Full diffraction theory numerical simulation of sound propagation in the ocean in the presence of sound-velocity variations

Abstract

We describe a numerical technique which uses a fast Fourier transform to make a plane-wave decomposition of the transmitter field. Spatial propagation is realized by multiplying the transmitter spectra with a spatial transfer function. An inverse FFT is performed on the resulting spectra to determine the field down range. Sound velocity variations, such as velocity gradients and those associated with turbulence which exist between the transmitter and receiver, are modeled. The distance between transmitter and receiver is broken up into slabs. The slab thickness is chosen to be the Rayleigh length of the smallest significant size in the problem. The velocity variations within a slab are modeled as a phase mask at the front of the slab. The remainder of the slab is assumed to be free of velocity variations. Since diffraction effects are not important over the Rayleigh length, the slab decomposition used represents a good model of the actual problem. We present results of simulations of direct path propagation in the presence of velocity gradients and turbulence.