Metadata Report for BODC Series Reference Number 566876

• 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 DISCO moored ADCP data set is of very high quality until 19/06/1999 19:00. After this point, data in the surface bins are noisier. Caution is advised when using data from surface bins after this point.

The high values for error velocity in some of the surface bins are consistent with the lower quality of the data and may be used to assist users when assessing the suitability of the data. The following notes may also be taken into consideration.

• E-W velocities between 19/06/1999 19:00 and 20/06/1999 03:00 - data from 3 surface bins (99m, 95m and 91m above seabed) appear too high.
• E-W velocities between 20/06/1999 03:00 and 06:30 - data from 3 surface bins (99m, 95m and 91m above seabed) appear too low.
• E-W velocities between 20/06/1999 06:30 and 13:40 - data from the surface bin (99m above seabed) appear too high.
• N-S velocities after 19/06/1999 20:00 - data from the surface bin (99m above seabed) become very variable with some spikes.
• N-S velocities between 20/06/1999 0:00 and 04:00, and between 10:00 and 16:00- data from 3 surface bins (99m, 95m and 91m above seabed) appear too low.

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

RDI Acoustic Doppler Current Profiler

Acoustic Doppler Current Profilers (ADCPs) use sound waves to determine vertical profiles of currents, and may be deployed fixed to the sea floor, attached to a surface buoy, mounted on the hull of a ship, towed behind a ship or lowered on a cable.

ADCPs transmit sound bursts into the water. Particles carried by the water currents scatter the sound back to the transducer. As echoes return from further ranges from the sensor, the instrument assigns different water depths to the returning signals. Motion of the scattering particles relative to the sound source causes a change in the frequency of the sound (known as Doppler shift). The ADCP measures this change to produce vertical profiles of water velocity at up to 128 depths throughout the water column.

Specifications:
number of depth cells 1 to 128;
size of depth cells 0.12 to 32.00 metres;
velocity range +/- 10 m/s.

DISCO ADCP Data Processing Notes

The different bins are stored relative to the height above the sea floor. For the current velocity data, there are 23 bins, from 11m above the sea floor to 99m above the sea floor. For the signal return amplitudes, there are 30 bins, from 11m above the sea floor to 127m above the sea floor. The high values for signal return amplitudes at bin heights of 107m and 111m indicate the presence of the sea surface.

The signal return amplitudes (or backscatter signal strength) have nominal units of decibels, but they should be seen as relative measurements rather than absolute values.

From the RDI manual: "RDI have not yet developed procedures for absolutely calibrating BroadBand backscatter measurements but BroadBand ADCPs (including Workhorses) are useful for relative measurements". Time variations in (decibels) relative to an 'arbitrary mean' are presented for particular depths.

General Data Screening carried out by BODC

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:
  • Times for instrument deployment and for start/end of data series
  • Length of record and the number of data cycles/cycle interval
  • Parameters expected 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 or depth 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 data values will not be altered.

The following types of irregularity, each relying on visual detection in the 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 then a Problem Report will be written rather than flagging the individual suspect values. Problem Reports are also used to highlight irregularities seen in the graphical data presentations.

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

• Maximum and minimum values of parameters (spikes excluded).
• The occurrence of meteorological events.

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

DISCO

DISCO was a multidisciplinary study of the routes, rates and controls on the biogeochemical cycling of dimethyl sulphide (DMS) within a bloom of the coccolithophorid alga, Emiliania huxleyi. The sampling took place on RRS Discovery cruise 241, between 5 June and 1 July 1999, in the northern North Sea. A survey of the region was carried out in order to locate an E. huxleyi bloom suitable for the study. The chosen bloom was labelled with SF6 tracer, and the biogeochemical process study followed the patch as it drifted in a SE direction and was eventually subducted under Norweigian coastal water on 26 June.

The research was organised by NERC's Plymouth Marine Laboratory and involved scientists from 8 institutions. DISCO was funded principally by NERC through Core Strategic and Responsive Mode Funds and by MOD DERA JGS Grant (TD/10/3/5).

Data Activity or Cruise Information

Data Activity

Proudman Oceanographic Laboratory Moored Instrument Rig #830

This rig was deployed as part of the DISCO project.

The instrument attached to the rig was a RDI Broadband 150 kHz Acoustic Doppler Current Profiler, serial number 1149.

The ADCP was accidentally turned upside down by a trawler on 20/06/1999 at approximately 16:00.

The ADCP was recovered deliberately by the Norwegian research ship `Michael Sars' on 08/09/2000 05:30 by trawling.

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

No Fixed Station Information held for the Series

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: