Metadata Report for BODC Series Reference Number 832674

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
Instrument Mounting research vessel
Originating Country United Kingdom
Originator Prof Geoff Millward
Originating Organization University of Plymouth Institute of Marine Studies (now University of Plymouth, School of Geography, Earth and Environmental Sciences)
Processing Status banked
Project(s) Land Ocean Interaction Study (LOIS)

Data Identifiers

Originator's Identifier CTD8
BODC Series Reference 832674

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1993-12-12 23:41
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval 1.0 decibars

Spatial Co-ordinates

Latitude 53.33733 N ( 53° 20.2' N )
Longitude 0.47883 E ( 0° 28.7' E )
Positional Uncertainty 0.0 to 0.01 n.miles
Minimum Sensor Depth 2.48 m
Maximum Sensor Depth 12.39 m
Minimum Sensor Height 5.61 m
Maximum Sensor Height 15.52 m
Sea Floor Depth 18.0 m
Sensor Distribution Variable common depth - All sensors are grouped effectively at the same depth, but this depth varies significantly during the series
Sensor 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 CODE Rank Units Short Title Title
DOXYPR01 1 Micromoles per litre WC_dissO2 Concentration of oxygen {O2 CAS 7782-44-7} per unit volume of the water body [dissolved plus reactive particulate phase] by in-situ Beckmann probe
OXYSBB01 1 Percent BKBeck Saturation of oxygen {O2 CAS 7782-44-7} in the water body [dissolved plus reactive particulate phase] by in-situ Beckmann probe and computation from concentration using Benson and Krause algorithm
POTMCV01 1 Degrees Celsius WC_Potemp Potential temperature of the water body by computation using UNESCO 1983 algorithm
PRESPR01 1 Decibars Pres_Z Pressure (spatial co-ordinate) exerted by the water body by profiling pressure sensor and corrected to read zero at sea level
PSALST01 1 Dimensionless P_sal_CTD Practical salinity of the water body by CTD and computation using UNESCO 1983 algorithm
SIGTPR01 1 Kilograms per cubic metre SigTheta Sigma-theta of the water body by CTD and computation from salinity and potential temperature using UNESCO algorithm
TEMPST01 1 Degrees Celsius WC_temp_CTD Temperature of the water body by CTD or STD

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 Challenger 108C CTD Data Documentation


The CTD profiles were taken with an RVS Neil Brown Systems Mk3B CTD incorporating a pressure sensor, conductivity cell, platinum resistance thermometer and a Beckmann dissolved oxygen sensor. The CTD unit was mounted vertically in the centre of a protective cage approximately 1.5 m square. Attached to the bars of the frame were a Chelsea Instruments Aquatracka fluorometer and a SeaTech red light (661 nm) transmissometer with a 25 cm path length.

Above the frame was a General Oceanics rosette sampler fitted with twelve 10-litre water bottles. These comprised a mixture of Niskin, general purpose Go-Flo and ultra-clean teflon lined Go-Flo bottles as dictated by sampling requirements. The bases of the bottles were 0.75 m above the pressure head and their tops 1.55 m above it. One bottle was fitted with a holder for twin digital reversing thermometers mounted 1.38 m above the CTD temperature sensor.

Above the rosette was a PML 2pi PAR (photosynthetically available radiation) sensor pointing upwards to measure downwelling irradiance. A second 2pi PAR sensor, pointing downwards, was fitted to the bottom of the cage to measure upwelling irradiance. It should be noted that these sensors were vertically separated by 2 metres with the upwelling sensor 0.2 metres below the pressure head and the downwelling sensor 1.75 metres above it.

No account has been taken of rig geometry in the compilation of the CTD data set. However, all water bottle sampling depths have been corrected for rig geometry and represent the true position of the midpoint of the water bottle in the water column.

Data Acquisition

On each cast the CTD was lowered to a depth of approximately 5 metres and held until the oxygen reading stabilised. It was then raised to the surface and lowered continuously at 0.5 to 1.0 m s -1 to the closest comfortable proximity to the sea floor. The upcast was done in stages between the bottle firing depths.

Data were logged by the Research Vessel Services ABC data logging system. Output channels from the deck unit were logged at 16 Hz by a microprocessor interface (the Level A) which passed time stamped averaged cycles at 1Hz to a Sun workstation (the Level C) via a buffering system (the Level B).

