In situ measurement of seawater salinity with an optical refractometer based on total internal reflection method.

ABSTRACT

An optical refractive index sensor used for underway seawater salinity monitoring is proposed. Due to the empirical relation to salinity, refractive index measurement provides an alternative solution to obtain salinity of seawater. We developed a compact refractive index sensor based on total internal reflection (TIR) method. Through the repeatability and stability experiment and temperature correction, the performance of the sensor has been demonstrated experimentally. To evaluate the applicability of the sensor under real turbid sea conditions, field performance of the TIR sensor has been tested on an oceanographic cruise in the eastern of Yangtze Estuary in July 2017. The underway monitoring results show good correlation with the results provided by commercial CTD profiler.