References of "Wautelet, Gilles"
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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 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 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 ▲]

Detailed reference viewed: 282 (69 ULg)
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 detailIonospheric variability which degrades the precision of real time GNSS applications
Wautelet, Gilles ULg; Lejeune, Sandrine; Warnant, René ULg

Poster (2008, November 18)

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See detailGalileo Local Component for the detection of atmospheric threats
Warnant, René ULg; Wautelet, Gilles ULg; Lejeune, Sandrine et al

Conference (2008, November)

Detailed reference viewed: 26 (7 ULg)
See detailGALOCAD User interface
Warnant, René ULg; Wautelet, Gilles ULg

Report (2008)

Detailed reference viewed: 26 (4 ULg)
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See detailEffects of small-scale atmospheric activity on precise positioning
Wautelet, Gilles ULg; Lejeune, Sandrine; Stankov, Stanimir et al

Report (2008)

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See detailLes GNSS et l’ionosphère
Warnant, René ULg; Lejeune, Sandrine; Wautelet, Gilles ULg

Conference given outside the academic context (2008)

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See detailGalileo Local Component for the detection of atmospheric threats
Warnant, René ULg; Bavier, Michaël; Brenot, Hugues et al

in Goodman, John (Ed.) Proceedings of the 12th International Ionospheric Effects Symposium (IES2008) (2008, May)

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See detailÉtude climatologique des irrégularités ionosphériques détectées à l'aide des GNSS
Wautelet, Gilles ULg

Master of advanced studies dissertation (2007)

Detailed reference viewed: 37 (12 ULg)
See detailStatistical study of ionospheric small-scale irregularities at mid-latitudes using GPS measurements
Wautelet, Gilles ULg; Warnant, René ULg

Conference (2007, July 11)

At the present time, Global Navigation Satellite Systems (GNSS) allow to obtain a precision of a few centimeters in real time using positioning techniques like the so-called Real Time Kinematics (RTK ... [more ▼]

At the present time, Global Navigation Satellite Systems (GNSS) allow to obtain a precision of a few centimeters in real time using positioning techniques like the so-called Real Time Kinematics (RTK). Nowadays, the ionosphere remains the most important error source affecting such GNSS applications. Indeed, the presence of small-scale irregular structures in the Total Electron Content (TEC) can strongly affect the reliability and the precision of high precision real time positioning applications. Those small-scale structures can have several origins: Traveling Ionospheric Disturbances, "noise-like" variability in TEC, scintillations. The Royal Meteorological Institute of Belgium (RMI) has developed a software which allows to monitor the TEC using GPS measurements (at one station). The software can also be used to detect small-scale irregularities in TEC by monitoring TEC temporal gradients (i.e. rate of change). The RMI has applied this software to the GPS data collected at Brussels from April 1993 up to now what represents a period of more than a Solar Cycle. The results obtained from this GPS-TEC software will be presented. First, the paper analyzes the different types of small-scale structures which have been observed in TEC. Then, a statistical study of those ionospheric irregularities is presented; we shall analyze their probability of occurrence and their amplitude (in TECU/min) depending on daytime, season, solar activity, geomagnetic activity... The results of our study which is financed by the GNSS Supervising Authority will allow to have a better understanding of the usual case/worst case conditions encountered in high precision positioning applications based on GNSS. [less ▲]

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See detailQuantification of Tropospheric Activity according to Double Differences Analysis of GNSS Phases Records.
Brenot, Hugues; Lejeune, Sandrine; Wautelet, Gilles ULg et al

Conference (2007)

Detailed reference viewed: 18 (2 ULg)