Atmospheric sound propagation near the ground

Abstract

The most important meteorological effects on sound propagation are refraction-ground attenuation, atmospheric absorption, and scattering by turbulence. The wind and temperature gradients cause refraction of the sound rays, and hence influence the sound level. The curvature of a nearly horizontal sound ray can be calculated by using measurements of wind and temperature. Atmospheric absorption is important for outdoor sound propagation. The absorption varies for different parts of the world. Results from some stations in Scandinavia are given. Atmospheric absorption for the high frequencies changes during different times of the year. The absorption for low frequencies varies both over the day and the year. The size of the annual and diurnal variance is frequency dependent. An increase in the accuracy of calculations of outdoor sound levels can be made by considering the local climate. The values of atmospheric absorption need to be calculated for the local climate instead of using some global mean value. The time has come to use data from local meteorological stations. Turbulence scatters sound into sound shadow zones and causes fluctuations of the phase and the amplitude of the sound waves.