5aSA4. Active classification of submerged shells insonified by dolphin ``clicks.''

Session: Friday Morning, December 6

Time: 9:15

Abstract:

Many echoes returned by various submerged shells when they are insonified by dolphin echolocation clicks have been examined. The details of the experimental tests the database collected have been described elsewhere. The signal processing analysis of the returned signatures attempted to understand how the animal performed his amazing target classification feats. The echoes were examined in the time, the frequency, and the joint time--frequency domains, and it has precisely been shown how specific features observable in these domains are directly related to the physical characteristics of the shells. The processing capitalizes on certain basic resonance features contained in the echoes, and from them it determines the size, shape, wall thickness, and the material composition of the shell and its filler substance. In the same way that these features give us the identifying characteristics of the targets with hardly any calculation required, it is believed that they also give them to the dolphin. This may explain the secret of their unique success. Emphasized here are features in the combined time--frequency domain, extracted by a variety of Wigner-type distributions belonging to the bilinear (or Cohen) class. The automation of the processing does not seem to be beyond present capabilities.