Total Electron Content Calculation Research Articles

Estimation and evaluation of hourly Meteorological Operational (MetOp) satellites' GPS receiver differential code biases (DCBs) with two different methods

Abstract. Differential code bias (DCB) is one of the Global Positioning System (GPS) errors, which typically affects the calculation of total electron content (TEC) and ionospheric modeling. In the past, DCB was normally estimated as a constant in 1 d, while DCB of a low Earth orbit (LEO) satellite GPS receiver may have large variations within 1 d due to complex space environments and highly dynamic orbit conditions. In this study, daily and hourly DCBs of Meteorological Operational (MetOp) satellites' GPS receivers are calculated and evaluated using the spherical harmonic function (SHF) and the local spherical symmetry (LSS) assumption. The results demonstrated that both approaches could obtain accurate and consistent DCB values. The estimated daily DCB standard deviation (SD) is within 0.1 ns in accordance with the LSS assumption, and it is numerically less than the standard deviation of the reference value provided by the Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC) Data Analysis and Archive Center (CDAAC). The average error's absolute value is within 0.2 ns with respect to the provided DCB reference value. As for the SHF method, the DCB's standard deviation is within 0.1 ns, which is also less than the standard deviation of the CDAAC reference value. The average error of the absolute value is within 0.2 ns. The estimated hourly DCB with LSS assumptions suggested that calculated results of MetOpA, MetOpB, and MetOpC are, respectively, 0.5 to 3.1 ns, −1.1 to 1.5 ns, and −1.3 to 0.7 ns. The root mean square error (RMSE) is less than 1.2 ns, and the SD is under 0.6 ns. According to the SHF method, the results of MetOpA, MetOpB, and MetOpC are 1 to 2.7 ns, −1 to 1 ns, and −1.3 to 0.6 ns, respectively. The RMSE is under 1.3 ns and the SD is less than 0.5 ns. The SD for solar active days is less than 0.43, 0.49, and 0.44 ns, respectively, with the LSS assumption, and the appropriate fluctuation ranges are 2.0, 2.2, and 2.2 ns. The variation ranges for the SHF method are 1.5, 1.2, and 1.2 ns, respectively, while the SD is under 0.28, 0.35, and 0.29 ns.

Evaluation of the dusk and early nighttime Total Electron Content modeling over the eastern Brazilian region during a solar maximum period

The ionosphere is one of the main sources of errors for the GNSS (Global Navigation Satellite System) users in low-latitude regions. The ionosphere delays the signal propagation, directly influencing the pseudorange estimation, which is fundamental for positioning estimation. This study aims at evaluating empirical and theoretical models that generate profiles of Total Electron Content (TEC), with respect to their ability to represent the spatiotemporal distribution of the ionospheric plasma. For this purpose, the TEC data calculated from measurements obtained by receivers from the Brazilian Network for Continuous Monitoring of GNSS Systems (RBMC) were compared with ionospheric models that provide the TEC values. The TEC calculation procedure is presented in the manuscript. The Klobuchar model, the empirical model IRI-2016, which has the NeQuick model integrated in its calculations, and the SAMI2 model were evaluated. Data from 2 years around solar maximum period was used considering averaged values over Brazilian region. The evaluations carried out between the TEC values obtained from the models and the real TEC data showed that the models have some deviations, therefore requiring future improvements. According to the results, the deviations may reach approximately 7 m and are originated from physical peculiarities on the spatial environment over the Brazilian region.

Comparison of TEC Calculations Based on Trimble, Javad, Leica, and Septentrio GNSS Receiver Data

A Global Navigation Satellite System (GNSS) receiver is, to some extent, a “black box” when its data is used for ionospheric studies. Our results based on Javad, Septentrio, Trimble, and Leica GNSS receivers have proven that the accuracy of the slant Total Electron Content (TEC) calculation can differ significantly depending on the GNSS receiver type/model, because TEC measurements depend on the carrier phase tracking technique applied in a receiver. The correlation coefficient between carrier phase noise in L1 and L2 channels is considered as a possible indicator that shows if the L1-aided tracking technique or independent tracking is applied inside a receiver. An empirical model of the TEC noise component was provided to determine the TEC noise value in different types/models of GNSS receivers.

An Updated Experimental Model of IG₁₂ Indices Over the Antarctic Region via the Assimilation of IRI2016 With GNSS TEC

In order to improve the accuracy of the International Reference Ionosphere (IRI)-2016 model for application in the Antarctic region, total electron content (TEC) data from the Global Navigation Satellite Systems (GNSS) observation data in 2018 are assimilated into the IRI-2016 model by updating the effective ionospheric parameter, IG12 index on a daily basis. The functional relationship between the IG12 index and the longitude, latitude, and the day of year (DOY) is fitted by using the spherical crown harmonic function and the polynomial, and finally establish an updated experiential model of IG12 indices over the Antarctic region. Conclusions that were reached were: 1) the updated IG12 index varies greatly over different geographical locations and 2) it is also apparent that the accuracy of the IRI-2016 model is worse in the perpetual night than that in the perpetual day. In order to verify our method, the TEC calculated by the IRI-2016 model driven by the updated IG12 index and that calculated by the original IRI-2016 model are compared with the GNSS-TEC, and the results show that the updated IRI-2016 model has improved the accuracy of the BIAS and root mean square (RMS) of the TEC calculation by 97% and 87%, respectively, on the fitting moments, while 75% and 54% on the predicting moments. In addition, compared with the original IRI-2016 model, it is found that the updated IRI-2016 model improves the accuracy of the NmF2 calculation by approximately 23% on average for the fitting time and 8% for the predicting time.

The Calculation and Analysis of the Total Electron Content Over Different Latitudes and Seasons Using the Numerical Trapezoidal and Simpson Methods

It has been shown in ionospheric research that calculation of the total electron content (TEC) is an important factor in global navigation system. In this study, TEC calculation was performed over Baghdad city, Iraq, using a combination of two numerical methods called composite Simpson and composite Trapezoidal methods. TEC was calculated using the line integral of the electron density derived from the International reference ionosphere IRI2012 and NeQuick2 models from 70 to 2000 km above the earth surface. The hour of the day and the day number of the year, R12, were chosen as inputs for the calculation techniques to take into account latitudinal, diurnal and seasonal variation of TEC. The results of latitudinal variation of TEC show anomally called equatorial ionization anomally which presents two crests about the geomagnetic equators. The mean absolute percent errors MAPE for two numerical methods using the electron density profiles shown above were 0.0253, 0.02273 and 0.0213, 0.0124 respectively. The results of seasonal variation of TEC show a larger values for spring and autumn equinoxes other than for summer and winter seasons. The MAPE for autumn equinox has the smallest value than for summer, winter seasons and spring equinox. The MAPE for spring equinox equals to 0.01093 and 0.01015 for Simpson and Trapezoidal methods respectively. For autumn, summer and winter, the MAPE equals to 0.005825 and 0.006629 and 0.04682 and 0.0454, 0.01253 and 0.01231 for Simpson and Trapezoidal methods respectively.

Comparison of GPS TEC with modelled values from IRI 2016 and IRI-PLAS over Istanbul, Turkey

The Total Electron Content (TEC) prediction performances of the empirical IRI model and IRI-PLAS model were investigated by comparing the GPS-based TEC values provided by the IONOLAB group. TEC values were obtained on equinox (March 21 and September 23) and solstice (June 21, and December 21) days in low (2009), medium (2012) and high (2015) solar activity periods at Istanbul, Turkey. The prediction performances of the models were statistically analyzed based on the differences between the GPS-TEC and the empirical models, considering the maximum and minimum deviations, the correlation analysis and the root mean square error (RMSE). As a result of the investigation, it is seen that the empirical models have similar predictive performances when the plasmaspheric effects are neglected, and the IRI-PLAS estimations are generally a little closer to the observed GPS-TEC values than all options of IRI-2016 model. Also, it can be said that “IRI2001”, one of the IRI-2016’s “topside” options, can make better predictions than other options and “IG” solar proxy option of IRI-PLAS model is a more appropriate option than the others in TEC calculations over Istanbul, Turkey.

