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Publisher Summary This chapter focuses on the process of regular observations of the thermal structure of the upper ocean by means of eXpendable Bathy Thermograph (XBT) measurements. XBT observations can be made from ships underway. The XBT sonde consists of a thermistor probe that is launched from the ship and that sinks with a well-known falling speed, transmitting its temperature signal to the recorder on board via a thin unwinding copper wire. As a result a temperature-depth registration is obtained down to depths of about 400, 700, or 1800 m, depending on the type of probe. The advantage of this method is that data can be obtained by ships of opportunity without interfering with their normal duties. Naval ships normally make XBT observations in connection with anti-submarine programs, but as a rule not at high spatial resolution. Since the beginning of the program in 1991, 16 sections have been accomplished. Although for operational reasons, the routes followed by the ships may differ, most of them are sufficiently close together to permit comparison and analysis of variability in time. |
