1pUW9. Second-order perturbations of peak-arrival times due to sound-speed disturbances.

Session: Monday Afternoon, December 2

Time: 3:40

Author: G. A. Athanassoulis
Location: Dept. of Naval Architecture and Marine Eng., Natl. Tech. Univ. of Athens, 15710 Zografos, Athens, Greece
Author: E. K. Skarsoulis
Location: Inst. of Appl. and Comput. Math., Crete, Greece


Ocean acoustic tomography has been commonly used in a linear framework, by assuming small perturbations of the ocean environment about a given background state. However, in the case of large sound-speed variations (e.g., seasonal changes) nonlinear dependencies of arrival times on the sound speed may become significant; such a case occurred in the THETIS-2 tomographic experiment conducted in 1994 in the western Mediterranean basin. Second-order arrival-time perturbations are studied here on a wave-theoretic basis, using the recently introduced notion of peak arrivals [G. A. Athanassoulis and E. K. Skarsoulis, J. Acoust. Soc. Am. 97, 3575--3588 (1995); Skarsoulis et al., J. Acoust. Soc. Am. 100 (August 1996)]. A second-order perturbation formula relating arrival-time with sound-speed perturbations is derived, containing background arrival times and also functional derivatives of the background field with respect to the sound speed. For the case of a range-independent environment the perturbation formula is further elaborated by exploiting normal-mode theory. Its performance is demonstrated using simulations motivated from the THETIS-2 environment. [Work partially supported by EU/MAST.]

ASA 132nd meeting - Hawaii, December 1996