*Editorial* **Editorial for the Special Issue "GNSS, Space Weather and TEC Special Features"**

**Serdjo Kos 1,\*, José Fernández <sup>2</sup> and Juan F. Prieto <sup>3</sup>**


For high-quality scientific communication in the field of technical and natural sciences, it is of utmost importance to ensure clarity of the text, logical mathematical argumentation, and the possibility of verifying the obtained theoretical results using appropriate experiments.

The publication of research results requires the skill of scientifically communicating relevant data and their mutual logical connection into a purposeful and comprehensible whole.

In the domain of electronic navigation, satellite navigation (GNSS) is one of the most important modern complex systems. GNSS is a key infrastructure for supporting the development and improvement of not only navigation and civil engineering infrastructures but also power grid systems, banking operations, global transportation systems, and global communication systems. Today, GNSS requires the use of several positioning networks and sensors, such as radio networks and micro electromechanical systems (MEMS), among others. Earth's atmosphere, especially the ionosphere, troposphere, etc., is a huge laboratory where multiple processes and phenomena occur that directly affect the propagation of electromagnetic waves. Like all complex systems, GNSS technology also undergoes certain evolutionary stages. Some factors affecting the future evolution of GNSS technology include the appearance of new signals and frequencies and the use of complementary technologies, but in the domain of GNSS technologies, it is essential to study the impact of space weather on GNSS systems. Another area of research related to GNSS technologies is vertical Total Electron Content (TEC) distribution and anomalies related to earthquakes and volcanic eruptions on Earth.

There are many challenges that must be addressed, because they affect the reliability, accuracy, and all other essential parameters of GNSS systems. This Special Issue seeks to address some of these issues by publishing manuscripts on topics such as GNSS risk assessment, different effects of space weather disturbances on the operation of GNSS systems, environmental impacts on the operation of GNSS systems, GNSS positioning error budgets, TEC special features in volcano eruptions. A total of 17 scientific papers are published. Some specific updates and improvements presented in this Special Issue include the following:

− Contribution to the research of the effects of Etna volcano activity on the features of the Ionospheric Total Electron Content behaviour—In this paper [1], volcanic activity was modeled using volcanic radiative power (VRP) data obtained using the Middle InfraRed Observation of Volcanic Activity (MIROVA) system. The estimated minimal night TEC values were averaged over defined index days of the VRP increase. During the analyzed period of 19 years, volcano activity was categorized according to pre-defined criteria. The influence of current space weather and short-term solar activity on TEC near the volcano was systematically minimized. The results showed

**Citation:** Kos, S.; Fernández, J.; Prieto, J.F. Editorial for the Special Issue "GNSS, Space Weather and TEC Special Features". *Remote Sens.* **2023**, *15*, 1182. https://doi.org/ 10.3390/rs15051182

Received: 28 January 2023 Revised: 13 February 2023 Accepted: 13 February 2023 Published: 21 February 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

mean/median TEC increases of approximately +3 standard deviations from the overall mean values, with peak values placed approximately 5 days before the VRP increase and followed by general TEC depletion around the time of the actual volcanic activity increase. Additionally, a TEC oscillation pattern was found over the volcano site with a half-period of 6.25 days. The results mainly indicate that the volcanic activity modified the ionospheric dynamics within the nearby ionospheric region before the actual VRP increase, and that the residual impact in the volcano's surrounding area could be attributed to terrestrial endogenous processes and air–Earth currents. These changes could be detected according to criteria predefined in the research: during quiet space weather conditions, while observing night-time TEC values, and within the limits of low short-term solar influence.


tive Noise (CEEMDAN) landslide displacement prediction. The CEEMDAN method was implemented to ingest a landslide Global Navigation Satellite System (GNSS) time series. The AMLSTM algorithm was then used to realize prediction work, in conjunction with multiple impact factors. The Baishuihe landslide was adopted to illustrate the capabilities of the model. The results showed that the CEEMDAN-AMLSTM model achieved competitive accuracy and has significant potential for landslide displacement prediction.


the Differential Global Positioning System (DGPS) (900 000 fixes), and the European Geostationary Navigation Overlay Service (EGNOS) (900 000 fixes). Research performed on real data showed that the reliability method provided a better estimate of navigation system positioning accuracy compared to the 2DRMS measure.


previously been investigated or published. The resultant positions of the coordinates were created by deviations in the coordinates along the *Y* and *Z* axes; in the vertical plane of space, the deviations of the coordinate X (horizontal plane) were mostly uniform and independent of deviations along the *Y* and *Z* axes. The proposed model showed the realized state of the statistical position equilibrium of the selected GNSS stations, which were observed using RTE values. Although it is of regional character, the model is suitable for application in larger areas with similar climatological profiles and for users who do not require the achievement of a maximum level of geodetic accuracy using Satellite-Based Augmentation Systems (SBAS) or other more advanced, time-consuming, and equipment-consuming positioning techniques.

A series of scientific papers were published in this Special Issue that have made a significant scientific contribution to its thematic domain (more detailed scientific contributions are presented for each published article); however, there are many questions and unknowns to be solved using appropriate scientific methods and research, for example, investigating and establishing the regularity of the dynamics of changes in the user coordinates X, Y, Z along the coordinate axes x,y,z as a function of the ionospheric delay of the satellite signal, or the effects of the influence of volcanic eruptions on satellite determination of the user's position.

Just as science itself has no end or completion, the scientific research conducted in the domain of this Special Issue is neither finished nor completed; however, it will continue to be conducted in the future, with the aim of developing a deeper understanding of and scientific explanations for a series of processes related to this topic.

**Funding:** This research was funded by the University of Rijeka grant number—uniri—ethnic—18–66 and by grant G2HOTSPOTS (PID2021-122142OB-I00) from the MCIN/AEI/10.13039/501100011033/ FEDER, UE. This work represents a contribution to CSIC Thematic Interdisciplinary Platform TELEDETEC.

**Data Availability Statement:** Data Availability are presented in each mentioned paper described in this Editorial article.

**Conflicts of Interest:** The author declares no conflict of interest.

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