Ionospheric Monitoring Research Articles

Про можливість зондування границь північного аврорального овалу за реєстраціями високочастотних сигналів на наддалеких радіолініях

Objective. Developing a technique for investigation of a dynamic of the equatorial boundary of the night side of the Northern auroral oval using data of registrations of scattered HF signals on superlong radio paths. Methods. Spectral, time, and time-frequency analysis of HF signals from time service stations, recorded at the Ukrainian Antarctic Akademik Vernadsky station (UAS). Selection of the spatial mode of signals scattered on the plasma inhomogeneities of the high latitude ionosphere of the northern hemisphere. The developed method is based on the measurement of the Doppler frequency shift and time of the group delay of the radio signal. Results. The possibility of studying the dynamics of the equatorial boundary of the night side of the Northern auroral oval using characteristics of scattered HF signals of time service stations registered at UAS is demonstrated. Conclusions. In the registrations of HF signals of the RWM station (55.75°N, 37.64°E) at UAS (65.25°S, 64.27°W) it is possible to select the mode scattered on the inhomogeneities of the high-latitude ionosphere of the northern hemisphere. The method for diagnosing the equatorial boundary of the auroral oval by observations on UAS of scattered radio signals from stations of the time service is proposed. It is convenient to use such stations as sources of the probe signal for diagnostic of the ionosphere so far as they have a number of advantages, including low relative frequency instability of master oscillators; weakly directed antennas and sufficiently powerful transmitters thanks to which their signals can be recorded in different regions of the globe; continuous work on a previously known schedule and, finally, the fact that they simultaneously emit at several frequencies, which expands the possibilities of their diagnostic use. The technique does not require additional transmitting devices and expensive antenna systems. The regular measurements using the suggested method allow carrying out the monitoring of auroral ionosphere, which will give the possibility for improving the existent models of its behavior.

Seeking Optimal GNSS Radio Occultation Constellations Using Evolutionary Algorithms

Given the great achievements of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission in providing huge amount of GPS radio occultation (RO) data for weather forecasting, climate research, and ionosphere monitoring, further Global Navigation Satellite System (GNSS) RO missions are being followingly planned. Higher spatial and also temporal sampling rates of RO observations, achievable with higher number of GNSS/receiver satellites or optimization of the Low Earth Orbit (LEO) constellation, are being studied by high number of researches. The objective of this study is to design GNSS RO missions which provide multi-GNSS RO events (ROEs) with the optimal performance over the globe. The navigation signals from GPS, GLONASS, BDS, Galileo, and QZSS are exploited and two constellation patterns, the 2D-lattice flower constellation (2D-LFC) and the 3D-lattice flower constellation (3D-LFC), are used to develop the LEO constellations. To be more specific, two evolutionary algorithms, including the genetic algorithm (GA) and the particle swarm optimization (PSO) algorithm, are used for searching the optimal constellation parameters. The fitness function of the evolutionary algorithms takes into account the spatio-temporal sampling rate. The optimal RO constellations are obtained for which consisting of 6–12 LEO satellites. The optimality of the LEO constellations is evaluated in terms of the number of global ROEs observed during 24 h and the coefficient value of variation (COV) representing the uniformity of the point-to-point distributions of ROEs. It is found that for a certain number of LEO satellites, the PSO algorithm generally performs better than the GA, and the optimal 2D-LFC generally outperforms the optimal 3D-LFC with respect to the uniformity of the spatial and temporal distributions of ROEs.

Ionospheric Detection of Explosive Events

AbstractThe ionospheric response to explosions which occur at or below the Earth's surface has been noted since the first detonations of nuclear devices during the early period of aboveground testing. Acoustic gravity waves and traveling ionospheric disturbances were detected in association with test explosions carried out by the Union of Soviet Socialist Republics in Novaya Zemlya in 1961. While research in this area has continued, the standards accepted by the Comprehensive Nuclear Test Ban Treaty for detection and confirmation of nuclear explosions have been based on (1) seismic, (2) hydroacoustic, (3) infrasound, and (4) radionuclide monitoring from ground detectors. We suggest that ionospheric sensing offers a complementary methodology that may allow for robust confirmation of explosive events. One method of ionospheric monitoring of explosive events is analysis of total electron content (TEC), available by processing data from Global Navigation Satellite System (GNSS) receivers distributed globally on land masses. Traveling ionospheric disturbances observed by their signature in TEC have been used to detect and confirm mine collapses, mine blasts, earthquakes, volcanic eruptions, and meteorite strikes as well as underground nuclear tests. While an integrated measurement like TEC is not as sensitive to small‐amplitude density perturbations as other methods, the existence of large networks of continuously operating GNSS stations makes this an intriguing new monitoring asset. We report on the current capabilities for detection of explosions via the ionosphere, the outstanding challenges, and prospects for future developments that have potential to augment the current standards for detection and confirmation of nuclear detonations. By leveraging the worldwide network of GNSS receivers, robust confirmation of impulsive events is possible. This methodology complements existing technologies approved by the Comprehensive Test Ban Treaty. The article outlines background theory, new approaches to monitoring of explosions, and challenges that remain to be addressed.

Влияние ионосферы и неоднородной структуры Земли на поляризационные характеристики магнитного поля в диапазоне частот 0.2-200 Hz в ближней зоне горизонтальной заземленной антенны

AbstractPolarization characteristics of the field of an on-Earth emitter located at the Kola Peninsula are experimentally measured at a distance that is no greater than the height of an effective ionospheric waveguide in the FENICS-2014 experiment. Variations in the field amplitude and orientation of the major axis of polarization ellipse are observed at lower frequencies upon significant changes of the K index of geomagnetic activity. Polarization characteristics of the horizontal component of magnetic field calculated with allowance for the ionosphere and two-layer Earth structure prove the observed sensitivity of the ultralow- and lower-frequency filed in the near-field zone to the state of ionosphere at lower conductivity of underlying medium. Theoretical results are compared with the experimental data. The results are important for deep sounding of the Earth and monitoring of ionosphere with the aid of controlled low-frequency ground sources.

Near real time ionospheric monitoring system over Malaysia using GPS Data: My-Iono Service

Recently, real time information on the local ionospheric condition is becoming an important need for space and ground based technological systems which are prone to be affected by the local ionospheric state. Knowledge on the impact from the sun activity to the equatorial and low latitude ionosphere is crucial for research and development purpose in all developing nations which are relying on space-based technology systems such as the Global Navigation Satellite System (GNSS). As the first action step to achieve deeper understanding and hands on experience on real time ionospheric monitoring, the National Space Agency of Malaysia (ANGKASA) in collaboration with Universiti Teknologi Malaysia (UTM) has developed the first near real time ionospheric and space weather monitoring system for Malaysia (My-Iono) in year 2015. This web-based platform operates based on the National R&D GPS Continuously operating reference station network (NRC-net). The system runs based on a locally derived algorithm called Equatorial Ionosphere Index (EIX). The EIX was formulated based on 10 years (2004 to 2013) GPS derived empirical Total Electron Content (TEC) data obtained frpm 78 My-RTKnet stations around Malaysia. The fundamental of My-Iono Service consists of vertical TEC maps with a latency of ∼ 2 mins over Malaysia and information on the current ionospheric status; Normal, Medium and Severe, time series of Mean VTEC for station specific, time series of RAte of Change of tEc (RACE) for station specific and time series of Ionospheric Zenith (Iz) Delay for station specific estimated in near real time using GPS observations. This paper presents on the development of My-Iono Service in terms of system design and architecture.

Variations in ionospheric D-region recombination properties during increase of its X-ray heating induced by solar X-ray flare

In this paper we present an analysis of parameters describing the effective recombination processes in the upper ionospheric D-region in the period of its additional heating by the X-radiation emitted during a solar X-ray flare. We present a procedure for calculation of the effective recombination coefficient and electron loss rate in the period when the X-radiation flux detected by the GOES satellite in the wavelength domain between 0.1 and 0.8 nm increases. The developed procedure is based on observational data obtained in the low ionospheric monitoring by the very low/low frequency radio waves and it is related to the considered area and time period. The obtained expressions are applied to data for the very low frequency signal emitted in Germany and recorded in Serbia during the solar X-ray flare detected by the GOES-14 satellite on May 5, 2010.

COMPARISON OF GNSS INDICES, IONOSONDES AND ALL-SKY IMAGERS IN MONITORING THE IONOSPHERE IN BRAZIL DURING QUIET AND DISTURBED DAYS

Abstract Measurements from the Global Navigation Satellite System (GNSS) have become a leading data source for ionospheric studies. Different technologies are used to monitor the ionospheric layer. It is possible to carry out this monitoring using GNSS networks through the indices of ionospheric irregularities, as well as through ionosondes and imagers. It has therefore become essential to correlate these forms of monitoring, presenting their advantages and disadvantages. With this in mind, the aim of this work was to perform an analysis of the behavior of the ionosphere in the Brazilian region through the ionospheric irregularity indices, along with ionosonde information and all-sky optical imagers, for a day of high solar activity (1 March 2014) and a day of low activity (12 April 2015). The results of each monitoring technique were compatible for the different scenarios, showing a moderate and positive correlation between the irregularity indices (FP) and ionosonde parameter. The imagers perform measures of greater spatial extent, however, they need favorable meteorological conditions. The ionosondes present a greater diagnostic capacity of the ionosphere but they are fewer in number than the imagers. The GNSS networks become ionosphere monitoring stations through the irregularity indices, enabling an increase in spatial resolution and a better understanding of ionospheric phenomena in the Brazilian territory.

The DST Group High‐Fidelity, Multichannel Oblique Incidence Ionosonde

AbstractDefence Science and Technology Group has developed a complete oblique incidence ionosonde system to enhance ionospheric monitoring capabilities in support of the Jindalee Operational Radar Network. The Digital Oblique Receiving System, and its counterpart, the Digital Oblique Transmitting System, feature a direct‐digital, multichannel chirp‐sounder design that allows flexible collection of high‐resolution ionograms across many simultaneous paths, without compromising dynamic range. This paper outlines the hardware and software components of the Digital Oblique Receiving System/Digital Oblique Transmitting System, including the onboard signal processing that removes radio frequency interference and fits a parameterized electron density profile to the ionogram. Additional control and data management tools that have enabled the system to be effectively transitioned into routine operations are also described. The typical performance is illustrated through a selection of sample ionograms, highlighting the applications of Digital Oblique Receiving System/Digital Oblique Transmitting System to a wide variety of ionospheric studies, including those requiring Doppler and angle‐of‐arrival observations.

Radiosounding of the High-Latitude Ionosphere with the Arktika-M Hydrometeorological Complex

The satellite ionosondes in highly elliptical orbits are proposed to be used for the task of continuous monitoring of the Arctic ionosphere. The monitoring scheme with the ionosonde location aboard the Arktika-M satellites is presented. The calculations of the vertical topside and transionospheric sounding using the SIMP1 ionospheric model are performed, which show the feasibility of continuous monitoring.

A modified three-dimensional ionospheric tomography algorithm with side rays

The three-dimensional ionospheric tomography (3DCIT) algorithm based on Global Navigation Satellite System (GNSS) observations have been developed into an effective tool for ionospheric monitoring in recent years. However, because the rays that come into or come out from the side of the inversion region cannot be used, the distribution of the rays in the edge and bottom part of the inversion region is scarce and the electron density cannot be effectively improved in the inversion process. We present a three-dimensional tomography algorithm with side rays (3DCIT-SR) applying the side rays to the inversion. The partial slant total electron content (STEC) of side rays in the inversion region is obtained based on the NeQuick2 model and GNSS-STEC. The simulation experiment results show that the algorithm can effectively improve the distribution of GNSS rays in the inversion region. Meanwhile, the iteration accuracy has also been significantly improved. After the same number of iterations, the iterative results of 3DCIT-SR are closer to the truth than 3DCIT, in particular, the inversion of the edge regions is improved noticeably. The GNSS data of the International GNSS Service (IGS) stations in Europe are used to perform real data experiments, and the inversion results show that the electron density profiles of 3DCIT-SR are closer to the ionosonde measurements. The accuracy improvement of 3DCIT-SR is up to 56.3% while the improvement is more obvious during the magnetic storm compared to the case of a calm ionospheric state .

Special issue \u201cGNSS and SAR Technologies for Atmospheric Sensing\u201d

Recent advances in the field of atmospheric and ionospheric sensing by GNSS and SAR technologies were discussed during two workshops held in February 2016 and October 2016 in Italy, hosted by GEOlab of Politecnico di Milano under partial support of the JSPS Bilateral Open Partnership Joint Research Projects. Another symposium was held in March 2017 at the Research Institute for Sustainable Humanosphere of Kyoto University, to discuss (1) the water vapor and ionospheric maps retrieval from space-borne and airborne SAR, (2) ionosphere and troposphere monitoring by the ground-based GNSS network and radio occultation, (3) mesoscale numerical weather prediction models and data assimilation, and (4) ground-based remote-sensing techniques, such as a wind profiling radar. This special issue collects high-quality papers that describe the findings reported during these three meetings, not limited to GNSS and SAR, but also including ground-based atmospheric sensing systems and numerical weather prediction models.

Software-defined radio technology for GNSS scintillation analysis: bring Antarctica to the lab

Global navigation satellite systems (GNSSs) are widely used to support logistics, scientific operations, and to monitor the polar ionosphere indirectly, which is a region characterized by strong phase scintillation events that severely affect the quality and reliability of received signals. Professional commercial GNSS receivers are widely used for scintillation monitoring; on the contrary, custom-designed solutions based on data grabbers and software receivers constitute novelty. The latter enables a higher level of flexibility and configurability, which is important when working in remote and severe environments. We describe the scientific, technological, and logistical challenges of installing an ionospheric monitoring station in Antarctica, based on a multi-constellation and multi-frequency GNSS data grabber and a software-defined radio receiver. Having access to the full receiver chain and to intermediate signal processing stages allows a deep analysis of the impact of scintillation and, in turn, a better understanding of the physical phenomenon. The possibility to process high-resolution raw intermediate frequency samples of the signal enables not only the computation of scintillation indexes with the same quality as professional devices but also the design and test of innovative receiver architectures and algorithms. Furthermore, the record and replay approach offers the possibility to process in the lab the signals captured on site, with high fidelity level. It is like being in Antarctica again, but with an unlimited set of receivers and higher computational, storage, and bandwidth resources. The main advantages and disadvantages of this approach are analyzed. Examples of monitoring results are reported, confirming the monitoring capabilities, showing the good agreement with commercial receiver outputs and confirming the validity of post-processing and re-play operations.

Global Ionosphere Mapping and Differential Code Bias Estimation during Low and High Solar Activity Periods with GIMAS Software

Ionosphere research using the Global Navigation Satellite Systems (GNSS) techniques is a hot topic, with their unprecedented high temporal and spatial sampling rate. We introduced a new GNSS Ionosphere Monitoring and Analysis Software (GIMAS) in order to model the global ionosphere vertical total electron content (VTEC) maps and to estimate the GPS and GLObalnaya NAvigatsionnaya Sputnikovaya Sistema (GLONASS) satellite and receiver differential code biases (DCBs). The GIMAS-based Global Ionosphere Map (GIM) products during low (day of year from 202 to 231, in 2008) and high (day of year from 050 to 079, in 2014) solar activity periods were investigated and assessed. The results showed that the biases of the GIMAS-based VTEC maps relative to the International GNSS Service (IGS) Ionosphere Associate Analysis Centers (IAACs) VTEC maps ranged from −3.0 to 1.0 TECU (TEC unit) (1 TECU = 1 × 1016 electrons/m2). The standard deviations (STDs) ranged from 0.7 to 1.9 TECU in 2008, and from 2.0 to 8.0 TECU in 2014. The STDs at a low latitude were significantly larger than those at middle and high latitudes, as a result of the ionospheric latitudinal gradients. When compared with the Jason-2 VTEC measurements, the GIMAS-based VTEC maps showed a negative systematic bias of about −1.8 TECU in 2008, and a positive systematic bias of about +2.2 TECU in 2014. The STDs were about 2.0 TECU in 2008, and ranged from 2.2 to 8.5 TECU in 2014. Furthermore, the aforementioned characteristics were strongly related to the conditions of the ionosphere variation and the geographic latitude. The GPS and GLONASS satellite and receiver P1-P2 DCBs were compared with the IAACs DCBs. The root mean squares (RMSs) were 0.16–0.20 ns in 2008 and 0.13–0.25 ns in 2014 for the GPS satellites and 0.26–0.31 ns in 2014 for the GLONASS satellites. The RMSs of receiver DCBs were 0.21–0.42 ns in 2008 and 0.33–1.47 ns in 2014 for GPS and 0.67–0.96 ns in 2014 for GLONASS. The monthly stability of the GPS satellite DCBs was about 0.04 ns (0.07 ns) in 2008 (2014) and that for the GLONASS satellite DCBs was about 0.09 ns in 2014. The receiver DCBs were less stable than the satellite DCBs, with a mean value of about 0.16 ns (0.47 ns) in 2008 (2014) for GPS, and 0.48 ns in 2014 for GLONASS. It can be demonstrated that the GIMAS software had a high accuracy and reliability for the global ionosphere monitoring and analysis.

Spatial and Temporal Ionospheric Monitoring Using Broadband Sferic Measurements

AbstractThe D region of the ionosphere (60–90 km altitude) is highly variable on timescales from fractions of a second to many hours, and on spatial scales up to many hundreds of kilometers. Very low frequency (VLF) and low‐frequency (LF) (3–30 kHz and 30–300 kHz) radio waves are guided to global distances by reflections from the ground and the D region. Therefore, information about its current state is encoded in received VLF/LF signals. VLF transmitters have been used in the past for D region studies, with ionospheric disturbances manifesting as perturbations in amplitude and/or phase. The return stroke of lightning is an impulsive VLF radiator, but unlike VLF transmitters, lightning events are distributed broadly in space allowing for much greater spatial coverage of the D region compared to VLF transmitter‐based remote sensing in addition to the broadband spectral advantage over the narrowband transmitters. The challenge is that individual lightning‐generated waveforms, or “sferics,” vary due to the lightning current parameters and uncertainty in the time/location information, in addition to D region ionospheric variability. These factors make it difficult to utilize the VLF/LF emissions from lightning in a straightforward manner. We describe a technique to recover the time domain and amplitude/phase spectra for both Bϕ and Br with high fidelity and consider the utility of our technique with ambient and varied ionospheric conditions. We demonstrate a technique to simulate sferics and infer a parameterized ionosphere with the Wait and Spies parameters (h and β) offering all of the tools needed for a global measurement.

Validation results of NmF2 and hmF2 derived from ionospheric density profiles of GNOS on FY-3C satellite

The first Global Navigation Satellite System Occultation Sounder (GNOS) which is compatible of both BeiDou System (BDS) and Global Positioning System (GPS) was successfully launched into orbit onboard the FengYun 3 C satellite (FY-3C) on September 23, 2013, and it has already gathered a large amount of ionosphere radio occultation (RO) data so far. However, the detailed analysis and validation of GPS ionosphere RO data have not been done up to now. Therefore, this paper discusses the configuration of the FY-3C GNOS, the methods and results of GPS ionosphere occultation processment, the quality analysis of the GPS ionosphere RO products, and the precision consistency between the GNOS GPS ionosphere RO product and ionosonde data. The peak electron density (NmF2) correlation coefficient is 0.97, the corresponding standard deviation is 16.08%. The peak value altitude (hmF2) correlation coefficient is 0.89, and the corresponding standard deviation is 23.79 km. The in-orbit operation of GNOS provides a basis data set for the monitoring, forecasting and research of ionosphere’s space weather.

High-Precision Ionosphere Monitoring Using Continuous Measurements from BDS GEO Satellites.

The current constellation of the BeiDou Navigation Satellite System (BDS) consists of five geostationary earth orbit (GEO) satellites, five inclined geosynchronous satellite orbit (IGSO) satellites, and four medium earth orbit (MEO) satellites. The advantage of using GEO satellites to monitor the ionosphereis the almost motionless ionospheric pierce point (IPP), which is analyzed in comparison with the MEO and IGSO satellites. The results from the analysis of the observations using eight tracking sites indicate that the ionospheric total electron content (TEC) sequence derived from each GEO satellite at their respective fixed IPPs is always continuous. The precision of calculated vertical TEC (VTEC) using BDS B1/B2, B1/B3, and B2/B3 dual-frequency combinationsis compared and analyzed. The VTEC12 precision based on the B1/B2 dual-frequency measurements using the smoothed code and the raw code combination is 0.69 and 5.54 TECU, respectively, which is slightly higher than VTEC13 and much higher than VTEC23. Furthermore, the ionospheric monitoring results of site JFNG in the northern hemisphere, and CUT0 in the southern hemisphere during the period from 1 January to 31 December 2015 are presented and discussed briefly.

Modelling the main ionospheric trough using the Electron Density Assimilative Model (EDAM) with assimilated GPS TEC

Abstract. The main ionospheric trough is a large-scale spatial depletion in the electron density distribution at the interface between the high- and mid-latitude ionosphere. In western Europe it appears in early evening, progresses equatorward during the night, and retreats rapidly poleward at dawn. It exhibits substantial day-to-day variability and under conditions of increased geomagnetic activity it moves progressively to lower latitudes. Steep gradients on the trough-walls on either side of the trough minimum, and their variability, can cause problems for radio applications. Numerous studies have sought to characterize and quantify the trough behaviour. The Electron Density Assimilative Model (EDAM) models the ionosphere on a global scale. It assimilates observations into a background ionosphere, the International Reference Ionosphere 2007 (IRI2007), to provide a full 3-D representation of the ionospheric plasma distribution at specified times and days. This current investigation studied the capability of EDAM to model the ionosphere in the region of the main trough. Total electron content (TEC) measurements from 46 GPS stations in western Europe from September to December 2002 were assimilated into EDAM to provide a model of the ionosphere in the trough region. Vertical electron content profiles through the model revealed the trough and the detail of its structure. Statistical results are presented of the latitude of the trough minimum, TEC at the minimum and of other defined parameters that characterize the trough structure. The results are compared with previous observations made with the Navy Ionospheric Monitoring System (NIMS), and reveal the potential of EDAM to model the large-scale structure of the ionosphere. Keywords. Ionosphere (midlatitude ionosphere; modelling and forecasting) – radio science (ionospheric physics)

Near real-time PPP-based monitoring of the ionosphere using dual-frequency GPS/BDS/Galileo data

Ionosphere delay is very important to GNSS observations, since it is one of the main error sources which have to be mitigated even eliminated in order to determine reliable and precise positions. The ionosphere is a dispersive medium to radio signal, so the value of the group delay or phase advance of GNSS radio signal depends on the signal frequency. Ground-based GNSS stations have been used for ionosphere monitoring and modeling for a long time. In this paper we will introduce a novel approach suitable for single-receiver operation based on the precise point positioning (PPP) technique. One of the main characteristic is that only carrier-phase observations are used to avoid particular effects of pseudorange observations. The technique consists of introducing ionosphere ambiguity parameters obtained from PPP filter into the geometry-free combination of observations to estimate ionospheric delays. Observational data from stations that are capable of tracking the GPS/BDS/GALILEO from the International GNSS Service (IGS) Multi-GNSS Experiments (MGEX) network are processed. For the purpose of performance validation, ionospheric delays series derived from the novel approach are compared with the global ionospheric map (GIM) from Ionospheric Associate Analysis Centers (IAACs). The results are encouraging and offer potential solutions to the near real-time ionosphere monitoring.

Application of satellites system based on different heights for ionospheric disturbances monitoring

Results of data processing on-board Langmuir probes of CHAMP and DEMETER satellites are presented. The characteristics of satellites are given. Analysis of ionospheric parameters before strong earthquake is performed. At the altitudes of the satellites anomalous changes in the ionosphere parameters were detected a few days before the seismic event. Frequency distribution of anomalous ionospheric disturbances is obtained.

Oblique Ionograms Automatic Scaling Algorithm OIASA application to the ionograms recorded by Ebro observatory ionosonde

The oblique ionograms automatic scaling algorithm (OIASA), developed at the INGV for the identification of trace of oblique ionograms, allows the determination of the maximum usable frequency (MUF) for communication between the transmitter and receiver, automatically rejecting poor quality ionograms. A test of the algorithm using data from a campaign of oblique soundings between Dourbes (50.1°N, 4.6°E) and Roquetes (40.8°N, 0.5°E) has been performed. Oblique soundings from three different campaigns have been studied, covering different geomagnetic conditions, in order to study the behavior of the autoscaling algorithm under quiet and perturbed geomagnetic periods. The reported results demonstrate that OIASA performance is not influenced by geomagnetic or ionospheric activity conditions. This demonstrates a satisfactory performance of the automatic scaling algorithm, even under different geomagnetic conditions, the potential application of OIASA as a near-real-time tool for ionospheric monitoring purposes, and its performance for tracking ionospheric effects caused by space weather events.