### ASA 126th Meeting Denver 1993 October 4-8

## 5aUW8. New algorithm for calculating normal modes in broadband
applications.

**Robert A. Koch
D. P. Knobles
**

**
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*Appl. Res. Lab., Univ. of Texas, P. O. Box 8029, Austin, TX 78713-8029
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A new algorithm for calculating the normal modes that are used to describe
underwater acoustic propagation is presented. The algorithm is especially
relevant for broadband normal mode calculations in which normal mode
eigenvalues, depth functions, and attenuations are needed. The new algorithm
uses an expansion technique to construct normal mode eigenvalues and depth
functions for some frequency from eigenvalues and depth functions previously
calculated at another, higher frequency. Comparisons of the estimated
eigenvalues, depth functions, and attenuations with exact results are presented
for several shallow water environments. A broadband propagation model that uses
normal mode sets calculated with the new algorithm has been developed.
Transmission loss and impulse responses based on estimated and exact normal
mode sets are compared. [This work was supported by the Office of Naval
Research through Block RL3B and Block CS3A.]