Modeling outdoor sound propagation in mountainous areas

Abstract

Detailed modeling of outdoor sound propagation in mountainous area imposes special requirements. The strong gradients in ground surface create propagation conditions that may lead to noise levels much higher than expected at some distance from the source partly due to a focusing effect. Meteorological conditions are particular: main winds following the valley, strong temperature gradients often including stable inversion, slope winds, etc. Because of these particular conditions, efficient modeling of outdoor sound propagation in mountainous area requires adaptations to be made to general purpose models. In this paper we will present possibilities for making time-domain models terrain following and consider options to decrease the memory requirements. For the higher frequency range and distances one is generally interested in, these adaptations are insufficient. Hence, a Green’s function parabolic equation model is added to the toolbox. To tackle the problem in three dimensions, a number of two-dimensional slices connecting the receiver point to all (segments of) sources considered is made. Propagation results for each slice are added. Numerical simulations are compared to field measurements made close to an Alpine highway.