A number of aircraft and ground-based weapon system noise models have been developed over the past 30 years to estimate noise levels from military operations. The results from these models are used to assess the potential for community and environmental impacts from existing and proposed operations. Current Department of Defense (DoD) noise models use common aircraft and weapon system source noise databases maintained by the Air Force Research Laboratory, U.S. Army Construction Engineering Research Laboratory, and Naval Facilities Engineering Command. However, these models and the source noise databases do not provide the capability to assess noise impacts due to airborne weapon operations. This project has developed a new computer model that addresses the generation and propagation of noise from air-weaponry operations. The model handles the complexity of the distributed noise events while maintaining accurate acoustical modeling that is required for environmental noise analysis.

The objectives of this project were:

• To characterize the noise generated by airborne weapon systems
• To evaluate and refine current weapon noise propagation algorithms for airborne platforms, and
• To incorporate these refined algorithms and additional data requirements into a new noise model whose output can be integrated with the existing DoD noise models.

The overall project consisted of three main elements. The first element involved the measurement of real, airborne weapon systems to characterize the noise data required for accurate modeling. The characterization of air-weaponry noise is complex because of the combination of various sources and aircraft platforms. The second element focused on the modification of noise propagation algorithms and statistical representation of the distributed sources. The modifications involved three-dimensional representations of the noise sources to properly describe the air-to-ground propagation and to account for potential shielding/interference from the aircraft itself. The final element involved the integration of the air-weaponry data and algorithms into a new computer model.

The findings from this project’s field measurements represent a significant advance in understanding the contribution of air-weaponry operations to the overall noise generated by DoD training operations. The field measurements have provided a firm technical foundation for the development of a new noise model for air weaponry noise. The new model provides a novel approach for calculating the distinct noise produced by these operations. The modeling approach utilizes a statistical volume of space for determining the distribution of firing points, which follows the same guidelines used for weapon safety footprint analysis. The noise from this statistical volume is then computed and scaled for the actual number of bullets fired. By combining the results of individual firing profiles occurring at a range, it is possible to compute the airborne weapon noise contour for an entire range.

Once this model has been validated, it will allow the DoD to more accurately estimate the noise environment from aircraft range operations and will provide a scientific foundation for range commanders in addressing criticisms from knowledgeable citizens on the appropriateness of these estimates. These tools will assist the DoD in being responsive to the requirements of the National Environmental Policy Act (NEPA), while protecting operational readiness from unreasonable restrictions based on today's limited knowledge of air-gunnery noise effects.