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

Marcio Aquino, Alan Dodson (Monday) and Giorgiana De Franceschi, Vincenzo Romano (Tuesday)

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.


Talks and First Class Posters
Monday November 17, 16:00 - 18:00, auditorium Rogier
Tuesday November 18, 09:00 - 10:50, auditorium Rogier

Poster Viewing
Monday November 17, 15:30-16:00, area in front of auditorium Rogier
The numbering of the posters can differ from the numbering in the overview without abstracts.

Talks and Highlighted Posters

More Posters

7 Poster   Accuracy assessment of the GNSS ionospheric corrections provided by the 3D data assimilation ionosphere model
      Solomentsev , Dmitry1; Khattatov, B2; Titov, A1; Cherniak, J1; Belokrylov, A3; Sorokin, S2
      1Central Aerological Observatory; 2National Research University of Information Technologies; 3Industrial Geodetic Systems Ltd
      Obtaining the precise ionospheric corrections for the navigation measurements is of great importance for the GNSS professionals. Both single and multi-frequency GNSS receivers suffer from the ionospheric signal delay. The amount of the signal delay is dependent on the current ionosphere state in the vicinity of the signal propagation path. The ionosphere itself is a complex unstable medium, which is strongly forced by the external factors (such as neutral thermosphere components and solar activity). These facts together make the calculation of the ionospheric corrections for the GNSS measurements a challenging and actual problem, which is still to be solved. The three-dimensional data assimilation model of the ionosphere has been developed by our team for the scientific research purposes. The data assimilation system updates the first-principle model results with the GNSS total electron content measurements, obtained from the variety of the ground-based networks. During a long series of the model results validation versus the independent observations (ionosondes, incoherent scatter radars, satellite measurements etc) the model has shown high accuracy in estimation of the ionospheric electron density in the altitude range from 80 to 20 00 km.   The data assimilation model results then have been applied to the GNSS corrections calculation. Since the three-dimensional fields of electron density are available, the first and second order errors were removed from the GNSS measurements in the post-processing mode. After the data have been corrected, several positioning algorithms including the RTKlib library were applied to obtain the precise receiver position. The positioning results were then compared to the raw measurements processing results, ionosphere-free combination results and the Klobuchar model performance. The presented experiment results have shown that the application of the ionospheric corrections, obtained from the data assimilation model sufficiently increases the accuracy of the positioning algorithms in a single frequency mode in comparison with raw measurements and the Klobuchar model corrections. The results of the described comparisons will be presented and discussed along with the data assimilation model validation time series and the scientific applications examples.
8 Poster   Characterization of Ionospheric Disturbances and their Relation to GNSS Positioning Errors at High Latitudes
      Jacobsen, K  S1; Dähnn, M1
      1Norwegian Mapping Authority
      We present results from an analysis of the distribution of ionospheric disturbances, measured by the Rate Of TEC Index (ROTI), and their relation to Precise Point Positioning (PPP) accuracy. The analysis is based on data for the entire year of 2012, for 10 receivers at latitudes from 59 to 79 degrees North. PPP solutions were computed using the GIPSY software.  The results show that elevated ROTI values occurs mainly in the cusp and nightside auroral oval regions. Elevated ROTI values are more common in the cusp, but in the nightside auroral oval they are stronger. The 3D position error is strongly correlated with ROTI for receivers that are affected by space weather, and increases exponentially with increasing ROTI.
9 Poster   Global Median Model of the Ionospheric Critical Frequency foF2 Based on GPS Radio-Occultation and Ground-Based Sounding Data
      Tsybulya, K1; Shubin, V2
      1Fiodorov Institute of Applied Geophysics; 2IZMIRAN 
