## 3aUW7. Improved narrow-band and broadband normal-mode algorithms for fluid ocean environments.

### Session: Wednesday Morning, May 15

### Time: 9:50

**Author: Evan K. Westwood**

**Location: Appl. Res. Labs., Univ. of Texas, P.O. Box 8029, Austin, TX 78713-8029**

**Abstract:**

Improvements have been achieved in the speed, robustness, and versatility
of a recently developed normal-mode algorithm for fluid ocean environments [S.
J. Levinson et al., J. Acoust. Soc. Am. 97, 1576--1585 (1995)]. The possibility
of missing modes has been eliminated by computing both the total phase of the
oscillatory mode function versus depth and the number of zeros of the function.
The root-finding algorithm computes both an error function and its derivative,
which allows cubic interpolation to be used to obtain eigenvalue guesses when a
root is bracketed. The efficiency of the root-finder is characterized by the
fact that the error function typically must be computed less than 3-1/2 times
per mode. An automated broadband capability has also been implemented. Analytic
first and second derivatives are used to interpolate the eigenvalues in
frequency as a fifth-order polynomial. For broadband computations where
inclusion of the continuum is desired, a false bottom may be automatically
inserted. Its thickness is specified in terms of acoustic wavelengths in the
medium and varies with the frequency, thus saving the computation of a
significant number of modes. [Work supported by ONR 321OA.]

from ASA 131st Meeting, Indianapolis, May 1996