Metadata Report for BODC Series Reference Number 65738

• 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

Plessey 9400 Conductivity, Temperature and Depth

The Plessey 9400 comprises a Plessey 6500 inductive conductivity sensor, a Plessey 4500 platinum resistance temperature sensor and a Plessey 4600 bonded strain pressure sensor.

RV Prince Madog Cruise DW13 CTD Data Documentation

Introduction

Documentation for the CTD data collected on RV Prince Madog Cruise DW13 (July 1978) by the School of Ocean Sciences, University College of North Wales, Menai Bridge, Gwynedd, U.K., under the direction of Steve Czitrom.

Instrumentation

The instrument used was a Plessey model 9400 CTD system. The complete system comprised a probe carrying the sensors and a deck unit containing a signal processor and a strip chart plotter. The sea and deck units were connected by a single core cable which was used to power the sea unit and retrieve its information. A separate logging system, designed and built by Kent Data Processing Ltd., was connected to the CTD processor for storing data on paper tape. It consisted of a channel selector, a pulse counter, a 5 hole code converter and a paper tape punching machine. On all stations the channel selector was set to complete a measurement cycle every 3 seconds and the CTD probe was lowered at an approximate rate of one third of a metre per second so that conductivity, temperature and depth measurements did not correspond to the same water sample.

Calibrations and Data Quality

Temperature and Salinity

A hydrocast was performed after every second CTD station for conductivity and temperature sensor calibration checks. Surface, mid-depth and bottom salinity and temperature samples were taken with NIO bottles after the CTD was back on deck. Each bottle carried 2 protected reversing thermometers and readings were made after equilibration to ambient temperature. Salinity was determined from samples drawn from the bottles using a Bissett Berman model 6230 salinometer.

The CTD temperature sensor calibration was checked using corrected reversing thermometer measurements while conductivity sensor calibrations were checked using in-situ conductivities derived from reversing thermometer readings and NIO bottle salinities.

A linear regression was carried out using the results from the NIO bottles and the CTD data. CTD conductivity and temperature records were chosen from the profiles so that the CTD depth measurement was close to the depth of the hydrocast sample. Measurements taken near strong vertical temperature or salinity gradients were not used in the regressions to prevent errors arising from internal waves, or inaccuracies in the determination of depth.

Fit of CTD Data to NIO Bottle Sample Values

Mean difference averaged over 10 cruises (DW6, DW8, DW9, DW10, DW11, DW12, DW13, DW14, DW15, DW16) in Liverpool Bay by Prince Madog during 1977-1979.

The regression slopes for conductivity and temperature did not differ significantly from 1.0. So the CTD temperatures and conductivities could be adequately calibrated by adding a constants equal to the mean differences. Further these mean differences for cruise DW13 not differ significantly from the values deltaT_o and deltaC_o obtained from averaging over the composite of all calibration points for the 10 cruises. Hence all the temperature and conductivity values were satisfactorily calibrated by adding deltaT_o and deltaC_orespectively to each value.

The accuracy of the temperature and conductivity sensors can be compared with the standard deviations about the regressions. In general, the standard deviations are larger than the uncertainties quoted by the manufacturers; this may be due to the hydrocast calibration samples having been taken at least 5 minutes after the CTD unit was back on deck. The CTD was found to be sufficiently accurate to register the 0.5 ppt salinity and 1.0 °C temperature differences encountered in a typical station in Liverpool Bay.

Depth

The performance of the CTD depth sensor was checked several times on each cruise by comparing its readings with those of the winch wire output counter. The depth sensor was found to be operating within specifications.

Data Processing

CTD records for each cast were synchronized so that the three measurements corresponded to the same water sample. The approximate synchronization was achieved by linearly interpolating conductivities and depths to the temperature sampling time. Conductivity and depth measurements, made before and and after the temperature record, were used for interpolation. Synchronized conductivity and temperature values were then used to obtain salinity. Serious salinity spiking was prevented by the synchronization scheme and the slow rate at which the CTD unit was lowered.

Reference

Czitrom, S. (1983).
Density stratification and associated front in Liverpool Bay. PhD thesis, University of Wales.

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: