Abstract
A new underwater acoustic propagation model that is well suited to modelling ship noise is described. The model describes the spatio-temporal evolution of the directional energy spectrum of a sound field. The governing equation can be thought of as an advection-diffusion equation for spectral energy in phase space (position, angle). Numerical simulations of sound fields excited by both isotropic compact sources and by highly anisotropic ship noise provide confidence that the model works well, with caveats that will be discussed. [Work supported by ONR.]