What is an XBT?
An eXpendable BathyThermograph (XBT) is a probe that is dropped from a ship and measures the temperature as it falls through the water. A very thin wire transmits the temperature data to the ship where it is recorded for later analysis. The probe is designed to fall at a known rate, so that the depth of the probe can be inferred from the time since it was launched.
The XBT Network
The XBT network consists of transects across all ocean basins where eXpendable BathyThermographs (XBTs) are used to collect temperature observations of the upper 1km of the ocean. The XBTs are deployed from research vessels and ships of the Ship Of Opportunity Program (SOOP).
The transects are sampled in two modes: High Density (HD) and Frequently repeated (FR). All XBT transects are reviewed through an international consortium with oversight by the SOOP Implementation Panel (SOOPIP). Some transects include time series with more than 30 years of data.
High Density XBT Transects
The high density (HD) XBT operation is designed to measure the upper ocean thermal structure in key regions with the objective of investigating the temporal variability of key surface and subsurface currents and of meridional heat transport in the Atlantic Ocean. XBT transects in HD mode are repeated approximately every approximately three months with XBTs deployed approximately 25km apart in order to measure the mesoscale structure of the ocean to diagnose the ocean circulation responsible for redistributing heat and other water properties globally. HD XBT transects are carried out globally with AOML taking the lead in most of the operations in the Atlantic Ocean. In addition AOML contributes with the HD data transmission and distribution of SIO HD XBT operations and has current international collaboration efforts with Australia, Italy, Brazil, and France. For example, during 2011 and 2012 AOML implemented 4 new HD transects as part of international collaboration, and increased the number of cruises per year in two transects in the North Atlantic. Go
Frequently-repeated XBT transects
Frequently-repeated (FR) XBT transects are mostly located in tropical regions in order to monitor strong seasonal to inter-annual variability. These transects typically run north/south, and cross the equator or intersect the low latitude eastern boundary. They are intended to capture the large-scale thermal response to changes in equatorial and extra-equatorial winds. Sampling is ideally on an exactly repeating track to allow separation of temporal and spatial variability, although some spread is possible and always expected. These transects are ideally covered 18 times per year with an XBT drop every 100 to 150km (or approximately 6 drops per day). This mode of sampling tries to draw a balance between the spatial undersampling, with good temporal sampling inherent in low-density deployments and the good spatial sampling, marginal temporal sampling in the HD deployments.
Due to budget restrictions and scientific and climate research data requirements, AOML has recently discontinued its FR transects to focus the resources and efforts on the XBT operation in HD mode.
Data from XBTs are sent from the ships of the SOOP to receiving stations onshore via satellite. These data is placed in the GTS and are made publicly available. The spatial domain is global and data is available since 1999. Go to XBT and GTS Data
Historical Low Density XBT Transects
Low-density (broadly spaced) XBT observations are used to investigate the large-scale, low-frequency modes of climate variability, while making no attempt to resolve the energetic, mesoscale eddies that are prevalent in much of the ocean, features that are investigated by XBT transects in high-density (HD) mode. These transects are ideally covered 12 times per year with an XBT drop every 150 to 200km (or approximately 4 drops per day). Sampling in LD mode has been the dominant mode in the early days of the SOOP network. Currently AOML SOOP deploys XBT's in high-density and frequently repeated mode.
AMVER-SEAS is a real-time ship and environmental data acquisition and transmission system. The AMVER-SEAS software acquires atmospheric, oceanographic data and transmits the data in real-time for addition to scientific and operational databases. AMVER-SEAS is employed on ships of the SOOP, and on NOAA, UNOLS, and Coast Guard Vessels. Go
The SEAS Profile Visualization Tool allows the monitoring of the XBT operation. This application shows real-time XBT profiles plots and locations for all the ships participating in AOML's SOOP project. Profiles can be selected by ship call sign and date intervals. This application requires Java Web Start. Go
The Oleander Project
The Oleander Project web page highlights some of the results of the XBT deployments onboard the MV Oleander. This project is an inter-institutional effort between the University of Rhode Island (URI), Stony Brook State University of New York (SUNY), the NOAA Northeast Fisheries Science Center (NOAA/NFSC), and NOAA/AOML to collect oceanographic data such as ocean currents, upper ocean temperature, sea surface salinity, and surface carbon dioxide (CO2) in the highly dynamic region between New Jersey and Bermuda (from the continental shelf, the Slope Sea, the Gulf Stream and part of the Sargasso Sea) through the aid of the SOOP. The Bermuda Container Line (BCL), owners of the MV Oleander, provides the vital role of supporting the unique collaboration by agreeing to equip their container vessel with oceanographic instrumentation and to collect the aforementioned data, at no extra charge. Go
NOAA AOML XBT/TSG
April 3, 2012. Miami, FL
First XBT Science Workshop (XSW-1)
July 7-8, 2011. Melbourne, Australia
NOAA AOML XBT/TSG
March 8-9, 2011. Miami, FL
NOAA AOML XBT/TSG
Miami, April 20-21, 2010
NOAA AOML XBT/TSG
Miami, May 12-13, 2009