Nonlinear effects in muzzle blast propagation are not confined to the near-field

The emission of high-intensity noise is an inevitable by-product of military training operations that can have repercussions in terms of auditory hazard and annoyance of nearby communities. Present models used for noise impact studies are essentially based on linear propagation. These models fail to predict accurately the propagation of sound from military sources such as jet noise, or impulse noise from firearms, guns, detonations and explosions. The broad spectrum, the directivity and the duration are specific to military noise sources and the large discrepancies observed with experimental data or within results from civilian noise propagation models
are related to the nonlinear propagation behaviour. The objective of this work is to assess and model the impact of acoustic nonlinearity on firearm noise propagation, with a special focus on persistence of nonlinear effects with distance. The strategy adopted in this work relies on two complementary tasks. The on-field acoustic measurements during Live Fire Exercises are used to collect a database of experimental muzzle blasts from various weapon systems and calibres. In parallel, a finite-differences in-house numerical solver, based on the Nonlinear Progressive Wave Equation (NPE), is used to simulate the atmospheric nonlinear propagation of blasts. Through the use of different time and frequency domain metrics, it was shown that, although the approach based on rule of thumbs and semi-empirical corrections proposed by commercial off-the-shelf software and standards may be sufficient in certain conditions, it most certainly leads to miscalculations when compared to real measurements. The effects of acoustic nonlinearity are shown to persist at least up to a distance of 300 m from the source, demonstrating that, if an accurate and physically consistent noise exposure prediction is sought, modelling firearm noise propagation in all its complexity is the recommended approach.