Metadata Report for BODC Series Reference Number 426074

• 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

The current data are noisy and should be used with care.

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

InterOcean Spherical Solid State Sensor Current Meter S4 series

The S4 family are self-contained current measuring sensors enclosing all necessary solid state electronics for acquiring, processing and outputting data. Data retrieval is accomplished through a serial port without opening the instrument.

The spherical shape of the S4 is a contributing factor in the rejection of the vertical components of water movement and there are no protruding parts or sensor support structures to interfere with the water flow.

The S4 measures the magnitude and direction of the horizontal current motion of the water. Water flows through the electromagnetic field created by the instrument, thereby producing a voltage which is proportional to the magnitude of the water velocity past the sensor. This voltage is then sensed by two pairs of titanium electrodes located symmetrically on the equator of the spherical housing which forms the sensor.

Manufacturer's specifications: Meter (sphere, diameter 25cm) is designed for depths down to 1000m (S4 standard: glass-filled cycloaliphalic epoxy construction with grooved surface for hydrodynamic stability) or down to 6000m (S4D, deep: annealed borosilicate glass version with smooth surface). The meter is shackled directly into the mooring cable by means of an axial titanium load bearing shaft.

Meter comprises:-

1. Electromagnetic, 2 axis current speed sensor, range 0 to 350cm/s (standard) 0 to 50 and 0 to 100cm/s (optional), resolution 0.2cm/s (standard) 0.03cm/s (0 to 50 range) 0.06cm/s (0 to 100 range), accuracy 2 per cent reading +/- 1cm/s. The sensor responds to the component of flow normal to its vertical axis.

2. Flux-gate magnetometer compass for heading information used to reference the current direction to magnetic north, compass range 360°, resolution 0.5°, accuracy 2°, tilt +/- 25° for specified accuracy.

3. Temperature stable quartz oscillator clock, accuracy 12 minutes/year.

4. Optional automatic tilt compensation i.e. the allowable tilt of the meter from the vertical at which the vertical cosine response is fully corrected, angle range +/- 45°, resolution 0.6°, accuracy (speed correction) 1 per cent (angle output) 0.25°.

5. Optional semiconductor (thermistor or platinum) temperature sensor, range -5 to +45 °C, resolution 0.05 °C, accuracy 0.2 °C, response time at 63 per cent 1 min (1.5 sec thermistor or 60msec platinum).

6. Optional conductive conductivity sensor, range 5 to 70mS/cm, resolution 0.1mS/cm, accuracy 0.2mS/cm (optional inductive sensor, range 1 to 70mS/cm).

7. Optional semiconductor strain gauge pressure sensor, range 0 to 1000dBar (70M option), resolution 1dBar (4mm with 70M option), accuracy 0.25 per cent fs.

8. Recorder, CMOS static RAM microprocessor, 64KByte (128K or 256KByte optional) performs vector averaging, burst sampling and adaptive sampling.

Available versions of the S4 are listed in the table below:

Further details are available from the manufacturer's specification sheet.

BODC Current Meter Screening

BODC screen both the series header qualifying information and the parameter values in the data cycles themselves.

Header information is inspected for:

• Irregularities such as unfeasible values
• Inconsistencies between related information. For example:
  • Depths of meter and sea bed.
  • Times for mooring deployment and for start/end of data series.
  • Length of record or number of data cycles, the cycle interval, the clock error and the period over which accrued.
  • Parameters stated as measured and the parameters actually present in the data cycles.
• Originator's comments on meter/mooring performance and data quality.

Documents are written by BODC highlighting irregularities which cannot be resolved.

Data cycles are inspected using time series plots of all parameters. Currents are additionally inspected using vector scatter plots and time series plots of North and East velocity components. These presentations undergo intrinsic and extrinsic screening to detect infeasible values within the data cycles themselves and inconsistencies as seen when comparing characteristics of adjacent data sets displaced with respect to depth, position or time. Values suspected of being of non- oceanographic origin may be tagged with the BODC flag denoting suspect value.

The following types of irregularity, each relying on visual detection in the time series plot, are amongst those which may be flagged as suspect:

• Spurious data at the start or end of the record.
• Obvious spikes occurring in periods free from meteorological disturbance.
• A sequence of constant values in consecutive data cycles.

If a large percentage of the data is affected by irregularities, deemed abnormal, then instead of flagging the individual suspect values, a caution may be documented. Likewise documents will highlight irregularities seen in the current vector scatter plots such as incongruous centre holes, evidence of mooring 'knock-down', abnormal asymmetry in tidally dominated records or gaps as when a range of speeds or directions go unregistered due to meter malfunction.

The term 'knock-down' refers to the situation when the 'drag' exerted on a mooring at high current speeds may cause instruments to tilt beyond the angle at which they are intended to operate. At this point the efficiency of the current sensors to accurately record the flow is reduced.

Inconsistencies between the characteristics of the data set and those of its neighbours are sought, and where necessary, documented. This covers inconsistencies in the following:

• Maximum and minimum values of parameters (spikes excluded).
• The orientation and symmetry of the current vector scatter plot.
• The direction of rotation of the current vectors.
• The approximate amplitude and periodicity of the tidal currents.
• The occurrence of meteorological events and, finally, for series for which no time check was possible, the phase.

This intrinsic and extrinsic screening of the parameter values seeks to confirm the qualifying information and the source laboratory's comments on the series. In screening and collating information, every care is taken to ensure that errors of BODC making are not introduced.

Project Information

Land Ocean Interaction Study (LOIS)

Introduction

The Land Ocean Interaction Study (LOIS) was a Community Research Project of the Natural Environment Research Council (NERC). The broad aim of LOIS was to gain an understanding of, and an ability to predict, the nature of environmental change in the coastal zone around the UK through an integrated study from the river catchments through to the shelf break.

LOIS was a collaborative, multidisciplinary study undertaken by scientists from NERC research laboratories and Higher Education institutions. The LOIS project was managed from NERC's Plymouth Marine Laboratory.

The project ran for six years from April 1992 until April 1998 with a further modelling and synthesis phase beginning in April 1998 and ending in April 2000.

Project Structure

LOIS consisted of the following components:

• River-Atmosphere-Coast Study (RACS)
  • RACS(A) - Atmospheric sub-component
  • RACS(C) - Coasts sub-component
  • RACS(R) - Rivers sub-component
  • BIOTA - Terrestrial salt marsh study
• Land Ocean Evolution Perspective Study (LOEPS)
• Shelf-Edge Study (SES)
• North Sea Modelling Study (NORMS)
• Data Management (DATA)

Marine Fieldwork

Marine field data were collected between September 1993 and September 1997 as part of RACS(C) and SES. The RACS data were collected throughout this period from the estuaries and coastal waters of the UK North Sea coast from Great Yarmouth to the Tweed. The SES data were collected between March 1995 and September 1996 from the Hebridean slope. Both the RACS and SES data sets incorporate a broad spectrum of measurements collected using moored instruments and research vessel surveys.

LOIS Shelf Edge Study (LOIS - SES)

Introduction

SES was a component of the NERC Land Ocean Interaction Study (LOIS) Community Research Programme that made intensive measurements from the shelf break in the region known as the Hebridean Slope from March 1995 to September 1996.

Scientific Rationale

SES was devoted to the study of interactions between the shelf seas and the open ocean. The specific objectives of the project were:

• To identify the time and space scales of ocean-shelf momentum transmission and to quantify the contributions to ocean-shelf water exchange by physical processes.

• To estimate fluxes of water, heat and certain dissolved and suspended constituents across a section of the shelf edge with special emphasis on net carbon export from, and nutrient import to, the shelf.

• To incorporate process understanding into models and test these models by comparison with observations and provide a basis for estimation of fluxes integrated over time and the length of the shelf.

Fieldwork

The SES fieldwork was focussed on a box enclosing two sections across the shelf break at 56.4-56.5 °N and 56.6-56.7 °N. Moored instrument arrays were maintained throughout the experiment at stations with water depths ranging from 140 m to 1500 m, although there were heavy losses due to the intensive fishing activity in the area. The moorings included meteorological buoys, current meters, transmissometers, fluorometers, nutrient analysers (but these never returned any usable data), thermistor chains, colour sensors and sediment traps.

The moorings were serviced by research cruises at approximately three-monthly intervals. In addition to the mooring work this cruises undertook intensive CTD, water bottle and benthic surveys with cruise durations of up to 6 weeks (3 legs of approximately 2 weeks each).

Moored instrument activities associated with SES comprised current measurements in the North Channel in 1993 and the Tiree Passage from 1995-1996. These provided boundary conditions for SES modelling activities.

Additional data were provided through cruises undertaken by the Defence Evaluation and Research Agency (DERA) in a co-operative programme known as SESAME.

Data Activity or Cruise Information

Data Activity

Proudman Oceanographic Laboratory Moored Instrument Rig #682

This rig was deployed as part of the LOIS Shelf-Edge Study at site S300.

The instruments were anchored by 1000kg of chain and kept erect by a 48" diameter buoy attached 25m below the sea surface.

Instruments deployed on the rig

Related Data Activity activities are detailed in Appendix 1

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

Fixed Station Information

LOIS (SES) Mooring and CTD Site S300

Site S300 was a fixed station where moorings were deployed during the Land-Ocean Interaction Study (LOIS) Shelf Edge Study (SES). It was also one of fourteen CTD sites on repeat section S, across the Hebridean Slope, occupied by cruises between March 1995 and September 1996.

Instrument Deployment History

The following tables summarise the instruments deployed at this site for which data may be available.

1995

1996

Each different letter in the tables above corresponds to an individual instrument record.

Glossary

• CM = Current meter (Aanderaa or S4)
• TChn = Thermistor chain
• Tr = Transmissometer
• NA = Nutrient analyser

Note

1. Transmissometers may have been fitted to some of the current meters.
2. Other instruments (colour sensors) may have been deployed.
3. Only periods for which useful data were returned are shown.

Related Fixed Station activities are detailed in Appendix 2

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: POLRIG#682

Related series for this Data Activity 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.

Appendix 2: LOIS(SES) S300

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.