On-Board Data Processing

The raw data comprised ADC counts. These were converted into engineering units (Volts for PAR meters, fluorometer and transmissometer; ml l -1 for oxygen; mohms cm -1 for conductivity; °C for temperature; decibars for pressure) by the application of laboratory determined calibrations. Salinity (Practical Salinity Units as defined in Fofonoff and Millard,1983) was calculated from the conductivity ratios (conductivity / 42.914) and a time lagged temperature using the function described in UNESCO Report 37 (1981) .

The data were submitted to BODC in this form on Quarter Inch Cartridge tapes in RVS internal format for post-cruise processing and databanking.

Post-Cruise Processing


The data were converted into the BODC internal format (PXF) to allow the use of in-house software tools, notably the workstation graphics editor. In addition to reformatting, the transfer program applied the following modifications to the data:

attenuance = -4 * ln (percent transmittance / 100)


Reformatted CTD data were transferred onto a high speed graphics workstation. Using custom in-house graphics editors, downcasts and upcasts were differentiated and the limits of the downcasts and upcasts were manually flagged.

Secondly, spikes on all the downcast channels were manually flagged. No data values were edited or deleted; quality control was achieved by modification of the associated quality control flag.

The pressure ranges over which the bottle samples were being collected were logged by manual interaction with the software. Usually, the marked reaction of the oxygen sensor to the bottle firing sequence was used to determine this. These pressure ranges were subsequently used, in conjunction with a geometrical correction for the position of the water bottles with respect to the CTD pressure transducer, to determine the pressure range of data to be averaged for calibration values.

Once screened on the workstation, the CTD downcasts were loaded into a database under the ORACLE Relational DataBase Management System. The fluorometer was obviously malfunctioning on this cruise. The signal was noisy and baseline drift between casts exceeded the total signal. Consequently, all fluorometer data were flagged as suspect after loading into the database.


With the exception of pressure, calibrations were done by comparison of CTD data against measurements made on water bottle samples or, for temperature, from the reversing thermometers mounted on the water bottles. In general, values were averaged from the CTD downcasts but where inspection on a graphics workstation showed significant hysteresis, values were manually extracted from the CTD upcasts.

All calibrations described here have been applied to the data.


The pressure offset was determined by looking at the pressures recorded when the CTD was clearly logging in air (readily apparent from the conductivity channel). The offsets formed two distinct value clusters. Consequently two calibrations have been applied thus:

CTD1 to CTD25 Corrected pressure = Observed pressure + 1.47
CTD26 to CTD31 Corrected pressure = Observed pressure + 0.57

The CTD temperature was compared with the digital reversing thermometers attached to the water bottles and was found to agree closely. Consequently, no correction has been applied to the temperature data.


Salinity was calibrated against water bottle samples measured on the Guildline 55358 Autolab Salinometer during the cruise. Samples were randomly taken from the bottles fired on 28 casts.

Samples were collected in glass bottles filled to just below the neck and sealed with plastic stoppers. Batches of samples were left for at least 24 hours to reach thermal equilibrium in the constant temperature laboratory containing the salinometer before analysis.

The correction offset for this cruise was found to be 0.00 ± 0.002, hence no calibration was required.


The dissolved oxygen sensor was calibrated against Winkler titration data as a primary standard and calibrated data from the Endeco underway sensor as a secondary standard. The oxygen titrations were undertaken using an automated titration technique similar to that described in Williams and Jenkinson (1982).

The following calibration equation was determined by regression analysis:

Corrected Oxygen = Observed Oxygen + 206 (R 2 = 50.8%, n=31)

The fluorometer malfunctioned on this cruise and consequently no CTD chlorophyll data are available. Users requiring chlorophyll data are referred to the water bottle and continuous underway data sets.


The light meter voltages were converted to µE/m 2 /s using the following equations determined by RVS in February 1990.

Downwelling PAR = exp (-4.977 * V + 7.0040) * 0.0375
Upwelling PAR = exp (-5.031* V + 6.8751) * 0.0375

Note that the scaling constant of 0.0375 is an empirical conversion from µW/cm 2 . The data may therefore be converted to W/m 2 by dividing by 3.75 if required.

