Propagation through an Anisotropic Random Medium I. The Single Scatter Region

Abstract

Propagation through a random medium with horizontal correlation lengths that are orders of magnitude larger than vertical correlation lengths is studied. In this first paper we consider a horizontal time-harmonic plane wave to be incident on a finite scattering volume. The spatial distribution of the scattered intensity is obtained using the single scatter theory, or Born approximation. The most significant result is the demonstration that for λ≪lHm and λ≫lVM, where λ is the acoustic wavelength, lHm is the minimum horizontal correlation length, and lVM is the maximum vertical correlation length; the energy is essentially forward scattered. The angular dependence of the scattered energy measured in a vertical plane is not controlled by the vertical correlation lengths, as one might intuitively expect, but is controlled by the larger horizontal correlation lengths. This suggests that the resolution limitation caused by the scattering of low-frequency acoustic signals by the ocean temperature microstructure will be considerably less than might be intuitively suspected.