Metadata Report for BODC Series Reference Number 1804855

• 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

Teledyne RDI Workhorse Sentinel 600 kHz Acoustic Doppler Current Profiler (ADCP)

The Workhorse Sentinel is a self-contained ADCP that can be used either on a mooring or mounted in the hull of a moving vessel. Its 4-beam design provides a redundant data source (in case of a blocked or damaged beam), an independent data quality measure (error velocity) and reduces the variance in data, thereby improving data reliability, quality and accuracy.

Real-time data can be transmitted to shore via a cable link or acoustic modem or they can be stored internally. Sensors for bottom tracking, pressure and directional wave measurements can be added to the instrument and a special casing is available for deeper applications.

Specifications

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

DML Aanderaa RCM current meter data and ADCP Workhorse: Originator's data processing

Summary of DML (formerly SMBA) Standard Procedures for Current Meter Data

Mooring System for Water Depths up to 200m

U shaped mooring i.e. pellet float to pellet line to sub-surface buoy to meter mooring line (with either in-line or A-frame mounting of meters) to anchor weight to ground line to anchor weight to marker buoy tow chain, then line to surface spar marker buoy and to pellet line and floats. The mooring is deployed in the order given and recovered in reverse order. Usually lengths of main wires are: buoy tow line D-15m, buoy tow chain 55m, sometimes buoy line is all chain, (prior to 1977 buoy tow line 2D used without chain), ground wire 2D (but never less than 150m), meter rope (excluding sub-surface buoy bridles and anchor bridles) D-X-3m where D is the depth of water and X is the depth of the sub-surface buoy. Generally X=30m but this may vary depending on the application of the mooring and the requirement for near surface current measurements. The mooring site is chosen by echo sounding to accord with the preset length of instrument line; however occasionally the length of the instrument line is adjusted on station. The site is positioned to an accuracy of 0.5nm using either Decca main chain, Loran or Satellite Navigation (GPS), depending on reception etc.

Data Processing

Speed is integrated over the sampling interval. Direction and, where measured, temperature and pressure, are taken as spot measurements at the end of the sampling interval. Direction is corrected for magnetic variation. Pressure measurements are not corrected for atmospheric pressure.

Parameter values i.e. speed, temperature and pressure are given at times incremented by the sample interval. The time assigned to each parameter is that of the end of the sampling interval. Time values are corrected for clock error should this occur.

Sea floor depths are relative to the instantaneous sea surface i.e. obtained from corrected echo soundings at the time of rig deployment (Matthew's corrections are applied).

Data at the 2nd bin (11 m above bed) from the ADCP's were exported and saved to ASCII files.

Calibrations

Each meter is calibrated against the manufacturer's formulae for direction and Plessey meters are calibrated for temperature; Aanderaa meters use the manufacturer's temperature calibrations. The manufacturer's velocity and pressure calibrations are used.

DML Aanderaa RCM current meters and ADCP Workhorse: BODC data processing

Data from 20 Aanderaa RCM current meters and 5 ADCP Workhorses arrived at BODC in ASCII format.

Only the 2nd bin from the ADCP's arrived at BODC.

Data were reformatted to a standard BODC format. The following table shows how the variables within the data files were mapped to appropriate standard BODC parameter codes:

The reformatted data were visualised using BODC's in-house visualisation software. Suspect data were marked by adding an appropriate quality control flag, missing data by both setting the data to an appropriate value and setting the quality control flag.

Project Information

No Project Information held for the Series

Data Activity or Cruise Information

Data Activity

Dunstaffnage Marine Laboratory Moored Instrument Rig#394

This rig was deployed in the Tiree Passage at site Y. The deployment forms part of the moored current meter series in the Tiree Passage, from 1981 to present.

The instruments formed a U-shaped mooring anchored by two 450kg weights, connected by a 100 metre ground wire. A spar marker buoy was attached to one of the weights, with a recovery line. The instruments, attached to the second weight, were held erect by a sub-surface buoy.

Instruments deployed on the rig

Mooring Rig#394 was also equipped a SeaBird MicroCAT and two Miniloggers but no metadata or data has been provided from these instruments.

Fixed Station Information

Fixed Station Information

Tiree Passage Mooring

The Tiree Passage Mooring (also referred to as Y Mooring) is a current meter mooring at 56° 37.2' N, 6° 24.0' W. It has been maintained by the Dunstaffnage Marine Laboratory (DML)/ Scottish Association for Marine Science (SAMS) since 1981. The mooring is serviced approximately 3 times a year. The Tiree Passage Mooring is the longest moored time series of flow and temperature on the NW European continental shelf.

Between 21/05/1993 and 17/09/1997 the mooring included two Aanderaa current meters located 11 m and 22 m above the sea floor except for the period between 09/05/1994 and 15/08/1994 when there was no top current meter. The proportion of good data returned was exceptionally high.

Gaps in the time series are caused by fluctuations in funding, mooring losses and instrument failures (additional gaps in the current time series, usually due to fouling of mechanical current meters).

Although conductivity sensors were fitted to the Aanderaa current meters from 1994 to 1997, the reliability of these sensors over long periods is questionable, and more work needs to be done in cross calibrating the calculated salinity against the salinity of coincident 'Ellett Line/Extended Ellett Line' CTD casts.

It should be noted that some data were submitted to BODC from PML and not DML. This was due the relocation of the Principal Investigator responsible for the data. He subsequently returned to DML.

Summary of Key Activities

Figure 1: Map showing the locations of the Tiree mooring data time series.

Figure 2: The typcial set up of the Tiree mooring.

References

Inall, M. and Griffiths, C., 2003 The Tiree Passage Time Series: 1981-2003 DEFRA MECN: Tiree Passage

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: DML Tiree Passage Mooring

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.