Lysbilde 1

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Ring laser gyro compassExperiences from Svalbard
and the importance of secant latitude RMS
Havbunnskartlegging og inspeksjon, Geilo 6.2.2008
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Aquadynes Inertial pallet

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Aquadyne Bergen
Jan Ådland used to represent IXSEA before he
joined Aquadyne to head our Bergen Office
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Original sketch by Georges Sagnac
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Mirror
Laser
Detector
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The sensor is rotating anti-clockwise
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Secant latitude RMS

• 1/cos(x) , x degrees north
• Multiply by specification (0.10)

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Local navigation frame-right hand co-ordinate
system
X-axis North Y-axis East Z-axis Nadir
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RMS heading error with latitude
RMS heading
Spitsbergen
Geilo
Tromsø
Asker
London
latitude
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IMU 01 and IMU 02 Heading Static at 78N
Individual random walk
degrees
hours
IMU 01 heading
IMU 02 heading
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Differences between IMU 01 og IMU 02 Heading
Static 78 N
degrees
hours
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Lodestar IMU 01 and IMU 02 Heading - Dynamic
78N
degrees
hours
IMU 01 Heading IMU 02 Heading
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Lodestar IMU 01 and IMU 02 Heading Dynamic 78N
degrees
hours
IMU 01 Heading /100 IMU 02 Heading
/100 Difference in Heading
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Statistical Background to the Analysis Heading
performance figures for inertial sensors are
usually given in terms of RMS or standard
deviation (SD).  
value
sample
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• Data Processing Method
• Long data sets were collected in static and
  dynamic conditions. This data was interpolated,
  re-sampled, differenced and finally the
  statistics computed.
• The processing steps were as follows.
• Output from two units recorded on same PC(with
  common time stamp) in Spitsbergen
  
  
• The data series were interpolated
• The interpolated data was re-sampled using common
  time series
• One re-sampled data set is now subtracted from
  the other re-sampled data set
• Statistics computed on the resulting differenced
  data

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The Variance Sum Law

• For two normally distributed independent data
  sets X and Y
• with variance and variance
• then .
• This law states that the variance of a data set,
  that represents the differences between two data
  sets X and Y,
• is the sum of the variance of X and the variance
  of Y.

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Aquadyne ASSolbråveien 411383
AskerNorwayPhone 47 66 98 71 50