Metadata Report for BODC Series Reference Number 734342

• 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 Quality Report

The following is adapted from the JR81 cruise report. There was found to be excessive rotation of the frame so a fin was added for stabilisation before Station 03 and was moved to a different upright before Station 11. On station 08 the SBE35 standards thermometer calibration slope and offset which had been input as 0 and 1 were corrected, this made an insignificant change to the values recorded. After Station 12 Niskin bottle 8 was found to be cracked and was replaced. After Station 17 there was orange slime on the LADCP and fin which was wiped off. On several of the deeper stations there was considerable spooling and respooling of the winch: Stations 10, 12, 15, 18, 23, 25 and 27 were particularly affected. The Underwater Unit failed at 1000m on the downcast of Station 26 (renamed Station 26a) which was repeated using the alternate Underwater Unit. On Station 26 the altimeter was not displayed to the screen as the channel had been changed and this had not been noticed. After the change of Underwater Unit the altimeter reading was found to drift slightly until the cable was changed before Station 29.

Data Access Policy

Open 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.

If the Information Provider does not provide a specific attribution statement, or if you are using Information from several Information Providers and multiple attributions are not practical in your product or application, you may consider using the following:

"Contains public sector information licensed under the Open Government Licence v1.0."

Narrative Documents

Instrument Description

CTD unit and auxiliary sensors

The CTD system used on the JR81 was the BAS Sea-Bird 911 plus, serial numbers 09P20391-0541 (Stations 01-26a) and 09P15759-0480 (Stations 26-32), with a 12 bottle frame and pylon. Only 10 Niskin bottles were fitted to the frame, bottles 2 and 3 were removed to accommodate the LADCP battery. The CTDs were fitted with the following scientific sensors:

The temperature and conductivity sensors were connected to two SBE 5 T submersible pumps (serial numbers; 52395 and 51813 (Stations 01-26a); 52400 and 51807 (Stations 26-32)).

The salinity samples from the CTD were analysed during the cruise using the BAS Guildline Autosal model 8400B (serial number 65763). The Autosal was standardised using batch P140 IAPSO Standard Seawatersupplied by Ocean Scientific International Ltd.

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 PA-200 altimeter

Digital precision altimeter with 200 kHz signal giving highly accurate height off seabed and subsea distance measurements. Operates effectively between -10 °C and 40 °C at heights up to 50 m above the seabed. Standard depth rating is 4000 m, with 700 and 6800 m options. This term can be used for either the MKI or MKII version, which will be identified elsewhere in the supporting metadata.

For more information, please see these documents:

https://www.bodc.ac.uk/data/documents/nodb/pdf/pa200_pa500-altimeters.pdf

https://www.bodc.ac.uk/data/documents/nodb/pdf/pa200_pa500_MKII-altimeters.pdf

BODC Processing

Data files for JR81 were provided by the originator in Pstar format. The 32 CTD data files selected for transfer had been bin averaged by pressure to 1db. Files averaged to 24Hz were also provided by the originator however the 1db data were considered to be of a sufficiently high resolution for processing. Each parameter selected for transfer was assigned a parameter code as follows:

The Matlab transfer function 360 was run to convert the Pstar files into an internal NetCDF format (QXF). The transfer automatically converted the conductivity channels from mS/cm to S/m. The parameters time (s) and scanno (scans) were not selected for transfer as the data were bin averaged by pressure. The coordinates of the data files were checked using Google Earth to make sure that they matched the cast locations described in the cruise report.

Data from file headers were separated off into tagged ASCII files which were later used in loading metadata to the database. The originator's Pstar files contained uncorrected water depths in the file headers, which were often shallower than the maximum sensor depths. Subsequently, water depth has been calculated, for all stations except station 26, by combining the pressure and altimeter data. To calculate the water depth, the pressure sensor maximum (db) was converted to the maximum depth (m) via the Matlab script 'ptodep' using the Saunders and Fofonoff method. This value was then added to the corresponding altimeter height above the seabed. The data file from station 26 (BODC ref 734631) contained no altimeter data, in this case the uncorrected water depth from the Pstar header has been used.

Data from the QXF files were visualised using the in-house editor Edserplo. Obvious data spikes were flagged as 'M', null values were flagged as 'N'. Overall, the data are of good quality and there were no significant data spikes present.

Saunders, P.M. / Fofonoff, N.P. , Deep-Sea Research and Oceanographic Abstracts, 23 (1), p.109-111, Jan 1976

Originator's Data Processing

The following information is adapted from the JR81 cruise report.

