Towards Cooperative Global Mapping of the Ionosphere: Fusion Feasibility for IGS and IRI with Global Climate VTEC Maps

Recommendations of the International Reference Ionosphere (IRI) Workshop 2017 in Taoyuan City, Taiwan and International GNSS Service (IGS) Workshop 2018 in Wuhan, China included establishment of an ionosphere mapping service that would fuse measurements from two independent sensor networks: IGS permanent GNSS receivers providing the vertical total electron content (VTEC) measurements and ionosondes of the Global Ionosphere Radio Observatory (GIRO) that compute the bottomside vertical profiles of the ionospheric plasma density. Using available GAMBIT software at GIRO, we introduced new VTEC products to its data roster: previously unavailable global average (climate) maps of VTEC and slab thickness based on climatological capabilities of IRI. Incorporation of the VTEC and τ maps into the GAMBIT Explorer environment provided data analysts with nearly 10-year history of the reference average VTEC records and opened access to the GAMBIT toolkit for evaluation and validation of the τ computations. This result is the first step towards establishing an infrastructure and the data workflow to provide GAMBIT users with the low latency and consistent quality and usability of the ionospheric weather-climate specifications. Combination of IGS-provided VTEC and GIRO-provided peak density of F2 layer NmF2 allows ground-based evaluation of the equivalent slab thickness τ, a derived property of the near-Earth plasma that characterizes the skewness of its vertical profile up to the GNSS spacecraft altitudes.

Download Full-text

Evaluation of the IGS–Global Ionospheric Mapping model over Egypt

10.5194/angeo-2018-92 ◽

2018 ◽

Author(s):

Mostafa Rabah ◽

Ahmed Sedeek

Keyword(s):

North Africa ◽

Evaluation Method ◽

Daily Basis ◽

Electron Content ◽

Vertical Total Electron Content ◽

International Gnss Service ◽

Ionospheric Correction ◽

Total Electron ◽

The North ◽

Using Data

Abstract. Global ionosphere maps (GIM) are generated on a daily basis at CODE using data from about 400 GPS/GLONASS sites of the IGS and other institutions. The vertical total electron content (VTEC) is modeled in a solar-geomagnetic reference frame using a Spherical Harmonics Expansion “SHE” up to degree and order 15. To cover the holes of the first GIM computation stage existing in the North Africa and over the Oceans resulting a shortage of GNSS station in North Africa, an optimum spatial-temporal interpolation technique was developed to cover these holes (Krankowski and Hernandez-Pajares, 2016). The current paper evaluates the ionospheric correction by Global Ionospheric Maps, GIM, provided in (IONEX) files produced by International GNSS Services “IGS”. The evaluation is performed based on investigating the effect of a given GIM ionospheric correction on kinematic relative positioning solutions. The evaluation was done using several baselines of different lengths in Egypt. The results show that there is no significant effect of the provided GIM values on the solution of kinematic processing. The results confirm that although there is a lack of International GNSS Service (IGS stations) over North Africa, GIMs have no effect in mitigating ionospheric error. A new value for the ionosphere correction VTEC values was obtained by a regional, developed algorithm based on zero-differenced phase ionospheric delay (ZDPID) (Tawfeek et al., 2018). These new values of VTEC were fed into GIMs for the specified stations data. A useful result was obtained for correcting the ionospheric error over kinematic solution of many baseline lengths up to 300 km which demonstrates validity of the proposed evaluation method.

Download Full-text

Analysis of a new regional ionospheric assimilated H2PT model for Europe

10.5194/egusphere-egu2020-1524 ◽

2020 ◽

Author(s):

Paulina Woźniak ◽

Anna Świątek ◽

Mariusz Pożoga ◽

Łukasz Tomasik

Keyword(s):

