OCEAN ACOUSTIC TOMOGRAPHY BASED ON PEAK ARRIVALS

The recently introduced notion of peak arrivals [Athanassoulis and Ska rsoulis, J. Acoust. Sec. Am. 97, 3575-3588 (1995)], defined as the sig nificant local maxima of the arrival pattern, is studied here as a mod eling basis for performing ocean tomography. Peak arrivals constitute direct theoretical counterparts of experimentally observed peaks, and offer a complete modeling of experimental observables, even in cases w here ray or modal arrivals cannot be resolved. The coefficients of the resulting peak-inversion system, relating travel-time with sound-spee d perturbations, are explicitly calculated in the case of range-indepe ndent environments using normal-mode theory. To apply the peak-inversi on scheme to tomography the peak identification and tracking problem i s examined from a statistical viewpoint; maximum-likelihood and least- square solutions are derived and discussed. The particular approach ad opted treats the identification and tracking problem in close relation to the inversion procedure; all possibilities of associating observed peaks with background arrivals are examined via trial inversions, and the best peak identification is selected with respect to a least-squa re criterion. The feasibility of peak tomography is subsequently demon strated using first synthetic data and then measured data from the THE TIS-I experiment. In the synthetic case the performance of the overall scheme is found to be satisfactory both with noise-free and noisy dat a. Furthermore, the identification, tracking, and inversion results us ing experimental acoustic data from THETIS-I are in good agreement wit h independent held observations. (C) 1996 Acoustical Society of Americ a.