Experimental research and analysis of salinity measurement based on optical techniques

The refractive index of salt water will change because of the variation of salinity, and the developed experimental setup exploits beam deviation caused by refraction due to the salinity of measured water at the receiving end face of a measurement cell. Based on a differential refractometer, a reference water cell filled with distilled water is partitioned by an oblique optical-transmission plate from a horizontal rectangular water tank, which, as a measurement element, is filled with measured salt water. Beam deviation caused by salinity change is detected by a position-sensitive detector (PSD). Experimental results indicate the feasibility of the developed system with a measurement resolution of 0.012‰ and repeatability error better than ±0.3‰. Errors which will affect the measurement performance are discussed and analyzed in detail.