'B' Type Pressure Gauges in the South Atlantic'

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'B' Type Pressure Gauges in the South Atlantic.
Simon Holgate Permanent Service for Mean Sea Level
www.pol.ac.uk
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General references. IOC Manuals I-III,
especially Manual III These can be downloaded
from http//www.pol.ac.uk/psmsl/training See
also Woodworth et al. (1996) Precise datum
control for pressure tide gauges, Marine
Geodesy, 19 (1), pp. 1-20
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Transducer pressure gauges.

• Usually a single transducer in the sea
• Poor datum control
• instrumental drift
• Approx. 2-3 cm accuracy with calibration
• best calibration with tide staff
• Excellent in hostile conditions
• - (e.g. under polar ice)
• Problem of density variation in rivers and for
  deep gauges

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Schematic of the 'transducer in the sea' pressure
system.
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B (or triple) pressure systems.

• Additional sensor at approximately MSL
• Millimetric datum control
• Requires sizable tidal range to work properly
• - Half tide sensor must spend approx.
• half tidal cycle out of water.
• - Most coastal and island sites fulfill this
• requirement, though lakes may not

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Schematic illustration of a pressure gauge setup
containing three pressure transducers.
All 3 transducers can drift as can the ocean
itself!
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Construction of the 'B' Gauge.

• Both B C transducers
• are at the same depth
• - ensures constant
• temperature for calibration
• - new all-in-one gauge also has barometer
• A at the same depth
• Pipe leads from mid-tide sensor to mid-tide
  point B
• - and from barometer to A in the
  all-in-one gauge
• All are housed in a tube to act as a
  mini-stilling well

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The 'B' gauge at Ascension Island.
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Principle of the triple point method.
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Datum control.

• The flat part of the B-A curve is immune
• to any problems with datum offsets
• or instrument drift
• The B-A curve is overlaid onto the C-A
• curve
• - the intersection of the flat line with the
• full curve defines the datum of the full
• curve

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B gauges in the South Atlantic.

• B gauges are now operated throughout the South
  Atlantic using the triple transducer system
• The principle of having a pressure measurement
  at approximately MSL has been incorporated into
  the UK bubbler network
• - additional bubbler outlet used at approx. MSL.
• Inevitably expensive because several transducers
  are required.
• - we are experimenting with the use of cheaper
  transducers (e.g. Druck instead of Digiquartz)

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The UK tide gauge network of 'B' and pressure
gauges in the South Atlantic.
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Data communications.

• Data returned by hourly emails from
• Ascension, St. Helena and Port Stanley
• facility to dial-up loggers directly
• Iridium from Ascension Island
• via local ISP from St. Helena Stanley
• Emails automatically banked in database
• real-time display available on web
• automatic weekly fast data sent to U of H
• rough and ready
• Research quality slow data produced on
• yearly basis.

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Real-time data from St. Helena.
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South Atlantic sites Ascension Island.
The tide gauge hut
The Lab - inside the hut
Iridium mast
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South Atlantic sites St. Helena.
View of Jamestown Harbour
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Equipment.
Iridium
The complete setup
Tele-modem
Digiquartz sensor
Logger board
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The future.

• Better communications through OrbComm
• field trials to be carried out
• real-time data from all South Atlantic and
• Antarctic sites
• Upgrade of Tristan da Cunha
• replace pressure gauge with radar
• Deployment of all-in-one gauges to all sites