Meteorological effects on wind turbine sound propagation

Immission sound measurements were performed near two wind turbines sites in Sweden. Data were collected continuously for two years to cover the seasonal and daily variation in the weather. Vertical profiles of meteorological parameters like wind speed, wind direction, temperature, and relative humidity were measured in parallel with the acoustic measurements. Large variations in the transmission of wind turbine sound were found under various refractive atmospheric conditions. The meteorological effects on wind turbine sound increase with distance and start to be important at distances somewhere between 400 and 1000 m from turbines. A comparison of commonly used wind turbine sound propagation models in Sweden such as ISO 9613-2 and Swedish Environmental Agency model is presented. It is shown that usage of a harder ground factor in ISO 9613-2, even though the actual ground is porous, improves the result.