Metadata Report for BODC Series Reference Number 970216

• 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

Problem Report

Dissolved Oxygen

All data from this channel should be used with caution as the values measured were unrealistic during this and several other cruises. Readings taken by the probe indicated that the sensor was constantly saturated. It is advised that the data should only be used for relative comparisons.

Data quality notes

LISST transmission and scattering

Users should be aware that the clear water values measured on different cruises are observed to increase and decrease at times, which is not consistent behaviour. In addition, the clear water scattering values are also sometimes less than and sometimes greater than those measured by the manufacturer at the time of last calibration (October 2006). This may be due to a problem with the instrument or the method in which the clear water values are measured.

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

Sea Bird Electronics SBE13 Dissolved Oxygen Sensor

The SBE 13 was designed as an auxiliary sensor for Sea Bird SBE 9plus, but can fitted in custom instrumentation applications. When used with the SBE 9 Underwater Unit, a flow-through plenum improves the data quality, as the pumping water over the sensor membrane reduces the errors caused by oxygen depletion during the periods of slow or intermittent flushing and also reduces exposure to biofouling.

The output voltage is proportional to membrane current (oxygen current) and to the sensor element's membrane temperature (oxygen temperature), which is used for internal temperature compensation.

Two versions of the SBE 13 are available: the SBE 13Y uses a YSI polarographic element with replaceable membranes to provide in situ measurements up to 2000 m depth and the SBE 13B uses a Beckman polarographic element to provide in situ measurements up to 10500 m depth, depending on the sensor casing. This sensor includes a replaceable sealed electrolyte membrane cartridge.

The SBE 13 instrument has been out of production since 2001 and has been superseded by the SBE 43.

Specifications

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

Prince Madog Cruise PD04_07 CTD Instrumentation

The CTD unit was a Sea-Bird Electronics 911plus system (SN P23655-0620), with dissolved oxygen sensor. The rosette sampling system was equipped with 5 litre sampling bottles (manufactured by Ocean Test Equipmetn Inc.). In addition the CTD was fitted with a red (660 nm) beam transmissometer, a fluorometer, a Sequoia Scientific Laser In-Situ Scattering and Transmissometry (LISST) particle analyser and a LI-COR Underwater Quantum Sensor. The Sea-Bird sensors SBE 3,4 and 13 Beckman were last calibrated by the manufacturer in January 2004. Also attached was a Sea-Bird SBE-35 Temperature Logger to supply an independent check of temperature. The table below lists more detailed information about the various sensors.

Change of sensors during cruise: None reported.

Water sampling device

Rosette sampling system equipped with 5 litre sampling bottles, manufactured by Ocean Test Equipment Inc.

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.

Turner Designs Self-Contained Underwater Fluorescence Apparatus (SCUFA)

The Turner Designs SCUFA is a submersible fluorometer for chlorophyll and dye tracing operations that has been designed to operate in a wide range of concentrations, environmental conditions as well as operational modes (profiling or moored deployments). The instrument includes an integrated temperature probe and software which allow for automatic correction of fluorescence data from temperature effects. The superior ambient light rejection eliminates the effects of sunlight and allows the SCUFA to be used in surface waters without the need for external pumps or light shields.

Each instrument can be customised to meet user requirements. Users can choose one of the following channels: chlorophyll a, cyanobacteria (phycocyanin or phycoerythrin pigments), rhodamine WT, fluorescein and turbidity. Instrument options include turbidity, internal data logging and automatic temperature correction.

Three versions of the SCUFA are available: SCUFA I, II and III. SCUFA I and II are used for chlorophyll a applications, while SCUFA III is used for Rhodamine WT. Models II and III include a turbidity channel that is not present on model I. The SCUFA has been out of production since 2008.

Specifications

The table below presents the specifications for the different channels.

Further details can be found in the manufacturer's brochure.

LI-COR LI-192 Underwater Quantum Sensor

The LI-192 Underwater Quantum Sensor is used to measure photosynthetic photon flux density and is cosine corrected. The sensor is often referred to as LI-192SA or LI-192SB (the LI-192SB model was superseded by LI-192SA). One of the main differences is that the LI-192SA model includes a built-in voltage output for interfacing with NexSens iSIC and SDL data loggers.

Sensor specifications, current at January 2012, are given in the table below. More information can be found in the manufacturer's LI-192SA andLI-192SB specification sheets.

Sensor Specifications

(Specifications apply to both models unless otherwise stated)

SeaTech Transmissometer

Introduction

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.

Specifications

• 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)

Notes

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.

Sequoia Laser In-situ Sediment Size Transmissometer (LISST)

The Sequoia LISST measures particle size distribution of suspended sediments by laser diffraction. This technique allows particles of various compositions to be measured with a single device and, because the particle volume is roughly of the same order for all sizes, the required dynamic range of the sensors is reduced compared with single-particle counters.

