Imaging of fast moving electron-density structures in the polar cap

The imaging of fast-moving electron-density structures in the polar cap presents a unique set of challenges that
are not encountered in other ionospheric imaging problems. GPS observations of total electron content in the polar
cap are sparse compared to other regions in the Northern Hemisphere. Furthermore, the slow relative motion
of the satellites across the sky complicates the problem since the velocity of the plasma can be large in comparison
and traditional approaches could result in image blurring. This paper presents a Kalman-filter based method
that incorporates a forward projection of the solution based on a model plasma drift velocity field. This is the
first time that the plasma motion, rather than just integrations of electron density, has been used in an ionospheric
imaging algorithm. The motion is derived from the Weimer model of the electric field. It is shown that this
novel approach to the implementation of a Kalman filter provides a detailed view of the polar cap ionosphere
under severe storm conditions. A case study is given for the October 2003 Halloween storm where verification
is provided by incoherent scatter radars.

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