Dolphin sonar target detection in noise

Abstract

Several different types of experiments have been conducted to determine the sonar detection capability of the Atlantic bottlenose dolphin. In one experiment, a dolphin's performance in detecting the presence or absence of a 7.62-cm-diam (− 28.3-dB target strength), water-filled, stainless steel sphere as a function of range was determined. The threshold range in Kaneohe Bay, Oahu, Hawaii was approximately 113 m. In another experiment, the same sphere was fixed at a range of 20 m, and the detection capability of two dolphins was determined as a function of the level of artificial masking noise. In a third experiment, a simulated phantom electronic target was used to simulate a target at 20 m, and the animal's detection performance as a function of noise was determined. Using the transient form of the sonar equation, it was found that the dolphins' performances as a function of the echo signal-to-noise ratio were very similar. Dolphins process echoes like an energy detector with an integration time of approximately 264 μs. The results from the various experiments conformed to the Urkowitz [Proc. IEEE 55, 523–531 (1967)] energy detector model. The dolphin detection sensitivity was also found to be approximately 6 to 8 dB lower than that of an ideal or matched-filter receiver.