The linear equation for estimating practical salinity has now been tested and confirmed to be within 5% accuracy. The largest room for error comes from the conductivity sensor temperature compensation, so it is important to be aware of the percentage to understand what the possible error is from PSS-78, especially at temperatures close to 0°C.
This equation is designed for dataloggers or any program that provides linear scaling for conductivity measurements with a temperature-compensated sensor. To implement this, simply calibrate the conductivity sensors as normal (View our Sensor Calibration article for more information on proper techniques) then input the conductivity values of the standards into this linear equation. Enter the obtained values into the scaling program and now the conductivity sensor is a practical salinometer.
Again, the obtained practical salinity values should not be substituted instead of PSS-78 or TEOS-10 standards in scientific literature, but properly understanding and programming these standards require a specialized skillset or extensive time to develop the skillset, which is not available to everyone. Current resources online are useful for single data point entry or batch entry, but they can only be done once data is exported, so the derived linear equation presented in this article provides a means of real-time salinity estimation accessible to anyone and usable with most devices.
In summary, the following equation estimates (<5% error) practical salinity for conductivity measurements taken with a temperature-compensated sensor at less than 200 dBar and temperature ranges of 5-35°C (for pHionics instruments and any others with 1.8-2.0%/°C temperature coefficient. 15-35°C range for sensors with <1.8% or >2.0%).
An example of entry into a scaling program can be found below after calibrating with 0 and 50 mS/cm calibration standards.
Conversion to practical salinity