Advantages of Geostationary Satellites for Ionospheric Anomaly Studies: Ionospheric Plasma Depletion Following a Rocket Launch

In this study, we analyzed signals transmitted by the U.S. Wide Area Augmentation System (WAAS) geostationary (GEO) satellites using the Variometric Approach for Real-Time Ionosphere Observation (VARION) algorithm in a simulated real-time scenario, to characterize the ionospheric response to the 24 August 2017 Falcon 9 rocket launch from Vandenberg Air Force Base in California. VARION is a real-time Global Navigation Satellites Systems (GNSS)-based algorithm that can be used to detect various ionospheric disturbances associated with natural hazards, such as tsunamis and earthquakes. A noise reduction algorithm was applied to the VARION-GEO solutions to remove the satellite-dependent noise term. Our analysis showed that the interactions of the exhaust plume with the ionospheric plasma depleted the total electron content (TEC) to a level comparable with nighttime TEC values. During this event, the geometry of the satellite-receiver link is such that GEO satellites measured the depleted plasma hole before any GPS satellites. We estimated that the ionosphere relaxed back to a pre-perturbed state after about 3 h, and the hole propagated with a mean speed of about 600 m/s over a region of 700 km in radius. We conclude that the VARION-GEO approach can provide important ionospheric TEC real-time measurements, which are not affected by the motion of the ionospheric pierce points (IPPs). Furthermore, the VARION-GEO measurements experience a steady noise level throughout the entire observation period, making this technique particularly useful to augment and enhance the capabilities of well-established GNSS-based ionosphere remote sensing techniques and future ionospheric-based early warning systems.

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GNSS total variometric approach: first demonstration of a tool for real-time tsunami genesis estimation

Scientific Reports ◽

10.1038/s41598-021-82532-6 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Michela Ravanelli ◽

Giovanni Occhipinti ◽

Giorgio Savastano ◽

Attila Komjathy ◽

Esayas B. Shume ◽

...

Keyword(s):

Real Time ◽

Ground Motion ◽

Data Stream ◽

Electron Content ◽

Warning Systems ◽

Time Data ◽

Total Electron ◽

Ground Shaking ◽

Variometric Approach ◽

Gnss Data

AbstractGlobal Navigation Satellite System (GNSS) is used in seismology to study the ground displacements as well as to monitor the ionospheric total electron content (TEC) perturbations following seismic events. The aim of this work is to combine these two observations in one real-time method based on the Total Variometric Approach (TVA) to include the GNSS real-time data stream in future warning systems and tsunami genesis estimation observing both, ground motion and TEC. Our TVA couples together the Variometric Approach for Displacement Analysis Stand-alone Engine (VADASE) with the Variometric Approach for Real-Time Ionosphere Observation (VARION) algorithms. We apply the TVA to the Mw 8.3 Illapel earthquake, that occurred in Chile on September 16, 2015, and we demonstrate the coherence of the earthquake ground shaking and the TEC perturbation by using the same GNSS data stream in a real-time scenario. Nominally, we also highlight a stronger kinetic energy released in the north of the epicenter and visible in both, the ground motion and the TEC perturbation detect at 30 s and around 9.5 min after the rupture respectively. The high spatial resolution of ionospheric TEC measurement seems to match with the extent of the seismic source. The GNSS data stream by TVA of both the ground and ionospheric measurement opens today new perspectives to real-time warning systems for tsunami genesis estimation.

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Real-Time Geophysical Applications with Android GNSS Raw Measurements

Remote Sensing ◽

10.3390/rs11182113 ◽

2019 ◽

Vol 11 (18) ◽

pp. 2113 ◽

Cited By ~ 8

Author(s):

Marco Fortunato ◽

Michela Ravanelli ◽

Augusto Mazzoni

Keyword(s):

