Wave Theory Modeling in Underwater Acoustics
The ocean acoustics environment is a complicated waveguide bounded above by a rough sea surface or ice cover and below by an inhomogeneous, elastic sea bed. Further, the acoustic properties of the water column are dependent on temperature, pressure and salinity, giving rise to a significant spatial and temporal variation. Analytical treatment of the propagation is limited to a very few, canonical problems, with the only alternative being numerical approaches. However, due to the complexity of the environment, no single numerical approach is capable of treating the general propagation problem. Therefore, a suite of numerical techniques have been developed and implemented, each applicable to a limited class of problems. Thus, normal mode approaches have been applied to longer range propagation problems with little bottom interaction and weak range dependence of the environment; parabolic equation methods have been applied to strongly range-dependent problems; and wavenumber integration or integral transform methods have been applied for short range propagation involving significant interaction with the elastic bottom. However, in recent years, each of these approaches have been further developed to incorporate more and more environmental effects, allowing a significant overlap in the areas of applicability. Further, the traditional restriction to 2-dimensional, one-way propagation scenarios has been abandoned, with a more realistic treatment of 3-dimensional propagation and reverberation problems as a result.