The Research On High Precision Sound Velocity Profile Measurement System

With the development of science and technology and the scarcity of terrestrial resources,humanity has shifted the focus of resource development to the ocean.The sound velocity profile in water is one of the important parameters to ensure the normal operation of sonar equipment.The sound velocity profiling system has a wide application in marine mapping,hydrographic survey,underwater navigation and positioning,and underwater channel measurement.This thesis aims to design and implement a high-precision sound velocity profiling system.Its sound velocity measurement part uses time-digital conversion technology(TDC).The main research contents are divided into the following parts:Firstly,study the law of seawater distribution and its impact factors and three commonly used empirical formulas to analyze their applicability in different environments.The principles of four typical direct measurement methods are introduced,and their difficulty in engineering and measurement accuracy are analyzed.Then introduce the measurement principle of TDC-GP22 chip,which is based on gate delay time measurement technology and the superiority of the chip in sound velocity measurement.Secondly,design the overall scheme and hardware part of the high-precision sound velocity profiling system.The hardware system adopts STM32 as the main control chip,and the ultrasonic transducer with the working frequency of 2MHz is selected.It includes a storage module,a sound velocity and temperature measurement module,and a pressure measurement module.Then,design the software part of the system,including embedded software and host computer display and control software.The embedded software part includes the main program,interrupt callback function,timer,real-time clock and driver of each interface,and transplants the FATFS file system in the memory card.The system successfully completed the measurement of sound velocity,temperature and depth in the water,and according to the time when the measurement was started,the measurement data was stored after the new file was created,and the file was closed after the water was discharged.In the development environment of VS2017,the host computer software based on MFC dialog box was designed for the system.The serial port configuration window,the sound velocity meter configuration window,the file list,and the sound velocity profile display window are designed.The upper computer and the lower computer communicate with each other through the RS232 serial port,and the communication protocol is realized in the upper computer software and the lower computer,and the control of the upper computer to the lower computer and the reading and deleting of the data are completed.Finally,after completing the system function,set up a calibration environment to calibrate the sound velocity measurement and temperature measurement.Firstly,verify the stability of the measurement of TDC-GP22 at different temperatures.Then,study the calibration method of the sound velocity meter and the fitting of the measured data with the true value was completed according to the least square method.After calibration,the sound velocity measurement accuracy is ±0.05 m/s in the range of 1400 m/s to 1550 m/s.Finally,carry out the field experiment in a certain sea area of Qingdao,and the measurement results are favorable compared with the international mainstream sound velocity meter.