Comparison of EISCAT and ionosonde electron densities: application to a ground-based ionospheric segment of a space weather programme

Space weather applications require real-time data and wide area observations from both groundand spacebased instrumentation. From space, the global navigation satellite system – GPS – is an important tool. From the ground the incoherent scatter (IS) radar technique permits a direct measurement up to the topside region, while ionosondes give good measurements of the lower part of the ionosphere. An important issue is the intercalibration of these various instruments. In this paper, we address the intercomparison of the EISCAT IS radar and two ionosondes located at Tromsø (Norway), at times when GPS measurements were also available. We show that even EISCAT data calibrated using ionosonde data can lead to different values of total electron content (TEC) when compared to that obtained from GPS.