Metadata Report for BODC Series Reference Number 844859

• 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: POLRIG994 ADV data

Data recorded by all three ADVs at the start of the deployment, from 06:00 UTC to 14:00 UTC 13 March 2007, were flagged. These first records were all taken after the instruments were activated but before the mooring deployment commenced.

Anomalously high standard deviation values were visible in the heading, pitch, roll, temperature and pressure channels in all three ADV datasets at 01:00 UTC 21 March 2007. This suggests that the mini-STABLE frame may have suffered a temporary knockdown at this time. No other data appear to be affected.

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

SonTek ADVOcean/Hydra acoustic doppler velocimeter

The ADVOcean-Hydra is an autonomous integrated ocean sensor system for the measurement of current and waves, CTD and turbidity. Include powerful data acquisition system, a high-resolution velocity sensor, a strain gage pressure sensor and can be integrated with external sensors. With the optional RPT pressure sensor, this powerful system is able to sample both pressure and velocity at up to 25 Hz, making it the definitive solution for studying nearshore processes.

For more information please click here for SonTek's Brochure or see a description on ADVs here.

Acoustic Doppler Velocimeters (ADVs)

The ADV is a single-point, high resolution current meter, capable of recording three-dimensional velocity vectors. The ADV measures the velocity of the water by analysing the Doppler effect (frequency shift) of sound emitted by the sensor. The ADV uses a separate receiver and transmitter, both of which are constructed to generate very narrow beam patterns - the transmitter generates sound with most of the energy focussed in a narrow cone and the receiver is sensitive to sound reflected from a narrow angular range. The transducers are mounted so that their beams intersect at a volume of water located at some distance away from the sensor. Where the beams intersect is the volume of water in which the measurements are made - known as the sampling volume.

The transmitter generates a short pulse of sound at a known frequency, which travels through the water along the axis of the transmitter. As the sound beam passes through the sampling volume the its energy is scattered in all directions by suspended particulate matter (e.g. sediment, micro-organisms, bubbles). An ADV typically requires a concentration of >~10 mg/l scattering material for its operation. A small portion of the sound energy is scattered back along the receiver's axis and is sampled by the ADV, then processed to measure the change in frequency. The Doppler shift measured by one receiver is proportional to the velocity of the scattering particles along the axis of the transmitter and the receiver.

The typical noise level of the ADV is ~1% of the maximum recorded value during a deployment. For example, if the maximum recorded velocity during a deployment was 1 m/s, the noise level would be around 0.01 m/s.

Originator's Data Processing: ADV data from POLRIG994

Sampling Strategy

Three Sontek Ocean/Hydra Acoustic Doppler Velocimeters (ADVs) were attached to Proudman Oceanographic Laboratory (POL) mini-STABLE benthic frame POLRIG994 for deployment on PD04_07. Prior to deployment all three ADVs were bench tested at POL to check their operation. The ADVs all triggered on receipt of a sync pulse from the mini-STABLE SyncGen3 central timing clock. New battery packs were fitted prior to deployment and all o-rings plus sealing faces cleaned, checked for damage and then re-greased using Dow Corning silicon grease. SyncGen3 was also upgraded to use an aluminium casing and end-cap, replacing the plastic versions used during LEACOAST2.

During the bench test, no problems were encountered although the compasses on instruments G250+B252 and G258+B233 needed re-orienting for sideways mounting. Compass checks were carried out prior to deployment and the necessary offsets corrected. The ADVs were set up using the factory calibrations supplied to POL technical staff. The instruments were set for 16 Hz recording at 20 minute bursts each hour on the hour using an external pulse from the SyncGen3 central timing clock. All three systems were set to record using ENU coordinates not the normal XYZ, at the Principal Scientific Officer (PSO)'s request.

Data Processing

After the instruments were recovered on cruise PD06_07, the data were downloaded from the loggers by POL staff and processed using Sontek ViewHydraPro software to generate MATLAB .MAT format files for analysis.

