scholarly journals Modelling Global Ionosphere Based on Multi-Frequency, Multi-Constellation GNSS Observations and IRI Model

2020 ◽  
Vol 12 (3) ◽  
pp. 439 ◽  
Author(s):  
Xiangdong An ◽  
Xiaolin Meng ◽  
Hua Chen ◽  
Weiping Jiang ◽  
Ruijie Xi ◽  
...  
Keyword(s):  
Geomagnetic Storms ◽  
A Priori ◽  
Global Navigation Satellite Systems ◽  
Electron Content ◽  
Dual Frequency ◽  
International Gnss Service ◽  
Iri Model ◽  
Total Electron ◽  
Satellite Systems ◽  
Gnss Observations

With the emergence of BeiDou and Galileo as well as the modernization of GPS and GLONASS, more available satellites and signals enhance the capability of Global Navigation Satellite Systems (GNSS) to monitor the ionosphere. However, currently the International GNSS Service (IGS) Ionosphere Associate Analysis Centers (IAACs) just use GPS and GLONASS dual-frequency observations in ionosphere estimation. To better determine the global ionosphere, we used multi-frequency, multi-constellation GNSS observations and a priori International Reference Ionosphere (IRI) to model the ionosphere. The newly estimated ionosphere was represented by a spherical harmonic expansion function with degree and order of 15 in a solar-geomagnetic frame. By collecting more than 300 stations with a global distribution, we processed and analysed two years of data. The estimated ionospheric results were compared with those of IAACs, and the averaged Root Mean Squares (RMS) of Total Electron Content (TEC) differences for different solutions did not exceed 3 TEC Unit (TECU). Through validation by satellite altimetry, it was suggested that the newly established ionosphere had a higher precision than the IGS products. Moreover, compared with IGS ionospheric products, the newly established ionosphere showed a more accurate response to the ionosphere disturbances during the geomagnetic storms.

scholarly journals Estimation and Analysis of GNSS Differential Code Biases (DCBs) Using a Multi-Spacing Software Receiver

Sensors ◽  
2021 ◽  
Vol 21 (2) ◽  
pp. 443
Author(s):  
Ye Wang ◽  
Lin Zhao ◽  
Yang Gao
Keyword(s):  
Primary Source ◽  
Intermediate Frequency ◽  
Global Navigation Satellite Systems ◽  
Electron Content ◽  
Software Receiver ◽  
International Gnss Service ◽  
Total Electron ◽  
Satellite Systems ◽  
Differential Code Biases ◽  
Gnss Observations

In the use of global navigation satellite systems (GNSS) to monitor ionosphere variations by estimating total electron content (TEC), differential code biases (DCBs) in GNSS measurements are a primary source of errors. Satellite DCBs are currently estimated and broadcast to users by International GNSS Service (IGS) using a network of GNSS hardware receivers which are inside structure fixed. We propose an approach for satellite DCB estimation using a multi-spacing GNSS software receiver to analyze the influence of the correlator spacing on satellite DCB estimates and estimate satellite DCBs based on different correlator spacing observations from the software receiver. This software receiver-based approach is called multi-spacing DCB (MSDCB) estimation. In the software receiver approach, GNSS observations with different correlator spacings from intermediate frequency datasets can be generated. Since each correlator spacing allows the software receiver to output observations like a local GNSS receiver station, GNSS observations from different correlator spacings constitute a network of GNSS receivers, which makes it possible to use a single software receiver to estimate satellite DCBs. By comparing the MSDCBs to the IGS DCB products, the results show that the proposed correlator spacing flexible software receiver is able to predict satellite DCBs with increased flexibility and cost-effectiveness than the current hardware receiver-based DCB estimation approach.

Validating the impact of various ionosphere correction on mid to long baselines and point positioning using GPS dual-frequency receivers

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Alaa A. Elghazouly ◽  
Mohamed I. Doma ◽  
Ahmed A. Sedeek
Keyword(s):  
Geomagnetic Storms ◽  
Global Navigation Satellite Systems ◽  
Electron Content ◽  
Assessment Procedure ◽  
Vertical Total Electron Content ◽  
Dual Frequency ◽  
Total Electron ◽  
Satellite Systems ◽  
Point Positioning ◽  
The Impact

