ASA 125th Meeting Ottawa 1993 May

5aAO6. Estimation of seismoacoustic properties of the ocean bottom by matched-field inversion.

N. Ross Chapman

M. L. McKirdy

Defence Res. Establishment Pacific, FMO Victoria, BC V0S 1B0, Canada

Matched-field processing of acoustic field data provides a straightforward but powerful method for estimating the elastic properties of the ocean bottom. The success of the inversion depends in part on having an efficient algorithm for searching the multidimensional parameter space of ocean bottom models. This paper considers the use of simulated annealing as a search algorithm for matched-field inversion (MFI), and presents results of inversions for data obtained from the PACIFIC ECHO experiments. A method is described for adaptively guiding the annealing process by adding a feedback loop that assesses the significance of the matched-field correlations for each parameter. The search is guided to regions of the parameter space associated with above-average correlations. Simulations for a vertical line array (VLA) are presented to demonstrate the limits on performance of MFI with respect to uncertainties in experimental geometry, and low signal-to-noise ratio. The method is applied to VLA data from thin-sediment PACIFIC ECHO environments where the age of the upper oceanic crust varied from 0.1 to 66 million years. The MFI results indicate an age dependence of the compressional and shear wave speeds of the basalt, and the values are significantly lower than those obtained for thickly sedimented crust.