Biosonar beam formation in the bottlenose dolphin: Evidence for focusing in stages.

Abstract

The idea that a dolphin biosonar beam is focused in a series of stages was put forth by Dr. Norris more than 50 years ago. Development of our finite element modeling (FEM) tools allowed us to test this hypothesis. We constructed an FEM model of a bottlenose dolphin (Tursiops truncatus) head from CT scans and tissue property measurements, and simulated the formation of the sonar beam. The sound transmission system within the dolphin forehead contains several tissue elements. The model allowed us to tease apart the functional contributions that these structures make to the formation of an echolocation beam. The simulations showed that the direction of the beam was consistent with prior biosonar investigations and illustrated that the narrowing of the sound transmission beam increases with various levels of refinement in structural (tissue) complexity. It appears as if each additional structure such as the melon, the air spaces, source location, and configuration adds to the effect of narrowing the beam, and their combined contribution is significant. [Work supported by the Chief of Naval Operations (Grant No. CNO45).]