The Ørsted Satellite Project

A Danish Microsatellite With a High Scientific Profile

Papers and reports


ABSOLUTE CALIBRATION AND ALIGNMENT OF VECTOR MAGNETOMETERS IN THE EARTH'S FIELD

 

Merayo, J.M.G. (1), P. Brauer (1), F. Primdahl (1,2), and J.R. Petersen (2)

 

  1. Technical University of Denmark, Department of Automation, Building 327, DK-2800 Lyngby, Denmark. Phone: +45 4525 3452, Fax: +45 45 88 71 33, E-mail: jmgm@iau.dtu.dk
  2. Danish Space Research Institute, Juliane Maries Vej 30, DK-2100 Copenhagen Ø, Denmark.

 

Abstract. The 12 coefficients of a vector magnetometer: 3 offsets, 3 scale factors, 3 non-orthogonal angles and 3 Euler angles are determined only by exposing the instrument to the Earth's magnetic field. Initially, a least-squares linearized scalar calibration is performed in order to estimate the first 9 parameters of the magnetometer in its intrinsic reference frame. This is done by relating the sum of the squares of the components to the squared output of an absolute scalar proton magnetometer. Finally, the last 3 parameters are obtained by comparing the output to that of a geodetically oriented reference vector magnetometer. In this case, a star camera attached to the instrument on a common optical bench is used to provide the bench attitude in celestial coordinates. Thereby, the relation between the magnetic sensor and the absolute star camera systems is established. The Swedish Astrid-2 satellite was set up at the Lovö magnetic observatory on the night 15-16 of May 1997. After turning the system into different directions relative to the magnetic field, the Astrid-2 triaxial magnetometer was successfully calibrated and the 12 parameters were found. These parameters were estimated with an absolute accuracy smaller than 1.5 nTRMS and an angular pointing accuracy of 6 arcsec. This inexpensive procedure has proven to be very reliable and robust, and it allows for a solution without local minima in the estimator cost function. It may be used for the pre-flight as well as for the in-flight calibrations of space-borne magnetometers. In flight the combined time delays of the instrumentation and a suitable IGRF model have to be taken into account.