### 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.