility in Walenstadt, Switzerland.

Experimental evaluation of earplug behavior in front of high-level impulse noise using laser Doppler vibrometer.

Hearing protection devices facing high-level impulse noises provide an attenuation, generally, between 20 and 40 dB. One reason for this limitation is the direct interactions between the protection device and the impulse waves. In the case of earplugs, direct transmissions through the earplug occur. These direct transmissions combine with the already well-studied indirect transmissions arising from wave propagation in the external ear's tissues (skin, cartilage, and bone). To evaluate the transmission induced directly by the earplug, an experimental protocol using a laser Doppler vibrometer was developed. Thus, the earplug's outer lateral face (OLF) displacements and acoustic pressure at the eardrum were measured simultaneously. Two earplugs (polyurethane foam and acrylonitrile butadiene styrene) inserted in an acoustic test fixture were stimulated with impulses ranging from 137 to 180 dB-peak. A slight earplug OLF movement in the ear canal varying from 1 µm to 0.1 mm could be observed, which is likely related to ear canal longitudinal compression. The earplug's OLF displacement and acoustic pressure variation at the eardrum strongly depended on the earplug type. These direct transmissions and underlying consequences considerably alter the protection efficiency.