Spectral broadening of sound scattered by advecting atmospheric turbulence

Scattering and spectral broadening of a monochromatic sound wave by atmosph eric turbulence that is flowing with a uniform constant horizontal wind is considered. The acoustic source and a detector are at rest and at different positions in a ground-fixed frame. Analytic expressions are derived for th e sound pressure scattered to the detector by a single eddy. Since distance s and the scattering angle change with time as the eddy flows through the s cattering volume, the detector signal has time-dependent amplitude and freq uency, for which general formulas are derived. A computer code is developed that calculates the scattered signal and its Fourier transform from a sing le eddy, or from a steady-state collection of eddies of many different scal e lengths that represents isotropic homogeneous turbulence flowing with the wind. The code utilizes a time-shift algorithm that reduces the calculatio n time substantially. Several numerical results from this code are presente d, including simulations of a recent experiment. The predicted spectral sha pe, including peak width and jaggedness, are in good agreement with experim ent. (C) 2001 Acoustical Society of America.