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Metadata Report for BODC Series Reference Number 380369


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 Deacon 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 CTD42008/wi
BODC Series Reference 380369
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1989-10-08 19:54
End Time (yyyy-mm-dd hh:mm) 1989-10-08 20:13
Nominal Cycle Interval 2.0 decibars
 

Spatial Co-ordinates

Latitude 61.46000 N ( 61° 27.6' N )
Longitude 8.27180 W ( 8° 16.3' W )
Positional Uncertainty Unspecified
Minimum Sensor or Sampling Depth 0.99 m
Maximum Sensor or Sampling Depth 671.42 m
Minimum Sensor or Sampling Height 23.58 m
Maximum Sensor or Sampling Height 694.01 m
Sea Floor Depth 695.0 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 42 CTD Data Documentation

Introduction

Documentation for CTD data collected on RRS Charles Darwin Cruise 42 (September - October 1989) 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 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 SeaTech 1m path transmissometer. Lowering and retrieval rates of 0.5 to 1.5m/s were employed and the sensors were flushed with distilled water on recovery. Bottle samples and reversing thermometer measurements were made on ascent and sea water samples were analysed using a Guildline Autolab Salinometer.

Throughout the cruise the CTD performed flawlessly except on the second station where noisy data were encountered. The CTD sea cable was then reterminated and there were no further problems.

A new conductivity cell was fitted en route to the first station. This required unsoldering the temperature sensor and enlarging the seating of the conductivity cell. The rewiring caused a shift in the calibration of the temperature sensor. A working calibration for both temperature and salinity was derived from digital reversing thermometers and salinity samples, the latter good to +/-0.002. A complete temperature recalibration was performed on return to the laboratory.

Calibration

Temperature

On the cruise 6 SIS digital reversing thermometers (RTM 4002) and one reversing pressure meter (RPM 6000) were available and were installed on the multisampler frames. After the first two casts it was apparent that even after the manufacturer's calibration corrections had been applied there were differences of the order of 0.01 °C between the values obtained by instruments on the same frame. The age of the digital reversing thermometers varied from about one year to 6 months and the differences encountered on the cruise suggested calibration drift rates of the order of 0.01 °C/year. The standard deviation of the observed differences for pairs of digital reversing thermometers and for CTD/digital reversing thermometer measurements is higher than previously observed but the unsteady conditions of measurement were largely responsible for this.

Pressure

The pressure sensor (RPM 6000) agreed well with the CTD pressure for the shallow casts (<850 dbars) but exhibited large differences for the moderately deep stations of the Charlie Gibbs Fracture Zone.

Salinity

Sea water samples drawn from 26 CTD casts were analysed in the constant temperature laboratory on Charles Darwin using a Guildline Autosal 8400 (Serial Number 42508) and standardised using Standard Seawater P111. Salinity determination from Guildline ration was performed on the cruise using Ocean Scientific International's software package 'Salinity'. This was highly efficient.

Oxygen

Dissolved oxygen samples were taken on 16 of the 26 CTD casts. Two samples were drawn from each Niskin bottle, giving a total of 250 samples for analysis by Winkler titration. The difference between the duplicates was generally better than 0.01 ml/l with standard deviation of 0.014 (for 338 samples, the remainder had much larger differences suggesting errors in the sampling or analysing procedure). This indicated that the accuracy of the measurements was better than 0.2 per cent compared to a possible accuracy of 0.1 per cent for the Winkler titration procedure.

Transmittance

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

Data Processing

Original values were averaged over an interval of one second and calibration coefficients and correction factors applied.

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. Only a limited amount of editing of the data was required. Data were sorted on pressure, averaged at 2 dbars and missing values were interpolated. Derived quantities were computed from algorithms published by Fofonoff and Millard (1983).

References

Crease, J. et. al. 1988.
The acquisition, calibration and analysis of CTD data. UNESCO Technical Papers in Marine Science. No. 54, 96pp.

Fofonoff, N.P. and Millard, R.C. 1983.
Algorithms for computation of fundamental properties of seawater. UNESCO Technical Papers in Marine Science. No. 44, 53pp.

Saunders, P.M., et. al. 1989.
RRS Charles Darwin Cruise 42, 22 Sep - 16 Oct 1989: Overflow studies in the Charlie-Gibbs Fracture Zone and near the Faeroe Islands. Institute of Oceanographic Sciences Deacon Laboratory, Cruise Report No. 209, 34pp.


Project Information


No Project Information held for the Series

Data Activity or Cruise Information

Cruise

Cruise Name CD42
Departure Date 1989-09-22
Arrival Date 1989-10-16
Principal Scientist(s)Peter M Saunders (Institute of Oceanographic Sciences Deacon 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
Q value below limit of quantification