SUMMARY

Sound waves are the only waves of a known physical nature capable of traveling through the ocean over a distance of many hundreds of kilometers. Because of its relative ease of propagation, people have applied underwater sound to a variety of purposes in their use and exploration of ocean. Shallow water acoustics is one of the most challenging branches of underwater acoustics. In contrast to deep-water propagation, where purely waterborne paths predominate, shallow water acoustics deals with strong sea bottom and surface interactions, multipath propagations, and complex variations in the water column. The sea bottom is the dominant environmental influence in shallow water. An accurate solution to the Helmholtz equation in a shallow water waveguide requires accurate seabed acoustic parameters (including sediment layer thickness, sediment sound speed profiles, density, and attenuations) to define a bottom boundary condition. Direct measurements of these bottom parameters are excessively time consuming, expensive, and spatially limited. Thus, inversion methods based on acoustic field measurements which can rapidly and efficiently estimate the bottom properties over a volume are very desirable. The proposed research will be accomplished by (1) Designing and performing an at-sea experiment; (2)Analyzing acoustic data collected from the Yellow Sea '96 experiment and Shallow Water '06 experiment conducted off the New Jersey coast; (3)Applying several characteristics of sound field to matched field processing based geoacoustic inversion and performing multi-parameter inversion by a global optimization method, such as genetic algorithms; (4) Comparing measured transmission loss as a function of frequency, range, and depth with the predictions based on the inverted bottom acoustic parameters; and (5) Discussing the uncertainty of geoacoustic parameter estimates.