Spatial Resolution ◽

Negative Impact ◽

Satellite System ◽

Electron Content ◽

Maximum Height ◽

Vertical Total Electron Content ◽

Dual Frequency ◽

International Gnss Service ◽

Statistical Parameters ◽

Total Electron

The signal emitted by the GNSS (Global Navigation Satellite System) satellite, on the way to the receiver located on the Earth&#8217;s surface, encounters a heterogeneous layer of ionized gas and free electrons, in which the radio wave is dispersed. As the ionosphere is the source of the highest-value errors among the different factors that affect GNSS positioning accuracy, it is necessary to minimize its negative impact. Various methods are used to compensate for the ionospheric delay, one of which is the usage of models. The intensity of the processes occurring in the ionosphere is closely related to the Sun activity. As a consequence, with respect to a given location on the Earth's surface, the activity of the ionosphere changes throughout the year and day. Therefore, a model dedicated to a specific region is especially important in case of high-precision GNSS applications. The assimilated H2PT model was based on the dual-frequency observations from GNSS stations belonging to EPN (EUREF Permanent Network), as well as on ionosondes participating in the DIAS (European Digital Upper Atmosphere Server) project. The H2PT model covers the Europe area, data with a 15-minutes interval were placed in similar to IONEX (IONosphere Map EXchenge) files in two versions of spatial resolution: 1- and 5-degree. Data provided by the H2PT model are the VTEC (Vertical Total Electron Content) values and the hmF2 (maximum height of the F2 layer) parameters. The subject of this research is the comparison of the H2PT model with NeQuick-G model and IONEX data published by IGS (International GNSS Service) in the context of TEC values as well as determining differences between regional hmF2 data and its commonly used fixed value for the entire globe, amounting to 450 km. In order to perform the analysis, appropriate visualizations were made and statistical parameters determined. Additionally, data from selected periods of positive and negative disturbances were analysed in details based on the developed time series. The relatively high temporal and spatial resolution is undoubtedly an advantage of the H2PT model, because unlike global models, the regional one allows conscientious analysis of the ionosphere characteristics for the area of Europe. Importantly, solutions regarding hmF2 show significant deviations from the fixed value approximated for the whole Earth. Taking into account the parameter appropriate for a given location and time during GNSS data processing may improve the obtained positioning quality.&#160;

Download Full-text

Redes neurais artificiais aplicadas na previsão do VTEC no Brasil

Boletim de Ciências Geodésicas ◽

10.1590/s1982-21702013000200005 ◽

2013 ◽

Vol 19 (2) ◽

pp. 227-246 ◽

Cited By ~ 1

Author(s):

Wagner Carrupt Machado ◽

Edvaldo Simões da Fonseca Junior

Keyword(s):

Total Electron Content ◽

Electron Content ◽

Vertical Total Electron Content ◽

International Gnss Service ◽

Total Electron ◽

De Se ◽

Pierce Point ◽

Global Ionospheric Maps

Uma forma de se prever o conteúdo total de elétrons na direção vertical (VTEC - Vertical Total Electron Content) usando a arquitetura de redes neurais artificiais (RNA) denominada de perceptrons de múltiplas camadas (MLP - MultipLayer Percetrons) é apresentada e avaliada nesta pesquisa. As entradas do modelo foram definidas como sendo a posição dos pontos ionosféricos (IPP - Ionospheric Pierce Point) e o tempo universal (TU), enquanto que a saída é o VTEC. As variações sazonais e de períodos mais longos são levadas em conta através da atualização do treinamento diariamente. Testes foram conduzidos sobre uma área que abrange o Brasil e sua vizinhança considerando períodos de alta e baixa atividade solar. As RNA foram treinadas utilizando informações dos mapas globais da ionosfera (GIM - Global Ionospheric Maps) produzidos pelo serviço internacional do GNSS (IGS - International GNSS Service) das 72 horas anteriores à época de início da previsão. As RNA treinadas foram utilizadas para prever o VTEC por 72 horas (VTEC RNA). Os VTEC RNA foram comparados com os VTEC contidos nos GIM (VTEC GIM). A raiz do erro médio quadrático (RMS) da diferença entre o VTEC GIM e o VTEC RNA variou de 1,4 a 10,7 unidades de TEC (TECU). O erro relativo mostra que a RNA proposta foi capaz de prever o VTEC com 70 a 85% de acerto.

