Methodology for Assessing the Impact of Wind Turbines on Civil Aviation Primary and Secondary Radars

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Modélisation des effets des scintillations ionosphériques sur la propagation des ondes électromagnétiques en bande L aux latitudes polaires.

The ionospheric plasma is located at the border between neutral atmosphere and outer space and many complex ionization reactions occur inside this turbulent medium. The Earth magnetic field and induced electric fields cause rapid fluctuations of electron density, both spatially and temporarily. When crossing this turbulent layer, RF signals show fast variations of amplitude and phase, especially at high latitudes. This phenomenon is called ionospheric scintillation and it is particularly feared by air navigation using GNSS services, since it degrades the availability and the integrity of signals.This PhD dissertation presents a complete modeling of the effects of ionospheric scintillation, with 3 anisotropy axes. It is based on a numerical approach using the multiple phase screens technique, both in 3D and 2D schemes, and on the analytical resolution of electromagnetic propagation equation, also both in 3D and 2D configurations. The limits of use of a 2D numerical scheme have been outlined by these original formulations of phase and log-amplitude variances and spectra. This complete modeling associated with a sensitivity study on these variances and spectra opens up interesting perspectives on data inversion, in order to better estimate the physical characteristics of the ionospheric medium.A la frontière entre l’atmosphère neutre et l’espace, le plasma ionosphérique est le siège de réactions physicochimiques complexes. Le champ magnétique terrestre et les champs électriques induits causent des fluctuations spatiales et temporelles de la concentration électronique. Ces irrégularités ionosphériques entraînent des variations rapides de l’amplitude et de la phase des signaux radioélectriques les traversant, notamment aux hautes latitudes. Ce phénomène est appelé scintillation ionosphérique et il est particulièrement craint par la communauté utilisatrice d’applications GNSS qui nécessite une disponibilité et une intégrité optimales des signaux.Le travail présenté dans cette thèse propose une modélisation complète, à 3 axes d’anisotropie, de la scintillation ionosphérique. Ce modèle est basé sur une approche numérique 3D et 2D, de type écrans de phase, et sur la résolution analytique des équations de propagation, en 3D et en 2D. Ces dérivations originales des variances et des spectres de log-amplitude et de phase ont mis en relief les limites de validité d’un modèle numérique 2D. L’étude de sensibilité menée sur les variances et les spectres ouvre également des perspectives d’inversion des données GNSS pour remonter aux caractéristiques du milieu ionosphérique

Validity of 2D electromagnetic approaches to estimate log-amplitude and phase variances due to 3D ionospheric irregularities

International audienceTo limit the computation time and the computer resource, 2D numerical approaches such as 2D Parabolic Wave Equation (2D-PWE) associated with 1D Multiple Phase Screens (1D-MPS) are classically used to estimate ionospheric scintillation effects on radio wave propagation.However, in the ionosphere, the turbulent fluctuations of the electron density responsible for the scintillation effects are clearly a three-dimensional process. This paper quantitatively assesses the errors potentially induced by the 3D to 2D dimensional reduction to predict ionospheric effects in terms of log-amplitude and phase variances. To that purpose, the ionospheric electron density fluctuations are described by an anisotropic turbulent spectrum with 3 axes of anisotropy. On the one hand, considering 4 typical configurations (2 equatorial and 2 polar radio links), scintillation effects are evaluated numerically, using 3D and 2D PWE-MPS numerical techniques. Some consequences of the dimensional reduction are then qualitatively discussed. On the other hand, an analytical framework that solves the 3D and 2D propagation equations in the Line-Of-Sight (LOS) coordinate system is proposed. Under weak scattering assumption, it allows assessing analytically the consequences of the dimensional reduction whatever the geometry of the transionospheric radio link, and, finally, allows 2D numerical schemes to be used advisedly for the prediction of ionospheric scintillation effects

Transionospheric propagation schemes: Analytical and numerical results for dimensional reduction

International audienceIn future, air navigation world-wide will be based on GNSS signals. The highest availability of service for positioning, velocity and time precision is then required. But in their travel from the satellite and to the receiver, GNSS signals cross the ionosphere: this perturbed atmospheric layer is responsible for the scintillation phenomenon that leads to abrupt signal intensity and phase changes at the receiver, and sometimes to a loss of signal track. These scintillations are more frequent at high and equatorial latitudes and are due to complex electromagnetic interactions between electrons, ions and the Earth magnetic field

