Search

Addressed is the physics of sound propagation through a shallow water waveguide whose seabed has a random rough surface. The basic coupled integral equations for the modal amplitudes can be split into forward and backward going coupled integral equations. Numerical solutions of the coupled equations are obtained for multiple roughness realizations from which ensemble averages can be obtained for the modal intensities and cross-mode coherence as a function of range. Sample calculations illustrate some of the basic characteristics of the average cross-mode coherence and intensity with and without seabed attenuation and for different source depths on range scales of 1500 acoustic wavelengths. [ABSTRACT FROM AUTHOR]

A two-way coupled mode approach based on an integral equation formalism is applied to sound propagation through internal wave fields defined at the 1999 Shallow Water Acoustics Modeling Workshop. Solutions of the coupled equations are obtained using a powerful approach originally introduced in nuclear theory and also used to solve simple nonseparable problems in underwater acoustics. The basic integral equations are slightly modified to permit a Lanczos expansion to form a solution. The solution of the original set of integral equations is then easily recovered from the solution of the modified equations. Two important aspects of the integral equation method are revealed. First, the Lanczos expansion converges faster than a Born expansion of the original integral equations. Second, even when the Born expansion diverges due to strong mode coupling, the Lanczos expansion converges. It is shown that the internal wave problems examined are essentially one-way propagation problems because one observes good agreement between the coupled mode solutions and those provided by an energy-conserving parabolic equation algorithm. In the Workshop examples, at both 25 and 250 Hz, significantly greater coupling between modes occurs in the linear internal wave field case than the nonlinear soliton case. [ABSTRACT FROM AUTHOR]

An optimization approach is used to estimate waveguide parameters for selected test cases of the Geoacoustic Benchmark Inversion Workshop held in Vancouver, June 1997. The approach uses multiple acoustic data samples to decouple the original N-dimensional problem into several smaller-dimensional problems. A nonlinear least squares approach is used to estimate parameters in each subset. The estimation of parameters in each subset proceeds until convergence is reached. Predicted values are in good agreement with the true values, which suggests that the decoupling of waveguide parameters allows a nonlinear least squares approach to be an effective tool in the inversion of ocean waveguide parameters. [ABSTRACT FROM AUTHOR]