Geoacoustic inversion in multiple source environments

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Date

2004-05-22

Authors

Ritterman, Eric Andrew

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Abstract

The sensitivity of geoacoustic inversion to noise corruption makes it difficult to implement a method to invert using ships of opportunity as sources because one cannot always assume a single source environment. Current methods to reject interfering signals in the inversion methodology are not adequate to suppress a loud interferer dominating a quiet source of interest. A spatial filtering method is tested on experimental data collected in the Gulf of Mexico in 1998. The filtering is intended to reject interfering signals while maintaining inversion sensitivity to geoacoustic parameters. The filter operates by rejecting unwanted signals incident on an array from different angles. It relies on a transformation of acoustic data from the element level into beam coefficients, which are then attenuated according to some desired filter response. These attenuated data are then transformed back to the element level. Several issues must be addressed in filter implementation: pseudo-inverse tolerance, sediment layering, and shallow angle contributions. Sensitivity of pseudo-inverse tolerance and shallow angle contributions increase when using arrays operating outside design frequency limits. However, even with sparsely sampled arrays, correct filter implementation can improve inversion results of a quiet source when in the presence of a loud interferer

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