Biosonar signal propagation in the harbor porpoise's (Phocoena phocoena) head: The role of various structures in the formation of the vertical beam

Abstract

Harbor porpoises (Phocoena phocoena) use narrow band echolocation signals for detecting and locating prey and for spatial orientation. In this study, acoustic impedance values of tissues in the porpoise's head were calculated from computer tomography (CT) scan and the corresponding Hounsfield Units. A two-dimensional finite element model of the acoustic impedance was constructed based on CT scan data to simulate the acoustic propagation through the animal's head. The far field transmission beam pattern in the vertical plane and the waveforms of the receiving points around the forehead were compared with prior measurement results, the simulation results were qualitatively consistent with the measurement results. The role of the main structures in the head such as the air sacs, melon and skull in the acoustic propagation was investigated. The results showed that air sacs and skull are the major components to form the vertical beam. Additionally, both beam patterns and sound pressure of the sound waves through four positions deep inside the melon were demonstrated to show the role of the melon in the biosonar sound propagation processes in the vertical plane.

Identification Algorithm of Uncertain Sonar Signals in Complex Marine Environment

“…The instantaneous frequency obtained after the direct Hilbert transform can also be negative which has no physical meaning. To solve this problem, empirical mode decomposition [8] is adopted to deal with the problem:…”

“…Therefore, understanding of underwater conditions becomes particularly important [1][2]. As an effective means of underwater detection and communication, underwater acoustic signals have been paid more and more attention by people [3].…”

Finite element simulation of broadband biosonar signal propagation in the near- and far-field of an echolocating Atlantic bottlenose dolphin (Tursiops truncatus)

“…There is a general consensus on the roles of the skull and air sacs from the results of prior numerical simulation research and experimental measurements (Aroyan et al, 1992;Houser et al, 2004;Au et al, 2010;Finneran et al, 2014;Cranford et al, 2014;Wei et al, 2014;Song et al, 2016;Wei et al, 2016;Wei et al, 2017;Wei et al, 2018). Although there are differences in the geometry of the air sacs and rostrum across species, these structures act as acoustic reflectors because of impedance mismatch between them and the surrounding soft tissues directing the waves forward to form a radiating beam.…”

“…In order to investigate the specific details of how these structures function and further increase our understanding of the mechanics of biosonar sound production and propagation, numerical modeling techniques have been applied to simulate the biosonar systems of odontocetes (Aroyan et al, 1992;Aroyan et al, 2001;Krysl et al, 2006;Cranford et al, 2014;Wei et al, 2014;Wei et al, 2016;Song et al, 2016;Wei et al, 2017;Wei et al, 2018). There is a general consensus on the roles of the skull and air sacs from the results of prior numerical simulation research and experimental measurements (Aroyan et al, 1992;Houser et al, 2004;Au et al, 2010;Finneran et al, 2014;Cranford et al, 2014;Wei et al, 2014;Song et al, 2016;Wei et al, 2016;Wei et al, 2017;Wei et al, 2018).…”

“…The numerical simulation results suggest the melon does slightly narrow the beam but it also functions as a collimator and impedance transformer. From a two-dimensional (2D) numerical simulation of sound propagating through a dolphin's head, Wei et al (2017) showed in a pictorial fashion how echolocation signals propagated through the melon of a harbor porpoise's head in the vertical plane. They also calculated the beam pattern and sound pressure at different positions as the sound traveled through the melon.…”