Abstract Due to the ionosphere delay, which has become the dominant GPS error source, it is crucial to remove the ionospheric effect before estimating point coordinates. Therefore, different agencies started to generate daily Global Ionosphere Maps (GIMs); the Vertical Total Electron Content (VTEC) values represented in GIMs produced by several providers can be used to remove the ionosphere error from observations. In this research, An analysis will be carried with three sources for VTEC maps produced by the Center for Orbit Determination in Europe (CODE), Regional TEC Mapping (RTM), and the International Reference Ionosphere (IRI). The evaluation is focused on the effects of a specific ionosphere GIM correction on the precise point positioning (PPP) solutions. Two networks were considered. The first network consists of seven Global Navigation Satellite Systems (GNSS) receivers from (IGS) global stations. The selected test days are six days, three of them quiet, and three other days are stormy to check the influence of geomagnetic storms on relative kinematic positioning solutions. The second network is a regional network in Egypt. The results show that the calculated coordinates using the three VTEC map sources are far from each other on stormy days rather than on quiet days. Also, the standard deviation values are large on stormy days compared to those on quiet days. Using CODE and RTM IONEX file produces the most precise coordinates after that the values of IRI. The elimination of ionospheric biases over the estimated lengths of many baselines up to 1000 km has resulted in positive findings, which show the feasibility of the suggested assessment procedure.

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

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

<p>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.</p>

scholarly journals Ionospheric Response to the Space Weather Events of 4-10 September 2017: First Chilean Observations

2019 ◽  
Vol 13 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Manuel Bravo ◽  
Carlos Villalobos ◽  
Rodrigo Leiva ◽  
Luis Tamblay ◽  
Pedro Vega-Jorquera ◽  
...  
Keyword(s):  
Total Electron Content ◽  
Space Weather ◽  
Global Navigation Satellite Systems ◽  
Time Interval ◽  
Electron Content ◽  
Dual Frequency ◽  
Field Station ◽  
Total Electron ◽  
Satellite Systems ◽  
Weather Events

Objective: The diurnal variations of several ionospheric characteristics during the Space Weather Events of 4-10 September 2017, for Chilean latitudes, will be reported. Materials and Methods: Observations were made using a recently installed ionosonde at the Universidad de La Serena field station (29°52'S; 71°15’W). Also, reported is the total electron content determined using the upgraded Chilean network of dual-frequency Global Navigation Satellite Systems (GNSS) receivers. Results: Sudden ionospheric disturbances are described in terms of the minimum reflection frequency determined from ionosonde records. An attempt to derive the extent of the effect on high frequency propagation paths in the region is made using simultaneous ionosonde observations at other locations. The geomagnetic storm ionospheric effects are discussed in detail using the observed diurnal variation of maximum electron concentration (NmF2), virtual height of the F-region (h’F/F2) and Total Electron Content (TEC). These are complemented with the time-latitude variation of TEC for the 70°W meridian. Conclusion: It is found that large increases of NmF2, h’F/F2 and TEC observed during 8 September 2017 storm are well described in terms of the evolution of the Equatorial Ionospheric Anomaly (EIA) over the same time interval. Known physical mechanisms are suggested to explain most of the observations.

scholarly journals Accuracy of Global Ionosphere Maps in Relation to Their Time Interval

2021 ◽  
Vol 13 (18) ◽  
pp. 3552
Author(s):  
Beata Milanowska ◽  
Paweł Wielgosz ◽  
Anna Krypiak-Gregorczyk ◽  
Wojciech Jarmołowski
Keyword(s):  
Solar Activity ◽  
Geomagnetic Storms ◽  
High Solar Activity ◽  
Time Interval ◽  
Electron Content ◽  
Dual Frequency ◽  
Total Electron ◽  
Low Latitudes ◽  
Globally Distributed ◽  
Gnss Observations

Global ionosphere maps (GIMs) representing ionospheric total electron content (TEC) are applicable in many scientific and engineering applications. However, the GIMs provided by seven Ionosphere Associated Analysis Centers (IAACs) are generated with different temporal resolutions and using different modeling techniques. In this study, we focused on the influence of map time interval on the empirical accuracy of these ionospheric products. We investigated performance of the high-resolution GIMs during high (2014) and low (2018) solar activity periods as well as under geomagnetic storms (19 February 2014 and 17 March 2015). In each of the analyzed periods, GIMs were also assessed over different geomagnetic latitudes. For the evaluation, we used direct comparison of GIM-derived slant TEC (STEC) with dual-frequency GNSS observations obtained from 18 globally distributed stations. In order to perform a comprehensive study, we also evaluated GIMs with respect to altimetry-derived vertical TEC (VTEC) obtained from the Jason-2 and Jason-3 satellites. The study confirmed the influence of GIMs time interval on the provided TEC accuracy, which was particularly evident during high solar activity, geomagnetic storms, and also at low latitudes. The results show that 120-min interval contributes significantly to the accuracy degradation, whereas 60-min one is sufficient to maintain TEC accuracy.

scholarly journals Comparative Study of the Influence of Full and Partial Halo Geomagnetic Storms on High Latitude Ionosphere

