Acoustic recordings of artillery shots feature the signatures of the shot's muzzle, projectile, and impact waves modulated by the environment. This study aims at improving the sensing of such shots using a set of synchronous acoustic sensors distributed over a 1 km2 area. It uses the time matching approach, which is based on finding the best match between the observed and pre-calculated times of arrivals of the various waves at each sensor. The pre-calculations introduced here account for the complex acoustic source with a 6-degrees-of-freedom ballistic trajectory model, and for the propagation channel with a wavefront-tracking acoustic model including meteorological and terrain effects. The approach is demonstrated using three recordings of artillery shots measured by sensors which are more than 10 km from the point of fire and distributed at several hundred meters away from and around the target points. Using only the impact wave, it locates the impact point with an error of a few meters. Processing the muzzle and impact and projectile waves enables the estimation of the weapon's position with a 1 km error. Sensitivities of the localization method to various factors such as the number of sensors, atmospheric data, and the number of processed waves are discussed.

Propagating impulse sounds are sensitive to the varying near-surface atmosphere. This study reports on an experimental assessment of this sensitivity under well-controlled outdoor conditions. The experiment, conducted over a flat terrain, features 14 synchronous acoustic sensors at ranges up to 450 m from reproducible, transient sources. It scanned over the upwind, crosswind, and downwind propagations, and also documents the temporal and spatial coherences of the acoustic field. Concurrent atmospheric measurements documented the near-surface, essentially wind-driven atmosphere, and included turbulence monitoring. The analysis reveals how the environmental propagation processes combine to form the large variety of recorded signatures. The deterministic versus stochastic variations of the signatures are distinguished, and both are shown to affect the time of arrival (wander) and the shape (spread) of the pulses. The study also discusses the potential impacts of these variations on acoustic sensing of transient signals like gun shots and explosions.

Upon firing, most weapons emit very loud sounds. These sounds propagate over the battlefield and are distorted by the atmospheric effects, absorbed by the ground, reflected on or diffracted around buildings or mountains. It is of obvious operational interest to develop sensing systems to localize these sound sources, with arrays of distributed sensors. This study develops an original sensing approach. It uses the time-matching method, based on finding the best match between pre-calculated times of arrivals (TOAs) of the shot sounds and measured TOAs from a set of synchronous, distributed sensors. Predicting the TOAs requires a physical model able to factor in the impact of complex 3-D environments (wind and sound speed gradients, obstacles), and of complex sound sources (e.g., combination of muzzle blast and supersonic projectile wave). A very fast interface-tracking model is used, based on Sethian's Fast-Marching method, for pre-calculating the TOAs in a general and comprehensive framework. Applications to localization of shots in urban environments and to localization of long range artillery gun are presented. They demonstrate that, compared to standard methods, the above matching-and-marching approach can work without classification, with less sensors, or with a much smaller baseline array.

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