Propagation of dolphin echolocation signals

Abstract

The propagational characteristics of high‐frequency echolocation signals (peak energies above 100 kHz) of the Atlantic bottlenose dolphin (Tursiops truncatus) in open waters 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‐rest” device so that the vertical beam pattern could be measured with a vertical array of hydrophones and the horizontal beam pattern could be measured with a horizontal array. The animal's 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 nearfield and farfield of the animal's sonic beam. The relationship of the signals measured with a contact hydrophone place 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 beamwidth was approximately 8.5° for both the horizontal and vertical beams. The major axis of the vertical beam was directed at an angle of 20° above the plane defined by the animal's teeth. it was also found that the farfield begins at approximately 0.5–0.6 m from the tip of the animal's rostrum.