Metadata Report for BODC Series Reference Number 40991


Metadata Summary

Data Description

Data Category Offshore sea floor pressure series
Instrument Type
NameCategories
Institute of Oceanographic Sciences MkII bottom pressure recorder  sea level recorders
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 C6BP2/PDFH4
BODC Series Reference 40991
 

Time Co-ordinates(UT)

Start Time (yyyy-mm-dd hh:mm) 1975-09-06 12:37
End Time (yyyy-mm-dd hh:mm) 1975-10-01 08:52
Nominal Cycle Interval 900.0 seconds
 

Spatial Co-ordinates

Latitude 50.81990 N ( 50° 49.2' N )
Longitude 10.91660 W ( 10° 55.0' W )
Positional Uncertainty 0.1 to 0.5 n.miles
Minimum Sensor Depth 172.0 m
Maximum Sensor Depth 172.0 m
Minimum Sensor Height 0.0 m
Maximum Sensor Height 0.0 m
Sea Floor Depth 172.0 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 Instantaneous - Depth measured below water line or instantaneous water body surface
Sea Floor Depth Datum Instantaneous - Depth measured below water line or instantaneous water body surface
 

Parameters

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)
PPSSRL01 1 Decibars RelBotPress Pressure (measured variable) exerted by the water body by fixed in-situ pressure sensor and corrected using co-located air pressure data expressed to unspecified datum by subtraction of a constant
 

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

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.

Data Processing Notes

Clock gained 3 seconds over 24 days 20 hours 14 minutes 57 seconds; the cycle interval and time values have been corrected.

Instrument Characteristics

Station C6

OSTG Mark II Number 2
Sensors OAR 4/1 (BODC Series Ref. 40991)
Vib 1/6 (BODC Series Ref. 40978)
SG 2/2 (BODC Series Ref. 41005)
DIG 5/1 (BODC Series Ref. 33804)
Nominal sampling interval 900 seconds
Integration period 900 seconds

This instrument was deployed on the same frame as an Aanderaa tide gauge.

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.


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