Metadata Report for BODC Series Reference Number 1113746

Metadata Summary

Data Description

Data Category CTD or STD cast
Instrument Type
Sea-Bird SBE 911plus CTD  CTD; water temperature sensor; salinity sensor
Sea-Bird SBE 3plus (SBE 3P) temperature sensor  water temperature sensor
Sea-Bird SBE 4C conductivity sensor  salinity sensor
Instrument Mounting lowered unmanned submersible
Originating Country United Kingdom
Originator Dr Stuart Cunningham
Originating Organization National Oceanography Centre, Southampton
Processing Status banked
Online delivery of data Download available - Ocean Data View (ODV) format
Project(s) RAPIDMOC

Data Identifiers

Originator's Identifier CTD_DI359_002_2DB
BODC Series Reference 1113746

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 2010-12-19 11:34
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval 2.0 decibars

Spatial Co-ordinates

Latitude 18.03850 N ( 18° 2.3' N )
Longitude 30.97290 W ( 30° 58.4' W )
Positional Uncertainty Unspecified
Minimum Sensor or Sampling Depth 0.99 m
Maximum Sensor or Sampling Depth 3504.23 m
Minimum Sensor or Sampling Height -0.53 m
Maximum Sensor or Sampling Height 3502.71 m
Sea Floor Depth 3503.7 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 Instantaneous - Depth measured below water line or instantaneous water body surface
Sea Floor Depth Datum Approximate - Depth is only approximate


BODC CODERankUnitsTitle
ACYCAA011DimensionlessSequence number
CNDCST011Siemens per metreElectrical conductivity of the water body by CTD
POTMCV011Degrees CelsiusPotential temperature of the water body by computation using UNESCO 1983 algorithm
PRESPR011DecibarsPressure (spatial coordinate) exerted by the water body by profiling pressure sensor and correction to read zero at sea level
PSALCC011DimensionlessPractical salinity of the water body by CTD and computation using UNESCO 1983 algorithm and calibration against independent measurements
SIGTPR011Kilograms per cubic metreSigma-theta of the water body by CTD and computation from salinity and potential temperature using UNESCO algorithm
TEMPCU011Degrees CelsiusTemperature of the water body by CTD and NO verification against independent measurements

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

RAPID Cruise D359 CTD instrument description

CTD unit and auxiliary sensors

The CTD configuration comprised a Sea-Bird Electronics 9plus system #09P-46253-0869, with accompanying Sea-Bird Electronics 11plus V2 deck unit #11P-24680-0587. The CTD frame was fitted with two Sea-Bird 3 Premium temperature sensors, two Sea-Bird 4 conductivity sensors, a digiquartz temperature compensated pressure sensor and a Tritech PA200 200kHz altimeter. All instruments (other than cast 001) were attached to a Sea-Bird-32 24 position carousel #32-37898-0518 containing 12 Ocean Test Equipment 10L water samplers (#1A, 3A, 5A, 7A, 9A, 11A, 13A, 15A, 17A, 19A, 21A and 23A) and were used in alternate positions on the CTD frame. This was to allow moored instruments to be strapped to the frame for calibration purposes. Cast 001 used 24 bottles and therefore included the remaining even numbered samplers (#2A, 4A, 6A, 8A, 10A, 12A, 14A, 16A, 18A, 20A, 22A and 24A). The table below lists more detailed information about the various sensors.

Sensor Unit Model Serial Number Full Specification Casts Last calibration date (YYYY-MM-DD) Comments
CTD underwater unit SBE 9plus 09P-46253-0869 SBE 9plus 1-15 - -
Temperature sensor SBE 3P 03P-2674 SBE 03P 1-15 2010-10-14 Primary sensor
Temperature sensor SBE 3P 03P-4105 SBE 03P 1-9 2010-10-14 Secondary sensor
Temperature sensor SBE 3P 03P-4872 SBE 03P 10-15 - Secondary sensor
Conductivity sensor SBE 4 04C-2571 SBE 04C 1-8 2010-08-27 Primary sensor
Conductivity sensor SBE 4 04C-3768 SBE 04C 9-15 - Primary sensor
Conductivity sensor SBE 04C 04C-3258 SBE 04C 1-15 2010-08-27 Secondary sensor
Pressure sensor SBE 9plus digiquartz 100898 - 1-15 2009-07-31 -
Altimeter Tritech PA-200kHz 6196.118171 - 1-15 - -

The salinity samples from the CTD were analysed during the cruise using a Guildline Autosal model 8400B(#68958).

Sea-Bird Electronics SBE 911 and SBE 917 series CTD profilers

The SBE 911 and SBE 917 series of conductivity-temperature-depth (CTD) units are used to collect hydrographic profiles, including temperature, conductivity and pressure as standard. Each profiler consists of an underwater unit and deck unit or SEARAM. Auxiliary sensors, such as fluorometers, dissolved oxygen sensors and transmissometers, and carousel water samplers are commonly added to the underwater unit.

Underwater unit

The CTD underwater unit (SBE 9 or SBE 9 plus) comprises a protective cage (usually with a carousel water sampler), including a main pressure housing containing power supplies, acquisition electronics, telemetry circuitry, and a suite of modular sensors. The original SBE 9 incorporated Sea-Bird's standard modular SBE 3 temperature sensor and SBE 4 conductivity sensor, and a Paroscientific Digiquartz pressure sensor. The conductivity cell was connected to a pump-fed plastic tubing circuit that could include auxiliary sensors. Each SBE 9 unit was custom built to individual specification. The SBE 9 was replaced in 1997 by an off-the-shelf version, termed the SBE 9 plus, that incorporated the SBE 3 plus (or SBE 3P) temperature sensor, SBE 4C conductivity sensor and a Paroscientific Digiquartz pressure sensor. Sensors could be connected to a pump-fed plastic tubing circuit or stand-alone.

Temperature, conductivity and pressure sensors

The conductivity, temperature, and pressure sensors supplied with Sea-Bird CTD systems have outputs in the form of variable frequencies, which are measured using high-speed parallel counters. The resulting count totals are converted to numeric representations of the original frequencies, which bear a direct relationship to temperature, conductivity or pressure. Sampling frequencies for these sensors are typically set at 24 Hz.

The temperature sensing element is a glass-coated thermistor bead, pressure-protected inside a stainless steel tube, while the conductivity sensing element is a cylindrical, flow-through, borosilicate glass cell with three internal platinum electrodes. Thermistor resistance or conductivity cell resistance, respectively, is the controlling element in an optimized Wien Bridge oscillator circuit, which produces a frequency output that can be converted to a temperature or conductivity reading. These sensors are available with depth ratings of 6800 m (aluminium housing) or 10500 m (titanium housing). The Paroscientific Digiquartz pressure sensor comprises a quartz crystal resonator that responds to pressure-induced stress, and temperature is measured for thermal compensation of the calculated pressure.

Additional sensors

Optional sensors for dissolved oxygen, pH, light transmission, fluorescence and others do not require the very high levels of resolution needed in the primary CTD channels, nor do these sensors generally offer variable frequency outputs. Accordingly, signals from the auxiliary sensors are acquired using a conventional voltage-input multiplexed A/D converter (optional). Some Sea-Bird CTDs use a strain gauge pressure sensor (Senso-Metrics) in which case their pressure output data is in the same form as that from the auxiliary sensors as described above.

Deck unit or SEARAM

Each underwater unit is connected to a power supply and data logging system: the SBE 11 (or SBE 11 plus) deck unit allows real-time interfacing between the deck and the underwater unit via a conductive wire, while the submersible SBE 17 (or SBE 17 plus) SEARAM plugs directly into the underwater unit and data are downloaded on recovery of the CTD. The combination of SBE 9 and SBE 17 or SBE 11 are termed SBE 917 or SBE 911, respectively, while the combinations of SBE 9 plus and SBE 17 plus or SBE 11 plus are termed SBE 917 plus or SBE 911 plus.


Specifications for the SBE 9 plus underwater unit are listed below:

Parameter Range Initial accuracy Resolution at 24 Hz Response time
Temperature -5 to 35°C 0.001°C 0.0002°C 0.065 sec
Conductivity 0 to 7 S m-1 0.0003 S m-1 0.00004 S m-1 0.065 sec (pumped)
Pressure 0 to full scale (1400, 2000, 4200, 6800 or 10500 m) 0.015% of full scale 0.001% of full scale 0.015 sec

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

BODC CTD Screening

BODC screen both the series header qualifying information and the parameter values in the data cycles themselves.

Header information is inspected for:

Documents are written by BODC highlighting irregularities that cannot be resolved.

Data cycles are inspected using depth series plots of all parameters. These presentations undergo screening to detect infeasible values within the data cycles themselves and inconsistencies when comparing adjacent data sets displaced with respect to depth, position or time.

Values suspected of being of non-oceanographic origin may be tagged with the BODC flag denoting suspect value.

The following types of irregularity, each relying on visual detection in the time series plot, are amongst those that may be flagged as suspect:

If a large percentage of the data is affected by irregularities, deemed abnormal, then instead of flagging the individual suspect values, a caution may be documented.

