Session - Modelling the Earth's ionosphere and solutions to counter ionospheric threats to GNSS applications

Marcio Aquino, Cathryn Mitchell, Giorgiana De Franceschi

The Earth's ionosphere is a complex system that is driven by many different factors such as solar radiation, electric and magnetic fields, and neutral atmosphere dynamics. New models and data to realise the state of the Earth's ionosphere are of interest to radio system users whose signals are affected by ionospheric propagation, in particular navigation and communications systems operating below 3 GHz. Global Navigation Satellites Systems (GNSS), which have become essential in support of a growing number of activities now embedded in modern society, are especially vulnerable to signal propagation through the ionosphere. In this context this session addresses models and solutions to mitigate ionospheric threats to GNSS and related applications. The TRANSMIT project, an FP7 funded Marie Curie Initial Training Network, has focused on the understanding and development of new models that can be tested for their usefulness in addressing radio system specification with a view to support the development of concepts and operational tools that could contribute to a service to assist European users in countering GNSS vulnerability to ionospheric phenomena. Results of this project are expected to be showcased in this session, as well as any other initiatives in this area. The session welcomes work in the areas of ionospheric tomography and imaging, radio occultation, scintillation and interference resilient receiver tracking models and implementations, real time positioning algorithms (e.g. for Precise Point Positioning) to mitigate ionospheric threats affecting legacy and new GNSS signals, scintillation and TEC prediction models and operational tools, as well as any other related topics. The main aim of the session is to stimulate discussion and encourage new collaborative work.

Invited Talks and First Class Posters

Monday November 17, 16:00 - 18:00

1 Oral - invited 4:00 pm The Added Value of New GNSS for Ionosphere Monitoring
      Warnant, R1; Wautelet, G1; Lonchay, M1
      1University of Liege 
      Local variability in the ionosphere Total Electron Content due to different types of ionospheric “disturbances” can strongly degrade the performances of GNSS-based high accuracy positioning. Real time GNSS applications are particularly vulnerable to these phenomena.   In this context, the University of Liege developed the so-called GPSTECMON software: based on GPS dual frequency measurements performed at a single station, GPSTECMON monitors the Total Electron Content and detects in real time the occurrence of ionospheric disturbances which can pose a threat to GNSS high accuracy applications. Then, the reconstructed information on the ionospheric activity is exploited to offer different services to GNSS users through an operational web site ( At European mid-latitudes, the most frequent disturbances are Medium-Scale Travelling Ionospheric Disturbances.   At the present time, ionosphere monitoring using GPS dual frequency L1/L2 measurements has different weaknesses: - Limited TEC accuracy: it ranges from 2 to 5 TECU; this is mainly due to the fact that the “classical” dual frequency TEC reconstruction techniques need code measurements to solve phase ambiguities; multipath, noise and hardware biases affecting code measurements limit the accuracy of the reconstructed TEC. In practice, an uncertainty of 5 TECU on TEC corresponds to an uncertainty of about 80 cm on the computation of the ionospheric error on the L1 carrier. Therefore, increased TEC accuracy is highly desirable. - Limited TEC spatial resolution: it depends on the number of satellites in view; in Liege (Belgium), the number of GPS satellites in view ranges from 8 to 15 with an average of 11. A proper modeling of local variability in TEC due to TID’s or to geomagnetic storms requires an increased spatial resolution. - Observational bias in the detection of irregularities: GPS based detection of moving structures like TIDs is limited due to satellite orbital movement. Indeed, most of GNSS satellites and, in particular, GPS satellites are placed on Medium Earth Orbits (MEO) at an altitude around 20 000 km. This means that they have a velocity with respect to the ionosphere. TIDs are moving structures and therefore have also a velocity with respect to the ionosphere. In practice TID detection will be affected by the relative velocity between the TID and the satellite. For a given TID, the fact that the satellite has a velocity which is parallel, anti-parallel (worst case) or perpendicular to the TID velocity has an influence. For example, if the TID has a velocity which is anti-parallel and of the same order of magnitude than the satellite velocity, there is a high probability that the TID will not be detected. In other words, the study of ionospheric disturbances using GPS satellites has an “observational bias” which makes their modelling more difficult.   The availability of new GNSS emitting new and more accurate signals and also the combination of the different GNSS will allow the development of improved data processing strategies for ionosphere monitoring and, as a consequence, improved services for GNSS users. The paper analyses the added value of new GNSS for ionosphere monitoring. In particular, the paper discusses the use of satellites with geostationary or inclined geosynchronous orbits to remove the orbital bias in the detection of ionospheric irregularities.
