Design And Development Of Seafloor Sediment Acoustic In Situ Measurement System Based On FPGA

Submarine sediment is an important research object in ocean observation.Its characteristics change with strong spatial differences and unpredictability,which has a certain impact on the effectiveness of marine equipment.In situ measurement of seafloor sediments is an effective method to obtain their related characteristics,which enables fixed-point,continuous and multiparameter cross-domain measurements of the seafloor boundary layer.In recent years,the domestic means of measuring the acoustic characteristics of seafloor sediments have been unable to meet the current demand for accurate,efficient and stable measurement of the characteristics of seafloor sound field.For this reason,this paper puts forward the overall design of the seafloor sediment acoustic in-situ measurement system based on the control of FPGA.Using FPGA as the main chip of the in-situ measurement system,it can not only control the signal generation(mid-high frequency),signal collection,data storage,data upload,etc.in the system,but also ensure the accuracy,efficiency and stability of the measurement system.The main work of this paper is as follows:1.Design the overall framework of an acoustic in situ measurement system for seafloor sediments.According to the practical application scenario of the system,the unit composition of the system is determined,including hardware unit,software unit,mechanical unit and measurement unit,in which hardware unit and software unit are the key design contents.The hardware unit includes the selection of main control chip(FPGA),the design of communication module,the design of data storage module,and so on.The software unit includes upper computer software(data processing program,real-time display software)and lower computer software(master program,signal generator program,instruction receiver program,instruction parser program,data storage program,data sending program,etc.).2.Design the hardware circuit of the acoustic in situ measurement system for seafloor sediments.It mainly includes the design and debugging of D/A conversion circuit,power amplifier circuit,voltage amplifier circuit,signal conditioning circuit,A/D conversion circuit.3.Designing and compiling the software unit of the seafloor sediment acoustic in-situ measurement system.According to the different transmission modes(UART communication,USB communication),the upper computer part uses the existing upper computer software to realize the functions of data communication(instruction sending and data receiving),waveform sampling parameter setting,waveform real-time display,file storage and reading.The lower computer uses Vivado software to write functions such as signal generation,data reception,data collection,data caching and storage,data sending,etc.4.Conduct performance tests of the internal hardware modules of the seafloor sediment acoustic in-situ measurement system and functional tests of the digital processing platform.The performance of signal generation module,power amplifier module,voltage amplifier module and transceiver transducer module are tested and verified,and the results show that each module has good performance,and real-time data and waveforms can be received by issuing instructions(setting parameters)under the upper computer software interface.The results show that the system software has good functions.5.Conduct actual testing of the measurement system.Apply the system to two experimental sites,a laboratory pool(water)and a beach(shallow sediment),to measure the acoustic parameters of seawater and sediment,respectively.Based on the sound wave test in the laboratory pool,according to the measurement results,the emission signal is of the same waveform,same distance,and different frequencies,corresponding to an average sound velocity of about 1489.37 m/s in water,with a relative error of about 0.49% compared to the sound velocity obtained from the empirical formula.The data shows good accuracy;Based on the sound wave testing of shallow sediment on the beach,different emission frequencies(5,10,15,20 k Hz)were used for testing,and it was found that the sound velocity of shallow sediment was basically between 1700 m/s and 1750 m/s.The results showed that the measurement system was relatively stable and reliable.