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Profiling CTDs

A CTD measures Conductivity, Temperature, and Depth. Despite the name, all CTDs actually measure pressure, which is not quite the same thing as depth. The relationship between pressure and depth is a complex one involving water density and compressibility as well as the strength of the local gravity field. The CTD data can be used to calculate salinity, density, sound velocity, and other parameters of interest. The term CTD is often used today to describe a package that includes the actual CTD as well as auxiliary sensors to measure other parameters (such as dissolved oxygen, pH, turbidity, fluorometer, altimeter, etc.) and a water sampler to collect water samples for later analysis in the lab. The term Sonde is sometimes used as an alternative to CTD.

A Profiling CTD measures water parameters as it travels through the water, whether lowered over the side of a ship with a winch to take measurements of a vertical column of water or integrated with an autonomous vehicle or glider. Common to all Sea-Bird Profiling CTDs:

  • Purposeful designs built to perform under the unique dynamic conditions found on varying measurement platforms
  • Pumped and ducted constant flow for matched temperature and conductivity response
  • Measurements are made on the same sample of water with a predictable delay and predictable flow effects
  • Aligning and coordinating measurements done with software or (for some models) automatically

See the following documents for more details on CTDs:

SBE 9plus
Premium profiling Conductivity, Temperature, Pressure, eight channels for auxiliary sensors, interface for dual C & T sensors, with 24 Hz sampling. Primary oceanographic research tool chosen by world's leading institutions.
Profiling Conductivity, Temperature, Pressure, and up to ten auxiliary sensors, with 16 Hz sampling, and internal memory and batteries.
SBE 19plus V2 with optional cage, SBE 5P pump, & SBE 43 DO sensor
Profiling or moored Conductivity, Temperature, Pressure, and up to seven auxiliary sensors, with 4 Hz sampling, and internal memory and batteries.
SBE 49 FastCAT CTD
Conductivity, Temperature, and Pressure at 16 Hz. No memory or internal power; intended for use on vehicles that can supply power and acquire data.
Glider Payload CTD with Pump
Measures conductivity, temperature, and pressure, and optionally, dissolved oxygen. Modular, low-power profiling instrument for autonomous gliders.
Slocum Glider Payload CTD
Low-power profiling CTD designed specifically for installation in Slocum gliders.
SBE 41 Argo CTD for Autonomous Profiling Floats
Autonomous profiling CTD for Argo and other programs, supplying more than 90% of the annual Argo program floats.
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