Acoustic reflectivity of a dolphin.
Backscatter measurements were made on a stationary Atlantic bottlenosed dolphin under controlled conditions. Three sets of measurements were made: (1) broadside aspect target strength as a function of frequency from 23 to 80 kHz; (2) relative target strength as a function of the polar angle about the animal using a short click signal having a peak frequency of 67 kHz; and (3) relative reflective strength of different portions of the animal's body. The mean target strength at the broadside aspect decreased from -11 to -24 dB as the frequency increased from 23 to 45 kHz. As the frequency increased from 45 kHz, the target strength rose to a local maximum of -18 dB at 66 kHz and then decreased to -23 dB at 79 kHz. Maximum target strength was measured at the broadside aspect and exceeded the minimum (tail aspect) target strength by 21 dB. The target strength at the head aspect was 5 dB below that of the broadside aspect. Most acoustic energy was reflected from the area between the dorsal and pectoral fins, corresponding to the location of the dolphin's lungs.
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Hawaii Institute of Marine Biology, University of Hawaii, Kailua 96734, USA.
D000818:Animals; D004289:Dolphins / Q000502:physiology*; D013017:Sound Localization / Q000502:physiology*