ASA 126th Meeting Denver 1993 October 4-8

5aPA12. Application of the CFFP to sound propagation in inhomogeneous media above a ground with an impedance discontinuity.

Y. L. Li Michael J. White

US Army Construction Eng. Res. Lab., P. O. Box 9005, Champaign, IL 61826-9005

Using the chirp fast field program (CFFP), a systematic method has been developed for numerical computation of sound propagation in an inhomogeneous atmosphere above a ground with an abrupt change in impedance. In situations where a noise is generated above one type of ground surface (say pavement) and travels beyond its edge, onto a second type of surface (e.g., grassy ground), each surface usually controls the rate of attenuation near it. When the air near the ground is refractive, it may emphasize the attenuation during downward refraction and eliminate it in upward refraction. Other effects of the inhomogeneous atmosphere are discussed. Several interesting examples will be presented.