Supercomputer modeling of delphinid sonar beam formation

Abstract

It has been established that some dolphins possess well‐developed acoustic orientation (echolocation) and information gathering abilities, though substantially less is known about the system of sound generation and beam formation. Dolphins use a narrowly focused sound beam that emanates from the forehead and rostrum during echolocation. The primary objectives of this study were to simulate the effects of modeled tissues on beam formation, and to test the viability of various hypothetical sound source locations. 2‐D simulations of sound propagation using parasagittal outlines from reconstructions of CT scans through the forehead tissues of two delphinids were conducted. Finite difference wave propagation programs were run on a Cray supercomputer. Preliminary simulations suggest that beam formation results primarily from reflection off of the skull and air sacs. These results do not depend strongly upon the precise values of velocity and density assumed for the bone. Beam angles closely approximate those measured by experimental methods for a source located in a region of the model corresponding to the monkey lip/dorsal bursae complex (MLDB), and not elsewhere. These results suggest that: (1) the skull and air sacs play the central role in beam formation; (2) the geometry of reflective tissue is more important than the exact acoustical properties assumed; and (3) experimentally observed beam patterns are best reproduced in the simulations when the sound source is placed in the region of the dolphin's head known as the MLDB (Cranford, 1988).