ASA 127th Meeting M.I.T. 1994 June 6-10

3aAB2. Acoustic backscatter from a dolphin.

Whitlow W. L. Au

Marine Mammal Res. Prog., Hawaii Inst. of Marine Biology, P.O. Box 1106, Kailua, HI 96734

Backscatter measurements of an Atlantic bottlenosed dolphin under controlled conditions were made. The target strength for a broadside aspect was measured as a function of frequency from 23 to 80 kHz. The relative target strength as a function of the polar angle about the animal was also measured using a transientlike click signal with a peak frequency of 67 kHz. Finally, the relative reflective strength of different portions of the animal's body was determined. 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 minimum at the tail aspect where the target strength was 21 dB below the broadside value. 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 fin and the pectoral fins, corresponding to the location of the dolphin's lungs.