An eXpendable BathyThermograph (XBT) is a temperature probe that is dropped into the ocean from a ship, either by hand or using using an automatic launching system. Temperatures are recorded as the probe drops at a known rate through about the upper kilometer of the ocean. By making measurements at the same location at regular intervals, it is possible to observe the evolution of the thermal structure of the upper ocean.

NOAA employs two sampling modes for deployment of XBT probes, each serving a different scientific purpose: Frequently Repeated (FR) and High Density (HD).

Frequently repeated XBT transects, located primarily in tropical regions, are designed to monitor strong seasonal-to-interannual variability in the presence of intra-seasonal oscillations and other small-scale variability. They are intended to capture the large-scale thermal response to changes in equatorial and extra-equatorial winds.

High density transects, used to observe smaller scale ocean features, are designed to resolve fronts and mesoscale eddies that are prevalent in much of the ocean, and boundary currents that transport large quantities of heat in regions where thermal gradients are large (and where sampling intervals ma, therefore, be as fine as 10-15km).

NOAA deployment of XBTs is managed in close cooperation with about two dozen other countries that contribute to this network under the framework of the JCOMM Ship of Opportunity Programme. NOAA scientists at the Atlantic Oceanographic and Meteorological Laboratory (AOML) arrange and conduct XBT deployments in the Atlantic Ocean; scientists at the Scripps Oceanographic Institution arrange and conduct XBT deployments in the Pacific Ocean.

XBT data are made available in near-real time on the Global Telecommunications System for weather forecasting efforts, and are freely available in quality controlled delayed more via the internet from the Global Temperature-Salinity Profile Program (GTSPP) operated by the NOAA National Oceanic Data Center (NODC). Delayed mode data are also archived and distributed by the French Coriolis Data Assembly Center. Final quality controlled XBT data merged with other temperature profiles can be found in the NODC World Ocean Database. In addition, NOAA Pacific XBT datasets are available at the Scripps Institution of Oceanography High Resolution XBT/XCTD Network Site; NOAA Atlantic XBT data sets are available at the NOAA Atlantic Oceanographic and Meteorological Laboratory XBT web site.

The Ship Of Opportunity Programme (SOOP), operating internationally under the auspices of the World Meteorological Organization (WMO) and the Intergovernmental Oceanographic Commission (IOC), oversees collection of upper ocean temperature profiles using eXpendable BathyThermographs (XBTs), mostly from volunteer vessels. The XBT deployments are designated by their spatial and temporal sampling goals or modes of deployment (Frequently Repeated, and High Density) and sample along well-observed transects, on either large or small spatial scales or at special locations such as boundary currents and chokepoints, all of which are complementary to the global array of Argo profiling floats. In addition to deploying XBTs, many ships of the Ship of Opportunity Programme serve as platforms for other scientific instruments, including TSGs (ThermoSalinoGraphs), xCTDs (eXpendable Conductivity Temperature and Depth), pCO₂ (CO₂ partial pressure instruments), ADCPs (Acoustic Doppler Current Profilers), and CRPs (Continuous Plankton Recorders).

The Ship Of Opportunity Program Implementation Panel (SOOPIP) serves to implement the XBT upper ocean data requirements established by the international scientific and operational communities. Annual assessment of transect sampling is undertaken by the Joint WMO-IOC Technical Commission for Oceanography and Marine Meteorology (JCOMMOPS). SOOPIP, which deals with ocean observations from ships, is one of the three components of the WMO-IOC Ship of Observations Team, the other two being the Voluntary Observing Ship Programme, which deals with surface meteorological observations, and the Automated Shipboard Aerological Programme, which deals with upper-air profiles.

International Coordination

• Ship of Opportunity Programme Implementation Panel

XBT Data

• Near-Real Time Data: Global Telecommunications System
• Delayed-Mode Data: Global Temperature-Salinity Profile Program
• Quality-Controlled Integrated Data: World Ocean Database
• NOAA Pacific Datasets
• NOAA Atlantic Datasets

Overview (OceanOb'09, 2009)

• Ship of Opportunity Program