EXpendable BathyThermograph (XBT) and Conductivity Temperature Depth (CTD) Observations

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.

Besides temperature, Conductivity Temperature Depth (CTD) is an electronic device used by oceanographers to also measure precise in-situ salinity (via conductivity), depth (via pressure) and density as the instrument is deployed in the water from a ship. The sensors for conductivity, temperature and pressure are attached to a frame along with optional auxiliary sensors, such as those for measuring oxygen concentration and fluorescence. As the CTD package is lowered on a hydrowire, scientists are able to determine the distribution of these sea water properties as a function of depth. The products below are based on XBT temperature profiles nominally produced from the surface to 1000 meters and CTD temperature and salinity profiles nominally produced from the surface to 1600 meters.

During several research missions in the Gulf of Mexico, NOAA/AOML and UM/RSMAS scientists, onboard the NOAA Ship Gordon Gunter, the R/V F.G. Walton Smith, and the NOAA ship Nancy Foster deployed XBT and CTD instruments near the location of the Deepwater Horizon oil rig. Several temperature and salinity sections from these missions can be viewed by clicking on the maps and links below.

The XBT and CTD data used in this site can be accessed via ftp.

Why are these observations helpful?

These products provide information about the large scale circulation in the Gulf of Mexico. They describe the surface temperature as well as the structure of oceanic thermal features at different depths. They also provide information about ocean heat content and can be used in the validation of numerical models currently being utilized in the Gulf of Mexico monitoring.

Temperature and Salinity Sections for July 1-18, 2010 (NOAA ship Nancy Foster)

The map below shows the location of XBT (circles) and CTD (triangles, most CTD deployments coincide in position with XBT deployments) observations carried out by NOAA/AOML scientists onboard the NOAA ship Nancy Foster between July 1-18, 2010. The map also shows the mean sea surface temperature (SST, °C) for the aforementioned dates, superimposed on the regional bathymetry (in meters). The location of the Deepwater Horizon is denoted by a star. Nine temperature sections were produced using the XBT and CTD profiles obtained by the scientists during their cruise in the Gulf of Mexico, and these sections can be viewed by clicking on the track number ( #1-magenta, #2-red, #3-brown, #4-green, #5-white, #6-blue, #8-purple, #9-orange, and #10-cyan) on the map. Additionally, six salinity sections were produced, using the CTD profiles, for tracks #1-magenta, #2-red, #3-brown, #4-green, #6-blue, and #8-purple. In all these sections the deployments locations of XBT and CTD are indicated by green and blue inverted triangles, respectively.

XBT and CTD Observations for July 1-18, 2010

Section #1 at 82°W (magenta triangles)

 temperature salinity

Section #2 at 83.7°W (red circles)

 temperature salinity

Section #3 at 24.7°N (brown circles)

 temperature salinity

Section #4 at 85.8°W (green circles)

 temperature salinity

Section #5 at 25.5°N (white circles)

 temperature

Section #6 at 25.5°N (blue circles)

 temperature salinity

Section #8 at 26.5°N (purple circles)

 temperature salinity

Section #9 at 88°W (orange circles)

 temperature

Section #10 at 88.2°W (cyan circles)

 temperature

Temperature Sections for June 7-10, 2010 (R/V F.G. Walton Smith)

The map below shows the location of XBT observations (red, green and purple dots) deployed by NOAA/AOML and UM/RSMAS scientists onboard the R/V F.G. Walton Smith between June 7-10, 2010. The map also shows the mean sea surface temperature (SST, °C) for the aforementioned dates, superimposed on the regional bathymetry (in meters). The location of the Deepwater Horizon is denoted by a star. Three temperature sections were produced using temperature profiles obtained by the scientists during their transit from Gulf Port, Mississippi to Miami, Florida, and these sections can be viewed by clicking on the observations (section 1-red, section 2-green, and section 3-purple dots) on the map.

XBT Observations for June 7-10, 2010

Temperature Sections for May 28-30, 2010 (NOAA Ship Gordon Gunter)

The map below shows the location of XBT deployments (red, purple and brown dots) by NOAA/AOML scientists onboard the NOAA Ship Gordon Gunter, and the mean sea surface temperature (SST, °C) for May 28-30, 2010 superimposed on the regional bathymetry (in meters). The location of the Deepwater Horizon is denoted by a star. The XBT probes were deployed in concentric patterns near the location of the Deepwater Horizon oil rig. Two temperature sections were produced using the temperature profiles from the outer circle, located north (red dots), and south (purple dots) of the sunken oil rig, and can be viewed by clicking on the observations on the map.

XBT Observations for May 28-30, 2010

Data source for SST: Remote Sensing Systems (RSS)