## 1 Introduction
The DEMETER satellite had been orbiting at a Sun-synchronous circular orbit, having an approximate altitude of 710 km and inclination of 98.2\({}^{\circ}\). The scientific payload on the DEMETER satellite included a Langmuir probe (LP) measuring Ne and electron temperature. DEMETER provided observations of electromagnetic fluctuations related to earthquakes [24; 25]. DEMETER data have also been examined in various ways to define the perturbations of the ionosphere caused by acoustic gravity waves from earthquakes [24; 25; 26; 27]. The ionospheric disturbances associated with preseismic activity were also investigated ina study based on DEMETER data, conducted by [PERSON] et al. [28], and studies combining GNSS and DEMETER data conducted by [PERSON] et al. [29] and [PERSON] et al. [30]. The existing satellite missions that include LPs amongst the scientific payloads are the first European Space Agency (ESA) constellation mission for Earth observation called Swarm [31; 32] and the Chinese-Italian space mission named the China Seismo-Electromagnetic Satellite (CSES) [33]. The Swarm constellation comprises three satellites, which compose the fifth Earth Explorer mission that was approved in ESA's Living Planet Program, and they were successfully launched on 22 November 2013. The orbits of Swarm Alpha (Swarm A) and Charlie (Swarm C) have an initial altitude of 460 km and inclination of 87.4\({}^{\circ}\), whereas Swarm Bravo (Swarm B) runs at an altitude of 530 km and at a 88\({}^{\circ}\) inclination angle. The research objective of the Swarm mission is to provide the best-ever survey of the geomagnetic field and electric field in the atmosphere using precise magnetometers and electric field instruments. Very frequently, Swarm data studies related to earthquakes incorporate magnetic data from all three satellites. There is published evidence of precursory signals in the magnetic data [34; 35], as well as works referring to co-seismic signals in the magnetic field [36; 37; 38]. [PERSON] et al. [35] referred to the extended number of earthquakes, including ones of smaller magnitudes, and showed one example of spectral recognition of disturbed signals, which is also an objective of our current study. [PERSON] et al. [39] analyzed the seismic precursory magnetic anomalies measured onboard Swarm together with different additional data, like thermal anomalies from other explorer satellites, like Terra and Aqua. Aside from the magnetic sensors, the Swarm payload also includes LPs and GNSS receivers for precise orbit determination, which can be used to observe in situ ionospheric Ne and topside TEC, respectively. [PERSON] et al. [40] jointly studied the variations in magnetic and electric field parameters as precursory to some moderate-magnitude earthquakes in Romania. A stronger event in Mexico was investigated by [PERSON] and [PERSON] [41] with the application of magnetic and Ne data, whereas [PERSON] et al. [42] have studied seismic sequences in Italy using a variety of Swarm observations. In terms of earthquake number, an extended study was conducted by [PERSON] et al. [43], who prepared a statistical assessment of magnetic and Ne disturbances related to 12 earthquakes of various magnitudes. The satellite of the CSES mission that is dedicated to monitoring electromagnetic fields was launched on 2 February 2018. It is equipped with instruments that are similar to Swarm's, capable of observing electric and magnetic fields from a Sun-synchronous orbit at an altitude of around 500 km, with an inclination of around 97.3\({}^{\circ}\). There are already works based on CSES data related to selected earthquakes by [PERSON] et al. [44] and groups of similar large earthquakes by [PERSON] et al. [45]. [PERSON] et al. [46], as well as [PERSON] et al. [45], analyzed CSES data focusing on precursory signals with respect to earthquakes. [PERSON] et al. [42] have also investigated possible LAIC effects prior to the M = 7.5 earthquake using, among the others, Swarm and CSES datasets. [PERSON] et al.