Suspended Particulate Matter

The attenuance data were calibrated in terms of suspended particulate material by regressing attenuance values at the bottle firing depths against gravimetric determinations of sediment load. Data from all three legs of CH108 were pooled to produce a single calibration.

The calibration obtained was:

Suspended particulate load = (attenuance + 0.8188) / 0.2286 (n=61; R 2 =81.0%)

It should be noted that the intercept of this calibration (-0.82) differs significantly from the theoretically predicted value of 0.37.

Data Reduction

Once all screening and calibration procedures were completed, the data set was binned to 2 db (casts deeper than 100 db) or 1 db (casts shallower than 100 db). The binning algorithm excluded any data points flagged suspect and attempted linear interpolation over gaps up to 3 bins wide. If any gaps larger than this were encountered, the data in the gaps were set null.

Oxygen saturation data in the database have been computed from the calibrated oxygen, temperature and salinity data using the algorithm of Benson and Krause (1984).

Data Warnings

There are no fluorometer data from this cruise.

The intercept of the transmissometer SPM calibration deviates significantly from the theoretically predicted value.


Benson B.B. and Krause D. jnr. 1984. The concentration and isotopic fractionation of oxygen dissolved in fresh water and sea water in equilibrium with the atmosphere. Limnol. Oceanogr. 29 pp.620.632.

Fofonoff N.P. and Millard Jr., R.C. 1982. Algorithms for Computation of Fundamental Properties of Seawater. UNESCO Technical Papers in Marine Science 44.

Williams P.J. leB, and Jenkinson N.W. 1982. A transportable microprocessor-controlled Winkler titration suitable for field station and shipboard use. Limnol.Oceanogr. 27 pp.567-585.

Project Information

Land Ocean Interaction Study (LOIS)


The Land Ocean Interaction Study (LOIS) was a Community Research Project of the Natural Environment Research Council (NERC). The broad aim of LOIS was to gain an understanding of, and an ability to predict, the nature of environmental change in the coastal zone around the UK through an integrated study from the river catchments through to the shelf break.

LOIS was a collaborative, multidisciplinary study undertaken by scientists from NERC research laboratories and Higher Education institutions. The LOIS project was managed from NERC's Plymouth Marine Laboratory.

The project ran for six years from April 1992 until April 1998 with a further modelling and synthesis phase beginning in April 1998 and ending in April 2000.

Project Structure

LOIS consisted of the following components:

Marine Fieldwork

Marine field data were collected between September 1993 and September 1997 as part of RACS(C) and SES. The RACS data were collected throughout this period from the estuaries and coastal waters of the UK North Sea coast from Great Yarmouth to the Tweed. The SES data were collected between March 1995 and September 1996 from the Hebridean slope. Both the RACS and SES data sets incorporate a broad spectrum of measurements collected using moored instruments and research vessel surveys.

Data Activity or Cruise Information


Cruise Name CH108C
Departure Date 1993-12-11
Arrival Date 1993-12-23
Principal Scientist(s)Geoff Millward (University of Plymouth Institute of Marine Studies)
Ship RRS Challenger

Complete Cruise Metadata Report is available here

Fixed Station Information

Fixed Station Information

Station NameLOIS (RACS) Humber-Wash Grid HW
CategoryOffshore area
Latitude53° 18.98' N
Longitude0° 46.43' E
Water depth below MSL

LOIS (RACS) Humber-Wash Grid HW

The Humber-Wash grid was one of two areas sampled during the LOIS(RACS) project. The measurements collected lie within an area with its centre point at 53.3163N 0.7739E and which stretches from the Wash to the Humber Estuary. Note: Site HW5 was also known as anchor station HAS1.

BODC image

CTD casts were performed by several cruises between December 1992 and July 1995.

Other Series linked to this Fixed Station for this cruise - 832601 832613 832625 832637 832649 832650 832662 832686 832698 832705 832717 832822 832834 832846 832858 832871 832883

Other Cruises linked to this Fixed Station (with the number of series) - CH108A (77) CH115A (50) CH115C (74) CH117A (22) CH117A0 (8) CH117B (9) CH118A (25) CH118B (73) CH118C (18) CH119A (26) CH119B (16) CH119C (51) CH99 (17)

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