Measurement of Ocean Salinity using a Capacitance based Sensor

Coastal processes like metabolic rates, circulation patterns etc., are influenced by temperature and salinity. This research addresses the requirement to measure the salinity of the marine ecosystem. Salinity of seawater is typically 35 g/kg, although lower in areas where rivers enter oceans. A capacitance-based sensor for the measurement of salinity has been developed, and tested using a LCR meter and a bride circuit with metal electrodes. In this regard, two pairs of electrode configurations, of different geometries, Flat-Plate and Co-axial electrodes have been analyzed. The sensor was tested with saline solutions of various concentrations – with a range of 0.1 – 35 g, at diverse temperatures to check the dependence of salinity on temperature. The sensor shows a good linearity compared to the LCR meter with the Co-axial electrode having higher performance with r
²
> 0.91. Of the two electrode configurations - the co-axial electrode exhibits better linearity (r
²
for Bridge Voltage = 0.83 and r
²
for Capacitance = 0.955) than the flat-plate electrode configuration (r
²
for Bridge Voltage = -0.105 and r
²
for Capacitance = -0.151). The sensor is compact and less expensive compared to its optical counterparts. The output of the sensor can be easily integrated to embedded hardware, for continuous monitoring.