Metadata Report for BODC Series Reference Number 475958

• 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

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.

LOIS (RACS) Holderness Experiment Data Collection and Processing

Data Collection and Processing - Waveriders

Datawell waverider buoys were deployed at sites N1, N2 and N3 with the buoys at the latter two sites recording directional data. Due to the shallow depths one rubber cord was used in each mooring, whereas two are recommended by Datawell to reduce mooring effects. Datawell waverider buoys calculate spectra and mean wave parameters on board before transmission to a shore station for storage (Datawell, 1995). Eight consecutive 200 second blocks are averaged after spectral analysis. The first and last 32 samples out of a total of 256 are tapered with a cosine taper and the taper is corrected for after averaging. Peak frequency and quality control flags were computed from the spectra. Quality control checks gave 2 per cent high frequency flags at N2 and 1 per cent at N3, with very few low frequency flags.

The recorded time for N1 data is the start of the burst, while the recorded time for N2 and N3 data is the time of receipt of transmission (approximately 40 minutes after the start time of the burst).

Data Collection and Processing - Pressure Recorders

Pressure wave recorders were mounted at 0.35m above the sea bed on PMPs (POL monitoring packages) deployed at stations N1 - N4 and S1 - S4. The pressure recorders used consisted of a pressure sensor in a standard Aanderaa casing. An oil-filled capillary tube was attached to the diaphragm housing to reduce flow effects on the sensor. Burst data were recorded at 2Hz for 20 minutes every 3 hours. Wolf gives details of the processing and correction procedures used on these data.

Data Collection and Processing - S4 Current Meters

InterOcean S4 current meters were mounted at 0.8m above the sea bed on PMPs (POL monitoring packages) deployed at stations N1 - N3 and S1 - S4. The current meters at the inner stations (N1 and S1) included a pressure sensor which allowed directional wave measurements to be made. this version of the S4 is referred to as the S4DW. The standard S4 meters measured 1 minute bursts of data while the S4DWs measured 20 minute bursts at 2Hz with consecutive samples averaged to give 1Hz output.

General Information

Winds were observed at three coastal locations. The observed local wind regime clustered about directions 000 degrees and 200 degrees with maximum speeds of 11.2 m/s and 17.4 m/s respectively.

Repeated CTD profiles were obtained for stations N2 - N4 and S2 - S4.

Instrument Intercomparison

Wolf describes the three instruments as giving acceptable agreement. The S4DWs and the waveriders are in quite close agreement for wave height and the peak wave period is in good agreement for all instruments most of the time. The bottom mounted instruments (as expected) do not always detect a high frequency peak, but are generally in close agreement validating the instrument response. The pressure recorder results for Hs show a gradual worsening in agreement with the waverider results, although other parameters remained in good agreement. Wolf discusses possible causes.

References

Datawell bv, Zomerlustraat 4, 2012 LM Haarlem, the Netherlands (1995).
Operation and Service Manual for "Directional Waverider" from serial no. 30109 and including 30076, 30101, 30106, 30108.

Prandle, D. (1994).
Holderness experiment - the observational programme. LOIS issue no. 2.

Wolf, J. (1996).
The Holderness Project Wave Data. Proudman Oceanographic Laboratory Internal Document No. 89.

Project Information

LOIS River-Atmosphere-Coast Study (LOIS - RACS)

Introduction

The Land-Ocean Interaction Study (LOIS) was a NERC research programme designed to study processes in the coastal zone. The Rivers, Atmosphere and Coasts Study (RACS) was a major component of LOIS that looked at land-sea interactions in the coastal zone and the major exchanges (physical, chemical and biological) between rivers and estuaries and the atmosphere. The study focused on the east coast of the UK from the Wash to the Tweed.

