Near‐horizontal propagation of sound over grassland

An extensive set of published measurements of the propagation of noise from jet aircraft on the ground across an airport for differing weather conditions is compared with predictions using modern propagation theory from values of ground impedance, assuming an acoustically homogeneous atmosphere. When the atmosphere is in fact reasonably homogeneous under neutral weather conditions, there is quantitative agreement between calculated and measured behavior. The intricate pattern of acoustic behavior, as a function of frequency and distance, produced by inhomogeneous atmospheric conditions (gradients of wind temperature turbulence) is explained qualitatively by the appropriate modes of propagation revealed by the theory. The role of surface and sky waves in particular is illustrated.