Download Full-text

Assessment of global ionospheric maps performance in the Brazilian region using ionosonde data

10.5194/egusphere-egu21-5440 ◽

2021 ◽

Author(s):

Gabriel Jerez ◽

Manuel Hernández-Pajares ◽

Fabricio Prol ◽

Daniele Alves ◽

João Monico

Keyword(s):

Solar Cycle ◽

Shape Function ◽

Assessment Method ◽

Slab Thickness ◽

Electron Content ◽

Vertical Total Electron Content ◽

Total Electron ◽

One Year ◽

Global Ionospheric Maps ◽

Function Peak

In this work, we present a new method for assessing global ionospheric maps (GIM) by means of ionosonde data. The method proposed is based on the critical frequency at the F2 layer directly measured by pairs of ionosondes to assess VTEC (vertical total electron content) values from GIMs. Four strategies were investigated and, the best one was the linear interpolation of squared foF2 based on the VTEC ratio. The analysis was based on the root mean square (RMS) of the differences between the measured and estimated foF2 values at the first ionosonde from each pair. The foF2 were estimated using the values measured at the second ionosonde and interpolated to the position of the first ionosonde with the VTEC values from the GIMs. Besides the RMS values, additional ionospheric indicators (slab thickness and shape function peak) were used to complement the daily analysis. This method was tested over one of the most challenging scenarios, the Brazilian region and near the last solar cycle peak. The assessment considered four ionosondes (combined in six pairs) and thirteen GIM products available at CDDIS (Crustal Dynamics Data Information System), CORG, CODG, EHRG, ESRG, ESAG, IGRG, IGSG, JPLG, UPRG, UPCG, UQRG, WHRG and WHUG. Analysis was conducted using daily, weekly, one year, and four years of data. The analysis with daily data showed that slab thickness and shape function peak could be helpful to identify periods and regions where this method could be applied. The weekly analysis was performed to select the best strategy to interpolate the foF2 values. The analysis of one-year data (2015) was performed considering all GIMs previously mentioned. CODG, IGSG, JPLG, UQRG, WHRG, and WHUG provided the best results, with mean rates of improvement up to 42% in comparison to not using any GIM. The four-year time series (2014-2017) were analyzed considering the two products with better performance for the one-year analysis (CODG and UQRG). With data from 2014-2017, CODG and UQRG provided improvement rates of up to 49%. In general, regional and temporal ionospheric influences could be noticed in the results, with expected larger errors closer to the solar cycle peak in 2014 and at locations with pairs of ionosondes with the larger distance apart. Therefore, we have confirmed the viability of the developed approach as an assessment method to analyze GIMs quality based on ionosonde data.

Download Full-text

Ionosphere VTEC modeling with the raw-observation-based PPP model：an advantage demonstration in the multi-frequency and multi-GNSS context

10.5194/egusphere-egu2020-12914 ◽

2020 ◽

Author(s):

Teng Liu ◽

Baocheng Zhang ◽

Yunbin Yuan ◽

Xiao Zhang

Keyword(s):

Rapid Development ◽

Global Navigation Satellite Systems ◽

Electron Content ◽

Vertical Total Electron Content ◽

Dual Frequency ◽

International Gnss Service ◽

Total Electron ◽

Satellite Systems ◽

Triple Frequency ◽

Global Navigation Satellite

The ionospheric delay accounts for one of the major errors that the Global Navigation Satellite Systems (GNSS) suffer from. Hence, the ionosphere Vertical Total Electron Content (VTEC) map has been an important atmospheric product within the International GNSS Service (IGS) since its early establishment. In this contribution, an enhanced method has been proposed for the modeling of the ionosphere VTECs. Firstly, to cope with the rapid development of the newly-established Galileo and BeiDou constellations in recent years, we extend the current dual-system (GPS/GLONASS) solution to a quad-system (GPS/GLONASS/Galileo/BeiDou) solution. More importantly, instead of using dual-frequency observations based on the Carrier-to-Code Leveling (CCL) method, all available triple-frequency signals are utilized with a general raw-observation-based multi-frequency Precise Point Positioning (PPP) model, which can process dual-, triple- or even arbitrary-frequency observations compatibly and flexibly. Benefiting from this, quad-system slant ionospheric delays can be retrieved based on multi-frequency observations in a more flexible, accurate and reliable way. The PPP model has been applied in both post-processing global and real-time regional VTEC modeling. Results indicate that with the improved slant ionospheric delays, the corresponding VTEC models are also improved, comparing with the traditional CCL method.

