A new approach for ionospheric TEC prediction at a GPS station

Kurzfassung

Ionosphere can adversely affect radio signals that propagate through the ionosphere. Due to this, ionosphere is considered as a major error source for space-based radio systems such as Global Navigation Satellite Systems (GNSS) and remote sensing radars. To aid single frequency operations the Global Positioning System (GPS) and global navigation satellite system Galileo broadcast ionospheric correction coefficients in the navigation message. The GPS/Galileo updates ionospheric coefficients every 24 hours that means the given corrections are predictions 24 hours ahead [Hoque et al. 2015]. Ionosphere induces propagation delay on signal which is directly proportional to the ionospheric total electron content called TEC. Therefore, the knowledge of the TEC and its prediction is of great importance for any radio systems that deals with trans-ionospheric signals. The GNSS signals propagate through the ionosphere on their way to receivers on the Earth’s surface. On one hand GNSS signals are affected by the ionosphere and on other hand when signals are transmitted in two or more frequencies they can effectively be used to estimate the ionospheric TEC utilizing the dispersive property of the ionosphere. An important characteristic of the GPS constellation is that the same satellite appears in the same part of the sky with a period of approximately 4 minutes less than one day. During this period a GPS satellite completes exactly two orbits in inertial space whereas the Earth completes one revolution. This brings the same ray path geometry when looking to the same satellite from a location on Earth. This repetition is known to be used in mitigating local multipath noises in the received signals. In the present study we found that this repetition can be successfully used for predicting TEC along a receiver-satellite link. The main source of ionospheric ionization is the solar extreme ultra violet (EUV) radiation at wave lengths < 130 nm. In addition to the photoionization by EUV radiation, energetic particles from the solar wind and cosmic rays contribute to the total ionization but to a much lesser extent. Thus, the TEC which is an integral measure of the electron density depends on local time, geographic / geomagnetic location, geomagnetic conditions, season and solar activity level. The daytime TEC values frequently exceed the nighttime values by one order of magnitude.