2 Oral - invited 4:20 pm TRANSMIT from an Industrial Partner’s Perspective
      de Jong, K1; Visser, H1; Memarzadeh, Y1
      1Fugro Intersite B.V.
      Fugro is a world leading provider of precise offshore Global Navigation Satellite System (GNSS) positioning services. Particularly in areas along the geomagnetic equator and in arctic regions, where many of Fugro’s activities take place, these services are frequently affected by effects due to space weather, such as ionospheric scintillations.  When asked to participate in TRANSMIT as an industrial partner in 2008, Fugro therefore immediately realized the benefits such a project could have for its operations.  In this presentation we will focus on the benefits gained over the years. These include: - A better understanding of scintillations from different points of view and for different applications, thanks to contacts with highly motivated researchers and other partners, at workshops, but also at the personal level.  - Involvement in state of the art research, based on our own data. - Access to data from scintillation monitors, which not only proved useful to detect scintillations, but also other effects, such as high phase noise and satellite clock anomalies. - New modules of our data analysis software, developed by TRANSMIT fellows, which are now routinely used in our daily network monitoring. - Increased awareness of the need of a data archiving system for our network data, as it provides a lot of valuable ionospheric information.  The overall conclusion is that TRANSMIT indeed has proved to be a very beneficial experience for Fugro. We hope we will be able to continue and extend our cooperation with project partners in the future.
3 Oral - invited 4:40 pm TRANSMIT Prototype: Tools for Mitigation of Ionospheric Threats to GNSS
      Sato, H1; Hlubek, N1
      The TRANSMIT prototype is a web-based demonstrator of the research results from the EC FP7 funded project Training Research and Applications Network to Support the Mitigation of Ionospheric Threats (TRANSMIT), a Marie Curie Initial Training Network (ITN). The applications implemented in the prototype aim to provide awareness of current ionospheric threats and improve solutions for the mitigation of ionospheric impacts for users of Global Navigation Satellite Systems (GNSS) and related services and applications.  The prototype demonstrator consists of three processors formed by six applications (called TRANSMIT processors). The processors have been developed by the TRANSMIT research fellows exploiting the varied expertise in their hosting institutions. In order to maximize the prototype research products, TRANSMIT processors are designed to be able to exchange their outcomes and use them as inputs to other related applications via the prototype network. The research topics covered by the processors are:  -Scintillation index S4 and TEC modeling -Accuracy in precise point positioning  -Tracking architecture for robust receivers -TEC map tools -Ionospheric model comparison -Asymmetry in ionosphere  The data flow in the prototype system is based on a cross-institutional network approach. The main concept of the prototype network is to clearly divide the functions of the partner institutions. The user portal and demonstrator is provided by the Space Weather Application Center – Ionosphere (SWACI) hosted by the German Aerospace Center. The data archive is hosted by the Italian National Institute of Geophysics and Volcanology (INGV). The  processors are hosted by the respective institutions, where the applications were developed, distributed over Europe. The TRANSMIT prototype service is accessible by sending queries and receiving the processed results via internet.   In this paper we will present the overview of the TRANSMT prototype and demonstrate selected outcome examples.
