Enhancing the ISIS-I Topside Digital Ionogram Database

Abstract

Selected original analog telemetry tapes from three of the topside-sounder satellites of the International Satellites for Ionospheric Studies (ISIS) program, namely Alouette 2, ISIS I, and ISIS II, were used in an earlier project to produce more than ½ million digital topside ionograms; the resulting digital topside ionograms from ISIS II were used to produce more than 86,000 globally distributed vertical topside ionospheric electron density profiles Ne(h) that cover a time span of more than a solar cycle. These Ne(h) were produced using the Topside Ionogram Scaler with True height algorithm auto-scaling software. Before attempting to automatically process Alouette-2 or ISIS-I ionograms, a data-enhancement project was initiated so as to increase the number of ionograms suitable for manual scaling and to increase the auto-processing success rate. These enhancements were mainly to correct problems that often occurred during the analog-to-digital conversion of the original telemetry tapes. Here we illustrate the improvements made 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 the predictions of the International Reference Ionosphere 2016 model. The results indicate the need to improve the available auto-processing software for the new ISIS-I digital ionograms and that International Reference Ionosphere 2016 predicts midlatitude winter topside Ne values that are too high in the late morning and at noon but too low in the early morning.