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Metadata Report for BODC Series Reference Number 1071428

Metadata Summary

Data Description

Data Category CTD or STD cast
Instrument Type
Neil Brown MK3 CTD  CTD; water temperature sensor; salinity sensor; dissolved gas sensors
Chelsea Technologies Group Aquatracka III fluorometer  fluorometers
Chelsea Technologies Group Alphatracka II transmissometer  transmissometers
Instrument Mounting lowered unmanned submersible
Originating Country United Kingdom
Originator Dr Stuart Cunningham
Originating Organization Southampton Oceanography Centre (now National Oceanography Centre, Southampton)
Processing Status banked
Online delivery of data Download available - Ocean Data View (ODV) format
Project(s) -

Data Identifiers

Originator's Identifier CTD13714
BODC Series Reference 1071428

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1999-09-27 03:35
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval 2.0 decibars

Spatial Co-ordinates

Latitude 61.42933 N ( 61° 25.8' N )
Longitude 9.99633 W ( 9° 59.8' W )
Positional Uncertainty 0.0 to 0.01 n.miles
Minimum Sensor or Sampling Depth 0.99 m
Maximum Sensor or Sampling Depth 1186.12 m
Minimum Sensor or Sampling Height 3.08 m
Maximum Sensor or Sampling Height 1188.21 m
Sea Floor Depth 1189.2 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 Instantaneous - Depth measured below water line or instantaneous water body surface


BODC CODERankUnitsTitle
CPHLPR011Milligrams per cubic metreConcentration of chlorophyll-a {chl-a CAS 479-61-8} per unit volume of the water body [particulate >unknown phase] by in-situ chlorophyll fluorometer
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
PSALST011DimensionlessPractical salinity of the water body by CTD and computation using UNESCO 1983 algorithm
SIGTPR011Kilograms per cubic metreSigma-theta of the water body by CTD and computation from salinity and potential temperature using UNESCO algorithm
TEMPST011Degrees CelsiusTemperature of the water body by CTD or STD
TVLTDZ011VoltsRaw signal (voltage) of instrument output by 25cm path length transmissometer

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

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

Neil Brown MK3 CTD

The Neil Brown MK3 conductivity-temperature-depth (CTD) profiler consists of an integral unit containing pressure, temperature and conductivity sensors with an optional dissolved oxygen sensor in a pressure-hardened casing. The most widely used variant in the 1980s and 1990s was the MK3B. An upgrade to this, the MK3C, was developed to meet the requirements of the WOCE project.

The MK3C includes a low hysteresis, titanium strain gauge pressure transducer. The transducer temperature is measured separately, allowing correction for the effects of temperature on pressure measurements. The MK3C conductivity cell features a free flow, internal field design that eliminates ducted pumping and is not affected by external metallic objects such as guard cages and external sensors.

Additional optional sensors include pH and a pressure-temperature fluorometer. The instrument is no longer in production, but is supported (repair and calibration) by General Oceanics.


These specification apply to the MK3C version.

Pressure Temperature Conductivity

6500 m

3200 m (optional)

-3 to 32°C 1 to 6.5 S cm-1

0.0015% FS

0.03% FS < 1 msec


0.003°C < 30 msec

0.0001 S cm-1

0.0003 S cm-1 < 30 msec

Further details can be found in the specification sheet.

RRS Discovery Cruise D242 CTD Instrumentation

The CTD profiles were taken using two Neil Brown System MkIIIc CTDs (DEEP03 and DEEP04), with a 24 bottle rosette frame.

Sensor Manufacturer/Model Serial Number Last calibration date Comments
CTD Neil Brown MkIIIc DEEP03 (Stations 13649-13676 and 13687-13757) - Incorporating oxygen sensor membrane, which was subsequently calibrated with discrete samples. There were problems with the oxygen sensor on casts 74 and 84.
DEEP04 (Stations 13630-13648 and 13677-13686) -
Transmissometer Chelsea Instruments MK II Alphatracka (25 cm pathlength) 161/2642/003 - -
Fluorometer Chelsea Instruments MK III Aquatracka 88/2960/163 - -
Altimeter Simrad - - -
Reversing thermometers SIS T995 - On rosette position 4
T1545 - On rosette position 1
Reversing pressure meters SIS P6394 - On rosette position 4
P6534 - On rosette position 1
LADCP - - - A package on loan from Woods Hole was used between casts 1 and 99. This was swapped to a Southampton-owned instrument for casts 101-111. A replacement Southampton instrument was used for casts 112-125.