Comparison of TEC Estimation Techniques using S1 and L5 Signals of IRNSS

Indian Regional Navigation Satellite System (IRNSS) is a satellite based navigation system developed by Indian Space Research Organization (ISRO). The positional accuracy of IRNSS is limited by several errors including ionospheric delay. Ionospheric delay can be estimated with precise calculation of total electron content (TEC). However, TEC is biased by multipath and thermal noise. Therefore, multipath and thermal noise free relative TEC measurements are made and compared with two other methods, namely, code TEC and IRNSS Receiver Software (IRS) techniques. In this investigation L5 (1176.45 MHz) and S1 (2492.028 MHz) signals from IRNSS 1A to 1G satellites are considered. The results indicate that relative TEC estimation technique removes the multipath and thermal noise from the TEC measurements. Further, the TEC for signals coming from various IRNSS satellites are evaluated by calculating the standard deviation (SD). In the analysis the data is divided into segments with duration of 1 h each. The results indicate that SDs for the relative TEC estimation (2.5 TECU in case of IRNSS 1B) are lesser than the other two techniques indicating the relative TEC can be used in the receiver for the estimation of ionospheric delay. Further, the high ratio of the operating frequencies indicates a better TEC estimation.

Observation of subsecond variations in auroral region total electron content using 100 Hz sampling of GPS observables

AbstractFirst ever auroral region total electron content (TEC) measurements at 100 Hz using a Septentrio PolaRxS Pro receiver are analyzed to discover ionospheric signatures which would otherwise be unobtainable with the frequently used lower sampling rates. Two types of variations are observed: small‐magnitude (amplitude) variations, which are present consistently throughout the data set, and larger‐magnitude (amplitude) variations, which are less frequent. Small‐amplitude TEC fluctuations are accounted for by the receiver phase jitter. However, estimated secondary ionospheric effects in the calculation of TEC and the receiver phase jitter were unable to account for the larger‐amplitude TEC fluctuations. These variations are also accompanied by fluctuations in the magnetic field, which seems to indicate that these fluctuations are real and of geophysical significance. This paper presents a technique and the capability of high‐rate TEC measurements in the study of auroral dynamics. Further detailed study is needed to identify the cause of these subsecond TEC fluctuations and associated magnetic field fluctuations.

Behaviour of electron content in the ionospheric D-region during solar X-ray flares

One of the most important parameters in ionospheric plasma research, also having a wide practical application in wireless satellite telecommunications, is the total electron content (TEC) representing the columnal electron number density. The F-region with high electron density provides the biggest contribution to TEC while the relatively weakly ionized plasma of the D-region (60 km { 90 km above Earth's surface) is often considered as a negligible cause of satellite signal disturbances. However, sudden intensive ionization processes, like those induced by solar X-ray flares, can cause relative increases of electron density that are significantly larger in the D-region than in regions at higher altitudes. Therefore, one cannot exclude a priori the D-region from investigations of ionospheric influences on propagation of electromagnetic signals emitted by satellites. We discuss here this problem which has not been sufficiently treated in literature so far. The obtained results are based on data collected from the D-region monitoring by very low frequency radio waves and on vertical TEC calculations from the Global Navigation Satellite System (GNSS) signal analyses, and they show noticeable variations in the D-region's electron content (TECD) during activity of a solar X-ray ?are (it rises by a factor of 136 in the considered case) when TECD contribution to TEC can reach several percent and which cannot be neglected in practical applications like global positioning procedures by satellites.

Orthogonal Decomposition Algorithm for Ionospheric Delay Estimation for Precise GPS Applications

The time delay of GPS link1 (L1) and link2 (L2) signals in ionosphere is one of the propagation path effects caused when the signal is travelling from satellite to receiver. The absence of the Selective Availability (SA) made the ionospheric delay as the predominant accuracy limiting factor for GPS. As the density of the ionized plasma varies, the velocity of the GPS signals differs from the velocity of light. Due to this the GPS radio frequency (RF) signals experience the group delay or phase advance. Hence the one way time transfer of the GPS is affected, inturn resulting in pseudorange error varying from few meters to tens of meters at zenith. To correct the GPS range measurements this delay is estimated using conventional Code Range technique which models the Total Electron Content (TEC). In this method the TEC is an additional parameter to be calculated and the accuracy of the TEC depends on the inter channel biases and solar activity. To overcome this, an orthogonal decomposition algorithm is proposed in this paper. The proposed algorithm decomposes the coefficient matrix derived from the linear combination of GPS measurements. The proposed algorithm not only avoids TEC calculation but also minimizes complex computations. The comparative analysis of the estimates of the proposed algorithm and conventional method are presented in this paper. The proposed algorithm is implemented and estimates are validated for the ephemerides data collected on 07th April 2015 from the Dual Frequency GPS (DFGPS) receiver located in the Department of Electronics and Communications Engineering (ECE), Andhra University College of Engineering (AUCE), Visakhapatnam (Lat:17.730N/Long:83.3190E). The proposed algorithm can be implemented for precise navigation and tracking applications like Category I (CAT I) precision approach (PA), Precise Point Positioning (PPP), geographic information systems (GIS) and Real Time Kinematic (RTK) positioning.

Fractal and wavelet analysis evaluation of the mid latitude ionospheric disturbances associated with major geomagnetic storms

Variations of the total electron content (TEC) of the ionosphere are mainly associated with major geomagnetic storms occurring with the arrival of coronal mass ejections (CMEs) to the Earth environment. The purpose of this paper is to show results of the analysis we made of the impact of all major geomagnetic storms (Dst<-200nT) on the ionosphere at mid latitudes, which have occurred since 2000. The analysis consists in the calculation of TEC of the ionosphere using data from several Mexican GPS stations, with the purpose of quantifying the impact into the ionosphere to these latitudes, through the variations in amplitude, Hurst index, that is roughness, and wavelet transform of the time series of TEC. Indeed, during the geomagnetic storms of April 7, 2000, July 16, 2000, October 30, 2003, November 20, 2003 and November 8, 2004, major ionospheric disturbances at mid latitudes took place with changes in amplitude of TEC going from 3.29 to 8.82 sigmas. These ionospheric disturbances were probably associated with prompt penetration electric fields (PPEFs) and equatorward neutral winds. On the other hand, during four geomagnetic storms (August 12, 2000, March 31, 2001, April 11, 2001 and May 15, 2005), there were negative ionospheric storms that pushed the TEC to significantly lower values. This has been interpreted as the presence of regions in which the neutral composition is changed. Also, in some cases during the disturbed days, the Hurst values were smaller than during the undisturbed days, i.e. during these geomagnetic storms, the roughness of the time series of TEC increased. The wavelet analysis showed a strong influence of the diurnal variation on TEC values (periodicities of 12h), and periodicities characteristics of ionospheric disturbances of 1–8h. It is found that large geomagnetic storms produce significant ionospheric disturbances at mid latitudes, as shown by the wavelet analysis and, in some cases, changes in the roughness of the time series of TEC as shown by the Hurst exponent.

Assessment of ionosphere models at Banting: Performance of IRI-2007, IRI-2012 and NeQuick 2 models during the ascending phase of Solar Cycle 24

The International Reference Ionosphere (IRI) and the NeQuick models have been recognised as the international standard for specifying Earth’s ionospheric parameters. However, the performance of these ionosphere models needs to be validated due to data scarcity from South-East Asian region for model development. This work presents the performance evaluation of IRI-2007, IRI-2012 and NeQuick 2 in estimating ionospheric Total Electron Content (TEC) at Banting (Geographic: 2.78°N, 101.51°E; Geomagnetic: 7.11°S, 173.77°E). For this purpose, TEC values estimated from these models have been compared with TEC values derived from dual-frequency Global Positioning System (GPS) data for the year 2011 (ascending phase of Solar Cycle 24). The results show that equatorial TEC exhibits semi-annual, annual, and seasonal variations with maximum values appearing during equinoctial months and minimum during solstitial months. Generally, ionospheric TEC produced by IRI and NeQuick 2 models are in good agreement with observed TEC. For diurnal variation, the IRI-2007 and NeQuick 2 models show good agreement during post-noon and post-midnight, respectively. Good correlation is observed during noon-time for all models. Disagreements between ionospheric models and observed TEC are found during post-sunset and post-midnight periods, with TEC deviation in the level of 11–14 TECU can be anticipated at 95% probability. On the other hand, TEC calculation from IRI-2012 is better than IRI-2007 and NeQuick 2 for monthly variation. All models score correlation coefficient above 0.9 with the highest correlation noticed during solstitial months. TEC deviation above 10 and up to 15 TECU can be expected in October with 95% probability. Overall, this work reveals that IRI and NeQuick 2 models are capable of predicting TEC with good correlation in most cases.

Statistical Comparison of Various Interpolation Algorithms for Grid-Based Single Shell Ionospheric Model Over Indian Region

Future Satellite Based Navigation Systems based on GPS, like US Wide Area Augmentation Sysytem (WAAS), are of global interest to the scientific community. Precise estimation of ionospheric delay is most crucial for successful implementation of the systems. Due to the complex ionospheric structure and large variation of Total Electron Content (TEC) in low latitudes, it is necessary to compare and validate the efficiency of the existing algorithms in this region. In this study, performances of the various interpolation algorithms for TEC calculation at ionospheric grid point (IGP) and user position for gridbased Single Shell Model have been tested for 72 test days of 2005. Based on the results obtained from this analysis, it has been found that, for the Indian region, it would be more suitable to use Ordinary Kriging in place of Planar Fit to estimate delay at an IGP (as used by US WAAS). It has also been found that Ordinary Kriging performs better than the Bilinear Interpolation technique at the user end.

TEC Measurements Through GPS and Artificial Intelligence

A reliable ionospheric model is very important in such fields as satellite positioning and surveying, radiocommunication, space weather and so on. In this way, a correct calculation of Total Electron Content would have many useful implications. In this paper, a novel approach based on Support Vector Machines and used for Total Electron Content estimation is described. It exploits Global Positioning System observables, with encouraging results.

Ionospheric tomography using Ørsted GPS measurements - preliminary results

Data from the Turbo-Rogue GPS receiver onboard the Danish Ørsted Satellite are used to derive satellite-to-satellite Total Electron Content (TEC). We present preliminary results obtaining Electronic Density fields from ionospheric tomography using TEC Ørsted data. TEC is based on single frequency measurements, since only the L1 signal is of good quality. The C/A pseudo range (C1) and the L1 phase are used to obtain the TEC measurement. Electron density profiles from individual occultations are derived, based on the Abel transform, and compared with the tomographical solution. The assumption of spherical symmetry in the Abel transform limits the accuracy of the profiles and often results in a bias. We select occultations observed along the orbital plane to minimize the spherical assymetry effects. The tomographic grid is also confined to a narrow torus close to the orbital plane. The TEC calculations are based on data from 6 hour (3.6 orbits) periods. Two days have been selected for this study, December 5, 1999 and February 12, 1999.

Comparison of total electron content calculated using the IRI with observations in China

Values of total electron content (TEC) calculated using the International Reference Ionosphere (IRI-86 and IRI-90) are compared with the observations at Xinxiang based on the Faraday rotation measurement. It is found that the IRI gives acceptable values with respect to the observations during low solar activity. Generally the IRI-90 is better than the IRI-86 and the URSI coefficients are better than the CCIR coefficients in the calculation of TEC. Making use of the foF2 and M(3000) F 2 calculated using the Asia Oceania Region F 2-layer mapping (AOR) instead of using the CCIR or the URSI coefficients, the IRI gives more accurate TEC values. In October-April during high solar activity, however, the IRI obviously underestimates TEC in the daytime, which could be due to an improper topside electron density profile.

Thermospheric modelling based on satellite and ground-based measurements

Methods, analytical expressions, and procedures are suggested for combining TEC (total electron content) calculations (based on Faraday rotation or differential-Dopper measurements), ground-based ionosende measurements, and the intensity of airglow emissions to study the upper atmosphere. For example, we have considered the possibility of determining ionized and neutral parameters at thermospheric altitudes by combining ground-based measurements of N e(h), TEC, and the airglow intensities at 6300 Å, 5200 Å, 7774 Å, and of other such lines. These combined data can be supplemented by in situ satellite measurements and EUV airglow observations at 1304 Å, 1356 Å, etc. This process will provide a data base for thermospheric modelling and for comparison with existing models.