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Abstract

Modeling of the topside ionosphere (from F peak to ~2000 km) suffers from a scarcity of data because ground ionosondes only reach up to the F peak. Millions of topside ionograms had been recorded by the Alouette 1,2 and ISIS 1,2 satellites between 1962 and 1990 that were never fully analyzed. The satellites carried topside sounders, the satellite equivalent of the ground-based ionosonde, and provided the first global view of the topside ionosphere. The topside sounders were designed as analog systems that recorded ionograms on 35 mm film for analysis by visual inspection. Many nations participated in the data analysis process that involved manual scaling of the ionograms and inversion into electron density profiles. But because of the tedious manual process only a small percentage of the recorded ionograms was converted to electron density profiles. We were able to digitize a significant portion of the 60 satellite years of analog data before the tapes were discarded. In a second step we worked with a team at the University of Massachusetts Lowell who developed the Topside Ionogram Scalar with True-Height inversion (TOPIST) software for the automated scaling and inversion of the traces on the digital ionograms into electron density profiles thus avoiding the very limiting manual process. As a result of our project close to a million digital topside ionograms and electron density profiles are now available for browsing/plotting/downloading at NASA's Space Physics Data Facility (https://spdf.gsfc.nasa.gov). We will review some of the science results based on the digital data.