Ionosphere : Research

Contents

Determination of the GNSS Signal Distribution above Europe

The objective of this study is to evaluate the potential, for atmospheric applications based on GNSS observations, of the current and future GNSS (GPS, GLONASS and Galileo) in association with the GNSS ground receiver stations from the EUREF Permanent Network among other European national networks. As atmospheric applications based on GNSS observations such as ionospheric tomography (see tutorial) are dependant of the GNSS signal distribution, such research contributes to determine the zone where GNSS signals are dense enough to obtain reliable and accurate representations of the ionosphere.

Monitoring of the Ionosphere and its Effect on GNSS Positioning

The scientists of the Solar-Terrestrial Center of Excellence (STCE) analyse GPS observations gathered during the geomagnetic storms. For example, the degradation of the "ionosphere-free" 5 minutes kinematic position repeatability during the October 2003 Halloween ionospheric storm was significant for stations in Northern Europe with outliers reaching 12 cm in the horizontal components, and 26 cm in the vertical component.

As ionospheric storms will become more frequent with the next solar maximum (predicted for 2013), kinematic GPS applications will be more affected. Hence the importance of having external information, such as TEC maps, is essential to increase the information about the ionosphere state and to prevent GNSS kinematic positioning users.

Ionospheric Tomography

The main objective of the ionospheric tomography project is to study the temporal and spatial distribution of electron concentration in the ionosphere, contributing to a better understanding of the ionosphere and its response to solar activity. Because of the short-term variability of the ionosphere, models based on long-term statistical records are generally unsuitable for accurate representations of the ionosphere at any given instant. For example, irregular features such as travelling ionospheric disturbances (TIDs) in the day and auroral structures at night are difficult to detect.

The goal of the ionospheric tomography, developed in this project, is to detect small-scale (in time and space) structures in the ionosphere. With the new radio navigation satellite signals (GPS L5, GLONASS, and Galileo) and the increasing number of permanent GNSS tracking stations, it is expected to reduce the influence of the a priori models in ionospheric tomography algorithms.

An additional goal will be that, using 3D maps of electron concentration updated regularly in time, the radio frequency system user will be able to apply corrections where and when required, especially during the next solar maximum in 2013.

Space Weather

The correlation between solar parameters such as Sunspot Numbers and 10.7cm radio flux ionospheric and the Total Electron Content (TEC) in the ionsophere on a global scale is investigated. Such correlation, which can reach up to 0.95, is a new research topic which is fundamental to better understand the influence of the solar activity during the different stages of the solar cyle on the earth ionosphere with respect to the geographic or geomagnetic latitudes and/or seasons.