1. An Automatic Instrument to Measure the Absolute Components of the Earth's Magnetic Field H.-U. Auster, M. Mandea, A. Hemshorn, E. Pulz, M. Korte

2. XII th IAGA Workshop, Belsk 2006 2 Outline  Fundamentals of the Method  Magnetic field along a rotation axis  Elimination of systematic measurement errors  Manually performed test of the method in Niemegk  Automation  Magnetometers  Mechanics & Optics  Controlling  Set up in Belsk  Outlook

3. XII th IAGA Workshop, Belsk 2006 3 Motivation Auster H.U., V.Auster, A new method for performing an absolute measurement of the geomagnetic field, Meas. Sci. Technol. 14, 1013-1017, 2003 Manually performed absolute measurement in Hermanus by rotation of a fluxgate magnetometer about two well defined axes Ongoing activities to automate absolute measurement  Automating of DI-Flux  Manipulation of vector proton magnetometer  Automating of rotation of a vector fluxgate magnetometer about two well defined axes

4. XII th IAGA Workshop, Belsk 2006 4 Magnetic field along a rotation axis (1) Co-ordinate systems  Red: arbitrary oriented fluxgate magnetometer  Black: Geophysical reference system  Relation between both: Euler angles Rotation about Precession angle  i variable   and  constant  B z = B z ( υ, φ )

5. XII th IAGA Workshop, Belsk 2006 5 Magnetic field along a rotation axis (2) Computation of field in rotation axis  Three independent measurements with arbitrary  I necessary  Magnitude of B in direction of rotation axis becomes independent from sensor orientation angles  and Matrix MB of measurement results Unit vector of sensor orientation

6. XII th IAGA Workshop, Belsk 2006 6 Measurement Procedure  Rotation A to adjust mechanical axis to azimuth marks  Rotation B to turn the sensor about the mechanical axes  Always 360° forward and backward  6 measurement stops each rotation direction (B and azimuth)  Rotation C for magnetometer calibration x y y x  Measurement time: 30 minutes

7. XII th IAGA Workshop, Belsk 2006 7 Elimination of systematic measurement errors  Magnetometer errors by scalar calibration  Rotation about two axes sufficient for full determination of linear transfer function (offsets, scale factors, non orthogonality)  Full Earth field magnetometer necessary, high requirements on linearity (10 -5 )  Orientation of rotation axes  Horizontal balance by level tube, misalignment of level tube eliminated by interchanging of its ends  Azimuth by telescope, misalignment of optical axis and rotation axis eliminated by rotation of telescope

8. XII th IAGA Workshop, Belsk 2006 8 Measurement Results of one year operation in Niemegk -  Z Standard deviation: 1.0nT 20052006

9. XII th IAGA Workshop, Belsk 2006 9 Measurement Results of one year operation in Niemegk -  D Standard deviation after trend and readjustment correction: 0.6nT 20052006

10. XII th IAGA Workshop, Belsk 2006 10 Measurement Results of one year operation in Niemegk - Magnetometer

11. XII th IAGA Workshop, Belsk 2006 11 Steps to automation  Magnetometers  Optical control  Mechanics: 3 Rotations  Rotation about measurement axis - arbitrary angles  Turn Table - arbitrary, but well known angle  Sensor rotation - arbitrary angle  Controlling  Hardware  Software

12. XII th IAGA Workshop, Belsk 2006 12 Magnetometers  two digital 3-axes fluxgate magnetometers  range: 64000nT  resolution: 0.01nT  Non linearity < 10 -5  Serial & Flashcard interface  Proton-Magnetometer  Range: 20000-64000nT  resolution 0.01nT  Serial & Flashcard interface basket magnetometer scalar magnetometer variometer

13. XII th IAGA Workshop, Belsk 2006 13 Performance of Magnetometers Variometer Basket magnetometer Observatory Data

14. XII th IAGA Workshop, Belsk 2006 14 Performance of Magnetometers Variometer - Obs Basket - Obs Variometer - Basket

15. XII th IAGA Workshop, Belsk 2006 15 Components of the optical system  Neodym Laser  Coupled in by fibre optics  PSD 2cm x 2cm  Resolution < 0.1 mm  Protected from stray light by  Band-filter (635nm)  Black tube  Azimuth Mark  Made by ceramics  Grounded in concrete Bild PSD

16. XII th IAGA Workshop, Belsk 2006 16 Performance of optical system ~ 15 m 0.2mm  = atan(0.2mm/15 m) ~ 3'' Stability of azimuth mark:  Quarzgut 0.5 ppm/°C  Displacement < 0.1 mm (h=2m,  T = 50°C)

17. XII th IAGA Workshop, Belsk 2006 17 Rotation A by Pneumatics  Pointing requirements:  1cm/20m  0.1mm/20cm  2arcmin  Well defined end positions necessary  7kg has to be rotated  Low friction by bearing  Importance of surface treatment  Pressure supply necessary (2 bar)

18. XII th IAGA Workshop, Belsk 2006 18 Rotation B & C by Piezo Motors (1)Application example (2)Linear motor (3)Rotation to linear conversation (4)Final solution using gravitation Attempts to develop non magnetic motors for sensor rotation

19. XII th IAGA Workshop, Belsk 2006 19 Control Unit  GPS controlled Timing  Motor control  rotation about measurement axis by piezo motor  Flip mechanism by piezo motor  Pneumatic control  Turn table rotation by two valves  Laser switching and PSD read out  Magnetometer control  Pre processing of data

20. XII th IAGA Workshop, Belsk 2006 20 Magnetic Requirements for Accommodation

21. XII th IAGA Workshop, Belsk 2006 21 Accommodation in Belsk

22. XII th IAGA Workshop, Belsk 2006 22 Outlook  System has to run permanently in Niemegk  Reliability have to be tested and improved  Redesign of laser optics and some mechanical parts  Option: Replacement of pneumatics by Piezo motor driven system  New design for lower latitudes

23. XII th IAGA Workshop, Belsk 2006 23 Acknowledgement  GFZ for personal and financial investigation  All the the people designed and manufactured the mechanics (in Niemegk Potsdam Braunschweig Lindau and Garching)  Magson for magnetometers and software support  Belsk observatory for support to install the facility

24. XII th IAGA Workshop, Belsk 2006 24 Measurement Results of one year operation in Niemegk -  H Standard deviation: 1.4nT