T. Risbo

Ørsted Initial Field Model

Magnetic measurements taken by the Orsted satellite during geomagnetic quiet conditions around Jan-uary 1, 2000 have been used to derive a spherical harmonic model of the Earths magnetic field for epoch 2000.0. The maximum degree and order of the model is 19 for internal, and 2 for external, source fields; however, coefficients above degree 14 may not be robust. Such a detailed model exists for only one previous epoch, 1980. Achieved rms misfit is < 2 nT for the scalar intensity and < 3 nT for one of the vector components perpendicular to the magnetic field. For scientific purposes related to the Orsted mission, this model supercedes IGRF 2000.

Ørsted satellite captures high‐precision geomagnetic field data

Space-based, high-precision magnetometry is essential for understanding a variety of phenomena ranging from secular variation of the Earths main field, through the signatures of crustal magnetism and the effects of plasma currents flowing externally to the Earth. Orsted, Denmarks first satellite, was launched on February 23, 1999 into a polar, low-Earth orbit to provide the first near-global set of high-precision geomagnetic observations since the Magsat mission of 1979–1980 (see Magsat Special Issue of Geophysical Research Letters., vol. 9, no. 4, pp. 239–379, 1982). With the new mapping of the Earths magnetic field, the International Geomagnetic Reference Field model (IGRF), a standard model used for navigation, prospecting, and other practical purposes, has been determined with improved precision for epoch 2000 [Olsen et al., 2000a; Mandea and Langlais, 2000]. The satellite has routinely provided high-precision vector data since August 1999, and the mission is continuing well beyond its nominal 14-month lifetime into 2001.

A high-precision triaxial fluxgate sensor for space applications: Layout and choice of materials

Abstract The construction of a triaxial fluxgate sensor with very high axis stability and low temperature coefficients is described. The axis orthogonalities change less than 2.1 s of are in the whole testing temperature range +20 to −10°C. The temperature coefficients for the sensitivities of the three axes are 6.7, 10.1 and 13.3 ppm K −1 , respectively. This high stability is achieved by using a newly developed ceramic, CSiC, as the supporting construction material.

The orthogonalization of magnetic systems

The construction of an orthogonal reference frame based on a set of three skew axes for a magnetic coil system and a magnetic sensor is discussed and presented. For a skew system, it is possible to define the coil axes and the magnetic axes as a dual set of axes that are linked to the system. Therefore, one orthogonal reference frame can be identified from the coil axes and another from the magnetic axes. Although this representation is not unique, it is the most intuitive visual representation as it is shown. The parametrizations based on the operation of the fluxgate transducer for the magnetic sensors compact spherical coil (CSC) (Orsted satellite) and compact detector coil (CDC) (Astrid-2 satellite) are analyzed and identified. In principle, only the transformation matrix that orthogonalizes the sensor is needed, but it is customary to express this matrix as a function of some non-orthogonal angles. Therefore, most relevant conventions from the literature are presented for comparison. All the representations agree for the case of small angle approximation, which is valid for most sensors.

In-flight spacecraft magnetic field monitoring using scalar/vector gradiometry

Earth magnetic field mapping from planetary orbiting satellites requires a spacecraft magnetic field environment control program combined with the deployment of the magnetic sensors on a boom in order to reduce the measurement error caused by the local spacecraft field. Magnetic mapping missions (Magsat, Oersted, CHAMP, SAC-C MMP and the planned ESA Swarm project) carry a vector magnetometer and an absolute scalar magnetometer for in-flight calibration of the vector magnetometer scale values and for monitoring of the inter-axes angles and offsets over time intervals from months to years. This is done by comparing the two magnetometer outputs for several days and for as many different external field directions and amplitudes in the satellite frame as available. The vector and the scalar sensor may be placed of the order of 2 m apart and at the end of an about 10 m long boom counted from the spacecraft centre-of-gravity. In line with the classical dual vector sensors technique for monitoring the spacecraft magnetic field, this paper proposes and demonstrates that a similar combined scalar/vector gradiometry technique is feasible by using the measurements from the boom-mounted scalar and vector sensors onboard the Oersted satellite. For Oersted, a large difference between the pre-flight determined spacecraft magnetic field and the in-flight estimate exists causing some concern about the general applicability of the dual sensors technique.

A method for the determination of three Euler angles for the SAC-C satellite magnetic mapper probe instrument package

Abstract The pre-flight determination of the relative orientation between the CSC vector magnetometer and the Star IMager in the Magnetic Mapper Probe on-board the Argentinean SAC-C satellite is described. Key elements of the instrumentation are given and the inter-calibration is attained using a temporary reference magnetometer and the satellite instrument package. The relative orientation is obtained with accuracy in the arcsec range. As opposed to previous methods the orientation of the reference magnetometer need not be known a priori, but is determined to within a few degrees, which is enough for the accurate determination of the CSC/SIM Euler angles.