The Real-Time Working Group (RTWG) of the International GNSS Service (IGS) is
dedicated to providing high-quality data and high-accuracy products for Global
Navigation Satellite System (GNSS) positioning, navigation, timing and Earth
observations. As one part of real-time products, the IGS combined Real-Time
Global Ionosphere Map (RT-GIM) has been generated by the real-time weighting
of the RT-GIMs from IGS real-time ionosphere centers including the Chinese
Academy of Sciences (CAS), Centre National d'Etudes Spatiales (CNES),
Universitat Politècnica de Catalunya (UPC) and Wuhan University
(WHU). The performance of global vertical total electron content (VTEC)
representation in all of the RT-GIMs has been assessed by VTEC from
Jason-3 altimeter for 3 months over oceans and dSTEC-GPS technique with
2¿d observations over continental regions. According to the
Jason-3 VTEC and dSTEC-GPS assessment, the real-time weighting technique is
sensitive to the accuracy of RT-GIMs. Compared with the performance of
post-processed rapid global ionosphere maps (GIMs) and IGS combined final GIM
(igsg) during the testing period, the accuracy of UPC RT-GIM (after the
improvement of the interpolation technique) and IGS combined RT-GIM (IRTG) is
equivalent to the rapid GIMs and reaches around 2.7 and 3.0 TECU (TEC unit,
1016¿el¿m-2) over
oceans and continental regions, respectively. The accuracy of CAS RT-GIM and
CNES RT-GIM is slightly worse than the rapid GIMs, while WHU RT-GIM requires a
further upgrade to obtain similar performance. In addition, a strong
response to the recent geomagnetic storms has been found in the global
electron content (GEC) of IGS RT-GIMs (especially UPC RT-GIM and IGS combined
RT-GIM). The IGS RT-GIMs turn out to be reliable sources of real-time global
VTEC information and have great potential for real-time applications including
range error correction for transionospheric radio signals, the monitoring of
space weather, and detection of natural hazards on a global scale. All the IGS
combined RT-GIMs generated and analyzed during the testing period are
available at https://doi.org/10.5281/zenodo.5042622 (Liu et al., 2021b)., his research has been supported by the
China Scholarship Council (CSC). The contribution from UPC-
IonSAT authors was partially supported by the European Union-
funded project PITHIA-NRF (grant no. 101007599) and by
the ESSP/ICAO-funded project TEC4SpaW. The work of An-
drzej Krankowski is supported by the National Centre for Research
and Development, Poland, through grant ARTEMIS (grant nos.
DWM/PL-CHN/97/2019 and WPC1/ARTEMIS/2019), Peer Reviewed, Postprint (published version)

This paper presents a new way of combining Abel inversion and the Chapman model with a linearly increasing scale height to retrieve ionospheric electron density vertical profiles from truncated-sounding radio-occultation data. A linear Vary–Chap model is used to cover the blind region due to data truncation, with parameters estimated by enumeration of the possible values in a grid centered around a set of parameters compatible with ionospheric physics. The resulting electron density is estimated with its corresponding error from the linear least-squares solution presenting the smaller post-fit residual on the input GNSS carrier-phase measurements. The results, tested on a set of representative GNSS RO measurements obtained by COSMIC/FORMOSAT-3, show that this method can retrieve EDVPs with a predominant absolute and relative error of 1010e-m-3 and 5%, respectively, and in less than 10 s per profile, which makes this method suitable for near real-time applications in upcoming missions such as EUMETSAT Polar System-Second Generation., The activity has been supported by the Radio-Occultation Meteorology Satellite Application Facility (ROM SAF), which is a decentralized operational RO processing center under EUMETSAT, and it has been developed in the context of the EC-funded PITHIA-NRF (H2020-INFRAIA-2018-2020 101007599) project. Estel Cardellach is supported by the grants CEX2020-001058-M-20-5 and PID2021-126436OB-C22., Peer Reviewed, Postprint (published version)

© 2022 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., In this article, we show the capability of a global navigation satellite system (GNSS) precise orbit determination (POD) low Earth orbit (LEO) data to detect anomalous ionospheric disturbances in the spectral range of the signals associated with earthquakes and tsunamis, applied to two of these events in Papua New Guinea (PNG) and the Solomon Islands during 2016. This is achieved thanks to the new PIES approach (POD-GNSS LEO Detrended Ionospheric Electron Content Significant Deviations). The significance of such ionospheric signals above the swarm LEOs is confirmed with different types of independent data: in situ electron density measurements provided by the Langmuir Probe (LP) onboard swarm LEOs, DORIS, and ground-based GNSS colocated measurements, as it is described in this article. In this way, we conclude the possible detection of the tsunami-related ionospheric gravity wave in PNG 2016 event, consistent with the most-recent theory, which shows that a tsunami (which is localized in space and time) excites a spectrum of gravity waves, some of which have faster horizontal phase speeds than the tsunami. We believe that this work shows as well the feasibility of a future potential monitoring system of ionospheric disturbances, to be made possible by hundreds of CubeSats with POD GNSS receivers among other appropriate sensors, and supported for real-time or near real-time confirmation and characterization by thousands of worldwide existing ground GNSS receivers., This work has been partially supported by the COSTO
ESA-funded project (ESA ITT AO/1-9514/18/NL/IA). Also
it was partially supported by the 2017 SGR-0851 grant of the
Generalitat de Catalunya and by the EU project 101007599 -
PITHIA-NRF. The data for this paper are available and they
can be requested from H. Yang (h.yang@upc.edu) and M.
Hernandez-Pajares (manuel.hernandez@upc.edu)., Peer Reviewed, Postprint (author's final draft)

