Dissertation Ionosphere

Dissertation Ionosphere-33
Physical, chemical, mathematical & earth Sciences : Earth sciences & physical geography Physical, chemical, mathematical & earth Sciences : Space science, astronomy & astrophysics Engineering, computing & technology : Aerospace & aeronautics engineering Nowadays, Global Navigation Satellite Systems (GNSSs) play a significant role in our modern society as they support a wide range of applications worldwide associated with utterly demanding performance requirements.However, GNSS performances in terms of accuracy, continuity and reliability are limited by the Earth’s ionosphere.

Physical, chemical, mathematical & earth Sciences : Earth sciences & physical geography Physical, chemical, mathematical & earth Sciences : Space science, astronomy & astrophysics Engineering, computing & technology : Aerospace & aeronautics engineering Nowadays, Global Navigation Satellite Systems (GNSSs) play a significant role in our modern society as they support a wide range of applications worldwide associated with utterly demanding performance requirements.However, GNSS performances in terms of accuracy, continuity and reliability are limited by the Earth’s ionosphere.

Finally, this Ph D thesis describes the design and benchmarks the performances of several categories of prototype mitigation strategies against ionospheric scintillations that target the stochastic modelling and the integrity monitoring stages of the SPP and PPP algorithms.

The design of the strategies is based on several types of ionospheric scintillation skymaps and the benchmark of their performances relies on the definition of several specific performance parameters.

This statistical analysis leads to the conclusion that high-end GNSS receivers operating in low-latitude regions can see their positioning performances affected by ionospheric scintillations during about 20%–30% of the time in case of active ionospheric conditions.

The addition of detrimental effects due to signal fading, cycle slips and losses of signal lock results in poor positioning performances in terms of accuracy, continuity and reliability during moderate-to-intense ionospheric scintillation events.

Cette analyse statistique mène à la conclusion que les récepteurs GNSS opérant dans des régions de basse latitude peuvent voir leurs performances de positionnement affectées par des scintillations ionosphériques durant 20%–30% du temps en cas de conditions de scintillations ionosphériques actives.

La combinaison d’effets néfastes engendrés par des atténuations de signal, des pertes de verrouillage de signal et des sauts de cycles entraîne une forte baisse des performances des algorithmes SPP et PPP en termes d’exactitude, de continuité et de fiabilité.Globally, all the prototype mitigation strategies designed in the framework of this Ph D thesis contribute to increase the accuracy, continuity and reliability performances of the SPP and PPP algorithms during low-to-moderate ionospheric scintillations.Strategies associated with ionospheric scintillation skymaps based on local spatial autocorrelation statistics outperform strategies based on interpolated skymaps.En particulier, les irrégularités dans la densité en électrons libres de l’ionosphère sont responsables d’effets de diffraction et de dispersion sur les signaux GNSS qui se propagent au travers de telles perturbations ionosphériques.Ces effets se traduisent par des fluctuations rapides de l’amplitude et de la phase des signaux GNSS, aussi désignées sous le vocable scintillations ionosphériques, qui peuvent sévèrement dégrader les performances des algorithmes de positionnement et de navigation par satellites.As the performances of the PPP algorithm rely on the precision of carrier phase measurements, the PPP algorithm is more sensitive to ionospheric scintillations than the SPP algorithm, which is based on code pseudorange measurements exclusively.In case of active ionospheric scintillation conditions, the Root-Mean-Square Error (RMSE) of the tridimensional PPP solution can be as high as 6.73 m and its success rate as low as 50% by comparison to 0.18 m and about 100%, respectively, during quiescent conditions.Etant donné que les hautes performances de l’algorithme PPP dépendent de la précision de mesures de phase, l’algorithme PPP est davantage sensible aux scintillations ionosphériques que l’algorithme SPP, basé exclusivement sur des mesures de code.En cas de scintillations ionosphériques sévères, la racine carrée de l’erreur quadratique moyenne (Root-Mean-Square Error – RMSE) de la solution PPP peut atteindre la valeur extrême de 6.73 m et s’associer à un taux de succès aussi faible que 50%, par comparaison à une valeur de 0.18 m et de 100%, respectivement, pendant des conditions nominales.In particular, small-scale irregularities and inhomogeneities in the ionospheric free-electron density are responsible for diffraction and scattering effects on GNSS signals that propagate through such ionospheric disturbances.These effects result in rapid fluctuations of the amplitude and phase of GNSS signals, also known as ionospheric scintillations, which can severely disrupt the performances of GNSS navigation and positioning algorithms.

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