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 ½ 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.