**3. Methodology**

#### *3.1. Electron Density Models*

The electron density in this study is obtained from two three-dimensional and timedependent electron density models: the Neustrelitz Electron Density Model (NEDM2020) [18] and the NeQuick 2 model [15]. For both models, the input values depending on solar activity are the solar radio flux index F10.7, month, geographic latitude and longitude, height, and universal time (UT). The output obtained is the electron concentration at the specified location and time.

The NeQuick 2 model was developed at the Aeronomy and Radiopropagation Laboratory of The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy, and at the Institute for Geophysics, Astrophysics, and Meteorology (IGAM) of the University of Graz, Austria. This model comprises vertical profiles consisting of multiple Epstein layers, and it derives essential electron peak density and height parameters through spatial and temporal interpolation from a comprehensive set of global maps. Consequently, NeQuick 2 incurs significant computational demands in terms of time and processing power [14].

On the other hand, the NEDM2020 model was developed at the German Aerospace Center in the Institute for Solar–Terrestrial Physics (DLR-SO), Neustrelitz, Germany. Including the NTCM model, this model relies on about 100 model coefficients and a set of empirically fixed parameters. Remarkably, the electron density values can be directly computed for any specified location and time without the requirement for the specialized temporal or spatial interpolation of parameters, making it faster than the NeQuick 2 model in terms of computational efficiency [21].

A model comparison of electron density profiles is presented in Figure 5 featuring one example at very low (first row) and mid-low (second row) elevation angle events. The first column displays the electron density per ray mapped along the specular point change using the NEDM2020 model. The subsequent columns (second, third, and fourth) illustrate the electron density profile comparison between the NEDM2020 and NeQuick 2 models for the incident, reflected, and direct rays, respectively.

**Figure 5.** Electron density variations along the change and model profile comparison for the incident, reflected, and direct rays at very low and mid-low elevation angles (F10.7 = 75).
