Efficient Acoustic Field Computation for Estimating Geoacoustic Bottom Parameters Using Matched-Field Inversion

Abstract

Matched-field inversion for source location, environmental properties, or a combination of the two (focalization) is based on comparing acoustic fields measured at an array of receivers to replica fields predicted for a variety of possible source positions and/or environmental parameters using a numerical propagation model. Although this approach is conceptually straightforward and widely applicable, it requires a large number of replica field computations and can be impractically slow if the propagation modeling is not carried out in an efficient manner. This is particularly true for environmental inversion and focalization problems where the expanded parameter search space generally requires a very large number of replica field computations, even if a relatively efficient optimization algorithm such as simulated annealing (SA) is employed. Therefore, to apply these methods to realistic problems, it is important that the propagation modeling be performed as efficiently as possible.

This paper presents a method of inversion using SA optimization and rapid acoustic field modeling based on the use of pre-computed mode functions and wave numbers which are stored in ‘look-up’ tables. The method is described together with the results of a study which established the optimum size of the grid elements required to achieve accurate propagation modeling and reliable matched-field inversion using this ‘look-up’ table method. An example is presented for a typical Arctic environment in which several of the unknown geoacoustic parameters are estimated using this efficient inversion method.