The following types of inconsistency are detected automatically by software:

Inconsistencies between the characteristics of the data set and those of its neighbours are sought, and where necessary, documented. This covers inconsistencies in the following:

This screening of the parameter values seeks to confirm the qualifying information and the source laboratory's comments on the series. In screening and collating information, every care is taken to ensure that errors of BODC's making are not introduced.

RAPID Cruise D359 BODC CTD data processing

The data arrived at BODC in 15 MSTAR format files representing the CTD casts conducted during cruise D359. The data contained in the files are the downcast data averaged to a 2db pressure grid. The casts were reformatted to BODC's internal NetCDF format. The following table shows the mapping of variables within the MSTAR files to appropriate BODC parameter codes:

Originator's variable Units Description BODC parameter code Units Comments
press dbar Pressure exerted by the water column PRESPR01 dbar Manufacturer's calibration applied.
temp1 °C Temperature of the water column by CTD (Primary sensor) TEMPCU01 °C ITS-90
temp2 °C Temperature of the water column by CTD (Secondary sensor) TEMPCU02 °C ITS-90
psal1 - Practical salinity of the water column (Primary sensor data) PSALCC01 - Calculated by Data Originator using calibrated conductivity.
psal2 - Practical salinity of the water column (Secondary sensor data) PSALCU02 - Calculated by Data Originator using uncalibrated conductivity.
potemp1 °C Potential temperature of the water column (Primary sensor) POTMCV01 °C Not transferred
potemp2 °C Potential temperature of the water column (Secondary sensor) POTMCV02 °C Not transferred
cond1 mS/cm Electrical conductivity of the water column (Primary sensor) CNDCST01 S/m /10. Calibrated by Data Originator with discrete salinity samples.
cond2 mS/cm Electrical conductivity of the water column (Secondary sensor) CNDCST02 S/m /10
depth metres Depth below surface converted from pressure using UNESCO algorithm DEPHPR01 metres Not transferred
time seconds Time in seconds since the origin defined in the metadata field data_time_origin - - Not transferred

The reformatted data were visualised using the in-house EDSERPLO software. Suspect data were marked by adding an appropriate quality control flag, and missing data marked by setting both the data to an appropriate value and setting the quality control flag.

Detailed metadata and documentation were compiled and linked to the data.

RAPID Cruise D359 Originator's CTD data processing

Sampling strategy

A total of 15 CTD casts were performed during the cruise along approximately 26.5°N, which includes the Eastern boundary, Mid Atlantic Ridge and Western boundary sections of the RAPIDMOC array. On each cast, up to 12 SBE37 MicroCATs were attached to the frame for calibration purposes. Acoustic releases were also tested on several casts. One cast (cast 001) used 24 water samplers as a test, so no MicroCATs were attached. The CTD casts provided start-point calibrations for instruments to be deployed and end-point calibrations for recovered instruments. For recovered instruments that were re-deployed, the post-deployment cast provided a pre-deployment calibration. The instruments were set to the fastest sampling rate and the CTD lowered as normal. On the upcast, the bottle stops were increased to 5 minutes to allow time for stabilisation and the provision of more accurate data. To allow the instruments to be attached to the CTD frame using bespoke attachments, up to 12 sample bottles were removed on all casts (excluding cast 001).

Data processing

Raw CTD data were transferred from the Sea-Bird deck unit to a LINUX machine via Sea-Bird software. The binary files are converted using Sea-Bird processing software (SBE Data Processing v7.20g). Physical units were calculated from the frequency data using the manufacturer's calibration routines and the data converted to ASCII format. The ASCII files were converted to MSTAR format and MEXEC programs run to process the data which included reducing the frequency of the data from 24Hz to 1Hz, calibrating the data, and averaging the downcast to a 2db pressure grid. A calibration was produced for the CTD primary conductivity sensor by merging the salinity sample data with the CTD data. Details of the MEXEC programs used and further details of the processing performed can be found in Cunningham et al. (2011).

Field calibrations

Independent conductivity samples, obtained from the bottles on the CTD frame and measured with the salinometer, were used to calibrate the CTD data. The calibration of the conductivity is applied to both the upward and downward profiles of the CTD by defining a factor, which represents the difference of conductivity between the bottles and the CTD. This factor is called the slope correction. It is defined by


The calibrated data can be produced by multiplying K with the raw data: Ccorrected=CCTD*K.

To ensure the accuracy of the measured bottle conductivities, the drifts of the standard salinometer samples were corrected to their theoretical values before calibration.


