Metadata Report for BODC Series Reference Number 33853
No Problem Report Found in the Database
Open Data supplied by Natural Environment Research Council (NERC)
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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.
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.
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.
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 56 (Northern North Sea) Data Processing Notes
Clock gained 6 seconds over 36 days, 16 hours; the cycle interval and time values have been corrected.
Instrument characteristics and calibration factors
|OSTG Mk II, logger 01, sensor VIB 1/1|
|Original sampling interval||15 minutes|
|Integration period||900 s|
|Temperature coefficient||1.7 mb/°C|
|Pressure sensitivity at 6.34°C||0.037 Hz/mb|
To convert pressure to elevation the following values should be used:
|Density (from CTD casts)||1028.623 kg/m3|
|Gravitational acceleration constant||9.819 m/s2|
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.
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|