Metadata Report for BODC Series Reference Number 41275

• 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

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.

Data Processing Notes

Clock gained 2 minutes 32 seconds over 35 days 2 hours 12 minutes 28 seconds; cycle interval and time values have been corrected.

Instrument Characteristics

JONSDAP 76 Rig 57

IOS Data Processing of Off-Shore Pressure Recorder Data

Data processing comprises 2 stages:-

1. Instrumental drift and depth are removed, thus the drift free series is produced with an artificial mean of zero.

2. Generally the pressure values have been obtained by integration and averaging over the sampling interval, followed by logging; hence the time value assigned to a data cycle has been chosen as the mid-point between the start and end time of each interval. Some pressure records have been sample rate reduced from the basic time step of the recorder to produce either hourly or 15 minute values, incorporating any timing corrections due to clock error.

Project Information

1976 Joint North Sea Data Acquisition Project (JONSDAP 76)

This was the third phase of the cooperative data collection programme JONSDAP, begun in 1970 by the countries bordering the North Sea. It consisted of two intensive measurement programmes:

• FLEX (the Fladen Ground Experiment)studied the development of the thermocline and the dynamics of the plankton bloom in spring in relation to the physical, chemical and biological environment. Measurements were concentrated in a square of side 100km for 100 days from March to June.
• INOUT was concerned with the general circulation of the North Sea and the storm surge problem. Currents flowing into and out of the open boundaries as well as at discrete points within the sea, were measured concentrating on a period of 40 days in the stormy season from March to April. Some 200 current meters (most also recorded temperature) were deployed, of which 30 were lost, together with 5 offshore tide gauges. More than 10 ships collected hydrographic data from over 83 stations . The Netherlands organised a collection of meteorological data. The northern boundary of INOUT was from Wick to 59° 20' N, 0° E then along this latitude to the Norwegian coast. The southern boundary crossed the English Channel from Portland to Cherbourg, approximately along the meridian 2° W.

One of the most important reasons for the cooperative exercise was the need to provide large data sets for the evaluation and running of physical and ecosystem numerical models.

Data underwent intradisciplinary processing and interdisciplinary evaluation.

Intercomparison of Instruments

There was no field comparison station for moored instrumentation.

Laboratory techniques in use for calibrating current meter compasses were compared and shortcomings eliminated prior to the exercise. The two main types (Plessey and Aanderaa) of current meter used in the exercise were compared in a simplistic way on four of the rigs and showed that at certain times the two types could give differing responses to the same velocity field simply because of differences in instrument and rig design. This point should be borne in mind whenever comparing data across instruments.

Previous JONSDAP Exercises

The first JONSDAP achieved the systematic collection of data from a network of moored stations and coastal observation sites in the North Sea in the period 1971 to 1973.

The second experiment (JONSDAP 73) was a programme of tide and current measurement in the Southern Bight of the North Sea from September to October 1973.

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:

SeaDataNet Quality Control Flags

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