Geoacoustic Inversion for the Workshop '97 Benchmark Test Cases Using Simulated Annealing

Abstract

This paper applies simulated annealing matched-field inversion to the Workshop '97 geoacoustic inversion benchmark test cases. The unknown parameters in these test cases include various combinations of sediment and basement geoacoustic properties (layer thickness, compressional and shear speeds, attenuations, and densities) and geometric parameters (water depth, and source range and depth). The sensitivity of the acoustic field data to the different parameters varies substantially. The simulated annealing inversion developed here minimizes a measure of mismatch based on the average Bartlett processor for acoustic data at a number of ranges. The replica pressure fields are computed by summing the modal components provided by an elastic normal mode model, which allows replica fields at multiple ranges to be calculated efficiently. A total of 15 different geoacoustic inversions are considered (three realizations each for five test cases). Excellent results are obtained in a reasonable amount of computation time for all cases. In particular, the final mismatch values are exceedingly small and relatively sensitive parameters (geometric parameters and sediment properties) are generally estimated to high precision. Relatively insensitive parameters (shear speeds and, in some cases, basement properties) are somewhat less well determined, but generally good estimates are obtained.