Real Time ◽

Noise Level ◽

Vertical Component ◽

Satellite System ◽

Electron Content ◽

Dual Frequency ◽

Total Electron ◽

Variometric Approach ◽

Global Navigation Satellite ◽

Slant Total Electron Content

The number of Android devices enabling access to raw GNSS (Global Navigation Satellite System) measurements is rapidly increasing, thanks to the dedicated Google APIs. In this study, the Xiaomi Mi8, the first GNSS dual-frequency smartphone embedded with the Broadcom BCM47755 GNSS chipset, was employed by leveraging the features of L5/E5a observations in addition to the traditional L1/E1 observations. The aim of this paper is to present two different smartphone applications in Geoscience, both based on the variometric approach and able to work in real time. In particular, tests using both VADASE (Variometric Approach for Displacement Analysis Stand-alone Engine) to retrieve the 3D velocity of a stand-alone receiver in real-time, and VARION (Variometric Approach for Real-Time Ionosphere Observations) algorithms, able to reconstruct real-time sTEC (slant total electron content) variations, were carried out. The results demonstrate the contribution that mass-market devices can offer to the geosciences. In detail, the noise level obtained with VADASE in a static scenario—few mm/s for the horizontal components and around 1 cm/s for the vertical component—underlines the possibility, confirmed from kinematic tests, of detecting fast movements such as periodic oscillations caused by earthquakes. VARION results indicate that the noise level can be brought back to that of geodetic receivers, making the Xiaomi Mi8 suitable for real-time ionosphere monitoring.

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Detection of tsunami induced ionospheric perturbation with ship-based GNSS measurements: 2010 Maule tsunami case study

10.5194/egusphere-egu2020-11583 ◽

2020 ◽

Author(s):

Michela Ravanelli ◽

James Foster

Keyword(s):

Real Time ◽

Hawaiian Islands ◽

Cost Effective ◽

Early Warning Systems ◽

Electron Content ◽

Ionospheric Disturbances ◽

Total Electron ◽

Tsunami Early Warning ◽

Phase Measurements ◽

Gnss Receivers

The VARION (Variometric Approach for Real-Time Ionosphere Observation) algorithm has been successfully applied to TIDs (Travelling ionospheric disturbances) detection in several real-time scenarios [1, 2]. VARION, thus, estimates sTEC (slant total electron content) variations starting from the single time differences of geometry-free combinations of GNSS carrier-phase measurements. This feature makes VARION suitable to also leverage GNSS observations coming from moving receivers such as ship-based GNSS receivers: the receiver motion does not affect the sTEC estimation process.The aim of this work is to use the observations coming from two GNSS receivers installed on a ship moving near Kauai Island in the Hawaiian archipelago to detect the TIDs connected to the 2010 Maule earthquake and tsunami [3]. Indeed, this earthquake triggered a tsunami that affected all the Pacific region and that reached the Hawaiian islands after about 15 hours. All our analysis was carried out in post-processing, but simulated a real-time scenario: only the data available in real time were used.In order to get a reference, the ship-based sTEC variations were compared with the ones coming from GNSS permanent stations situated in the Hawaiian Islands. In particular, if we considered the same satellite, the same TID is detected by both ship and ground receivers. As expected, the ship-based&#160; sTEC variations are a little bit noisier since they are coming from a kinematic platform.Hence, the results, although preliminary, are very encouraging: the same TIDs is detected both from the sea (ships) and land (permanent receivers).&#160; Therefore, the VARION algorithm is also able to leverage observations coming from ship-based GNSS receivers to detect TIDs in real-time.In conclusion, we firmly believe that the application of VARION to observation coming from ship-based GNSS receivers could really represent a real-time and cost-effective tool to enhance tsunami early warning systems, without requiring the installation of complex infrastructures in open sea.References[1] Giorgio Savastano, Attila Komjathy, Olga Verkhoglyadova, Augusto Mazzoni, Mattia Crespi, Yong Wei, and Anthony J Mannucci, &#8220;Real-time detection of tsunami ionospheric disturbances with a stand-alone gnss receiver: A preliminary feasibility demonstration, &#8221;Scientific reports, vol. 7, pp. 46607, 2017.[2] Giorgio Savastano, Attila Komjathy, Esayas Shume, Panagiotis Vergados, Michela Ravanelli, Olga Verkhoglyadova, Xing Meng, and Mattia Crespi, &#8220;Advantages of geostationary satellites for ionospheric anomaly studies: Ionospheric plasma depletion following a rocket launch,&#8221;Remote Sensing, vol. 11, no. 14, pp. 1734, 2019[3] https://earthquake.usgs.gov/earthquakes/eventpage/official20100227063411530_30/executive

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An innovative methodology for locating ionosphere layer height: case study on 2011 Tohoku-Oki earthquake and tsunami

10.5194/egusphere-egu21-15151 ◽

2021 ◽

Author(s):

Michela Ravanelli ◽

Giovanni Occhipinti

Keyword(s):

