Metadata Report for BODC Series Reference Number 1745325

• 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

Instrument Description for JR20071029 (JR184) CTD

CTD Unit and Auxiliary Sensors

The CTD unit comprised a Sea-Bird Electronics (SBE) 9plus underwater unit, an SBE 11plus deck unit, a BAS 24-way frame and 24x12 L OTE Water Samplers; all of which were mounted on a stainless steel 24-way CTD frame. Attached to the CTD were two SBE 3P temperature sensors, two SBE 4C conductivity sensors and one Paroscientific Digiquartz pressure sensor.

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.

Tritech Digital Precision Altimeter PA200

This altimeter is a sonar ranging device that gives the height above the sea bed when mounted vertically. When mounted in any other attitude the sensor provides a subsea distance. It can be configured to operate on its own or under control from an external unit and can be supplied with simultaneous analogue and digital outputs, allowing them to interface to PC devices, data loggers, telemetry systems and multiplexers.

These instruments can be supplied with different housings, stainless steel, plastic and aluminum, which will limit the depth rating. There are three models available: the PA200-20S, PA200-10L and the PA500-6S, whose transducer options differ slightly.

Specifications

Common specifications are presented below

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

Originator's processing document for JR20071029 (JR184) CTD data

Sampling strategy

A total of 7 CTD casts were performed during JR20071029 (JR184), which sailed from Stanley (Falkland Islands) on 29 October 2007 and docked in Stanley (Falkland Islands) on 21 November 2007.

Data Processing

CTD data were collected at 24Hz and logged via the deck unit to a PC running Seasave Win32 version 5.30b (Sea-Bird Electronics, Inc.), which allows real-time viewing of the data. The procedure was to start data logging, deploy the CTD, then stop the instrument at 10m wire out, where the CTD package was left for at least two minutes to allow the seawater-activated pumps to switch on and the sensors to equilibrate with ambient conditions.

The following processing was performed by the Originator using the SBE Data Processing software (Seasave Version 5.30b):

• 1.Data conversion to convert raw data to engineering units
• 2. Wild edit to flag bad data using two passes; the first estimates the standard deviation and the second replaces the appropriate data with badflag
• 3. Cell thermal mass to remove thermal mass effects from measured conductivity using a recursive filter. Alpha was 0.03 and 1/beta was 7.0
• 4. Translate to create output in ascii format to be read in Matlab

The originator then proceeded to process the data further in Matlab using scripts provided by Hugh venables. The procedures included:

• 1. 6. ctdread.m - reads in the SBE file, stores data in Matlab arrays
• 2. offpress.m - replaces any data where the CTD pumps were off with NaNs. There was no pressure offset applied to the data
• 3. editctd.m - manual removal of the 10 m soak prior to the CTD cast, and any data collected at the end of the upcast when the CTD was out of the water. Selected data for all variables is set to NaN. Followed by interactive despiking of the primary and secondary conductivity and temperature; selected data points, plus for the other sensors, are set to NaN
• 4. interpol.m - linearly interpolates to fill data gaps generated by editctd
• 5. salcalapp.m - calculates salinity, potential temperature and sigma-theta, sigma-2 and sigma-4
• 6. splitcast.m - splits the CTD cast into the downcast and upcast
• 7. fallrate.m - removes any data points on the downcast where pressure is less than the previous record or if the fall rate is <0.25 m s^-1
• 8. gridctd.m - averages the downcast and upcast data to 2db
• 9. fill_to_surf.m - missing data at the surface is filled with values from the next non-NaN line

• Field calibrations

  No samples were taken for calibration purposes so data remain uncalibrated.

Processing by BODC of RRS James Clark Ross JR20071029 (JR184) CTD data

The files were processed at the British Antarctic Survey and were sent to BODC in matlab and csv formats. The following parameters were sent: time, press, primary and secondary temperature, salinity, conductivity, potemp1, potemp2, sigma0, sigma2 and sigma4 but not all were transferred as they were either not relevant, or it was not clear how the originator obtained them.

In addition to the raw CTD data, BODC were provided with the intermediate versions created at by the different processing procedures. The fully processed CTD data binned to 2 dbar downcast bins were then reformatted to BODC's internal NetCDF format. The following table shows the mapping of the originator's variables to the appropriate BODC parameter codes:

Additional variables (secondary temperature, conductivity, salinity, potential temperature and density) are avaiable upon request.

The reformatted data were visualised using the in-house EDSERPLO software. Suspect data were marked by adding an appropriate quality control flag, and missing data by setting the data to an appropriate value and applying the quality control flag.

Project Information

BAS Long Term Monitoring and Survey

Introduction

The Long Term Monitoring and Survey project (LTMS) has been running since the British Antarctic Survey (BAS) was created. This project is one of the BAS core projects, with several groups of scientists collecting various types of data e.g biological, geological, atmospheric, among others.

Data collection is achievable through a wide scope of instruments and platforms, e.g. the Antarctic research stations, autonomous instrument platforms deployed on or from BAS research ships, BAS aircrafts, satellite remote sensing and others.

Scientific Objectives

This project was implemented in order to measure change and variability in the Earth system. Its long term duration allows for the monitoring of processes that could be missed in shorter term studies and experiments. The data collected is also used to check and improve the reliability of models used to stimulate and predict the behavior of the Earth system.

The main objectives are:

• Topographic survey
• Geosciences survey
• Biological survey and monitoring
• Atmospheric and oceanographic monitoring

Data Availability

The data sets obtained through this project are available to the academic community.

Data Activity or Cruise Information

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

Fixed Station Information

Western Core Box

The British Antarctic Survey undertakes cruises to determine krill biomass as part of the ongoing assessment of the status of the marine ecosystem in the region of South Georgia. This unique time series, known as the Western Core Box, which has taken place since 1996 is funded by Natural Environment Research Council (NERC) British Antarctic Survey Long Term Monitoring programme.

The survey area is located in an on and off shelf survery area (figure.1), which comprises of an acoustic grid survey of 8 transects each of 80 km in length. Standard data collection includes underway biological echosounder acoustic transaects, CTD profiles, stratified and targetted RMT8 hauls of macrozooplankton and micronekton and a set of moorings which provide temporal coverage and a year round set of observations.

The specific aims of the WCB are:

• To quantify the interannual variability and long-term change in the mesoscale distribution and abundance of Antarctic krill.
• To quantify the the interannual variability and long-term change in the mesoscale distribution and abundance of other plankton/micronekton.
• To examine interannual varaibility in the context of environmental variability (climate variability).
• To examine prey availiability in the context of predator and fishery demand.

Figure 1. Western Core Box Survey Area (BAS, 2017).

A list of Western Core Box cruises are shown below.

References

British Antarctic Survey (2017). POETS-WCB. Available at: https://www.bas.ac.uk/project/poets-wcb/ [Accessed 2017].

Related Fixed Station activities are detailed in Appendix 1

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:

Appendix 1: Western Core Box

Related series for this Fixed Station are presented in the table below. Further information can be found by following the appropriate links.

If you are interested in these series, please be aware we offer a multiple file download service. Should your credentials be insufficient for automatic download, the service also offers a referral to our Enquiries Officer who may be able to negotiate access.