Experimental study on outdoor sound propagation under various meteorological conditions

From the winter of 2018 through the spring of 2021, outdoor sound propagation experiments were repeatedly conducted three times a day on weekdays at a glider airfield in Hokkaido, Japan. In each experiment, impulse responses at the points of 155 m and 300 m from sound sources were measured. The ground surface condition of the experimental field was grass-covered in summer and snow-covered in winter. The monthly averages of sound pressure levels under upwind, downwind, and calm conditions were calculated every month. The data show that the seasonal variation depends on wind conditions, propagation distance, and frequencies. At the point of 300 m from sound sources, the seasonal variations are small under downwind conditions, whereas the range of variations is about 10 dB at high frequencies under upwind conditions and calm conditions. The relationship between vector wind speed and excess attenuation is discussed focusing on differences in atmospheric stability, snowfall, and snow cover conditions, respectively. We also introduce trial calculation results assuming the logarithmic-liner effective sound speed profiles and the parameters of turbulence proposed in previous studies.