Metadata Report for BODC Series Reference Number 640997

• 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

Open Data supplied by Natural Environment Research Council (NERC)

You must always use the following attribution statement to acknowledge the source of the information: "Contains data supplied by Natural Environment Research Council."

Narrative Documents

Sea-Bird Electronics SBE 911 and SBE 917 series CTD profilers

The SBE 911 and SBE 917 series of conductivity-temperature-depth (CTD) units are used to collect hydrographic profiles, including temperature, conductivity and pressure as standard. Each profiler consists of an underwater unit and deck unit or SEARAM. Auxiliary sensors, such as fluorometers, dissolved oxygen sensors and transmissometers, and carousel water samplers are commonly added to the underwater unit.

Underwater unit

The CTD underwater unit (SBE 9 or SBE 9 plus) comprises a protective cage (usually with a carousel water sampler), including a main pressure housing containing power supplies, acquisition electronics, telemetry circuitry, and a suite of modular sensors. The original SBE 9 incorporated Sea-Bird's standard modular SBE 3 temperature sensor and SBE 4 conductivity sensor, and a Paroscientific Digiquartz pressure sensor. The conductivity cell was connected to a pump-fed plastic tubing circuit that could include auxiliary sensors. Each SBE 9 unit was custom built to individual specification. The SBE 9 was replaced in 1997 by an off-the-shelf version, termed the SBE 9 plus, that incorporated the SBE 3 plus (or SBE 3P) temperature sensor, SBE 4C conductivity sensor and a Paroscientific Digiquartz pressure sensor. Sensors could be connected to a pump-fed plastic tubing circuit or stand-alone.

Temperature, conductivity and pressure sensors

The conductivity, temperature, and pressure sensors supplied with Sea-Bird CTD systems have outputs in the form of variable frequencies, which are measured using high-speed parallel counters. The resulting count totals are converted to numeric representations of the original frequencies, which bear a direct relationship to temperature, conductivity or pressure. Sampling frequencies for these sensors are typically set at 24 Hz.

The temperature sensing element is a glass-coated thermistor bead, pressure-protected inside a stainless steel tube, while the conductivity sensing element is a cylindrical, flow-through, borosilicate glass cell with three internal platinum electrodes. Thermistor resistance or conductivity cell resistance, respectively, is the controlling element in an optimized Wien Bridge oscillator circuit, which produces a frequency output that can be converted to a temperature or conductivity reading. These sensors are available with depth ratings of 6800 m (aluminium housing) or 10500 m (titanium housing). The Paroscientific Digiquartz pressure sensor comprises a quartz crystal resonator that responds to pressure-induced stress, and temperature is measured for thermal compensation of the calculated pressure.

Additional sensors

Optional sensors for dissolved oxygen, pH, light transmission, fluorescence and others do not require the very high levels of resolution needed in the primary CTD channels, nor do these sensors generally offer variable frequency outputs. Accordingly, signals from the auxiliary sensors are acquired using a conventional voltage-input multiplexed A/D converter (optional). Some Sea-Bird CTDs use a strain gauge pressure sensor (Senso-Metrics) in which case their pressure output data is in the same form as that from the auxiliary sensors as described above.

Deck unit or SEARAM

Each underwater unit is connected to a power supply and data logging system: the SBE 11 (or SBE 11 plus) deck unit allows real-time interfacing between the deck and the underwater unit via a conductive wire, while the submersible SBE 17 (or SBE 17 plus) SEARAM plugs directly into the underwater unit and data are downloaded on recovery of the CTD. The combination of SBE 9 and SBE 17 or SBE 11 are termed SBE 917 or SBE 911, respectively, while the combinations of SBE 9 plus and SBE 17 plus or SBE 11 plus are termed SBE 917 plus or SBE 911 plus.

Specifications

Specifications for the SBE 9 plus underwater unit are listed below:

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

Aquatracka fluorometer

The Chelsea Instruments Aquatracka is a logarithmic response fluorometer. It uses a pulsed (5.5 Hz) xenon light source discharging between 320 and 800 nm through a blue filter with a peak transmission of 420 nm and a bandwidth at half maximum of 100 nm. A red filter with sharp cut off, 10% transmission at 664 nm and 678 nm, is used to pass chlorophyll-a fluorescence to the sample photodiode.

The instrument may be deployed either in a through-flow tank, on a CTD frame or moored with a data logging package.

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

WETLabs C-Star transmissometer

This instrument is designed to measure beam transmittance by submersion or with an optional flow tube for pumped applications. It can be used in profiles, moorings or as part of an underway system.

Two models are available, a 25 cm pathlength, which can be built in aluminum or co-polymer, and a 10 cm pathlength with a plastic housing. Both have an analog output, but a digital model is also available.

