APPLICATION OF THE REVERBERATION-LIMITED FORM OF THE SONAR EQUATION TO DOLPHIN ECHOLOCATION

The target detection range of two echolocating Atlantic Bottlenose dolphins as a function of target depth in Kaneohe Bay, Hawaii, was determined by Murchison [A. E. Murchison, Ph.D. dissertation, Univ. of Calif., Santa Cruz (1980)]. The threshold range decreased monotonically as the depth of the 6.35-cm-diam solid-steel sphere increased and approached the bottom. For the target lying on the bottom, the 50% correct detection threshold detection range was approximately 70 m. The scattering strength of the bottom in Kaneohe Bay at approximately the same location of the Murchison's experiment was recently measured using a simulated dolphin echolocation signal and a transducer tilted at the appropriate grazing angle. The bottom scattering strength along with the target strength of the 6.35-cm sphere and the dolphin threshold range were incorporated into the generalized form of the sonar equation for a reverberation-limited situation and a detection threshold of 4.0 dB was calculated. This detection threshold compared well with the 2.3 dB obtained in an experiment in which the dolphin was required to detect a target in the presence of a clutter screen.