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Metadata Report for BODC Series Reference Number 963698

Metadata Summary

Data Description

Data Category Bathythermograph -expendable
Instrument Type
Lockheed Martin Sippican T-7 XBT probe  bathythermographs; water temperature sensor; Expendable bathythermographs
Instrument Mounting research vessel
Originating Country United Kingdom
Originator Dr Jeff Evans
Originating Organization University of Cambridge, Scott Polar Research Institute
Processing Status banked
Online delivery of data Download available - Ocean Data View (ODV) format
Project(s) Autosub Under Ice

Data Identifiers

Originator's Identifier T7_00012
BODC Series Reference 963698

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 2003-03-05 17:04
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval -

Spatial Co-ordinates

Latitude 65.87468 S ( 65° 52.5' S )
Longitude 70.25242 W ( 70° 15.1' W )
Positional Uncertainty 0.05 to 0.1 n.miles
Minimum Sensor or Sampling Depth 2.0 m
Maximum Sensor or Sampling Depth 368.3 m
Minimum Sensor or Sampling Height -7.3 m
Maximum Sensor or Sampling Height 359.0 m
Sea Floor Depth 361.0 m
Sea Floor Depth Source CRREP
Sensor or Sampling Distribution Variable common depth - All sensors are grouped effectively at the same depth, but this depth varies significantly during the series
Sensor or Sampling Depth Datum Approximate - Depth is only approximate
Sea Floor Depth Datum Unspecified -


BODC CODERankUnitsTitle
ACYCAA011DimensionlessSequence number
DEPHCV011MetresDepth (spatial coordinate) relative to water surface in the water body by computation from probe free-fall time using unspecified algorithm
SVELCV011Metres per secondSound velocity in the water body by computation from temperature and salinity by unspecified algorithm
TEMPET011Degrees CelsiusTemperature of the water body by expendable bathythermograph (XBT)

Definition of Rank

  • Rank 1 is a one-dimensional parameter
  • Rank 2 is a two-dimensional parameter
  • Rank 0 is a one-dimensional parameter describing the second dimension of a two-dimensional parameter (e.g. bin depths for moored ADCP data)

Problem Reports

No Problem Report Found in the Database

Maximum Instrument Depth Greater Than Sea Floor Depth


It is possible for the maximum depth of a CTD/XBT cast to exceed the estimated sea floor depth at a given location.

The depth of a CTD unit is calculated from its measurements of pressure using an algorithm which makes assumptions about the density profile of the water column and XBT depth is often estimated from an assumed descent rate. Similarly, total water depth is calculated from the two-way travel time of sound waves through the water column making assumptions about the velocity of the sound waves. All of these calculations may contain errors, and the depth of a CTD/XBT unit may therefore appear to be below the sea floor.

Other Instrument Types

It is possible that instrument depths are taken from instantaneous measurements whereas water depth is read from a chart or corrected to a datum, such as mean sea level. If this occurs and the instrument depth has been read at high tide it is possible that an instrument mounted on the sea floor will have a depth half of the tidal range below the sea floor depth.

Data Access Policy

Open Data supplied by Natural Environment Research Council (NERC)

You must always use the following attribution statement to acknowledge the source of the information: "Contains data supplied by Natural Environment Research Council."

Narrative Documents

Lockhead Martin T7 XBT probe

The XBT's deployed on this cruise were orignally manufactured by Sippican, which was acquired by Lockhead Martin sometime after this cruise ended.

An XBT probe is an expendable free-fall temperature probe that provides a profile of measured temperature against depth calculated from a fall-rate model. The T-7 XBT Probe can be used within a maximum depth of 760m, may be deployed at a ship speed of up to 15 knots and has a vertical resolution of 65cm.

Further details can be found in the manufacturer's specification sheet.

BODC processing

The data were submitted to BODC in the XBT .EDF (Export Data File) format. The data were transferred to NetCDF format using BODC generated Matlab code. This involves mapping each of the originator's variables to a BODC parameter code. The table below shows the parameter mapping.

Originator's variable Units Description BODC Parameter Code Units
Depth metres Depth from probe free-fall time DEPHCV01 metres
Temperature degrees C Temperature of the water column by XBT TEMPET01 degrees C
Sound Velocity metres per second Sound velocity in the water column SVELCV01 metres per second

The depth of the falling XBT probe is estimated using time passed. As the XBT records continuously until the probe's wire has run out sometimes the XBT hits the sea floor before it has finished recording. Consequently, many of the profiles provided to BODC were deeper than the sea floor depth recorded by the originators. In these profiles, there was a noticeable change in the data when the probe hit the bottom. This could be verified by comparing the depth this change occurs to the originator's recorded sea floor depth. Using this change as a guide for the sea floor, the data were flagged after this point with the appropriate BODC data quality control flag. The following series were affected, 963662, 963674, 963698, 963778, 963791, 963809, 963858, 963883, 963895, 963902, 963914, 963999.

Subsequently, the data were screened using BODC in-house visualisation software. Any suspect data points were flagged with the appropriate BODC quality control flag.

Originator's processing

36 XBT casts were made throughout JCR84. T5 instruments were used in deep waters (>760 m) and T7 instruments were used in shallow waters (<760 m). The casts were made from the starboard side of the ship due to access considerations. The ship was slowed to a speed of 6 knots or less during T5 casts, while T7s were done at <15 knots. Most of the T5 casts went to the full T5 depth of 1830 m. Sound velocity profiles (SVPs) obtained from the XBT deployments were input to the EM120 multibeam swath bathymetry system and used in the relevant surveys.

Instrument type Casts
T5 1,2,3,4,5,10,11,12,13,14,15,16,20,21,22a,22b,29,30,31,32,33,34,
T7 6,7,8,9,17,18,19,23,24,25,26,27,28,35

The cruise report and more information on XBTs can be found via the JR84 metadata Report.

Individual SVP profiles were calculated from the XBT data by the system software, assuming a constant salinity. The *.EDF files (calculated sound velocity profiles) generated by the XBT system software were transferred to the multibeam swath bathymetry data processing workstation, and the data then imported into the multibeam swath bathymetry data acquisition system across the network.

The following salinities were assumed for each given cast in order to calculate the sound velocity profiles.

Cast(s) Assumed salinity (ppt) File name
1 33.93 T5_0002.EDF
2 33.90 T5_0004.EDF
3 33.90 T5_0006.EDF
4 33.50 T5_0007.EDF
5 33.50 T5_0008.EDF
6 33.60 T7_0009.EDF
7 33.58 T7_0010.EDF
8 33.46 T7_0011.EDF
9 33.55 T7_0012.EDF
10 33.55 T5_0013.EDF
11 33.56 T5_0014.EDF
12 33.51 T5_0015.EDF
13 33.50 T5_0016.EDF
14 33.40 T5_0017.EDF
15 32.96 T5_0018.EDF
16 33.50 T5_0019.EDF
17 33.30 T7_0020.EDF
18 33.40 T7_0021.EDF
19 32.20 T7_0022.EDF
20 33.40 T5_0023.EDF
21 33.30 T5_0024.EDF
22a 33.30 T5_0025.EDF
22b 33.30 T5_0026.EDF
23 33.30 T7_0027.EDF
24 33.30 T7_0028.EDF
25 33.0 T7_0029.EDF
26 33.30 T7_0030.EDF
27 33.40 T7_0031.EDF
28 33.20 T7_0032.EDF
29 33.30 T5_0033.EDF
30 33.27 T5_0034.EDF
31 33.30 T5_0035.EDF
32 32.78 T5_0036.EDF
33 33.55 T5_0037.EDF
34 33.56 T5_0038.EDF
35 33.60 T7_0039.EDF

Project Information

AutoSub Under Ice (AUI) Programme

AutoSub was an interdisciplinary Natural Environment Research Council (NERC) thematic programme conceived to investigate the marine environment of floating ice shelves with a view to advancing the understanding of their role in the climate system.

The AUI programme had the following aims:

  • To attain the programme's scientific objectives through an integrated programme based on interdisciplinary collaborations and an international perspective
  • To develop a data management system for the archiving and collation of data collected by the programme, and to facilitate the eventual exploitation of this record by the community
  • To provide high-quality training to develop national expertise in the use of autonomous vehicles in the collection of data from remote environments and the integration of such tools in wider programmes of research
  • To stimulate and facilitate the parameterising of sub-ice shelf processes in climate models, and to further demonstrate the value of autonomous vehicles as platforms for data collection among the wider oceanographic and polar community

Following the invitation of outline bids and peer review of fully developed proposals, eight research threads were funded as part of AUI:

Physical Oceanography

  • ISOTOPE: Ice Shelf Oceanography: Transports, Oxygen-18 and Physical Exchanges.
  • Evolution and impact of Circumpolar Deep Water on the Antarctic continental shelf.
  • Oceanographic conditions and processes beneath Ronne Ice Shelf (OPRIS).