Chelsea Technologies Group Aquatracka MKIII fluorometer

The Chelsea Technologies Group Aquatracka MKIII is a logarithmic response fluorometer. Filters are available to enable the instrument to measure chlorophyll, rhodamine, fluorescein and turbidity.

It uses a pulsed (5.5 Hz) xenon light source discharging along two signal paths to eliminate variations in the flashlamp intensity. The reference path measures the intensity of the light source whilst the signal path measures the intensity of the light emitted from the specimen under test. The reference signal and the emitted light signals are then applied to a ratiometric circuit. In this circuit, the ratio of returned signal to reference signal is computed and scaled logarithmically to achieve a wide dynamic range. The logarithmic conversion accuracy is maintained at better than one percent of the reading over the full output range of the instrument.

Two variants of the instrument are available, both manufactured in titanium, capable of operating in depths from shallow water down to 2000 m and 6000 m respectively. The optical characteristics of the instrument in its different detection modes are visible below:

Excitation Chlorophyll a Rhodamine Fluorescein Turbidity
Wavelength (nm) 430 500 485 440*
Bandwidth (nm) 105 70 22 80*
Emission Chlorophyll a Rhodamine Fluorescein Turbidity
Wavelength (nm) 685 590 530 440*
Bandwidth (nm) 30 45 30 80*

* The wavelengths for the turbidity filters are customer selectable but must be in the range 400 to 700 nm. The same wavelength is used in the excitation path and the emission path.

The instrument measures chlorophyll a, rhodamine and fluorescein with a concentration range of 0.01 µg l-1 to 100 µg l-1. The concentration range for turbidity is 0.01 to 100 FTU (other wavelengths are available on request).

The instrument accuracy is ± 0.02 µg l-1 (or ± 3% of the reading, whichever is greater) for chlorophyll a, rhodamine and fluorescein. The accuracy for turbidity, over a 0 - 10 FTU range, is ± 0.02 FTU (or ± 3% of the reading, whichever is greater).

Further details are available from the Aquatracka MKIII specification sheet.

Chelsea Technologies Group ALPHAtracka and ALPHAtracka II transmissometers

The Chelsea Technologies Group ALPHAtracka (the Mark I) and its successor, the ALPHAtracka II (the Mark II), are both accurate (< 0.3 % fullscale) transmissometers that measure the beam attenuation coefficient at 660 nm. Green (565 nm), yellow (590 nm) and blue (470 nm) wavelength variants are available on special order.

The instrument consists of a Transmitter/Reference Assembly and a Detector Assembly aligned and spaced apart by an open support frame. The housing and frame are both manufactured in titanium and are pressure rated to 6000 m depth.

The Transmitter/Reference housing is sealed by an end cap. Inside the housing an LED light source emits a collimated beam through a sealed window. The Detector housing is also sealed by an end cap. A signal photodiode is placed behind a sealed window to receive the collimated beam from the Transmitter.

The primary difference between the ALPHAtracka and ALPHAtracka II is that the Alphatracka II is implemented with surface-mount technology; this has enabled a much smaller diameter pressure housing to be used while retaining exactly the same optical train as in the Mark I. Data from the Mark II version are thus fully compatible with that already obtained with the Mark I. The performance of the Mark II is further enhanced by two electronic developments from Chelsea Technologies Group - firstly, all items are locked in a signal nulling loop of near infinite gain and, secondly, the signal output linearity is inherently defined by digital circuitry only.

Among other advantages noted above, these features ensure that the optical intensity of the Mark II, indicated by the output voltage, is accurately represented by a straight line interpolation between a reading near full-scale under known conditions and a zero reading when blanked off.

For optimum measurements in a wide range of environmental conditions, the Mark I and Mark II are available in 5 cm, 10 cm and 25 cm path length versions. Output is default factory set to 2.5 volts but can be adjusted to 5 volts on request.

Further details about the Mark II instrument are available from the Chelsea Technologies Group ALPHAtrackaII specification sheet.

