O the Application of Horizontal Ray Theory to Acoustic Propagation in the Ocean Waveguide

This dissertation is concerned with the description of wave propagation in inhomogeneous waveguides with curved boundaries. Horizontal ray theory, a 3-D analytical approximation method, is extended to multilayered waveguides and practical methods of implementation are developed. Higher order corrections are developed as integrals of lower order solutions. The ordinary differential equations for the lowest order approximation are integrated for translationally invariant and cylindrically symmetric environments. These solutions do not have the invariance or symmetry of the waveguide in which they propagate and exhibit three-dimensional propagation effects. The solution for cylindrically symmetric waveguides is employed in an examination of the effect of a seamount on the propagation of acoustic signals in the ocean waveguide. Isovelocity water and a rigid ocean bottom were assumed in order to facilitate the calculation. Local propagation effects induced by this simple geometric vertical structure and sound speed profile are compared with local propagation effects induced by a more realistic vertical structure and profile in order to validate the conclusions concerning propagation near the seamount. The effects of source and receiver depths and sub-bottom attenuation on the deflection effects of the seamount are also examined. In addition to blockage, it is found that enhanced geometrical spreading in the horizontal plane makes a significant contribution to the decrease in acoustic intensity when the source and receiver are on opposite sides of the seamount. It is also found that the seamount generates convergence zones in the horizontal plane. These convergence zones are a possible explanation for observed convergence zones in measured propagation near the Dickens seamount in the Northeast Pacific.