Propagation of Atlantic bottlenose dolphin echolocation signals

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Abstract
The propagational characteristics of high‐frequency echolocation signals (peak energies above 100 kHz) of the Atlantic bottlenose dolphin T u r s i o p s t r u n c a t u s in open water were determined by a series of measurements conducted while the animal performed a target‐detection task. The animal was trained to station in a ’’chin‐cup’’ device so that the vertical beam pattern of the projected echolocation signals could be measured with a vertical array of hydrophones and the horizontal beam pattern could be measured with a horizontal array. The projected echolocation signals as a function of distance from the animal out to 2 m were measured with a horizontal array of hydrophones placed directly in front of the animal. These measurements were used to study the relationship of the signals in the near and far fields of the animal sound source. The relationship of the signals measured with a contact hydrophone placed on the animal’s rostrum and on the melon with the signals measured at 1 m and at the target was also studied. It was found that the 3‐dB broadband beamwidth was approximately 10° in both the horizontal and vertical planes. The major axis of the vertical beam was directed at an agnle of 20° above the plane defined by the animal’s teeth. It was also found that the acoustic pressure of the echolocation signals began to satisfy the farfield criterion of decaying inversely with distance at approximately 0.5–0.6 m from the tip of the animal’s rostrum.

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