### ASA 125th Meeting Ottawa 1993 May

## 2aAO5. Coupled modes in a waveguide with a range-dependent rigid basement.

**Gregory Gillette
**

**
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*The Johns Hopkins Univ., Appl. Phys. Lab., STA Group, Johns Hopkins Rd.,
Laurel, MD 20723
*

*
*
Previous coupled mode approaches to acoustic propagation in ocean
waveguides either (1) apply strictly to the case where interfaces other than
the (free) ocean surface are range-independent, or else (2) they satisfy the
boundary conditions at such interfaces approximately. In this paper coupled
mode theory is extended to give a solution that exactly satisfies the boundary
condition on a range-varying rigid basement. This is achieved by transforming
the coordinate system so that at each range the basement coincides with a
coordinate surface, and the partial separation of variables is construed with
respect to the coordinate that is normal to that surface. Related work by other
researchers is discussed, and the numerical implementation of the theory is
described. Results for basements exhibiting both upsloping and downsloping
regions are presented, and the exchange of radiated power between the modes is
investigated for these cases.