2021 ◽  
Vol 4 (2) ◽  
pp. 41-52
Author(s):  
Dominic Chukwuebuka Obiegbuna ◽  
Francisca Nneka Okeke ◽  
Kingsley Chukwudi Okpala ◽  
Orji Prince Orji ◽  
Gregory Ibeabuchi Egba ◽  
...  
Keyword(s):  
Geomagnetic Storm ◽  
Global Positioning System ◽  
High Latitude ◽  
Geomagnetic Storms ◽  
Electron Content ◽  
Dual Frequency ◽  
Total Electron ◽  
Global Positioning ◽  
High Latitude Ionosphere ◽  
Gnss Observations

We have studied and compared the effects of full and partial halo geomagnetic storms on the high latitude ionosphere. The study used the total electron content (TEC) data obtained from the global positioning system (GPS) to examine the level of response of high latitude ionosphere around Ny Alesund, Norway to full and partial halo geomagnetic storms of June 23rd 2015 and January 1st 2016 respectively. This study was carried out using a dual frequency ground based GNSS observations at high latitude (NYAL: 78.56oN, 11.52oE) ionospheric station in Norway. The vertical TEC (VTEC) was extracted from Receiver Independent Exchange (RINEX) formatted GPS-TEC data using the GOPI Software developed by Seemala Gopi. The GOPI software is a GNSS-TEC analysis program which uses ephemeris data and differential code biases (DCBs) in estimating slant TEC (STEC) prior to its conversion to VTEC. From the results, the responses of the high latitude before the storm days were more positive than on the storm days. Also the overall response of the high latitude to the full halo geomagnetic storm was more positive with more impact than that of the partial halo geomagnetic storm.

scholarly journals Granger causality analysis of deviation in total electron content during geomagnetic storms in the equatorial region

2021 ◽  
Vol 68 (1) ◽  
pp. 1-25
Author(s):  
Sumitra Iyer ◽  
Alka Mahajan
Keyword(s):  
Granger Causality ◽  
Total Electron Content ◽  
Geomagnetic Storms ◽  
Spatial Scales ◽  
Equatorial Region ◽  
Global Navigation Satellite Systems ◽  
Electron Content ◽  
Causality Analysis ◽  
Total Electron ◽  
Satellite Systems

AbstractThe total electron content (TEC) in the ionosphere widely influences Global Navigation Satellite Systems (GNSS) especially for critical applications by inducing localized positional errors in the GNSS measurements. These errors can be mitigated by measuring TEC from stations located around the world at various temporal and spatial scales and using them for advanced forecasting of TEC. The TEC can be used as a tool in understanding space weather phenomena such as geomagnetic storms which cause disruptions in the ionosphere. This paper examines the causal relationship between perturbations in TEC caused by geomagnetic storms. The causality between two geomagnetic indices auroral electrojet (AE) and disturbed storm index (Dst) and TEC is investigated using Granger causality at two low-latitude stations, Bangalore and Hyderabad. The outcomes of this study strengthen the regional understanding and modeling of ionospheric parameters which can contribute towards the global efforts for modeling and reducing the ionospheric effects on trans-ionospheric communication and navigation. The causal inferences combined with the data-driven model can be useful in identifying the correct and informative physical quantities to improve the forecasting models.

scholarly journals An SBAS Integrity Model to Overbound Residuals of Higher-Order Ionospheric Effects in the Ionosphere-Free Linear Combination

2020 ◽  
Vol 12 (15) ◽  
pp. 2467
Author(s):  
Stefan Schlüter ◽  
Mohammed Mainul Hoque
Keyword(s):  
Linear Combination ◽  
Global Navigation Satellite Systems ◽  
Vertical Position ◽  
Electron Content ◽  
Dual Frequency ◽  
Total Electron ◽  
Satellite Systems ◽  
Position Errors ◽  
Global Navigation Satellite ◽  
Ray Bending

The next generation of satellite-based augmentation systems (SBAS) will support aviation receivers that take advantage of the ionosphere-free dual-frequency combination. By combining signals of the L1 and L5 bands, about 99% of the ionospheric refraction effects on the GNSS (Global Navigation Satellite Systems) signals can be removed in the user receivers without additional SBAS corrections. Nevertheless, even if most of the negative impacts on GNSS signals are removed by the ionospheric-free combination, some residuals remain and have to be taken into account by overbounding models in the integrity computation conducted by safety-of-live (SoL) receivers in airplanes. Such models have to overbound residuals as well, which result from the most rare extreme ionospheric events, e.g., such as the famous “Halloween Storm”, and should thus include the tails of the error distribution. Their application shall lead to safe error bounds on the user position and allow the computation of protection levels for the horizontal and vertical position errors. Here, we propose and justify such an overbounding model for residual ionospheric delays that remain after the application of the ionospheric-free linear combination. The model takes into account second- and third-order ionospheric refraction effects, excess path due to ray bending, and increased ionospheric total electron content (TEC) along the signal path due to ray bending.

