Design Of Bat 3D Sonar Beam Visualization System Based On Microphone Array

Animal sound signals mediate a series of life events such as predation defense,resource competition,and spouse selection,and are important information carriers for maintaining the stability and balance of animal communities.The reason why vocal animals have evolved unique sound signals is a hot topic in ecology and evolutionary biology.It is the key to elucidating the adaptive evolution of animal environments and also provides a new perspective for deciphering species formation.Bats have a special niche and unique sound behavior in the ecosystem.After a long period of evolution,their sound behaviors have diversified and complicated characteristics.Therefore,it is of great significance to analyze the function of bat echolocation for behavioral ecology.The sonar beam is a function of direction and frequency of the sound intensity of the sonar signal.The three-dimensional sonar beam of an echolocating bat determines its perception of the space environment at a specific frequency and time.The adjustment of the sonar beam ensures continuous detection of the surrounding environment by the bat in flight,selective focus on objects of interest,and continuous tracking of mobile prey.Therefore,the sonar beam is an important feature of the bat sonar system.At present,the research on three-dimensional sonar beams of bats is very few,and most of them use mathematical modeling and numerical analysis methods.In order to more accurately understand the characteristics of bat echolocation sonar beams,this paper aims to build a bat three-dimensional sonar beam visualization system based on experimental measurements to provide a more scientific,visual,and intuitive reference for bat sonar beam research.To reconstruct the three-dimensional sonar beam pattern of a bat,it is necessary to obtain the vocal intensity of the bat sonar signal in both direction and frequency.In order to achieve high-precision positioning of the bat flight position,a complete set of Vicon system including8 high-speed infrared network cameras(Vicon 5 with a collection frequency of 240 frames per second)and supporting data generation software from Oxford Metrics Limited in the United Kingdom was used to obtain bat position data.In order to realize the synchronous collection of bat barking data in space,a dual U-shaped microphone array composed of 27 ultrasonic microphones was built,and a host computer software system for multi-channel synchronous sound data collection was designed based on the Labview platform.In order to visually represent the characteristics of bat echolocation sonar beams,this paper proposes a visualization method for constructing bat three-dimensional sonar beams using array signal processing technology and three-dimensional visualization technology.Based on the sound beam spherical visualization model,Matlab platform was used to process and analyze the collected multi-channel bat echolocation data and position data to realize thethree-dimensional visualization of the bat sonar beam.First,the moving average algorithm was used to filter the bat flight trajectory,the bat flight direction was obtained by the central difference method,and the coordinate system was transformed to establish the bat as the center coordinate system.Secondly,the sound source localization algorithm based on Time Difference Of Arrival(TDOA)is studied,the delay time is estimated using the basic cross-correlation algorithm,and the excitation signal with a known position is generated to determine the arrangement coordinates of the microphone array.The location of the algorithm is analyzed.Then,the atmospheric sound propagation and attenuation theory based on the point source model is used to compensate and correct the multi-channel bat sonar data.The single-call data of bats is extracted using the Voice Activity Detection(VAD)method,and spectrum analysis is performed to obtain the bat sound intensity parameters.By displaying the sound direction and sound intensity of the extracted bat sonar signal in a spherical coordinate system centered on the bat,it is displayed with a color chart to achieve the purpose of visualizing the bat sonar beam.Finally,the Sobel edge detection method was used to detect the sonar beam edge in the binary sonar beam pattern,and the bat sonar beam parameters were extracted.In order to verify the effectiveness of the bat three-dimensional sonar beam visualization system,a constant-frequency bat named Rhinolophus ferrumequinum obstacle avoidance flight experiment was conducted.A bat flight experimental platform was set up in a sound absorption room with a volume of 7 × 4.5 × 2.7m~3,and the multi-channel echolocation data and position data of 5 constant-frequency R.ferrumequinum bats in 300 obstacle avoidance flight experiments were collected.The designed bat 3D sonar beam visualization system was used to obtain the 3D sonar beam and sonar beam parameters of R.ferrumequinum's sonar waves.This visualization system test results and the sonar beam parameter extraction results show that as the avoiding obstacles gradually approaching the exit,R.ferrumequinum will increase its beam width in both the horizontal and vertical directions.The bat sonar beam visualization method system proposed in this paper can not only be used to study the bat sonar beam adjustment strategy when the constant frequency bat avoids obstacles,but also to study other characteristics research of bat sonar beam systems.