RRS Discovery Cruise D242 CTD Processing

Originator's Data Processing

  • Sampling Strategy

    Two WOCE-standard CTD packages (DEEP03 and DEEP04) were used during D242, collectively generating 125 profiles. Discrete water samples were also obtained on the casts for calibration of the conductivity and oxygen sensors. Various data quality issues were encountered, which necessitated swapping between the units at various stages of the cruise. These are summarised in the table below. For further details, users should refer to both the cruise and data quality report.

    Stations Cast numbers CTD package Comments
    13630-13648 001-019 DEEP04 Conductivity cell displayed hysteresis on upcast
    13649-13676 020-047 DEEP03 Concerns about the stability of the temperature sensor
    13677-13686 048-057 DEEP04 Replacement conductivity cell still displaying hysteresis on upcast
    13687-13757 058-125 DEEP03 -

    In addition to these issues, the downcast salinity profiles obtained from both packages were also unusually noisy throughout the cruise.

  • Data Processing

    Raw CTD data were captured and stored in three ways: 1) to the hard disk of the CTD acquisition PC 2) to the RVS Level A system 3) directly from the CTD deck unit onto the SOC DAPS (Southampton Oceanography Centre - Data Acquisition Processing Software) system. Data from the latter source were used for further processing.

    The DAPS system checks for pressure jumps and subsequently produces 1 sec averages of the raw 25 Hz data. Two ASCII files are generated for each cast, one for CTD profile data, the other for bottle firing data. Post processing of these output files was conducted in the Pstar environment.

  • Field Calibrations

    A description of the CTD calibrations applied to instrumentation is presented below:


    Raw temperatures were scaled according to:

    Traw = 0.0005 Traw

    then calibrated using the following coefficients:

    T = -2.1443 + 0.991259 Traw (DEEP03)

    T = 0.1309 + 0.999278 Traw (DEEP04)

    Due to a lag between the conductivity and temperature sensor measurements, the time rate of change of temperature was used to "speed up" the temperature measurements according to:

    T = T + τ δ T / δ t

    where the rate of change of temperature is determined over a 1 sec interval. The time constants, τ = 0.25 (DEEP03) and τ = 0.20 (DEEP04), were used.


    Raw pressure measurements were first scaled according to:

    Praw = 0.1 Praw

    then calibrated using the following coefficients:

    P = -39.3 + 1.07489 Praw (DEEP03)

    P = -37.8 + 1.07378 Praw (DEEP04)

    Following laboratory calibration, no further corrections were deemed necessary for temperature dependence or pressure hysteresis on either instrument.


    Raw conductivities were scaled according to:

    Craw = 0.001 Craw

    then calibrated using the following coefficients:

    C = -0.002 + 0.964 Craw (DEEP03)

    C = -0.0238 + 0.9552 Craw (DEEP04)

    This was followed by the cell material deformation correction:

    C = C [1 + α * (T - Tθ) + β * (P - Pθ)]

    where α = -6.5e-6C-1, β = 1.5e-8dbar-1, Tθ = 15°C and Pθ = 0dbar.

    Further adjustments were made to conductivity following comparisons of CTD data with bottle conductivities. The process differed between the two sensors to account for the hysteresis in DEEP04. DEEP03 corrections were performed directly to the CTD upcast conductivities, whilst casts obtained from DEEP04 had downcast conductivity corrected directly. The cruise report contains full details of offsets and the residuals (bottle salinity-CTD salinity) from the subsequent conversion to salinity.

    Fluorometer and Transmissometer

    The calibration of the CTD's voltage digitiser is given as:

    V = -5.027 + 1.534e-4 Vraw - 3.704e-12(Vraw ) 2 (DEEP03)

    V = -5.656 + 1.727e-4 Vraw - 2.244e-12(Vraw ) 2 (DEEP04)

    Transmissometer clear air and blank voltage readings were also obtained throughout the cruise for further calibration of the sensor, these are documented in the cruise report.

    Oxygen sensor

    The program oxyca3 was used to obtain the best fit of downcast CTD oxygen data to measured oxygen samples, based on the model of Owens and R.C. Millard, 1985. This is used to calibrate the 1 Hz CTD files using program oxygn3. The 2 db files are subsequently recalculated and merged with the original sample files.

