Conductivity-Temperature-Depth (CTD)
D1. Physical and chemical oceanography and marine meteorologyDefinition
Standard oceanographic instrument package for profiling water column properties.
The CTD is the standard oceanographic profiling instrument, measuring electrical conductivity (for salinity), temperature, and pressure (for depth) as it is lowered through the water column. Mounted on a rosette with Niskin bottles and added sensors (oxygen, fluorescence, transmissometer), it is the workhorse of repeat hydrography. Modern CTDs resolve temperature to about 0.001 degrees Celsius and salinity to about 0.002, replacing the older Nansen-bottle and reversing-thermometer method.