Matched field inversion of broadband data using the freeze bath method

This paper presents a statistical freeze bath method for geoacoustic invers ion that emphasizes the search for a distribution of models that fit the da ta well. Contrary to simulated annealing optimization, the freeze bath samp les the multidimensional model parameter space at constant freeze probabili ty, corresponding to fixed temperatures for each parameter. The sampling pr ocess uses a heat bath algorithm asa Boltzmann sampling tool to carry out a global search over the model parameter space. The conventional heat bath a lgorithm is modified to sample on a fuzzy grid in order to access the entir e range of parameter values. The inversion provides a set of good models th at indicates how well the model parameters are constrained by the data, and reveals the degree of correlation between parameters. The efficiency of th e search process is improved by reparameterizing the original model paramet ers to a new set based on the eigenvectors of the model covariance matrix. The inversion performance of the freeze bath is demonstrated using simulate d data for a simple geoacoustic model. The method is applied to shallow wat er broadband data obtained during the Hare Strait geoacoustic tomography ex periment to estimate a geoacoustic profile at the site. (C) 1999 Acoustical Society of America. [S0001-4966(99)04910-3].