ASA 126th Meeting Denver 1993 October 4-8

2pUW4. Complex effective depth and mode eigenvalues for a layered elastic waveguide.

C. T. Tindle N. R. Chapman

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

The complex effective depth [Z. Y. Zhang and C. T. Tindle, J. Acoust. Soc. Am. 93, 205--213 (1993)] has been investigated for a shallow water waveguide with a layered elastic bottom. For multiple layers, both the complex effective depth and the reflection coefficient for the bottom have oscillatory structure as a result of resonant effects in the layers of the sediment. Under these conditions and for elastic layers, some of the normal mode eigenvalues can be difficult to find, as a simple mode counting procedure is not available. The complex effective depth leads to a formulation of a eigenvalue problem in terms of a phase integral. The phase integral is a function of complex wave number and a normal mode exists whenever it is a multiple of (pi). A path exists in the complex plane along which the phase integral is real and monotonic. The path passes through all eigenvalues for both trapped and leaky modes and these can be found systematically. [Work supported by DND.]