Global Positioning System, or GPS, plays an important role in everyday life. More particularly, precise positioning applications constitute a continuously growing sector whose surveyors, civil ...engineers and more recently farmers represent the principal users. Ionospheric irregularities are considered as the main threat for those applications as their occurrence and their effects on positioning are generally unknown or unmodeled. This paper aims at setting up a local climatological model of such irregularities which can be used as a forecasting tool. The model is based upon a time series of GPS-derived ionospheric irregularities in Belgium covering 10 years of data (period 2002–2011). Our climatological model is twofold: its first component describes the daily variability and is derived from a principal component analysis (PCA) which allows us to retrieve the main patterns of the time series. With the use of low order polynomial and harmonic functions, the second component describes the influence of solar cycle and seasons on irregularity occurrence. Moreover, a statistical autoregressive formulation adapts the model to current conditions. Model validation covers both low and active solar activity periods (years 2008 and 2011) and shows that model accuracy varies with solar conditions and season: values are lower during winter and active solar activity periods, where modeling error can reach up to 60% of the observed value. During summer, model performance is clearly improved, with relative errors generally smaller than 20% for periods of low but also active solar activity.
► Modeling and forecasting ionospheric irregularities for GPS users. ► Use of principal component analysis to retrieve main patterns in time series. ► Modeling error is larger during winter than during summer.
The
modelling of the total electron content (TEC) plays an important role in global navigation satellite systems (GNSS) accuracy, especially for
single-frequency receivers, the most common ones ...constituting the mass market. For the latter and in the framework of Galileo, the
NeQuick model has been chosen for correcting the ionospheric error contribution and will be integrated into a global algorithm providing the users with daily updated information.
In order to reach the ionosphere error correction level objective, the model itself as well as its use for Galileo are
investigated. In our comparison process, we take advantage of various ionosphere data from several European stations (Dourbes in Belgium, El Arenosillo and Roquetes in Spain) where
ionosonde and GPS TEC data are available for different solar activity levels. These data allow us to study NeQuick representation of the ionosphere at
mid-latitudes. Constraining the model with ionosonde measurements, we investigate the difference between GPS-derived vertical TEC and corresponding values from NeQuick for a
high solar activity level (year 2002). With this approach, we reach
residual errors of less than 20% in standard deviation. We especially highlight the
improvements from the latest (second) version of NeQuick and show the
critical importance of the topside formulation.
The ionospheric effect remains one of the main factors limiting the accuracy of Global Navigation Satellite Systems (GNSS) including Galileo. For single frequency users, this contribution to the ...error budget will be mitigated by an algorithm based on the NeQuick global ionospheric model. This quick-run empirical model provides flexible solutions for combining ionospheric information obtained from various sources, from GNSS to ionosondes and topside sounders. Hence it constitutes an interesting simulation tool not only serving Galileo needs for mitigation of the ionospheric effect but also widening the use of new data.
In this study, we perform slant TEC data ingestion – the optimisation procedure underlying the Galileo single frequency ionospheric correction algorithm – into NeQuick for a dozen locations around the world where both an ionosonde and a GPS receiver are installed. These co-located instruments allow us to compare measured and modelled vertical TEC showing for example global statistics or dependence towards latitude. We analyse measurements for the year 2002 (high solar activity level) giving an insight into the situation we could observe when Galileo reaches its Full Operation Capability, during the next solar maximum.
At last we compare Galileo and GPS ionospheric corrections. For Galileo, we end up with an underestimation of 11% and 4% depending on the version of NeQuick embedded in the algorithm, as well as a 22% standard deviation. This means respectively twice, five and 1.5 times better than GPS.
Global Navigation Satellite System (GNSS) measurements of the Total Electron Content (TEC) from local (Dourbes, 50.1°N, 04.6°E) and European IGS (International GNSS Service) stations were used to ...obtain the TEC changes during the geomagnetic storms of the latest solar activity cycle. A common epoch analysis, with respect to geomagnetic storm intensity, season, and latitude, was performed on data representing nearly 300 storm events. In general, the storm-time behaviour of TEC shows clear positive and negative phases, relative to the non-storm (median) behaviour, with amplitudes that tend to increase during more intense storms. The most pronounced positive phase is observed during winter, while the strongest and yet shortest negative phase is detected during equinox. Average storm-time patterns in the TEC behaviour are deduced for potential use in ionosphere prediction services.
