R. J. Cederberg
Michael D. Collins
Naval Res. Lab., Washington, DC 20375
The forward model is an important component of a matched-field inversion algorithm. The forward model must be efficient because it is often necessary to compute a large number of replica fields during the parameter search. An efficient forward model will be described for an experimental configuration involving a source and a vertical array separated by up to several tens of wavelengths in range. The operators of the self-starter and the split-step Pade solution are combined into a single operator that acts on a delta function to give the field on the array. On a parallel-processing computer, this approach provides the replica field in the computation time it takes to solve a single tridiagonal system in a conventional parabolic equation algorithm. This efficiency gain is not achieved by sacrificing accuracy. The approach typically involves the solution of about ten tridiagonal systems. Finite-difference based separation of variables solutions typically require the solution of hundreds or thousands of similar tridiagonal systems. The efficiency of the rapid forward model will be demonstrated for the matched-field inversion problem of estimating the parameters of the ocean bottom.