Could the Beirut Explosion perturb the Ionosphere? Pre-results Using TEC-GNSS observations.

2021 ◽  
Author(s):  
Mohamed Freeshah ◽  
Xiaohong Zhang ◽  
Erman Şentürk ◽  
Xiaodong Ren ◽  
Muhammad Arqim Adil ◽  
...  
Keyword(s):  
Ammonium Nitrate ◽  
Space Weather ◽  
Global Navigation Satellite Systems ◽  
Electron Content ◽  
Free Electrons ◽  
Total Electron ◽  
Satellite Systems ◽  
Underground Nuclear Explosions ◽  
Nuclear Explosions ◽  
Global Navigation Satellite

<p>Natural hazards such as shallow earthquakes and volcanic explosions are known to generate acoustic and gravity waves at infrasonic velocity to propagate in the atmosphere layers. These waves could induce the layers of the ionosphere by change the electron density based on the neutral particles and free electrons coupling. Recently, some studies have dealt with some manmade hazards such as buried explosions and underground nuclear explosions which could cause a trigger to the ionosphere. The Global Navigation Satellite Systems (GNSS) provide a good way to measure ionospheric total electron content (TEC) through the line of sight (LOS) from satellite to receiver. The carrier-to-code leveling (CCL) technique is carried out for each continuous arc where CCL eliminates potential ambiguity influence and it degrades the pseudo-range noise. Meanwhile, the CCL retains high precision in the carrier-phase. In this study, we focus on the Beirut Explosion on August 4, 2020, to check slant TEC (STEC) variations that may be associated with the blast of Beirut Port. The TECs were analyzed through the Morlet wavelet to check the possible ionospheric response to the blast. An acoustic‐gravity wave could be generated by the event which could disturb the ionosphere through coupling between solid earth-atmosphere-ionosphere during the explosion. To verify TEC disturbances are not associated with space weather, disturbance storm-time (Dst), and Kp indices were investigated before, during, and after the explosion. The steady-state of space weather before and during the event indicated that the observed variations of TEC sequences were caused by the ammonium nitrate explosion. There was a large initial explosion, followed by a series of smaller blasts, about ~30 seconds, a colossal explosion has happened, a supersonic blast wave radiating through Beirut City. As a result of the chemistry behind ammonium nitrate’s explosive, a mushroom cloud was sent into the air. We suggest that these different explosions in strength and time could be the reason for different time arrival of the detected ionospheric disturbances over GNSS ground-based stations.</p>

scholarly journals Assessing Global Ionosphere TEC Maps with Satellite Altimetry and Ionospheric Radio Occultation Observations

Sensors ◽  
2019 ◽  
Vol 19 (24) ◽  
pp. 5489 ◽  
Author(s):  
Wei Li ◽  
Longqiang Huang ◽  
Shaocheng Zhang ◽  
Yanju Chai
Keyword(s):  
High Latitude ◽  
Satellite Altimetry ◽  
Radio Occultation ◽  
Lower Latitude ◽  
Electron Content ◽  
Dual Frequency ◽  
International Gnss Service ◽  
Night Time ◽  
Scaling Factors ◽  
Total Electron

As global navigation satellite system (GNSS)stations are sparsely distributed in oceanic area, oceanic areas usually have lower precision than continental areas on a global ionosphere maps (GIM). On the other hand, space-borne observations like satellite altimetry (SA) and ionospheric radio occultation (IRO) have substantial dual-frequency observations in oceanic areas, which could be used for total electron content (TEC) retrieval. In this paper, the Jason-2 SA and Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) IRO products were used to assess the precision of IGS GIM products. Both the systematic biases and scaling factors between the international GNSS service (IGS) GIM TEC and space-borne TEC were calculated, and the statistical results show that the biases and the scaling factors obviously vary under different temporal-spatial conditions. This analysis shows that these differences are variable with diurnal and latitude factors, that is, the differences in biases during the day time are higher than those during the night time, and larger biases are experienced at lower latitude areas than at high latitude areas. The results also show that in the southern hemisphere middle-high latitude area and some other central oceanic areas, the space-borne TEC values are even higher than GIM TEC values. As the precision of space-borne TEC should be evenly distributed around different areas on Earth, it can be explain that the TEC in these areas is undervalued by the current GIM model, and the space-borne SA and IRO techniques could be used as complementary observations to improve the accuracy and reliability of TEC values in these areas.

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