Numerical study of biosonar beam forming in finless porpoise (Neophocaena asiaeorientalis)

Abstract

Finless porpoise (Neophocaena asiaeorientalis) is known to use the narrow band signals for echolocation living in the Yangtze River and in the adjoining Poyang and Dongting Lakes in China. In this study, the sound velocity and density of different tissues (including melon, muscle, bony structure, connective tissues, blubber, and mandibular fat) in the porpoise’s head were obtained by measurement. The sound velocity and density were found out to have a linear relationship with Hounsfield unit (HU) obtained from the CT scan. The acoustic property of the head of the porpoise was reconstructed from the HU distribution. Numerical simulations of the acoustic propagation through finless porpoise’s head were performed by a finite element approach. The beam formation was compared with those of the baiji, Indo-pacific humpback dolphin, and bottlenose dolphin. The role of the different structures in the head such as air sacs, melon, muscle, bony structure, connective tissues, blubber, and mandibular fat on biosonar beam was investigated. The results might provide useful information for better understanding of the sound propagation in finless porpoise’s head.