Methods for Correction of the Altitude Electron-Density Profiles of the IRI Model for the Bottomside Ionosphere from Satellite Sounding Data

We offer a comparative analysis and a brief description of three methods for reconstruction of altitude dependences of the ionospheric electron density from topside satellite ionograms containing traces of sounding signal reflections from the Earth’s surface. In all methods, topside profiles are calculated from the x trace of the ionogram in the classical way. To reconstruct the electrondensity profiles in the bottomside ionosphere and refine the cutoff frequency and the altitude of the F2-layer maximum, frequency dependences of the group paths of signals reflected both from the Earth’s surface and from the F2 region in the topside ionosphere are simultaneously used. In two methods, the desired profiles are represented by layers of model distributions with a limited number of parameters, the values of which are found by minimizing the deviations of the calculated group paths from the experimental ones. The resulting profiles can be mapped into IRI model profiles using the cutoff frequency and the altitude of the F2-layer maximum, as well as two parameters determining the shape of the profile in the F region, which are additionally calculated. A new (third) method is given in which the entire bottomside ionosphere is represented by the corrected profile from the IRI model. The profile is fitted to the experimental data by varying the key parameters of the model. Verification of the methods in a model experiment using rocket measurements of the electron density showed that the reconstructed profiles are in good agreement in the F region with each other and with the rocket profile. A fundamental possibility for diagnosing the F1 layer based on high-accuracy experimental data is shown. Examples of calculations of the total (from the satellite altitude) profiles using the satellite ISIS-2 ionograms are given. Recommendations on the practical use of the methods are formulated.