Metadata Report for BODC Series Reference Number 813406
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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.
These specification apply to the MK3C version.
3200 m (optional)
|-3 to 32°C||1 to 6.5 S cm-1|
0.03% FS < 1 msec
0.003°C < 30 msec
0.0001 S cm-1
0.0003 S cm-1 < 30 msec
Further details can be found in the specification sheet.
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.
The transmissometer is designed to accurately measure the the amount of light transmitted by a modulated Light Emitting Diode (LED) through a fixed-length in-situ water column to a synchronous detector.
- Water path length: 5 cm (for use in turbid waters) to 1 m (for use in clear ocean waters).
- Beam diameter: 15 mm
- Transmitted beam collimation: <3 milliradians
- Receiver acceptance angle (in water): <18 milliradians
- Light source wavelength: usually (but not exclusively) 660 nm (red light)
The instrument can be interfaced to Aanderaa RCM7 current meters. This is achieved by fitting the transmissometer in a slot cut into a customized RCM4-type vane.
A red LED (660 nm) is used for general applications looking at water column sediment load. However, green or blue LEDs can be fitted for specilised optics applications. The light source used is identified by the BODC parameter code.
Further details can be found in the manufacturer's Manual.
RRS Challenger 40 CTD Data Documentation
The CTD unit was a Neil Brown Mk. 3 incorporating a pressure sensor, conductivity cell, platinum resistance thermometer, and a Beckmann dissolved oxygen sensor. This was mounted vertically in the centre of a protective cage.
Attached to bars of the frame were an Aquatracka logarithmic response fluorometer and a Seatech red light (661 nm) transmissometer with a 25 cm path length.
To the side of the frame was a rosette sampler which could be fitted with up to 12, 1.7 litre Niskin bottles. The base of the bottles were in line with the pressure head. One bottle was fitted with a holder for twin reversing thermometers mounted marginally above the CTD temperature sensor.
Operational procedure and data logging
On each cast the CTD was lowered to a depth of approximately 5 metres and held until the instrument stabilised. It was then raised to the surface and lowered continuously at 0.5 to 1 m/s to as close as possible to the sea floor. The upcast was done in stages between the bottle firing depths.
Data were logged by the Research Vessel Services ABC data logging system. The deck unit outputs were sampled at 32 Hz by a microprocessor interface (the Level A) which passed time stamped averaged cycles at 1 Hz to a Sun workstation (the Level C) via a buffering system (the Level B).
The raw data comprised ADC counts. These were converted into engineering units (Volts for fluorometer and transmissometer: ml/l for oxygen: mmho/cm for conductivity: °C for temperature) by the application of laboratory determined calibrations and salinity was computed using the algorithm in Fofonoff and Millard (1983). The data were submitted to BODC in this form.
Within BODC the data were reformatted on an IBM main-frame. At this stage transmissometer air readings recorded during the cruise were used to correct the transmissometer voltage to the manufacturer's specified voltage by ratio. The voltages were then converted to percentage transmittance (multiplied by 20.0) and dissolved oxygen converted to µM (multiplied by 44.66).
Next the data were loaded onto a Silicon Graphics workstation. A sophisticated interactive screening program was used to delimit the downcast, mark the depth range of water bottle firings and flag any spikes on all of the data channels.
The data were returned to the IBM and the downcasts loaded into a database under the Oracle relational database management system. At this stage percentage transmittance was converted to attenuance to eliminate the influence of instrument path length using the equation:
|Attenuance = -4.0 * loge (% trans/100)|
Calibration sample data were merged into the database and files of sample value against CTD reading at the bottle depth were prepared for the Principal Investigators to determine the calibrations. Due allowance was made for rig geometry. Note that CTD downcast values were generally used although the bottles were fired on the upcast. The validity of an assumed static water column for the duration of the cast was checked on the graphics workstation and upcast values substituted if necessary.
Sigma-T values were calculated using the algorithm presented in Fofonoff and Millard (1983).
For each cast the mean pressure reading logged whilst the instrument was in air was determined. The average of these, determined as -0.37 db, was added to each pressure value.
Two digital reversing thermometers were fired at the bottom of each cast. The mean of the two temperatures was regressed against CTD temperature to give the calibration equation:
|Calibrated temp (°C) = Raw temp * 0.99814 + 0.0131|
A sample was taken from the bottom bottle of each cast and salinity was determined using a Guildline Autosal. The bottle salinities were regressed against CTD salinity to give the calibration equation:
|Calibrated salinity (PSU) = Raw salinity * 0.9749 + 0.87138|
No extracted chlorophyll values were determined on this cruise. Consequently, no chlorophyll calibration was possible.