Sampling strategy

A Conductivity-Temperature-Depth (CTD) probe was used to vertically profile the temperature and salinity of the water column. 32 full depth stations were sampled: a test station, a station at the Rothera Time Series (RaTS) Station and 30 stations across the Drake Passage section (plus one failed cast on Station 26). At each CTD station on JR81, all ten Niskin bottles were closed and sampled for salinity analysis and subsequent CTD conductivity calibration. Bottles were closed using the SeaBird software rather than by pressing the fire button on the Deck Unit. Logging was stopped when the CTD reached the surface. A thermometer was set to record on each bottle firing and to report a 24 second average temperature for comparison with the CTD measurements.

A Viglen Contender P4 1.4 GHz was attached to the Deck Unit. The Deck Unit was switched on whilst the CTD was on deck just before deployment and the control for the pylon usually 'homed'. Data were logged using the SeaBird seasave Win32 software version 5.25 running within the Windows environment. Calibration data were entered in seasave. Logging to the pc was normally started when the CTD was on the deck in order to obtain deck pressure values.

Data Processing

The raw data were logged as a binary file 81ctdNN.dat where NN is the station number. The time variable recorded in the data file is datacycles after the start of logging, the sampling rate is 24Hz. The logging start time has to be obtained from the file header and derives from the pc clock. The time on the pc clock was therefore periodically synchronised with the ship's master clock. Data files were backed up to the pc network (N:) drive and copied to the UNIX system which was mounted as the U: drive where further processing was carried out. The SeaBird SBEDataPro conversion utility was used to convert the logged binary data to ASCII files and also to apply the cell thermal mass correction using the standard coefficients (a = 0.03 and b = 1/7).

The temperature and conductivity sensors are separated in space within the pumped system and the seawater first passes the temperature sensor and then the conductivity sensor. Values for the conductivity advance were estimated by choosing the time shifts to minimise the noise in the derived salinities. The misalignment was reduced by delaying the primary conductivity by 1 datacycle (1/24 seconds) and advancing the secondary conductivity by 1 datacycle.

After the thermal mass correction had been applied, the data were transferred to the UNIX machine jruf by copying to a mounted "U-drive" on the pc. Once on the UNIX system the data were processed using pstar data format and c-shell scripts.

Field Calibrations

The CTD conductivity sensors were calibrated against the bottle sample salinity measurements. For each cast, a cshell script botcond was run, to calculate sample conductivity from bottle salinity, CTD pressure and (primary) temperature. Bottle minus CTD conductivity was calculated for each sample and for both CTD conductivity sensors.

Apart from the inevitable few outliers the conductivity calibration was of very good quality. There was no significant dependence of either conductivity sensor on pressure, temperature or time. The primary conductivity was too low by 0.0035 ± 0.0010 mS/cm and the secondary by 0.0002 ± 0.0009 mS/cm. These adjustments were therefore applied to the sensors.

The SBE35 data were compared to the data from both the primary and secondary temperature sensors of the SBE911plus using data extracted in the 24 seconds after each was fired. Near the surface, as expected, the comparisons are quite noisy. Below 1000m the mean differences between both the CTD temperatures and the SBE35 were 0.001±0.001°C, the SBE35 being colder than both CTD sensors. No correction is applied as the nominal accuracy of both the standards thermometer and the CTD temperature sensors is 0.001°C. The difference between the two CTD temperature sensors is of order 0.0001°C.

Salinities, potential temperatures and potential densities calculated with peos83 to give the master file 81ctdNN.24Hz. The downcast data cycles were extracted and the downcast averaged to 1db to give the file 81ctdNN.1db. The master file (81ctdNN.24Hz) was averaged to 1Hz using pavrge to give the file 81ctdNN.1Hz. The winch data were also read in as part of the CTD processing using the script win0 which requires the station number and start and stop times for the cast.

Project Information

World Ocean Circulation Experiment (WOCE)

The World Ocean Circulation Experiment (WOCE) was a major international experiment which made measurements and undertook modelling studies of the deep oceans in order to provide a much improved understanding of the role of ocean circulation in changing and ameliorating the Earth's climate.

WOCE had two major goals:

• Goal 1. To develop models to predict climate and to collect the data necessary to test them.

• Goal 2. To determine the representativeness of the Goal 1 observations and to deduce cost effective means of determining long-term changes in ocean circulation.

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: