expendable bathythermograph

instrument

Also known as: XBT

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Last updated

June 26, 2026

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An expendable bathythermograph (XBT) is an oceanographic instrument used to record underwater temperature and pressure. Unlike traditional bathythermographs, XBTs are designed to be dropped from moving platforms like ships or aircraft. They transmit data wirelessly from depths up to 300 meters (1,000 feet).1

XBTs detect temperature changes using a thermistor and determine depth based on a known fall rate. The sensor unit is connected to the research platform by a cable that unwinds simultaneously from both the platform and the sensor, allowing for accurate readings even from a vessel moving at full speed. This makes XBTs highly useful for surveying large ocean areas.21

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undersea exploration
Water sampling for temperature and salinity
An expendable bathythermograph (XBT) was developed during the 1970s and has come into increasingly wider use. Unlike the BT, this instrument requires an electrical system aboard the research platform. It detects temperature variations by means of a thermistor (an electrical resistance element made of a semiconductor…
Read More
An expendable bathythermograph (XBT) was developed during the 1970s and has come into increasingly wider use. Unlike the BT, this instrument requires an electrical system aboard the research platform. It detects temperature variations by means of a thermistor (an electrical resistance element made of a semiconductor…
Read More