Metadata Report for BODC Series Reference Number 326177

• 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

Guildline 8705 CTD

The 8705 CTD is a conductivity-temperature-pressure profiler designed for marine applications down to depths of 6000 m. The instrument includes an anodised aluminium tube with a steel cage to protect the temperature and conductivity sensors and a urethane cap to protect the pressure sensor.

Specifications

* Conductivity specifications are given in terms of equivalent salinity

Further details can be found in the manufacturer's specification sheet.

RV Cirolana Cruise 6/1989 CTD Data Documentation

Instrumentation

The CTD used was S/N 41136.

Calibrations and Data Quality

Pressure and temperature sensors were corrected using coefficients determined after laboratory calibrations. Water samples collected during the ascent of the CTD for salinity analysis with a Guildline salinometer were used to calibrate the conductivity sensor.

Pressure

The pressure sensor was calibrated with a dead weight tester before and after the cruise, during June and August 1989. However, the temperature of the sensor was near 7.5degC for all of the August calibration and during the June calibration the temperature/pressure values did not reflect the conditions encountered during the cruise. The calibration was repeated using appropriate temperature/pressure coordinates during November: see Fig. 1.

P(COR) = P(CTD) + PA*T(COR) + PB*P(CTD) + PC

where:

T(COR) = corrected CTD temperature.
PA = -8.4343 E-2
PB = 3.1313 E-3
PC = 2.09

This calibration was in good agreement with that suggested by comparing pressures derived from unprotected thermometers and those recorded by the CTD.

Temperature

Good agreement was obtained between pre- and post-cruise calibrations using platinum resistance thermometers (although only PRT 2503 gave reliable measurements).

DSRTs were used on each CTD cast and suggested a correction which differed from the laboratory calibration by 16 mK, within the tolerance of the thermometers.

Temperatures were corrected using the pre-cruise calibration of June 1989:

T(COR) = T(CTD) + TA* T(CTD)* T(CTD) + TB*T(CTD) + TC
TA = -3.2311 E-5
TB = 7.1947 E-5
TC = 2.75 E-4

Conductivity ratio

The conductivity ratio of the water sample salinity, CR(WS), at its in situ pressure and temperature was compared with that measured by the CTD, CR(CTD). The ratio CR(WS):CR(CTD) was then fitted by least squares to satisfy the equation

[CR(WS)/CR(CTD)]= CA * T(CTD) + CB * P(CTD) + CC
where T(CTD) and P(CTD) are the corrected CTD temperature and pressure.

The variation in the ratio CR(WS): CR(CTD) is seen in Fig. 2.

Solving the above equation and calculating an estimate of CTD salinity yielded an rms difference between water sample and CTD salinity of 0.003 for 95 observations. This is within the expected tolerance of the CTD and no attempt was made to determine cell factors, CF, for each station.

CR(COR) = CR(CTD) * [CF * (CA * T(COR) + CB * P (POR) + CC]

where

CF = 1.0
CA = -0.29928 E-5
CB = 6.10159 E-9
CC = 1.00145

Fig. 3 shows how effective these coefficients are in correcting the CTD estimates of salinity.

Ken Medler
14 June 1991

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: