David E. Norris
Graduate Program in Acoust., Penn State Univ., 202 New ARL, State College, PA 16804
Dennis W. Thomson
Penn State Univ., State College, PA 16804
Propagation of sound and noise in the atmosphere depends sensitively upon the ambient wind and temperature profiles. Because diurnal changes in the atmosphere's boundary layer (BL) are strongly controlled by heating and cooling of the earth's surface, BL wind and temperature profiles tend to have, at least in a mean sense, repeatable structural similarity. To evaluate potential operational use of parabolic equation (PE) propagation models, 11 characteristic atmospheric profiles were defined in terms of potential temperature and wind. The resulting mean sound-speed profiles were then used in the PE models to calculate up, down, and cross-wind sound-pressure levels. A continuous point source was used, having frequencies from 100 to 2000 Hz, and the surface was assumed flat with constant ground impedance. From these results, a model was developed that relates atmospheric conditions to the deviations in sound-pressure level apart from standard spherical spreading values. The effects of refraction such as caustics and shadow zones are noted. As part of this study, the consequences of parameterizing the state of the atmosphere into a limited set of classes was also examined.