No dissolved oxygen calibration samples were taken on this cruise and therefore no calibration was possible. All CTD oxygen values have been flagged as suspect to reflect this.
No suspended matter determinations were made on this cruise. Consequently, there are no transmissometer channels other than attenuance.
No chlorophyll data are available, only uncalibrated voltages.
No dissolved oxygen data are available.
No suspended matter data are available.
Fofonoff, N.P and Millard, R.C. Jr. (1983). Algorithms for the computation of fundamental properties of sea water.
North Sea Project
The North Sea Project (NSP) was the first Marine Sciences Community Research project of the Natural Environment Research Council (NERC). It evolved from a NERC review of shelf sea research, which identified the need for a concerted multidisciplinary study of circulation, transport and production.
The ultimate aim of the NERC North Sea Project was the development of a suite of prognostic water quality models to aid management of the North Sea. To progress towards water quality models, three intermediate objectives were pursued in parallel:
- Production of a 3-D transport model for any conservative passive constituent, incorporating improved representations of the necessary physics - hydrodynamics and dispersion;
- Identifying and quantifying non-conservative processes - sources and sinks determining the cycling and fate of individual constituents;
- Defining a complete seasonal cycle as a database for all the observational studies needed to formulate, drive and test models.
Proudman Oceanographic Laboratory hosted the project, which involved over 200 scientists and support staff from NERC and other Government funded laboratories, as well as seven universities and polytechnics.
The project ran from 1987 to 1992, with marine field data collection between April 1988 and October 1989. One shakedown (CH28) and fifteen survey cruises (Table 1), each lasting 12 days and following the same track, were repeated monthly. The track selected covered the summer-stratified waters of the north and the homogeneous waters in the Southern Bight in about equal lengths together with their separating frontal band from Flamborough head to Dogger Bank, the Friesian Islands and the German Bight. Mooring stations were maintained at six sites for the duration of the project.
|Table 1: Details of NSP Survey Cruises on RRS Challenger|
|CH28||29/04/88 - 15/05/88|
|CH33||04/08/88 - 16/08/88|
|CH35||03/09/88 - 15/09/88|
|CH37||02/10/88 - 14/10/88|
|CH39||01/11/88 - 13/11/88|
|CH41||01/12/88 - 13/12/88|
|CH43||30/12/88 - 12/01/89|
|CH45||28/01/89 - 10/02/89|
|CH47||27/02/89 - 12/03/89|
|CH49||29/03/89 - 10/04/89|
|CH51||27/04/89 - 09/05/89|
|CH53||26/05/89 - 07/06/89|
|CH55||24/06/89 - 07/07/89|
|CH57||24/07/89 - 06/08/89|
|CH59||23/08/89 - 04/09/89|
|CH61||21/09/89 - 03/10/89|
Alternating with the survey cruises were process study cruises (Table 2), which investigated some particular aspect of the science of the North Sea. These included fronts (nearshore, circulation and mixing), sandwaves and sandbanks, plumes (Humber, Wash, Thames and Rhine), resuspension, air-sea exchange, primary productivity and blooms/chemistry.
|Table 2: Details of NSP Process cruises on RRS Challenger|
|CH34||18/08/88 - 01/09/88||Fronts - nearshore|
|CH36||16/09/88 - 30/09/88||Fronts - mixing|
|CH56||08/07/89 - 22/07/89||Fronts - circulation|
|CH58||07/08/89 - 21/08/89||Fronts - mixing|
|CH38||24/10/88 - 31/10/88||Sandwaves|
|CH40||15/11/88 - 29/11/88||Sandbanks|
|CH42||15/12/88 - 29/12/88||Plumes/Sandbanks|
|CH46||12/02/89 - 26/02/89||Plumes/Sandwaves|
|CH44||13/01/89 - 27/01/89||Resuspension|
|CH52||11/05/89 - 24/05/89||Resuspension|
|CH60||06/09/89 - 19/09/89||Resuspension|
|CH48||13/03/89 - 27/03/89||Air/sea exchanges|
|CH62||05/10/89 - 19/10/89||Air/sea exchanges|
|CH50||12/04/89 - 25/04/89||Blooms/chemistry|
|CH54||09/06/89 - 22/06/89||Production|
In addition to the main data collection period, a series of cruises took place between October 1989 and October 1990 that followed up work done on previous cruises (Table 3). Process studies relating to blooms, plumes (Humber, Wash and Rhine), sandwaves and the flux of contaminants through the Dover Strait were carried out as well as two `survey' cruises.
|Table 3: Details of NSP `Follow up' cruises on RRS Challenger|
|CH62A||23/10/89 - 03/11/89||Blooms|
|CH64||03/04/90 - 03/05/90||Blooms|
|CH65||06/05/90 - 17/05/90||Humber plume|
|CH66A||20/05/90 - 31/05/90||Survey|
|CH66B||03/06/90 - 18/06/90||Contaminants through Dover Strait|
|CH69||26/07/90 - 07/08/90||Resuspension/Plumes|
|CH72A||20/09/90 - 02/10/90||Survey|
|CH72B||04/10/90 - 06/10/90||Sandwaves/STABLE|
|CH72C||06/10/90 - 19/10/90||Rhine plume|
The data collected during the observational phase of the North Sea Project comprised one of the most detailed sets of observations ever undertaken in any shallow shelf sea at that time.
