Stolle, C., Schlüter, S., Jacobi, C., Jakowski, N., Heise, S., Raabe, A. (2005): Three-Dimensional Monitoring of the Polar Ionosphere with Ground- and Space-Based GPS. - In: Reigber, C., Lühr, H., Schwintzer, P., Wickert, J. (Eds.), Earth Observation with CHAMP: Results from Three Years in Orbit, Spinger, 477-482.