Long-term salinity observations by surface drifters with sound speed sensor

Well known traditional approach for getting the sea surface salinity (SSS) data from surface drifters suggests:

- salinity calculation from conductivity & temperature [e.g., SBE37-SI];

- assumption that seawater is a mixture of salts and water;

- drift of SSS sensor due to biofouling and pollution;

- complicated calibration procedure;

- expensive.

We offer the alternative approach with the following features:

- salinity calculation from sound velocity & temperature (SVT) [e.g., J.T. Allen et al., 2017];

- sound velocity is sensitive to the total mass fraction of all dissolved matters in seawater;

- simple calibration procedure;

- simple methods of anti-fouling, long-term stability;

- low-cost.

The new SVT module has been developed and thoroughly investigated in laboratory as well as in-situ. Long-term research of the new sensor operated under intensive biology fouling showed that sensor keeps the quality of salinity observations for months with ±0.05 ‰ accuracy.

The SVT module and salinity bias after 120 days in-situ

This development allowed creating the drifter for study of the ocean’s active layer and salinity variability below ice during its freezing and melting.

The buoys can keep operation for one year.