Real Time ◽

Physical Models ◽

Electron Content ◽

Ionospheric Disturbances ◽

Mean Velocity ◽

Total Electron ◽

Ionospheric Models ◽

Innovative Methodology ◽

Variometric Approach ◽

Pierce Point

One of the main issues in GNSS ionosphere seismology is to localize the exact height of the single thin layer (Hion) with which the ionosphere is approximated. Hion is generally assumed to be the altitude of the maximum ionospheric ionization (hmF2), i.e., in the ionospheric F-layer. In this sense, Hion is often&#160; be presumed from physical principles or ionospheric models. The determination of &#160;Hion is, therefore, fundamental since it affects the coordinates of the ionospheric pierce point (IPP) and subsequentely of the sub-ionospheric pierce point (SIP).In this work, we present a new developed methodology to determine the exact localization of Hion. We tested this approach on the TIDs (Travelling ionospheric disturbances) connected with the 2011 Tohoku-Oki earthquake and tsunami [1]. In detail, we computed the slant Total Electron Content (sTEC) variations at different Hion (in the range from 100 to 600 km) with the VARION (Variometric Approach for Real-Time Ionosphere Observation) algorithm [2,3], then we interpolated the different pattern in sTEC values related to different waves detected in the ionosphere (AGWepi, IGWtsuna and AWRayleigh) finding the mean velocity value of these waves. Subsequentely, the minimized difference between the estimated propagation velocity and the values from physical models fix us the correct Hion.Our results show a Hion of 370 km, while ionopshere model IRI 2006 located the maximum of ionospheric ionization at an height of 270 km. This difference is important to understand how a different Hion can impact on the location of the sTEC perturbation, affecting the shape and the extent of the source from TEC observations.&#160;&#160;&#160;&#160;References[1] https://earthquake.usgs.gov/earthquakes/eventpage/official20110311054624120_30/executive[2] Giorgio Savastano, Attila Komjathy, Olga Verkhoglyadova, Augusto Mazzoni, Mattia Crespi, Yong Wei, and Anthony J Mannucci, &#8220;Real-time detection of tsunami ionospheric disturbances with a stand-alone gnss receiver: A preliminary feasibility demonstration, &#8221;Scientific reports, vol. 7, pp. 46607, 2017.[3] Giorgio Savastano, Attila Komjathy, Esayas Shume, Panagiotis Vergados, Michela Ravanelli, Olga Verkhoglyadova, Xing Meng, and Mattia Crespi, &#8220;Advantages of geostationary satellites for ionospheric anomaly studies: Ionospheric plasma depletion following a rocket launch,&#8221;Remote Sensing, vol. 11, no. 14, pp. 1734, 2019

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Ionosphere Monitoring with Multi-Frequency and Multi-GNSS Android Smartphone: A Feasibility Study Towards GNSS Big Data Applications for Geosciences

10.5194/egusphere-egu2020-9450 ◽

2020 ◽

Author(s):

Marco Fortunato ◽

Michela Ravanelli ◽

Augusto Mazzoni

Keyword(s):

Real Time ◽

Electron Content ◽

Monitoring Networks ◽

Atmospheric Conditions ◽

Mass Market ◽

Total Electron ◽

Ionosphere Monitoring ◽

Variometric Approach ◽

Gnss Measurements ◽

Static Conditions

The release of Android GNSS Raw Measurements API, (2016) and the growing technological development introduced by the use of multi-GNSS and multi-frequency GNSS chipsets &#8211; changed the hierarchies within the GNSS mass-market world. In this sense, Android smartphones became the new leading products. Positioning performances and quality of raw GNSS measurements have been studied extensively. Despite the greater susceptibility to multipath and cycle slip due to the low cost antenna used, a positioning up to sub-meter accuracy can be achieved. Among the improvements in positioning and navigation, the availability of GNSS measurements from Android smartphones paved new ways in geophysical applications: e.g. periodic fast movements reconstruction and ionospheric perturbances detection. &#160;In fact, considering the number of Android smartphones compatible with the Google API, additional costless information can be used to densify the actual networks of GNSS permanent stations used to monitor atmospheric conditions. However, an extensively analysis on the reconstruction of ionospheric conditions with Android raw measurements is necessary to prove the accuracy achievable in future ionosphere monitoring networks based on both permanent GNSS station and Android smartphone.The aim of this work is to assess the performance of multi-frequency and multi-GNSS smartphone &#8211; in particular, Xiaomi Mi 8 and Huawei Mate 20 X &#8211; in the reconstruction of real-time sTEC (slant Total Electron Content) variations meaningful of ionospheric perturbations. A 24-hour dataset of 1Hz GNSS measurements in static conditions was collected from the two smartphones in addition to data collected from M0SE, one of the EUREF/IGS permanent stations. The VARION (Variometric Approach for Real-time Ionosphere Observations) algorithm, based on the variometric approach and developed within the Geodesy and Geomatics Division of Sapienza University of Rome, was used to retrieve sTEC variations for all the observation periods.The results, although preliminary, show that it is possible to study also from the smarthphone the trend of sTEC variations with elevation: lower elevation angles cause noisier sTEC variations. RMSE of the order of 0.02 TECU/s are found for elevation angles higher than 20 degrees as it happens for permanent stations. At the same time, the sTEC variations were compared to the overall measurements noise, due to both environmental and receiver noise, in order to statistically define the correlation between RMSE and derived sTEC variation.Although the results obtained in this work are encouraging, still further analyses need to be carried out especially at latitudes where ionosphere conditions and perturbations play a major role. However, the possibility to perform such analyses on datasets collected worldwide is prevented from their availability. The last part of this work is therefore focused on the identification of a methodology to share with the GNSS community to collect, store and share GNSS measurements from Android smartphones to enable the researchers to enlarge the spatial and temporal boundaries of their research in the field of ionosphere modelling with mass-market devices.&#160;

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Real-Time Monitoring and Logging of Ionospheric Scintillation and Total Electron Content

2019 Sixth International Conference on Aerospace Science and Engineering (ICASE) ◽

10.1109/icase48783.2019.9059198 ◽

2019 ◽

Author(s):

Hina Magsi ◽

Arslan Ahmed ◽

Arif Hussain

Keyword(s):

Real Time ◽

Total Electron Content ◽

Ionospheric Scintillation ◽

Electron Content ◽

Real Time Monitoring ◽

Total Electron

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Real-Time Global Ionospheric Map and Its Application in Single-Frequency Positioning

Sensors ◽

10.3390/s19051138 ◽

2019 ◽

Vol 19 (5) ◽

pp. 1138 ◽

Cited By ~ 7

Author(s):

Liang Zhang ◽

Yibin Yao ◽

Wenjie Peng ◽

Lulu Shan ◽

Yulin He ◽

...

Keyword(s):

Real Time ◽

Total Electron Content ◽

Precise Point Positioning ◽

Single Frequency ◽

Electron Content ◽

Vertical Total Electron Content ◽

Total Electron ◽

Time Service ◽

Point Positioning ◽

Raw Observations

The prevalence of real-time, low-cost, single-frequency, decimeter-level positioning has increased with the development of global navigation satellite systems (GNSSs). Ionospheric delay accounts for most errors in real-time single-frequency GNSS positioning. To eliminate ionospheric interference in real-time single-frequency precise point positioning (RT-SF-PPP), global ionospheric vertical total electron content (VTEC) product is designed in the next stage of the International GNSS Service (IGS) real-time service (RTS). In this study, real-time generation of a global ionospheric map (GIM) based on IGS RTS is proposed and assessed. There are three crucial steps in the process of generating a real-time global ionospheric map (RTGIM): estimating station differential code bias (DCB) using the precise point positioning (PPP) method, deriving slant total electron content (STEC) from PPP with raw observations, and modeling global vertical total electron content (VTEC). Experiments were carried out to validate the algorithm’s effectiveness. First, one month’s data from 16 globally distributed IGS stations were used to validate the performance of DCB estimation with the PPP method. Second, 30 IGS stations were used to verify the accuracy of static PPP with raw observations. Third, the modeling of residuals was assessed in high and quiet ionospheric activity periods. Afterwards, the quality of RTGIM products was assessed from two aspects: (1) comparison with the Center for Orbit Determination in Europe (CODE) global ionospheric map (GIM) products and (2) determination of the performance of RT-SF-PPP with the RTGIM. Experimental results show that DCB estimation using the PPP method can realize an average accuracy of 0.2 ns; static PPP with raw observations can achieve an accuracy of 0.7, 1.2, and 2.1 cm in the north, east, and up components, respectively. The average standard deviations (STDs) of the model residuals are 2.07 and 2.17 TEC units (TECU) for moderate and high ionospheric activity periods. Moreover, the average root-mean-square (RMS) error of RTGIM products is 2.4 TECU for the one-month moderate ionospheric period. Nevertheless, for the high ionospheric period, the RMS is greater than the RMS in the moderate period. A sub-meter-level horizontal accuracy and meter-level vertical accuracy can be achieved when the RTGIM is employed in RT-SF-PPP.