The version of record of this article, first published in Earth, planets and space, is available online at Publisher’s website: http://dx.doi.org/10.1186/s40623-023-01940-2, On 30 October 2020 at 11:51 UT, a magnitude 7.0 earthquake occurred in the Dodecanese sea (37.84°N, 26.81°E, 10 km depth) and generated a tsunami with an observed run-up of more than 1 m on the Turkish coasts. Both the earthquake and the tsunami produced acoustic and gravity waves that propagated upward, triggering co-seismic and co-tsunamic ionospheric disturbances. This paper presents a multi-instrumental study of the ionospheric impact of the earthquake and related tsunami based on ionosonde data, ground-based Global Navigation Satellite Systems (GNSS) data and data from DORIS beacons received by Jason3 in the Mediterranean region. Our study focuses on the Total Electron Content to describe the propagation of co-seismic and co-tsunami ionospheric disturbances (CSID, CTID), possibly related to gravity waves triggered by the earthquake and tsunami. We use simultaneous vertical ionosonde soundings to study the interactions between the upper and lower atmosphere, highlighting the detection of acoustic waves generated by the seismic Rayleigh waves reaching the ionosonde locations and propagating vertically up to the ionosphere. The results of this study provide a detailed picture of the Lithosphere-Atmosphere–Ionosphere coupling in the scarcely investigated Mediterranean region and for a relatively weak earthquake., Upper Atmosphere Physics and Radiopropagation Working Group, Marcocci,
C., Pezzopane, M., Pica, E., Romano, V., Sabbagh, D., Scotto, C., & Zuccheretti, E.
(2020). Electronic Space Weather upper atmosphere database (eSWua)—HF
data, version 1.0 (1.0). Istituto Nazionale di Geofsica e Vulcanologia (INGV).
https://doi.org/https://doi.org/10.13127/ESWUA/HF. GNSS stations providers:
(a) Uranus network (http://uranus.gr) operated by the Tree Company corpora‑
tion National Observatory of Athens (NOA) network, http://geodesy.gein.noa.
gr:8000/nginfo/ (Ganas et al. 2008; Chousianitis et al. 2021). HxGN SmartNet
operated by the Metrica SA (https://www.metrica.gr). (b) Turkish National
Permanent GNSS Network-Active (TNPGN-Active/CORS-TR) https://www.
tusaga-aktif.gov.tr/. (c) The DORIS measurements and orbits were obtained
from https://cddis.gsfc.nasa.gov/archive/doris/data. The authors thank Dr.
Laura Scognamiglio and Dr. Paola Baccheschi from INGV for their support to
interpret the seismograms. Anna Belehaki acknowledges fnancial support
provided by the PITHIA-NRF Horizon 2020 Grant Agreement 101007599 of
the European Commission. Elvira Astafyeva acknowledges the support of the
French National Research Agency (ANR), project IONO-DIET (Grant ANR22-CE49-0011), and the French Space Agency (CNES), project “RealDetect”., Peer Reviewed, Postprint (published version)

In this paper, we propose a method for the generation of real-time global ionospheric map (RT-GIM) of vertical total electron content (VTEC) from GNSS measurements. The need for interpolation arises from the fact that the ionospheric pierce point (IPP) measurements from satellites to stations are not distributed uniformly over the ionosphere, leaving unfilled gaps at oceans or poles. The method we propose is based on using a high-quality historical database of post-processed GIMs that comprises more than two solar cycles, calculates the GIM by weighted superposition on a subset of the database with the compatible solar condition. The linear combination of GIMs in the database was obtained by minimizing a ℓ2 distance between VTEC measurements at the IPPs and the VTECs from the database, adding a ℓ1 penalization on the weights to assure a sparse solution. The process uses a Sun-fixed geomagnetic reference frame. This method uses the atomic decomposition/least absolute shrinkage and selection operator (LASSO), which will be denoted as atomic decomposition interpolator of GIMs (ADIGIM). As the computation is done in milliseconds, the interpolation is performed in real time. In this work, two products were developed, denoted as UADG and UARG, the UADG in real time and UARG with a latency of 24 h to benefit from the availability of a greater number of stations. The altimeter JASON3 VTEC measurements were used as reference. The quality of interpolated RT-GIMs from day 258 of 2019 to 155 of the year 2020 is compared with other RT/non-RT GIM products such as those from International GNSS Service (IGS), Centre National d’Etudes Spatiales (CNES), Chinese Academy of Sciences (CAS), Polytechnic University of Catalonia (UPC) and others. The RT ADIGIM performance proved to be better, nearly as good as the rapid or final GIMs computed retrospectively with delays of hours to days. Besides, the non-RT ADIGIM quality is as good or better than most GIM products. The oceanic regions have been included in the assessment which showed that ADIGIM interpolation gives the best estimation (referred to JASON3). The developed method, UADG, will constitute the next-generation UPC RT-GIM, and also UARG will improve the current product UQRG (the current UPC rapid GIM product computed retrospectively) due to its complementary information., This work has been partially supported by the Project PID2019-107579RB-I00 (MICINN). Also was partially supported by the 2017 SGR-0851 Grant of the Generalitat de Catalunya and by the EU Project 101007599 - PITHIA-NRF., Peer Reviewed, Postprint (author's final draft)

The rapid fluctuations in the electron content of the ionosphere can significantly affect the performance and reliability of communication and GNSS systems. These fluctuations are closely linked to space weather and can result in simultaneous changes in the total electron content of the ionosphere across multiple regions globally. We show the existence of statistically significant synchronous connections between geographical locations when observing fluctuations in electron content. The two findings concerning rapid fluctuations in the electron content of the ionosphere are: a) Evidence of synchronous teleconnections in rapid local electron content variations across a wide range of geographical regions of the globe, and b) The influence of the solar cycle on the geographic distribution of teleconnections is relatively minor, primarily impacting the frequency of teleconnections per unit of time. We characterize teleconnection patterns for different space weather variables throughout the 2016-2022 study period, encompassing the descending and ascending phases of solar cycles 24 and 25. Previous research has mainly focused on the impact of ionospheric irregularities in limited regions, weather conditions, and short time periods, while our findings indicate the occurrence of this phenomenon globally and during both high and low space weather activity., The work of Heng Yang was supported in part by the Natural Science Foundation of Chongqing, China, under Grant cstc2021jcyj-msxmX0191, and in part by the Science and Technology Research Program of Chongqing Municipal Education Commission of China under Grant KJQN202101414 and Grant KJQN202201423. This work was supported by the project PID2019-107579RB-I00 (MICINN). The work has been performed coinciding with the execution of the PITHIA-NRF H2020 project (H2020-INFRAIA-2018-2020101007599)., Peer Reviewed, Postprint (published version)

The ionosphere is a dynamic region of the Earth’s upper atmosphere that exhibits various fluctuations in electron density. These fluctuations can be estimated using measurements from the global navigation satellite system (GNSS). In this article, our focus is on characterizing the probability distribution of total electron content (TEC) fluctuations and their temporal duration. The findings of this study, conducted over half a solar cycle and involving more than 100 stations distributed worldwide, demonstrate that the distribution of rapid ionosphere electron content fluctuations follows a power-law behavior, both in amplitude and duration. This explains the occurrence of occasional extreme values of amplitude and duration. In addition, despite significant differences in space weather conditions during the solar cycle, including geomagnetic storms, the power-law distributions of both the rate of change in TEC index amplitude and duration of bursts of activity, exhibit the same shape parameter ( α ), which is similar to the values observed during less active periods. Another finding is the statistical independence of amplitude and duration. The observed power-law distribution and its temporal and spatial dependencies provide practical insights for developing robust models and algorithms for ionospheric impact mitigation in GNSS positioning and navigation systems. Moreover, these findings have implications for space weather monitoring and forecasting, contributing to the assessment of ionospheric disturbances and for a wide range of technological systems, including telecommunication networks among GNSS., This work was supported in part by Project PID2019- 107579RB-I00/AEI/10.13039/501100011033 and in part by the PITHIA-NRF H2020 Project under Grant H2020-INFRAIA-2018-2020101007599. The work of Heng Yang was supported in part by the Natural Science Foundation of Chongqing, China, under Grant cstc2021jcyj-msxmX0191; and in part by the Science and Technology Research Program of Chongqing Municipal Education Commission of China under Grant KJQN202101414 and Grant KJQN202201423., Peer Reviewed, Postprint (published version)

The determination of the ionospheric perturbation degree is essential to describe the ionosphere state for space weather monitoring. A new method for estimating the spatial and temporal components of the Vertical Total Electron Content (VTEC) gradient is introduced. The new method is based on VTEC estimated at each grid point of Global Ionosphere Map (GIM) by the UPC-IonSAT research group of the Universitat Politècnica de Catalunya. Depending on the requirement, the VTEC spatial gradients can be derived at selected regions or grid points of the GIM on a global scale. According to the comparison with previous studies over the Europe region during quiet ionosphere state and two severe geomagnetic storms, the new method has proven to be reliable and has a great potential for the monitoring of ionospheric perturbation degree on a global scale. In addition, the associated warning of disturbed ionosphere might be available in the context of the on-going development of real-time GIMs., This research has been done under the
partial support of the ESA and European
Commission (EC) funded eMONI-
TOR/MoNEWIC (H2020-ESA-037)
project and the EC funded PITH-
IA-NRF (H2020-INFRAIA-2018-2020
101007599) project., Peer Reviewed, Postprint (published version)

The ionospheric storms have adverse effects on the radio communications, satellite communications and also the Global Navigation Satellite Systems (GNSS) application. A new Ionospheric storm Scale from Universitat Politècnica de Catalunya (UPC) Global Ionosphere Map (GIM), IsUG, is introduced for characterizing the ionospheric state on a global scale. The IsUG is based on the Vertical Total Electron Content (VTEC) derived from the continuously computed UPC Quarter-of-an-hour time resolution Rapid GIM (UQRG), taking as reference the ones during the period 1997 to 2014. It is similar to the I-scale index previously introduced, although it was over Japan and based on raw GNSS data. The dependence of the VTEC on season, local time and geographical location at each grid point of UQRG is removed by normalizing (i.e., by substracting the mean and dividing by the corresponding standard deviation) the percentage deviation of hourly median VTEC. After validating IsUG versus I-scale, the IsUG distribution is presented and analyzed at global scale during a severe geomagnetic storm from 7 to 10 November 2004 as an example of the potentialities of the new index. The results suggest that the IsUG global map has a great potential for the scientific study of ionospheric storms from a global perspective and also for space weather warning considering the accuracy of the recently developed real-time GIMs., This research has
been done under the partial support
of the European Space Agency and
European Commission funded eMON-
ITOR/MoNEWIC (H2020-ESA-037)
project and the European Commission
funded PITHIA-NRF (H2020-IN-
FRAIA-2018-2020 101007599) project., Peer Reviewed, Postprint (published version)

This paper presents a novel technique to estimate DCBs from GPS transmitters and receivers on-board Low Earth Orbit (LEO) satellites. The technique consists of obtaining the DCBs as residuals from the difference between the ionospheric combination of the code and the associated ionospheric delay. The ionospheric delay is computed with TOMION, a background-model-free ionospheric tomographic technique based on dual-frequency GPS carrier phase data only, and solved with a Kalman filter. Thus, DCBs are also estimated epoch-wise from the LEO Precise Orbit Determination (POD) GPS receiver as a secondary product. The results for GPS satellite DCBs, obtained exclusively from the three MetOp LEO POD GPS receivers over four consecutive weeks, are in full agreement (i.e., at the level of a few tenths of ns) with those reported independently with other techniques from hundreds of ground-based receivers exclusively, by JPL and CODE analysis centers., The work has been performed coinciding with the execution of the PITHIA-NRF H2020 project (H2020-INFRAIA-2018-2020101007599), Peer Reviewed, Postprint (published version)

The UQRG data are openly accessible (https://cddis.nasa.gov/archive/gnss/products/ionex) from Crustal Dynamics Data Information System (Noll, 2010). The Kp index is available (ftp://ftp.gfz-potsdam.de/pub/home/obs/Kp_ap_Ap_SN_F107) from GeoForschungsZentrum (Matzka et al., 2021) and Dst index is accessible (http://wdc.kugi.kyoto-u.ac.jp/dstdir/) from World Data Center for Geomagnetism, Kyoto (World Data Center for Geomagnetism et al., 2015)., The ionospheric storms have adverse effects on the radio communications, satellite communications and also the Global Navigation Satellite Systems (GNSS) application. A new Ionospheric storm Scale from Universitat Politècnica de Catalunya (UPC) Global Ionosphere Map (GIM), IsUG, is introduced for characterizing the ionospheric state on a global scale. The IsUG is based on the Vertical Total Electron Content (VTEC) derived from the continuously computed UPC Quarter-of-an-hour time resolution Rapid GIM (UQRG), taking as reference the ones during the period 1997 to 2014. It is similar to the I-scale index previously introduced, although it was over Japan and based on raw GNSS data. The dependence of the VTEC on season, local time and geographical location at each grid point of UQRG is removed by normalizing (i.e., by substracting the mean and dividing by the corresponding standard deviation) the percentage deviation of hourly median VTEC. After validating IsUG versus I-scale, the IsUG distribution is presented and analyzed at global scale during a severe geomagnetic storm from 7 to 10 November 2004 as an example of the potentialities of the new index. The results suggest that the IsUG global map has a great potential for the scientific study of ionospheric storms from a global perspective and also for space weather warning considering the accuracy of the recently developed real-time GIMs., The first author is grateful for the financial support of the China Scholarship Council (CSC). This research has been done under the partial support of the European Space Agency and European Commission funded eMONITOR/MoNEWIC (H2020-ESA-037) project and the European Commission funded PITHIA-NRF (H2020-INFRAIA-2018-2020 101007599) project.

The determination of the ionospheric perturbation degree is essential to describe the ionosphere state for space weather monitoring. A new method for estimating the spatial and temporal components of the Vertical Total Electron Content (VTEC) gradient is introduced. The new method is based on VTEC estimated at each grid point of Global Ionosphere Map (GIM) by the UPC-IonSAT research group of the Universitat Politècnica de Catalunya. Depending on the requirement, the VTEC spatial gradients can be derived at selected regions or grid points of the GIM on a global scale. According to the comparison with previous studies over the Europe region during quiet ionosphere state and two severe geomagnetic storms, the new method has proven to be reliable and has a great potential for the monitoring of ionospheric perturbation degree on a global scale. In addition, the associated warning of disturbed ionosphere might be available in the context of the on-going development of real-time GIMs., Q. Liu is grateful for the financial support of the China Scholarship Council. This research has been done under the partial support of the ESA and European Commission (EC) funded eMONITOR/MoNEWIC (H2020-ESA-037) project and the EC funded PITHIA-NRF (H2020-INFRAIA-2018-2020 101007599) project.