This instrument has been updated to provide a high resolution RS232 data output, while maintaining the same design and characteristics.

Specifications

Further details are available in the manufacturer's specification sheet or user guide.

James Clark Ross JR57 CTD Data Document

Sampling strategy

A Conductivity-Temperature-Depth (CTD) probe was used to vertically profile the temperature and salinity of the water column. Associated instrumentation profiled the light transmission and fluorescence of the water column and captured up to twelve discrete samples. A total of 37 CTD casts were performed during the cruise. At each CTD station on JR57, all twelve Niskin bottles were closed and sampled for salinity analysis.

Instrumentation and data processing by originator

• CTD unit and auxiliary sensors

  The CTD system used on the JR57 was the BAS Sea-Bird 911 plus (serial number: 09P15759-0480). The CTD was fitted with seven scientific sensors:

  Sensor	Serial Number	Last calibration date
  Primary temperature-SBE 3 plus	T32191	22/06/2000
  Primary conductivity-SBE 4C	C41913	22/06/2000
  Pressure-Digiquartz pressure transducer series 410K-105	067241	28/06/1999
  Secondary temperature-SBE 3 plus	T32307	22/06/2000
  Secondary conductivity sensor-SBE 4C	C41912	22/06/2000
  Transmissometer	cdt-396dr	17/10/2000
  Fluorometer-Chelsea Instruments Aquatracka Mk.III	088216	07/01/2000

  The temperature and conductivity sensors were connected to two SBE 5 T submersible pumps (serial numbers 051813 and 051807). In addition to these, an altimeter was fitted to permit accurate near-seabed approach, but the altimeter data were not processed alongside the data from the other sensors. Also fitted to the water sampler was a SBE 35 high precision thermometer (serial number 3515759-005).

• Sampling device

  The CTD was connected to a SBE 32, 12 position carousel water sampler carrying twelve 10 litre Niskins.

  The salinity samples from the CTD were analysed during the cruise using the BAS Guildline Autosal model 8400B (serial number 63360) with measurements being made using Ocean Scientific standards P137 (K15 = 0.99995, S = 34.998, date of preparation = 09/12/1999) and P133 (K15 = 0.99986, S = 34.995, date of preparation = 11/11/1997). Once conductivity measurements had been made for each sample they were entered into a Quattro Pro spreadsheet for conversion to salinity, with the resultant data being written out as ASCII and transferred to JRUF for subsequent processing in Pstar.

• Data Acquisition and Initial Processing

  a) SBE 911 Plus

  The general procedure was to start data logging, deploy, and then stop with the CTD at 10 dbar pressure. After a 5 minute soak at this level, the package was raised nearly to the surface, then lowered to the target depth without stopping. The Niskin bottles were closed on the upcast. The downcast data were calibrated and averaged to 2 dbar intervals to form the final CTD product. Data were logged via an SBE 11 plus deck unit. The data average rate was set to 1, producing 24 Hz raw data.

  b) SBE35 high precision thermometer

  The SBE35 was set to record temperatures as the mean of 8.8 seconds of data.

  The processed data, together with the raw Sea-Bird, configuration and bottle files, were supplied to BODC for banking.

• Problems

  There were some problems with the capture and processing of the discrete salinity samples as it was noticed the some of the Niskins leaked on deck after recovery of the CTD package. Some O-ring seals were replaced, and on two occasions complete Niskins were replaced. A second problem was the instability of the conductivity readings given by the Autosal8400B. A stable reading could not be obtained with flow through the cell. The problem was handled by using the same manual averaging procedure on the samples and standards which should not have affected data quality but it did require more user effort than would have normally been required. A number of salinity bottles were found to have badly chipped necks and were discarded.

BODC post-processing and screening

• Reformatting

  The data were converted from Pstar format into BODC internal format (QXF) to allow use of in-house visualisation tools.

• Screening

  Reformatted CTD data were transferred onto a graphics work station for visualisation using the in-house editor SERPLO. No data values were edited or deleted. Flagging was achieved by modification of the associated quality control flag to 'M' for suspect values and 'N' for nulls.

• Banking

  Once BODC quality control screening was complete, the CTD QXF files were archived in the BODC National Oceanographic Database and the associated metadata were loaded into an ORACLE Relational Database Management System.

Quality control report

• Salinity

  The data seem to be of good quality and no flagging was required.

• Temperature

  The data seem to be of good quality and no flagging was required.

• Pressure

  The data seem to be of good quality and no flagging was required.

• Transmittance

  While mainly good quality, some of the data were flagged for spikes in transmittance.

• Chlorophyll-a

  As with transmittance some of the data were flagged for spikes although the majority of the data seemed to be good.

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: