Design And Analysis Of Ultrasonic Measurement Method For Red Tide Algae

The outbreak of red tide will seriously affect the Marine ecosystem and environment,causing casualties and losses.Combining underwater acoustics with Marine information technology to develop microalgae acoustic detection technology has great application value for the monitoring,prediction,as well as prevention and control of Marine ecological disasters.At present,red tide monitoring is mainly realized by counting algae cells through on-site sampling,or indirectly measuring chlorophyll in seawater by sensors and remote sensing.Although underwater acoustic monitoring has the advantage of real-time in situ monitoring,it is still difficult in the research to realize accurate concentration measurement and particle size analysis for micrometer scale algae monitoring.Based on the acoustic scattering of common red tide dinoflagellates,the theoretical numerical simulation of concentration estimation was discussed and analyzed in this paper.The results show that the low concentrations are significantly linear correlation,and with the increase of the number of algal cells,the increasing trend of backscattering intensity slows down,then gradually enters the platform fluctuation area,and finally decreases due to the strong attenuation effect.In this paper,we designed and built a programmable transmitting and receiving integrated ultrasonic detection system,taking Prorocentrum donghaiense and Akashiwo sanguinea as examples,and the monitoring results were consistent with the results of ADV validation experiment.Time-frequency analysis in frequency domain can improve the performance of concentration characterization.The designed dual-frequency detection and multi-signal excitation detection at the same frequency can basically realize the preliminary perception of the particle size of algae cells.The main innovations of this paper are as follow:Firstly,the equivalent simplified model of algal cells combined with the fluid sphere model was proposed to establish the stratified comprehensive measurement model of algal cells,and the variation trend of the acoustic theoretical numerical analysis of algal fluid with large span and multi-frequency and multi-particle size was given.Secondly,the relationship between microalgae concentration and acoustic backscattering intensity was revealed,which proves the effectiveness of ultrasonic detection method in detecting the warning critical concentration range of two kinds of target red tide algae.Thirdly,the frequency domain signal analysis method was introduced to improve the performance of the autonomous platform system;the time-frequency analysis of multi-signal excitation mode basically realized the preliminary perception of the particle size of the target red tide algae cells.