Metadata Report for BODC Series Reference Number 52887


Metadata Summary

Data Description

Data Category Waves (statistics)
Instrument Type
NameCategories
Institute of Oceanographic Sciences shipborne wave recorder  wave recorders
Instrument Mounting vessel at fixed position
Originating Country United Kingdom
Originator -
Originating Organization Institute of Oceanographic Sciences Taunton
Processing Status banked
Project(s) -
 

Data Identifiers

Originator's Identifier JOHNMURRAY78
BODC Series Reference 52887
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1978-07-16 04:02
End Time (yyyy-mm-dd hh:mm) 1978-08-29 06:42
Nominal Cycle Interval 10800.0 seconds
 

Spatial Co-ordinates

Latitude 60.25000 N ( 60° 15.0' N )
Longitude 10.50000 W ( 10° 30.0' W )
Positional Uncertainty Greater than 10 n.miles
Minimum Sensor Depth 1.95 m
Maximum Sensor Depth 1.95 m
Minimum Sensor Height 1009.05 m
Maximum Sensor Height 1009.05 m
Sea Floor Depth 1011.0 m
Sensor Distribution Fixed common depth - All sensors are grouped effectively at the same depth which is effectively fixed for the duration of the series
Sensor Depth Datum Instantaneous - Depth measured below water line or instantaneous water body surface
Sea Floor Depth Datum Chart reference - Depth extracted from available chart
 

Parameters

BODC CODE Rank Units Short Title Title
AADYAA01 1 Days Date(Loch_Day) Date (time from 00:00 01/01/1760 to 00:00 UT on day)
AAFDZZ01 1 Days Time(Day_Fract) Time (time between 00:00 UT and timestamp)
AZDRZZ01 1 Seconds Duration Sample duration
DEPHPM01 1 Metres PhysMeasDep Depth below surface of the water body by physical measurement
GMNLMB01 1 Metres WaveMin_SBWR Minimum level of waves on the water body by shipborne wave recorder and manual record analysis
GMXLMB01 1 Metres WaveMax_SBWR Maximum level of waves on the water body by shipborne wave recorder and manual record analysis
GTDHMB01 1 Metres Hs_SBWR Significant height of waves {Hs} on the water body by shipborne wave recorder and manual record analysis
GTKCMB01 1 Metres Wave2ndMax_SBWR Second maximum level of waves on the water body by shipborne wave recorder and manual record analysis
GTKDMB01 1 Metres Wave2ndMin_SBWR Second minimum level of waves on the water body by shipborne wave recorder and manual record analysis
GTZAMB01 1 Seconds Tz_SBWR_Man Average zero crossing period of waves {Tz} on the water body by shipborne wave recorder and manual record analysis
 

Definition of Rank

  • Rank 1 is a one-dimensional parameter
  • Rank 2 is a two-dimensional parameter
  • Rank 0 is a one-dimensional parameter describing the second dimension of a two-dimensional parameter (e.g. bin depths for moored ADCP data)

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.

Sensor Depth For a shipborne wave recorder (SBWR) this is the depth of the SBWR water inlets below the mean water level of the vessel.For an F.M. pressure transducer it is the depth of the sensor below the mean water level for the duration of the record.
Record Duration The period of record selected for analysis from the total available record
T z The zero crossing period (the record duration divided by the number of times the record trace crosses the mean water level of the record in an upwards direction)
T c The crest period (the record duration divided by the number of crests in the record)
A The height of the highest crest above the mean water level
B The height of the second highest crest above the mean water level
C The depth of the lowest trough below the mean water level
D The depth of the second lowest trough below the mean water level (C and D are taken as positive)
H 1 The highest wave (A+C)
H 2 The second highest wave (B+D)
H s The Tucker Draper significant wave height
H rms The root-mean-square wave height

During processing the following checks are performed:

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

Cruise Name JM8/78
Departure Date 1978-07-12
Arrival Date 1978-09-01
Principal Scientist(s)Trevor H Guymer (Institute of Oceanographic Sciences Wormley Laboratory)
Ship RRS John Murray

Complete Cruise Metadata Report is available here


Fixed Station Information

Fixed Station Information

Station NameJASIN 78 Wave Station
CategoryOffshore location
Latitude60° 15.00' N
Longitude10° 30.00' W
Water depth below MSL1011.0 m

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:

Flag Description
Blank Unqualified
< Below detection limit
> In excess of quoted value
A Taxonomic flag for affinis (aff.)
B Beginning of CTD Down/Up Cast
C Taxonomic flag for confer (cf.)
D Thermometric depth
E End of CTD Down/Up Cast
G Non-taxonomic biological characteristic uncertainty
H Extrapolated value
I Taxonomic flag for single species (sp.)
K Improbable value - unknown quality control source
L Improbable value - originator's quality control
M Improbable value - BODC quality control
N Null value
O Improbable value - user quality control
P Trace/calm
Q Indeterminate
R Replacement value
S Estimated value
T Interpolated value
U Uncalibrated
W Control value
X Excessive difference

SeaDataNet Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:

Flag Description
0 no quality control
1 good value
2 probably good value
3 probably bad value
4 bad value
5 changed value
6 value below detection
7 value in excess
8 interpolated value
9 missing value
A value phenomenon uncertain