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

XII th IAGA Workshop, Belsk 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

XII th IAGA Workshop, Belsk Motivation Auster H.U., V.Auster, A new method for performing an absolute measurement of the geomagnetic field, Meas. Sci. Technol. 14, , 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

XII th IAGA Workshop, Belsk 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 )

XII th IAGA Workshop, Belsk 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

XII th IAGA Workshop, Belsk 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

XII th IAGA Workshop, Belsk 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

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

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

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

XII th IAGA Workshop, Belsk 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

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

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

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

XII th IAGA Workshop, Belsk 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

XII th IAGA Workshop, Belsk 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)

XII th IAGA Workshop, Belsk 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)

XII th IAGA Workshop, Belsk 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

XII th IAGA Workshop, Belsk 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

XII th IAGA Workshop, Belsk Magnetic Requirements for Accommodation

XII th IAGA Workshop, Belsk Accommodation in Belsk

XII th IAGA Workshop, Belsk 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

XII th IAGA Workshop, Belsk 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

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