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<p>In January 2002, time synchronized underwater pictures and echolocation signals of a free-swimming bottlenose dolphin were recorded. More than 80 experimental trial runs were recorded at the Space and Naval Warfare Center's Marine Mammal Facility in San Diego, California. The apparatus recorded 30 underwater images per second and sonar signals up to 400 kHz. Data analysis shows wide transmitting beam patterns at frequencies lower than 135 kHz contain a majority of the energy in the echolocation signal, agreeing with previously documented work. However, further analysis shows significant energy at higher frequencies. Early in the experiment, the dolphin steered narrow high frequency signals and adjusted the energy content in those different frequencies while scanning the target. To emit these high frequency components, the dolphin changed the wave shape of the emitted sound pulse. As the experiment progressed, the animal's task became routine and the high frequency signals were noticeably absent until low frequency noise was projected into the water, at which time the high frequencies were again present in the emitted sound pulses. Resultant transmitting beam patterns provide excellent evidence of the presence of high frequency sound emissions, and also indicate how these signals are used during echolocation tasks.
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<br>Subjects: Echolocation (Physiology); Bottlenose dolphin; Mines (Military explosives); Detection; Biosonar; Tursiops Truncatus; bottlenose dolphin; mine detection</div>
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Lemerande, Tobias J.</div>
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