Ionospheric Electron Density Distribution Research Articles

An Improved Iterative Algorithm for Ionospheric Tomography Reconstruction by Using the Automatic Search Technology of Relaxation Factor

AbstractAn improved ionospheric tomography algorithm is developed for the tomographic reconstruction of the ionospheric electron density distribution based on the automatic search technology of relaxation factor, in which the automatic search technology is a training process to optimize the relaxation factors of the iterative algorithm. In comparison with some classical tomography algorithms, the proposed algorithm can not only greatly improve the efficiency of inversion but also obtain ionospheric electron density images with high fidelity. A careful validation of the proposed algorithm is performed by conducting numerical experiments with Global Positioning System simulation and real data, and according to the results of the quantitative comparison and statistical analysis, compared with other classical ionospheric tomography algorithms, the proposed algorithm exhibits significantly reconstruction accuracy.

3-D ionospheric tomography from dense GNSS observations based on an improved two-step iterative algorithm

Computerized ionospheric tomography (CIT) can image 3-D ionospheric variations from ground Global Navigation Satellite System (GNSS) observations. However, due to the sparse and inhomogeneous ground GNSS observations, the prior information from the empirical models (e.g., IRI-2012 and NeQuick 2) have to be used, which affect the reconstructed results in the CIT, particularly the peak parameters of the F2 layer, namely foF2 and M(3000)F2. In this paper, an improved two-step CIT algorithm is developed to image the ionospheric electron density (IED) distribution up to 2000 km over Japan using dense GNSS Earth Observation Network (GEONET) observations operated by the Geospatial Information Authority (GSI) of Japan. Firstly, we update the IRI-2012 using the ground-based GNSS observations. The NeQuick-2 is used to provide the vertical ionospheric profile, and foF2 and M(3000)F2 derived from CCIR model in NeQuick 2 are improved by the B-spline modeling methods. Secondly, the updated IRI-2012 is input as a prior value and the multiplicative algebraic reconstruction technique (MART) is implemented to reconstruct the IED distribution. The reconstructed results are validated by the simulation and observation results from ground-based GNSS, GNSS Radio Occultation (GNSS-RO) observations and ionosonde measurements. The results demonstrate the feasibility and superiority of our new method. The standard deviations of TEC residual errors from the updated NeQuick 2 are at least 20% less than those from the original NeQuick 2 model, and the updated NeQuick 2 has better performance for the ionospheric correction.

Model based Computerized Ionospheric Tomography in space and time

Reconstruction of the ionospheric electron density distribution in space and time not only provide basis for better understanding the physical nature of the ionosphere, but also provide improvements in various applications including HF communication. Recently developed IONOLAB-CIT technique provides physically admissible 3D model of the ionosphere by using both Slant Total Electron Content (STEC) measurements obtained from a GPS satellite - receiver network and IRI-Plas model. IONOLAB-CIT technique optimizes IRI-Plas model parameters in the region of interest such that the synthetic STEC computations obtained from the IRI-Plas model are in accordance with the actual STEC measurements. In this work, the IONOLAB-CIT technique is extended to provide reconstructions both in space and time. This extension exploits the temporal continuity of the ionosphere to provide more reliable reconstructions with a reduced computational load. The proposed 4D-IONOLAB-CIT technique is validated on real measurement data obtained from TNPGN-Active GPS receiver network in Turkey.

Disturbances of the thermosphere-ionosphere-plasmasphere system and auroral electrojet at 30°E longitude during the St. Patrick's Day geomagnetic storm on 17–23 March 2015

This study presents an analysis of geomagnetic disturbances and ionospheric electron density distribution during the 2015 St. Patrick's Day geomagnetic storm. To study those we have used the satellite-borne and ground-based observations. The St. Patrick's geomagnetic storm covers the interval of 15–23 March 2015, when solar eruptive phenomena (a long-enduring C9-class solar flare and associated CME's on 15 March) and a strong geomagnetic storm on 16–18 March (Dst dropped as strong as –228 nT) were reported. This geomagnetic storm is still the strongest one observed in the current solar cycle. The severe geomagnetic storm on 17-18 March 2015 led to complex effects on the ionosphere. We consider major features of the positive and negative ionospheric storms development at European mid- and high-latitudes. One of the interesting phenomena was observation of the positive ionospheric disturbances during the recovery phase. Using the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) we examined the main physical processes that played a major role in dramatic changes of the total electron content and the F2 layer peak electron density during this storm event.

Real-Time Ionosphere Monitoring by Three-Dimensional Tomography over Japan

This paper reports on the development of a real-time three-dimensional ionospheric tomography technique using GNSS measurements. GPS measurement data from 200 GPS receivers distributed throughout Japan are analyzed in real time to calculate ionospheric Total Electron Contents (TECs). The three-dimensional ionospheric electron density distribution was reconstructed using the tomography technique from the slant TEC data. The tomography results were found to be in good agreement with both the electron density profiles obtained by radio occultation measurements by the COSMIC satellite and the ionospheric peak densities obtained by vertical radio sounding measurements (ionosondes). The real-time ionospheric tomography system commenced operation in March 2016 and it continuously produces three-dimensional electron density distributions over Japan every 15 min with latency of about 6 min. This system is a very powerful tool for monitoring the ionosphere in real time, which could both improve the performance of GNSS-based systems and further the understanding of ionospheric variations.

Robust Computerized Ionospheric Tomography Based on Spaceborne Polarimetric SAR Data

Due to the dispersion nature of the ionosphere, the spaceborne polarimetric synthetic aperture radar (PolSAR) systems at L or lower frequencies will generally experience more severe effects in comparison to frequencies above L-band. Correspondingly, according to the mechanism of how ionosphere destroys the scattering matrix of PolSAR data, the total electron content (TEC), an important input in computerized ionospheric tomography (CIT), can be retrieved by model inversion. Thus, this paper presents a technique of CIT based on the spaceborne PolSAR data. The CIT technique is a means to obtain the spatial distribution of ionospheric electron density from the TEC values. Because of the high spatial resolution of spaceborne SAR, the kilometer-scale TEC information can be obtained by the PolSAR data where such resolution was previously inaccessible. The spatial distribution of ionospheric electron density with high resolution can therefore be obtained. In addition, the potential limitation of previous CIT based on SAR imaging information is the difficulty in requiring strong point targets with high signal-to-clutter (SCR) ratio in scenes. In contrast, the CIT reconstruction based on scattering matrix information can be easily realized without aforementioned special requirements. In this paper, by using the simulated data of the Advanced Land Observing Satellite (ALOS) Phased-Array L-band Synthetic Aperture Radar (PALSAR) full-pol data, the International Reference Ionosphere (IRI) 2007, and the International Geomagnetic Reference Field (IGRF) models, the reconstruction of ionospheric electron density distribution is first simulated to validate the feasibility of the proposed technique. Then, possible effects of SAR system and model errors on the reconstruction results are also simulated and analyzed to show the applicability.

Variable pixel size ionospheric tomography

A novel ionospheric tomography technique based on variable pixel size was developed for the tomographic reconstruction of the ionospheric electron density (IED) distribution. In variable pixel size computerized ionospheric tomography (VPSCIT) model, the IED distribution is parameterized by a decomposition of the lower and upper ionosphere with different pixel sizes. Thus, the lower and upper IED distribution may be very differently determined by the available data. The variable pixel size ionospheric tomography and constant pixel size tomography are similar in most other aspects. There are some differences between two kinds of models with constant and variable pixel size respectively, one is that the segments of GPS signal pay should be assigned to the different kinds of pixel in inversion; the other is smoothness constraint factor need to make the appropriate modified where the pixel change in size. For a real dataset, the variable pixel size method distinguishes different electron density distribution zones better than the constant pixel size method. Furthermore, it can be non-chided that when the effort is spent to identify the regions in a model with best data coverage. The variable pixel size method can not only greatly improve the efficiency of inversion, but also produce IED images with high fidelity which are the same as a used uniform pixel size method. In addition, variable pixel size tomography can reduce the underdetermined problem in an ill-posed inverse problem when the data coverage is irregular or less by adjusting quantitative proportion of pixels with different sizes. In comparison with constant pixel size tomography models, the variable pixel size ionospheric tomography technique achieved relatively good results in a numerical simulation. A careful validation of the reliability and superiority of variable pixel size ionospheric tomography was performed. Finally, according to the results of the statistical analysis and quantitative comparison, the proposed method offers an improvement of 8% compared with conventional constant pixel size tomography models in the forward modeling.