This article belongs to the Special Issue GNSS Atmospheric Modelling., This paper characterizes, with static and roving GNSS receivers in the context of precision agriculture research, the hybrid ionospheric-geodetic GNSS model Wide-Area Real-Time Kinematics (WARTK), which computes and broadcasts real-time corrections for high-precision GNSS positioning and navigation within sparse GNSS receiver networks. This research is motivated by the potential benefits of the low-cost precise WARTK technique on mass-market applications such as precision agriculture. The results from two experiments summarized in this work, the second one involving a working spraying tractor, show, firstly, that the corrections from the model are in good agreement with the corrections provided by IGS (International GNSS Services) analysis centers computed in post-processing from global GNSS data. Moreover, secondly and most importantly, we have shown that WARTK provides navigation solutions at decimeter-level accuracy, and the ionospheric corrections significantly reduce the computational time for ambiguity estimation: up to convergence times for the 50%, 75% and 95% of cases equal or below 30 s (single-epoch), 150 s and 600 s approximately, vs. 1000 s, 2750 s and 4850 s without ionospheric corrections, everything for a roving receiver at more than 100 km far away from the nearest permanent receiver. The real-time horizontal position errors reach up to 3 cm, 5 cm and 12 cm for 50%, 75% and 95% of cases, respectively, by constraining and continuously updating the ambiguities without updating the permanent receiver coordinates, vs. the 6 cm, 12 cm and 32 cm, respectively, in the same conditions but without WARTK ionospheric corrections., This research was funded under the European Commission H2020 project Advanced Multi-Constellation EGNSS Augmentation and Monitoring Network and its Application in Precision Agriculture (AUDITOR-GA687367). This manuscript has been written thanks to the partial support of the ongoing EC funded PITHIA-NRF (H2020-INFRAIA-2018-2020 101007599) project., Peer reviewed

This article belongs to the Special Issue New Insights in GNSS Remote Sensing for Ionosphere Monitoring and Modeling., This paper presents a novel technique to estimate DCBs from GPS transmitters and receivers on-board Low Earth Orbit (LEO) satellites. The technique consists of obtaining the DCBs as residuals from the difference between the ionospheric combination of the code and the associated ionospheric delay. The ionospheric delay is computed with TOMION, a background-model-free ionospheric tomographic technique based on dual-frequency GPS carrier phase data only, and solved with a Kalman filter. Thus, DCBs are also estimated epoch-wise from the LEO Precise Orbit Determination (POD) GPS receiver as a secondary product. The results for GPS satellite DCBs, obtained exclusively from the three MetOp LEO POD GPS receivers over four consecutive weeks, are in full agreement (i.e., at the level of a few tenths of ns) with those reported independently with other techniques from hundreds of ground-based receivers exclusively, by JPL and CODE analysis centers., This research was funded by EUMETSAT in the context of the project Assessment of GRAS Ionospheric Measurements for IonosphericModel Assimilation (GIMA, number EUM/CO/21/4600002530/RN). The work has been performed coinciding with the execution of the PITHIA-NRF H2020 project (H2020-INFRAIA-2018-2020101007599)., Peer reviewed

Vertical total electron content (VTEC) has great importance in describing the ionosphere. VTEC values are commonly distributed in regular grids by means of so-called global ionospheric maps (GIMs) and regional ionospheric maps (RIMs). Although considerable research has been conducted to develop regional and global models, there is no clear understanding of the benefits of using RIMs over GIMs. Aiming to contribute to this discussion, our investigation presents a comparison between seven global and regional ionospheric maps considering two approaches: (a) ionosonde data-based assessment and (b) global navigation satellite systems (GNSS) positioning assessment. A challenging low latitude ionosphere scenario, the Brazilian region, was selected during a week with an active geomagnetic storm. The assessment results with ionosonde data have shown better performance of the RIM products named OTHR and OTRG. Among the global products, CODG and UQRG have shown the best performances. The worst results were obtained with the RIM named Instituto Nacional de Pesquisas Espaciais. The assessment with GNSS positioning led to larger and noisier errors close to the equatorial anomaly. Two of the analyzed RIMs presented expected large errors in stations at the edges of the coverage area. To overcome this issue, a hybrid product was proposed to extend the RIM covered region. The proposed hybrid product (OTRG) presented the best results in the GNSS positioning domain., This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—Finance Code 001 and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP: 2021/05285-0). UPC-IonSAT also thanks the partial support of the PITHIA NRF EU project (Grant 101007599). We acknowledge the IGS IAACs, in particular CODE, for providing the ionospheric data, INPE for providing the ionospheric regional maps and the ionosonde data, IBGE for providing the GNSS data, and the National Institute of Science and Technology for GNSS in Support of Air Navigation (INCT GNSS-NavAer), funded by CNPq (465648/2014-2), FAPESP (2017/50115-0), and CAPES (88887.137186/2017-00). We are also greatful to the Bundeswehr GeoInformation Centre (BGIC) and the German Space Situation Awareness Centre (GSSAC) for funding the “Operational tool for ionosphere mapping and prediction” (OPTIMAP) project., Peer reviewed

This article belongs to the Special Issue Ionospheric and Magnetic Signatures of Space Weather Events at Middle and Low Latitudes: Experimental Studies and Modelling (2nd Edition)., The ionospheric response at middle latitudes to geomagnetic storms is not yet very well understood. Total electron content (TEC) variations associated with eight strong geomagnetic storms between 2015 and 2022 obtained from GNSS receivers in the eastern area of the North Atlantic (Portuguese continental and insular territory) are studied in an attempt to fill this gap. It was found that for most of the studied geomagnetic storms, TEC variations are synchronous for the longitudinal ranges from 27° W and 9° W. In the southern part of the studied region (around 32° N), the amplitude of TEC variations is, in general, significantly higher than in the northern part (around 39° N). Some of the studied geomagnetic storms were associated with TEC variations that we interpret as effects of post-sunset equatorial plasma bubbles that travelled well north from their habitual region. Additionally, though most of the studied storms were accompanied by reports on different kinds of malfunction of GNSS systems (GPS; GALILEO and other), there is no clear pattern in their appearance in dependence on the geomagnetic/ionospheric storms’ strength, commencement time, and its characteristics, in general., IA is supported by Fundação para a Ciência e a Tecnologia (FCT, Portugal) through the research grants UIDB/04434/2020 and UIDP/04434/2020. This study is a contribution to the PRIME project (EXPL/CTA-MET/0677/2021, FCT, Portugal) and JP is supported by this project. The PITHIA-NRF project has received funding from European Union’s Horizon 2020 research and innovation programme under grant agreement no. 101007599., Peer reviewed

