title: Nearfield and farfield measurements of dolphin echolocation beam patterns: No evidence of focusing.
abstract: The potential for bottlenose dolphins to actively focus their biosonar transmissions was examined by measuring emitted clicks in four dolphins using horizontal, planar hydrophone arrays. Two hydrophone configurations were used: a rectangular array with hydrophones 0.2 to 2 m from the dolphins and a polar array with hydrophones 0.5 to 5 m from the dolphins. The biosonar task was a target change detection utilizing physical targets at ranges from 1.3 to 6.3 m with all subjects and "phantom" targets at simulated ranges from 2.5 to 20 m with two subjects. To provide a basis for evaluating the experimental data, sound fields radiated from flat and focused circular pistons were mathematically simulated using transient excitation functions similar to dolphin clicks. The array measurements showed no evidence that the dolphins adaptively focused their click emissions; axial amplitudes and iso-amplitude contours matched the pattern of the simulation results for flat transducers and showed a single region of maximum amplitude, beyond which spherical spreading loss was approximated.
authors: U.S. Navy Marine Mammal Program, Space and Naval Warfare Systems Center Pacific, Code 71510, 53560 Hull Street, San Diego, California 92152, USA.
authors: James J
authors: JJ
authors: Finneran
authors: National Marine Mammal Foundation, 2240 Shelter Island Drive, #200, San Diego, California 92106, USA.
authors: Jason
authors: J
authors: Mulsow
authors: National Marine Mammal Foundation, 2240 Shelter Island Drive, #200, San Diego, California 92106, USA.
authors: Brian
authors: B
authors: Branstetter
authors: National Marine Mammal Foundation, 2240 Shelter Island Drive, #200, San Diego, California 92106, USA.
authors: Patrick
authors: P
authors: Moore
authors: National Marine Mammal Foundation, 2240 Shelter Island Drive, #200, San Diego, California 92106, USA.
authors: Dorian S
authors: DS
authors: Houser
mesh_terms: D000818:Animals; D050681:Bottle-Nosed Dolphin / Q000502:physiology*; D004455:Echolocation / Q000502:physiology*; D005260:Female; D008297:Male; D013016:Sound; D013018:Sound Spectrography; D014159:Transducers