Metadata Report for BODC Series Reference Number 291329

• 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 165A CTD Data Documentation

Introduction

This data document covers the CTD data collected during RRS Discovery cruise 165A (26th January to 26th February 1987) under the direction of J. Luyten to the eastern S Atlantic and SW Indian Ocean.

CTD Data Logging and Reduction

Logging, reduction and calibration of the Neil Brown Instrument Systems (NBIS) CTD are fully described by PRS, to which the reader is referred for details. Likewise, further editing of SeaSoar CTD data is described by PRS. Only a brief summary will be given here.

All CTD data are initially logged on an NBIS deck unit, written to a DIGIN format tape for backup, displayed on a BBC microcomputer and transferred to a Level A microcomputer, which edited the 16 hz (8 hz for shallow SeaSoar CTD) data before averaging them to one sample per second. The averaged data were then passed to a PDP11/34 computer for calibration and further processing. This route was used throughout Cruise 165A, with only a very few part casts having to be recovered from backup DIGIN tapes or Level C data. Cruise specific calibration information is described below.

Deep CTD Calibration

Pressure

CTD pressures on Cruise 164 and 165A were checked against a Precision Echo Sounder as described by PRS. The Cruise 165A data were included in that comparison, from which it was concluded that CTD pressures were correct within a few metres. The calibration used was

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

Temperature

The few reversing thermometer values from the ten casts on Cruise 165A gave no grounds for modifying the long term stable laboratory calibration

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

Salinity

The conductivity cell had fouled three casts before the end of the previous cruise. Using a conductivity ratio of 0.99937 it was concluded that salinities for the last three casts of Cruise 164 were 0.019 too high. After a 16-day break between the last cast of Cruise 164 and the first of Cruise 165A, it was not too surprising that the salinity corrections had changed from -0.019 to about 0.007. Statistics for the 6 levels at which samples were drawn for casts 11462-71 are given in Table 1. Differences between mean bottle and CTD salinities range from 0.008 to -0.002, with some hint of a trend with depth or salinity (Table 1a, right hand column). A simple way to reduce this possible 0.010 salinity trend was to recalibrate salinity as shown in Table 1b, which was done.

Oxygen

The oxygen sensor drifted less during Cruise 165A than it had on Cruise 164, and it was on occasion possible to fit values of C, ALPHA and BETA in the equation

0(cal)(m/l) = C*0(RAW)*EXP(ALPHA*T(L) + BETA*P)*0(sal)(T,S)

to calibration values from several casts at once (Table 2). T(L) was taken, as before, to be the unlagged CTD temperature. From the standard deviations of bottle minus CTD differences, we estimate the oxygens to be correct within 0.2 ml/l, the quoted error of the Beckman oxygen sensor.

Table 1a. Salinity calibrations on Cruise 165A

Table 1b. Comparison of corrected salinities

S(CORR) = 0.9909095*S(CTD) + 0.3213

Table 2. Oxygen calibration constants on Cruise 165A

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: