Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Ocean Engineering

First Advisor

James H. Miller


This study examines underwater acoustic propagation in a shallow water environment, concentrating upon the impact of nonlinear internal waves. During internal wave activity, acoustic signals can fluctuate significantly due to complex three-dimensional multi-mode and multipath interference effects. Experimental measurements from the Shallow Water '06 experiment provide oceanographic and acoustic data during instances where the acoustic track is nearly parallel to an approaching internal wave train. Distinct events show internal waves modulate the acoustic field substantially. Propagation modeling using the Monterey-Miami Parabolic Equation algorithm simulates an internal wave train moving in a straight-line fashion. Horizontal refraction dominates in the nearly parallel configuration, and three specific scenarios are exemplified in both measured and modeled data: refraction (prior to the internal wave's arrival), defocusing (as a soliton spreads acoustic energy), and focusing (as two solitons create a horizontal sound channel). Normal mode decomposition and statistical analysis provide insight into the temporal and spatial acoustic fluctuations. At very small angles off-parallel, focusing effects are dramatically reduced, and refraction prior to the internal wave's arrival becomes an important factor to consider. In the exactly parallel scenario, refraction remains important, but is a second order effect compared to focusing.