Long-range acoustic propagation: ground and meteorological effects

The propagation phenomena of sound waves emitted into the environment by terrestrial sources (transport, industry, etc.) are complex and involve a large number of parameters, the main ones being related, on the one hand, to the physical characteristics of the medium within which acoustic waves propagate (air) and, on the other hand, to boundary conditions (natural or artificial ground, obstacles, etc.). A good understanding of the propagation medium means that various mechanisms need to be taken into account in modeling, such as :

• geometric divergence ;

• molecular absorption ;

• reflection on boundary surfaces ;

• the various diffraction phenomena ;

• the influence of vertical temperature and wind speed profiles;

• the influence of atmospheric turbulence.

Depending on the complexity of the problem, different approaches are possible. Over the last thirty years, various authors [1] have tackled this important problem in successive stages, integrating an additional parameter at each step.

In the next few paragraphs, we'll look at the various analytical models that already allow us to consider a large number of situations. New numerical approaches, better suited to more complex situations, and the geostatistical approach will be discussed later.