## 2aAO10. Internal wave effects on normal mode processing.

### Session: Tuesday Morning, December 3

### Time: 10:30

**Author: Brian Sperry**

**Location: Dept. of Ocean Eng., MIT, Cambridge, MA 02139**

**Author: Arthur Baggeroer**

**Location: Dept. of Ocean Eng., MIT, Cambridge, MA 02139**

**Abstract:**

A normal mode description is often useful for interpreting long-range
propagation in deep water. For modal travel time measurements to be effective in
applications such as acoustic thermometry, an understanding of the effects of
interactions with internal waves is necessary. In this work, individual
realizations of an ocean with a GM internal wave spectrum are generated. A
wide-angle, finite-element PE code is used to provide the full-wave acoustic
solution, which is then projected onto a set of mode shapes to obtain the
complex mode coefficients. Particular attention is paid to the phase accuracy of
the coefficients, a potential problem area in propagating the PE to very long
ranges. The sensitivity of the coefficients to the choice of mode basis set
(local modes versus a background mode set) is demonstrated. The main area of
focus is understanding the resulting time spread of the individual modal
arrivals. While most of the spread is due to mode coupling, a portion of it
results from ``adiabatic dispersion,'' where a single mode sees different parts
of the water column as frequency varies over the source spectrum. The general
frequency dependence of the modal propagation and coupling is investigated as
well. [Work supported by ONR.]

ASA 132nd meeting - Hawaii, December 1996