A new boundary-element method for predicting outdoor sound propagation over uneven ground is presented. This allows the sound field around complex boundaries (various absorptive properties and shapes) and in the presence of refraction to be calculated accurately. The total sound pressure is expressed as the sum of the incident pressure and the pressure scattered by the obstacles in the propagation medium, involving layer potentials. The Green’s function used in this formulation takes meteorological and ground effects into account and relies on recent models for propagation in inhomogeneous media, such as normal modes, residue series, the parabolic equation, or the fast-field program. In this paper, this new method, called Meteo-BEM, is derived, based on both boundary-element methods (BEM) in a quiescent medium, and propagation models in inhomogeneous media. The hypothetical case of a rigid, thin noise barrier on a flat ground, under a known sound-speed gradient condition, is studied. Comparison of numerical simulations with experimental results shows that this new method is a powerful tool for outdoor sound propagation prediction, which gives rise to many applications and developments.

A number of reference numerical models can be used to perform outdoor sound propagation prediction in a complex environment. Most of time, either they consume little computational time by not taking all phenomena into account at the same time, or they are more complete but their calculation times are prohibitive. This paper presents some principles which can be used in reference numerical models to reduce calculation times in predicting long-range outdoor sound propagation under complex environments. Limits, assumptions and approximations used to predict outdoor sound propagation are discussed here in terms of their impact on accuracy for typical road traffic configurations as a function of frequency, geometry of the site and atmospheric conditions.

RésuméCet article présente une nouvelle méthode hybride permettant de coupler différents modèles numériques de propagation acoustique en milieu extérieur complexe. L'objectif est de développer un outil puissant permettant de prendre en compte des topographies complexes ainsi que des profils météorologiques évolutifs. Le travail est réalisé en couplant deux modèles numériques de propagation extérieure afin d'utiliser la puissance de chacun d'entre eux en fonction de la configuration étudiée. AbstractIn this paper a new hybrid method which allows coupling between different complex outdoor sound propagation models is presented. The aim is to develop a powerful tool able to take complex topographies and range dependant meteorological profile into account. The work is achieved by coupling two outdoor propagation models and using the advantages of each of them for a given setup.

In a complex outdoor environment, meteorological factors have been found to affect the sound field. On one hand, boundary element methods are particularly well adapted to calculate the sound pressure above complex boundaries (various absorbing properties and shapes) in a homogeneous atmosphere. On the other hand, a few models have been recently developed to describe the acoustic propagation in inhomogeneous media (normal modes, residue series, parabolic equation, fast field program...). Meteo-BEM is a new hybrid formulation taking advantage of the power of the boundary element methods, and including meteorological effects using as the appropriate Green’s function these recent propagation models in inhomogeneous media. In this paper, the theory of BEM, together with sound propagation in inhomogeneous media, is briefly recalled. The new hybrid model is then presented. The case of a rigid thin-noise barrier on a flat ground under a known sound-speed gradient condition is studied. Results from Meteo-BEM are then compared to measurement data for validation. It is shown that this new model allows one to calculate accurately the sound field in a complex outdoor environment and offers promising further developments.