A CTD profiler is one of the fundamental instruments used in physical oceanography. It measures key seawater properties, primarily conductivity, temperature and pressure/depth, allowing scientists to calculate salinity and examine how water characteristics vary throughout the water column.

CTD measurements are used to study ocean circulation, water-mass structure, stratification and changes in marine environmental conditions. The instrument can be deployed from a research vessel and lowered through the water column to obtain high-resolution vertical profiles.