Bathythermograph
A bathythermograph (composed of the Greek bathýs : deep, thermós : warm and graphein : scratch, write) is a device for measuring the water temperature as a function of the pressure (or the depth in the water, which is proportional to the pressure ). The Bathythermograph was invented by the American Spilhaus in 1937 and is mainly used in the Navy to determine the sonar propagation ratios . A bimetal is used to determine the temperature and a measuring cell is used to determine the pressure, as in the case of the can barometer . With these two mechanically acting sensors, the temperature is scratched as a function of the depth with a tip on a coated glass plate. These sensors are located in a robust, slim measuring body that is lowered from the ship with a wire.
Despite the heavy, robust construction, the Bathythermograph can only be used at low speed, so that the ship almost has to stop. That is why it has now been replaced by the XBT (Expendable Bathythermoghraph) , which has been manufactured by the American company Sippican since 1960. With the XBT, the temperature is measured with a thermistor. The depth is determined as a function of time when the rate of descent of the free-falling measuring body is constant to a good approximation. The device is connected to a measuring recorder on board the ship with a very thin insulated double wire . This wire is coiled in the measuring body and in the on-board device so that it does not have to move relative to the water: The movement of the falling measuring body is unrolled from the supply reel there and the movement of the ship, which is moving very fast, from the coil in the on-board device. When the wire is unwound, it breaks and the measuring probe is lost (around 5 million probes have been sold by Sippican so far). Nevertheless, this loss is economical because the probe costs less than the fuel used to stop the ship.
A further development of the XBT is the AXBT (Airborne Expendable Bathythermograph) . The AXBT is not used from the ship, but from a buoy such as a sonobuoy . The measurement signal is transmitted to the aircraft by radio like a sonobuoy.
literature
- RJ Urick: Principles of Underwater Sound , 2nd ed., McGraw-Hill, New York 1975. ISBN 0-07-066086-7 , p. 5; 106-108