Meteorological effects on the 3D sound propagation inside an inhomogeneous forest area

The influence of trees on sound propagation is currently discussed to reduce the sound exposure near transport infrastructure or industrial areas. This influence is direct due to reflection and scattering at the trees themselves as well as indirect through meteorological and ground effects modified by the trees. Previous investigations provide a mixed picture of sound attenuation within forested areas, in particular for the temporally and spatially variable meteorological influence. Thus, a three-dimensional model chain of atmospheric and acoustic models was adapted and applied to special meteorological and vegetation-specific conditions. A meteorological mesoscale model was applied to simulate temperature and wind fields within an inhomogeneous forest site. The meteorological quantities are used as diurnally variable input data for the acoustic FDTD (finite-difference time-domain)-model to simulate the sound propagation. Thereby, the effects of vegetation elements, impedance ground surface, and sound refraction are considered. The simulations are related to outdoor measurements, which were performed in early autumn 2011 near Dresden (Germany). The sound propagation of artificial signals was measured along sound paths of up to 190m length through a clearing as well as through an old spruce stand. Results of the comparison between measurement and model simulations are presented and possible applications of these results with regard to noise protection aspects are discussed. The model results confirm the measured diurnal cycle of sound levels at the receiver positions. Simulations with and without trees suggest an excess attenuation of the trees by about 4 dB per 100m already for low frequencies.