Sound propagation in a turbulent atmosphere near the ground: An approach based on the spectral representation of refractive-index fluctuations

A new. rigorous approach is presented for the computation of the fluctuatin g field of a monopole source in a nonrefracting, turbulent atmosphere above a ground surface. The time-averaged sound pressure level is considered. as well as statistical distributions of the sound pressure level, The computa tion is based on the Rytov solution of the wave equation for a turbulent me dium, evaluated for the half-space above the ground surface. The solution t akes into account the ground reflection of scattered waves, which has been neglected in previous work on this subject. The present approach is based o n a Fourier-Stieltjes representation of refractive-index fluctuations, and makes use of a turbulent image atmosphere to account for the ground reflect ion of scattered waves, This approach is rigorous only for a rigid ground s urface, but it is shown that it also yields a good approximation for a fini te-impedance ground surface. The accuracy of the solution is demonstrated b y comparison with results of numerical computations with the parabolic equa tion method for a turbulent atmosphere. The assumption of a nonrefracting a tmosphere implies that direct application of the solution is limited to pro pagation over relatively small distances. However, this study can also be c onsidered as a basis for a generalized solution for a downward refracting a tmosphere, which can be applied for larger propagation distances. (C) 2001 Acoustical Society of America.