References of "Warnant, René"
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See detailGalileo ? Bien plus qu’un système de positionnement !
Warnant, René ULg

Conference given outside the academic context (2010)

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See detailSeasonal variations of storm-time TEC at European middle latitudes
Stankov, Stanimir; Stegen, Koen; Warnant, René ULg

in Advances in Space Research (2010), 46(10), 1318-1325

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See detailGéodésie géométrique et astronomie de position
Warnant, René ULg

Learning material (2010)

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See detailSIDC Telescience
Warnant, René ULg; Bidaine, Benoît ULg; Brenot, Hugues et al

Report (2010)

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See detailInfluence of geometry in the case of relative positioning with GNSS
Wautelet, Gilles ULg; Lejeune, Sandrine; Lonchay, Matthieu ULg et al

Poster (2009, November 18)

Relative positioning with GNSS is generally used to achieve precise positions in the frame of critical applications (surveying, photo-control...). On this basis, we have developed a software which allows ... [more ▼]

Relative positioning with GNSS is generally used to achieve precise positions in the frame of critical applications (surveying, photo-control...). On this basis, we have developed a software which allows to compute a positioning error due to the ionosphere only using reference stations belonging to the Belgian Dense Network (BDN). This network consists in 66 GPS (dual-frequency) receivers over the whole Belgium. The drawback of this method is that this computation needs the design matrix which contains coefficients depending on satellite constellation geometry. Therefore, like for absolute positioning, a poor geometry (evaluated by the Dilution of Precision, or DOP) can also lead to large positioning error that cannot be separated from the one due to ionospheric effects, and in particular the small-scale structures. The main goal of this paper is to build a similar index to DOP for relative positioning in our software to be able to separate the ionospheric effects from the geometric ones. The final step is to study the feasability of a service for users of relative positioning using the BDN. The objective is to give in post-processing the positioning accuracy degradation for all BDN baselines and to associate a colour scheme to the different degradation classes created. [less ▲]

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See detailTotal Electron Content monitoring using triple frequency GNSS: results with GIOVE-A data
Spits, Justine; Warnant, René ULg

in Proceedings of the Second International Colloquium - Scientific and Fundamental Aspects of the Galileo Programme (2009, October)

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See detailIonosphere Modelling Based on the NeQuick Model and GNSS Data Ingestion
Bidaine, Benoît ULg; Warnant, René ULg

in Second International Colloquium - Scientific and Fundamental Aspects of the Galileo Programme (2009, October)

As for other GNSS, the ionospheric effect remains one of the main factors limiting Galileo accuracy. For single frequency users, this contribution to the error budget will be mitigated by a global ... [more ▼]

As for other GNSS, the ionospheric effect remains one of the main factors limiting Galileo accuracy. For single frequency users, this contribution to the error budget will be mitigated by a global algorithm based on the NeQuick model. This quick-run empirical model provides flexible solutions for combining ionospheric information obtained from various systems, from GNSS to ionosondes and topside sounders thanks to which NeQuick has been designed. 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 available thanks to the future European system. NeQuick provides the electron density as a function of location, time and solar activity. Thanks to numerical integration, the total content in free electrons of the ionosphere (Total Electron Content, TEC) can be deduced as well as the ionospheric propagation delay depending linearly on TEC on satellite-to-receiver path. The model is particularly suited to be used within an optimization procedure called ingestion. In this framework, an “effective ionization level” Az plays the role of the solar activity input in order to fit a specific dataset. For Galileo single frequency operation, daily Az values will be computed from slant TEC measurements performed within the ground segment. In this study, we perform slant TEC ingestion for a dozen of locations around the world where both an ionosonde and a GPS receiver are installed. These collocated instruments allow us to compare measured and modelled vertical TEC in different ways showing for example global statistics or dependence towards latitude. We analyze such results for the year 2002 (high solar activity level) giving an interesting insight in the situation we could observe when Galileo reach its Full Operation Capability, during the next solar maximum. [less ▲]

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See detailOn the TEC short-term forecast with corrections based on the average ionospheric response to background and storm-time geomagnetic conditions
Stankov, Stanimir; Warnant, René ULg; Kozarev, R.

in Geophysical Research Abstracts (2009, April), 11(Abs. No EGU2009-13283),

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See detailLocal electron density reconstruction from simultaneous ground-based GNSS and ionosonde measurements
Stankov, Stanimir; Warnant, René ULg; Stegen, Koen

in Geophysical Research Abstracts (2009, April), 11(Abs. No EGU2009-10956),

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See detailMeasuring Total Electron Content with GNSS: Investigation of Two Different Techniques
Bidaine, Benoît ULg; Warnant, René ULg

in The Institution of Engineering and Technology 11th International Conference on Ionospheric Radio Systems and Techniques (IRST 2009) (2009, April)

The ionosphere widely affects Global Navigation Satellite Systems (GNSS) applications, inducing among others a delay in GNSS measurements. This delay is closely linked to the Total Electron Content (TEC ... [more ▼]

The ionosphere widely affects Global Navigation Satellite Systems (GNSS) applications, inducing among others a delay in GNSS measurements. This delay is closely linked to the Total Electron Content (TEC) of the ionosphere, a major parameter which can hence be monitored using GNSS. To this extent, phase measurements are taken as a basis for their lower noise level. Levelling strategies have then to be defined for the phase measurements are obtained with an initial unknown number of cycles called ambiguity. The most common technique, referred to as carrier-to-code levelling, consists in using the differences between code and phase measurements and their average on a continuous set of epochs. This option, chosen at the Royal Meteorological Institute (RMI) of Belgium to compute TEC for Belgian GPS stations, requires code hardware delays estimation. Another has been proposed which takes benefit from Global Ionospheric Maps (GIMs) to compute a reference TEC used for ambiguity resolution. In order to understand the consequences of using one method or the other, we compare slant TEC data obtained from both techniques for a mid-latitude station (Brussels) during a high solar activity period (2002). We observed large differences (6.8 TECu on average) showing features apparently related to ionospheric and geomagnetic activity. We attribute these observations to a combination of effects originating in code delays estimation, multipath and noise as well as GIMs errors. We try to differentiate between these effects by focusing on several days and satellites. We concentrate for example on days presenting large TEC differences and geomagnetic disturbances simultaneously (or not) or on satellites displaying recurrent patterns on consecutive days. Finally we highlight the impact of the choice of GIMs involved in sTEC calibration. To this extent, we analyse vertical TEC statistics showing a general underestimation from RMI data. The highest bias (5.8 TECu) is obtained for the UPC GIMs used in the second levelling technique. [less ▲]

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See detailEffects of ionospheric small-scale structures on GNSS
Wautelet, Gilles ULg; Lejeune, Sandrine; Warnant, René ULg

in The Institution of Engineering and Technology 11th International Conference on Ionospheric Radio Systems and Techniques (IRST 2009) (2009, April)

Nowadays, Global Navigation Satellite Systems or GNSS allow to measure positions in real-time with an accuracy ranging from a few meters to a few centimeters mainly depending on the type of observable ... [more ▼]

Nowadays, Global Navigation Satellite Systems or GNSS allow to measure positions in real-time with an accuracy ranging from a few meters to a few centimeters mainly depending on the type of observable (code or phase measurements) and on the positioning mode used (absolute or differential). The best precisions can be reached in differential mode using phase measurements. In differential mode, mobile users improve their positioning precision thanks to so-called “differential corrections” provided by a fixed reference station. For example, the Real-Time Kinematic technique (RTK) allows to measure positions in real-time with a precision usually better than a decimeter. In practice, the ionospheric effects on GNSS radio signals remain the main factor which limits the precision and the reliability of real-time differential positioning. As differential applications are based on the assumption that the measurements made by the reference station and by the mobile user are affected in the same way by ionospheric effects, these applications are influenced by gradients in TEC between the reference station and the user. For this reason, local variability in the ionospheric plasma can be the origin of strong degradations in positioning precision. In this paper, we characterize local variability in the ionosphere which can pose a threat to high precision real-time differential positioning. GNSS carrier phase measurements can be used to monitor local TEC variability: small-scale ionospheric structures can be detected by monitoring TEC high frequency changes at a single station; as ionospheric disturbances are moving, we can expect that such structures will induce TEC temporal variability which can be detected at a single station. We applied this method (called the “one-station” method) to the GPS data collected at the permanent (mid-latitude) station of Brussels from 1994 to 2007 and performed a climatological study of the ionospheric structures on this period which covers more than one solar cycle. Two main types of structures have been observed: Traveling Ionospheric Disturbances (TID’s) and “noise-like” structures. TID’s have strong seasonal and solar cycle dependence when noise-like structures are “ionospheric variability” which is usually observed during geomagnetic storms. The largest Rate of TEC (RoTEC) detected at Brussels during the period considered in our study were observed during severe geomagnetic storms. Moreover, we found that strong irregularities occur even during solar minimum. This means that, even during periods where the probability of occurrence of ionospheric irregularities is very low, large RoTEC can occur. The one-station method allows to measure variability in time but GNSS differential applications are affected by variability in space between the user and the reference station. Therefore, in a second step, we measured TEC differential variability (using double differences of phase measurements) during few typical ionospheric conditions: quiet ionospheric activity, medium and large amplitude TID’s and noise-like variability due to a severe geomagnetic storm. We also analyzed the effects of the baseline length and orientation on the residual ionospheric term. As a last step, we developed a software which reproduces positioning conditions experienced by RTK users on the field. We used this software to assess positioning errors due to the different ionospheric conditions considered in the previous step. Again, the largest effects were observed during the occurrence of geomagnetic storms. [less ▲]

