The expendable bathythermograph, or XBT, is a device for obtaining a record of temperature as a function of depth from a moving ship. The bathythermograph, or BT is a small torpedo-shaped device that holds a Temperature Sensor and a Transducer to detect changes in Hydrostatic pressure The Mathematical concept of a function expresses dependence between two quantities one of which is given (the independent variable, argument of the function
Temperature is measured with a thermistor within an expendable, weighted casing. A thermistor is a type of Resistor with resistance varying according to its Temperature. 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. Electrical wiring in general refers to insulated conductors used to carry Electricity, and associated devices 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. Lockheed Martin ( is a large multinational Aerospace manufacturer and advanced technology Company formed in 1995 by the merger of An XBT which also measures conductivity, allowing salinity to be computed, is termed an XCTD.
Uses
- Oceanography: to obtain information on the temperature structure of the ocean. Oceanography (from the greek words Ωκεανός meaning Ocean and γράφω meaning to write also called oceanology or
- Submarine and Anti-submarine warfare: to determine the layer depth (thermocline) used by submarines to avoid active sonar search. Naval warfare is divided into three operational areas Surface warfare, Air warfare and underwater warfare. Anti-submarine warfare (ASW or in older form A/S is a branch of Naval warfare that uses surface Warships Aircraft, space craft or other Submarines The thermocline (sometimes metalimnion) is a thin but distinct layer in a large body of water such as an ocean or lake in which temperature changes more rapidly with depth Sonar (which started as an Acronym for sound navigation and ranging) is a technique that uses Sound propagation (usually underwater to navigate
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