Influence of salt ions on the refractive index of seawater solution under different temperature

The optical properties of seawater are of great significance to the monitoring of marine safety and marine environment by means of optical sensing. In order to further study the relationship between the refractive index (RI) of different salt solutions, temperature and salinity, two experiments are carried out. The effect of temperature and mass fraction on RI of single component solution, and the effect of type and quantity of ions on the RI of mixed solutions when the mass fraction is kept constant at 3.5% are studied. Experiment results show that mass fraction coefficient of NaCl, MgCl₂ and MgSO₄ are 1.74×10^-4 , 2.54×10^-4 and 1.94×10^-4 , respectively. Mass fraction coefficient of NaCl is lower than that of MgCl₂ and MgSO₄. In the second experiment, it is found that the effect of valence state on RI is higher than that of ion number, and the RI of bivalent solution is higher than that of monovalent solution. Not only the temperature and salinity of seawater, but also the components of seawater salt ions have different effects on the RI. Since the intrinsic relationship between RI and salinity is not suitable for different sea areas, the study of the relationship between the RI of single solution or a binary mixed solution and temperature and salinity is of great significance for the modulation process of optical salinity sensing.