Chapter 7 Final remarks

摘要

With rapid development of new scientific and technological systems which transmit signals through the upper atmosphere, accurate modeling of the ionosphere has turned more crucial. Within the IGS, the Ionosphere WG has been providing daily GIM of VTEC since 1998. The IGS GIM is being widely used for different scientific and civilian purposes, therefore increase in the accuracy and reliability of their products is essential. From long term analysis, it is believed that the IGS VTEC maps have an accuracy of few TECU in areas well covered with GNSS receivers; conversely, in areas with poor coverage, the accuracy can be degraded by a factor of up to five (Feltens et al., 2010). On the other hand, dual-frequency satellite missions, such as several altimetry missions or the F/C mission, provide valuable information about the ionosphere globally. Combining these data with the ground-based GNSS data, significantly improves the accuracy and reliability of the VTEC maps by closing the observation gaps that arise when using ground-based data only. The developed GIM are considered as 2D maps of VTEC, as they model VTEC in longitude and latitude, and contain the temporal variation implicitly. Due to the fact that 2D models of VTEC provide information about the integral of the whole electron content along the vertical or slant ray-path, when information about the ionosphere at different altitudes is needed, these maps are not useful; e.g. when electron density profile is required, or when satellite to satellite observation is being performed. In this case a 3D modeling of the ionospheric parameters is required. To model ionospheric parameters in 3D, the parameters of electron density, e.g. the F2-peak electron density, and its corresponding F2-peak height could be modeled - assuming the plasmaspheric contribution to be known for the time being. For this, the parameters of the electron density are modeled in longitude, latitude, and height.