Temporal signal processing of dolphin biosonar echoes from fish prey

Abstract

Dolphins that emit whistle signals (except for sperm whales) project short broad- band biosonar clicks containing about 5 to 7 cycles with exponential decaying envelope and Q (center frequency over bandwidth) between 2 and 3. The broadband nature of the biosonar clicks allow for good temporal resolution of echo highlights, which in turn allows for the discriminations of different targets including fish prey. Most of the echoes from fish originate from signals reflecting off the swim bladder of fish. Different species of fish have swim bladders of different shape, size, and orientation so that echoes from these species can often be discriminated from temporal cues. The echoes contain many highlights as the signals reflect off different surfaces and parts of the fish body and swim bladder. This presentation will discuss the temporal characteristics of echoes from fish prey, which are highly aspect dependent and will discuss the six temporal parameters that were used in a support vector machine (SVM) to discriminate between species. Results suggest how dolphins can classify fish based on their echoes and provide some insight as to which features might enable the classification.