GNSS Radio Occultation: Identification of criticisms in electron density profile retrieval during moderate/high solar activity

NeQuick2 is a quick-run ionospheric electron density model designed for trans-ionospheric propagation applications with improved profile representation of the entire ionosphere (bottom and top side). In this work, NeQuick2 has been used to produce synthetic electron density data in order to define test case scenarios that have been used to study the ionospheric effects on Radio Occultation (RO) signals. Such data will be used to identify possible criticalities both in the standard retrieval algorithms and in the standard ionospheric compensation procedures. As far as the RO data inversion technique in the ionosphere is concerned, the onion-peeling algorithm is the one commonly used. In the framework of this work, it has been implemented and it has been used to extract electron density profiles from the limb sounding total electron content (TEC) measurements (limb TEC in what follows) simulated within the controlled environment generated using NeQuick2. Because of the implicit assumption of electron density spherical symmetry distribution, the onion-peeling algorithm could give erroneous results (e.g. in the retrieved peak electron density) when strong horizontal ionospheric electron density gradients are present, as it could happen in the Equatorial Ionization Anomaly (EIA) region. Indeed, this contribution mainly aims to point out the impact of the solar activity on the electron density profiles retrieval, considering limb sounding observation strategy.