Cunningham, S.A., Wright, P.G., Collins, J. (ed.) (2011) RRS DiscoveryCruise D359, 17 Dec 2010 - 14 Jan 2011. RAPID Mooring cruise report. Southampton, UK, National Oceanography Centre, Southampton, 197pp. (National Oceanography Centre Southampton Cruise Report, No. 09)

Project Information

Monitoring the Meridional Overturning Circulation at 26.5N (RAPIDMOC)

Scientific Rationale

There is a northward transport of heat throughout the Atlantic, reaching a maximum of 1.3PW (25% of the global heat flux) around 24.5°N. The heat transport is a balance of the northward flux of a warm Gulf Stream, and a southward flux of cooler thermocline and cold North Atlantic Deep Water that is known as the meridional overturning circulation (MOC). As a consequence of the MOC northwest Europe enjoys a mild climate for its latitude: however abrupt rearrangement of the Atlantic Circulation has been shown in climate models and in palaeoclimate records to be responsible for a cooling of European climate of between 5-10°C. A principal objective of the RAPID programme is the development of a pre-operational prototype system that will continuously observe the strength and structure of the MOC. An initiative has been formed to fulfill this objective and consists of three interlinked projects:

The entire monitoring array system created by the three projects will be recovered and redeployed annually until 2008 under RAPID funding. From 2008 until 2014 the array will continue to be serviced annually under RAPID-WATCH funding.

The array will be focussed on three regions, the Eastern Boundary (EB), the Mid Atlantic Ridge (MAR) and the Western Boundary (WB). The geographical extent of these regions are as follows:


Baehr, J., Hirschi, J., Beismann, J.O. and Marotzke, J. (2004) Monitoring the meridional overturning circulation in the North Atlantic: A model-based array design study. Journal of Marine Research, Volume 62, No 3, pp 283-312.

Baringer, M.O'N. and Larsen, J.C. (2001) Sixteen years of Florida Current transport at 27N Geophysical Research Letters, Volume 28, No 16, pp3179-3182

Bryden, H.L., Johns, W.E. and Saunders, P.M. (2005) Deep Western Boundary Current East of Abaco: Mean structure and transport. Journal of Marine Research, Volume 63, No 1, pp 35-57.

Hirschi, J., Baehr, J., Marotzke J., Stark J., Cunningham S.A. and Beismann J.O. (2003) A monitoring design for the Atlantic meridional overturning circulation. Geophysical Research Letters, Volume 30, No 7, article number 1413 (DOI 10.1029/2002GL016776)

RAPID- Will the Atlantic Thermohaline Circulation Halt? (RAPID-WATCH)

RAPID-WATCH (2007-2014) is a continuation programme of the Natural Environment Research Council's (NERC) Rapid Climate Change (RAPID) programme. It aims to deliver a robust and scientifically credible assessment of the risk to the climate of UK and Europe arising from a rapid change in the Atlantic Meridional Overturning Circulation (MOC). The programme will also assess the need for a long-term observing system that could detect major MOC changes, narrow uncertainty in projections of future change, and possibly be the start of an 'early warning' prediction system.

The effort to design a system to continuously monitor the strength and structure of the North Atlantic MOC is being matched by comparative funding from the US National Science Foundation (NSF) for the existing collaborations started during RAPID for the observational arrays.

Scientific Objectives

This work will be carried out in collaboration with the Hadley Centre in the UK and through international partnerships.

Mooring Arrays

The RAPID-WATCH arrays are the existing 26°N MOC observing system array (RAPIDMOC) and the WAVE array that monitors the Deep Western Boundary Current. The data from these arrays will work towards meeting the first scientific objective.

The RAPIDMOC array consists of moorings focused in three geographical regions (sub-arrays) along 26.5° N: Eastern Boundary, Mid-Atlantic Ridge and Western Boundary. The Western Boundary sub-array has moorings managed by both the UK and US scientists. The other sub-arrays are solely led by the UK scientists. The lead PI is Dr Stuart Cunningham of the National Oceanography Centre, Southampton, UK.

The WAVE array consists of one line of moorings off Halifax, Nova Scotia. The line will be serviced in partnership with the Bedford Institute of Oceanography (BIO), Halifax, Canada. The lead PI is Dr Chris Hughes of the Proudman Oceanographic Laboratory, Liverpool, UK.

All arrays will be serviced (recovered and redeployed) either on an annual or biennial basis using Research Vessels from the UK, US and Canada.

Modelling Projects

The second scientific objective will be addressed through numerical modelling studies designed to answer four questions:

Data Activity or Cruise Information


Cruise Name D359
Departure Date 2010-12-17
Arrival Date 2011-01-14
Principal Scientist(s)Stuart A Cunningham (National Oceanography Centre, Southampton)
Ship RRS Discovery

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
Q value below limit of quantification