Field measurements on wind effects to propagation of road traffic noise over open and flat ground

There has been carried out a number of experimental studies with regard to wind effects to outdoor sound propagation. Most of the studies deal with propagation from steady-state point source such as a loudspeaker in case of field measurements. However, wind effects to more realistic sources, such as road traffic noise sources which are considered to be time-varying line sources, are hardly known in public literature. In the present study, the wind effects to acoustic propagation from a straight road with intense traffic to an open and flat field were investigated through field measurements in order to specifically illustrate the effects of such sources. Two measurement points were placed at 40 m and 140 m distance from the subject road. The results show that (1) The standard deviations of sound pressure levels (SPLs) at the measurement points were around 2 dB for both receiver distances. (2) The effect of perpendicular component of wind velocity to the road direction was slightly stronger than the ASJ Model which was mostly derived from point-source experiments. (3) The effect of source time-variance was effectively taken out by taking the difference in SPLs at the nearby and distant measurement points, in which case the standard deviations of the excess attenuation were reduced to around 1.3 dB. (4) Slight tendency of coherence magnitude of sound pressure between the receivers converging to zero with increasing turbulent kinetic energy is observed in 125 Hz and 250 Hz bands. Meanwhile, the effect of parallel wind velocity component to the road still remained unclear and thus requires further investigations.