4 Oral 5:00 pm An Industry based Perspective on the Effects of Solar Radio Bursts on GNSS Receivers
      Vadakke Veettil, S1; Aquino, M1; de Jong , K2; Visser, H2
      1University of Nottingham; 2Fugro Intersite B.V. 
      Intense solar radio bursts occurring in the L-Band can impact the tracking performance of Global Navigation Satellite Systems (GNSS) receivers located in the sunlit hemisphere of the Earth. Significant decrease in the GNSS signal carrier-to-noise ratio (C/N0) is observed, which can lead to the complete loss of lock on the satellite signals. Previous experimental evidence has revealed that high-precision GPS positioning on Earth’s entire sunlit side was partially disrupted during solar radio bursts. Hence, solar radio bursts are a potential threat to safety-critical systems based on GNSS. Consequently monitoring these events is important for suitable warnings to be issued in support to related services and applications. Despite such relevant experimental evidence, not enough emphasis or research effort has been given to this phenomenon, which is characterized by low probability of occurrence, but also by high impact when it occurs. This paper presents the results from investigations on the impact of the solar radio burst of 24 September 2011 on GNSS receivers from an industrial point of view. It exploits data from the GNSS based service provider Fugro, collected by reference station receivers. The impact of this radio burst on the availability of Fugro’s real-time precise point positioning (PPP) services and on the quality of the L-band data link used to broadcast this service are presented and discussed.
5 Oral 5:15 pm Space Weather Effects over EGNOS Performance in the North of Europe
      Pintor, P1; Roldan, R2; Gomez, J1; De la Casa, C1; Fidalgo, R  M1
      1ESSP; 2ESSP SAS
      Solar cycle #24 is generating a period of high solar activity. This increased activity affects the geomagnetic behavior of the ionosphere. The continuous observation of EGNOS performances since the beginning of this solar cycle and particularly the focus on EGNOS performance degradation has shown a dependency due to the behavior of the ionosphere at high latitudes.  The dependence of EGNOS performance with the variations observed in the ionospheric behavior is known, and has been especially relevant since the beginning of the solar activity increase linked to the current solar cycle. This kind of events affects not only EGNOS but also other SBAS systems under geomagnetic storm conditions. This is considered as an intrinsic limitation in single frequency SBAS systems. In the past, some areas of Europe were more sensitive to the variations in the behavior of the ionosphere. The current EGNOS release (2.3.2), deployed in October 2013, increased the robustness of EGNOS against this kind of events, correcting some issues which were observed during autumn of 2012. A new release ESR2.4.1 will be deployed during 2015, including additional improvements related to ionosphere monitoring. However, even if these new releases provide a higher stability to ionospheric disturbances, some degradation can still be expected during periods with very high geomagnetic activity. Several indicators can be used to measure the status of the ionosphere such as the K and A indexes or the SSN. The dependence of EGNOS performance with the indicators is known and has been especially relevant since the increase of the solar activity in 2011. Other indicators, such as the disturbance storm time (Dst), have been investigated as an alternative mean to detect ionospheric events. However, the use of these indicators presents also some limitations such as temporal resolution, geographical applicability or different level of correlations wrt EGNOS performance.  These limitations show that the information provided by these indexes needs to be used carefully in order to understand the impact of the ionospheric behavior in the performance of SBAS.  The effect of the ionospheric disturbances can be easily observed through the observation of the Horizontal Protecion Level (HPL). The HPL is a bound of the horizontal error and is calculated with the EGNOS information broadcast according to MOPS 229D. This parameter is an integrity monitor to decide if a specific operation (for example, an LPV) can be initiated, and so, it can be used to measure, during a given period, the performance of the system, in terms of availability, for a particular operation.  EGNOS performance appeared to be degraded with values of HPL well above the 40m operational limit in the North of Europe during several periods along the solar cycle #24. EGNOS integrity was always guaranteed every single epoch for the whole service area but its availability was reduced. From SBAS standards, it is known SBAS systems model its ionospheric corrections and integrity information from TEC estimated by its algorithms. TEC disturbances are known to be also correlated to geomagnetic storms and local time and these storms, at the same time can be traced to exchanges between the Earth’s magnetosphere and the interplanetary conditions originated by the Sun. In order to analyze the geomagnetic conditions affecting EGNOS, the method of analysis focuses on the negative variations of interplanetary magnetic field z component (Bz) and solar wind speed sudden increases and other factors.  This paper provides a summary of the different analyses performed by ESSP relative to the existing correlation between the EGNOS performance measured over the north region of the EGNOS service area, some ionospheric indicators and some solar events.
1 First class poster 5:30 PM Characterization of High Latitude GPS Sensed Ionospheric Irregularities:  Case Studies
      Ghoddousi-Fard, R1; Prikryl, P1; Oksavik, K2; van der Meeren, C2; Lahaye, F1; Danskin, D1
      1Natural Resources Canada; 2Birkeland Centre for Space Science, Department of Physics and Technology, University of Bergen / Arctic Geophysics, The University Centre in Svalbard
      Rate of change of 1Hz GPS phase differences at two frequencies are being monitored in near-real-time and used as proxy ionospheric disturbance indices at the Canadian Geodetic Survey (CGS) of Natural Resources Canada from about 165 globally distributed stations including Real-Time International GNSS Service stations as well as other high rate stations operated by CGS. It has been shown that such indices correlate well with the phase scintillation index during weak to moderate phase scintillation over high latitudes.   GPS phase rate variations over Canada and adjacent regions have been analyzed during 2013 and early 2014. With more than 40 stations being monitored over the region a significant coverage of ionospheric pierce points during each 24 hours in geomagnetic latitude and local hour is achieved. Maps of occurrence of phase scintillation as a function of local hour and geomagnetic latitude are studied toward characterization of occurrence of irregularities.   A number of scintillation events over polar, auroral and sub-auroral latitudes correlated with coronal mass ejections or high-speed solar wind streams have been identified and their analysis is complemented with observations from dedicated scintillation receivers from Canadian High Arctic Ionospheric Network (CHAIN) and a new multi-constellation receiver network in Svalbard.
2 First class poster 5:35 PM GNSS Observational Bias in the Frame of Ionospheric Studies
      Wautelet, G1; Warnant, R1
      1University of Liège
      Ionospheric disturbances such as Traveling Ionospheric Disturbances (TIDs) affect high-accuracy positioning with Global Navigation Satellite Systems (GNSS). Besides, GNSS satellites are also considered as “satellites of opportunity” for ionospheric research. Indeed, each constellation being made up of about 30 satellites, receivers are able to track several satellites simultaneously, and therefore to perform multiple ionospheric observations at a given epoch. In the frame of ionospheric studies with GNSS, it is common use to assimilate the ionosphere to a simple geometric shape. Generally, ionospheric plasma is assumed to be confined into a spherical shell, infinitesimally thin, containing all free electrons. The intersection of this layer and a given satellite-to-receiver link is called the Ionospheric Pierce Point (IPP). Using moving satellites to monitor the Total Electron Content (TEC) and its variations in time and space induces some observational biases. Indeed, there is a relative movement between the moving observer (the satellite), the moving structure (the ionospheric disturbance) and the receiver station which is also moving due to the Earth rotation. As a consequence, one-way measurements are affected by the relative movement between the IPPs and the ionospheric disturbance. More precisely, only the projection of the velocity vector of the IPPs v on the direction of propagation of the disturbance k matters. In other words, one can expect no relative effect if both directions are perpendicular, i.e. if v · k = 0. The consequence resulting from this relative motion, which is elevation-dependent (IPP velocity may change with a ratio of 1:7 according to satellite elevation), is that apparent TID wavelength and period are distorted with respect to their true value. Besides this purely geometrical effect, ionospheric measurements with GNSS also suffer from the so-called aliasing effect, related to the observation sampling rate. Indeed, a signal (here a TID) is resolved properly if the time step between measurements is not kept shorter than its timescale (i.e. its period). As a result, long sampling rates will make the observed signal as if it has a longer period than it actually has. In addition, the amplitude of a TID is also distorted if the latter is not properly resolved by GNSS observations, which leads generally to under-estimated values. In this context, the aim of this paper is to identify geometrical conditions leading to distortions in the observation of TIDs with GNSS, which are the most common source of ionospheric disturbances over mid-latitudes. Based on simulation of several GNSS constellations (GPS, GLONASS, Galileo, Beidou) but also of measurements related to geostationary satellites, it is proposed to study the reconstruction of a simulated TID observed from a single GNSS station on Earth. The TID is modeled by a simple planar wave in the TEC, with a given wavelength, period and direction of propagation. Analysis of geometric and aliasing effect will be separately assessed by considering several values of these propagation parameters, considering both small-scale (wavelengths smaller than 50km) and large-scale TIDs (wavelengths larger than 1000km). The different orbit configurations of GNSS constellations (Medium-Earth Orbit for GPS, GLONASS, Galileo and Beidou, Inclined Geosynchronous Orbit for Beidou or Geostationary Orbit for EGNOS, WAAS and Beidou) offer a variety of different geometrical conditions, resulting in different observational biases. Because of their low IPP velocity, inclined geosynchronous and geostationary orbits are expected to better reconstruct TIDs than medium-earth ones used by GPS, GLONASS or Galileo systems.
3 First class poster 5:40 PM Mitigation of the Impact of Scintillations on GNSS Positioning in the Scope of the TRANSMIT Project Prototype
      Kieft, P
      University of Nottingham
      TRANSMIT (Training Research and Applications Network to Support the Mitigation of Ionospheric Threats) is an EU funded Marie Curie Actions project. The final outcome of the TRANSMIT project is a prototype of a web based service, whose functionality comes from an underlying distributed system, comprising a database at INGV (Italian National Institute for Geophysics and Vulcanology) , processors (at the participating universities) and a web front-end at DLR (German Aerospace Centre). This ‘prototype’ service aims to provide the users of Global Navigation Satellite Systems (GNSS) and related applications with information on ionospheric threats, and a demonstration of the capabilities of improved ionospheric perturbations mitigation solutions.   This paper concentrates on the research behind one of the processors, as well as its functionality and implementation in the TRANSMIT prototype, which aims to demonstrate a tool to mitigate the impact of ionospheric scintillation on the GNSS positioning computation.   Small scale (in the order of a few hundred meters), time varying irregularities in electron density in the ionosphere can cause scattering and diffraction of the radio signals passing through them. The result for the observer is a signal which is rapidly changing in phase (phase scintillation) and intensity (amplitude scintillation). The impact for a GNSS receiver can range from a complete loss of lock (signal no longer available), cycle slips on the phase measurements or a degraded accuracy of the phase and code ranges that can lead to poor positioning accuracy.   The scintillation mitigation method during the positioning computation stage is limited to the repair of cycle slips and finding the ‘best’ stochastic model which will achieve a balance between the decreased accuracy of the affected ranges and the degradation of the geometry, which in itself can lead to degradation in positioning accuracy. The reduction of the amount of ‘losses of lock’ is improved through a novel PLL design (demonstrated within another TRANSMIT prototype processor).  This processor of the TRANSMIT prototype service will perform a position calculation for different, currently used stochastic models (e.g.: elevation based, signal-to-noise-ratio based), and will provide a comparison of their performance during scintillation events with the TRANSMIT algorithms. The TRANSMIT algorithms comprise a stand-alone solution and an augmented solution using scintillation information from a network of scintillation monitoring receivers. The user of this processor of the prototype service will be able to choose from a set of selected events, start the calculation process (Single Point Positioning or Precise Point Positioning) and will be presented with the (comparison) results.
4 First class poster 5:45 PM Designing a GNSS Carrier Tracking Architecture Robust to Ionospheric Scintillation
      Susi, M1; Andreotti, M2; Aquino, M1
      1University of Nottingham; 2Novatel
      Electron density irregularities in the ionosphere are responsible for random amplitude and phase fluctuations of trans-ionospheric signals, a phenomenon known as scintillation. Amplitude scintillation may produce deep signal fading and push the signal intensity below the receiver tracking threshold. Furthermore, phase scintillation increases the carrier Doppler shift and can even make it larger than the phase locked loop (PLL) bandwidth.  As a consequence large phase errors, cycle slips or even losses of signal lock can occur. Moreover, even if this phenomenon usually affects only a portion of the sky, it can still decrease the final position solution accuracy and also impair GNSS operation when the number of healthy satellite links is not enough.  A possible approach to mitigate scintillation effects on GNSS is to increase the robustness of GNSS receivers and in particular of their PLL, that is the receiver part most sensitive to scintillation effects. A conventional PLL requires a short integration time or a wide carrier loop bandwidth to follow the fast dynamics due to phase scintillation.  On the other hand a long integration time or a narrow carrier loop bandwidth should be preferred to reduce the noise produced by amplitude scintillation. To solve this trade off, the use of adaptive tracking schemes, such as Kalman Filter (KF) based PLLs, represents a suitable strategy. The use of a KF allows optimizing the loop filter by minimizing the phase error. However to ensure the optimality of the KF, the correct dynamic model should be defined. This is not a trivial task in the presence of variable working conditions, such as under the occurrence of scintillation. In fact, the assumed dynamic model would no longer be suitable when the noise and dynamic levels change significantly due to scintillation,.  In order to overcome this issue, this paper proposes a self-tuning KF based PLL. The algorithm monitors the scintillation level by computing on the fly some key parameters as p, T, namely the slope and strength of the phase scintillation spectrum, and the carrier to noise ratio. Then the above parameters are used to tune the covariance matrix and the measurement noise of the KF on the fly.  The proposed algorithm, implemented into a software receiver, is assessed using both high latitude and equatorial scenarios. Specifically, high frequency signal perturbations were extracted from real data collected at high latitudes (in Bronnoysund, Norway, ~65oN geographic latitude) through a NovAtel professional scintillation monitoring receiver (the GSV4004B). Finally, these perturbations were superimposed onto GPS signals using a Spirent GS8000 hardware simulator. Moreover, Intermediate Frequency (IF) GPS and Galileo real equatorial data collected in Vietnam during a period of high solar activity are  used to assess the algorithm in equatorial scenarios. The above data were collected using a USRP N210 front end driven by a rubidium clock.  The tracking performance of the proposed algorithm is compared to that of the Septentrio PolaRxS professional scintillation monitoring receiver, in terms of the resulting phase error, cycle slips and loss of lock occurrence. Finally, the effectiveness of the scintillation parameters computation is also tested by using the Septentrio PolaRxS receiver as benchmark.
