Impact of ground reflections on firearms noise exposure metrics

Abstract

Outdoor measurements of weapons noise exposure are influenced by ground reflections. This paper analyzes the reflections’ impact on A-weighted equivalent level (LAeq) for two measurement campaigns involving standing shooters and dozens of elevated microphones. Although it is only a marginally accurate model of a gunshot waveform, the modified Friedlander equation was used to model the direct and reflected muzzle blast waveforms over a perfectly reflective surface. The calculation of the reflection’s effect on LAeq indicates a 2–3 dB increase relative to the free-field contribution over a relatively large spatial range. Validation of this model for most locations where the measured direct and reflected waveforms was well separated yields acceptable agreement for LAeq (<1 dB). Some challenges with the model development and comparison are discussed. This study contributes to improved weapons training safety and may eventually suggest revisions to the military noise exposure standard, MIL-STD-1474E. [Work supported by Air Force Research Laboratory through Ball Aerospace Technology Corporation.]