The Thermosalinograph or TSG is an instrument mounted near the water intake of ships to continuously measure sea surface temperature and conductivity while the ship is in motion. Various programs have been developed to assist in the collection and analysis of TSG data. The data can be used to calculate salinity, density, sound velocity, and other parameters. There are various types of thermosalinographs available on the market today.
Ship of Opportunity Program (SOOP)
Global Ocean Observing System (GOOS)
The thermosalinograph uses a conductivity cell to measure conductivity which can then be translated into a value of salinity. Also a thermistor cell measures the temperature of the surface water, which when combined with the conductivity can tell you the density of the water as well as its sound velocity.