Metadata Report for BODC Series Reference Number 78884

• 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.

RRS Discovery Cruise 127 CTD Data Documentation

Introduction

This data document covers the CTD data collected on RRS Discovery Cruise 127 (April 1982) by the Department of Oceanography, Liverpool University, Liverpool UK, under the direction of E.D. Barton.

Instrumentation

The instrument used was the University of Liverpool's Neil Brown MK III CTD with no modifications. This instrument has been described by Brown and Morrison (WHOI-78-23). No serious problems were encountered with the data acquisition or processing. The calibrations were satisfactory.

Sensor resolution was as follows:

Sampling Protocol

Casts were usually to a depth of approximately 600m with data collection on the downcast. A General Oceanics Rosette Sampler was attached 1 metre above the CTD. Regions of weak or no vertical gradient were chosen during the downcasts as likely calibration points, and water samples and reversing thermometer measurements were made on upcasts to provide in-situ calibration.

During the upcasts such sites were relocated with the CTD, the winch was stopped and, if conditions were not varying substantially, a Niskin bottle sample was taken and the CTD readings were noted. If the reversing thermometers were used, a five minute soak period was allowed for them to attain thermal equilibrium. In general, 2 or 3 protected thermometers were used for each sample.

The CTD sampling rate was approximately 30 scans/sec of pressure, temperature and conductivity.

CTD station positions were determined by satellite navigation and sea floor depths by precision depth recorder.

Calibration

Pressure

Before each cruise the pressure sensor was adjusted at zero and at full scale against a dead weight tester. Checks were also made at intermediate pressures. These showed no significant deviation from linearity.

Temperature

Comparisons were made against reversing thermometers. Nine protected thermometers were used. 25 good comparisons were made with three thermometers against CTD temperatures, and one comparison with two (discounting misfires and delayed reversals). The mean difference from 77 individual comparisons was 0.047 °C (CTD high); standard deviation 0.041 °C. The CTD temperatures were adjusted down by the mean difference. There was no evidence of any trend in the comparison. The mean difference was very much larger than that found on RRS Shackleton Cruise 2/81 because the CTD temperature board had been replaced.

Salinity

Comparisons were made with 106 water bottle sample salinities (using the corrected temperature values). Most bottle casts used 3 to 4 Niskin bottles at each sample depth as it was feared that some might be leaking and producing poor salinities (as had been found on previous cruises). In almost all cases the water bottle salinities agreed to within 0.005 PSU where no strong gradients were present. The mean difference from the comparisons was 0.042 PSU (CTD high); standard deviation 0.015 PSU. No clear trends were detected, so the salinities were adjusted down by the mean difference.

Data Processing

Data were mainly processed on board ship (using a PDP-11 computer). Spikes were removed by eliminating values that lay beyond prescribed values or had excessive gradients compared with surrounding values. Data were averaged over 1 second intervals and nominal calibration corrections applied.

The CTD was fitted with a fast response thermistor; therefore no time constant correction was applied.

Data were transferred to the University of Liverpool computer on magnetic tape where further editing and error checking was carried out. New calibration constants based on water bottle and reversing thermometer measurements made during the cruise were applied. There were no significant gaps in the data. Salinity has been calculated in Practical Salinity Units, as recommended by UNESCO.

The data set is edited, calibrated and 1 second averages linearly interpolated to 2dbar intervals.

References

Fofonoff, N.P. and Millard Jr., R.C. (1983).
Algorithms for the computation of fundamental properties of sea water. UNESCO Technical Paper on Marine Science 44.

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: