Conductivity Temperature Depth (CTD Survey)

CTD stands for Conductivity, Temperature, and Depth, and represents a suite of electronic instruments designed to monitor how the conductivity and temperature of water vary with depth. The instrument is important in all areas of marine science, offering important insights into the physical, chemical, and even biological properties of the water column. A CTD consists of a series of small probes that can either be deployed independently or integrated into various observation platforms, including remotely operated vehicles, gliders, or stationary observation buoys.

On research vessels, a CTD is typically attached to a larger metal water sampling framework called a rosette, which is lowered into the water using a cable. The rosette is often equipped with multiple water sampling bottles, called Niskin bottles. These bottles remain open when the rosette is deployed and can be activated to close, allowing water samples to be collected at specific depths for future analysis. CTDs may also include additional instruments, such as sensors to measure oxygen, water pH, nitrate and chlorophyll concentrations, turbidity, and water current velocity. All of these measurements are checked in relation to depth.