Metadata Report for BODC Series Reference Number 33797

• 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

IOS Off-Shore Pressure Recorder Mark II

This instrument was developed by Marconi Space and Defence Systems Limited in conjunction with I.O.S. Bidston. The data logger can sample a maximum of 20 input channels at periodic intervals and record their values by means of an incremental tape recorder in a computer compatible format. Any input channel is capable of sampling either D.C. or frequency modulated A.C. inputs - the FM inputs can be sampled for periods of 15/64, 15/16, 3.75, 15 or 60 seconds or continuously (i.e. the integrating time is virtually equal to the sampling period of the data from the channels).

The number of channels scanned can be truncated to less than 20 and the sampling interval can be 1.875, 3.75, 7.5, 15, 30 or 60 minutes. Sensor packs used with the logger incorporate both a pressure and a temperature sensor and are completely self contained units with their own sensor electronics and power supplies. Different types of pressure sensor based on either strain gauge, vibrating wire or quartz crystal systems have been used on the tide gauge. A brief description of each is given below.

1. The strain gauge sensor has been developed using a Bell and Howell type 4-306 transducer and operates as a phase shift oscillator whose frequency is controlled by the ratio of output to input voltage of the transducer Wheatstone bridge network.

2. The vibrating wire sensor consists of a tungsten wire stretched between a rigid frame and a diaphragm and mounted in a magnetic field. Any movement of the diaphragm due to a change of pressure will increase or decrease the tension of the wire and hence change its natural frequency of oscillation. The wire is connected in the feedback loop of an amplifier and thus makes a variable frequency oscillator where frequency is a function of pressure. To achieve temperature compensation for the coefficient of expansion of the wire, the coefficient of expansion of the supporting frame is designed to balance the expansion of the wire. These sensors are manufactured by Vibroton and Ocean Applied Research.

3. Two types of quartz crystal pressure sensor have been used. The Digiquartz pressure sensor consists of a convoluted bellow linked to a 40kHz quartz crystal resonator coupled by piezoelectric action to an electronic resonator. The Hewlett Packard Oceanographic sensor consists of a 5MHz quartz resonator coupled by piezoelectric action to an electronic oscillator and mounted in an oil filled case adjacent to a pressure case containing the electronic circuitry. A second closely matched quartz crystal resonator is mounted in the pressure case and is therefore not exposed to hydrostatic pressure and is used for temperature compensation by heterodyning the frequency outputs of the two crystals.

The data logger and batteries are housed in a 56cm diameter aluminium sphere with sufficient space for the sensor batteries, acoustic release electronics and ancillary sensor electronics. The sphere and a number of sensor packs are mounted in an aluminium sub-frame which in turn is protected by a heavy steel outer frame. The Mk II tide gauge is usually deployed using a U-shaped mooring (i.e. buoy or pellet float to wire rope to tide gauge to ground line to anchor to wire rope to buoy), but W-shaped moorings are used in conjunction with either current meters or thermistor chains. A W-shaped mooring comprises pellet float to pellet line to sub- surface buoy to current meter or thermistor line to anchor weight to ground line to tide gauge to ground line to anchor weight to wire rope to surface buoy.

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 C4 (SW Continental Shelf) Data Processing Notes

Clock lost 11 seconds over 46 days, 4.5 hours; the cycle interval and time values have been corrected.

Instrument characteristics and calibration factors

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

No CTD casts were taken. The above density was computed from mean surface temperatures and ICES salinity. A current meter was also deployed on this mooring.

Project Information

No Project Information held for the Series

Data Activity or Cruise Information

Data Activity

Mooring Information

Mooring held 2 meters.

Related Data Activity activities are detailed in Appendix 1

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:

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: SC4

Related series for this Data Activity are presented in the table below. Further information can be found by following the appropriate links.

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