Research On The Mechanisms Of Biosonar Operation In The Representative Hunting Behaviour Of Cetaceans

Over millions of years of evolution,cetaceans have developed a sonar system that can be adapted to various marine environments.The cetacean uses its sonar system mainly for underwater hunting,on the one hand to obtain vital target information during hunting,and on the other hand to repel and round up prey.The study of cetacean biosonar mechanisms is therefore of great importance for the improvement of existing sonar systems.However,the poor controllability of biological experiments in cetacean biology has led to research progressing beyond the observation of signals and biological behaviour to the mechanics of cetacean biogenic sonar behaviour.As a result,it is still impossible to explain how cetaceans use their biosonar to achieve complex hunting functions,and this has limited the development of bionic sonar.This paper therefore combines acoustic simulation and signal analysis methods to investigate the mechanism of biosonar operation in cetacean hunting behaviour.As two major groups of cetaceans,toothed whales and baleen whales are fundamentally different in terms of their hunting organs and hunting habits.This paper therefore investigates the mechanism of bio-sonar operation in toothed whales and baleen whales separately.On the one hand,a static model is developed to investigate the information processing methods used by toothed whales to extract target features,based on the adaptive target detection,differentiation and identification processes of toothed whales.Based on this static model,the information processing mechanism of the toothed whale is investigated based on the active modulation of target features.On the other hand,the physical mechanism of baleen whales actively controlling their biosonar to sound in bubble nets to form 'sound walls' is investigated in relation to the biological behaviour of baleen whales' biosonars in conjunction with seizures.Based on known biological experimental results of toothed whale detection of underwater suspended and buried targets,this paper proposes a finite element-based virtual echo generation method to construct a simulated toothed whale echo information extraction model.Firstly,the sonar signals and directional beams emitted by the measured toothed whales are combined to simulate the bio-sonar sounding unit.In addition,the virtual echo generation method generates echoes of hovering targets and buried targets respectively to build a complete target echo information processing link for the detection and identification process of toothed whales.Combining the above transceiver signal characteristics and parameters,the physical generation mechanism of underwater target echoes is analysed by elastic scattering theory.The time domain results show that the tooth whale echolocation signal can excite the re-radiated echoes of the elastic column shell to carry target characteristic information.In order to determine the characteristic components of the echoes used by the toothed whale to detect and identify the target,this paper uses the fractional order Fourier transform method to filter out the specular reflection components and extract the pure elastic echoes.Based on this,we simulated the toothed whale's experiment of distinguishing the thickness of the column shell through pools and numerical simulations,and compared the difference in target recognition performance between the intact and elastic echoes,showing evidence that the toothed whale may use the time-frequency characteristics of the elastic echo component to achieve subtle perceptual distinction between different targets.In this paper,we model the buried target of a toothed whale,which is another important target detection mode,and simulate the process of feeding on prey in the mud and sand.The equivalent fluid model is used to model the sandy and muddy seabed separately,and the equivalent fluid density,sound velocity and corresponding sound attenuation coefficients are calculated analytically for the sandy and muddy seabed.The seabed transmission coefficients of the emitted beams of the toothed whales at different grazing angles were calculated by combining the seabed model with the acoustic model of the head of the toothed whale,and the effects of the grazing angle and the bottom texture on the received echoes of the toothed whale were quantified.The buried target echoes were simulated at the optimum swept angle.The results suggest that may adapt their transmitting beams to the complex background environment of different seafloor substrates by adjusting the grazing angle of their transmitting beams.The results also provide a static analytical model for further research into the biological mechanisms of toothed whale detection of buried targets.Based on a static analysis model of toothed whale target detection,this paper focuses on the experimental target detection data of beluga whales and wide-nosed dolphins in order to explore the dynamic process of active modulation of biogenic sonar emission parameters by target characteristic information.In order to extract signals within the echolocation pulse train,this paper proposes a correlation detector with the biological vocalisation pattern as the correction criterion to correct for missed and false detections after extraction.Through the temporal and frequency analysis of a series of single-pulse echolocation signals,it is found that the energy distribution within the tooth whale detection burst can be continuously adjusted by the multi-component structure of the single-pulse signal,and that the energy distribution within the burst can be classified into constant frequency type and swept frequency type.This paper proposes a bionic dynamic pulse train model,which reconstructs the measured data and uses a static finite element model to generate virtual echoes in biological experiments,and establishes a dynamic transceiver link for tooth whale target detection to reconstruct the signal transceiver process in tooth whale target detection experiments.From the results,it is found that the swept frequency type burst can achieve fine target feature extraction by improving the local signal-to-noise ratio,while the constant frequency type will focus on observing target features in specific frequency bands,which implies that the toothed whale may achieve optimal target detection and identification by transmitting echolocation bursts with different types of energy distribution.This paper focuses on the sonar-assisted behaviour of baleen whales,with a focus on the most representative humpback whale bubble net sound wall hunting behaviour.Firstly,a three-dimensional bubble net model is constructed based on the geometric parameters of the bubble net,and a linear equivalent modelling of the medium inside the bubble net is established based on the measured bubble size distribution at sea,and the acoustic propagation parameters of the bubble net model are calculated analytically.The 3D finite element model is used to numerically calculate the sound field of the 3D spiral bubble network and the cylindrical bubble network,and the effects of bubble size distribution and gas volume fraction on the sound effect of the bubble network are discussed.The results show that humpback whale hunting sound can produce a strong concentrating effect within the bubble net,which can generate a strong sound pressure field and mass velocity field within the bubble net wall,while a relatively 'quiet' area will be formed in the centre of the bubble net wrapped in bubble-free water.In order to assess the response of prey to the bubble net wall,this paper combines the hearing curve of herring with the resonant frequency of the swim bladder to demonstrate that the wall effect of humpback whale bubble nets can effectively assist humpback whales to achieve large-scale seizures,and further reveals the mechanism of seizure by humpback whale bio-sonar.