Low Density and Frequently Repeated XBT Lines

The current low density (LD) and frequently repeated (FR) AOML network is comprised of data usually from Ship Of Opportunity Program (SOOP) XBT lines around the globe.

Expendable BathyThermographs (XBTs)

An XBT is a probe that is dropped from a ship and measures the temperature as it falls through the water. Two very small wires transmit 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.

Frequently-repeated XBT lines (FR)

Frequently-repeated XBT lines are mostly located in tropical regions in order to monitor strong seasonal to inter-annual (SI) variability. These lines 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 lines are ideally covered 18 times per year with an XBT drop every 100 to 150 km (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.

All XBT lines are reviewed through an international consortium with oversight by the SOOP Implementation Panel (SOOPIP). Some lines include time series measurements providing more than 30 years of data.

SEAS

AMVER SEAS 2K is a Windows based real-time ship and environmental data acquisition and transmission system. The AMVER software creates a series of reports, which describe point of departure, route and arrival of a ship. These reports are transmitted using Standard-C and include ships in a real-time search and rescue database. The SEAS 2K software acquires atmospheric and oceanographic data and transmits the data in real-time to the Global Telecommunication System (GTS) and to operational databases to be used by scientists. SEAS 2K is employed on ships of the Volunteer Observing System (VOS), Ship of Opportunity Program (SOOP) and on NOAA, UNOLS, Coast Guard vessels.

SEAS 2K is installed on more than 350 ships of the SOOP and over 200,000 AMVER SEAS met messages are transmitted per year. Additionally, 50 ships of the SOOP are deploying XBTs using SEAS 2K software. This includes low, frequently repeated and high density modes. NOAA/AOML and Scripps are the principal users of this software. National Marine Fisheries Service is running an Antarctic line (AX22) using this software. Go to SEAS - AMVER/SEAS page

Real-time Data

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 Lines (LD)

Low-density (LD, 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 lines are ideally covered 12 times per year with an XBT drop every 150 to 200 km (or approximately 4 drops per day). Sampling in LD mode has been the dominant mode in the early days of the SOOP network.