## 1 Introduction  
Studies of seismically induced ionospheric disturbances (SIIDs) are typically limited to selected large earthquakes or to the list of events that have a significant magnitude and directly trigger local SIIDs. However, tectonic processes are very complex and related to various types of motions of the Earth's lithosphere, as well as to the generation of electric charge and chemical reactions [1; 2; 3]. The accumulated energy is released from the lithosphere and generates acoustic waves and atmospheric gravity waves that may travel to the atmosphere through weak zones in the Earth's crust that are located at tectonic plate boundaries [4]. These waves cause disturbances in the temperature, pressure, and electromagnetic field [5; 6]. The generated atmospheric gravity waves propagate right up to the ionosphere. When these waves reach the ionosphere, they cause detectable changes in the electron density (Ne) and total electron content (TEC). A strong electric field can also be induced prior to an earthquake, and this is characterized by radioactive particle emanation (mainly radon) and increased conductivity, causing electric field anomalies [2; 7]. There is also an electrostatic channel of seismo-ionospheric coupling described by [PERSON] [8] and [PERSON] et al. [7], in which positive ionization holes are generated from the stressed ground. According to their origin, the ionospheric disturbances can be divided into two categories. The first one refers to the Sun's activity, e.g., the solar flare eruption or coronal mass ejection, while the second one includes anthropogenic and natural events on the Earth. Both categories have different scales and duration times. The disturbances from Earth-based sources last for several hours or days, and their scale is about hundreds or thousands of kilometers [9; 10]. Importantly, the ionospheric anomalies caused by earthquakes or volcano eruptions arise from a process called lithosphere-atmosphere-ionosphere coupling (LAIC) [11; 12; 13; 14; 15]. Due to several tens of satellites and thousands of stations, ground-based Global Navigation Satellite System (GNSS) data are the most promising for research on SIIDs. This fact comes from one main reason: ground-based GNSS observations provide the only reliable spatial view of SIIDs and enable recognition of their spatial shapes and movement velocity. A vast majority of undertaken research related to SIID analyses based on ground-based GNSS data was focused on the identification of different kinds of ionospheric waves and their propagation after large earthquake events [9; 16; 17; 18; 19; 20; 21]. Some of the authors apply statistical analyses of TEC responses to the earthquakes over a longer time span, which are typically a basis for studies on earthquake precursors and preseismic disturbances [22; 23]. The application of ground-based GNSS data is focused on the locations where the stations provide spatially dense observations. There is, however, a limited number of dense GNSS networks. The ground GNSS stations have a heterogeneous distribution worldwide. Moreover, there are also many places along the subducting plate boundaries where GNSS stations are very sparse or unavailable. A low density of GNSS stations significantly impedes the identification of SIIDs in many interesting places and limits the study of them on a global scale. However, the observed increasing number of explorer satellite missions dedicated to global ionosphere observation can significantly extend the global approach. Low Earth orbiting (LEO) satellites can visit all the regions of the Earth, which is interesting for the global investigation of LAIC. An example of a completed satellite mission that was designed to monitor the variations in the atmosphere related to earthquakes is the French DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions) mission, active from 2004 to 2010.