North Sea Project Sandwaves and Sandbanks Process Study
Sandwave fields cover at least 15000 km2 of the Southern Bight of the North Sea. Drag coefficients based on measured pressure gradients were recorded and sea bed photography used to test bedload prediction formulae. The sand covering much of the southern North Sea is mobile forming banks that are interleaved with mud. Current meter moorings placed either side of a bank were used to estimate its associated circulation and contribution to dispersion. A 3 dimensional model using wave-current interaction enhancing bed stress is being applied to fine grid (~100m) bathymetry and is being tested using detailed measurements of near-bed currents and turbulence obtained from the STABLE (Sediment Transport And Boundary Layer Equipment) rig.
|Principal Scientist(s)||Michael B Collins (University of Southampton Department of Oceanography)|
Complete Cruise Metadata Report is available here
Fixed Station Information
|Station Name||NSP Sandbanks Experiment|
|Latitude||53° 1.80' N|
|Longitude||2° 11.00' E|
|Water depth below MSL||34.0 m|
NSP Sandbank Process Studies Moorings
The sandbank process studies carried out investigations into the influence of sandbanks on regional water flow patterns, including water and sand movement, in the Norfolk Banks region of the southern North Sea. It complimented a similar investigation into drag and sediment movement over sandwaves off the Dutch coast.
Moorings deployed included rigs with pressure sensors, a variety of current meters and STABLE (Sediment Transport and Boundary Layer Equipment).
The rigs deployed during this experiment lie within a box bounded by co-ordinates 53° 10.66' N, 002°4.07' E at the southwest corner and 53° 22.09' N, 002° 17.89' E at the northeast corner.
The deployment history for this station is summarised below:
|Rig / Instrument Identification||Meter Type||Start Date||Data Return(Days)||Comments|
|CH40/STABLE1||SM||19Nov88||3.0||One minute mean data for current speed and pressure only.|
- WR = Water Level Recorder
- CM = Current Meter
- SM = STABLE
Related Fixed Station activities are detailed in Appendix 1
The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:
|<||Below detection limit|
|>||In excess of quoted value|
|A||Taxonomic flag for affinis (aff.)|
|B||Beginning of CTD Down/Up Cast|
|C||Taxonomic flag for confer (cf.)|
|E||End of CTD Down/Up Cast|
|G||Non-taxonomic biological characteristic uncertainty|
|I||Taxonomic flag for single species (sp.)|
|K||Improbable value - unknown quality control source|
|L||Improbable value - originator's quality control|
|M||Improbable value - BODC quality control|
|O||Improbable value - user quality control|
The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:
|0||no quality control|
|2||probably good value|
|3||probably bad value|
|6||value below detection|
|7||value in excess|
|A||value phenomenon uncertain|
|Q||value below limit of quantification|
Appendix 1: NSP Sandbanks Experiment
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.
