Metadata Report for BODC Series Reference Number 750944

• 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

It is not clear in the originator information which direction is to or from and channel GPEDFA01 is clearly different from all the other directions. There is a large amount of absent values in channels GSD2VA01, GWDPVA01, GWSDVA01, GSH2VA01.

Data Quality report WTR_BOUEE_GIRASSOL2

There are gaps during the following periods:

• From 25/11/2001 to 04/12/2001
• From 22/12/2001 to 18/01/2002
• From 22/03/2002 to 17/05/2002
• From 10/05/2003 to 22/05/2003
• From 21/06/2003 to 19/07/2003

Some data were flagged M as suspicious, because they were spikes, as following:

• Channel GMWDWR01 (mean direction): cycle 341
• Channel GPEDFA01 (peak direction of global sea-state): cycle 70
• Channel GSD2VA01 (mean direction of system swell 2): cycles 341, 381, 591, 617, 624, 718, 1794, 2100, 3186, 3818, 4350, 4728, 4835, 5169, 5175, 5615, 6533, 7559
• Channel GWDPVA01 (peak direction of system wind): cycles 54, 1524, 2098, 3017, 3397, 3399, 3404, 5020, 5213, 5860, 6534, 6547, 6574, 6865, 6985
• Channel GWSDVA01 (mean direction of system wind): cycles 54, 4006, 4096, 5176, 6534, 6865, 6985

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

Datawell Directional Waverider Buoy

General

The Datawell Datawell Directional Waverider is a 90cm diameter spherical buoy which measures wave height, period and direction. The directional measurement is based on a translational principle so that horizontal motions rather than wave slopes are measured. Consequently the measurement is independent of buoy roll motions and a relatively small spherical buoy may be used. A single point vertical mooring ensures adequate symmetrical horizontal buoy response to resolve small motions at low frequencies. Two 15m lengths of rubber cord are normally included in the mooring. Data are transmitted to a shore based station and/or an Argos satellite.

Sensors

• Heave-pitch-roll sensor Hippy40
• Three axis fluxgate compass
• Two fixed "x" and "y" accelerometers
• Temperature sensor

Principles of Measurement

The Directional Waverider measures vertical accelerations by means of an accelerometer placed on a gravity stabilised platform. This platform is formed by a disk which is suspended in the fluid within a plastic sphere placed in the bottom of the buoy. Two vertical coils are wound around the plastic sphere and one small horizontal coil is placed on the platform. The pitch and roll angles are defined by the amount of coupling between the fixed coils and the coil on the platform. This coupling is measured. The result of the measurement gives the sine of the angles between the coil axes (x and y axes) and the horizontal plane (=platform plane). The fluxgate compass measures the components of the Earth's magnetic field in the direction of the x, y and z axes. All of these measurements define the buoy's position with respect to fixed (north, south and vertical) coordinates.

A transformation matrix of the relation between vector components in buoy coordinates and fixed coordinates is formed. The acceleration of the buoy is measured in the x and y directions (two fixed accelerometers) and in the vertical direction (accelerometer mounted on a stabilised platform).

With the help of the transformation matrix and these measured accelerations, the accelerations in the north-south and east-west directions can be calculated. All the analogue outouts of the sensors are filtered using a low-pass filter with a cut-off frequency of 1.5Hz. At this frequency, the buoy's motions are already strongly attenuated due to the small wavelengths compared to the buoy's dimensions (geometric attenuation).

The filter outputs are sampled at a rate of 3.84Hz. As transformation calculations are performed at this rate by the on-board processor, the three accelerations are available at the same rate. By means of further digital processing, the acceleration data are filtered (low-pass 10th order filter with a cut-off at 0.6Hz) and double integrated to give three translation signals in the frequency range 0.033Hz - 0.6Hz (3dB) (0.05Hz - 0.55Hz 0.31dB). These translation signals are transmitted over the radio link in real time.

A complete spectrum is calculated every half hour. Parameters are calculated at each of 64 frequency points (0.025Hz - 0.100HZ at 0.005Hz intervals and 0.110Hz to 0.580Hz at 0.010Hz intervals). The parameters calculated at each frequecny point are: mean direction, angle of spread, second harmonics of angular energy distribution check factor and relative power density.

Reference

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.

BODC Processing

Data were received by BODC in ASCII format file. These series were reformatted to the internal QXF format using BODC transfer function 419.

The transfer includes a program, provided by the originator, which generates a time series with a unique time and categorizes the wave data as swell first component, swell second component and wind sea.

The following table shows how the variables within the file were mapped to the appropriate BODC parameter codes:

Where Hs means the Significant Wave Height.

Following transfer to QXF, the data were screened using BODC's in-house visualisation software, EDSERPLO. Any data considered as suspect were flagged 'M'.

Girassol Wave Processing

On behalf of TOTAL, Meteomer collected raw data from a direction waverider. The buoy was moored close to the GIRASSOL platform, to ensure correct representation of the impacts of waves on the platform. Data recording was continuous with a 1.28Hz sampling frequency. The operator worked on the measurements every 30 minutes for spectral analysis which provided wave parameters that were directly compared with values given in the report (we assume that these values are predicted spectra, but the originator notes do not state this clearly). The operations manager had at his disposal a "wave per wave" analysis to determine the features of the sea state. A Mini-M Inmarsat satellite communication system allowed data transmission towards France so that measurements were analyzed and compared with the predicted spectra and allowed for further calibration with prediction models.

Theses raw data sampled every 0.78125 s are available and stored in the BODC archive.

On behalf of TOTAL, Ifremer have computed the wave spectra every three hours from the sea surface elevation time histories. The magnetic declination was accounted for in the data and the directions are referenced to true North.

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, offshore ocean monitoring, Block 17

ELF ANGOLA required ocean monitoring services from March 2001 to July 2004. MeteoMer measured the following parameters :

• Waves (Directional Datawell waverider)
• Motion of the Floating Production, Storage and Offloading (FPSO) vessel (Hippy 80 - Datawell)
• Motion of the Single Buoy Mooring (Hippy 80 - Datawell)
• Wind of the FPSO (VAISALA Marine Automated Weather Station)
• Current profiles (ADCP RDI 300 khz and 75 khz)

Data Activity or Cruise Information

Data Activity

SIMORC Moored Instrument Girassol_Wave

The generic position of this site is 07° 41.9129' S, 11° 40.2949' E with a water depth of 1475 m.

A Directional Waverider was dropped on an independent mooring line releasable with release and lost sinker. An artificial bottom was created at 200m depth, by the use of a mooring line composed of steel cable, sub-surface float and intermediary floats to relieve the cable weight, acoustic release, mooring on the bottom with a lost sinker.

This particular mooring was deployed on 08/03/2001 and was removed on 07/07/2004. This current mooring was set on behalf of TOTAL in Angola Girassol and consisted of the following series.

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 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: 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.