Development And Field Experiment Research Of Seawater Salinity Measurement Device Based On Optical Photoelectric Detection

Ocean is the largest body of water on the earth,covering more than 70% of the surface area of the earth.Studying the ocean and exploring the ocean is an important issue in the development of human society.China's construction of a maritime power and the development of a marine economy are inseparable from the innovation and development of marine science and technology.As the most basic component of the marine environment,seawater is the basis for studying the ocean.Seawater salinity is an important parameter for complex solutions of seawater.Studying the distribution and change of seawater salinity in various sea areas is an important topic of ocean mapping and is also the basis for studying various hydrological phenomena in the ocean.After the introduction of the latest salinity standard TEOS-10,the optical method of measuring salinity has caused a wide range of research booms,and the development of relevant seawater salinity field measurement devices for on-site measurement research is a hot spot.At present,the optical salinity measurement methods at home and abroad are mainly developed by the conventional refraction method.Although high precision and stability can be obtained,the disadvantages of being easily disturbed by turbid water bodies cannot be overcome.Therefore,in the coastal coastal waters,the existing optical salinity field measurement devices have certain application problems,and the correct acquisition of salinity parameters cannot be achieved under specific application scenarios such as turbid environment in the estuary area.Therefore,in view of the characteristics of marine site salinity measurement environment and the requirements of turbid environment measurement,this thesis proposes an on-site measurement of seawater salinity based on optical critical angle method,and completes the development of the measuring device and the research of specific experimental problems in the field measuring environment.The research lays the foundation for the application of eht TIR method in seawater salinity high-precision field measurement.The main research contents of the thesis are as follows:(1)This thesis firstly analyzes and summarizes the relationship between seawater salinity and refractive index measurement,and obtains the correspondence between seawater salinity and refractive index and temperature.The optical salinity measurement method based on refractive index measurement is summarized,and the advantages and disadvantages of the above technology in marine field application are summarized and summarized.It is proposed to measure the salinity of seawater by the critical angle method based on total internal reflection to compensate for the shortcomings of traditional optical methods that are easily interfered by turbid environment.(2)Based on the specific conditions of optical methods in marine field measurement applications,based on the theoretical advantages of optical methods for measuring salinity,a TIR sensor that can be applied to marine field measurements is designed to complete the real marine environment.The salinity is measured on site.Aiming at the small variation range of seawater salinity refractive index,the optimization and improvement of the optical system of the prototype are carried out,the signal of the effective light field of the system is enhanced,and the signal-to-noise ratio(SNR)of the measurement system is improved to achieve the purpose of stable on-site measurement.(3)Through a series of laboratory experiments,the resolution of the refractive index of the prototype was determined.The results of the measurement are then evaluated from the aspects of measurement repeatability and long-term measurement stability,confirming whether the device can be stabilized in long-term marine site environmental measurements,and fully verifying the reliability of the designed critical angle salinometer.In addition,through the mechanical deviation correction technology,the critical Angle salinity meter is protected from the interference of mechanical deviation in long-term use process.On this basis,the relationship between seawater salinity,temperature and refractive index is fully considered,and the influence of temperature change on the measurement system is analyzed.Through the complete temperature experiment,the applicable temperature compensation parameters of the system are obtained.The formula reduces the error that the temperature brings to the measurement system.(4)Further research was conducted on the problem of seawater turbidity causing interference with current optical salinity measurement methods.By using the Forma turbidity standard solution to simulate the turbid environment in the estuary of the ocean,the influence of the turbid environment on the measurement of the spot by the refraction method and the critical angle method is analyzed.It is fully verified that the measurement method of the critical angle salinity is more traditional in the turbid environment.The superiority of the method.On this basis,the anti-interference algorithm for processing the reflected spot image is proposed innovatively,which improves the anti-interference ability of the critical angle method and the measuring device in the turbid environment.(5)The relevant measuring experiments were carried out in the actual marine environment using the developed TIR sensor.In the summer of 2016,the “Dongfanghong 2” marine scientific research vessel participated in the investigation of the Yellow Sea and Ocean Ocean Scientific Research.The TIR sensor was used to complete the navigation measurement of the sea surface refractive index parameters of the Yellow Sea and the Bohai Sea.The feasibility of the measurement in the marine environment was verified.In the summer of 2017,in the case of improving the accuracy of the critical angle salinometer measurement and the optimization of temperature compensation,taking the “Runjiang 1” scientific research vessel to participate in the Changjiangkou marine site scientific research In the process of ocean experiment,the synchronous test of TIR sensor and conductivity CTD was realized,and the experiment of diurnal tidal salinity change and profile salinity measurement was completed,and the applicability of the TIR sensor in a marine measurement environment was verified.According to the synchronous test of the TIR sensor and the conductivity CTD,the correlation coefficient of the measurement reached 0.994.An effective measurement of seawater salinity using a TIR sensor in a seawater field measurement environment is achieved.