      Currently the most widely used model of ionospheric parameters modeling is International Reference Ionosphere (IRI). The model median of the F2 layer critical frequency (foF2) was based mostly on ground-based ionospheric sounding data for the 1954–1964 period (CCIR coefficients) and the 1975-1979 period (URSI coefficients). The network of ionospheric sounding stations is rather sparse and does not cover the entire globe. In particular, ground-based stations are numerous in the Northern Hemisphere mid-latitudes but there are few of them near the equator and in the Southern Hemisphere. Also, very few data points are available over the oceans. We make an attempt to create an improved global median model for the most important ionospheric parameter - the F2 layer critical frequency foF2 using our experience with the SMF2 model for the F2 layer peak height (hmF2). Both models are based, first of all, on GPS radio-occultation data provided by receivers onboard satellites CHAMP (~300 000 foF2 values), GRACE (~100 000) and COSMIC (~3 500 000). These massive set of data was not available when the CCIR and URSI coefficient sets were compiled. Also for the presented model, foF2 series produced by 234 ground-based ionospheric sounders were used to supplement the satellite data set for the 1957-2012 period. To estimate the precision of the developed model we made comparisons with independent data sets obtained in different seasons on ionospheric stations on different latitudes. In general, the model gives smaller errors than IRI, especially on low latitudes and in the Southern hemisphere.
10 Poster   Space weather case studies on disturbed VLF radio propagation in the lower ionosphere
      Danielides, M1; Skripachev, V2
      1Danielides Space Science Consulting; 2Moscow State Technical University, Moscow Institute Radiotechnics, Electronics and Automatics
      Since the early 20ies century the importance of the condition of Earth ionosphere for long range radio communication is known and presumable nowadays almost completely understood. However, the development and especially the distribution of low-cost software defined radio wave receivers (SDRs) is an on-going process and opens new opportunities for investigating Earths lower ionosphere, utilizing globally distributed VLF monitoring networks based on SDR technology.  The aim of this presentation is i) to compare some of the existing VLF receiver types and networks, ii) present the InFlaMo network (www.inflamo.org) and its different SDR receivers, and iii) show results of combined experiments of ground based instrumentation, e.g. VLF transmitters, receivers and ionospheric heaters. Results from those case studies are compared with an ionospheric fluid model. On outcome is that for single locations of VLF receivers the daily and annual variations can now be numerically forcasted. That enables us to make a quick and automated nowcasting of space weather signatures from a broad VLF spectrum.
11 Poster   Augmentation of EGNOS Open Service by Locally Adapted Ionospheric Model
      Vukovic, J1; Kos, T1
      1University of Zagreb, Faculty of Electrical Engineering and Computing
      Global Navigation Satellite Systems (GNSS) provide positioning, navigation and timing solutions that can be used by users with different requirements. Performance of GNSS is affected by several error sources and the ionosphere is recognized as the major one. Ionospheric error varies depending on the time of day, season, position of the receiver, solar activity and the Earth’s geomagnetic field. The ionospheric error is quantified by the amount of Total Electron Content (TEC) on the path between satellite and receiver. This error is frequency dependent so it can be estimated using two frequencies in the satellite-receiver communication.   Vast majority of GNSS receivers still uses only one frequency and they rely on global ionospheric models to calculate and mitigate ionospheric error.  Such models can perform well in non-disturbed ionospheric conditions. However, in the time of high solar activity and sudden ionospheric changes, single frequency GNSS receivers’ performance degrades severely. To overcome this problem, Satellite-Based Augmentation Systems (SBAS) can be used. Using networks of dual-frequency GNSS receivers the current ionospheric error over some region is estimated. The calculated correction parameters are transmitted to the receivers by geostationary satellites. European Geostationary Navigation Overlay Service (EGNOS) provides Safety-of-Life (SoL) service with emphasis on integrity, primarily for usage in aviation, and Open Service (OS) with emphasis on accuracy, intended for non-SoL usage. EGNOS OS coverage area extends over most of the European Civil Aviation Conference (ECAC) region, but the eastern border area remains uncovered. In case of ionospheric disturbances, coverage is additionally disrupted because of lack of Ranging and Integrity Monitoring Stations (RIMS) in that area.  This research identifies effects of different solar and geomagnetic conditions on EGNOS ionospheric correction performance in middle latitudes, especially on its eastern borders. The observed period is within the current solar cycle 24, as EGNOS OS became operational in 2009. The reference data are TEC obtained from dual-frequency GNSS stations’ RINEX observation files. Such TEC is affected by inter-frequency biases (IFB), produced by the receiver and the satellites, and has to be calibrated before being used as a reference value.   After recognizing areas with permanent or ionospheric-condition-dependent lack of EGNOS ionospheric corrections, a solution with locally adapted ionospheric model is proposed. Even though there are no RIMS stations in the recognized area, several GNSS stations with publicly available data are situated there. Local reference TEC can be used to modify a global ionospheric model in a way to adapt the model to the local ionospheric conditions. The model of choice is NeQuick 2, a global model able to compute ionospheric density between any two given points, designed for simple and fast execution. The NeQuick 2 model can be locally adapted if the local ionization level is used as a model input instead of a solar flux index. Further research will determine the distance from reference data source where such a locally fitted model would provide the level of ionospheric correction similar to EGNOS, i.e. the area in which it could augment EGNOS OS.
12 Poster   Characterization of Ionospheric Effects and Investigation of their Influence on Current GNSS Observing System
      Cokrlic, M1; Galas, R1
      1Technische Universität Berlin 
      Ionosphere has critical influence on the trans-ionospheric communication- and navigation systems, and thus it is one of the critical factor that has influence on the Global Navigation Satellite Systems (GNSS). Mitigation of the ionospheric threads is one of the most interesting topics in the research and development area to improve availability, reliability and precision of the GNSS systems. GNSS signals, passing through the ionosphere, are affected by the free electrons and can be refracted or dispersed. Thus they are carrying ionospheric characteristics and signatures that can be isolated and studied. Because of that and of the relatively low cost of the GNSS receivers, and availability of the data from the already existing continuously operating reference GNSS networks, studying and monitoring of the ionosphere on a global scale and with high spatial- and time resolution become available. From the other side, ionospheric perturbations can degrade accuracy of the positioning for more than hundred meters and even make the PVT (position, velocity and time) estimations impossible or false. Thus information about the state of the ionosphere must be available in real time to enhance availability and to improve navigation accuracy.   The state of the ionosphere can be characterized by a couple of basic parameters. Some of them can be evaluated from GNSS observations: Total Electron Content (TEC), Rate of TEC (ROT), Rate of change of TEC (ROTI), amplitude (S4) – and phase (σφ) scintillation indexes. These parameters can be estimated form GPS networks or from a single GNSS station.  We are developing software tools to derive magnitudes of those ionospheric parameters in a very challenging real-time single station mode. Some of the modules, like e.g. calculation of S4, TEC and ROT, are already validated and some others are still in the testing phase. The tools are needed in order to detect and to analyze ionospheric perturbations in real- or near- real time and to investigate if some new approaches for generation of navigation-corrections can be developed. Our main goal is to provide such corrections, or at least warning messages on ionospheric irregularities, for near-real-time (or even real-time) single user receiver based processing, like  e.g. single station PPP (Precise Point Positioning).  Within the TRANSMIT project, participation in the development and operation of PanEuropean network is foreseen. The network covers mostly European area, but it is planned to extend it to the south until the equator. Thus, the Techniche Universitat Berlin (TUB) deploy its monitoring station in Ethiopia (equatorial area), where ionospheric anomalies occur more often and are stronger then in the midlatitudes. In this paper our software, and very first results from the operating TUB/TRANSMIT station in Ethiopia (temporary integrated into the PanEuropean network) will be presented.
13 Poster   2D Monitoring of Midlatitude Ionospheric Parameters by Using IRI-Plas-GK
      Arikan, F1; Deviren, M  N1; Gulyaeva, T2
      1HACETTEPE UNIVERSITY; 2IZMIRAN 
      Ionosphere is an important layer of atmosphere that lies between 100 km and 1000 km altitude. Ionosphere is also important for HF and satellite communications, space-based navigation, positioning and guidance systems. Solar, geomagnetic, gravitational and seismic activities cause variations in ionosphere. Total Electron Content (TEC) is one of the main observables to monitor the variability of ionosphere. International Reference Ionosphere Extended to Plasmasphere (IRI-Plas) is accepted by International Organization for Standardization (ISO) as the standard model of ionosphere. IRI-Plas TEC provides the TEC up to GPS satellite height that represents the background ionosphere. For a given location, time and date, IRI-Plas provides the estimates of the electron density, TEC, electron temperature, ion temperature, and ion composition based on the monthly averages. In IRI-Plas, TEC data can be also provided externally as input for the proper scaling of topside and plasmasphere extensions. In this study IRI-Plas is further modified to assimilate ionosonde foF2 and hmF2 estimates along with GPS-TEC, at chosen locations in a region to produce a 2-D map of desired ionospheric parameters such as foF2, hmF2, plasma frequency at a given height or height of a specific electron density distribution. The 2-D map is automatically drawn using Universal Kriging with Linear Trend that employs Matern Function for semivariogram. The Matern function coefficients are extracted by Particle Swarm Optimization technique. To monitor the ionospheric parameters (TEC, height, frequency, electron density, ion concentration, ion and electron temperature) with respect to each other, Modified IRI-Plas with Kriging, IRI-Plas-GK is prepared by IONOLAB. Thus, high resolution space-time automatic maps of ionospheric parameters can be used to model the ionosphere and investigate the effects of Space Weather. This study is supported by the joint grant from TUBITAK 112E568 and RFBR 13-02-91370-CT_a.
