The primary tool for a physical oceanographer is a measuring system, dedicated for measurements in seawater of electrical conductivity, temperature, and pressure, which traditionally called a CTD (stands for Conductivity, Temperature, Depth). This measuring system is also being named a “submersible salinometer” or STD (Salinity, Temperature, Depth). The directly measured parameters of a CTD-system are used to calculate the practical salinity and density of seawater using the Practical Salinity Scale 1978 and the Thermodynamic Equation of State 2010 of seawater. Density in particular is an important property in ocean science because small spatial changes in density result in spatial variations in pressure at a given depth, which in turn drives the ocean circulation.
I have worked with СTD-systems for about 40 years and I want to present here my compendium on the history of СTD-systems international development. If you have any additional information on the development of СTD-systems, or if you want to comment on the presented material, please let me know. Have a good reading!