High-Resolution Measurement of a Bottlenose Dophin's ( Trusops truncatus ) Biosonar Transmission Beam Pattern In the Horizontal Plane

• Main Authors: Finneran, James J., Branstetter, Brian K., Houser, Dorian S., Moore, Patrick W., Mulsow, Jason, Martin, Cameron, Perisho, Shuan
• Format: Text
• Language: unknown
• Published: The Aquila Digital Community 2014
• Subjects: antennas; acoustical properties; linear filters; acoustic noise; signal processing; hydrophone; energy flux density; animal echolocation; bioacoustics of mammals; regression analysis; toothed whale
• Online Access: https://aquila.usm.edu/student_pubs/107; http://lynx.lib.usm.edu/login?URL=https://asa.scitation.org/doi/pdf/10.1121/1.4895682

Previous measurements of toothed whale echolocation transmission beam patterns have utilized few hydrophones and have therefore been limited to fine angular resolution only near the principal axis or poor resolution over larger azimuthal ranges. In this study, a circular, horizontal planar array of 35 hydrophones was used to measure a dolphin's transmission beam pattern with 5° to 10° resolution at azimuths from −150° to +150°. Beam patterns and directivity indices were calculated from both the peak-peak sound pressure and the energy flux density. The emitted pulse became smaller in amplitude and progressively distorted as it was recorded farther off the principal axis. Beyond ±30° to 40°, the off-axis signal consisted of two distinct pulses whose difference in time of arrival increased with the absolute value of the azimuthal angle. A simple model suggests that the second pulse is best explained as a reflection from internal structures in the dolphin's head, and does not implicate the use of a second sound source. Click energy was also more directional at the higher source levels utilized at longer ranges, where the center frequency was elevated compared to that of the lower amplitude clicks used at shorter range.