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Metadata Report for BODC Series Reference Number 84251

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
SeaTech transmissometer  transmissometers
Instrument Mounting research vessel
Originating Country United Kingdom
Originator -
Originating Organization Institute of Oceanographic Sciences Wormley Laboratory (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 CTD15034
BODC Series Reference 84251

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1987-05-24 08:42
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval 5.0 decibars

Spatial Co-ordinates

Latitude 62.20660 N ( 62° 12.4' N )
Longitude 2.56000 W ( 2° 33.6' W )
Positional Uncertainty 0.1 to 0.5 n.miles
Minimum Sensor or Sampling Depth 2.48 m
Maximum Sensor or Sampling Depth 1694.04 m
Minimum Sensor or Sampling Height 17.96 m
Maximum Sensor or Sampling Height 1709.52 m
Sea Floor Depth 1712.0 m
Sea Floor Depth Source -
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
PPOPPR011PercentPotential transmittance (red light wavelength) per unit length of the water body by red light transmissometer and correction to a path length of 1m and for seawater compressibility
PRESPR011DecibarsPressure (spatial coordinate) exerted by the water body by profiling pressure sensor and correction to read zero at sea level
PSALPR011DimensionlessPractical salinity of the water body by conductivity cell and computation using UNESCO 1983 algorithm
TEMPST011Degrees CelsiusTemperature 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

Public domain data

These data have no specific confidentiality restrictions for users. However, users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgment.

The recommended acknowledgment is

"This study uses data from the data source/organisation/programme, provided by the British Oceanographic Data Centre and funded by the funding body."

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.

SeaTech Transmissometer


The transmissometer is designed to accurately measure the the amount of light transmitted by a modulated Light Emitting Diode (LED) through a fixed-length in-situ water column to a synchronous detector.


  • Water path length: 5 cm (for use in turbid waters) to 1 m (for use in clear ocean waters).
  • Beam diameter: 15 mm
  • Transmitted beam collimation: <3 milliradians
  • Receiver acceptance angle (in water): <18 milliradians
  • Light source wavelength: usually (but not exclusively) 660 nm (red light)


The instrument can be interfaced to Aanderaa RCM7 current meters. This is achieved by fitting the transmissometer in a slot cut into a customized RCM4-type vane.

A red LED (660 nm) is used for general applications looking at water column sediment load. However, green or blue LEDs can be fitted for specilised optics applications. The light source used is identified by the BODC parameter code.

Further details can be found in the manufacturer's Manual.

RRS Challenger Cruise 15/87 CTD Data Documentation


Documentation for CTD data collected on RRS Challenger Cruise 15/87 (May - June 1987) by the Institute of Oceanographic Sciences (Deacon Laboratory) Godalming, Surrey, UK., under the direction of P. M. Saunders.


The instrument used was a Neil Brown Instrument Systems CTD which measured pressure, temperature and conductivity and was fitted with a Beckman dissolved oxygen electrode. The CTD was used alongside a General Oceanics Rosette Multisampler with 12 water bottles, a 10kHz pinger, a bottom echo sounder and a Sea Tech transmissometer. Lowering and retrieval rates of 0.5 to 1.5 m/s were employed and the sensors were flushed with distilled water on recovery. Bottle samples and reversing thermometer measurements were made on ascent and the sea water samples were analysed using a Guildline Autolab Salinometer. Reversing thermometers were calibrated before and after the cruise.



The calibration equation based on laboratory measurements was taken to be:

P = 0.1 * PRAW - 7.0

No attempts were made to test these estimates with reversing thermometers on this cruise. A small systematic underestimate of pressure at depth arises from the temperature sensitivity of the strain gauge sensor. Since its magnitude, 3.5db for 10°C change, is small no correction has been made.


Laboratory calibrations were carried out after the cruise and the following equation obtained:

T = 0.00049953 * TRAW + 0.026

This has remained virtually unchanged since the purchase of the platinum resistance sensor in 1983: thus only a few comparisons were made with reversing thermometers - these are shown in the table below.


Salinity is not calibrated in the laboratory at IOS: hence the cell factor is carried forward from cruise to cruise. A value of 0.99971 was adopted to calculate salinity on-board ship. Approximately 380 samples of salinity were analysed on the ship using a Guildline Bench Salinometer, standardised against IAPSO Standard Seawater (batch P105, K15 = 0.99988). This revealed that the nominal salinity of the CTD needed to be corrected by between 0.009 and 0.015 during the cruise. The table below compares the salinities derived from the rosette sampler with the CTD values.


Due to a defective sensor and the lack of a spare no oxygen measurements were made.


Potential transmittance was computed. The instrument SN035 was employed and corrections were made for the air calibration, manufacturer's provided sensitivity, change in refractive index with pressure, temperature and salinity and for the increase in mass of clear water in the 1m path of the instrument with increasing pressure.

Data Processing and Quality

Fit of CTD Data to Rosette Sample Values

Difference between CTD and Rosette Measurements:

Variable Range Mean difference R.M.S. Number
Temperature, °C <3 °C - 0.001 0.002 7
  >3 °C - 0.005 0.005 4
Salinity, PSU 0-2000 db + 0.0002 0.0024 380

Original values were averaged over an interval of one second and calibration coefficients and correction factors applied. A time constant correction algorithm was employed to compensate for the slower response of the platinum resistance thermometer. Differences between successive values of each parameter were examined; the mean difference and its standard deviation calculated and values greater than several standard deviations from the mean difference were checked. Genuinely suspect data were then replaced by interpolated values.

It is noteworthy that the provisional salinity data required more editing than usual. Very sharp temperature gradients occurred at a number of stations, especially 15062 and 15063, where falls of 5°C occurred within 10m. In these sharp and prolonged gradient regions salinity spikes appeared despite the algorithms developed to take account of the different time constants of the temperature and conductivity sensors. These spikes were removed by the median sorting technique described by Pollard (1985) and linear interpolations made. A very small number of poor values survived but were picked off when temperature-salinity plots were made.

Derived quantities were computed from algorithms published by Fofonoff and Millard (1983). To remove the effect of ships heave data cycles were sorted by pressure before all values were averaged at 5db intervals, centred on 2.5db, 7.5db...


Saunders, P.M. and Gould, W.J. (1988).
CTD data from RRS Challenger Cruise 15/87 around the Faroe Islands. Institute of Oceanographic Sciences Deacon Laboratory, Report No. 256, 79pp.

Pollard, R.T. (1985).
CTD data from Northeast Atlantic collected on RRS Discovery Cruise 132 in February 1983. Institute of Oceanographic Sciences Deacon Laboratory, Report No. 192, 99pp.

Fofonoff, N.P. and Millard Jr., R.C. (1983).
Algorithms for the computation of fundamental properties of sea water. UNESCO Technical Paper on Marine Science 44.

Project Information

No Project Information held for the Series

Data Activity or Cruise Information


Cruise Name CH15
Departure Date 1987-05-09
Arrival Date 1987-06-05
Principal Scientist(s)W John Gould (Institute of Oceanographic Sciences Wormley Laboratory)
Ship RRS Challenger

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