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Global and Regional High-Resolution VTEC Modelling Using a Two-Step B-Spline Approach

Remote Sensing ◽

10.3390/rs12071198 ◽

2020 ◽

Vol 12 (7) ◽

pp. 1198 ◽

Cited By ~ 3

Author(s):

Andreas Goss ◽

Michael Schmidt ◽

Eren Erdogan ◽

Florian Seitz

Keyword(s):

Real Time ◽

Spectral Resolution ◽

The State ◽

Single Frequency ◽

External Information ◽

Electron Content ◽

Intermediate Step ◽

Total Electron ◽

B Spline ◽

Hourly Data

The ionosphere is one of the largest error sources in GNSS (Global Navigation Satellite Systems) applications and can cause up to several meters of error in positioning. Especially for single-frequency users, who cannot correct the ionospheric delay, the information about the state of the ionosphere is mandatory. Dual- and multi-frequency GNSS users, on the other hand, can correct the ionospheric effect on their observations by linear combination. However, real-time applications such as autonomous driving or precision farming, require external high accuracy corrections for fast convergence. Mostly, this external information is given in terms of grids or coefficients of the vertical total electron content (VTEC). Globally distributed GNSS stations of different networks, such as the network of the International GNSS Services (IGS), provide a large number of multi-frequency observations which can be used to determine the state of the ionosphere. These data are used to generate Global Ionosphere Maps (GIM). Due to the inhomogeneous global distribution of GNSS real-time stations and especially due to the large data gaps over oceanic areas, the global VTEC models are usually limited in their spatial and spectral resolution. Most of the GIMs are mathematically based on globally defined radial basis functions, i.e., spherical harmonics (SH), with a maximum degree of 15 and provided with a spatial resolution of 2.5 ° × 5 ° in latitude and longitude, respectively. Regional GNSS networks, however, offer dense clusters of observations, which can be used to generate regional VTEC solutions with a higher spectral resolution. In this study, we introduce a two-step model (TSM) comprising a global model as the first step and a regional model as the second step. We apply polynomial and trigonometric B-spline functions to represent the global VTEC. Polynomial B-splines are used for modelling the finer structures of VTEC within selected regions, i.e., the densification areas. The TSM provides both, a global and a regional VTEC map at the same time. In order to study the performance, we apply the developed approach to hourly data of the global IGS network as well as the EUREF network of the European region for St. Patrick storm in March 2015. For the assessment of the generated maps, we use the dSTEC analysis and compare both maps with different global and regional products from the IGS Ionosphere Associated Analysis Centers, e.g., the global product from CODE (Berne, Switzerland) and from UPC (Barcelona, Spain), as well as the regional maps from ROB (Brussels, Belgium). The assessment shows a significant improvement of the regional VTEC representation in the form of the generated TSM maps. Among all other products used for comparison, the developed regional one is of the highest accuracy within the selected time span. Since the numerical tests are performed using hourly data with a latency of one to two hours, the presented procedure is seen as an intermediate step for the generation of high precision regional real-time corrections for modern applications.

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Low-Earth-Orbit observations for space weather and space climate

10.5194/egusphere-egu2020-12209 ◽

2020 ◽

Author(s):

Irina Zakharenkova ◽

Iurii Cherniak ◽

Sergey Sokolovskiy ◽

William Schreiner ◽

Qian Wu ◽

...

Keyword(s):

Electron Density ◽

Plasma Density ◽

Space Weather ◽

Ionospheric Plasma ◽

Radio Occultation ◽

Satellite Orbit ◽

Electron Content ◽

Gps Measurements ◽

Total Electron ◽

Ionospheric Plasma Density

Many of the modern Low-Earth-Orbiting satellites are now equipped with dual-frequency GPS receivers for Radio Occultation (RO) and Precise Orbit Determination (POD). The space-borne GPS measurements can be successfully utilized for ionospheric climatology and space weather monitoring. The combination of GPS measurements, which include RO observations and POD measurements from the upward-looking GPS antenna, provides information about electron density distribution (profile) below the satellite orbit and an integrated Total Electron Content (TEC) above the satellite representing an important data source for electron density climatology above the F2 layer peak on a global scale. We demonstrate the advantages of using space-borne LEO GPS measurements, both RO and upward-looking, for Space Weather activity monitoring including specification of ionospheric plasma density structures at different altitudinal domains of the ionosphere in quiet and disturbed conditions. After the great success of the COSMIC-1 (Constellation Observing System for Meteorology, Ionosphere, and Climate) mission operating since 2006, the six COSMIC-2 satellites were launched into a 24 deg inclination orbit in June 2019. The COSMIC-2 scientific payloads with the advanced Tri-GNSS Radio-Occultation Receiver System provide multiple observation types including multi-GNSS TEC (limb and overhead), RO electron density profiles, amplitude/phase scintillation indices, in-situ ion densities and velocities. The COSMIC-2 advanced instruments allow detection of ionospheric plasma density structures of various scales, and the monitoring of high-rate amplitude and phase scintillations both above and below a satellite orbit. The COSMIC-2 multi-instrumental observations will contribute to a better understanding of the equatorial ionosphere morphology and future forecasting of ionospheric irregularities and radio wave scintillations that harmfully affect satellite-to-Earth communication and navigation systems. We present results of post-event analyses for severe space weather events demonstrating a great potential and contribution of the COSMIC-1/2 missions in combination with the ground-based GNSS receivers and other LEO missions like C/NOFS, DMSP, MetOp, TerraSAR-X, and Swarm for monitoring the space weather effects in the Earth&#8217;s ionosphere.

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Efficient global ionospheric modeling based on multi-source and massive observation data

10.5194/egusphere-egu2020-16618 ◽

2020 ◽

Author(s):

Xulei Jin ◽

Shuli Song ◽

Wei Li ◽

Na Cheng

Keyword(s):

Real Time ◽

Rapid Development ◽

Electron Content ◽

Vertical Total Electron Content ◽

Observation Data ◽

Total Electron ◽

Ionospheric Modeling ◽

Virtual Observation ◽

Data Missing ◽

Modeling Strategy

Abstract Ionosphere is an important error source of satellite navigation and a key component of space weather. With the rapid development of multiple Global Navigation Satellite System (GNSS) and other ionospheric research technologies, and the high precision and near real-time requirements for ionospheric products, it is necessary to carry out a research on multi-source data fusion, massive data processing and near-real-time solution of global ionosphere model (GIM); therefore, we modified the traditional ionospheric modeling technology and generate the GIM products (GIM/SHA). In view of the defect of ground-based GNSS data missing in the ocean regions, the method of adding virtual observation stations to the data missing regions in a large range was adopted, which not only enhanced the accuracy of the GIM in the ocean regions, but also avoided the weight determination among different data sources. In terms of near-real-time modeling, the multi-threaded parallel modeling strategy was adopted. Four GNSS (GPS, GLONASS, BEIDOU, Galileo) observation data, eight virtual observation stations and a server with a CPU frequency of 2.1 GHz and 16 threads were utilized. It took less than 30 minutes to construct the GIM by using parallel modeling strategy, which was 10.3 times faster than serial modeling strategy. The accuracy of the GIM/SHA was verified by using the ionospheric products of International GNSS Service (IGS) Ionosphere Associate Analysis Centers (IAACs) in the period of day of year (DOY) 200-365, 2019. Compared with the ionospheric products of CODE, ESA/ESOC, JPL, UPC, EMR, CAS and WHU, the vertical total electron content (VTEC) root mean squares (RMSs) were 1.09 TEC units (TECu), 1.51TECu, 2.32TECu, 1.88TECu, 2.24TECu, 1.25TECu and 1.38TECu, respectively. The result shows that the GIM/SHA have comparable accuracy with IGS ionospheric products. Satellite altimetry data was exploited to verify the accuracy of GIM/SHA in ocean regions, and it can be concluded that the accuracy of the GIM in ocean regions can be significantly reinforced by adding virtual observation stations in ocean regions. Multi-system and multi-frequency differential code bias (DCB) products (DCB/SHA) were simultaneously generated. Compared with IGS DCB products, the satellite DCB RMSs of DCB/SHA were 0.16ns for GPS, 0.08ns for GLONASS, 0.17ns for BEIDOU and 0.14ns for Galileo; the GNSS receiver DCB RMSs of DCB/SHA were 0.69ns for GPS, 1.06ns for GLONASS, 0.75 for BEIDOU and 1.03ns for Galileo. It can be proved that the accuracy of DCB/SHA are comparable to IGS DCB products.Keywords Multi-GNSS; GIM; Virtual observation station; Near real-time; VTEC; DCB

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