Amplitude fluctuation effects in shallow water acoustic scattering by internal waves

Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1995This thesis investigates the amplitude fluctuation effects in acoustic scattering due to shallow water internal waves. Theoretically, it uses the adiabatic approximation and perturbation methods to statistically evaluate acoustic transmission fluctuations caused by internal waves in the ocean; it also investigates acoustic mode coupling effect due to internal waves. Numerically, this thesis simulates the shallow water internal wave (IW) field using the Garrett-Munk internal wave spectrum model and then evaluates acoustic transmission in the simulated internal wave field with the Kraken normal mode program. Theoretical calculations are also performed using the theory developed in this thesis. Comparisons are made between theory and numerical calculations. The results presented and discussed in this thesis are related to the following issues: coherent and incoherent intensity fluctuations for adiabatic approximation, acoustic mode coupling due to IW's, transmission loss difference between adiabatic and coupled mode methods, and their dependence on range, IW amplitude and frequency