    There were various issues with the oxygen sensor throughout the cruise. In some instances the data were unusable and set to null by the originator. The table below summarises these. Separate originator data quality comments relating to preserved oxygen data are noted in the data quality report.

    Stations Cast numbers Comment
    13649-13698 020-068 Oxygen data unrealistic
    13704-13705 073-074 Sensor failure
    13711-13714 080-083 High oxygen current values before failure on Station 13714
  • Post-cruise investigations

    The persistent problems encountered during D242 prompted a further investigation post cruise. The salinity spiking was attributed possibly to the presence of a horizontal flat bar on the CTD rosette frame, which resulted in the temperature and conductivity sensors measuring slightly different water masses. The source of the salinity hysteresis proved more difficult to identify. Full details of these investigations are documented in the Southampton CTD data quality report.

    Ultimately, the well-mixed, less noisy calibrated upcast data were deemed to be the most suitable final dataset for D242.

BODC Processing

  • Reformatting

    The data arrived at BODC as 125 Pstar files at 2 db resolution. These were reformatted to the internal QXF format. The following table shows which variables were mapped to BODC parameter codes and how this was achieved.

    Units Description BODC
    Units Comments
    press dbar Pressure exerted by the water column PRESPR01 dbar Calibrated by originator. Additional comparison with auxiliary pressure meters made by originator
    temp °C Temperature of the water column TEMPST01 °C Calibrated by originator. Additional comparison with reversing thermometers made by originator
    salin - Practical salinity of the water column PSALST01 - Calibrated against bottle data, by originator
    oxygen µmol/l Dissolved oxygen DOXYPR01 µmol/l Calibrated against bottle data, by originator
    fluor mg m-3 Concentration of chlorophyll-a CPHLPR01 mg m-3 Conversion from volts to concentration carried out by originator. No further details known.
    chtran volts Transmissometer output TVLTDZ01 volts -
  • Calibration

    Sigma theta and potential temperature were generated by BODC. Oxygen saturation was also calculated for those series containing dissolved oxygen measurements.

  • Quality control

    The reformatted data were visualised using the in-house EDSERPLO software. Suspect data were marked by adding an appropriate quality control flag.


Cunningham, S.A., 1999. Cruise Report No.28. RRS Discovery Cruise 242. 07 Sep - 06 Oct 1999 Atlantic - Norwegian Exchanges.

Holliday, N.P., 2000. Southampton Oceanography Centre Internal Document No.62. CTD Data Quality on Discovery Cruise D242.

Owens, W.B., Millard, R.C., 1985. A new algorithm for CTD oxygen calibration. Journal of Physical Oceanography, 15(5), 621-631.

Project Information

No Project Information held for the Series

Data Activity or Cruise Information


Cruise Name D242
Departure Date 1999-09-07
Arrival Date 1999-10-06
Principal Scientist(s)Stuart A Cunningham (Southampton Oceanography Centre)
Ship RRS Discovery

Complete Cruise Metadata Report is available here

Fixed Station Information

Fixed Station Information

Station NameLine Q (Iceland Ridge/Faroe Bank Channel)
CategoryOffshore route/traverse

Line Q (Iceland Ridge/Faroe Bank Channel)

Line Q is a repeat CTD survey line that has been occupied on several occasions since the 1980s. The section lies on the flanks of the Iceland Ridge in close proximity to the exit of the Faroe Bank Channel. Measurements made as part of repeat Line Q lie within a box bounded by co-ordinates 61° 24.5' N, 10° 3.6' W at the southwest corner and 61° 58.0' N, 08° 54.9' W at the northeast corner.

Related Fixed Station activities are detailed in Appendix 1

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

Appendix 1: Line Q (Iceland Ridge/Faroe Bank Channel)

Related series for this Fixed Station are presented in the table below. Further information can be found by following the appropriate links.

If you are interested in these series, please be aware we offer a multiple file download service. Should your credentials be insufficient for automatic download, the service also offers a referral to our Enquiries Officer who may be able to negotiate access.