Vers une caractérisation du milieu ionosphérique par inversion des spectres de signaux GPS aux hautes latitudes

International audienceA la traversée de l’ionosphère, les signaux GPS peuvent subir des affaiblissements et des sauts de phase et d’amplitude, causant des erreurs de localisation et parfois le décrochage des récepteurs. Les scintillations ionosphériques dues aux variances de TEC sont à l’origine de ces perturbations. Leur modélisation et leur prédiction sont donc importantes pour la communauté utilisatrice de signaux GNSS. La technique Parabolic Wave Equation (PWE)-Multiple Phase-Screen (MPS), développée à l’Onera, permet cette modélisation : elle consiste à propager le signal électromagnétique (résolution de l’équation de propagation par PWE), à travers une série d’écrans de phase (MPS) modélisant de façon statistique le milieu ionosphérique. Ces écrans de phase sont générés à partir d’un bruit blanc gaussien pondéré par le spectre du milieu ionosphérique. Ce dernier, issu de la théorie de la turbulence ionosphérique, est fonction des principales caractéristiques du milieu (orientation du champ magnétique terrestre, dimension maximale de la forme d’anisotropie…). Les spectres de l’amplitude et de la phase du signal transionosphérique, mesurés par des récepteurs GPS, dépendent de ces termes caractéristiques. Le travail d’inversion sur de tels spectres pourrait permettre de remonter à une de ces grandeurs physiques du milieu. Les premières conclusions de cette étude théorique et numérique seront présentées ici, ainsi que les perspectives données par l’exploitation des spectres réels mesurés par des récepteurs situés à différentes latitudes en Norvège

Discrete Turbulent Spectrum Modelling for 2D Split-Step Electromagnetic Propagation Schemes

International audienceThe multiple phase screen method is widely used for modelling the electromagnetic propagation in a turbulent medium. In this technique, the turbulent phase screens are classically generated from a continuous Von-Karman Kolmogorov scintillation spectrum. Recent works led to the development of an auto-coherent split-step wavelet propagation method based on a discrete formulation of the parabolic wave equation. In this configuration, the use of continuous spectra is no more suitable. In this paper, we propose an auto-coherent generation method of the turbulent phase screens. To do so, a discrete formulation of the classical Von-Karman Kolmogorov spectrum is introduced. The impact of the modelled turbulence is finally discussed through the computation of the log-amplitude variance to validate this approach

3D to 2D approximation effect on propagation modeling, impact on scintillation indices in polar region

International audienceIonospheric scintillations, in particular at equatorial and polar latitudes, are responsible of GNSS receiver loss of lock and accuracy decreasing. To improve the future GNSS systems, an understanding of the effect of the ionospheric irregularities is necessary, completed by an accurate propagation modeling across this layer. The inhomogeneous ionospheric layer responsible for the scintillation effects is classically represented by its spectral density function (or spectrum) in propagation modeling. The inhomogeneity spectrum is anisotropic due to Earth magnetic field influence and to induced ionospheric currents [6]. Propagation across this inhomogeneous layer can be modeled by asymptotic methods based on Rytov theory when the ionospheric turbulence is weak [8][9], and by numerical approach as Parabolic Wave Equation (PWE) resolution associated with Multiple Phase Screen (MPS) [5][3]. The PWE-MPS technique is valid in strong scattering regime and can consider a variability of ionospheric turbulence characteristics along the path. As PWE-MPS technique in 3D can be time and memory space consuming, some authors assume a dimensional reduction of the problem from 3D to 2D [1]. The latter is assumed to be valid in equatorial region, where the irregularities are highly elongated along the earth magnetic field, mainly perpendicularly to the Line Of Sight direction for earth satellite links [2][7]. Nevertheless, the validity of this approximation for other configurations, as for instance in polar region where the morphology of irregularities is different, is still open. This paper proposes to quantify the consequences of the dimensional reduction on the prediction of log-amplitude and phase variances from 2D numerical schemes

Main results of the CO2 -DISSOLVED project: first step toward a future industrial pilot combining geological storage of dissolved CO 2 and geothermal heat recovery

International audienceThe CO2-DISSOLVED project, funded by the ANR (French National Research Agency) is a techno-economic study assessing the feasibility of a new concept combining geothermal energy and CCS (Kervévan et al., 2013). This design combines capture, injection, and storage of dissolved CO2 (rather than supercritical) in a deep saline aquifer with geothermal heat recovery