Metadata Report for BODC Series Reference Number 325703

• 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 6/1981 CTD Data Documentation

Calibrations and Data Quality

Thirty-one CTD profiles and associated calibration data were available from this cruise. Suitable calibration coefficients have been calculated as described below. Only one profile descended to below 3000m but this did indicate good agreement between the corrected data and the theta-S relationship suggested by Peter Saunders.

Pressure

No pre-cruise or post-cruise calibration was available. The earliest pressure calibration of this CTD (S/N 45056) using a dead weight tester dates from April/May 1983 and this was applied to the pressure data:

P(COR) = P(CTD) + deltaP

where:

deltaP = a * T(COR) + b * P(CTD) + c
a = 0.857466
b = 0.331988 E-2
c = -11.96

Temperature

In the absence of post- or pre-cruise calibrations of the temperature sensor, a comparison was made between recorded CTD and DSRT temperatures. Differences ranged between -10 and +60 mK, but it is believed likely that errors associated with thermometers, rather than variability in the CTD sensor, caused this spread (at this time no restricted range thermometers were available; they would have had ranges -2 to 12 °C or -2 to 25 °C). A mean difference was calculated and applied as a correction:

T(COR) = T(CTD) + deltaT
where deltaT = 0.164 E-1

Conductivity Ratio

A comparison between CTD conductivity ratio and the conductivity ratio of water samples at the corrected CTD pressure and temperature was used to determine suitable calibration coefficients:

[CR(WS)/CR(CTD)] = a * T(COR) + b * P(COR) + c

Then corrected CTD conductivity ratio is given by:

CR(COR) = CR(CTD) * (a * T(COR) + b * P(COR) + c).

From the distribution of the ratio CR(CTD):CR(WS) it seemed that the calibration was best served by dividing the data into 3 groups.

A comparison between water sample and CTD salinity indicated rms differences of 0.005 (N=25), 0.003 (N=32) and 0.003 (N=19) respectively. After correction of the sensors 89% of the differences between the CTD and water sample salinity are within ±0.006.

One profile descended beyond 3000m. Comparison of the theta-S distribution with the linear relationship suggested by Peter Saunders suggests that the coefficients are providing an effective calibration of the CTD sensors.

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: