Diffraction of sound over curved ground

Abstract

Theory for predicting the diffraction of sound (creeping waves) into shadow regions, resulting from propagation in either a stratified medium or above a convex curved surface, is well known and has been used mostly in underwater sound. This theory has also been extended more recently to the case of a stratified atmosphere. However, this theory generally has not been used to predict the energy diffracted over curved ground, such as rolling hills on berms. More commonly, the diffracted energy in these cases has been predicted by adapting theory valid for thick barriers or wedges. The creeping wave theory may be more appropriate in cases such as the diffraction of sound over berms, or of sound of very low frequency over rolling ground. Preliminary experiments have been performed over convex curved (radius of curvature < 100 m) ground of finite and infinite impedance in the frequency range between 250 and 8000 Hz using propagation distances up to 30 m. Controlled measurements are also planned indoors over a carefully constructed curve surface. The measurements are compared with various aspects of theory.