Expendable bathythermograph
Encyclopedia
The expendable bathythermograph
, or XBT, is a device for obtaining a record of temperature as a function
of depth from a moving ship.
Temperature is measured with a thermistor
within an expendable, weighted casing. Depth is determined by a priori knowledge of the rate at which the casing sinks and the time of each recorded data value. A pair of fine copper wires which pay out from both a spool retained on the ship and one dropped with the instrument, provide a data transfer line to the ship for shipboard recording. Eventually, the wire runs out and breaks, and the XBT sinks to the ocean floor. Since the deployment of an XBT does not require the ship to slow down or otherwise interfere with normal operations, XBT's are often deployed from vessels of opportunity, such as cargo ships or ferries. Airborne versions (AXBT) are also used; these use radio frequencies to transmit the data to the aircraft during deployment.
The XBT was invented in the early-1960s by former The Sippican Corporation (TSC), today Lockheed Martin Sippican
, which has manufactured over 5 million XBT's. An XBT which also measures conductivity
, allowing salinity to be computed, is termed an XCTD.
Bathythermograph
The bathythermograph, or BT, is a small torpedo-shaped device that holds a temperature sensor and a transducer to detect changes in water temperature versus depth. Lowered into the water from an underway ship, the BT records pressure and temperature changes as it is dropped through the water...
, or XBT, is a device for obtaining a record of temperature as a function
Function (mathematics)
In mathematics, a function associates one quantity, the argument of the function, also known as the input, with another quantity, the value of the function, also known as the output. A function assigns exactly one output to each input. The argument and the value may be real numbers, but they can...
of depth from a moving ship.
Temperature is measured with a thermistor
Thermistor
A thermistor is a type of resistor whose resistance varies significantly with temperature, more so than in standard resistors. The word is a portmanteau of thermal and resistor...
within an expendable, weighted casing. Depth is determined by a priori knowledge of the rate at which the casing sinks and the time of each recorded data value. A pair of fine copper wires which pay out from both a spool retained on the ship and one dropped with the instrument, provide a data transfer line to the ship for shipboard recording. Eventually, the wire runs out and breaks, and the XBT sinks to the ocean floor. Since the deployment of an XBT does not require the ship to slow down or otherwise interfere with normal operations, XBT's are often deployed from vessels of opportunity, such as cargo ships or ferries. Airborne versions (AXBT) are also used; these use radio frequencies to transmit the data to the aircraft during deployment.
The XBT was invented in the early-1960s by former The Sippican Corporation (TSC), today Lockheed Martin Sippican
Lockheed Martin
Lockheed Martin is an American global aerospace, defense, security, and advanced technology company with worldwide interests. It was formed by the merger of Lockheed Corporation with Martin Marietta in March 1995. It is headquartered in Bethesda, Maryland, in the Washington Metropolitan Area....
, which has manufactured over 5 million XBT's. An XBT which also measures conductivity
Conductivity (electrolytic)
The conductivity of an electrolyte solution is a measure of its ability to conduct electricity. The SI unit of conductivity is siemens per meter ....
, allowing salinity to be computed, is termed an XCTD.
Uses
- OceanographyOceanographyOceanography , also called oceanology or marine science, is the branch of Earth science that studies the ocean...
: to obtain information on the temperature structure of the ocean. - SubmarineSubmarine warfareNaval warfare is divided into three operational areas: surface warfare, air warfare and underwater warfare. The latter may be subdivided into submarine warfare and anti-submarine warfare as well as mine warfare and mine countermeasures...
and Anti-submarine warfareAnti-submarine warfareAnti-submarine warfare is a branch of naval warfare that uses surface warships, aircraft, or other submarines to find, track and deter, damage or destroy enemy submarines....
: to determine the layer depth (thermoclineThermoclineA thermocline is a thin but distinct layer in a large body of fluid , in which temperature changes more rapidly with depth than it does in the layers above or below...
) used by submarines to avoid active sonarSonarSonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...
search.