Variations of Regional VTEC Model due to Ionospheric Scintillation Occurrence

Global Navigation Satellite Systems (GNSS) which are extensively used for various purposes such as navigation, surveying, remote sensing and telecommunication, are strongly affected by the Earth's upper atmosphere, the ionosphere. Ionosphere is a very complex medium that is ionized by the radiation of high energy particles from Sun and cosmic rays. When a GNSS electromagnetic signal passes through this region, it may experience rapid amplitude fluctuations or an unexpected phase change, which is referred to as ionospheric scintillation. Ionospheric scintillation is caused by small scale irregularities in the electron density and is one of the dominant propagation disturbances for microwave signals. These irregularities severely affect the accuracy and reliability of GNSS measurements; therefore it is necessary to investigate ionospheric scintillation and its effects on GNSS observations. The focus of this paper is to detect ionospheric scintillation effects on GPS observations and also on regional Vertical Total Electron Content (VTEC) models over Iran's region, during different periods of solar activity. The results show that effectiveness of this phenomenon depends on geographic location, local time, and global geomagnetic storm index (kp index). The required data for this study are the ground-based measurements of permanent GPS stations over Iran (IPGN), established by the National Cartographic Center of Iran (NCC).