Modeling of the near to far acoustic fields of an echolocating bottlenose dolphin and harbor porpoise

Abstract

Echolocation signals emitted by odontocetes can be roughly classified into three broad categories: broadband echolocation signals, narrowband high-frequency echolocation signals, and frequency modulated clicks. Previous measurements of broadband echolocation signal propagation in the bottlenose dolphin (Tursiops truncatus) did not find any evidence of focusing as the signals travel from the near-field to far-field. Finite element analysis (FEA) of high-resolution computed tomography scan data was used to examine signal propagation of broadband echolocation signals of dolphins and narrowband echolocation signals of porpoises. The FEA results were used to simulate the propagation of clicks from phonic lips, traveling through the forehead, and finally transmission into the water. Biosonar beam formation in the near-field and far-field, including the amplitude contours for the two species, was determined. The finite element model result for the simulated amplitude contour in the horizontal plane was consistent with prior direct measurement results for Tursiops, validating the model. Furthermore, the simulated far-field transmission beam patterns in both the vertical and horizontal planes were also qualitatively consistent with results measured from live animals. This study indicates that there is no evidence of convergence for either Tursiops or Phocoena as the sound propagates from the near-field to the far-field.

The Distinctive Forehead Cleft of the Risso’s Dolphin (Grampus griseus) Hardly Affects Biosonar Beam Formation

“…More details can be found in Wei et al [ 13 , 14 ], where the same approach was used to construct FE sound propagation models for a harbor porpoise and a bottlenose dolphin, respectively. The finite element analysis (FEA) results of the two species matched direct measurements from live, echolocating animals [ 13 , 14 , 20 ], proving the reliability of this approach.…”

“…We set a point source (i.e., monopole) at the right set of phonic lips since the size of the phonic lips was significantly smaller than the wavelengths [ 10 , 30 ]. The waveform of the source was modeled as a short-duration, broadband pulse, consisting of a dampened oscillation [ 20 ]. It simulated the instantaneous process of the right phonic lips opening and slapping back together after the airstream passed between them, causing the associated surrounding tissues to vibrate.…”

“…Finite-element (FE) models have been widely used to investigate the mechanisms involved in sound production, propagation, and reception in a number of animal groups, including odontocete species [ 10 , 11 , 13 , 14 , 15 , 17 , 18 , 19 , 20 ], bats [ 21 ], and fish [ 22 , 23 , 24 ]. These models are typically based on computed tomography (CT) images of the anatomical structures.…”