14 Poster   Distribution Of Modelling Spatial Processes Using Geostatistical Analysis
      Grynyshyna-Poliuga, O1; Stanislawska, I1
      1Space Research Centre Polish Academy of Science
      The Geostatistical Analyst uses sample points taken at different locations in a landscape and creates (interpolates) a continuous surface. The Geostatistical Analyst provides two groups of interpolation techniques: deterministic and geostatistical. All methods rely on the similarity of nearby sample points to create the surface. Deterministic techniques use mathematical functions for interpolation. Geostatistics relies on both statistical and mathematical methods, which can be used to create surfaces and assess the uncertainty of the predictions. The first step in geostatistical analysis is variography: computing and modelling a semivariogram. A semivariogram is one of the significant functions to indicate spatial correlation in observations measured at sample locations. It is commonly represented as a graph that shows the variance in measure with distance between all pairs of sampled locations. Such a graph is helpful to build a mathematical model that describes the variability of the measure with location. Modeling of relationship among sample locations to indicate the variability of the measure with distance of separation is called semivariogram modelling. It is applied to applications involving estimating the value of a measure at a new location. Our work presents the analysis of the data following the steps as given below: identification of data set periods, constructing and modelling the empirical semivariogram for single location and using the Kriging mapping function as modelling of TEC maps in mid-latitude during disturbed and quiet days. Based on the semivariogram, weights for the kriging interpolation are estimated. Additional observations do, in general, not provide relevant extra information to the interpolation, because the spatial correlation is well described with the semivariogram.
15 Poster   Galileo Robust Tracking Algorithms Under Ionospheric Scintillation
      Vuckovic, M
      University of Nova Gorica 
      The presence of the free electrons in the ionosphere may affect the propagation of radio waves such as Global Navigation Satellite System (GNSS) signals causing rapid temporal fluctuations in both amplitude and phase. This phenomenon, known as scintillation, can affect the performance of the GNSS receivers decreasing the final accuracy and, in a worst case, leading to the total loss of lock. The number of the free electrons varies in complex manner with geographical location, time, season solar and magnetic activity causing negative impact on GNSS systems especially in the equatorial and polar regions where a very high scintillation activity may occur.  On the other hand, the GNSS signals have been used for measuring the scintillation effects for decades. Design and implementation of the new GNSS systems, such as European Galileo system, should bring more robust signals and thus improve sensitivity of the propagating signals in presence of scintillation.  In a bid to develop a state of the art tools to mitigate the ionospheric effects to GNSS a Marie Curie Initial Training Network titled Training Research and Applications Network to Support the Mitigation of Ionospheric Threats (TRANSMIT) was proposed and founded by European Commotion. Furthermore, in a scope of the TRANSMIT project a special sub-project call “Scientific and Industrial Applications Reliant on GNSS” was developed to bring some novel methods capable of mitigating the ionospheric effects at receiver level. According to this, currently available Galileo signals collected at equatorial region were used in order to investigate the ionospheric impact on Galileo signals. A few attempts have been done experimenting with different tracking algorithms. Except traditional third order Phase Lock Loop (PLL) a Kalman Filter (KF) was implemented into a software receiver and in-phase and quadrature-phase samples of the prompt correlator were used to estimate two typically used scintillation parameters called, S4 index and SigmaPhi index. As described in [1], real data were used to verify the results obtained in this study.  [1] Susi, M. et al., “Design of a robust receiver architecture for scintillation monitoring”, submitted to IEE ION PLAN Conference 2014, Monterey, California.