Metadata Report for BODC Series Reference Number 290603

• 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.

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 Discovery 164 CTD Data Documentation

Introduction

This document covers the CTD data collected during RRS Discovery cruise 164 (19^th December 1986 to 21^st January 1987) under the direction of Dr R.T. Pollard from the Institute of Oceanographic Sciences Deacon Laboratory. The data were collected in the S Atlantic and SW Indian Ocean.

Instrumention

The instrument used was a Neil Brown Instrument Systems (NBIS) CTD, which measured pressure, temperature and conductivity. The CTD was used alongside a General Oceanics Rosette Multisampler with 12 Niskin bottles and a 10 kHz pinger. The sensors were flushed with distilled water on recovery. Bottle samples and reversing thermometer measurements were made on descent and the sea water samples were analysed using a Guildline Autolab Salinometer.

Reversing thermometers were calibrated before and after the cruise.

Sampling Protocol

Lowering and retrieval rates of 0.5 to 1.0 m/s were employed. All casts were full depth, most proceeding to within 10-30 m of the bottom.

Data were initially logged at 16 hz from the NBIS CTD onto an NBIS deck unit, which had been enhanced by IOS with an ASCII interface, allowing raw data to be written to a 1600 bpi 0.5 inch magnetic tape. Data are then passed to a microcomputer which edited and averaged the raw data to 1 hz, using algorithms developed by Pollard et al. (1986). All SMP messages from all instruments were archived using a Plessey 68000 and a UNIX based Plessey 68000 was available for further processing. CTD data were then analysed using editing, utility and display programs (Pollard, 1983). Further details of the processing can be found in Pollard et al. (1987).

Calibration

Pressure

Raw pressure R(raw) was calibrated to dbar P(cal) by the formula

P(cal) = 0.1 * P(raw) - 12.0

The pressure calibration was checked by comparing the CTD depth at the bottom of each cast with the value derived from the IOS Precision Echo Sounder. In total, 35 values fell within a Gaussian distribution which tailed off at 15m, and these values yielded:

D(pes) - D(ctd) = 0.4 +/- 6.3

From this it was deduced that pressures were therefore probably correct within a few decibars.

Temperature

CTD temperatures were calibrated at sea using the most recent laboratory calibration

T(C) = T(raw) * 0.0005 * 0.9990317 + 0.0258

which reinforced the long-term stability of the platinum resistor calibration. Reversing thermometers were deployed at two depths on all casts, to check for gross errors and, on the evidence gained, no change was made to the CTD temperature calibration.

Salinity

An overall correction of 0.050 given by all 165 values for casts 11404-58, with a standard deviation of 0.005, was applied. Casts 11401-03 were individually corrected by 0.027, 0.036 and 0.045 respectively. After cast 11458, a new conductivity sensor had to be installed, and calibration points available for casts 11459-61 were found to be unreliable. Therefore, a correction of -0.019 was applied to all three casts.

Oxygen

Offsets between up-casts and down-casts were minimised by replacing lagged temperature by unlagged CTD temperature. It was found that the calibration drifted enough that casts had to be fitted individually. Most CTD values were believed to be within 0.1 ml/l of their true value, or certainly 0.2 ml/l.

References

Pollard, R.T. 1983. PSTAR shipboard data processing programs. Institute of Oceanographic Sciences, Marine Physics Group. (Unpublished manuscript)

Pollard, R.T., Holford, D., Ellis, S., Read, J.F. and Smithers, J. 1986.
CTD data from the Northeast Atlantic Ocean 37°-47° N, 10°-16° W collected on RRS Discovery Cruise 145 in late winter 1984. Institute of Oceanographic sciences, Report No. 223.

Pollard, R.T., Read, J.F., Smithers, J. 1987.
CTD sections across the Southwest Indian Ocean and Antarctic Circumpolar Current in Southern Summer 1986/7. Institute of Oceanographic sciences, Report No. 243.

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: