title: High-resolution measurement of a bottlenose dolphin's (Tursiops truncatus) biosonar transmission beam pattern in the horizontal plane.
abstract: 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.
authors.affiliation: U.S. Navy Marine Mammal Program, Space and Naval Warfare Systems Center Pacific, Code 71510, 53560 Hull Street, San Diego, California 92152.
authors.forename: James J
authors.initials: JJ
authors.lastname: Finneran
authors.affiliation: National Marine Mammal Foundation, 2240 Shelter Island Drive, #200, San Diego, California 92106.
authors.forename: Brian K
authors.initials: BK
authors.lastname: Branstetter
authors.affiliation: National Marine Mammal Foundation, 2240 Shelter Island Drive, #200, San Diego, California 92106.
authors.forename: Dorian S
authors.initials: DS
authors.lastname: Houser
authors.affiliation: National Marine Mammal Foundation, 2240 Shelter Island Drive, #200, San Diego, California 92106.
authors.forename: Patrick W
authors.initials: PW
authors.lastname: Moore
authors.affiliation: National Marine Mammal Foundation, 2240 Shelter Island Drive, #200, San Diego, California 92106.
authors.forename: Jason
authors.initials: J
authors.lastname: Mulsow
authors.affiliation: Naval Research Enterprise Internship Program (NREIP), 1818 N Street Northwest, Suite 600, Washington, DC 20036.
authors.forename: Cameron
authors.initials: C
authors.lastname: Martin
authors.affiliation: Department of Psychology, University of Southern Mississippi, 118 College Drive, #5025, Hattiesburg, Mississippi 39406.
authors.forename: Shaun
authors.initials: S
authors.lastname: Perisho
mesh_terms: D000161:Acoustic Stimulation; D000162:Acoustics / Q000295:instrumentation; D000818:Animals; D001307:Auditory Perception; D001522:Behavior, Animal; D050681:Bottle-Nosed Dolphin / Q000502:physiology* / Q000523:psychology; D004455:Echolocation; D004867:Equipment Design; D008297:Male; D009038:Motion; D011312:Pressure; D011571:Psychoacoustics; D012815:Signal Processing, Computer-Assisted; D013016:Sound; D013018:Sound Spectrography; D013997:Time Factors; D014160:Transducers, Pressure; D014828:Vocalization, Animal