Metadata Report for BODC Series Reference Number 37725
No Problem Report Found in the Database
Open Data supplied by Natural Environment Research Council (NERC)
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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 32 seconds over 29 days 11 hours 14 minutes 28 seconds; the cycle interval and time values have been corrected.
|OSTG Mk I||No. 4|
|Nominal sampling interval||900secs|
|Actual sampling interval||14.99980mins|
IOS Data Processing of Off-Shore Pressure Recorder Data
Because the pressure is integrated over 890 seconds and then logged, the time value assigned to a data cycle has been chosen as the mid-point between the start and end of each integration period.
Instrumental drift and depth have been removed, thus a drift free series is produced with an artificial mean value.
No Project Information held for the Series
No Data Activity or Cruise Information held for the Series
No Fixed Station Information held for the Series
The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:
|<||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.)|
|E||End of CTD Down/Up Cast|
|G||Non-taxonomic biological characteristic uncertainty|
|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|
|O||Improbable value - user quality control|
|0||no quality control|
|2||probably good value|
|3||probably bad value|
|6||value below detection|
|7||value in excess|
|A||value phenomenon uncertain|
|Q||value below limit of quantification|