Research On The Method Of Coastal Acoustic Tomography Flow Measurement

Coastal acoustic tomography is one of the main methods for large area observation in offshore ocean observation.Traditional marine survey methods often collect marine environmental parameters by carrying ADCP,CTD and other instruments on scientific research ships,but this method can only measure the marine environmental information of points or lines,and cannot obtain large-scale and long-term synchronous marine environmental information in real time.The coastal acoustic tomography observation technology can make up for the shortcomings of traditional marine survey methods.We can obtain large-scale,long-term,continuous marine environmental elements information,such as seawater temperature,velocity,salinity,etc.by setting up a few stations and placing fewer instruments.This paper mainly studies the application of coastal acoustic tomography in flow measurement.The basic principle of coastal acoustic tomography flow measurement is that the average velocity on the station line can be deduced by the time difference of acoustic signal reciprocal propagation between two stations,and the horizontal two-dimensional flow field can be retrieved by gridding the average velocity on multiple stations and multiple lines.In view of the shortage of river flow measurement and monitoring in China,this paper proposes the idea of using coastal acoustic tomography technology to measure river flow,realizes the purpose of long-term monitoring of river flow through coastal acoustic tomography technology,and verifies the feasibility of flow measurement method based on coastal acoustic tomography technology.This paper includes the introduction of the background of coastal acoustic tomography technology,the sound line simulation of the experimental environment and the field experimental measurement results.Firstly,the propagation theory of underwater acoustic signal based on sound line model is introduced,and the theoretical methods of measuring the average velocity between two stations and retrieving the horizontal velocity field between multiple stations by coastal acoustic tomography are introduced.In this paper,a coastal acoustic tomography system is used to measure the flow in the channel where Datong hydrological station is located.In the experimental area,the vertical sound velocity profile of the Yangtze River was obtained by vertical lowering and upward pulling thermohaline bathymeter,which was applied to the bellhop ocean acoustic propagation model to simulate the sound line propagation between stations in the experimental area.In this experiment,three acoustic tomography stations were set up.Based on the average velocity of the two measuring lines across the section,we calculated the average velocity of the river,and used single line and double line methods to calculate the average flow of the section.The error between the single line method and the Yangtze River hydrological network is less than 7%.In order to verify the feasibility of acoustic tomography observation of velocity field in the actual sea area,a small-scale horizontal flow field observation experiment was carried out in the sea area east of zhairuoshan island in Zhoushan by using four coastal acoustic tomography systems.The horizontal velocity field and the direction of the coastal water in the east of zhairuoshan island are successfully observed,which fully demonstrates the feasibility of using the coastal acoustic tomography technology to observe the small-scale flow field.