Study Of Ionospheric Tomography Based On Multi-constellation GNSS Data

With the emergence of Global Positioning System(GPS), Computerized Ionospheric Tomography(CIT) using GPS data and Computerized Tomography(CT) has become a main method to monitor the CIT can not only effectively make up for the shortcoming of the traditional ionospheric detection techniques, but also provide a new theory and technology for determining the fine structure of the ionosphere. However, because of insufficient measurements and limited angles, the result of CIT based on only GPS data is not always good. With the development of multi-constellation Global Navigation Satellite System(GNSS), besides GPS, GALILEO, GLONASS and BDS have come on the scene. Multi-Constellation satellite systems possess more visible satellites, so that more satellite signals go through the ionosphere and get more real ionospheric Total Electron Content(TEC) measurements.In result, more accurate ionospheric electron density by means of CIT can be achieved.In this thesis, the ionospheric electron density in the European region has been reconstructed by means of MIDAS using multi-constellation GNSS data as data source Multi-Constellation GNSS data has been preprocessed to get TEC measurements using dual-frequency carrier phase observation. Then, the ionospheric electron density in March 2013 has been inverted with MIDAS and the accuracy of results was analysed and validated. Meanwhile, ionospheric responses to two geomagnetic storms on 17 March 2013 and 17 March 2015 have been reconstructed to detect the abnormal behavior of the ionosphere over mid latitude Europe, as well as the characteristics and differences of two storms.The work here validated the results of tomographic inversions based on the multi-constellation GNSS data. It is proved that the CIT based on multi-constellation data can reconstruct the ionospheric structure more accurately than that based on GPS data alone. Furthermore, the CIT based on multi-constellation GNSS data play an important role in the detection of abnormal ionospheric structures under the influence of geomagnetic storms.