Noise propagation over a surface of variable impedance

Abstract

Previous analyses of sound propagation over uniform plane surfaces suggest that, for fixed source and receiver locations, only a limited portion of the surface makes an important contribution to the character of the received signal. Experiments in an anechoic chamber are reported which examine this hypothesis and which give insight into the magnitudes of critical scale sizes for surfaces of variable ground impedance. An estimate of the minimum size of the ground region most strongly affecting the received sound is obtained from data taken with finite sized surfaces of finite impedance centered at the probable reflection point. The data is interpreted using a theoretical model using concepts similar to those in Kirchhoff's theory of diffraction. [Work supported by NASA Langley Research Center.]