Metadata Report for BODC Series Reference Number 748976

• 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

SIMORC Data Quality Report: Angola Girassol ADCP Current ANGL5CURR

Speed data are very noisy. There is a large amount of absent values for current data. There is a small amount of absent values for temperature data.

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

RD Instruments 150kHz Broad Band Acoustic Doppler Current Profiler

This instrument is designed for mooring deployment and has an operating frequency of 150 kHz. The instrument uses Doppler-technology to achieve accurate and non-intrusive measurements and it can come with pressure and temperature sensors. It can be used in real time measurement situations or can log to an internal recorder powered by internal batteries.

Specifications

*Ranges are for systems using a transducer beamwidth of 3° and depth cell size of 8 m in typical water conditions. Range decreases about 10% each time cell size is halved.

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.

BODC Processing

Data were received by BODC in ASCII format files. These were reformatted to the internal QXF format using BODC transfer function 370. The following table shows how the variables within the file were mapped to the appropriate BODC parameter codes:

Following transfer to QXF, the data were screened using BODC's in-house visualisation software, EDSERPLO. The following problems were noted with the data:

Series: 748939 The screening of LCDAAP01 shows the following spikes which were accordingly flagged:

• bin 2 cycles 2191, 2452, 2743, 3263, 3273
• bin 3 cycles 2743, 3169, 3270
• bin 5 cycle 2757
• bin 6 cycles 2738, 3270
• bin 7 cycle 3273
• bin 8 cycle 3270
• bin 11 cycles 2757, 3273

Series: 743940 The screening of TEMPPR01 shows a suspicious variation of the temperature for cycle 1 and 2, which were accordingly flagged.

Originator's data Processing notes

SIMORC Total Angola Bloc17, Current data, 1997, Data processing

Initial validation checks were applied to the data to flag erroneous values for editing prior to further analysis. Consideration was given to:

• Timing of data points.
• Data points outside the physical limits of the sensors or the environment.
• Rates of change between data points.

Checks were made for timing errors by comparing the data with the recorded switch-on and switch-off times manually on the log sheets. Directional data were corrected for magnetic declination to give results expressed in Degrees True. The local magnetic declination is 7.2 ° W.

Time series of all data were plotted, and reviewed by an experienced oceanographer, to allow identification and removal of erroneous records. A number of anomalous increases in current speed (i.e. spikes) were identified and manually removed.

Additionally, routine ADCP quality control was performed on the ADCP data. Workhorse ADCP data for the upper 7m of the water column were error-flagged due to contamination from acoustic side lobe reflection from the surface. Records with less than 25% good pings were also flagged.

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

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.

ELF EXPLORATION ANGOLA, Girassol, Deep Water Current Measurements

Period: September 1997 - October 1998.

The goal of this was to observe and characterize the nature of the current regime in this area. This study is a preliminary to the riser design for the Girassol field production well (2 km east from the mooring position).

This deployment was divided into five phases, to allow approximately 75 day intervals between visits for data retrieval and equipment maintenance.

Data Activity or Cruise Information

Data Activity

SIMORC: TOTAL Data, Angola, Block 17, ADCP Current 23/07/1998 - 26/10/1998 Data Activity

This site is part of the Total facility.

The generic position of the site is 7.67 °S, 11.6825 °E with a water depth of 1385 m.

The objective of the year-long study was to observe and characterise the nature of the current regime in this area. The data were used to help in riser design of a Girassol field production well, located approximately 2 km east of the mooring position.

5 current moorings, consisting of 2 ADCP and 6 current meters, were deployed during this study.

This particular mooring had been set from a vessel by FugroGeos on behalf of Total in the Angola Block 17 Girassol and consisted of the following instruments.

For details of the 4 other moorings refer to series: 747844, 747912, 747997, 748048.

CTD profiles were recorded after the deployment and prior to the recovery to calibrate against the mooring.

Related Data Activity activities are detailed in Appendix 1

Fixed Station Information

Fixed Station Information

SIMORC: Total Angola, Block 17 Girassol, Fixed Station Document

This site is part of the Total facility.

The moorings deployed lie within a box bounded by co-ordinates 7.7° S, 11.65° E at the southwest corner and 7.67° S, 11.6825° E at the northeast corner.

The GIRASSOL platform, Block 17, offshore Angola consists of a Floating Production, Storage and Offloading vessel (FPSO) and a Single Buoy Mooring (SBM).

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

Between September 1997 and October 1998

A current meter mooring occupied this site. In addition to time series data obtained from the moored instruments, CTD profiles were conducted following the deployment and prior to the recovery of the mooring to be used for calibration purposes.

Between March 2001 and July 2004

Wind, current and wave data have been collected on behalf of Total on the Girassol field.

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: SIMORC TTL Angola Block17 Curr Jul 98

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: ANGOLA GIRASSOL

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.