A fast ray-tracing technique for sound propagation in a stratified moving medium

摘要

A new method is suggested for the evaluation of sound field in a moving stratified atmosphere above an absorbing ground. The new method stems from a recent development on a high-frequency approximation of sound propagation outdoors in the presence of wind and temperature gradients[K M Li, J. Acoust. Soc. Am. 95, 1840-1852]. The present work attempts to implement the new method numerically with vertical variations in temperature and vectorial wind velocity as input parameters. Although the algorithm is applied to atmospheric sound propagation, the general idea can be applied to othe branches of wave propagation such as the transmission of sound in an ocean environment. The determination of the ray path is simplified by the introduction of an apparent index of refraction that has included the Doppler effect due to the motion of the medium. Instead of using a 'hit-and-miss' approach, we use an iterative scheme that would find all eigenrays. The search of eigenrays is based on a fourth-order Runge-Kutta algorithm with adjustable step sizes. We also remark that the leading term of the high-frequency solution is identical to that derived by the classical ray theory but the new method is based on a rigorous estimation of a Fourier integral. Furthermore, a close examination of the new solution reveals that the total sound field is composed of three terms, namely, a direct wave, a (geometrically) reflected wave and a ground wave, respectively. However, the classical ray theory does not predict the existence of the ground wave component. Numerical results from the new ray-tracing methods are presented and compared with other numerical schemes such as the Fast Field Program (FFP).