Which instruments are commonly used to measure ocean salinity?

CTD sensors and salinometers are specifically designed to measure the physical properties of seawater, including salinity. CTD stands for Conductivity, Temperature, and Depth, which are critical parameters for understanding ocean water characteristics. The conductivity part of the CTD sensor is especially important for salinity measurements since the conductivity of seawater is directly related to its salt concentration.

Salinometers are instruments solely focused on measuring salinity accurately by determining the concentration of salts in the water. Both CTD sensors and salinometers provide vital data for oceanographic studies, making them essential tools for marine scientists studying ocean properties and processes.

Other instruments listed, like thermometers, primarily measure temperature and are not equipped to assess salinity. Sonar devices are used for mapping underwater topography or detecting objects in water but do not provide information on salinity. GPS technology is utilized for positioning and navigation purposes and is unrelated to measuring ocean salinity. Thus, the choice of CTD sensors and salinometers as the correct answer highlights the specific tools and techniques used in marine science for salinity measurement.