Scattering calculations using the characteristic rays of the coherence function

Abstract

We use the two-scale expansion developed previously to determine the intensity variation in the neighborhood of caustics, to show how we may calculate the scattering of acoustic radiation in a random medium with a variable speed of sound profile. Equations are derived which show how the coherence function varies along the characteristic rays (identical to the rays of geometrical acoustics in the parabolic approximation). Conditions are given for simplifying the equations for high-frequency quasi-isotropic scattering. The problems that arise when the medium is highly anisotropic are discussed and an approximate solution is given. It is also shown how to calculate the intensity variation due to scattering in the neighborhood of a caustic.