Metadata Report for BODC Series Reference Number 52887

• 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 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

Institute of Oceanographic Sciences Shipborne Wave Recorder

The IOS shipborne wave recorder (SBWR) (1,2) consists of a pair of heave transducers (accelerometers), a pair of pressure transducers, a signal processing unit and a data recorder. One heave transducer and one pressure transducer are mounted together on each side of the vessel close to the centre of pitch and 1-3m below the water-line. This reduces the influence of pitch and roll to negligible proportions. The heave transducers measure the longer period waves, while the pressure transducers measure the short period waves. Waves of up to 30m height and 25 seconds period can be measured; the lower detectable limit depends on the installation depth of the pressure units.

The two heave transducer signals are added and integrated twice, while the two pressure transducer signals are added and filtered. The two resulting signals are added for output to a data logger and/or chart recorder.

Calibration is carried out at intervals of from one to three years. The three year period applies to Trinity House lightvessels which are on station for this period between major refits. The heave and pressure transducers are calibrated separately. Each heave transducer is mounted in gimbals on an arm which is then rotated vertically. The signal from the transducer is amplified and fed to the chart recorder. The instrument sensitivity can then be adjusted with reference to the chart record. Each pressure transducer is calibrated statically by subjecting it to a series of discrete pressures and comparing its output voltage to the original calibration.

In general a 17 minute record is taken every 3 hours; 12 minutes (sometimes less) of each record is then analysed. When readings are taken the vessel should be stationary, or nearly so (speed less than two knots), to avoid distorting the wave periods. The system is relatively accurate for long wave periods.

During data processing, significant wave height was corrected to compensate for both the frequency response of the electronics and the hydrodynamic attenuation of the pressure fluctuations (Derbyshire, 1961); this correction was considered unreliable for Tz values of less than five seconds. However, later comparisons of SBWR, Waverider buoy and Geostat altimeter measurements by Pitt (1991) enabled a more reliable empirically- based correction procedure to be developed. This latest correction factor varies with the length of the recording vessel. The data held by BODC have had the original correction removed and the Pitt correction applied, however there is still some doubt as to the accuracy with which short period waves have been measured (Pitt, pers. comm.).

References

Haine, R.A. (1980).
Second generation shipborne wave recorder. Transducer Technology, 2, 25-28.

Pitt, E.G. (1991).
A new empirically-based correction procedure for shipborne wave recorder data. Applied Ocean Research, 13(4), 162-174.

Tucker, M.J. (1956).
A shipborne wave recorder. Transactions of the Institution of Naval Architects, London, 98, 236-250.

Non-Spectral Wave Parameters

This document briefly describes the non-spectral wave parameters used by IOS. They are described in greater detail by Tucker (1963).

All of these parameters may not be present for a given site.

During processing the following checks are performed:

• H₁>H_s
• A>B
• C>D
• T_z>T_c

Reference

Tucker, M.J. (1963).
Analysis of records of sea waves. Proceedings of the Institution of Civil Engineers, 26, 305-316.

RRS John Murray JASIN Wave Data Processing

Introduction

This document covers the wave data recorded by RRS John Murray during the Joint Air-Sea Interaction Project (JASIN) experiment (July - August 1978). The data were collected and processed by the Wormley Laboratory (now known as the Deacon Laboratory) of the Institute of Oceanographic Sciences (IOS).

Instrumentation

Measurements were made using an IOS Shipborne Wave Recorder (SBWR) (Tucker, 1956) fitted with the pressure transducer inlets 1.95 metres below mean water level. Measurements were made when the vessel was steaming at 0.5 knots or less.

Data Processing

Data were recorded on a paper chart recorder for 17 minutes every three hours; a 10 to 12 minute period of each record was later manually analysed in the laboratory using the Tucker-Draper method (Draper, 1963).

During data processing, significant wave height was corrected to compensate for both the frequency response of the electronics and the hydrodynamic attenuation of the pressure fluctuations (Derbyshire, 1961; equation 1 with k = 2.5); this correction was considered unreliable for Tz values of less than five seconds. However, later comparisons of SBWR, Waverider buoy and Geostat altimeter measurements by Pitt (1991) enabled a more reliable empirically-based correction procedure to be developed.

This latest correction factor varies with the length of the recording vessel (40m). The data held by BODC have had the original correction removed and the Pitt correction applied, however there is still some doubt as to the accuracy with which short period waves have been measured (Pitt, pers. comm.).

Calibration Protocols

Calibration is carried out before installation of the instrument. The accelerometers and pressure units are calibrated separately. Each accelerometer is placed in gimbals in a rig in which it is driven through a one metre vertical circle; the output signal is electronically multiplied to give an apparent ten metre signal and the instrument is adjusted as necessary. The pressure units are calibrated statically by exposure to a series of discrete pressures. Successive overall calibrations which agree to within six percent are considered acceptable.

References

Darbyshire, M. (1961).
A method of calibration of shipborne wave recorders. Deutsche Hydrographische Zeitschrift, 14 (2), 56-63.

Draper, L. and Graves, R. (1968).
Waves at Varne Light Vessel, Dover Strait. National Institute of Oceanography, Report No. A34, 6 pp (12 figs).

Pitt, E.G. (1991).
A new empirically-based correction procedure for shipborne wave recorder data. Applied Ocean Research, 13(4), 162-174.

Tucker, M.J. (1956).
A shipborne wave recorder. Transactions of the Institution of Naval Architects (London), 98, 236-250.

Project Information

No Project Information held for the Series

Data Activity or Cruise Information

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

Fixed Station Information

JASIN 1978 Wave Station

With the exception of two periods of a couple of days, RRS John Murray occupied a fixed station during the Joint Air-Sea Interaction Project (JASIN) experiment (July - August 1978), making radiosonde, meteorological station and wave measurements. The station was located at position 60° 15' N, 010° 30' W apart from during the periods 23-25 August and 28-29 August when the ship relocated to 59° 46' N, 012° 30' W. Whilst on station the ship kept within two nautical miles of the nominal position. The water depths (determined using the GEBCO 2002 1-minute grid) at these two sites are 1011 metres and 1214 metres respectively.

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: