Modeling of ionospheric scintillation

A signal, such as from a GNSS satellite or microwave sounding system, propagating in the randomly inhomogeneous ionosphere, experiences chaotic modulations of its amplitude and phase. This effect is known as scintillation. This article reviews basic theoretical concepts and simulation strategies for modeling the scintillation phenomenon. We focused our attention primarily on the methods connected with the random phase screen model. For a weak scattering regime on random ionospheric irregularities, a single phase screen model enables us to obtain the analytic expression for phase and intensity scintillation indices, as well as the statistical quantities characterizing the strength of scintillation-related fades and distortions. In the case of multiple scattering, the simulation with multiple phase screens becomes a handy tool for obtaining these indices. For both scattering regimes, the statistical properties of the ionospheric random medium play an important role in scintillation modeling and are discussed with an emphasis on related geometric aspects. As an illustration, the phase screen simulation approaches used in the global climatological scintillation model GISM is briefly discusse

Anisotropic scintillation indices for low elevation angles

This contribution deals with the extension of the flat-earth model to a spherical one. The correlation properties of ionospheric electron density fluctuations responsible for scintillation occurrence are modeled conventionally as the ellipsoidal surfaces of constant value for the autocorrelation. The relative position of such ellipsoids and the radio-wave ray path modulates the scintillation strength and has purely geometrical origin. The information on communication link geometry is used for proper generation of phase screens used further for simulation of wave propagation through randomly inhomogeneous ionosphere. For clarity and simplicity we have used also the single phase screen model and derived the analytic formulas for amplitude and phase scintillation indices following the approach of C. Rino'79. We show that the accounting of the finiteness of earth-/ ionospheric-shell- curvature yields the non-divergent values for scintillation indices at low elevation angles. Additionally to this, the regions of geometric enhancement of scintillation at low elevations appear to be displaced from the corresponding regions predicted within the flat-earth approximation. The found discrepancy is important for proper determination of regions of high scintillation activity at high latitudes, e.g., as regions mapped on sky plots for a certain groundbased receiver. Incorporation of the proposed geometric model in the scintillation climatological models such as the GISM or the WBMOD will be consistent with their extension to low elevation angles and, hence, will be useful for some aforementioned user-cases. C. L. Rino, "A power law phase screen model for ionospheric scintillation: 1. Weak scatter," Radio Sci., 14, November 1979, pp. 1135-1145, doi: 10.1029/RS014i006p01135

Global Ionospheric Scintillation Model: current status and further development strategies

When a electromagnetic wave propagates through a random inhomogeneous medium, scattering by the refractive index inhomogeneities can lead to a wide variety of phenomena that have been the subject of extensive study and modelling. The Global Ionospheric Scintillation Model (GISM) is primarily intended to model the phenomena relevant for the GNSS applications and provides the amplitude and phase scintillation indices. Due to the three dimensional nature of the GISM model it is capable to describe a variety of communication geometries such as satellite-ground station or satellite-satellite communication link. Moreover, it can calculate the scintillation maps at specific altitude allowing to obtain the 3D picture of scintillation. Recently the GISM model has been handed over to the newly established DLR Institute of Solar-Terrestrial Physics. Since then the model underwent several modernization steps. For example, the programming paradigm has been changed to the object-oriented one in order to bring more flexibility into the code. In the present contribution we present the first results of our works and discuss strategies for further development, extension, and validation of the GISM

Statistical characterization of strong and mid solar flares and sun EUV rate monitoring with GNSS

The global network of permanent Global Navigation Satellite Systems (GNSS) receivers has become an useful and affordable way of monitoring the Solar EUV flux rate, especially -for the time being- in the context of Major and Mid geoeffective intensity Solar Flares (M. Hernandez-Pajares et al., SpaceWeather, doi:10.1029/2012SW000826, 2012). In fact the maturity of this technique (GNSS Solar FLAre Indicator, GSFLAI) has allowed to incorporate it in operational real-time (RT) conditions, thanks to the availability of global GNSS datastreams from the RT International GNSS Network (M. Caissy et al, GPS World, June 1, 2012), and performed in the context of the MONITOR and MONITOR2 ESA-funded projects (Y. Beniguel et al., NAVITEC Proc., 978-1-4673-2011-5 IEEE, 2012). The main goal of this presentation is to summarize a detailed recent study of the statistical properties of Solar Flares (E. Monte and M. Hernandez-Pajares, J. Geophys. Res., doi:10.1002/2014JA020206, 2014) by considering the GNSS proxy of EUV rate (GSFLAI parameter) computed independently each 30 seconds during the whole last solar cycle. An statistical model has been characterized that explains the empirical results such as (a) the persistence and presence of bursts of solar flares and (b) their long tail peak values of the solar flux variation, which can be characterized by: (1) A fractional Brownian model for the long-term dependence, and (2), a power law distribution for the time series extreme values. Finally, an update of the Solar Flares’ occurrence during the recent months of Solar Activity, gathered in RT within MONITOR2 project, will close the paper.Postprint (published version

