Underway salinity measurements with thermosalinographs
Thermosalinograph (TSG) are instruments installed in the ship hull of a merchant ship (VOS: voluntary operating ships) or research vessels having a sea water throughflow. They continuously measure the temperature and conductivity of the sea water from which the salinity is calculated, providing salinity data along the ship routes from 3 to 15 m depth, dependig on the construction of the ship's hull. By calibration and maintaining the instrument free of contamination, the data quality reach 0.01. The data are gathered inthe frame of the European Gosud Project.
In the figure above, the salinity along the ship routes of the German Research Vessel Poseidon in August 2012 is overlaid to a salinity map derived from the SMOS satellite measurements of the same month. The SMOS salinity in this region are reliable only since May 2012 because before this date, Radio Frequency Interference (RFI) influenced too much the data quality.
Though the data originate in different depths (from SMOS at exactly the sea surface and from the TSG at about 4 m depth), and though the absolute salinity values differ, the structure of the salinity distribution is very similar: the low salinity along the coast of Greenland reflect the distribution of the summerly melt water advected southward by the East Greenland Current. More details are found in Köhler et al., (2015): Quality assessment of spaceborne sea surface salinity observations over the northern North Atlantic.