Analysis and Modeling of Echolocation Signals Emitted by Mediterranean Bottlenose Dolphins
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Analysis and Modeling of Echolocation Signals Emitted by Mediterranean Bottlenose Dolphins Maria Greco and Fulvio Gini Dipartimento di Ingegneria dell’Informazione, Elettronica, Informatica, Telecomunicazioni Universit`a di Pisa, via G. Caruso 16, 56122 Pisa, Italy Received 21 January 2005; Revised 31 May 2005; Accepted 22 August 2005 Recommended for Publication by Jacques Verly We analyzed the echolocation sounds emitted by Mediterranean bottlenose dolphins. We extracted the click trains by visual inspection of the data files recorded along the coast of the Tuscany with the collaboration of the CETUS Research Center. We modeled the extracted sonar clicks as Gaussian or exponential multicomponent signals, we estimated the characteristic parameters and compared the data with the reconstructed signals based on the estimates. Results about the estimation and the data fitting are largely shown in the paper. Copyright © 2006 Hindawi Publishing Corporation. All rights reserved.
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INTRODUCTION
Dolphins have a rich vocal repertoire that has been categorized into three classes: (i) broadband, short-duration clicks, called sonar clicks, used in echolocation for orientation, perception, and navigation; (ii) wideband pulsed sounds, called burst pulses, used in social contexts; (iii) narrowband frequency-modulated whistles also used in social contexts. This work is devoted to the analysis and modeling of echolocation signals emitted by the tursiops truncatus (bottlenose dolphin) living in the Tuscany Archipelago Park in both audio and ultrasonic bands. Dolphins use a range of frequencies extending from 1 to 150 KHz. Communication signals (burst pulses and whistles) have a range of frequencies from 1 to 25 KHz. Generally, sonar signals have a range of frequencies from 25 to 150 KHz. Dolphins can emit at the same time and independently sounds of various natures. Bottlenose dolphins have a remarkable range of hearing extending from less than 1 KHz to more than 120 KHz and a range of frequency-dependent sensitivity of nearly 100 dB μPa. Dolphins have excellent frequency discrimination capability and are capable of determining changes in frequency as small as 0.2–0.4%. This degree of discrimination is comparable to that observed in
humans, but it is preserved across a much broader range of frequencies. The broad range of hearing and sensitivity and excellent frequency discrimination has likely evolved as part of the biological sonar system (echolocation) used by dolphins for exploitation of a visually limited marine environment. Dolphins respond to pure-tone signals in a similar manner as humans. Therefore, the spectral filtering property of the dolphin ear can be modeled by a bank of contiguous constant-Q filters, as for humans. Other hearing characteristics that are similar for dolphins and humans include frequency discrimination and sound localization capabilities in three-dimensional space. Marine mammals do not use their mouths and throats to generate the sound—vocal chords rely on air. In dolphins, sound is produced below t
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