Uncertainty and environmental effects in outdoor firearm noise propagation

Outdoor noise measurement is highly uncertain due to its strong dependence on environmental conditions. In firearm noise studies, these uncertainties are amplified by the impulsive nature of the noise and the lack of large datasets, making long-term meteorological averaging and stochastic techniques impractical. Numerical models also face limitations, with most commercial software relying on coefficient-based environmental predictions. This study investigates uncertainties and environmental effects in outdoor firearm noise propagation, combining experimental and numerical approaches to understand their impacts. The expanded uncertainty of systematic (Type B) uncertainties contribute up to ±4.1 dB, while random (Type A) uncertainties, influenced by environmental variability, range from ±0.5 to ±10 dB, predominantly affecting mid- to high-frequency bands at extended distances. A refined 2D Nonlinear Progressive Equation (NPE) model is used to simulate varying terrains and atmospheric conditions. Results reveal that sound-dampening terrains, such as grass, cause significant amplitude and spectral shifts compared to asphalt, with attenuations up to 10 dB at specific frequencies and distances. Downwind conditions enhance high-frequency propagation, while upwind scenarios reduce signal strength, with notable effects indicatively happening beyond 65 m. The findings highlight the importance of environmental characterization and advanced modeling as complementary tools for understanding and contextualizing uncertainties in firearm noise studies, supporting the development of improved methodologies for military and civilian acoustic applications.