Metadata Report for BODC Series Reference Number 499543

• 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.

Bon Entente SeaSoar Data Documentation

Introduction

Documentation for the SeaSoar data collected on Bon Entente 10/09/86 - 06/10/86 off the Coast of Portugal by the School of Ocean Sciences, University of Wales, Bangor, under the direction of E.D. Barton.

Instrumentation

The SeaSoar is an instrument which enables a standard Neil Brown Mark III CTD to be towed beneath the sea surface at controllable depths. The vehicle used was capable of carrying a large suite of sensors, at speeds up to 10 knots (5 m s^-1) and to a maximum depth of 400 m in optimal conditions, following a controlled and adjustable path. The SeaSoar comprises an underwater vehicle, into which is mounted a Neil Brown Mark III CTD and Chelsea Instruments fluorometer, and a deck unit which controls the pitch of the SeaSoar wings enabling the vehicle to climb or dive as required.

Sampling

The streamlined SeaSoar vehicle was towed using a faired cable at a speed of about 4 m s ^-1 . This enabled the instrument to cycle between 0 and 325 m depth, approximately every 10 - 12 minutes, which gives a spatial horizontal resolution of about 2 km. The Neil Brown Mark III CTD sampled every second for pressure, temperature, conductivity and chlorophyll.

Calibration

Because of the continuous and undulating path of the SeaSoar instrument, the CTD instrument salinity calibration was done by taking water bottle samples from the continuously pumped onboard source. Samples from the surface pump were taken just prior to the SeaSoar reaching the surface because the SeaSoar was trailing the ship by some 600 m. In this way it was intended that the water masses sampled by the water bottle and the SeaSoar should be similar. The salinity samples were drawn from the water bottles and analysed on a Guildline 8400A Autosal salinometer. The in situ sample bottle salinities were compared with the CTD salinities when the SeaSoar was near-surface. A few of the in situ calibration differences were much larger than the others, as much as several standard deviations, and were eliminated from the data set. These usually occurred in regions of strong horizontal or vertical gradients where spatial errors are most likely to occur. A linear calibration equation was determined by least-squares linear regression between the in situ water bottle salinities and the surface SeaSoar readings.

The SeaSoar CTD surface temperatures were calibrated against the Thermosalinograph (THS) temperatures which had been calibrated in the laboratory. A linear calibration equation was determined by comparing the THS temperatures and the SeaSoar surface temperatures by a least-squares linear regression technique. The CTD pressure sensor had been calibrated in the laboratory prior to the cruise. The fluorometer was calibrated against the surface water bottle samples as described for salinity.

Data Processing

The data were gridded by the SURFACE-II (Sampson 1975) system into files with a horizontal time separation of 12 minutes (navigation data were added later) and a vertical spacing of 5 m using an octant gridding procedure. By using the octant search procedure specified the data were effectively filtered, each grid node having been smoothed over a distance of approximately 5 km in the horizontal and 20 m in the vertical. The available navigation data were merged with the SeaSoar data, which were then organised into files representing cruise grid lines. The data files were then examined and any remaining spikes in the data were removed interactively, the data points that were rejected being replaced by linearly interpolated values.

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: