Target classification in shallow waters by time-frequency filtering

Abstract

Efficient sonar target recognition must be based on a set of relevant parameters extracted from the echoes and directly related to the geometrical and mechanical properties of the target. Previous studies have shown that a wideband approach based either on simple spectral modeling or on time-frequency analysis is particularly suited to the understanding of echo formation mechanisms and to the classification in the free field (recognition rate as high as 96%). In shallow waters, the influence of the boundaries considerably reduces the performance of these methods due to the presence of several spurious echoes superimposed to the target echo components. Classification performance can be improved by using a method based on time-frequency filtering matched to a free-field reference target response. This method will be described and applied to experimental data issued from tank experiments. Several typical configurations have been first investigated: free-field, semi-infinite space for a set of targets (shells and solid targets of different shapes). It gives more than encouraging results, especially for the recognition of a spherical shell (about 100% of recognition). The method is now extended to a shallow-water configuration including seabed interaction.