Metadata Report for BODC Series Reference Number 474931

• Metadata Summary

• Problem Reports

• Data Access Policy

• Narrative Documents

• Project Information

• Data Activity or Cruise Information

• Fixed Station Information

• BODC Quality Flags

• SeaDataNet Quality Flags

Metadata Summary

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.

Further details can be found in the specification sheet.

Cruise Bon Entente 1/86 CTD Sampling and Calibration Procedures

Instrumentation

A Neil Brown Instruments Mark III conductivity-temperature depth (CTD) probe was used to obtain continuous profiles of temperature, conductivity and pressure at each station. A General Oceanics 12-bottle rosette water sampler was mounted above the CTD. The CTD was fitted with a 6000 db pressure sensor, the fast response thermistor was disabled and the platinum resistance thermometer was used without the time constant being applied to correct for the time lag. The time constant is so small (235 ms) that errors induced by not applying a recursive filter are well within the error range of the CTD.

Calibrations

The CTD probe was calibrated for pressure, temperature and conductivity by John Smithers of the Institute of Oceanographic Sciences, Wormley. Water samples were taken from the rosette Niskin bottles at selected depths to provide in-situ calibration data. Protected reversing thermometers were mounted on one rosette bottle. The Niskin bottles were tripped during the up-cast, and the CTD data to be compared with the samples were recorded at the actual depth at which each bottle was fired. Salinity samples were drawn from selected bottles, and were analysed on a Guildline 8400A Autosal salinometer. The Guildline Autosal determines water sample salinity with a precision of ±0.002 and an accuracy of ±0.003. The reversing thermometers have an accuracy of ±0.02 °C and were corrected using calibrations supplied by IOS.

A few of the in-situ calibration differences were much larger than the others, as much as several standard deviations. These usually occurred in regions of strong vertical gradients and were eliminated from the in-situ calibration data set. The remaining temperature differences between the calibrated temperature readings and the corrected reversing thermometer were within or close to the stated accuracy of the reversing thermometers, so no additional temperature correction was applied. The CTD pressure at the surface was noted and was always within the stated accuracy of the pressure sensor (±6.0 dbar), so the only pressure calibrations applied were those supplied by IOS. The calibrations for pressure and temperature of the CTD supplied by IOS were:

T(cor) = (T(ctd) * 1.00763) + 2.34379e-2
P(cor) = (P(ctd) * 1.00053325) - 5.6

The sample bottle conductivities were calculated using the sample bottle salinity values with the CTD temperature and pressure values. A value of 42.914 mmho cm-1 for the conductivity of standard seawater at 15 °C (Culkin and Smith 1980) was used to convert the measured sample bottle conductivity ratios to conductivity. Sample bottle conductivities were compared to the CTD conductivities. The average and standard deviation were outside the stated accuracy of the CTD and so a linear calibration was determined from salinity bottle conductivities (see Fig. 1).

General Data Screening carried out by BODC

BODC screen both the series header qualifying information and the parameter values in the data cycles themselves.

Header information is inspected for:

• Irregularities such as unfeasible values
• Inconsistencies between related information, for example:
  • Times for instrument deployment and for start/end of data series
  • Length of record and the number of data cycles/cycle interval
  • Parameters expected and the parameters actually present in the data cycles
• Originator's comments on meter/mooring performance and data quality

Documents are written by BODC highlighting irregularities which cannot be resolved.

Data cycles are inspected using time or depth series plots of all parameters. Currents are additionally inspected using vector scatter plots and time series plots of North and East velocity components. These presentations undergo intrinsic and extrinsic screening to detect infeasible values within the data cycles themselves and inconsistencies as seen when comparing characteristics of adjacent data sets displaced with respect to depth, position or time. Values suspected of being of non-oceanographic origin may be tagged with the BODC flag denoting suspect value; the data values will not be altered.

The following types of irregularity, each relying on visual detection in the plot, are amongst those which may be flagged as suspect:

• Spurious data at the start or end of the record.
• Obvious spikes occurring in periods free from meteorological disturbance.
• A sequence of constant values in consecutive data cycles.

If a large percentage of the data is affected by irregularities then a Problem Report will be written rather than flagging the individual suspect values. Problem Reports are also used to highlight irregularities seen in the graphical data presentations.

Inconsistencies between the characteristics of the data set and those of its neighbours are sought and, where necessary, documented. This covers inconsistencies such as the following:

• Maximum and minimum values of parameters (spikes excluded).
• The occurrence of meteorological events.

This intrinsic and extrinsic screening of the parameter values seeks to confirm the qualifying information and the source laboratory's comments on the series. In screening and collating information, every care is taken to ensure that errors of BODC making are not introduced.

Project Information

No Project Information held for the Series

Data Activity or Cruise Information

Cruise

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:

SeaDataNet Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle: