Wave shape estimation of delphinid sonar signals, a parametric model approach

A parametric model estimation is presented for a number of echo location clicks of Thrsiops truncatus and Sousa chinensis. Our candidate for the signal-fitting procedure is the Gabor elementary signal; a Gaussian-enveloped harmonic oscillation as proposed by Gabor (1947). Application of this wave form is indicated by the low product of time duration and frequency bandwidth, which reaches the theoretical lower bound in the case of the Gabor signal. Examples are taken from a portfolio of delplunid sonar signals collected over the past 16 years by the Delft Dolphin Research Team. The portfolio covers echo location signals recorded in restricted environments and from free-ranging dolphins. The Sousa chinensis sonar click has not been previously described. Agreement of the actual wave form and the proposed model on an energy basis leaves us with a figure of merit down to 0.3% for a Tursiops echolocation signal. The possible occurrence of internal reverberations and their influence on the description of the sonar click are incorporated in the overall model forming.