Metadata Report for BODC Series Reference Number 1741834

• 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 Dissolved Oxygen Sensor SBE 43 and SBE 43F

The SBE 43 is a dissolved oxygen sensor designed for marine applications. It incorporates a high-performance Clark polarographic membrane with a pump that continuously plumbs water through it, preventing algal growth and the development of anoxic conditions when the sensor is taking measurements.

Two configurations are available: SBE 43 produces a voltage output and can be incorporated with any Sea-Bird CTD that accepts input from a 0-5 volt auxiliary sensor, while the SBE 43F produces a frequency output and can be integrated with an SBE 52-MP (Moored Profiler CTD) or used for OEM applications. The specifications below are common to both.

Specifications

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

Instrument Description for JR20101221 (JR245, JR246, JR247) 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, one Paroscientific Digiquartz pressure sensor, one SBE 43 dissolved oxygen sensor, one CTG Aquatracka MKIII fluorometer and one CTG WETLabs C-Star transmissometer an a Biospherical QCD-905L underwater PAR sensor. An additional independent SBE35 temperature sensor was attached to the frame to perform observations each time a bottle is fired.

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.

SeaBird SBE35 Deep Ocean Standards Thermometer

The SBE 35 is a high precision thermometer that can be used in fixed point cells or at depths up to 6800 m. It is not affected by shock and vibration, allowing it to be used in calibration laboratories and for thermodynamic measurement of hydro turbine efficiency.

The SBE35 can be used with the SBE32 Carousel Water Sampler and with a real-time or autonomous CTD system. In this case, an SBE35 temperature measurement is collected each time a bottle is fired and the value is stored in EEPROM (Electrically Erasable Programmable Read-Only Memory), eliminating the need for reversing thermometers while providing a high accuracy temperature reading.

The SBE35 is standardized in water triple point (0.0100 °C) and gallium melting point (29.7646 °C) cells, following the methodology applied to the Standard-Grade Platinum Resistance Thermometer (SPRT). However, it does not need a resistance bridge, making it more cost-efficient than an SPRT.

Temperature is determined by applying an AC excitation to reference resistances and an ultrastable aged thermistor. Each of the resulting outputs is digitized by a 20-bit A/D converter. The AC excitation and ratiometric comparison uses a common processing channel, which removes measurement errors due to parasitic thermocouples, offset voltages, leakage currents and gain errors.

Specifications

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

Chelsea Technologies Group Aquatracka MKIII fluorometer

The Chelsea Technologies Group Aquatracka MKIII is a logarithmic response fluorometer. Filters are available to enable the instrument to measure chlorophyll, rhodamine, fluorescein and turbidity.

It uses a pulsed (5.5 Hz) xenon light source discharging along two signal paths to eliminate variations in the flashlamp intensity. The reference path measures the intensity of the light source whilst the signal path measures the intensity of the light emitted from the specimen under test. The reference signal and the emitted light signals are then applied to a ratiometric circuit. In this circuit, the ratio of returned signal to reference signal is computed and scaled logarithmically to achieve a wide dynamic range. The logarithmic conversion accuracy is maintained at better than one percent of the reading over the full output range of the instrument.

Two variants of the instrument are available, both manufactured in titanium, capable of operating in depths from shallow water down to 2000 m and 6000 m respectively. The optical characteristics of the instrument in its different detection modes are visible below:

* The wavelengths for the turbidity filters are customer selectable but must be in the range 400 to 700 nm. The same wavelength is used in the excitation path and the emission path.

The instrument measures chlorophyll a, rhodamine and fluorescein with a concentration range of 0.01 µg l^-1 to 100 µg l^-1. The concentration range for turbidity is 0.01 to 100 FTU (other wavelengths are available on request).

The instrument accuracy is ± 0.02 µg l^-1 (or ± 3% of the reading, whichever is greater) for chlorophyll a, rhodamine and fluorescein. The accuracy for turbidity, over a 0 - 10 FTU range, is ± 0.02 FTU (or ± 3% of the reading, whichever is greater).

Further details are available from the Aquatracka MKIII 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.

