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


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