ASA 127th Meeting M.I.T. 1994 June 6-10

3aUW13. A normal mode model for multilayered acoustoelastic ocean environments based on an analytic reflection coefficient method.

Evan K. Westwood

C. T. Tindle

N. R. Chapman

Defence Res. Establishment Pacific, FMO Victoria, BC V0S 1B0, Canada

A normal mode model has been developed for underwater acoustic propagation in an ocean environment with multilayered elastic media below and/or above the water column. The compressional (p-) and shear (s-) wave sound speeds may either be constant or have a gradient (1/c[sup 2] linear with depth) in each layer. Mode eigenvalues are found by analytically computing the downward- and upward-looking plane-wave reflection coefficients R[sub 1] and R[sub 2] at a reference depth in the water and searching the complex k plane for points where R[sub 1]R[sub 2]=1. The complex k-plane search is greatly simplified by following the path along which |R[sub 1]R[sub 2]|=1. The |R[sub 1]R[sub 2]|=1 path connects all the modes, which are found as points on the path where the phase of R[sub 1]R[sub 2] is a multiple of 2(pi). The direction of the path is found from the analytic derivative d(R[sub 1]R[sub 2])/dk. Leaky modes are found, and multiple channels are handled. The eigenvalue finding algorithm appears to be robust and efficient. [Work supported by the ARL Independent Research and Development Program.] [sup a)]On leave from Appl. Res. Lab., The Univ. of Texas at Austin. [sup b)]On leave from Dept. of Phys., Private Bag 92019, Univ. of Auckland, Auckland, New Zealand.