Repeat high resolution expendable Bathythermograph (XBT) transects have been collected along a number of commercial shipping routes spanning the Pacific Ocean, the Drake Passage, and Tasmania to Dumont d'Urville. On each of the transects generally four surveys are conducted per year. Temperature data are usually collected by a scientist on board the vessel using an automatic XBT launcher designed at Scripps Institution of Oceanography (SIO). The launcher holds 6 XBT probes which are pre-programmed to drop at specific locations (using GPS) or times. The XBT probes are Sippican "Deep Blue", which are rated to 760 m depth, but typically return temperature to a depth of around 850 m at ship speeds of 15 to 18 knots. Sequential XBT casts are separated by 30-40 km along track, with closer station spacings of 10 km near boundaries, across the equator and in topographically varying regions. Sampling begins and ends near the 200 m isobath at the coastal endpoints of the tracks.

Prior to 1994 profiles were collected using a modified analog-to-digital (A/D) conversion board as described by Roemmich and Cornuelle (1987). From 1994 through 2004 a Sippican MK12 data acquisition system was employed, with the modification of the user interface driver programs. These programs were developed at SIO to provide a more user-friendly environment for the ship board data collectors, and to eventually enable collection by non-scientific personnel such as the ship's crew. Profiles are currently collected using AMVER SEAS 2K Windows based software and the Sippican MK21 data acquisition system. AMVER SEAS 2K was developed by NOAA's Atlantic Oceanographic and Meteorological Laboratory (AOML). It incorporates many of SIO's older data acquisition functions. See the poster page for a description of AMVER SEAS 2K.

Thermistor resistance is converted to temperature using a logarithmic fit (Steinhart and Hart, 1968). Depth is calculated using the original fall-rate equation provided by Sippican:

Original Sippican Deep Blue XBT fall rate equation:

       z (meters) = 6.472 t - 0.00216 t**2 (t in seconds)

The raw temperature/depth data are vertically averaged to 2 m bins and archived as ASCII files with date and time information. Position is provided by a GPS navigational system which is generally directly linked to the data acquisition system. Most quality control, such as removing wire breaks and temperature spikes, is done aboard the ship. Final quality control is completed at SIO, where the data are translated to the 1995 Hanawa et al corrected fall rate equation and further vertically averaged to 10 m bins to form a more compressed version of the data.

Hanawa et al (1995) Deep Blue XBT fall rate equation:

      z (meters) = 6.691 t - 0.00225 t**2 (t in seconds)

Note the .10 files available for download from this site reflect the Hanawa et al 1995 fall rate equation.

Cruise tracks and along track temperature/depth cross-sections are displayed for each cruise. The location of each individual XBT cast is indicated by the tick marks along the top axis of the temperature sections. These cross-sections have been constructed using an objective mapping routine to regularly grid the data in depth and latitude (or longitude). The routine employs a high signal-to-noise ratio so as to retain the true spatial structure.
The data are also available from the National Oceanographic Data Center (NODC).

References