Originator's processing document for JR20101221 (JR245, JR246, JR247) CTD data

Sampling strategy

A total of 24 CTD casts were performed during JR20101221 (JR245/JR246/JR247), which sailed from Stanley (Falkland Islands) on 21 December 2010 and docked in Stanley (Falkland Islands) on 19 January 2011.

Data Processing

CTD data were collected at 24Hz and logged via the deck unit to a PC running Seasave Win32 version 5.37b (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 pumps are typically expected to switch on between 30 and 60 seconds after the instrument is deployed, but during the cruise they could take up to 2.5 minutes to switch on.

After the 10 m soak, the CTD was raised to as close to the surface as wave and swell condition allowed and then lowered to within 10 m of the seabed or to the maximum depth specified. Bottles were fired on the upcast, where the procedure was to stop the CTD winch, hold the package in situ for a few seconds to allow sensors to equilibrate, and then fire a bottle. The sensor averages these readings to produce one value for each bottle fire. Short times between firing pairs of bottles led to no SBE35 readings for the second bottle of the pair.

Bottle firing depths were determined by water sample and calibration requirements. Water samples from 20 m was taken from every station cast and most core box casts for chlorophyll, POC and lugols. Salinity samples were taken from 20 m and other depth with low vertical salinity gradient to calibrate the CTD conductivity and salinity.

For each CTD cast the following raw data files were generated:

• jr245ctd[NNN].dat (binary data file)
• jr245ctd[NNN].con (ascii configuration file containing calibration information)
• jr245ctd[NNN].hdr (header file containing sensor information)
• jr245ctd[NNN].bl (ascii file containing bottle fire information)

where [NNN is the cast number of the CTD data series.

The following processing was performed by the Originator using the SBE Data Processing software (Seasave Version 5.37b):

1. DatCnv was used to read in the raw CTD data file (.hex) which contained the data in engineering units and apply calibrations as appropriate through the instrument configurations (.con) file.
2. CellTM was run using alpha = 0.03 and 1/beta = 7 remove the conductivity cell thermal mass effects from the measured conductivity.
3. Wild Edit was run to remove spikes in the pressure channel.
4. Bottle Summary was run to create a .btl file containing the average, standard deviation, min and max values recorded by the CTD instrument suite at bottle firings.

The originator then proceeded to process the data further in Matlab using scripts written by Brian King. The procedures included:

1. Reading .cnv data into Matlab
2. Renaming of variables
3. Application of oxygen hysteresis correction
4. Matlab equivalent of Sea-Bird's loop edit. Flags data if two or more consecutive points are considered bad, to allow for noise in the speed calculation at 24 Hz
5. Plot 24 Hz profiles to allow for visual checking
6. Averaging to 1 Hz and calculation of salinity
7. Bottom of cast identification and addition to the datacycle file
8. Split the cast between up and downcast and averages to 2 dbar
9. Merging of times from CTD
10. Merging of CTD times with navigation data
11. Depth calculation from known positions
12. Bottle oxygen conversion from µmol l^-1 to µmol kg^-1
13. Residuals between samples and ctd bottles averages calculation

Field Calibrations

Temperature

A total of 291 temperature data points from the SBE 35 temperature sensor were recorded and used for calibration purposes. After excluding a small number of outliers, an offset was found to be of approximately 2x10^-3°C.

Salinity

A total of 99 salinity samples were collected and analysed using a Guildline Autosal Salinometer in order to calibrate the salinity sensors attached to the CTD. A small number of outliers were excluded from the final calibration. an offset of -2x10^-3 was found, howveer it was not applied as it was deemed that the temperature calibration would acount for this offset.

Processing by BODC of RRS James Clark Ross 20101221 (JR245, JR246, JR247) CTD data

The files were processed and calibrated at the British Antarctic Survey and were sent to BODC in mstar format. The following parameters were sent: time, press, primary and secondary temperature, salinity and conductivity, pressure_temp, altimeter, oxygen, fluor, transmittance, potemp, potemp2, sigma0, sigma2, sigma4, depth, calibrated temperature, depth, salinity, potemp, 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 calibrated 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 (primary and secondary uncalibrated temperature, salinity and conductivity and calibrated and uncalibrated depth) 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

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: