Sea-Bird CTDs (Conductivity, Temperature, Depth) precisely measure electrical conductivity to derive salinity, which is the saltiness or dissolved salt content (such as sodium chloride, magnesium and calcium sulfates, and bicarbonates) of a body of water. Salinity is an important factor in determining many aspects of the chemistry of natural waters and of biological processes within it, and is a thermodynamic state variable that, along with temperature and pressure, governs physical characteristics like the density and heat capacity of the water.
Sea-Bird manufactures a large number of conductivity sensors, for use in a wide range of applications. The conductivity sensors are categorized into the following groups:
- Conductivity only — SBE 4 (4M, 4C), 7
- Conductivity in a CTD — SBE 9plus, 16plus V2, 16plus-IM V2, 19plus V2, 25plus, 37 (SM, SMP, SMP-ODO, SI, SIP, SIP-IDO, IM, IMP, IMP-ODO), 41/41CP, 49, 52-MP, Glider Payload CTD
- Conductivity in a thermosalinograph — SBE 21, 45
- Conductivity (optional) and Pressure — SBE 26plus, 53
Shown below are descriptions of Conductivity only sensors. See Profiling CTDs, Moored / Time Series Instruments, Shipboard Thermosalinographs, and Pressure Sensors for other instruments that include conductivity sensors.