Download Full-text

MGR-DCB: A Precise Model for Multi-Constellation GNSS Receiver Differential Code Bias

Journal of Navigation ◽

10.1017/s0373463315000922 ◽

2015 ◽

Vol 69 (4) ◽

pp. 698-708 ◽

Cited By ~ 6

Author(s):

Mohamed Abdelazeem ◽

Rahmi N. Çelik ◽

Ahmed El-Rabbany

Keyword(s):

Total Electron Content ◽

Satellite System ◽

Mean Difference ◽

Electron Content ◽

Vertical Total Electron Content ◽

International Gnss Service ◽

Total Electron ◽

Differential Code Bias ◽

Gnss Receiver ◽

Code Bias

In this study, we develop a Multi-constellation Global Navigation Satellite System (GNSS) Receiver Differential Code Bias (MGR-DCB) model. The model estimates the receiver DCBs for the Global Positioning System (GPS), BeiDou and Galileo signals from the ionosphere-corrected geometry-free linear combinations of the code observations. In order to account for the ionospheric delay, a Regional Ionospheric Model (RIM) over Europe is developed. GPS observations from 60 International GNSS Servoce (IGS) and EUREF reference stations are processed in the Bernese-5·2 Precise Point Positioning (PPP) module to estimate the Vertical Total Electron Content (VTEC). The RIM has spatial and temporal resolutions of 1° × 1° and 15 minutes, respectively. The receiver DCBs for three stations from the International GNSS Service Multi-GNSS Experiment (IGS-MGEX) are estimated for three different days. The estimated DCBs are compared with the MGEX published values. The results show agreement with the MGEX values with mean difference and Root Mean Square Error (RMSE) values less than 1 ns. In addition, the combined GPS, BeiDou and Galileo VTEC values are evaluated and compared with the IGS Global Ionospheric Maps (IGS-GIM) counterparts. The results show agreement with the GIM values with mean difference and RMSE values less than 1 Total Electron Content Unit (TECU).

Download Full-text

The cooperative IGS RT-GIMs: a reliable estimation of the global ionospheric electron content distribution in real time

Earth System Science Data ◽

10.5194/essd-13-4567-2021 ◽

2021 ◽

Vol 13 (9) ◽

pp. 4567-4582

Author(s):

Qi Liu ◽

Manuel Hernández-Pajares ◽

Heng Yang ◽

Enric Monte-Moreno ◽

David Roma-Dollase ◽

...

Keyword(s):

Real Time ◽

Geomagnetic Storms ◽

Quality Data ◽

Electron Content ◽

Vertical Total Electron Content ◽

International Gnss Service ◽

Strong Response ◽

Total Electron ◽

The Real ◽

Testing Period

Abstract. 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).

Download Full-text

Characterization of GPS-TEC in a low-latitude region over Thailand during 2010-2012

Annals of Geophysics ◽

10.4401/ag-6717 ◽

2015 ◽

Vol 58 (5) ◽

Author(s):

V. Rajesh Chowdhary ◽

Nitin K. Tripathi ◽

Sanit Arunpold ◽

Durairaju Kumaran Raju

Keyword(s):

Ultra Violet ◽

Electron Content ◽

Vertical Total Electron Content ◽

Dual Frequency ◽

Chiang Mai ◽

International Gnss Service ◽

Total Electron ◽

Gps Tec ◽

First Results ◽

June July

This paper presents the first results of vertical total electron content (VTEC) data from (1) a dual-frequency GPS receiver installed at the Chiang Mai University in Chiang Mai (CHGM, 18.480 N, 98.570 E) as part of SCINDA (Scintillation Network and Decision Aid) and (2) the International GNSS Service (IGS) station Pathum Wan (CUSV, 13.735 N, 100.533 E) with magnetic latitude of 8.69°N and 3.92°N respectively in Thailand, from August 2010 to July 2012. In the equatorial ionization anomaly (EIA) region, these two stations are separated at a distance of 668 km. Observed GPS-TEC values were found to be the highest between 1500 and 1900 Local Time (LT) throughout the study period at both the stations. The GPS-TEC data from both the stations was plotted diurnal, monthly and seasonal analyses were performed. The equinox (March, April, September, and October) and solstice (January, February, June, July, and December) periods had maximum and minimum diurnal peak variations, respectively, of the GPS-TEC. High TEC values are attributed to extreme solar ultra-violet ionization coupled with upward vertical E×B drift. A comparison of the GPS-TEC data from both the stations for the study period shows that the CHGM station recorded higher values of TEC than the CUSV station because of the formation of an ionization crest over the CHGM station. The GPS-TEC values also exhibited an increasing trend-because of the approach of solar cycle 24. For data validation, the diurnal, monthly, and seasonal variations in the measured TEC were compared with the TEC modelled in the International Reference Ionosphere (IRI) models (IRI-2007 and the recently released IRI-2012 model). The IRI-2007 shows good agreement with the data from 2010 to 2011 from both stations and IRI-2012 agrees well with the data from 2012 onwards compared to IRI-2007.