Ionosphere tomography using wavelet neural network and particle swarm optimization training algorithm in Iranian case study

Computerized tomography provides valuable information for imaging the ionospheric electron density distribution. We use a wavelet neural network with a particle swarm optimization training algorithm to solve pixel-based ionospheric tomography. This new method is called ionospheric tomography based on the neural network (ITNN). In this method, vertical and horizontal objective functions are minimized. Due to a poor vertical resolution of ionospheric tomography, empirical orthogonal functions are used as vertical objective function. For numerical experimentation, observations collected at 38 GPS stations on 2 days in 2007 (April 3 and July 13) from the Iranian permanent GPS network (IPGN) are used. Ionosonde observations (ź = 35.7382°, ź = 51.3851°) are used for validating the reliability of the proposed method. The modeling region is between 24°E to 40°E and 44°N to 64°N. The results of the ITNN method have been compared to those of the international reference ionosphere model 2012 (IRI-2012) and the spherical cap harmonics (SCHs) method as a local model. The minimum relative error for ITNN is 1.41% and the maximum relative error is 24.03%. Also, the root-mean-square error of 0.1932 × 1011 (el/m3) has been computed for ITNN, which is less than the RMSE of the IRI-2012 and SCHs method. The comparison of ITNN results with IRI-2012 and SCHs method shows that the proposed approach is superior to those of the traditional methods.

Detection of ionospheric anomalies during intense space weather over a low-latitude GNSS station

The operational availability of Global Navigation Satellite System is affected by large-scale irregularities of the ionosphere. The space weather events induce several intense irregularities and cause the non-linear distribution of ionospheric electron density. Monitoring of ionospheric responses due to extreme space weather events plays a key role in trans-ionospheric radio wave propagation. In the present analysis, a novel technique based on wavelet transform has been implemented for the analysis and detection of ionospheric anomalies during two intense space weather events that occurred in 2013. The investigations have been carried out using the ionospheric observable, Total Electron Content (TEC), derived from the Global Positioning System (GPS) receiver located at an Equatorial Ionisation Anomaly region, KL University, Guntur, India (Geographic Lat.16.37°N, Geographic Long. 80.37°E). The effects of geomagnetic storms (Sym-H ≤ −100 nT) on the perturbations of ionospheric TEC have been investigated. The algorithm of Continuous wavelet transform has been used to study and characterise the presence of ionospheric anomalies in the local time-scale plane. It can detect spatial and temporal details of ionospheric anomaly intensity during strong solar-terrestrial and geophysical events. It is observed that during the main phase of the geomagnetic storm that occurred during 17 March 2013, TEC enhanced by 7 TECU, while a suppression of 10 TECU in the GPS-TEC can be noticed during the main phase of the 29 June 2013 storm. The variation in the intensity of ionospheric TEC anomalies during storm time has been detected and compared to the intensity of the space weather events measured through solar and geomagnetic indices (F10.7, Sym-H, IMF Bz and IEF Ey).

Study of TEC fluctuation via stochastic models and Bayesian inversion

AbstractWe propose stochastic processes to be used to model the total electron content (TEC) observation. Based on this, we model the rate of change of TEC (ROT) variation during ionospheric quiet conditions with stationary processes. During ionospheric disturbed conditions, for example, when irregularity in ionospheric electron density distribution occurs, stationarity assumption over long time periods is no longer valid. In these cases, we make the parameter estimation for short time scales, during which we can assume stationarity. We show the relationship between the new method and commonly used TEC characterization parameters ROT and the ROT Index (ROTI). We construct our parametric model within the framework of Bayesian statistical inverse problems and hence give the solution as an a posteriori probability distribution. Bayesian framework allows us to model measurement errors systematically. Similarly, we mitigate variation of TEC due to factors which are not of ionospheric origin, like due to the motion of satellites relative to the receiver, by incorporating a priori knowledge in the Bayesian model. In practical computations, we draw the so‐called maximum a posteriori estimates, which are our ROT and ROTI estimates, from the posterior distribution. Because the algorithm allows to estimate ROTI at each observation time, the estimator does not depend on the period of time for ROTI computation. We verify the method by analyzing TEC data recorded by GPS receiver located in Ethiopia (11.6°N, 37.4°E). The results indicate that the TEC fluctuations caused by the ionospheric irregularity can be effectively detected and quantified from the estimated ROT and ROTI values.

