Development of an analytical model for outdoor sound propagation within the harmonoise project

The Harmonoise project started in august 2001 and ran for three years. The main objective of the project was to provide new predictions methods for the mapping of environmental noise as required by the European Noise Directive COM 2000/49. Aside new predictions schemes for noise emission from road and railway vehicles, the project developed two propagation models: a "reference" model based on numerical simulations and an "engineering" model based on analytical and heuristic solutions. In this paper, the development and validation of the analytical propagation model will be presented. Various analytical and heuristic models have been proposed in the past; the Nord2000 project being the most recent attempt to provide a comprehensive prediction scheme combining all important propagation effects due to ground reflections, diffraction and meteorological refraction. All along its development, the Harmonoise project has taken advantage of the work carried out under the Nord2000 project. Similarities and differences between both models will be pointed out throughout this paper. Within the Harmonoise project, the prediction scheme was build and validated with respect to typical situations occurring in the mapping of road and railway noise; specifically, the project focused on sources close to the ground, propagation distances up to 1 km and under moderate atmospheric refraction conditions. Extensions of the propagation model to higher sources and larger distances are studied in a follow-up project, named IMAGINE, with application to aircraft and industrial noise sources.