Three-dimensional adiabatic mode parabolic equation method and its applications

Abstract

Complex zone of the ocean is often characterized by horizontal variations of environmental parameters(bathymetry, sound speed profile, bottom properties etc.), initiating redistribution of the sound field in horizontal plane, which is the so-called three-dimensional (3D) effect. Based on the adiabatic mode parabolic equation method, modeling of 3D effects is carried out, in which the eigenvalues and eigenfunctions are calculated by the standard normal mode model KRAKEN, and the amplitude corresponding to each mode is computed by the wide-angle parabolic equation model RAM. The present 3D model is very efficient and can give clear physical meaning, but it can be only applied to a waveguide whose properties vary gradually with horizontal range due to the adiabatic assumption between different modes. This model is then used to analyze the horizontal refraction caused by internal waves and by a coastal wedge. The numerical results show that there are several areas in the horizontal plane, corresponding to different structures of intensity distributions. Moreover, the redistribution of the sound field in horizontal plane depends on source frequency and mode number. Frequency and modal dependences lead to variations of spectrum, distortion of signal with some spectrum, and spatiotemporal fluctuations of the sound field.