Broad band pulsar radiation can be effectively used to monitor the properties of the magneto-ionic media through which it propagates. Faraday rotation calculated from polarised pulsar observations provides an integrated product of electron densities and the line-of-sight component of the magnetic field in the intervening plasma. In particular, a time-variable effect mainly associated with the rapidly changing column density of the Earth’s ionosphere and plasmasphere heavily dominates the observed Faraday rotation of pulsar radiation. In this work, we aim to carry out a performance test of three GNSS-based models of the ionosphere using observations of PSR J0332+5434 taken with the LOw Frequency ARray (LOFAR). As it was shown in Porayko et al. (Month Not Roy Astron Soc 483(3):4100–4113, 2019. https://doi.org/10.1093/mnras/sty3324. arXiv:1812.01463), the conventional single layer model (SLM), which assumes that the ionosphere is a thin slab at a fixed effective height, is not capable of fully accounting for the ionospheric Faraday rotation in pulsar data. The simplified physics of the SLM is upgraded within IRI-Plas (International Reference Ionosphere and Plasmasphere) extended SLM and the dual-layer voxel TOmographic Model of the Ionosphere (TOMION), both of which partially account for the thickness and vertical dynamics of the terrestrial plasma. Although the last two improve the reconstruction of the ionospheric Faraday rotation, none of the considered models completely purge the observed residual variations. With this study, we show that the long term LOFAR observations of Faraday rotation of pulsars provide an excellent tool to test and improve models of the magneto-ionic content of the Earth’s atmosphere., This work has been partially supported by the EU project 101007599 - PITHIA-NRF. N.P. is supported by the Max-Planck Society as part of the “LEGACY” collaboration with the Chinese Academy of Sciences on low-frequency gravitational wave astronomy. N.P. is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Projektnummer PO 2758/1–1, through the Walter–Benjamin programme. J.P.W.V. acknowledges support by the Deutsche Forschungsgemeinschaft (DFG) through the Heisenberg programme (Project No. 433075039). J.K. is financially supported by the D-LOFAR II (grant 05A20PB1). We would like to thank V. Venkatraman Krishnan and anonymous referees for carefully reading the paper. This paper is based on data obtained with the German stations of the International LOFAR Telescope (ILT), constructed by ASTRON van Haarlem et al. (2013) and operated by the GLOW consortium (https://www.glowconsortium.de/) during station-owners time and proposals LC0_014, LC1_048, LC2_011, LC3_029, LC4_025, LT5_001, LC9_039, LT10_014. We made use of data from Jülich (DE605) LOFAR station supported by the BMBF Verbundforschung project D-LOFAR I (grant 05A08LJ1); and the Norderstedt (DE609) LOFAR station funded by the BMBF Verbundforschung project D-LOFAR II (grant 05A11LJ1). The observations of the German LOFAR stations were carried out in the stand-alone GLOW mode, which is technically operated and supported by the Max-Planck-Institut für Radioastronomie, the Forschungszentrum Jülich and Bielefeld University. We acknowledge support and operation of the GLOW network, computing and storage facilities by the FZ-Jülich, the MPIfR and Bielefeld University and financial support from BMBF D-LOFAR III (grant 05A14PBA) and D-LOFAR IV (grants 05A17PBA and 05A17PC1), and by the states of Nordrhein-Westfalia and Hamburg., Open Access funding enabled and organized by Projekt DEAL., Peer reviewed

These data are used to produce Figure 1 of the paper "Validation of global ionospheric models using long term pulsar observations with the LOFAR radio telescope" by Nataliya K. Porayko, Maaijke Mevius, Manuel He'rnandez-Pajares, Caterina Tiburzi, German Olivares Pulido, Qi Liu, Joris P. W. Veriest, Joern Kuensemoeller, Krishnakumar Moochickal Ambalappat, Ann-Sofie Bak Nielsen, Marcus Brueggen, Victoria Graffigna, Ralf-Juergen Dettmar, Michael Kramer, Stefan Oslowski, Dominik J. Schwarz, Golam M. Shaifullah, Olaf Wucknitz., PITHIA-NRF – Plasmasphere Ionosphere Thermosphere Integrated Research Environment and Access services: a Network of Research Facilities 101007599; European Commission., Peer reviewed

This article belongs to the Special Issue Advances in GNSS Positioning and GNSS Remote Sensing., The time evolution of the total number of free electrons in the Earth’s ionosphere, i.e., the Global Electron Content (GEC), during more than two solar cycles is analyzed in this work. The GEC time series has been extracted from the Global Ionospheric Maps (GIMs) of Vertical Total Electron Content (VTEC) estimated by UPC-IonSAT with TOMION-v1 software from global GPS measurements since the end of 1996. A dual-layer voxel-based tomographic model solved with a forward Kalman scalar filter, from dual-frequency carrier GPS data only, provides the so-called UQRG GIM after VTEC kriging interpolation, with a resolution of 15 min in time, 5° in longitude and 2.5° in latitude. UQRG is one of the best behaving GIMs in the International GNSS Service (IGS).In this context, the potential application of the GEC spectrum evolution as a potential space weather index is discussed and demonstrated., This research was partially funded by the European Union (PITHIA-NRF project, grant number H2020-INFRAIA-2018-2020101007599). The last part of the work has been performed coinciding with the starting of the DISPEC project (HORIZON-CL4-2023-SPACE-01-71)., Peer reviewed

The 3D ionosphere structure is of interest in many fields such as radio frequency communication and global navigation satellite system (GNSS) applications. However, the limited temporal and spatial coverage of measurements poses a challenge for 3D electron density modeling. To overcome this challenge, we explore the use of kriging interpolation technique. The kriging interpolation is performed to obtain 3D representation of the ionosphere over electron density measurements retrieved by GNSS radio-occultation (RO) data. RO measurements are first reduced to “shape function,” the ratio of electron density to vertical total electron content (VTEC), aiming to create a background model. Then, the empirical residual semivariogram is analyzed for variation characteristics of the shape functions under different solar geomagnetic conditions. Finally, 3D kriging is adopted for shape function interpolation. Compared to the modeling results without kriging, the maximum root mean square error (RMSE) reduction reaches 3.4×10-4km-1, which amounts to 3.4×1011el/m3 of electron density when VTEC is assumed as 100 TECU. This improvement accounts for 17.8% of root mean square (RMS) of shape function., The first author thanks the financial support by Chinese Scholarship Council and University of Alcalá for the 2023–24 Giner de los Ríos Programme Grant. This research was supported by the National Natural Science Foundation of China (Grant No. 42404034, 42074032, 42030109). The second author has contributed to this work in the context of the EU projects 101007599—PITHIA-NRF and DISPEC (HORIZON-CL4-2023-SPACE-01-71)., Peer reviewed

This work presents a summary of the continuous non-stop (hereinafter 24/7) real-time measurement and warning system for EUV solar activity, which is based on worldwide multifrequency Global Navigation Satellite Systems (GNSS) observations. The system relies on continuous tracking of the intensity of expected global patterns in the Earth's ionosphere's free electron distribution, which are associated with solar flares. The paper includes a discussion on the foundations of GNSS Solar Astronomy, along with details on its real-time implementation that began in 2011. Furthermore, a summary of the corresponding validation is provided, comparing it to external and direct solar EUV flux measurements obtained from SOHO-SEM. Finally, there will be a brief mention of the ongoing efforts to extend this technique to detect huge extra-solar sources., This work has been supported by the projects MONITOR (funded by ESA/ESTEC in 2010, Contract No. 4000100988, and by ESA/EGNOS project office in 2014) and GNSS Astronomy (ESA/ESTEC Contract No. 4000133257/20/NL/GLC in 2021). This paper has been performed coinciding with the execution of PITHIA-NRF H2020 project (H2020-INFRAIA-2018–2020101007599), Peer reviewed

