Effects of Seabed Properties on Acoustic Wave Fields in a Seismo-Aoustic Ocean Waveguide

Acoustic wave fields in an ocean waveguide with a sediment layer having continuously varying density and sound speed overlying an elastic subbottom is considered in this analysis. The objective of this study is to investigate the effects of seabed acoustic properties,including the density and sound speed of sediment layer and subbottom, on the characteristics of the wave fields. This geometry offers a good environmental model which closely resembles a realistic ocean waveguide.This noise model was first proposed by Kuperman and Ingenito in the study of surface-generated ambient noise using normal mode approach.Recent experimental data provided by Hamilton have shown that the sediment layer in the seabed experiences a transitional change in which the density and the sound speed vary continuously from one value at the top to another at the bottom of the layer.Traditionally, in treating wave propagation in a such environment,the medium is represented by a series of layers,each of which has a uniform property within the layer.While this approximation may reasonably describe the variations of the medium as a whole,the details of the acoustic constituent may only be seen when these variations are properly accounted for.Moreover, the subbottom is taken to be a uniform elastic medium that is capable of supporting both compressional and shear waves.For the study of reflection from seabed, various kinds of sound speed and density profiles are employed.The wavenumber spectrum has clearly shown the various kinds wave components in the waveguide,in particular, the Scholte wave mode.The noise intensity in the water column is dominated by the modal and continuous spectrum.For the set of parameters chosen,the horizontal correlation lengths of the noisefield tend to increase as the noise sources becomes more correlated, however, the vertical correlation tends to reduce. This indicates that the coherency of the noise field is controlled both by the noise sources and waveguideproperties.