*3.4. Peak Electron Density Height*

Diurnal variations significantly impact the ionosphere, where daytime and nighttime conditions manifest contrasting characteristics. The properties of the ionosphere, such as height, ionized particle concentration, and the presence of distinct layers, change dynamically over time. Regions characterized by high electron densities are designated as the D, E, and F layers. In diurnal cycles, the F layer undergoes separation into two distinct layers termed the F1 and F2 during daytime, while the D layer experiences complete dissipation throughout the nocturnal period [27]. This shifts the height at which the high electron concentration is found. In order to analyze changes in the ionospheric altitude, the height corresponding to the maximum peak of the electron density profile (*Hm*) is used as the reference point. *Hm* is obtained for both the incident and reflected rays using the NEDM2020 model.

The LEO GNSS-R space-borne configuration, which enables the simultaneous collection of data from multiple reflections, presents several advantages for ionospheric studies. Firstly, thanks to the fast trajectory change of the LEO satellite, the GNSS-R signal rapidly scans along the ionospheric layers, providing a snapshot view of ionospheric structures [8]. Secondly, the ability to obtain peak electron density points at different locations within a short time interval allows for the mapping of ionospheric structures at varying distances. Assuming the Earth's radius is 6371 km, with a maximum electron density ionospheric shell at a 300 km height, the distance between the incident and reflected *Hm* points varies depending on the elevation angle as observed in Figure 6.

**Figure 6.** Distances between peak electron density height points depending on the elevation angle change at 300 km height.

#### **4. Results**