Equatorial Plasma Bubbles (EPBs) play a crucial role in modulating plasma density and electron content within the equatorial ionosphere. In this work, we present an advanced and more robust version of the method developed by Blanch E et al. (2018, J Space Weather Space Clim., 8, 38–32) for detecting EPBs using data from the Global Navigation Satellite System (GNSS). The enhancements introduced in this version significantly improve the EPB detection process, achieving a notable reduction in the false positive rate compared to the previous approach. These refinements include the application of more rigorous statistical techniques to achieve a more accurate fit for the background Total Electron Content (TEC), leading to better characterization of EPBs through improved estimation of disturbance shapes. Applying the capabilities of this new method in a dense network of GNSS sensors, we have developed an interferometric procedure for estimating EPB drift velocities, including both speed and direction. This procedure provides valuable insights into the dynamic behavior of EPBs in the Caribbean region during 2014. Our analysis reveals a predominant eastward propagation pattern of EPBs, closely aligned with modified dip isolines. Furthermore, by integrating the results from the GNSS-based method with quasi co-located digisondes, we applied a conceptual model to estimate EPB velocities along their drift direction. This model has been tested across different geographical sectors and validated through comparisons with results from other independent studies. This cross-verification confirms the reliability of the methods for capturing EPB characteristics. This approach improves the precision of EPB detection and contributes to a deeper understanding of their spatiotemporal dynamics and behavior, providing a valuable framework for characterizing these phenomena in the equatorial ionosphere., Authors wish to express their gratitude to the International GNSS Service, the Crustal Dynamics Data Information System Data Center, and the National Oceanic and Atmospheric Administration for making the data available. Global Ionospheric Radio Observatory (GIRO) (Reinisch & Galkin, (2011), and GIRO data providers (USAF NEXION Digisonde network, whose Program Manager is Annette Parsons, Jicamarca and Ramey) for making Digisonde data available. This research has been funded by EU Projects PITHIA-NRF (GA 101007599) and T-FORS (GA 101081835), in which V.N-P, D.A., A.S., and V.dP are participating. The editor thanks Claudio Cesaroni and an anonymous reviewer for their assistance in evaluating this paper., Peer reviewed

Global Navigation Satellite Systems radio occultation (RO) is a valuable and relevant source of information from the atmosphere. Many efforts have been made to provide methods of validation of RO profiles, however, no clear methodology for filtering the profiles from RO can be easily found. In this study, we present strategies to filter RO electron density profiles over a low latitude region. Different methods are applied considering minimum values, manual filtering, (Formula presented.) range, and discrepancies with reference to the Chapman profile. The assessment is performed by means of ionosonde data for two years (2014–2015). The results show that assuming a minimum electron density limit slightly smaller than zero consistently with electron density estimation errors under very low actual values can provide significant improvements. In this study, the use of a − (Formula presented.) el/ (Formula presented.) limit led to better rates of retained profiles (65% vs. 32%) and a reduction in (Formula presented.) root mean square (RMS) (12% vs. 7%) compared to the exclusion of all profiles with negative values. When considering only electron density values above 100 km in altitude, there is still a significant loss of about 20% in the number of profiles with the same reference values (84% vs. 63%), with a similar performance in the (Formula presented.) RMS. The best performance is obtained with the strategies: (Formula presented.) range of occurrence (200–450 km) and the outliers identification (5 standard deviations limit), leading to a (Formula presented.) RMS reduction of about 26% and 19%, and a (Formula presented.) RMS reduction of 34% and 25%, respectively, while keeping 91% and 82% of the original profiles., We acknowledge University Corporation for Atmospheric Research (UCAR) for providing the COSMIC data and INPE for providing the ionosonde data. This study was financed in part by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP: 2021/05285-0 and 2022/00276-5). UPC-IonSAT also thanks the partial support of the PITHIA NRF EU project (Grant 101007599). We also acknowledge the National Institute of Science and Technology for GNSS in Support of Air Navigation (INCT GNSS-NavAer), funded by CNPq (465648/2014-2), FAPESP (2017/50115-0), and CAPES (88887.137186/2017-00). The Article Processing Charge for the publication of this research was funded by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) (ROR identifier: 00x0ma614)., The Article Processing Charge for the publication of this research was funded by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) (ROR identifier: 00x0ma614)., Peer reviewed

The determination of the ionospheric perturbation degree is essential to describe the ionosphere state for space weather monitoring. A new method for estimating the spatial and temporal components of the Vertical Total Electron Content (VTEC) gradient is introduced. The new method is based on VTEC estimated at each grid point of Global Ionosphere Map (GIM) by the UPC-IonSAT research group of the Universitat Politècnica de Catalunya. Depending on the requirement, the VTEC spatial gradients can be derived at selected regions or grid points of the GIM on a global scale. According to the comparison with previous studies over the Europe region during quiet ionosphere state and two severe geomagnetic storms, the new method has proven to be reliable and has a great potential for the monitoring of ionospheric perturbation degree on a global scale. In addition, the associated warning of disturbed ionosphere might be available in the context of the on-going development of real-time GIMs., This research has been done under the
partial support of the ESA and European
Commission (EC) funded eMONI-
TOR/MoNEWIC (H2020-ESA-037)
project and the EC funded PITH-
IA-NRF (H2020-INFRAIA-2018-2020
101007599) project., Peer Reviewed

The rapid fluctuations in the electron content of the ionosphere can significantly affect the performance and reliability of communication and GNSS systems. These fluctuations are closely linked to space weather and can result in simultaneous changes in the total electron content of the ionosphere across multiple regions globally. We show the existence of statistically significant synchronous connections between geographical locations when observing fluctuations in electron content. The two findings concerning rapid fluctuations in the electron content of the ionosphere are: a) Evidence of synchronous teleconnections in rapid local electron content variations across a wide range of geographical regions of the globe, and b) The influence of the solar cycle on the geographic distribution of teleconnections is relatively minor, primarily impacting the frequency of teleconnections per unit of time. We characterize teleconnection patterns for different space weather variables throughout the 2016-2022 study period, encompassing the descending and ascending phases of solar cycles 24 and 25. Previous research has mainly focused on the impact of ionospheric irregularities in limited regions, weather conditions, and short time periods, while our findings indicate the occurrence of this phenomenon globally and during both high and low space weather activity., The work of Heng Yang was supported in part by the Natural Science Foundation of Chongqing, China, under Grant cstc2021jcyj-msxmX0191, and in part by the Science and Technology Research Program of Chongqing Municipal Education Commission of China under Grant KJQN202101414 and Grant KJQN202201423. This work was supported by the project PID2019-107579RB-I00 (MICINN). The work has been performed coinciding with the execution of the PITHIA-NRF H2020 project (H2020-INFRAIA-2018-2020101007599)., Peer Reviewed

This paper presents a novel technique to estimate DCBs from GPS transmitters and receivers on-board Low Earth Orbit (LEO) satellites. The technique consists of obtaining the DCBs as residuals from the difference between the ionospheric combination of the code and the associated ionospheric delay. The ionospheric delay is computed with TOMION, a background-model-free ionospheric tomographic technique based on dual-frequency GPS carrier phase data only, and solved with a Kalman filter. Thus, DCBs are also estimated epoch-wise from the LEO Precise Orbit Determination (POD) GPS receiver as a secondary product. The results for GPS satellite DCBs, obtained exclusively from the three MetOp LEO POD GPS receivers over four consecutive weeks, are in full agreement (i.e., at the level of a few tenths of ns) with those reported independently with other techniques from hundreds of ground-based receivers exclusively, by JPL and CODE analysis centers., The work has been performed coinciding with the execution of the PITHIA-NRF H2020 project (H2020-INFRAIA-2018-2020101007599), Peer Reviewed

