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The imaging of fast-moving electron-density structures in the polar cap presents a unique set of challenges that&#13; are not encountered in other ionospheric imaging problems. GPS observations of total electron content in the polar&#13; cap are sparse compared to other regions in the Northern Hemisphere. Furthermore, the slow relative motion&#13; of the satellites across the sky complicates the problem since the velocity of the plasma can be large in comparison&#13; and traditional approaches could result in image blurring. This paper presents a Kalman-filter based method&#13; that incorporates a forward projection of the solution based on a model plasma drift velocity field. This is the&#13; first time that the plasma motion, rather than just integrations of electron density, has been used in an ionospheric&#13; imaging algorithm. The motion is derived from the Weimer model of the electric field. It is shown that this&#13; novel approach to the implementation of a Kalman filter provides a detailed view of the polar cap ionosphere&#13; under severe storm conditions. A case study is given for the October 2003 Halloween storm where verification&#13; is provided by incoherent scatter radars

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