Propagation of noise above ground having an impedance discontinuity

Controlled measurements above ground with an impedance discontinuity are described. The measurements were made outdoors with a source above asphalt and a receiver above grass, and indoors above surfaces of known impedance in the absence of atmospheric turbulence. The results were obtained for several sources and receiver heights and for various percentages of hard–soft ground to propagation distances of 2.4 m indoors and 10 m outdoors. The measurements are also extended to include the case of a source above ground of finite impedance but which is still harder than the ground on the receiver side. The measurements are compared with recent theory which includes semiempirical solutions and solutions obtained numerically from Green’s theorem. Good agreement between the measured results and all the theories is obtained in most cases. However, in more extreme situations, including the ‘‘soft–softer’’ ground case, the semiempirical solutions are in difficulty. Earlier work [Nicolas et al., J. Acoust. Soc. Am. 73, 44–54 (1983)] is also extended by calculating the insertion loss of a barrier on ground with an impedance discontinuity. The previously measured insertion loss is recompared with the predicted insertion loss and good agreement is now obtained.