Propagation of beluga whale echolocation signals

Abstract

The propagation characteristics of high-frequency echolocation signals (peak energies above 100 kHz) of the beluga whale, Delphinapterus leucas were determined by a series of measurements conducted while the animal performed a target-detection task. The whale was trained to station on a “bite-plate” so that its projected beam could be measured in the vertical and horizontal planes using a vertical and horizontal array of hydrophones, respectively. The transitional region between the acoustic near- and farfields was also located by using an array of hydrophones that extended directly in front of the animal, in the horizontal plane. Three distinct modes of signals were observed. Mode 1 signals had interclick intervals that were longer than the time required for the signals to travel to the target and back (two-way transit time). Mode 2 signals had interclick intervals shorter than the two-way transit time, and mode 3 signals had high-repetition rates with interclick intervals from 1–3 ms. The vertical and horizontal beam patterns of the mode 1 signals had similar 3-dB beamwidths of approximately 6.5°. The major axis of the vertical beam was directed at an angle of 5° above the plane defined by the animal's teeth. The near- to farfield transistion region was found to be approximately 0.88 to 1 m from the tip of the animal's mouth.