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

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. 22.11.2018 | A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

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 22.11.2018 | A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

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 22.11.2018 | A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

Example Data Set (steps 1-28) 22.11.2018 | A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

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: Babsolute @ tstart 22.11.2018 | A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

Comparison with Niemegk Base Line 22.11.2018 | A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

Example 1: Changchun Sept. 15th 22.11.2018 | A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

Example Changchun Sept. 16th 22.11.2018 | A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

Example Changchun Sept. 14th (H-component) Wrong angle setting by observer Data could be corrected (270.1 -> 270.0) One magnetometer component was saturated (>54000nT) Readings are removed from data set 22.11.2018 | A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

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 22.11.2018 | A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |

Many thanks for supporting our measurements in Changchun 22.11.2018 | A. Geese, U. Auster, M. Korte | DI3 - Improved Absolute Directional Measurement |