The ionospheric storms have adverse effects on the radio communications, satellite communications and also the Global Navigation Satellite Systems (GNSS) application. A new Ionospheric storm Scale from Universitat Politècnica de Catalunya (UPC) Global Ionosphere Map (GIM), IsUG, is introduced for characterizing the ionospheric state on a global scale. The IsUG is based on the Vertical Total Electron Content (VTEC) derived from the continuously computed UPC Quarter-of-an-hour time resolution Rapid GIM (UQRG), taking as reference the ones during the period 1997 to 2014. It is similar to the I-scale index previously introduced, although it was over Japan and based on raw GNSS data. The dependence of the VTEC on season, local time and geographical location at each grid point of UQRG is removed by normalizing (i.e., by substracting the mean and dividing by the corresponding standard deviation) the percentage deviation of hourly median VTEC. After validating IsUG versus I-scale, the IsUG distribution is presented and analyzed at global scale during a severe geomagnetic storm from 7 to 10 November 2004 as an example of the potentialities of the new index. The results suggest that the IsUG global map has a great potential for the scientific study of ionospheric storms from a global perspective and also for space weather warning considering the accuracy of the recently developed real-time GIMs., This research has
been done under the partial support
of the European Space Agency and
European Commission funded eMON-
ITOR/MoNEWIC (H2020-ESA-037)
project and the European Commission
funded PITHIA-NRF (H2020-IN-
FRAIA-2018-2020 101007599) project., Peer Reviewed

This paper presents a new way of combining Abel inversion and the Chapman model with a linearly increasing scale height to retrieve ionospheric electron density vertical profiles from truncated-sounding radio-occultation data. A linear Vary–Chap model is used to cover the blind region due to data truncation, with parameters estimated by enumeration of the possible values in a grid centered around a set of parameters compatible with ionospheric physics. The resulting electron density is estimated with its corresponding error from the linear least-squares solution presenting the smaller post-fit residual on the input GNSS carrier-phase measurements. The results, tested on a set of representative GNSS RO measurements obtained by COSMIC/FORMOSAT-3, show that this method can retrieve EDVPs with a predominant absolute and relative error of 1010e-m-3 and 5%, respectively, and in less than 10 s per profile, which makes this method suitable for near real-time applications in upcoming missions such as EUMETSAT Polar System-Second Generation., The activity has been supported by the Radio-Occultation Meteorology Satellite Application Facility (ROM SAF), which is a decentralized operational RO processing center under EUMETSAT, and it has been developed in the context of the EC-funded PITHIA-NRF (H2020-INFRAIA-2018-2020 101007599) project. Estel Cardellach is supported by the grants CEX2020-001058-M-20-5 and PID2021-126436OB-C22., Peer Reviewed

The ionosphere is a dynamic region of the Earth’s upper atmosphere that exhibits various fluctuations in electron density. These fluctuations can be estimated using measurements from the global navigation satellite system (GNSS). In this article, our focus is on characterizing the probability distribution of total electron content (TEC) fluctuations and their temporal duration. The findings of this study, conducted over half a solar cycle and involving more than 100 stations distributed worldwide, demonstrate that the distribution of rapid ionosphere electron content fluctuations follows a power-law behavior, both in amplitude and duration. This explains the occurrence of occasional extreme values of amplitude and duration. In addition, despite significant differences in space weather conditions during the solar cycle, including geomagnetic storms, the power-law distributions of both the rate of change in TEC index amplitude and duration of bursts of activity, exhibit the same shape parameter ( α ), which is similar to the values observed during less active periods. Another finding is the statistical independence of amplitude and duration. The observed power-law distribution and its temporal and spatial dependencies provide practical insights for developing robust models and algorithms for ionospheric impact mitigation in GNSS positioning and navigation systems. Moreover, these findings have implications for space weather monitoring and forecasting, contributing to the assessment of ionospheric disturbances and for a wide range of technological systems, including telecommunication networks among GNSS., This work was supported in part by Project PID2019- 107579RB-I00/AEI/10.13039/501100011033 and in part by the PITHIA-NRF H2020 Project under Grant H2020-INFRAIA-2018-2020101007599. The work of Heng Yang was supported in part by the Natural Science Foundation of Chongqing, China, under Grant cstc2021jcyj-msxmX0191; and in part by the Science and Technology Research Program of Chongqing Municipal Education Commission of China under Grant KJQN202101414 and Grant KJQN202201423., Peer Reviewed

The version of record of this article, first published in Earth, planets and space, is available online at Publisher’s website: http://dx.doi.org/10.1186/s40623-023-01940-2, On 30 October 2020 at 11:51 UT, a magnitude 7.0 earthquake occurred in the Dodecanese sea (37.84°N, 26.81°E, 10 km depth) and generated a tsunami with an observed run-up of more than 1 m on the Turkish coasts. Both the earthquake and the tsunami produced acoustic and gravity waves that propagated upward, triggering co-seismic and co-tsunamic ionospheric disturbances. This paper presents a multi-instrumental study of the ionospheric impact of the earthquake and related tsunami based on ionosonde data, ground-based Global Navigation Satellite Systems (GNSS) data and data from DORIS beacons received by Jason3 in the Mediterranean region. Our study focuses on the Total Electron Content to describe the propagation of co-seismic and co-tsunami ionospheric disturbances (CSID, CTID), possibly related to gravity waves triggered by the earthquake and tsunami. We use simultaneous vertical ionosonde soundings to study the interactions between the upper and lower atmosphere, highlighting the detection of acoustic waves generated by the seismic Rayleigh waves reaching the ionosonde locations and propagating vertically up to the ionosphere. The results of this study provide a detailed picture of the Lithosphere-Atmosphere–Ionosphere coupling in the scarcely investigated Mediterranean region and for a relatively weak earthquake., Upper Atmosphere Physics and Radiopropagation Working Group, Marcocci,
C., Pezzopane, M., Pica, E., Romano, V., Sabbagh, D., Scotto, C., & Zuccheretti, E.
(2020). Electronic Space Weather upper atmosphere database (eSWua)—HF
data, version 1.0 (1.0). Istituto Nazionale di Geofsica e Vulcanologia (INGV).
https://doi.org/https://doi.org/10.13127/ESWUA/HF. GNSS stations providers:
(a) Uranus network (http://uranus.gr) operated by the Tree Company corpora‑
tion National Observatory of Athens (NOA) network, http://geodesy.gein.noa.
gr:8000/nginfo/ (Ganas et al. 2008; Chousianitis et al. 2021). HxGN SmartNet
operated by the Metrica SA (https://www.metrica.gr). (b) Turkish National
Permanent GNSS Network-Active (TNPGN-Active/CORS-TR) https://www.
tusaga-aktif.gov.tr/. (c) The DORIS measurements and orbits were obtained
from https://cddis.gsfc.nasa.gov/archive/doris/data. The authors thank Dr.
Laura Scognamiglio and Dr. Paola Baccheschi from INGV for their support to
interpret the seismograms. Anna Belehaki acknowledges fnancial support
provided by the PITHIA-NRF Horizon 2020 Grant Agreement 101007599 of
the European Commission. Elvira Astafyeva acknowledges the support of the
French National Research Agency (ANR), project IONO-DIET (Grant ANR22-CE49-0011), and the French Space Agency (CNES), project “RealDetect”., Peer Reviewed

