CTD (instrument)

A CTD instrument is an oceanography sonde (French for probe) used to measure the electrical conductivity, temperature, and pressure of seawater.

[2] Other sensors may be added to the cluster, including some that measure chemical or biological parameters, such as dissolved oxygen and chlorophyll fluorescence, the latter an indication of the concentration of microscopic photosynthetic organisms (phytoplankton) contained in the water.

The instrument is lowered into the water in what is called the downcast to a determined depth or to a few meters above the ocean floor, generally at a rate of about 0.5 m/s.

The CTD overcame the limitations of an earlier similar system also developed by Brown, called an STD.

[3] Prior to this, the Mechanical Bathythermograph (MBT) was the norm The advantage of CTD casts is the acquisition of high-resolution data.