Processing Undertaken by BODC: ADV data on POLRIG994

BODC Processing

The data were supplied to BODC by the Data Originator as Matlab format .MAT files. These were reformatted to the BODC internal QXF format using BODC transfer function 390. The following table shows how the variables within the .MAT files were mapped to appropriate BODC parameter codes:

The data were screened by BODC using their in-house EDSERPLO visualisation software and any anomalous data were 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

Proudman Oceanographic Laboratory Dee Experiment

Introduction

Sediment transport process models are a vital tool in allowing scientists to predict sediment transport and forecast seabed and coastal morphodynamic evolution. It is however, difficult to obtain accurate models due to the complex inter-dependence of sediment processes in the bottom boundary layer. This inter-dependence is governed by interactions between the sediment transport triad; the bed, the hydrodynamics and the mobile sediments.

Scientific Objectives

• To use a varying suite of instruments to make co-located measurements of the sediment triad
• To provide a framework to allow assessment and improvement of the latest sediment transport models
• To address dynamics of suspended sediments in terms of supply of material to the coastal zone from estuaries
• Development of a new description of suspended sediment and water opacity to improve simulation of coastal primary productivity

Fieldwork

The study site chosen by POL for this research was the Dee Estuary, Liverpool Bay. POL performed fieldwork in the Hilbre Channel on the eastern side of the Estuary and the Welsh Channel on the western exit of the Estuary, with emphasis placed on two repeat stations, HC and WC. The fieldwork started in February 2005 and has been summarised below:

Funding

The Dee Experiment project was core funded by POL under Programme 2 (Shallow coastal seas) Theme 5 (Coastal and sediment processes) of POL's Science Programme 2001 - 2006. From March 2007 onwards, this core funding was replaced by funding from NERC's Oceans 2025 programme and the Dee Experiment research continued as part of Oceans 2025 Work Package 3.3.

Data Activity or Cruise Information

Data Activity

Dee Experiment mini-STABLE deployment POLRIG944

The mini-STABLE benthic frame was deployed in the Dee Estuary, Liverpool Bay as part of the UK Proudman Oceanographic Laboratory (POL) Dee Experiment. The mooring was deployed at Site WC from 14:34 UTC 13 March 2007 to 08:29 UTC 19 April 2007.

Deployment and recovery information

The mini-STABLE frame was of a tripod design (see image) with the following overall dimensions (all measurements +/- 0.005 m):

(Image courtesy of Dr. Richard Cooke, POL (2007))

The instrumentation mounted on mini-STABLE during this deployment is detailed in the below table:

The ADVs were mounted at separate heights on a vertical pole with each transmitter axis pointing horizontally, i.e. perpendicular to the sea surface/sea bed. The heights above the bed are as follows:

Related Data Activity activities are detailed in Appendix 1

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

Fixed Station Information

Dee Estuary Station WC

This station is located within the Welsh Channel of the Dee Estuary, Liverpool Bay. It is one of two stations repeatedly visited by the Proudman Oceanographic Laboratory (POL) in the Dee. All activities at this site occurred within a box bounded by co-ordinates 53.371°N, 3.31791°W at the north-east corner and 53.36642°N, 3.33817°W at the south-west corner. Typical depth ranges encountered within the box are 7 m - 17 m.

POL activites can be separated into two groups. These are (i) repeat CTD profiles over tidal cycles; (ii) mooring deployments.

The deployment history, to date, for this station is summarised below:

The CTD instrument package for these cruises was a Sea-Bird 911plus, with beam transmissometer, fluorometer, LICOR PAR sensor, LISST-25, and oxygen sensor.

The mooring deployment history for this site is as follows:

Key:

ADCP: Acoustic Doppler Current Profiler
ABS: Acoustic Backscatter Sensor
ADV: Acoustic Doppler Velocimeter
LISST: Laser In-Situ Scattering Transmissometer
SBE-37 MicroCAT: Conductivity and Temperature Sensor

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: 263

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: Dee Estuary Station WC

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.