ПЕЛЕНГОВАНИЕ ВЧ СИГНАЛОВ, РАССЕЯННЫХ ИОНОСФЕРНЫМИ НЕОДНОРОДНОСТЯМИ, С ПОМОЩЬЮ МАЛОРАЗМЕРНЫХ АНТЕНН

PACS number: 94.20.Bb Purpose: A modification of the Doppler Interferometry Technique is suggested to enable estimating angles of arrival of comparatively broadband HF signals scattered by random irregularities of the ionospheric plasma with the use of small-size near-omnidirectional antennas. Desing/methodology/approach: The technique is based on the measurements of cross-spectra phases of the probe radiation recorded at least in three spaced points. Findings: The developed algorithm has been used to investigate the angular and time-and-frequency characteristics of HF signals propagating at frequencies above the maximum usable one for the direct radio path Moscow–Kharkiv. The received signal spectra show presence of three families of spatial components attributed, respectively, to scattering by plasma irregularities near the middle point of the radio path, ground backscatter signals and scattering of the sounding signals by the intense plasma turbulence associated with auroral activations. It has been shown that the regions responsible for the formation of the third family components are located on the equatorial slope of the maximum of the precipitating particle energy. The drift velocity and direction of the polar ionosphere plasma has been determined. Conclusions: The obtained estimates are consistent with the classical conception on the magnetospheric convection and plasma convection in the polar regions and do not contradict to the results of investigations of the auroral ionosphere dynamics using the SuperDARN network. Key words: ionospheric plasma, scattering, direction finding, polar ionosphere, auroral oval, velocity and direction of plasma drift Manuscript submitted 01.06.2016 Radio phys. radio astron. 2016, 21(3): 231-241 REFERENCES 1. Afraimovich, E. L., 1982. Interference methods of ionospheric radio sounding. Moscow: Nauka Publ. (in Russian). 2. Reinisch, B. W., 1996. Modern Ionosondes. In: H. Kohl, K. Schlegel, eds. Modern Ionosphere Science. Katleburg-Lindau: European Geophysical Society, pp. 440–458. 3. Reinisch, B. W. and Galkin, I. A., 2008. A new digisonde for research and monitoring applications. In: XXIX GA URSI, August 7-16, 2008: Abstracts. Chicago, Illinois, USA, p. 131. 4. REINISCH, B. W., SCALI, J. L. and HAINES, D. M., 1998. Ionospheric drift measurements with ionosondes. Ann. Geophys. vol. 41, no. 5-6, pp. 695–702. DOI: 10.4401/ag-3812. 5. GALUSHKO, V. G., 1997. Frequency-and-angular sounding of the ionosphere. 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Three‐dimensional modeling of high‐latitude scintillation observations

AbstractGlobal Navigation Satellite System signals exhibit rapid fluctuations at high and low latitudes as a consequence of propagation through drifting ionospheric irregularities. We focus on the high‐latitude scintillation problem, taking advantage of a conjunction of European Incoherent Scatter Radar (EISCAT) observations and a GPS scintillation monitor viewing the same line of sight. Just after 20:00 UT on 17 October 2013, an auroral E region ionization enhancement occurred with associated phase scintillations. This investigation uses the scintillation observations to estimate the ionospheric electron density distribution beyond the spatial resolution of EISCAT (5–15 km along the line of sight in this case). Following the approach of Deshpande et al. (2014), signal propagation is modeled through a specified density distribution. A multiple phase screen propagation algorithm is applied to irregularities conforming to the description of Costa and Kelley (1977) and constrained to match the macroscopic conditions observed by EISCAT. A 50‐member ensemble of modeled outputs is approximately consistent with the observations according to the standard deviation of the phase (σp). The observations have σp = 0.23 rad, while the ensemble of modeled realizations has σp = 0.23 + 0.04–0.04. By comparison of the model output with the scintillation observations, we show that the density fluctuations cannot be a constant fraction of the mean density. The model indicates that E region density fluctuations whose standard deviation varies temporally between 5 and 25% of the mean (EISCAT‐observed) density are required to explain the observed phase scintillations.

Monitoring of the Earth’s ionosphere by a small satellite constellation

Existing radar aids for the research of the ionosphere and ionosondes allow only local diagnostics of the ionosphere. Creating a network of traditional tools of radio sounding of ionosphere is quite difficult and expensive. Using constellations of LEO satellites in ionospheric radio-tomography problems is today a promising direction of ionospheric research that allows getting the latest update about its condition. It is necessary to develop new, highly efficient methods and tools for solving problems of this class. An approach for the reconstruction of vertical distribution of ionospheric electron density by processing satellite-to-satellite signals is discussed in the article. The form of a promising orbital constellation of small satellites that makes it possible to obtain the cross section of the ionospheric electron density in the plane of the orbit is determined. It was found that the problem of 2D reconstruction of electron density vertical distribution in the ring layer of the ionosphere can be solved during the orbital period of the satellite in the constellation, the number of satellites in which is 5 to 7, depending on the height of the orbit. It is shown that as the number of vehicles in the constellation increases up to the amount that fills the orbit, the reconstruction time could be reduced to 10 minutes. It is shown that the problem is reduced to a few-view tomography problem using the method of convolutional filtering.

