Search the data

Metadata Report for BODC Series Reference Number 57112


Metadata Summary

Data Description

Data Category CTD or STD cast
Instrument Type
NameCategories
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 WPRDA013BW
BODC Series Reference 57112
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1985-02-28 11:43
End Time (yyyy-mm-dd hh:mm) -
Nominal Cycle Interval 2.0 decibars
 

Spatial Co-ordinates

Latitude 31.93330 N ( 31° 56.0' N )
Longitude 26.99660 W ( 26° 59.8' W )
Positional Uncertainty 0.1 to 0.5 n.miles
Minimum Sensor or Sampling Depth 0.99 m
Maximum Sensor or Sampling Depth 5188.12 m
Minimum Sensor or Sampling Height 13.88 m
Maximum Sensor or Sampling Height 5201.01 m
Sea Floor Depth 5202.0 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
 

Parameters

BODC CODERankUnitsTitle
DOXYPR011Micromoles per litreConcentration of oxygen {O2 CAS 7782-44-7} per unit volume of the water body [dissolved plus reactive particulate phase] by in-situ Beckmann probe
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.

Specifications

These specification apply to the MK3C version.

Pressure Temperature Conductivity
Range

6500 m

3200 m (optional)

-3 to 32°C 1 to 6.5 S cm-1
Accuracy

0.0015% FS

0.03% FS < 1 msec

0.0005°C

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

Introduction

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.

Specifications

  • 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)

Notes

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 Charles Darwin Cruise 1/85 CTD Data Documentation

Introduction

This document covers the CTD data collected on RRS Charles Darwin Cruise 1/85 (February 1985) by the Institute of Oceanographic Sciences (Deacon Laboratory), Godalming, Surrey, UK., under the direction of P. M. Saunders.

Instrumentation

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.

Sampling Protocol

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.

Calibrations

Pressure

The deck pressure offset was stable and a value of 11 db was assumed for all stations. The table below shows differences in pressures determined from pairs of reversing thermometers (protected and unprotected) and simultaneous observations of CTD pressure.

Temperature

Laboratory calibrations of January and June 1985 confirm the stability of the platinum resistance sensor. A comparison is given in the table below between the CTD temperatures and reversing thermometers, separating the deep and shallow measurements.

Salinity

The sample measurements were slightly fresher by about 0.002PSU than the usual potential temperature (POTT) - practical salinity (S) relationship for POTT less than 2.6 °C of:

S = 34.698 + 0.098*POTT

This has been attributed to a slightly saline batch of standard sea water (P91).

The cell factor required to bring provisional CTD salinities into agreement with this relation was determined for each station. The table below compares salinities derived from the rosette sampler and Guildline salinometer with the CTD values.

Oxygen

From a sample value of oxygen concentration (determined by the Winkler method) the fractional saturation content was obtained by normalising it by the appropriate saturation value. The Beckman oxygen cell also measures fractional saturation F, given by the equation:

ln F = ln I + ln C + aT + bp

where

I = oxygen probe current
T = ambient temperature (electrode temperature ignored)
p = pressure

The electrode current exhibits a time dependent lag which has been corrected using the expression:

LAG (secs) = 70 e -0.14 * T(ambient) °C

A correction was made to each station to bring the dissolved oxygen in the deep water (below 3500db) to 5.67 ml/l. The comparison between sample oxygen concentrations and CTD oxygen values is shown in the table.

Transmittance

Potential transmittance, which takes account of the increasing mass of clear water in the 1m path of the instrument with increasing depth, was calculated.

Fit of CTD Data to Rosette Sample Values

  Difference between CTD and Rosette Measurements
Variable Range Mean difference R.M.S. Number
Pressure (db) 0-2000 db -1 2 7
  2000-5400 db -2 6 28
Temperature (°C) 5-23 °C +0.003 0.005 10
  2-5 °C +0.006 0.006 35
Salinity (PSU) 0-2000 db -0.003 0.010 10
  2000-5400 db +0.001 0.002 43
Oxygen (ml/l) 0-2000 db +0.11 0.10 10
  2000-5400 db -0.02 0.06 30

The depth of the 5 °C isotherm is approximately 1800 db.

Data Processing

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 in relation to the other sensors.

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.

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 2db intervals, centred on 1db, 3db and so on.

References

Saunders, P.M. (1985).
CTD data from the Madeira Abyssal Plain: Charles Darwin Cruise 1/85. Institute of Oceanographic Sciences, Report 217.

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

Cruise Name CD1
Departure Date 1985-02-13
Arrival Date 1985-03-04
Principal Scientist(s)W John Gould (Institute of Oceanographic Sciences Wormley Laboratory)
Ship RRS Charles Darwin

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