Computer Modelling of Urban Noise Propagation

Abstract

The nature of noise propagation through the urban fabric is not well understood and this reflects the difficulty in obtaining good quality data. The most promising approach to developing urban noise prediction models is computer simulation. Reflections from building facades are a mixture of specular and diffuse. However, as the order of reflection increases the relative fraction of energy reflected purely specularly will decrease and the reflection characteristics will resemble those of the pure diffuse case. It is proposed that an appropriate approach to the development of propagation models could be based upon specular reflections for the lower orders of reflections and diffuse reflections for higher orders of reflection. An alternative statement of the above is that the specular approach would be most appropriate for modelling near field propagation whilst the diffuse approach might be more appropriate for modelling mid and far field propagation. Two approaches to the development of diffuse prediction models have been identified. The radiosity method would allow the investigation of the effect of the disposition of individual buildings on noise propagation but would be computationally demanding if applied to large scale studies. Conversely, an approach based upon the classical diffusion equation is potentially capable of being applied to large scale studies but will not yield any local detail. It is suggested that both approaches might be suitable for incorporating into a comprehensive model for far field urban noise propagation.