Dynamap: Sensitivity analysis of the acoustic calculation model with respect to environmental variables inside and outside urban areas

Within the DYNAMAP project, which aims to produce a dynamic noise map in different physical context, it is useful to preliminarily define the sensitivity of the acoustic model, with respect to some environmental variables. Starting with an analysis of the relevance of noise attenuation factors, function of the distance and the type of sources, it was decided to explore the sensitivity of the acoustic model with respect to weather conditions, in suburban context, and vehicular traffic flow conditions, in urban context. The noise calculation algorithm adopted is XPS 31-133/NMPB. The sensitivity of the model with respect to the occurrence of favourable or homogeneous weather conditions, has been assessed through repeated simulations in which only weather conditions vary. The refraction of sound rays in the atmosphere layers (favourable conditions) results in a greater persistence of the sound wave near the ground and therefore in a greater interaction with it. Hence the characteristics of land cover appear to be a discriminating factor to evaluate the influence of weather conditions on noise propagation. Several scenarios have been simulated calculating noise levels at an array of receptors with varying weather conditions, ground type and relative source-receiver height. Source conditions were instead kept constant. The results can guide the acquisition of local weather information required in the simulation process according to the different weather conditions settings. In urban areas instead, traffic flow conditions have a direct influence on the sound power of the road source. Through different scenarios, the relationship between sound power of road source is then calculated in function of: type of flow (continuous, accelerated, decelerated and interrupted), percentage of heavy vehicles, average speed. Some possible approaches to modelling of traffic conditions in urban context are here proposed and evaluated.