Research On Key Techniques Of Fishery Detection Based On Broad-band Ultrasonic Transducer

In recent years,in the field of fishery hydro-acoustics,broad-band scientific fish finders have become a research hotspot,especially for the identification of aquatic animal targets,the estimation of individual size and biomass.By using the broad-band technique,the echo characteristics in the whole frequency band range can be obtained,that is,the frequency spectrum of the target echo scattering can be obtained,which greatly increases the amount of information,especially in favor of improving the discriminating accuracy of the target.At present,there are some developments in the area of broadband transducer,but there is a lack of broadband data acquisition and processing software.So it is necessary to develop broadband data acquisition and processing software based on broad-band transducer independently.In this paper,a fishery broadband measurement system based on broadband transducer is proposed to collect,record and process broadband acoustic data of broadband transducer.The main purpose of this paper is to develop a fishery broad-band measurement system based on broadband transducer.The system is expected to acquire and record the broad-band data and the pulse compression processing function of the broad-band data,and the echo images and volume-backward scattering spectra of the specified frequencies can be inverted from the compressed broad-band data and the body length and density distribution of the target organisms can be estimated.The broad-band measurement system integrates broad-band ultrasonic transducer and PicoScope 4262 dual-channel oscilloscope.The software mainly constructs the application program based on.NET Framework through C # programming language,constructs the UI interface of the system,realizes the acquisition,real-time display and record function of broad-band transducer data;and using Matlab programming language to realize the function of post-processing of compression-pulsed data.In this paper,using the broad-band transducer as the main equipment,C #programming and Matlab algorithm as the main methods,respectively,the broadband acoustic data acquisition,display and storage system,as well as broadband acoustic data pulse compression and compression data postprocessing.Firstly,research broad-band transducer data receiving instrument to complete the data display and recording;then,according to the principle of pulse compression,the processing method of pulse compression of broadband acoustic data is studied;finally,the post-processing method of compressed broadband acoustic data is studied,the system calibration,the inversion of specific frequency echo image and volume-backward scattering frequency spectrum,and the estimation of body length and density distribution of target organisms are carried out.The main results of this paper are as follows:1.Design a data real-time display and acquisition system based on broadband transducer using C# and Matlab mixed programming.The system can effectively realize the real-time display and acquisition and recording function of data based on broadband transducer after data acquisition and verification by laboratory signal generator and offshore experiments.Moreover,the method of C #and Matlab mixed programming can increase the speed of operation and improve the efficiency of data acquisition and finally storage in CSV format.2.According to the principle of pulse compression technology,using Matlab programming language to pulse compression of broad-band data,and then using 15.9 mm standard ball of broadband data pulse compression verification test.Theoretical analysis and test results show that pulse compression technology can effectively improve the signal to noise ratio and distance resolution of broadband systems.3.A system calibration of the pulse compression broadband data was carried out using the echo data of the standard ball of 15.9mm.The echo image at the specified frequency was then inverted according to the volume-backward scattering coefficient and the signal to noise ratio size distribution of the frequency in the range of 20–200 kHz.Then the Antarctic krill aggregates in the broad-band backscatter data are selected as the area of interest for post-processing and their volume-backscatter spectra are calculated.Using DWBA model,the length density distribution of the detected Antarctic krill aggregations is inferred from the reserved volume-backscatter spectra by least square method.