Glaciology and Sea Ice

  • Autosub investigation of ice sheet boundary conditions beneath Pine Island Glacier.
  • Observations and modelling of coastal polynya and sea ice processes in the Arctic and Antarctic.
  • Sea ice thickness distribution in the Bellingshausen Sea.

Geology and Geophysics

  • Marine geological processes and sediments beneath floating ice shelves in Greenland and Antarctica: investigations using the Autosub AUV.


  • Controls on marine benthic biodiversity and standing stock in ice-covered environments.

The National Oceanography Centre Southampton (NOCS) hosted the AUI programme with ten further institutions collaborating in the project. The project ran from April 2000 until the end of March 2005, with some extensions to projects beyond this date because of research cruise delays. The following cruises were the fieldwork component of the AUI project:

Table 1: Details of the RRS James Clark Ross AUI cruises.

Cruise No. Cruise No. synonyms Dates Areas of study
JR20030218 JR84 28 February 2003 to 4 April 2003 Amundsen Sea, Antarctica
JR20040813 JR106, JR106a, JR106N (North) 10 August 2004 to 30 August 2004 Northeast Greenland Continental Shelf, Greenland
JR20040830 JR106b, JR106S (South) 30 August 2004 to 16 September 2004 Kangerlussuaq Fjord, Greenland
JR20050203 JR97, JR097 3 February 2005 to 11 March 2005 Fimbul Ice Shelf and Weddell Sea, Antarctica . This cruise was redirected from the Filcner-Ronne Ice Shelf to the Fimbul Ice Shelf because of unfavourable sea-ice conditions.

All the cruises utilised the AutoSub autonomous, unmanned and untethered underwater vehicle to collect observations beneath sea-ice and floating ice shelves. AutoSub can be fitted with a range of oceanographic sensors such as:

  • Conductivity Temperature Depth (CTD) instruments
  • Acoustic Doppler Current Profillers (ADCP)
  • A water sampler
  • Swath bathymetry systems
  • Cameras

In addition to use of AutoSub during each cruise measurements were taken from ship. These varied by cruise but included:

  • Ship underway measurements and sampling for parameters such as:
    • Salinity
    • Temperature
    • Fluorescence
    • Oxygen 18 isotope enrichment in water
    • Bathymetry using a swath bathymetry system
  • Full-depth CTD casts for with observations of samples taken for parameters such as:
    • Salinity
    • Temperature
    • Fluorescence
    • Optical transmissivity
    • Dissolved oxygen
    • Oxygen 18 isotope enrichment in water
    • Water CFC content
  • Sea floor photography and video using the WASP system
  • Sea floor sampling with trawls/rock dredges
  • Sea ice observations (ASPeCt), drifters and sampling

The AutoSub project also included numerical modelling work undertaken at University College London, UK.

The project included several firsts including the first along-track observations beneath an ice shelf using an autonomous underwater vehicle. The AutoSub vehicle was developed and enhanced throughout this programme and has now become part of the NERC equipment pool for general use by the scientific community. Further information for each cruise can be found in the respective cruise reports (links in Table 1).

Data Activity or Cruise Information


Cruise Name JR20030218 (JR84)
Departure Date 2003-02-28
Arrival Date 2003-04-04
Principal Scientist(s)Adrian Jenkins (British Antarctic Survey)
Ship RRS James Clark Ross

Complete Cruise Metadata Report is available here

Fixed Station Information

No Fixed Station Information held for the Series

BODC Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:

Flag Description
Blank Unqualified
< Below detection limit
> In excess of quoted value
A Taxonomic flag for affinis (aff.)
B Beginning of CTD Down/Up Cast
C Taxonomic flag for confer (cf.)
D Thermometric depth
E End of CTD Down/Up Cast
G Non-taxonomic biological characteristic uncertainty
H Extrapolated value
I Taxonomic flag for single species (sp.)
K Improbable value - unknown quality control source
L Improbable value - originator's quality control
M Improbable value - BODC quality control
N Null value
O Improbable value - user quality control
P Trace/calm
Q Indeterminate
R Replacement value
S Estimated value
T Interpolated value
U Uncalibrated
W Control value
X Excessive difference

SeaDataNet Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:

Flag Description
0 no quality control
1 good value
2 probably good value
3 probably bad value
4 bad value
5 changed value
6 value below detection
7 value in excess
8 interpolated value
9 missing value
A value phenomenon uncertain
B nominal value
Q value below limit of quantification