Download Full-text

Assessment of Global Ionospheric Maps Performance by Means of Ionosonde Data

Remote Sensing ◽

10.3390/rs12203452 ◽

2020 ◽

Vol 12 (20) ◽

pp. 3452

Author(s):

Gabriel O. Jerez ◽

Manuel Hernández-Pajares ◽

Fabricio S. Prol ◽

Daniele B. M. Alves ◽

João F. G. Monico

Keyword(s):

System Analysis ◽

Shape Function ◽

Assessment Method ◽

Slab Thickness ◽

Electron Content ◽

Vertical Total Electron Content ◽

Total Electron ◽

One Year ◽

Global Ionospheric Maps ◽

Function Peak

This work presents a new method for assessing global ionospheric maps (GIM) using ionosonde data. The method is based on the critical frequency at the F2 layer directly measured by ionosondes to validate VTEC (vertical total electron content) values from GIMs. The analysis considered four different approaches to using foF2. The study was performed over one of the most challenging scenarios, the Brazilian region, considering four ionosondes (combined in six pairs) and thirteen GIM products available at CDDIS (Crustal Dynamics Data Information System). Analysis was conducted using daily, weekly, one year (2015), and four years (2014–2017) of data. Additional information from the ionosphere was estimated to complement the daily analysis, such as slab thickness and shape function peak. Results indicated that slab thickness and shape function peak could be used as alternative indicators of periods and regions where this method could be applied. The weekly analysis indicated the squared frequency ratio with local time correction as the best approach of using foF2, between the ones evaluated. The analysis of one-year data (2015) was performed considering thirteen GIMs, where CODG and UQRG were the two GIMs that presented the best performance. The four-year time series (2014–2017) were analyzed considering these two products. Regional and temporal ionospheric influences could be noticed in the results, with expected larger errors during the solar cycle peak in 2014 and at locations with pairs of ionosondes with the larger distance apart. Therefore, we have confirmed the viability of the developed approach as an assessment method to analyze GIMs quality based on ionosonde data.

Download Full-text

Ionosonde Total Electron Content Evaluation Using IGS Data

10.5194/angeo-2019-131 ◽

2019 ◽

Author(s):

Telmo dos Santos Klipp ◽

Adriano Petry ◽

Gabriel Sandim Falcão ◽

Jonas Rodrigues de Souza ◽

Eurico Rodrigues de Paula ◽

...

Keyword(s):

Electron Density ◽

Total Electron Content ◽

Confidence Score ◽

Transition Function ◽

Electron Content ◽

Maximum Height ◽

Vertical Total Electron Content ◽

International Gnss Service ◽

Total Electron ◽

Account Electron

Abstract. In this work, a period of two years (2016–2017) of vertical total electron content (VTEC) from ionosondes operating in Brazil is compared to the International GNSS Service (IGS) data. Sounding instruments from National Institute for Space Research (INPE) provided the ionograms used, which were filtered based on confidence score (CS) and C-level flags evaluation. Differences between TEC from IGS maps and ionograms were accumulated in terms of root mean square error (RMSE). It has been noticed the TEC values provided by ionograms are systematically underestimated, which is attributed to a limitation in the electron density modeled for the ionogram topside that considers maximum height only around 800–900 Km, while IGS takes in account electron density from GNSS stations up to the satellite network orbits. The ionogram topside profiles covering the plasmasphere were re-modeled using an adaptive alpha-Chapman exponential decay that includes a transition function between the F2 layer and plasmasphere, and electron density integration height was extended to compute TEC. Chapman parameters for the F2 layer were extracted from each ionogram, and plasmaspheric scale height was set to 10,000 Km. Our analysis has shown the plasmaspheric basis electron density, assumed to be proportional to the electron peak density, plays an important role to reduce the RMSE values. Depending on the proportionality coefficient choice, mean RMSE reached a minimum of 5.32 TECU, that is 23 % lower than initial ionograms TEC errors.

Download Full-text