Metadata Report for BODC Series Reference Number 767704

• 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 quality report C9107080D1

Datacycles 1 to 3 and 5184 to 5190 were flagged because they appear before and after the deployment. In LCEWEL01 (current eastward component), datacycle 971 was flagged 'M' because it is a spike. Several suspected spikes were noticed in the current direction channel and were flagged accordingly.

The scatter plot shows a gap in direction at approximately 354 degrees.

Data Access Policy

SIMORC data access conditions

The data collated and held at BODC on behalf of the SIMORC project are restricted. However, the data will be available to download from the Official SIMORC Website, as part of the project protocol. The data set will initially include data from the oil companies TOTAL, Shell and BP.

Narrative Documents

Instrument Description

Coastal Leasing MiniFlow Current Meter

The Coastal Leasing MiniFlow measures currents using the proven Marsh-McBirney electromagnetic velocity sensor, and heading (cf. schema below).

The MiniFlow has a memory of 150 kb RAM and an accuracy of ±2% of reading.

Standard Sensors

Optional Sensors

For more information from the manufacturer, please refer to:

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.

BODC Processing

Data were received by BODC in comma separated value ASCII format files. Since the originator provided monthly files, the BODC concatenated the data per deployment and instrument. Files were renamed with the format: C/year/month/depth/deployment. For example, C91070801D1.mat contains data of the mooring deployed in July 1991 from the current meter at 80m depth during the first deployment.

Concatenation and splitting were done as follows:

These series were reformatted to the internal QXF format using BODC transfer function 415. The following table shows how the variables within the file were mapped to the appropriate BODC parameter codes:

^* The originator did not specify that the time is GMT.

^** The direction data were corrected to true north by subtracting the average magnetic declination of 6.6417 W, which was calculated thanks to the National Geographic Data Center calculation (cf. following web link).

National Geographic Data Center calculation

TOTAL CONGO Current Processing Document

Every 20 minutes, a 30-second average of current velocity was recorded.

The originator corrected part of the data as following:

• The offsets before and after the campaign were measured. These two values were averaged in order to calculate the average offset, which was then removed from the data. When the instruments were not re calibrated, only the offset measured before the campaign was removed from the data. Yet, it is not clear from the originator's document what the offset was applied to: speed, direction, northward component or eastward component.
• Temperature data were corrected from the data measured during the calibration after the campaign and/or during the measurement of the tests for predeployment.
• The northward and eastward components (in ft.s^-1) were converted into speed (in cm.s^-1) and direction (in degrees magnetic), then the non significant values (i.e. values recorded during the recovery or the deployment of mooring) or spike values were removed from the data files.

Project Information

System of Industry Metocean data for the Offshore and Research Communities (SIMORC)

The EU-funded SIMORC project is a collaborative effort between MARIS (Netherlands), BODC (UK), the International Association of Oil and Gas Producers (OGP) and IOC-IODE to provide a harmonised and quality controlled metocean data set from data collected by oil and gas producers, accessible through the SIMORC protocol.

Data Activity or Cruise Information

Data Activity

SIMORC Mooring NKossa#1

This particular mooring was deployed on 16/07/1991 and was removed on 26/09/1991. It was set from a subsurface mooring on behalf of TOTAL in Congo NKossa and consisted of the following instruments.

Where MSL = Mean Sea Level

For details of the 3 other moorings refer to series: 767728, 767765, 767790.

Related Data Activity activities are detailed in Appendix 1

Fixed Station Information

Fixed Station Information

Congo NKossa Fixed Station Document

This site is part of the Total offshore facility.

The moorings deployed lie within a box bounded by co-ordinates 5.28695 ° S, 11.5583° E at the southwest corner and 5.2333° S, 11.6167° E at the northeast corner. The water depth is 170 m.

Various deployments were taken from or near this station over a number of years.

Between July 1991 to July 1992

4 moorings, each consisting of 3 current meters, were deployed during this study.

Current data have been collected by I.D. Scope on behalf of Total from the NKossa Station, offshore Congo, as follows:

Where CM = Current Meter

Between September 1993 and May 1995

4 moorings, each consisting of 1 waverider, were deployed during this study.

Wave data have been collected by Meteomer on behalf of Total from the NKossa Station, offshore Congo, as follows:

Where WRB = Waverider Buoy

Between January 1997 and December 1998

The position of the instrument was 5.2333' S; 11.6167' E with a water depth of 180 m.

Wind data have been collected on behalf of Total by an anemometer installed on a Floating Production Storage and Offloading (FPSO) from the NKossa Station, offshore Congo, with the following series:

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: Nkossa#1

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: Congo Nkossa

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.