Metadata Report for BODC Series Reference Number 33700

Metadata Summary

Data Description

Data Category Offshore sea floor pressure series
Instrument Type Tide gauge (unspecified)
Instrument Mounting fixed benthic node
Originating Country United Kingdom
Originator -
Originating Organization Institute of Oceanographic Sciences Bidston Laboratory (now National Oceanography Centre, Liverpool)
Processing Status banked
Project(s) -

Data Identifiers

Originator's Identifier 731/973/154
BODC Series Reference 33700

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1973-06-03 00:00
End Time (yyyy-mm-dd hh:mm) 1973-07-05 23:00
Nominal Cycle Interval 3600.0 seconds

Spatial Co-ordinates

Latitude 51.04830 N ( 51° 2.9' N )
Longitude 6.94330 W ( 6° 56.6' W )
Positional Uncertainty 0.1 to 0.5 n.miles
Minimum Sensor Depth 95.0 m
Maximum Sensor Depth 95.0 m
Minimum Sensor Height 0.0 m
Maximum Sensor Height 0.0 m
Sea Floor Depth 95.0 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 Chart reference - Depth extracted from available chart
Sea Floor Depth Datum Chart reference - Depth extracted from available chart


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)
PRSTPS01 1 Decibars TotPressSeaFL Pressure (measured variable) exerted by the water body plus atmosphere by fixed in-situ pressure sensor

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

Type 1 Off-Shore Tide Gauge

This instrument was developed at I.O.S. Wormley. It incorporates a seabed mounted pressure transducer interfaced to a 12 channel Normalair-Garret data logger housed in a 56cm diameter aluminium pressure sphere. The frequency modulated (FM) transducer consists of a diaphragm which when flexed by changing hydrostatic pressure varies the gap of a parallel plate timing capacitor in an LC oscillator circuit. The pressure casing enclosing the transducer circuitry is evacuated so that absolute rather than relative pressure is measured. The frequency output is divided down to about 100Hz and is counted over a period of 890 seconds to average out the unwanted fluctuations due to waves: this sampling period gives 50dB (99.999 p. cent) attenuation of energy from 10 second period waves, but only 0.006dB (0.14 p. cent) attenuation of semi diurnal tidal energy.

The integration period of 890 seconds and the subsequent 10 second scanning and recording sequence are controlled by 900 second pulses from a crystal clock. The reading from each channel is recorded serially in either 3 or 4 decade BCD on 0.25 inch magnetic tape and a parity bit is added during each scan by the digital serializer. A synchronizing signal is recorded on a second track of the tape to assist in translating the magnetic tape during the data processing.

The sphere containing the data logger and interfacing electronics is mounted in a tripod frame made of tubular steel with the pressure transducer mounted on the base of the framework and beneath the sphere. The tripod is supported on a disposable heavy ballast frame consisting of welded girders and the two frames are connected by 3 corrodible magnesium alloy links and a pyrotechnic release mechanism. The recorders are deployed as pop up moorings and released by acoustic release.

IOS Calibration and Data Processing of Off-Shore Tide Gauge Data

Calibration of pressure/frequency sensors and thermistors are carried out using the facilities and staff at I.O.S. Bidston with the exception of pre 1975 pressure/frequency sensors, which were calibrated in the pressure chamber at I.O.S. Wormley.

The data are copied from the logger magnetic tape to 9 track magnetic tape and disk. The data are either listed or plotted as an initial check. A program is then used to check the data from the temperature sensor channels, calculate and plot the temperature values and store them (if temperature sensor channels are available).

A second program performs a similar function for the pressure sensor channel, using the pressure frequency coefficient to convert each pressure frequency to the frequency at the reference temperature and calculating the pressures using the pressure frequency calibration. The data values, generally at 15 minute intervals, but occasionally at 10 minute intervals, of pressure are then plotted and stored. If waterhead is required, it may be computed by subtracting atmospheric pressure and applying the hydrostatic relation:-

H = P / ( d * g )
H = waterhead (cm)
P = pressure (0.01 mb)
d = density (kg/m3)
g = gravitational acceleration (m/s2)

Station C (Celtic Sea) Data Processing Notes

Clock gained 25 seconds over 34 days, 18.5 hours; the cycle interval and time values have been corrected. An interpolation program was used to produce hourly values, on the hour, of the pressure record.

Instrument characteristics and calibration factors

OSTG Type 1, logger 41, sensor FM 4882/7
Original sampling interval 15 minutes
Integration period 890s
Temperature coefficient 37.01Hz/°C
Pressure sensitivity at 8.4°C 0.977Hz/cm

To convert pressure to elevation the following values should be used:

Density (from CTD casts) 1026.86kg/m 3
Gravitational acceleration constant 9.812m/s 2

Complete record of sphere temperature but sea temperature circuit failed on deployment. Temperature record was taken from bottom mounted current meter and used for correction of frequency record.

Project Information

No Project Information held for the Series

Data Activity or Cruise Information

No Data Activity or Cruise Information held for the Series

Fixed Station Information

No Fixed Station Information held for the Series

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