Acoustic Wave Propagation in Urban Environments

The United States Army is continuously improving upon its situational awareness in operational environments. This is particularly difficult in an urban scene because line of sight is limited and because the acoustic interaction between and over the top of the buildings is not yet fully understood. Once this is fully understood the acoustic detection, classification, and localization can be accomplished through the use of well-placed acoustic sensors. This work focuses on application of acoustic wave-propagation computations to investigate the effects of urban environments on sound propagation. The objective of this work is to present models and wave-field results that illustrate in detail acoustic propagation and its interactions with buildings in an urban environment. Our computations are performed by a three-dimensional (3D) finite-difference time-domain code. This code operates on high-performance computers to create high fidelity data sets of acoustic waves propagating in urban scenes. These scenes are acquired from urban modeling templates produced by the Army Materiel Systems Analysis Activity (AMSAA) with areas distinguished by Urban Terrain Zones. This study examines a single source propagating through a portion of the AMSAA "Small City Periphery" urban template. The results show how acoustic waves propagate from a source through urban scenes. The propagation contains multi-path reflections between buildings that channel sound energy down streets, and wavefronts that travel between and over the tops of buildings. The results show that while some sound may travel over two to three story buildings before returning to ground level, a majority of the sound energy propagates between the buildings. We conclude that 3D finite difference time domain analysis is a practical tool for investigating acoustic propagation and its interactions with buildings in an urban environment.