Sound Field Coherence Behind a Low Barrier in a Turbulent Atmosphere without the Presence of a Ground Surface

The turbulence in the atmospheric boundary layer causes the sound propagation to take place in a random medium. The influence on the sound can be strong especially in acoustic shadow regions, which can be caused by refraction, ground attenuation or geometry, e.g. by a noise barrier. Here, situations with a noise barrier that is low in comparison with its distance to source and receiver are studied in two dimensions. Previous studies on turbulence effects have been made on the increased sound level in shadow regions as well as on the reduced coherence in line-of-sight situations and in shadow regions caused by refraction. Here, the main focus is instead on the reduced coherence of the sound field in the shadow region behind a noise barrier. Analytical as well as numerical results are presented whose implications are relevant for future studies on the sound level increase in shadow regions when the receiver is located above a ground surface. As one of the results it is concluded that the turbulence causes a larger coherence loss for screened cases than for line-of-sight cases.