### ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

## 5pUW2. Advances in underwater acoustic normal-mode computations.

**Scott J. Levinson
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Carol V. Sheppard
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**
Stephen K. Mitchell
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**
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*Appl. Res. Labs., Univ. of Texas at Austin, Austin, TX 78713
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Recently, an efficient, numerically robust algorithm for calculating
acoustic normal modes was shown to have more than an order of a magnitude
improvement in speed while maintaining high accuracy over other algorithms
(submitted to JASA by the authors, June '94). A limitation remains, however, in
its dependence on presampled wave numbers in the search for the roots of the
characteristic equation (eigenvalues). Since coarse wave-number presampling may
result in some eigenvalues remaining undetected, the presampling part of this
code is the most time consuming portion---particularly for multichannel
environments. We introduce a new approach which overcomes this problem.
Analytic derivatives (up to sixth order) are calculated to locally approximate
the numerically robust characteristic equation with Pade' approximants when
finding successive eigenvalues. The requirement of wave-number presampling is
thereby avoided and eigenvalue root finding is achieved with a superlinear
convergence property. Its speed and accuracy will be compared with previous
methods for single and multichannel ocean acoustic environments. [Work
supported by the Advanced Surveillance Acoustic Prediction System (ASAPS)
Development for IUSS Program of the Space and Naval Warfare Systems Command
(SPAWAR, PMW 181-1).]