CTDinstrument

CTDinstrument is a class of oceanographic instruments designed to measure conductivity, temperature, and depth of seawater as a function of depth. These devices are typically lowered from a research vessel on a cable and are used to produce high-resolution vertical profiles that reveal the structure of the water column, including salinity and density distributions essential for studying ocean circulation and water mass formation.

A CTD instrument typically consists of a submerged housing containing sensors for conductivity, temperature, and pressure (depth). In many systems, additional sensors are used to monitor dissolved oxygen, chlorophyll fluorescence, turbidity, colored dissolved organic matter, and pH or nitrate. A rosette frame holding water sampling bottles, usually Niskin bottles, is commonly integrated with the CTD to collect discrete samples at selected depths for chemical analyses.

Operation typically involves lowering the CTD instrument to the target depth while real-time data are acquired and monitored. After reaching designated depths, the rosette bottles close to capture water samples. Data are corrected for sensor drift and environmental effects during calibration and post-processing, and salinity is computed from conductivity alongside temperature and pressure to yield a comprehensive hydrographic profile.

CTDinstrument is central to modern physical oceanography and climate research. They support studies including mapping ocean stratification, characterizing water masses, validating satellite salinity data, and informing models of ocean circulation. Notable manufacturers include Sea-Bird Scientific and other producers of CTD systems.