Regional ionosphere modeling using spherical cap harmonics and empirical orthogonal functions over Iran

The ionosphere is the ionized part of the upper region of the atmosphere extending from 60 to 1500 km above the earth’s surface. In this layer, free electrons are produced during the interaction of extreme ultra violet and x-ray radiation with the upper neutral atmosphere. Knowledge of the ionospheric electron density distribution is important for scientific studies and practical applications. In this paper, a new computerized ionospheric tomography reconstruction technique is developed to estimate electron density profiles over Iran. In this method, a functional based model is used to represent the electron density in space. The functional based model uses empirical orthogonal functions and spherical cap harmonics to describe the vertical and horizontal distribution of the electron density, respectively. The degree and the number of basis functions are chosen so that, the relative error of results is minimized. For this purpose, ionosonde observations (Lat. = 35.73°, Lon. = 51.38°) at 2007.04.03 is used. To apply the method for constructing a 3D-image of the electron density, GPS measurements of the Iranian permanent GPS network (at 2012/08/11) has been used. The modeling region is between 24 to 40 N and 44 to 64 W. The result of 3D-model has been compared to that of the international reference ionosphere model 2012 (IRI-2012). The analysis conducted in this paper indicates that the choice of spherical cap harmonics to 3 (Kmax = 3) and empirical orthogonal function in 3 (Q = 3), the regional reconstructed error is less than 36 %. The results show the advantages of this method in modeling of the ionosphere electron density on local and regional scales.

Research on ionospheric tomography based on variable pixel height

A novel ionospheric tomography technique based on variable pixel height was developed for the tomographic reconstruction of the ionospheric electron density distribution. The method considers the height of each pixel as an unknown variable, which is retrieved during the inversion process together with the electron density values. In contrast to conventional computerized ionospheric tomography (CIT), which parameterizes the model with a fixed pixel height, the variable-pixel-height computerized ionospheric tomography (VHCIT) model applies a disturbance to the height of each pixel. In comparison with conventional CIT models, the VHCIT technique achieved superior results in a numerical simulation. A careful validation of the reliability and superiority of VHCIT was performed. According to the results of the statistical analysis of the average root mean square errors, the proposed model offers an improvement by 15% compared with conventional CIT models.

Simultaneous multiplicative column-normalized method (SMART) for 3-D ionosphere tomography in comparison to other algebraic methods

Abstract. The accuracy and availability of satellite-based applications like GNSS positioning and remote sensing crucially depends on the knowledge of the ionospheric electron density distribution. The tomography of the ionosphere is one of the major tools to provide link specific ionospheric corrections as well as to study and monitor physical processes in the ionosphere. In this paper, we introduce a simultaneous multiplicative column-normalized method (SMART) for electron density reconstruction. Further, SMART+ is developed by combining SMART with a successive correction method. In this way, a balancing between the measurements of intersected and not intersected voxels is realised. The methods are compared with the well-known algebraic reconstruction techniques ART and SART. All the four methods are applied to reconstruct the 3-D electron density distribution by ingestion of ground-based GNSS TEC data into the NeQuick model. The comparative case study is implemented over Europe during two periods of the year 2011 covering quiet to disturbed ionospheric conditions. In particular, the performance of the methods is compared in terms of the convergence behaviour and the capability to reproduce sTEC and electron density profiles. For this purpose, independent sTEC data of four IGS stations and electron density profiles of four ionosonde stations are taken as reference. The results indicate that SMART significantly reduces the number of iterations necessary to achieve a predefined accuracy level. Further, SMART+ decreases the median of the absolute sTEC error up to 15, 22, 46 and 67 % compared to SMART, SART, ART and NeQuick respectively.

Comparisons of ionospheric electron density distributions reconstructed by GPS computerized tomography, backscatter ionograms, and vertical ionograms

AbstractGlobal Positioning System (GPS) computerized ionosphere tomography (CIT) and ionospheric sky wave ground backscatter radar are both capable of measuring the large‐scale, two‐dimensional (2‐D) distributions of ionospheric electron density (IED). Here we report the spatial and temporal electron density results obtained by GPS CIT and backscatter ionogram (BSI) inversion for three individual experiments. Both the GPS CIT and BSI inversion techniques demonstrate the capability and the consistency of reconstructing large‐scale IED distributions. To validate the results, electron density profiles obtained from GPS CIT and BSI inversion are quantitatively compared to the vertical ionosonde data, which clearly manifests that both methods output accurate information of ionopsheric electron density and thereby provide reliable approaches to ionospheric soundings. Our study can improve current understanding of the capability and insufficiency of these two methods on the large‐scale IED reconstruction.

An LS-MARS method for modeling regional 3D ionospheric electron density based on GPS data and IRI

The methods of developing an accurate and effective ionospheric electron density (IED) model have greatly interested ionosphere researchers. Numerous scholars have proposed many effective and reliable models and methods of global positioning system (GPS)-based computerized ionospheric tomography (CIT) in the past decades. This study introduced a new function-based CIT method, namely the LS-MARS (Least Squares method-Multivariate Adaptive Regression Splines), combining MARS with IEDs calculated by International Reference Ionosphere (IRI) to automatically choose the best representing basis functions for the three-dimensional (3D) electron density inside that modeling area. This selected basis functions was substituted into the observation equation of the GPS total electron content (TEC) to calculate the design matrix. Finally, the weighted damped least squares (WDLS) were adopted to reestimate the IED model coefficients. In contrast to common function-based CIT methods, the LS-MARS can be used to attain optimal 3D model automatically, flexibly, adaptively based on the IRI without a priori knowledge of the IED distribution mathematical function. The findings indicated that the LS-MARS model had a smaller recovery TEC error than did the MARS_IRI2012 model, and the VTEC calculated using the LS-MARS model was closer to the VTEC obtained from International GNSS Service (IGS) final IONEX files than was the VTEC calculated using the MARS_IRI2012 and IRI2012. Therefore, this method exhibits strong modeling effectiveness and reliability, and can be an efficient alternative method for estimating regional 3D IED models.

Ionospheric assimilation of radio occultation and ground-based GPS data using non-stationary background model error covariance

Abstract. Ionospheric data assimilation is a powerful approach to reconstruct the 3-D distribution of the ionospheric electron density from various types of observations. We present a data assimilation model for the ionosphere, based on the Gauss–Markov Kalman filter with the International Reference Ionosphere (IRI) as the background model, to assimilate two different types of slant total electron content (TEC) observations from ground-based GPS and space-based FORMOSAT-3/COSMIC (F3/C) radio occultation. Covariance models for the background model error and observational error play important roles in data assimilation. The objective of this study is to investigate impacts of stationary (location-independent) and non-stationary (location-dependent) classes of the background model error covariance on the quality of assimilation analyses. Location-dependent correlations are modeled using empirical orthogonal functions computed from an ensemble of the IRI outputs, while location-independent correlations are modeled using a Gaussian function. Observing system simulation experiments suggest that assimilation of slant TEC data facilitated by the location-dependent background model error covariance yields considerably higher quality assimilation analyses. Results from assimilation of real ground-based GPS and F3/C radio occultation observations over the continental United States are presented as TEC and electron density profiles. Validation with the Millstone Hill incoherent scatter radar data and comparison with the Abel inversion results are also presented. Our new ionospheric data assimilation model that employs the location-dependent background model error covariance outperforms the earlier assimilation model with the location-independent background model error covariance, and can reconstruct the 3-D ionospheric electron density distribution satisfactorily from both ground- and space-based GPS observations.

An Abel inversion method assisted by background model for GPS Ionospheric Radio Occultation data

The classical inversion of Global Positioning System (GPS) Ionospheric Radio Occultation (IRO) data is Abel inversion method, in which the spherical symmetry of the ionospheric electron density distribution is assumed. This assumption can cause some errors for the inversion of IRO data. In this paper, the error characteristics are discussed and a new IRO retrieval method is developed, which uses electron density gradient information of reconstructed ancillary model derived from classic Abel inversion to correct Total Electron Content (TEC) and then combines the corrected TEC with the spherical symmetric Abel inversion method. The inversion results from the simulated data of the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) IRO are compared with reference profiles by directly interpolation, and show that the new retrieval method is more effective.