In this paper, we propose a method for the generation of real-time global ionospheric map (RT-GIM) of vertical total electron content (VTEC) from GNSS measurements. The need for interpolation arises from the fact that the ionospheric pierce point (IPP) measurements from satellites to stations are not distributed uniformly over the ionosphere, leaving unfilled gaps at oceans or poles. The method we propose is based on using a high-quality historical database of post-processed GIMs that comprises more than two solar cycles, calculates the GIM by weighted superposition on a subset of the database with the compatible solar condition. The linear combination of GIMs in the database was obtained by minimizing a ℓ2 distance between VTEC measurements at the IPPs and the VTECs from the database, adding a ℓ1 penalization on the weights to assure a sparse solution. The process uses a Sun-fixed geomagnetic reference frame. This method uses the atomic decomposition/least absolute shrinkage and selection operator (LASSO), which will be denoted as atomic decomposition interpolator of GIMs (ADIGIM). As the computation is done in milliseconds, the interpolation is performed in real time. In this work, two products were developed, denoted as UADG and UARG, the UADG in real time and UARG with a latency of 24 h to benefit from the availability of a greater number of stations. The altimeter JASON3 VTEC measurements were used as reference. The quality of interpolated RT-GIMs from day 258 of 2019 to 155 of the year 2020 is compared with other RT/non-RT GIM products such as those from International GNSS Service (IGS), Centre National d’Etudes Spatiales (CNES), Chinese Academy of Sciences (CAS), Polytechnic University of Catalonia (UPC) and others. The RT ADIGIM performance proved to be better, nearly as good as the rapid or final GIMs computed retrospectively with delays of hours to days. Besides, the non-RT ADIGIM quality is as good or better than most GIM products. The oceanic regions have been included in the assessment which showed that ADIGIM interpolation gives the best estimation (referred to JASON3). The developed method, UADG, will constitute the next-generation UPC RT-GIM, and also UARG will improve the current product UQRG (the current UPC rapid GIM product computed retrospectively) due to its complementary information., This work has been partially supported by the Project PID2019-107579RB-I00 (MICINN). Also was partially supported by the 2017 SGR-0851 Grant of the Generalitat de Catalunya and by the EU Project 101007599 - PITHIA-NRF., Peer Reviewed

The Real-Time Working Group (RTWG) of the International GNSS Service (IGS) is
dedicated to providing high-quality data and high-accuracy products for Global
Navigation Satellite System (GNSS) positioning, navigation, timing and Earth
observations. As one part of real-time products, the IGS combined Real-Time
Global Ionosphere Map (RT-GIM) has been generated by the real-time weighting
of the RT-GIMs from IGS real-time ionosphere centers including the Chinese
Academy of Sciences (CAS), Centre National d'Etudes Spatiales (CNES),
Universitat Politècnica de Catalunya (UPC) and Wuhan University
(WHU). The performance of global vertical total electron content (VTEC)
representation in all of the RT-GIMs has been assessed by VTEC from
Jason-3 altimeter for 3 months over oceans and dSTEC-GPS technique with
2¿d observations over continental regions. According to the
Jason-3 VTEC and dSTEC-GPS assessment, the real-time weighting technique is
sensitive to the accuracy of RT-GIMs. Compared with the performance of
post-processed rapid global ionosphere maps (GIMs) and IGS combined final GIM
(igsg) during the testing period, the accuracy of UPC RT-GIM (after the
improvement of the interpolation technique) and IGS combined RT-GIM (IRTG) is
equivalent to the rapid GIMs and reaches around 2.7 and 3.0 TECU (TEC unit,
1016¿el¿m-2) over
oceans and continental regions, respectively. The accuracy of CAS RT-GIM and
CNES RT-GIM is slightly worse than the rapid GIMs, while WHU RT-GIM requires a
further upgrade to obtain similar performance. In addition, a strong
response to the recent geomagnetic storms has been found in the global
electron content (GEC) of IGS RT-GIMs (especially UPC RT-GIM and IGS combined
RT-GIM). The IGS RT-GIMs turn out to be reliable sources of real-time global
VTEC information and have great potential for real-time applications including
range error correction for transionospheric radio signals, the monitoring of
space weather, and detection of natural hazards on a global scale. All the IGS
combined RT-GIMs generated and analyzed during the testing period are
available at https://doi.org/10.5281/zenodo.5042622 (Liu et al., 2021b)., his research has been supported by the
China Scholarship Council (CSC). The contribution from UPC-
IonSAT authors was partially supported by the European Union-
funded project PITHIA-NRF (grant no. 101007599) and by
the ESSP/ICAO-funded project TEC4SpaW. The work of An-
drzej Krankowski is supported by the National Centre for Research
and Development, Poland, through grant ARTEMIS (grant nos.
DWM/PL-CHN/97/2019 and WPC1/ARTEMIS/2019), Peer Reviewed

© 2022 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., In this article, we show the capability of a global navigation satellite system (GNSS) precise orbit determination (POD) low Earth orbit (LEO) data to detect anomalous ionospheric disturbances in the spectral range of the signals associated with earthquakes and tsunamis, applied to two of these events in Papua New Guinea (PNG) and the Solomon Islands during 2016. This is achieved thanks to the new PIES approach (POD-GNSS LEO Detrended Ionospheric Electron Content Significant Deviations). The significance of such ionospheric signals above the swarm LEOs is confirmed with different types of independent data: in situ electron density measurements provided by the Langmuir Probe (LP) onboard swarm LEOs, DORIS, and ground-based GNSS colocated measurements, as it is described in this article. In this way, we conclude the possible detection of the tsunami-related ionospheric gravity wave in PNG 2016 event, consistent with the most-recent theory, which shows that a tsunami (which is localized in space and time) excites a spectrum of gravity waves, some of which have faster horizontal phase speeds than the tsunami. We believe that this work shows as well the feasibility of a future potential monitoring system of ionospheric disturbances, to be made possible by hundreds of CubeSats with POD GNSS receivers among other appropriate sensors, and supported for real-time or near real-time confirmation and characterization by thousands of worldwide existing ground GNSS receivers., This work has been partially supported by the COSTO
ESA-funded project (ESA ITT AO/1-9514/18/NL/IA). Also
it was partially supported by the 2017 SGR-0851 grant of the
Generalitat de Catalunya and by the EU project 101007599 -
PITHIA-NRF. The data for this paper are available and they
can be requested from H. Yang (h.yang@upc.edu) and M.
Hernandez-Pajares (manuel.hernandez@upc.edu)., Peer Reviewed