## 2aAO14. Fast normal-mode approximation of tomographic arrival patterns.

### Session: Tuesday Morning, December 3

### Time: 11:30

**Author: E. K. Skarsoulis**

**Location: Inst. of Appl. and Comput. Math., F.O.R.T.H., 71110 Heraklion, Crete, Greece**

**Abstract:**

The wave-theoretic calculation of arrival patterns for the needs of ocean
acoustic tomography is computationally expensive due to the large number of
computation frequencies necessary for properly synthesizing a broadband signal
in the time domain. A scheme for approximate fast normal-mode calculations of
broadband acoustic signals in the time domain is proposed, based on a
second-order Taylor expansion of eigenvalues and eigenfunctions with respect to
frequency. For the case of a Gaussian impulse source, a closed-form expression
is obtained for the pressure in the time domain. Using perturbation theory,
analytical expressions are derived for the first and second frequency
derivatives of eigenvalues and eigenfunctions. The proposed approximation
significantly accelerates arrival-pattern calculations, since the eigenvalues,
eigenfunctions, and their derivatives need to be calculated at a single
frequency, the central frequency of the tomographic source. Furthermore, it
offers a satisfactory degree of accuracy for the lower- and intermediate-order
modes. This is due to the fact that essential wave-theoretic mechanisms such as
dispersion and frequency dependence of mode amplitudes are contained in the
representation up to a sufficient order. Numerical results demonstrate the
efficiency of the method. [Work partially supported by EU/MAST.]

ASA 132nd meeting - Hawaii, December 1996