Simultaneous observations of the main trough using GPS imaging and the EISCAT radar

Images of the winter-time ionosphere over Northern Scandinavia in January 2002 from two independent experimental techniques are presented. In the first case, observations of differential phase delay from the GPS satellites are used in an inversion algorithm, called MIDAS (Multi Instrument Data Analysis Software), to estimate the spatial distribution of electron concentration. The second approach uses the European Incoherent Scatter (EISCAT) radar situated near Tromso in northern Norway to gather independent data for comparison with the MIDAS images. The EISCAT data are plotted as "fan plots" that show electron concentration as a function of latitude and range, whilst the MIDAS results are presented in the form of latitude-altitude crosssections at the locations and times coincident with the radar scans. Wide-area maps of Total Electron Content (TEC) are also shown for the post-noon period. The position and time evolution of the trough seen in the MIDAS images is confirmed by four scans of the EISCAT radar in the afternoon period. The results demonstrate that GPS imaging is capable of locating the main trough, and confirm the potential of MIDAS imaging as a tool for routine monitoring of the ionosphere.