RACS included several sub-components

• BIOTA - A study of salt marshes of the Humber and Wash
• RACS (A) - An atmospheric chemistry study looking at air mass changes from the Wash into East Anglia
• RACS (C) - A study of the estuaries, coasts and coastal waters between Great Yarmouth and Berwick upon Tweed.
  1. The coastal oceangraphic survey
  2. The Humber estuarine study
  3. The Tweed estuarine study
  4. The Holderness experiment
• RACS (R) - A study of rivers that drain into the North Sea

RACS (A) was coordinated by the University of East Anglia and RACS (C) by the Plymouth Marine Laboratory.

RACS (A)

The bulk of the RACS (A) data set was collected during two field campaigns in the winter (October/November) of 1994 and the summer (May/June) of 1995. During these campaigns data were collected continuously from the University of East Anglia Atmospheric Observatory at Weybourne on the north Norfolk coast. An instrumented vessel was stationed offshore to provide a second sampling site to allow changes in a given air mass to be monitored. The Imperial College Jetstream research aircraft made one flight during each campaign to provide a link between the two surface stations. The Jetstream made four additional flights in 1996 and 1997.

RACS (C)

The coastal oceanographic survey

The coastal oceanographic data set was collected during a series of 17 RRS Challenger cruise legs. Most cruises covered two survey grids. One from Great Yarmouth to the Humber designed around the distribution of the sandbanks and a second simple zig-zag grid from the Humber to Berwick on Tweed. A large number of anchor stations, usually over one or two tidal cycles, were worked in the area of the Humber mouth or the Holderness coast.

The Humber estuarine study

The Humber estuarine data set was collected during a series of 33 campaigns on the Environment Agency vessels Sea Vigil and Water Guardian in the Humber, Trent and Ouse river systems at approximately monthly intervals between June 1993 and December 1996. Each campaign consisted of two or three one-day cruises. The tracks covered the estuary from the tidal limits of both Trent and Ouse to Spurn Point. Instrumental and sample data are available from a series of fixed stations that were sampled during every campaign.

The Tweed estuarine study

The Tweed estuarine data set was collected during a series of 13 campaigns using RV Tamaris in association with a rigid inflatable vessel at approximately monthly intervals between July 1996 and July 1997. Each campaign covered the tidal reaches of the River Tweed.

The Holderness experiment

The Holderness Experiment was designed to monitor the process of sediment transport along the Holderness coastline. It consisted of three moored instrument deployments during the winters of 1993-1994, 1994-1995 and 1995-1996. Mooring platforms were deployed at eight stations along two lines off the Holderness coast. A northerly and a southerly line of four stations each were used (N1 - N4 and S1 to S4) with the lowest numbers being inshore. Both lines were approximately perpendicular to the coast, although the S4 station lay to the south of the S line, off Spurn Head.

Data Activity or Cruise Information

Data Activity

Proudman Oceanographic Laboratory Rig#719

This rig was deployed as part of the LOIS RACS study at site S2

Fixed Station Information

Fixed Station Information

LOIS RACS (Holderness Experiment) Mooring Site S2

The site was occupied for both phase 1 (October 1994 to February 1995) and phase 2 (November 1995 to January 1996) of the Holderness Experiment by a POL Monitoring Platform (PMP) seabed mooring. This included an ADCP (zero data return in phase 1), a transmissometer, an S4 electromagnetic current meter, a pressure gauge and an EMP2000 environmental monitoring package (temperature, salinity, pH and OBS turbidity). No transmissometer or EMP2000 was fitted for the first phase 2 deployment.

The pressure gauge was programmed to sample at high frequency in burst mode, which allowed the derivation of 1-D wave spectra. Basic wave statistics (H_s and T_z) have been computed.

The data returns from the instruments were as follows:

The mean sea level water depth at the station was 18m and magnetic variation at the time of the deployments was 4 degrees west. This station is coincident with the station designated HMD that was occupied during the Holderness Experiment trial from October to December 1993.

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: Holderness Site S2

Related series for this Fixed Station are presented in the table below. Further information can be found by following the appropriate links.

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