Matched-field replica model optimization and bottom property inversion in shallow water

Matched-field replica models based on an inaccurate knowledge of geoacousti c parameters such as bottom attenuation, shear, and interfacial sound-speed discontinuities, can predict an incorrect number of propagating modes for a shallow-water channel. The resulting degradation in the matched-field amb iguity surface can be substantially reduced by obtaining optimal replica mo dels via modal-sum-limit optimization or bottom-property inversion. The use of these techniques for multi-tone (70, 95, 145, and 195 Hz) source-tow da ta recorded near San Diego during the first Shallow-Water Evaluation Cell E xperiment (SWellEX-1) significantly increased matched-field correlation lev els and improved source localization relative to results obtained with a pr evious nonoptimized model. The predicted number of propagating modes was al so reduced substantially. The inversion for bottom properties (attenuation, interfacial sound-speed discontinuities, no shear) provided sediment atten uation estimates which agree well with Hamilton's models and were an order- of-magnitude greater than that used in the nonoptimized model, which accoun ts for the reduction in the number of modes. A simulated modal decompositio n using the inverted optimal replica model verifies the number of modes pre dicted by the modal-sum-limit optimization. [S0001-4966(00)00103-X].