Metadata Report for BODC Series Reference Number 425998

• 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 Access Policy

Open Data

These data have no specific confidentiality restrictions for users. However, users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgment.

If the Information Provider does not provide a specific attribution statement, or if you are using Information from several Information Providers and multiple attributions are not practical in your product or application, you may consider using the following:

"Contains public sector information licensed under the Open Government Licence v1.0."

Narrative Documents

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

MAFF Wave-Model Comparison

In order to validate and improve operational wave predictions from the Meteorological Office Fine Mesh Wave Model, wave measurements were made at inshore and offshore sites at three UK locations (Lyme Bay, Mablethorpe off the Lincolnshire Coast and Morecambe Bay).

BODC hold the wave measurements made at these six sites and the associated model output. The Marine Advisory Service (Commercial Services), of the Meteorological Office should be contacted regarding model output availability.

Data Activity or Cruise Information

No Data Activity or Cruise Information held for the Series

Fixed Station Information

Fixed Station Information

Barrow Offshore Wave Data October 1992 to November 1993

Introduction

Hydraulics Research Wallingford Ltd., on behalf of the National Rivers Authority / Ministry of Agriculture Fisheries and Food, measured waves at two sites off Barrow-in-Furness, Lancashire. A Datawell directional waverider buoy was deployed off the seaward limit of the navigation channel to Barrow and a pressure wave recorder was installed on a navigation tower further inshore. A data report has been published (Ryder 1993). The majority of the information presented here is taken from this report.

Instrumentation

The Datawell directional waverider buoy is described in a separate document.

The nearshore pressure system was purpose built and consisted of:

• A precision differential pressure transducer (Druck model PDCR830, range 0-20m) connected to the surface by a vented cable.
• A surface electronics unit including a pressure compensator and a UHF radio link powered by battery/wind generator.
• A shore based receiver linked to an IBM compatible PC to analyse and log the data.

The pressure sensor was secured to No. 1 navigation tower close to the sea at approximately Chart Datum. The receiving station for this and the waverider was in the Light House on Walney Island. The pressure sensor measured the changing wave-induced pressure. These pressure fluctuations decrease with increasing water depth, with higher frequency variations being attenuated more than low frequency signals. This attenuation may be neglected at tidal frequencies, but is significant at typical wave periods.

The attenuation may generally be corrected for using linear wave theory. However, at high frequencies the attenuation becomes so large that the signal at the sea bed is of the same order of magnitude as noise on the pressure signal and it is no longer possible to obtain an estimate of the surface spectral energy. It is therefore necessary to omit the spectral estimates with frequencies above some cut-off value when computing the wave parameters.

In this study an empirical relationship between high frequency cut-off (Fc) and water depth (D) was derived to be:

Fc=3.8/D-0.112.

The precise choice of the cut-off has only a small effect on the wave height estimates as it is generally well below the spectral peak period. The mean zero-crossing period however, is strongly dependent on the high frequency tail of the wave spectrum and therefore the cut-off frequency. It will be necessary to take the cut-off used into acount when comparisons are made between observed and model results.

Problems

• The waverider was cut adrift during May 1993. This resulted in 10 days loss of data.
• The nearshore sensor was out of commission during February and May 1993 as a result of physical damage.
• There were other shorter periods of data loss as a result of interference to the telemetry signal and when the nearshore sensor was occasionally exposed at low water.

Results

Offshore the waves were predominantly from the west to southwest. This is consistent with the directions of the longest open fetches. Maximum heights of nearly 6m (mean period 8 seconds) were recorded during January 1993. Wave steepness indicates that the waves were predominantly locally generated.

At the inshore recorder waves were significantly attenuated by the shallow water with the largest values being observed over high water. Maximum values of 1.5m were observed during January 1993.

Reference

Ryder, D.K. (1993). Morecambe Bay, Lancashire Wave Recording (Final report covering the period 8 October 1992 to 11 November 1993). Hydraulics Research Wallingford Limited, Report No. EX2933 (4 pp, 7 figs, 2 tables).

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: Barrow No. 1 Navigation Tower

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.