A'Hemshorn E'Pulz M'Korte U'Auster M'Mandea

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A.Hemshorn E.PulzM.KorteU.AusterM.Mandea
GAUSS Improvements to the Geomagnetic
AUtomated SyStem
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Absolute measurements Challenges

• Magnetometer errors must be cancelled
• Orientation towards a geographical reference
  frame must be known
• Automated absolute measurements strongly
  demanded for remote places
• Provide a simple measurement procedure
• Provide non-magnetic realization

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Magnetic field along a rotation axis (I)

• Take a three component magnetometer
• Rotate it along a very stable, well defined axis
• Take measurements at three different positions
  during this rotation

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Magnetic field along a rotation axis (II)

• -gt The field along the rotation axis can easily
  be calculated
• -gt Two different rotation axes scalar
  measurement provides the full vector
• -gt Alignment errors play no role

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Optical components

• Neodym Laser
• PSD 2 cm x 2 cm
• Resolution lt 0.1 mm
• Protected from stray light by bandfilter, black
  tube
• Azimuth Mark
• Made by ceramics, grounded in concrete
• Requirements 1nT 4 arcsec
• gt 0.3 mm resolution in 15 m distance

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Optical components
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Calibration of the sensor

• Rotation about two axes
• additional knowledge of intensity
• allows full determination of all calibration
  parameters (offsets, scale factors,
  non-orthogonality)

Magnetometer for absolute measurement
Scalar Magnetometer
Variometer
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Mechanical System

• Three rotations have to be performed
• Rotation about the measurement axis
• Shifting of the rotation axis to get a second
  component
• Rotation of the magnetometer about a third axis
  for calibration purposes
• Motions are driven by piezo motors

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Setup in Niemegk
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Previous Results
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Previous Results
?Z 0.4 nT
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Whats new?

• Motors have been exchanged
• Nanomotion types
• Optical encoders to return to previous position
  (not needed, but makes life simpler)
• Laser has been exchanged
• No longer a diode close to the magnetometer, but
  coupled in by fibre optics

-gt Performance since May 2008 -gt Already more
than 300 single absolutes have been carried out
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Preliminary Results
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Outlook

• Test for long term stability
• Reliabilty of motors
• Stability of azimuth marks
• Dependance on temperature/ season/ humidity?
• Improve processing software