Enhancing the ISIS-I Topside Digital Ionogram Database

Selected original analog telemetry tapes from three of the topside-sounder satellites of theInternational Satellites for Ionospheric Studies (ISIS) program, namely Alouette 2, ISIS I, and ISIS II, wereused in an earlier project to produce more than million digital topside ionograms; the resulting digitaltopside ionograms from ISIS II were used to produce more than 86,000 globally distributed vertical topsideionospheric electron density profiles Ne(h) that cover a time span of more than a solar cycle. These Ne(h) wereproduced using the Topside Ionogram Scaler with True height algorithm auto-scaling software. Beforeattempting to automatically process Alouette-2 or ISIS-I ionograms, a data-enhancement project wasinitiated so as to increase the number of ionograms suitable for manual scaling and to increase theauto-processing success rate. These enhancements were mainly to correct problems that often occurredduring the analog-to-digital conversion of the original telemetry tapes. Here we illustrate the improvementsmade to the ISIS-I digital topside ionograms and compare Ne values at the satellite altitude and Ne(h)profiles, based on the manual scaling of selected ionograms, to both the auto-scaled values and thepredictions of the International Reference Ionosphere 2016 model. The results indicate the need to improvethe available auto-processing software for the new ISIS-I digital ionograms and that International ReferenceIonosphere 2016 predicts midlatitude winter topside Ne values that are too high in the late morning andat noon but too low in the early morning