Analysis of motion and bottom scattering effects on underwater acoustic propagation

The effects of motion and and scattering attenuation in a shallow ocean acoustic waveguide are investigated using the parabolic equation method. First, the effects of uniform horizontal source and receiver motion on the intensity of an underwater-acoustic pressure field are studied. The surface and bottom of a stationary ocean are taken to be horizontal, the sound speed may be range-and-depth dependent, and the source emits a cw signal. A Galilean transformation is used to convert the source-receiver motion problem into a fixed receiver-moving source problem in an ocean with a horizontal current. A parabolic equation incorporating an apparent current due to receiver motion and an approximate Doppler frequency shift due to source and receiver motion is derived from the wave equation. All motion effects are seen to manifest themselves in a single parameter, the "effective" sound-speed, once an appropriate time-interval limit is found. Next, a scattering layer is introduced at a horizontal water-bottom interface to account for effects of attenuation due to bottom volume scattering. Using a wide-angle parabolic equation, a formula for the local mean of intensity is found for a model consisting of three isospeed fluid layers. The sensitivity of the theoretical mean to environmental parameters is studied, and the standard deviation of intensity is also examined. Comparisons are made between three-layer model statistics and data from a recent New Jersey Shelf experiment. Results from the inclusion of a scattering layer for the prediction of relative intensity statistics are evaluated over a wide range of acoustic frequencies. Finally, work on the ability of analytic models incorporating bottom volume scattering to match experimental acoustic properties is extended. An analytic treatment of propagation in a multi-layered shallow ocean is developed for a wide-angle PE propagation model. The local mean of intensity is analytically determined and its sensitivity to parameters such as the number of layers, acoustic frequency, and scattering layer attenuation is investigated. Comparisons are made between intensity and intensity statistics for the multi-layer models and experimental intensity data.