Ocean acoustic tomography based on peak arrivals

The recently introduced notion of peak arrivals [Athanassoulis and Skarsoulis, J. Acoust. Soc. Am. 97, 3575–3588 (1995)], defined as the significant local maxima of the arrival pattern, is studied here as a modeling 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 where ray or modal arrivals cannot be resolved. The coefficients of the resulting peak-inversion system, relating travel-time with sound-speed perturbations, are explicitly calculated in the case of range-independent environments using normal-mode theory. To apply the peak-inversion scheme to tomography the peak identification and tracking problem is examined from a statistical viewpoint; maximum-likelihood and least-square solutions are derived and discussed. The particular approach adopted 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-square criterion. The feasibility of peak tomography is subsequently demonstrated using first synthetic data and then measured data from the THETIS-I experiment. In the synthetic case the performance of the overall scheme is found to be satisfactory both with noise-free and noisy data. Furthermore, the identification, tracking, and inversion results using experimental acoustic data from THETIS-I are in good agreement with independent field observations.