Local variability in total electron content can seriously affect the accuracy of GNSS real-time applications. We have developed software to compute the positioning error due to the ionosphere for all ...baselines of the Belgian GPS network, called the Active Geodetic Network (AGN). In a first step, a reference day has been chosen to validate the methodology by comparing results with the nominal accuracy of relative positioning at centimeter level. Then, the effects of two types of ionospheric disturbances on the positioning error have been analyzed: (1) Traveling ionospheric disturbances (TIDs) and (2) noise-like variability due to geomagnetic storms. The influence of baseline length on positioning error has been analyzed for these three cases. The analysis shows that geomagnetic storms induce the largest positioning error (more than 2 m for a 20 km baseline) and that the positioning error depends on the baseline orientation. Baselines oriented parallel to the propagation direction of the ionospheric disturbances are more affected than others. The positioning error due to ionospheric small-scale structures can be so identified by our method, which is not always the case with the modern ionosphere mitigation techniques. In the future, this ionospheric impact formulation could be considered in the development of an integrity monitoring service for GNSS relative positioning users.
Triple frequency GNSS will be fully operational within the next decade, opening opportunities for new applications. Dual frequency GNSS already allow to study the ionosphere through the estimation of ...Total Electron Content (TEC). However, the precision is limited by the ambiguity resolution process. This paper studies a triple frequency TEC monitoring technique in which the use of Geometry-Free and Iono-Free linear combinations improves the ambiguity resolution process and therefore the precision of TEC. We have tested it on a set of triple frequency Giove-A/-B data from January and December 2008. The conclusions achieved are (1) TEC values are affected by an error of about 2–2.5
TECU produced through the ambiguity resolution process; (2) the error caused by the Geometric Free phase combination delays (hardware, multipath, noise, antenna phase center) on TEC is about 0.2
TECU; (3) the total error on TEC approximately reach 2–3
TECU.
Ionospheric disturbances are known to have adverse effects on the satellite-based communication and navigation. One particular type of ionospheric effects, observed during major geomagnetic storms ...and threatening the integrity performance of both ground-based and space-based GNSS augmentation systems, is the sharp increase/decrease in the ionospheric delay that propagates in horizontal direction, thus called for convenience ‘moving ionospheric wall’. This paper presents preliminary results from researching such anomalous ionospheric delay gradients at European middle latitudes during the storm events of 29 October 2003 and 20 November 2003. For the purpose, 30-s GPS data from the Belgian permanent network was used for calculating and analysing the slant ionospheric delay and total electron content values. It has been found that, during these two particular storm events, substantial gradients did occur in Europe although they were not so pronounced as in the American sector.
Global Navigation Satellite Systems (GNSS) are very useful tools to study the ionosphere. Nevertheless, the precision of the usual dual frequency total electron content (TEC) monitoring technique is ...affected by code delays (hardware and multipath), and is therefore limited. This paper introduces a TEC monitoring technique based on triple frequency GPS and Galileo measurements. The three steps of this technique are validated on triple frequency simulated data. In fact, as it is not affected by code delays, the precision of the reconstructed TEC is improved in regards with the dual frequency technique.
Real time kinematic, or RTK, is a high-accuracy GPS relative positioning technique, which allows to measure positions in real time with an accuracy usually better than 1 decimeter. Ionospheric ...small-scale variability can strongly degrade RTK accuracy. In this paper, we present a method allowing to assess in a direct quantitative way the influence of the ionospheric activity on RTK accuracy. We apply this method to two different ionospheric situations: a day where strong travelling ionospheric disturbances (TIDs) were detected (December 24, 2004) and a day where a severe geomagnetic storm was observed (November 20, 2003). We show that on a 4
km baseline, strong TIDs have the same influence as the ionospheric variability induced by a geomagnetic storm on RTK accuracy: in both cases errors of more than 1.5
m are observed.
A new empirical model nowcasting and predicting a proxy to the geomagnetic K index is developed, which is based on the combined use of solar wind parameters and ground-based magnetic data. The ...present approach implements the previously developed solar wind-based MAK model, calibrating its values with magnetogram-derived K index. The new model is named as Hybrid Dourbes K (HDK) model. The HDK nowcast model provides the quantity Kdf, obtained by solar wind-based Ksw and corrected with a combination of differences between several past values of Kd and Ksw. The model error of the nowcast Kdf is found to be 0.38
KU, or nearly twice less than that of the MAK model. Kdf has a good predictability. Prediction made by weighted extrapolation 6
h ahead carries an error of 1.0
KU, while for the first 1
h the error is 0.58
KU only.
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