|Series Identifier||Data Category||Start date/time||Start position||Cruise|
|592508||Offshore sea floor pressure series||1988-11-17 08:37:30||53.2475 N, 2.2982 E||Not applicable|
|592489||Offshore sea floor pressure series||1988-11-17 19:37:30||53.3682 N, 2.0678 E||Not applicable|
|611514||Currents -subsurface Eulerian||1988-11-19 13:11:00||53.2408 N, 2.2447 E||Not applicable|
|813191||CTD or STD cast||1988-11-19 20:18:00||53.22317 N, 2.241 E||RRS Challenger CH40|
|813209||CTD or STD cast||1988-11-20 10:37:00||53.30583 N, 2.13117 E||RRS Challenger CH40|
|813210||CTD or STD cast||1988-11-20 11:30:00||53.30867 N, 2.14333 E||RRS Challenger CH40|
|813222||CTD or STD cast||1988-11-20 12:03:00||53.31183 N, 2.1495 E||RRS Challenger CH40|
|813234||CTD or STD cast||1988-11-20 12:48:00||53.31367 N, 2.16133 E||RRS Challenger CH40|
|813246||CTD or STD cast||1988-11-20 13:54:00||53.31483 N, 2.16133 E||RRS Challenger CH40|
|813258||CTD or STD cast||1988-11-20 14:37:00||53.327 N, 2.181 E||RRS Challenger CH40|
|813271||CTD or STD cast||1988-11-20 15:12:00||53.33483 N, 2.19233 E||RRS Challenger CH40|
|813283||CTD or STD cast||1988-11-20 16:12:00||53.34433 N, 2.21217 E||RRS Challenger CH40|
|813295||CTD or STD cast||1988-11-20 16:58:00||53.35017 N, 2.2245 E||RRS Challenger CH40|
|813302||CTD or STD cast||1988-11-20 17:53:00||53.265 N, 2.23617 E||RRS Challenger CH40|
|813314||CTD or STD cast||1988-11-20 18:40:00||53.27483 N, 2.254 E||RRS Challenger CH40|
|813326||CTD or STD cast||1988-11-20 19:20:00||53.293 N, 2.2645 E||RRS Challenger CH40|
|813664||CTD or STD cast||1988-11-20 19:56:00||53.30383 N, 2.27817 E||RRS Challenger CH40|
|813338||CTD or STD cast||1988-11-20 21:09:00||53.227 N, 2.22917 E||RRS Challenger CH40|
|813351||CTD or STD cast||1988-11-20 21:34:00||53.22883 N, 2.23133 E||RRS Challenger CH40|
|813363||CTD or STD cast||1988-11-20 22:11:00||53.22483 N, 2.23417 E||RRS Challenger CH40|
|813375||CTD or STD cast||1988-11-20 22:50:00||53.22183 N, 2.233 E||RRS Challenger CH40|
|813387||CTD or STD cast||1988-11-20 23:36:00||53.227 N, 2.2375 E||RRS Challenger CH40|
|813399||CTD or STD cast||1988-11-21 00:11:00||53.22583 N, 2.23133 E||RRS Challenger CH40|
|813418||CTD or STD cast||1988-11-21 01:04:00||53.22067 N, 2.244 E||RRS Challenger CH40|
|813431||CTD or STD cast||1988-11-21 01:34:00||53.22633 N, 2.23717 E||RRS Challenger CH40|
|813443||CTD or STD cast||1988-11-21 02:03:00||53.22633 N, 2.243 E||RRS Challenger CH40|
|813455||CTD or STD cast||1988-11-21 02:34:00||53.22267 N, 2.24467 E||RRS Challenger CH40|
|813467||CTD or STD cast||1988-11-21 03:04:00||53.227 N, 2.2405 E||RRS Challenger CH40|
|813479||CTD or STD cast||1988-11-21 03:33:00||53.22317 N, 2.24433 E||RRS Challenger CH40|
|813480||CTD or STD cast||1988-11-21 04:04:00||53.22383 N, 2.245 E||RRS Challenger CH40|
|813492||CTD or STD cast||1988-11-21 04:34:00||53.2265 N, 2.243 E||RRS Challenger CH40|
|813511||CTD or STD cast||1988-11-21 05:06:00||53.22433 N, 2.23817 E||RRS Challenger CH40|
|813523||CTD or STD cast||1988-11-21 05:35:00||53.22383 N, 2.24533 E||RRS Challenger CH40|
|813535||CTD or STD cast||1988-11-21 06:04:00||53.223 N, 2.244 E||RRS Challenger CH40|
|813547||CTD or STD cast||1988-11-21 06:37:00||53.228 N, 2.23683 E||RRS Challenger CH40|
|813559||CTD or STD cast||1988-11-21 07:03:00||53.22267 N, 2.24283 E||RRS Challenger CH40|
|813560||CTD or STD cast||1988-11-21 07:34:00||53.22317 N, 2.24667 E||RRS Challenger CH40|
|813676||CTD or STD cast||1988-11-21 07:45:00||53.22083 N, 2.2475 E||RRS Challenger CH40|
|813572||CTD or STD cast||1988-11-21 08:07:00||53.22383 N, 2.239 E||RRS Challenger CH40|
|813584||CTD or STD cast||1988-11-21 08:38:00||53.22817 N, 2.23233 E||RRS Challenger CH40|
|813596||CTD or STD cast||1988-11-21 09:09:00||53.2285 N, 2.23133 E||RRS Challenger CH40|
|813603||CTD or STD cast||1988-11-21 10:25:00||53.23583 N, 2.2265 E||RRS Challenger CH40|
|813615||CTD or STD cast||1988-11-21 11:51:00||53.22533 N, 2.232 E||RRS Challenger CH40|
|813688||CTD or STD cast||1988-11-21 12:57:00||53.26333 N, 2.1985 E||RRS Challenger CH40|