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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 26, issue 11
Ann. Geophys., 26, 3491–3499, 2008
https://doi.org/10.5194/angeo-26-3491-2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 26, 3491–3499, 2008
https://doi.org/10.5194/angeo-26-3491-2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.

  10 Nov 2008

10 Nov 2008

GALS – Gradient Analysis by Least Squares

M. Hamrin1, K. Rönnmark1, N. Börlin2, J. Vedin1, and A. Vaivads3 M. Hamrin et al.
  • 1Department of Physics, Umeå University, Umeå, Sweden
  • 2Department of Computing Science, Umeå University, Umeå, Sweden
  • 3Swedish Institute of Space Physics, Uppsala, Sweden

Abstract. We present a method, GALS (Gradient Analysis by Least Squares) for estimating the gradient of a physical field from multi-spacecraft observations. To obtain the best possible spatial resolution, the gradient is estimated in the frame of reference where structures in the field are essentially locally stationary. The estimates are refined iteratively by a least squares method.

We show that GALS is not very sensitive to the spacecraft configuration and resolves structures much smaller than the characteristic size of the spacecraft distribution. Furthermore, GALS requires little user input.

GALS has been tested on synthetic magnetic field data and data from the Cluster FGM instrument. GALS will also be useful for other types of data. The results indicate that GALS is robust and superior to the curlometer method for estimating the current from magnetic field measurements.

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