The instrument includes optics for producing a collimated laser beam, a detector array, electronics for signal amplification and processing, a data storage and scheduling computer and a battery system. The primary measurement is the scattering of laser light at a number of angles, which is mathematically inverted to give a grain size distribution, and also scaled to obtain the volume scattering function. The size distribution is presented as concentration in each of 32 logarithmically-spaced grain-size class bins. Optical transmission, water depth and temperature are recorded as supporting measurements.

Several models are available and although the principals of operation are the same, their specifications vary slightly. The specifications for model LISST-100 are provided below.

Specifications

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

Prince Madog Cruise PD04_07 CTD Processing

Sampling Strategy

A total of 103 CTD casts were performed during the cruise. 2 stations were sampled in Liverpool Bay and remaining sampling was carried out over two 25 hour tidal cycles in the Welsh and Hilbre Channels in the Dee Estuary. Rosette bottles were fired near-bed on numerous profiles in order to obtain independent temperature and salinity samples. Water bottle samples were also taken from the near-surface and near-bed bottle for filtering to determine suspended sediment load, by the School of Ocean Sciences.

Data were logged at 24 Hz onto a PC running SEASAVE, Sea-Bird's data acquisition software. It should be noted, however, that the CTD PC logging and operating system suffered technical difficulties throughout this cruise. As a result, full downcast and full upcast data are available for only 61 of 103 casts. Full downcast and partial upcast data are available for 16 casts. There are also 26 casts where only the downcast was successfully recorded. The raw Sea-Bird data, configuration and bottle files were supplied to BODC for further processing.

BODC post-processing and screening

Sea-Bird Processing

The raw CTD files were processed through the Sea-Bird SBE Data Processing software version 5.35. Binary (.DAT) files were converted to engineering units and ASCII format (.CNV) using the DATCNV program.

Sea-Bird software program ALIGNCTD was run to advance conductivity by 0s and oxygen by 3s (within the typical range given in the Sea-Bird manual). No adjustment was made to the temperature channel as the fast sensor response time renders this unnecessary, according to the Sea-Bird literature.

To compensate for conductivity cell thermal mass effects, the data files were run through CELLTM, using alpha = 0.03, 1/beta = 7, typical values for this CTD model given in the Sea-Bird literature. After running WILD EDIT, FILTER was run on the pressure channel using the recommended time filter of 0.15 seconds. Next, a minimum CTD velocity of 0.0 m s^-1 was used for LOOP EDIT in order to exclude scans where the CTD was travelling backwards due to ship's heave. Salinity, density and oxygen concentration were then calculated and added to the output files using the DERIVE program. The files were then averaged to 0.5 second intervals using BINAVERAGE.

Reformatting

The data were converted from ASCII format into BODC internal format (QXF). The following table shows the mapping of variables within the original files to appropriate BODC parameter codes:

Reformatted CTD data were transferred onto a graphics work station for visualisation using the in-house editor Edserplo. Data that were considered unrealistic were flagged as suspect.

Once quality control screening was complete, the CTD downcasts were banked. Finally, the data were binned against pressure at 0.5 dbar increments.

Calibrations

Salinity

37 independent salinity samples, obtained from the CTD rosette, were used to calibrate the CTD. 3 points were deemed to be outliers (casts C021, C027 and C051) and were removed from the analysis. The salinity offset (bottle salinity - CTD salinity) was examined to see if it varied with pressure or bottle salinity. Significant relationships at 95% confidence were found between offset and bottle salinity (R2=37.3%). A calibration equation was derived from the relationship between mean offset and bottle salinity as follows, based on 34 observations: calibrated salinity = CTD salinity * 1.14417 - 4.5881.

The calibration residuals ranged from -0.191 to 0.3301. The mean offset of the dataset with outliers removed is -0.1031

Temperature

93 independent temperature values were compared to pressure and CTD temperature. 1 point was identified as an outlier (cast C063 at depth 1.104m) and was removed from the analysis. The offset between CTD temperature and SBE-35 temperature was found not to be significantly different from zero at 95% confidence. Therefore, there was no adjustment to the CTD temperature resulting from the application of manufacturer's coefficients during initial processing.

The mean offset with the outlier removed is -0.0018

Pressure

There were no casts where the CTD was logging in air, so it was not possible to determine a pressure offset. No adjustments were made to the values resulting from application of manufacturer's coefficients during the intial processing.

Beam attenuation

Coefficients M and B were calculated, allowing calibration of the transmissometer with air readings taken during the cruise. M and B are calculated according to SBE Application Note No. 7:

Where Tw is the percent transmission for pure water for the instrument (92.98%); W0 is the voltage output in pure water (4.649 volts); A0 is the manufacturer's air voltage (4.661 volts); Y0 is the manufacturer's blocked path voltage (0.000 volts); A1 is the cruise maximum air voltage (4.526 volts); Y1 is the current blocked path voltage (0.0000 volts). For this cruise, M and B were calculated to be 20.5966 and 0, respectively.