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See detailModeling medium-scale TEC structures observed by Belgian GPS receivers network
Kutiev, Ivan; Marinov, Pencho; Fidanova, Stefka et al

in Advances in Space Research (2009), 43

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See detailHybrid model for nowcasting and forecasting the K index
Kutiev, Ivan; Muhtarov, Plamen; Andonov, Borislav et al

in Journal of Atmospheric & Solar-Terrestrial Physics (2009), 71

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See detailTrans-ionospheric GPS signal delay gradients observed over mid-latitude Europe during the geomagnetic storms of October-November 2003
Stankov, Stanimir; Warnant, René ULg; Stegen, Koen

in Advances in Space Research (2009), 43(9), 1314-1324

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See detailIonospheric slab thickness - Analysis, modelling and monitoring
Stankov, Stanimir; Warnant, René ULg

in Advances in Space Research (2009), 44(10), 1295-1303

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See detailLocal ionospheric activity – nowcast and forecast services
Stankov, Stanimir; Warnant, René ULg; Stegen, Koen et al

Conference (2009)

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See detailIono slab monitoring service
Stankov, Stanimir; Warnant, René ULg; Stegen, Koen

Conference (2009)

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See detailMitigation of ionospheric effects on GNSS
Warnant, René ULg; Foelsche, Ulrich; Aquino, Marcio et al

in Annals of Geophysics (2009), 52(3-4), 373-390

The effects of the ionosphere remain one of the main factors which limit the precision and the reliability of many GNSS applications. It is therefore indispensable on the one hand to improve existing ... [more ▼]

The effects of the ionosphere remain one of the main factors which limit the precision and the reliability of many GNSS applications. It is therefore indispensable on the one hand to improve existing mitigation techniques and on the other hand to assess their remaining weaknesses. Mitigation techniques depend on the type of application considered. Therefore, specific mitigation techniques have to be developed. The paper summarizes work performed on this topic in the frame of WP 3.2 “Mitigation techniques” of COST296. [less ▲]

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See detailDevelopment of products for GNSS users at the Belgian Solar-Terrestrial Centre of Excellence
Warnant, René ULg; Lejeune, Sandrine; Stankov, Stanimir et al

Conference (2008, December)

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See detailTowards an Improved Single-Frequency Ionospheric Correction: Focus on Mid-Latitudes
Bidaine, Benoît ULg; Warnant, René ULg

in 4th ESA Workshop on Satellite Navigation User Equipment Technologies NAVITEC (2008, December)

The modelling of the Total Electron Content (TEC) plays an important role in global satellite navigation systems (GNSS) accuracy, especially for single frequency receivers, the most common ones ... [more ▼]

The modelling of the Total Electron Content (TEC) plays an important role in global satellite navigation 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. It has been designed to calculate the electron density at a given point of the ionosphere according to the time conditions and the solar activity. This electron density can be integrated along the path from the receiver to the considered satellite to provide the TEC. For Galileo, a parameter Az (“effective ionisation level”) will be provided to the model as solar activity information and will be daily updated by the ground stations. In order to reach the ionosphere error correction level objective (70% or 20 TECu whichever is larger), the model itself as well as its use for Galileo are investigated. Different situations have to be considered: different latitude regions (space conditions), different hours, seasons and years (time conditions) and specific phenomena appearance (magnetic storms, Travelling Ionospheric Disturbances – TIDs). In addition the results can be compared to different data sets among which GPS slant or vertical TEC (sTEC or vTEC) measurements, Global Ionospheric Maps, ionosonde profiles, topside soundings but also other ionosphere models results such as IRI. In our comparison process, we take benefit of various ionosphere data from several European stations (Chilton in UK, Dourbes in Belgium, El Arenosillo and Roquetes in Spain, Pruhonice in Czech Republic) 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. We investigate the difference between GPS-derived vTEC and corresponding values from NeQuick for the latest years (between solar maximum in 2000 and minimum in 2007) in order to observe the temporal dependencies towards Universal Time, season and solar activity. On the one hand, we use ionosonde data to constrain the model so that we can concentrate on its formulation of the profile only. We especially highlight the improvements from the latest (second) version of NeQuick and show the critical importance of the topside formulation. On the other hand, we analyse the model residual errors for the same situations computing vTEC through the Galileo algorithm. [less ▲]

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