Series IdentifierData CategoryStart date/timeStart positionCruise
380401CTD or STD cast1989-10-10 17:59:0061.5353 N, 9.4898 WRRS Charles Darwin CD42
380413CTD or STD cast1989-10-10 20:19:0061.582 N, 9.754 WRRS Charles Darwin CD42
380425CTD or STD cast1989-10-10 22:55:0061.657 N, 9.54 WRRS Charles Darwin CD42
380437CTD or STD cast1989-10-11 00:51:0061.746 N, 9.399 WRRS Charles Darwin CD42
380449CTD or STD cast1989-10-11 02:52:0061.835 N, 9.225 WRRS Charles Darwin CD42
380450CTD or STD cast1989-10-11 04:59:0061.938 N, 8.999 WRRS Charles Darwin CD42
381729CTD or STD cast1990-07-20 13:33:0061.8933 N, 9.0883 WRRS Charles Darwin CD50
381742CTD or STD cast1990-07-20 15:03:0061.8133 N, 9.2783 WRRS Charles Darwin CD50
381766CTD or STD cast1990-07-20 17:08:0061.7283 N, 9.435 WRRS Charles Darwin CD50
381791CTD or STD cast1990-07-20 18:53:0061.645 N, 9.615 WRRS Charles Darwin CD50
1071293CTD or STD cast1999-09-26 02:25:0061.966 N, 8.91517 WRRS Discovery D242
1252666Water sample data1999-09-26 02:38:0061.966 N, 8.91517 WRRS Discovery D242
1071300CTD or STD cast1999-09-26 03:54:0061.92633 N, 8.998 WRRS Discovery D242
1252678Water sample data1999-09-26 04:10:0061.92633 N, 8.998 WRRS Discovery D242
1071312CTD or STD cast1999-09-26 05:36:0061.88467 N, 9.09017 WRRS Discovery D242
1252691Water sample data1999-09-26 05:50:0061.88467 N, 9.09017 WRRS Discovery D242
1071324CTD or STD cast1999-09-26 07:11:0061.84717 N, 9.16817 WRRS Discovery D242
1252709Water sample data1999-09-26 07:27:0061.84717 N, 9.16817 WRRS Discovery D242
1071336CTD or STD cast1999-09-26 10:34:0061.80717 N, 9.2405 WRRS Discovery D242
1252710Water sample data1999-09-26 10:53:0061.80717 N, 9.2405 WRRS Discovery D242
1071348CTD or STD cast1999-09-26 12:36:0061.75183 N, 9.34433 WRRS Discovery D242
1252722Water sample data1999-09-26 12:56:0061.75183 N, 9.34433 WRRS Discovery D242
1071361CTD or STD cast1999-09-26 14:34:0061.70133 N, 9.4335 WRRS Discovery D242
1252734Water sample data1999-09-26 14:53:0061.70133 N, 9.4335 WRRS Discovery D242
1071373CTD or STD cast1999-09-26 16:31:0061.66117 N, 9.52367 WRRS Discovery D242
1252746Water sample data1999-09-26 16:49:0061.66117 N, 9.52367 WRRS Discovery D242
1071385CTD or STD cast1999-09-26 18:30:0061.62233 N, 9.60667 WRRS Discovery D242
1252758Water sample data1999-09-26 18:50:0061.62233 N, 9.60667 WRRS Discovery D242
1071397CTD or STD cast1999-09-26 20:35:0061.58283 N, 9.70317 WRRS Discovery D242
1252771Water sample data1999-09-26 20:57:0061.58283 N, 9.70317 WRRS Discovery D242
1071404CTD or STD cast1999-09-26 22:48:0061.53467 N, 9.77167 WRRS Discovery D242
1252783Water sample data1999-09-26 23:22:0061.53467 N, 9.77167 WRRS Discovery D242
1071416CTD or STD cast1999-09-27 01:20:0061.48717 N, 9.87183 WRRS Discovery D242
1252795Water sample data1999-09-27 01:44:0061.48717 N, 9.87183 WRRS Discovery D242
1252802Water sample data1999-09-27 04:00:0061.42933 N, 9.99633 WRRS Discovery D242
1071441CTD or STD cast1999-09-27 08:33:0061.40883 N, 10.06017 WRRS Discovery D242
1252814Water sample data1999-09-27 08:59:0061.40883 N, 10.06017 WRRS Discovery D242