Low-frequency sound scattering by internal waves in the ocean

In this paper, long-range propagation of low-frequency sound through an ocean waveguide with random inhomogeneities in the sound speed is studied. Closed equations for the mean field and correlation function of the sound field are derived using the Chernov method. These equations can be considered as a generalization of equations derived by Dozier and Tappert [ J. Acoust. Soc. Am. 63 , 353-365 ( 1978 ) ], which accounts for 3D effects and cross-modal correlations. The equations derived in this paper in a general form are similar to the equations obtained by many other authors. However, without simplifications these equations are difficult to solve even numerically due to high dimension of the matrices appearing in the equations. Some simplifications of the equations for the mean field and correlation function are suggested that account for narrowness of the angular spectrum of the scattered acoustic field and which make these equations amenable for numerical implementation. To study solutions of the simplified equations, they are additionally averaged along the sound propagation path. This allows us to obtain some analytical results. Using the theory developed, the horizontal coherence length of the sound field is estimated for the GM spectrum of internal waves.