1. DI3 – A new Procedure for Absolute Directional Measurements
Anne Geese, Uli Auster, Monika Korte

2. Motivation
High performance 3D magnetometers, accommodated on movable vehicles, are nowadays available and well tested – particularly in our institute due to the space heritage.
Experience with 3D magnetometers for absolute measurement exists from our automated system „GAUSS“ which is continuously in operation since more than two years.
Equipping a theodolite with a three component magnetometer obviously must give additional information and thus have an advantage compared to a single axis instrument.
| A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

3. Components Zeiss Theodolite (010B)
Vector compensated fluxgate magnetometer (Magson / TU-BS)
Full Earth field range with non linearity less than 2 * 10-5
Resolution 0.1nT
Flown on various ESA and NASA space missions
PDA (0.2nT in 1m)
connected with magnetometer via Bluetooth interface
| A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

4. Procedure Azimuth mark readings (2)
Angle readings have to be typed in PDA
Fetching of magnetometer measurements
Setting of predefined angles during horizontal rotation + magnetometer measurements
12 settings sensor up and 12 sensor down
Setting of predefined angles during vertical rotation + magnetometer measurements
12 x HC (can be arbitrary), 12 x HC+180°
30min: 6 readings, 48 settings
= 54 absolute measurements
| A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

5. Example Data Set (steps 1-28)
| A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

6. Data Processing Scalar Calibration Orientation of Magnetometer Sensor
Determination of sensor non orthogonality, scale values and offsets
Input: |BFG| = |BProton| Result: B in magnetometer system
Orientation of Magnetometer Sensor
Determination of misalignment angles
Input: BTheodolite = const. Result: B in theodolite system
Rotation to azimuth mark and geographic north
Horizontal rotation towards observatory system
Input: HC readings + Azimuth angle, Result: B in geographic system
Reduction of Variation
Removing of variation influence, time of absolute measurement reduced to first reading
Input: dD, dH, DZ Result: tstart
| A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

7. Comparison with Niemegk Base Line
| A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

8. Example 1: Changchun Sept. 15th
| A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

9. Example Changchun Sept. 16th
| A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

10. Example Changchun Sept. 14th (H-component)
Wrong angle setting
by observer
Data could be corrected
( > 270.0)
One magnetometer component was saturated (>54000nT)
Readings are removed from data set
| A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

11. Conclusion
Requirements on fluxgate magnetometer are high but not too strong:
High linearity (10-5) – affects the calibration
High thermal stability (low thermal inertia, isotropic sensor design)
Test series in Niemegk shows feasibility of method
Advantage 1: The usage of the 3D magnetometer allows the determination of an error bar of an absolute measurement for the first time
Advantage 2: The usage of the 3D magnetometer on the theodolite improves the reliability of the absolute measurement significantly
All steps are guided by PDA-software -> easy to handle for semi-professional observer
Errors can be detected and removed offline
| A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

12. Many thanks for supporting our measurements in Changchun
| A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |