GROUND EFFECT FOR A-WEIGHTED NOISE IN THE PRESENCE OF TURBULENCE AND REFRACTION

Closed-form approximations, of ground effect for continuous A-weighted noise from a point source near to finite impedance ground, obtained b y Li et al. [J. Acoust. Sec. Am. 88, 1170-1172 (1990)] and Makarewicz [J. Acoust. Sec. Am. 82, 1706-1711 (1987); 88, 1172-1175 (1990)], are extended to take account of more general models for ground impedance i ncluding revised variable-porosity, thin-layer, and rough porous groun d where the roughness is small compared with incident wavelengths. The influences of both turbulence and weak atmospheric refraction within the illuminated zone are included. Approximate relationships between o ptimum ground effect for A-weighted noise, ground parameters, source s pectrum, source height, and receiver height are predicted and explored . For low source heights and noise sources with A-weighted spectra wit h low peak frequencies, it is possible to indicate ground surface para meters that will give significantly higher excess attenuation than tho se typical of grass-covered ground. It is predicted that, in the illum inated zone, the optimum ground effect parameters are fairly robust to weak refraction effects. (C) 1997 Acoustical Society of America.