Time-frequency filters for target classification

This paper presents a new sonar target classification approach based on the use of time-frequency filters. Their design is carried out from the free f ield response of a reference target, and more precisely from the analysis o f echo formation mechanisms in the time-frequency plane. The study of the r elevance and the robustness of this approach in approximately real sonar co nditions is conducted from experimental measurements in a tank. A data base is set up that contains a large set of target responses in the free field, near different interfaces and in waveguide situations. First, the efficien cy of the method for the recognition of a nickel molybdenum spherical shell , corresponding to a class of man made targets whose size is much smaller t han the sonar beam (finite size) is shown (100% of recognition). Second, a classification procedure between different targets of finite size is conduc ted: more than 85% of good classification is obtained (except for the marbl e solid target). Finally, in the presence of numerical noise, the method is found to be robust even for a low signal to noise ratio. (C) 1999 Acoustic al Society of America. [S0001-4966(99)04510-5].