NONLINEAR INVERSION FOR OCEAN-BOTTOM PROPERTIES

High-resolution methods based on simulated annealing and full-wave sound propagation models are developed for nonlinear inversion for ocean-bottom properties. Simulated annealing is used to search the high-dimensional parameter space of ocean bottoms for the parameter set corresponding to the best replica field. The parabolic equation method is used to solve range-dependent inversion problems. For data taken by Lynch et al. from a range-dependent region of the Gulf of Mexico [J. Acoust. Soc. Am. 89, 648-665 (1991)], this approach achieves excellent agreement between the theoretical and measured acoustic pressures. The recovered sediment parameters suggest that a sound-speed boundary layer exists in the upper part of the sediment and that the depth of an interface in the sediment is range dependent. For locally range-independent problems, inversion is performed in wave-number space. Large efficiency gains are possible with this approach because the number of wave-number samples required for inversion is much smaller than the number of wave-number samples required for computing replica fields.