M and B are then inserted into the following equations (from SBE Application Note No. 7) to obtain calibrated beam attenuation: Light transmission [%] = (M * voltage output) + B Beam attenuation coefficient c = - (1/z) * ln (light transmission [decimal])

Where M and B are the calibration coefficients, z is the transmissometer path length (0.2m), light transmission[decimal] is light transmission [%] divided by 100, c = beam attenuation (m^-1)

Dissolved oxygen

The data are uncalibrated, as there were no field samples taken for calibration.

Fluorescence

The data are uncalibrated, as there were no field samples taken for calibration.

LISST transmission and scattering

The data are currently uncalibrated. However, the voltages can be calibrated to give optical transmission, beam attenuation, total volume concentration and Sauter mean diameter according to the following manufacturer's constants and calculations:

Where cal = total volume concentration calibration constant = 160, a = Sauter mean diameter calibration constant = 0.09, V_SO = clearwater scattering output = 0.150 V (see note below), V_TO = clear water transmission output = 3.215 V (see note below), V_Soff = scattering output offset = 0.10 V, V_Toff = transmission output offset = 0.10 V. Measured outputs are scattering = V_S and transmission = V_T.

N.B. The clear water values quoted above are supplied by the manufacturer. Ideally these should be replaced by values determined by the LISST calibration cast, during which the instrument is placed in a tank of clean water. However, there is suspicion that these values may not be accurate. There are abnormally high values for some cruises, which the manufacturer suggests may be due to the calibration dip occurring in insufficiently clear water. Therefore, manufacturer's values have been quoted along with values measured by the instrument during previous cruises. Users are advised to use their own discretion in deciding which coefficients to apply.

PAR

During instrument deployment, no effort was made to avoid data collection possibly being affected by ship shadowing. The LI-COR LI 192SB sensor number 33 was calibrated from raw voltages using the CEFAS supplied equation: PAR = 0.157508*exp(volts*3.42410)

References

Benson, B. B. and Krause, D., 1984. The concentration and isotopuc fractionation of oxygen dissolved in freshwater and seawater in equilibrium with the atmosphere. Limnol. Oceanogr., 29(3),620-632

Fofonoff, N. P. and Millard, R. C., 1983. Algorithms for computations of fundamental properties of seawater. UNESCO Technical Papers in Marine Science No. 44, 53pp.

UNESCO, 1981.Background papers and supporting data on the International Equation of State of Seawater 1980. UNESCO Technical Papers in Marine Science No. 38, 192pp.

Project Information

Proudman Oceanographic Laboratory Dee Experiment

Introduction

Sediment transport process models are a vital tool in allowing scientists to predict sediment transport and forecast seabed and coastal morphodynamic evolution. It is however, difficult to obtain accurate models due to the complex inter-dependence of sediment processes in the bottom boundary layer. This inter-dependence is governed by interactions between the sediment transport triad; the bed, the hydrodynamics and the mobile sediments.

Scientific Objectives

• To use a varying suite of instruments to make co-located measurements of the sediment triad
• To provide a framework to allow assessment and improvement of the latest sediment transport models
• To address dynamics of suspended sediments in terms of supply of material to the coastal zone from estuaries
• Development of a new description of suspended sediment and water opacity to improve simulation of coastal primary productivity

Fieldwork

The study site chosen by POL for this research was the Dee Estuary, Liverpool Bay. POL performed fieldwork in the Hilbre Channel on the eastern side of the Estuary and the Welsh Channel on the western exit of the Estuary, with emphasis placed on two repeat stations, HC and WC. The fieldwork started in February 2005 and has been summarised below:

Funding

The Dee Experiment project was core funded by POL under Programme 2 (Shallow coastal seas) Theme 5 (Coastal and sediment processes) of POL's Science Programme 2001 - 2006. From March 2007 onwards, this core funding was replaced by funding from NERC's Oceans 2025 programme and the Dee Experiment research continued as part of Oceans 2025 Work Package 3.3.

Data Activity or Cruise Information

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

Fixed Station Information

Dee Estuary Station WC

This station is located within the Welsh Channel of the Dee Estuary, Liverpool Bay. It is one of two stations repeatedly visited by the Proudman Oceanographic Laboratory (POL) in the Dee. All activities at this site occurred within a box bounded by co-ordinates 53.371°N, 3.31791°W at the north-east corner and 53.36642°N, 3.33817°W at the south-west corner. Typical depth ranges encountered within the box are 7 m - 17 m.

POL activites can be separated into two groups. These are (i) repeat CTD profiles over tidal cycles; (ii) mooring deployments.

The deployment history, to date, for this station is summarised below:

The CTD instrument package for these cruises was a Sea-Bird 911plus, with beam transmissometer, fluorometer, LICOR PAR sensor, LISST-25, and oxygen sensor.

The mooring deployment history for this site is as follows:

Key:

ADCP: Acoustic Doppler Current Profiler
ABS: Acoustic Backscatter Sensor
ADV: Acoustic Doppler Velocimeter
LISST: Laser In-Situ Scattering Transmissometer
SBE-37 MicroCAT: Conductivity and Temperature Sensor

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: Dee Estuary Station WC

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.