Monitoring And Application Of GNSS Regional Ionospheric TEC

As ionosphere is the important part of sun-earth space environment, on the one hand ionospheric delay is the main error source of the navigation and positioning users of GNSS, on the other hand using GNSS beacon to calculate Total Electron Content (TEC) has been the leading technology of monitoring ionospheric activity. The realistic data of IGS tracking stations in China was used to calculate and monitor regional TEC in order to obtain the variable regularity and statistical characteristics in this paper. In the case of data processing, this paper chose the Kriging method which was often used in Geostatiscs. By comparing the result of experiment, it was proved the precision of Kriging method was higher than the traditional Least Square fitting polynomial method.The primary researching results of this paper are as follows:1. Programming the algorithm of calculating TEC through the carrier phase smoothing pseudorange code using GNSS double frequency observation data to archive the requirement of obtaining the real time or near real time TEC, including the sub-algorithm of detecting cycle slip by ionosphere residual error method, plotting tracks of the ionospheric pierce points (IPPs) and calculating the system-combined instrument bias by Kaman filtering method.2. Introducing NeQuick model which is prepared to be adopted in GALILEO system in detail, studying this model can help us understand the difference of GNSS sub-system. To achieve this aim, TEC in the region of Beijing and Wuhan were calculated through this model, and these results were also compared with the reference TEC. That showed that the model calculating TEC of Wuhan is more precise that that of Beijing.3. IONEX format was introduced and the TEC diurnal, seasonal and annual variation of Beijing area was obtained with this file. Through the power spectrum analyzing, we got that the signal of diurnal variation was clearly stronger that other period variation signal.4. TEC time series, Rate of TEC (RTEC) and RTEC Index (RTECI) were calculated during the different ionosphere activity period and the TEC varying regularity and characteristics were concluded. This paper also attempted to advise using RTECI to replace the Kp index to express the ionosphere activity extent. The figures of auto-correlation function of different period was studying and the varying rule was obtained by statistics analyzing, also get the conclusion that was the correlation time was different as the different ionospheric activity. This result would be the reference as the user use the ionospheric error corrected model of reference station.5. This paper introduced Geostatiscs principle and Kriging method into the field of calculating the TEC by GNSS signal. It also studied how to fit the variogram model and calculate the parameter of the model. The conclusion that the precision of Kriging method is higher than the fitting polynomial method through a practical example. Moreover, the TEC maps plotting by different method were compared, the result showed that the resolution of TEC map by Kriging was higher that GIM, and was smoother than inverse distance weighting method. At last, we found that the distribution of Kriging error was clearly girdle band feature.