Geometric enhancement for scintillation modeling

Continuous improvement of scintillation models is an important task required for adequate analysis and prediction of scintillation events caused by ionospheric irregularities. Some improvement can be achieved by an improved geometric description of small-scale perturbations in the ionosphere. Recently we revise the classical results of Ref. [1] obtained in the flat-earth approximation and generalized them for the case when the finite curvature of the earth has to be considered. Assuming that the earth is spherical, we obtained the analytic expressions for phase and intensity scintillation indices [2] in the approximation of a single thin phase changing screen. The obtained results for spherical-earth geometry are divergence-free and represent the appropriate position of the enhancement maximum as a function of the dip angle for field-aligned ionospheric irregularities. Thus, the spherical-earth model is suitable for scintillation modeling and forecasting in such user cases as limb sounding, reflectometry, positioning at small elevation angles. Implementation of the proposed geometric considerations in the Global Ionospheric Scintillation Model is also briefly discussed 1 C. L. Rino, "A power law phase screen model for ionospheric scintillation: 1. Weak scatter," Radio Sci., 14, 1135 (1979) 2 D.V. Vasylyev, Y. Bèniguel, M. Kriegel, V. Wilken, J. Berdermann, "Modeling ionospheric scintillation," 12, 22, (2022

MONITOR Ionospheric Monitoring System: GNSS performance estimation

MONITOR is a project from the European Space Agency’s GNSS Evolutions Programme started in 2010, dedicated to the collection of data and products during active periods of solar activity for later understanding of the impact of ionospheric effects on EGNOS and Galileo system performance. In the frame of this project several tasks have been achieved, in particular the deployment of a network of scintillation receivers (Novatel + Septentrio + GISMO) mainly at low and high latitudes, the development of a real time Central Archiving and Processing Facility (CAPF) and the development of dedicated processors to generate user oriented outputs for TEC, scintillation, and space weather issues. This project, in its new phase started in 2014, is moving forward with an improved and updated scope, addressing in addition to general ionospheric monitoring, the generation of dedicated products and reports to EGNOS system evolution, international collaboration in related ionospheric topics including feasibility studies in Africa. The main new features are: an upgraded data archiving system providing improved accessibility, the integration of data from SAGAIE network from French Space Agency, CNES and the exploitation of its data for new products, new station deployment in regions of interest (mainly in West and Central Africa and in high latitudes in Europe), and the upgrade and development of new products allowing better analysis of geophysical conditions during periods of compromised system performance and service. As an example, the Along Arc TEC Rate (AATR index) is computed routinely, as it has proven to be a clear indicator of ionospheric activity that degrades SBAS system performance. In addition, Monitor already produces VTEC maps (obtained using various techniques and algorithms), several space weather indicators including solar flare detection, ROTI maps, indices related to the quality of measurements and scintillation analysis tools. This paper focuses on the relationship of an SBAS system (EGNOS, WAAS) to the ionosphere’s variability and will analyse in detail the ionospheric parameters leading to a decrease or compromise of system performance. Several case studies will highlight significant EGNOS events for this purpose. The paper will demonstrate how AATR is able to discriminate availability degradation due to ionospheric events from other effects. The ionosphere scintillation aspects and the last developments of the GISM model will also be addressed for this issue.Peer ReviewedPostprint (author's final draft

St. Patrick’s Day 2015 geomagnetic storm analysis based on Real Time Ionosphere Monitoring

A detailed analysis is presented for the days in March, 2015 surrounding St. Patrick’s Day 2015 geomagnetic storm, based on the existing real-time and near real-time ionospheric models (global or regional) within the group, which are mainly based on Global Navigation Satellite Systems (GNSS) and ionosonde data. For this purpose, a variety of ionospheric parameters is considered, including Total Electron Content (TEC), F2 layer critical frequency (foF2), F2 layer peak (hmF2), bottomside halfthickness (B0) and ionospheric disturbance W-index. Also, ionospheric high-frequency perturbations such as Travelling Ionospheric Disturbances (TIDs), scintillations and the impact of solar flares facing the Earth will be presented to derive a clear picture of the ionospheric dynamicsPostprint (published version

A Global Tool for the Prediction of HF Surface Wave Propagation

International audienceThis paper deals with the problem of HF surface wave radar. The goal is to integrate in a unique tool the antenna radiation and the propagation calculations in order to make the analysis consistent

Un outil global pour la prévision de propagation par onde de sol

National audienc

A precise technique for ground wave radiation and propagation over an irregular surface

International audienc