Outdoor Sound Propagation: A Short Review on Analytical and Numerical Approaches

Prediction of sound pressure levels at medium and large distances from road, railway and industrial sources, has been of considerable interest in environmental acoustics for several years. At the beginning, the fundamental hypotheses were very simplified: homogeneous and isotropic propagation medium with perfectly reflecting grounds. Then, during the following years, various parameters were successively taken into account. In that way, different sound propagation effects in the vicinity of absorbing or mixed grounds, with or without barriers, fluctuating atmospheric conditions with or without turbulence were considered. In a first approach, all these works were based on analytical methods (Ray tracing technique, Geometrical Theory of Diffraction, Creeping wave theory, etc.). In the recent years, new numerical methods were investigated (Parabolic Equation approach, Finite and Boundary Element Techniques, etc.). These different methods have been highlighted through adapted softwares able to predict sound pressure levels for a rather large number of situations. These computing codes, indexed as research and/or commercial softwares have been highly validated. In spite of the increasing improvements of the theoretical modelling and resolution methods, which became possible due to the new computing technologies, progresses are still possible. This paper deals with analytical and numerical approaches, pointing out in particular their respective validity domains.