5 First class poster 5:50 PM Effect of Interference in the Estimation of Ionospheric  Scintillation Indices with GNSS.
      Romero, R1; Dovis, F1
      1Politecnico di torino 
      Irregular electron concentrations in the ionosphere are known to cause rapid fluctuations in the amplitude and phase of satellite signals, a phenomenon known as scintillation. The occurrence of scintillation depends on solar and geomagnetic activity, season, local time, geographic location and frequency of the satellite signal.  For Global Navigation Satellite System (GNSS) receivers, ionospheric scintillations can considerably degrade the performance by inducing cycle slips, losses of lock of the signals and reduced accuracy of the PVT solution.   Ionospheric Scintillation Monitoring Receivers (ISMR) are specialized receivers able to track and monitor scintillations in order to collect data that can be used to analyze the phenomenon. This is normally done by computing the S4 and Phi60, namely the amplitude and phase scintillation indices, in a minute by minute basis. Within this work we deal with a specific environment of an ISMR where the monitoring of scintillation activity is threatened by the presence of Radio Frequency Interference (RFI) in the operation area. RFI is, among the different error sources that corrupt satellite navigation waveforms, a particularly harmful error since in some cases it cannot be mitigated by a simple correlation process. This is indeed a problem that may affect the detection of ionospheric scintillation when monitored by GNSS signals, and has been quantified in several scenarios based on different characteristics of the satellite signal, the interference and the receiver configuration .  The work proposed here is being developed within the framework of TRANSMIT (Training Research and Applications Network to Support the Mitigation of Ionospheric Threats), a Marie Curie Initial Training Network aiming to develop new techniques to detect and monitor Ionospheric threats with the introduction of new prediction and forecasting models, mitigation tools and improved system design. In particular, the  work package (WP)  of the TRANSMIT project  titled “Scientific and Industrial Application Reliant on GNSS”,  is  dedicated to the  assessment of ionospheric  effects on  GNSS and related applications and is steered by industrial requirements.
6 First class poster 5:55 PM Mitigating the Effects of Spherical Symmetry Hypothesis from  Ionospheric Radio Occultation (RO) Data Inversion with the help of Model Data
      Shaikh, M1; Nava, B2; Notarpietro, R1
      1Politecnico di Torino; 2The Abdus Salam International Center for Theoretical Physics
      Spherical symmetry is a common assumption applied to the Radio Occultation (RO) observations in the ionosphere. The corresponding techniques are very effective for RO data inversion especially in the case of small horizontal electron density gradients present in the ionosphere. Nevertheless, during geomagnetic disturbed periods or in specific geographic regions, like the equatorial anomaly region, large electron density gradients may be experienced which could lead to the failure of spherical symmetry hypothesis producing erroneous electron density (Ne(h)) profiles as output. We had performed a thorough study on the qualitative and qualitative aspects of Ionospheric asymmetry. As a result, we developed an asymmetry index [1] that, with the help of a suitable background ionosphere, is able to quantify the level of asymmetry present in the ionosphere with respect to time, location and prevailing solar and geomagnetic activity. This work is an attempt to mitigate the effects of spherical symmetry hypothesis in RO data inversion algorithms. We have implemented a simple technique based on the NeQuick2 model adaptation to RO-derived TEC. It relies on the minimization of a cost function involving experimental and model-derived TEC data to determine the NeQuick2 input parameters at the wanted locations and time. These parameters are then used to evaluate the electron density profile Ne(h) along the ray perigee positions associated to the relevant RO event. We performed our analysis on one month’s experimental data (approximately 29,000 RO events in September 2006) downloaded from the COSMIC mission database ( In particular the differences between peak densities derived from the profiles obtained with model-assisted technique and the corresponding experimental peak densities obtained from collocated ionosondes have been considered. The results indicate that, even if the technique was able to avoid the presence of negative electron density values in the reconstructed profiles, it could not improve in all cases the results of spherical symmetry hypothesis. In this paper, we have presented a description of the adopted approach together with our initial results towards developing the model assisted RO data inversion.       In the scenario of TRANSMIT project prototype implementation, we are going to evaluate global asymmetry maps (not shown to the users) with their associated inversion error (DVTEC and DNmF2) plots considering background ionosphere computed using NeQuick2, IRI and MIDAS. By querying these global maps of asymmetry, and for a given geometry of RO event, we will try to predict the expected level of asymmetry present in the ionosphere and its potential impact on RO inverted products using estimates of delta_NmF2 and delta_VTEC. Also, initial results obtained in attempt to develop the model assisted RO data inversion (currently being developed) will also be shown.