Spatiotemporal Variation Of Ionospheric TEC In Low Latitudes Based On Grid Data

With the rapid progress of GNSS(Global Navigation Satellite System),the application of GNSS technology in the ionosphere has gradually become a research focus.The temporal and spatial changing features of the total electron content in the ionosphere play a vital role in ionospheric detection.Accurately acquiring and understanding the changing features of the total electron content is of great significance for ionospheric modeling and prediction.Based on this,this paper conducts related research on the accuracy and consistency of global ionospheric grid products,the temporal and spatial changing features of the IRI-2106 model under different solar activities,and the forecast accuracy of the time series model.The main study details and result of this thesis are as follows:1.Based on IGS center ionospheric products,the consistency and accuracy of CODE,CAS,WHU and UPC global ionospheric grid data are analyzed.The experimental results show that:(1)The difference in the average deviation of the ionospheric TEC among the four ionospheric analysis centers is related to the different modeling methods adopted by the ionospheric analysis centers;The standard deviations between the analysis centers show seasonal and periodic changes.The annual cycle changes may be the reason why the ionosphere is affected by the seasons and solar activities.(2)The standard deviation of CODE-IGS TEC is relatively small in high and low years of solar activity,which shows that the ionospheric products between CODE and IGS have good consistency.(3)The global ionospheric grid data of the four ionospheric analysis centers of CODE,CAS,WHU,and UPC have a system deviation of 1TECu from the final GIM of IGS.The final GIM VTEC value of IGS is higher than that of other types of final GIM;The maximum difference between the two mainly occurs in low-latitude areas and ocean areas.2.Based on the CODE center ionospheric products,the low-latitude region ionospheric IRI-2016 model TEC and the daily variation,monthly average variation and seasonal variation characteristics of the bias are analyzed.The experimental results show that:(1)The ionospheric VTEC phase in 2015 is higher than 2016 and 2017,and the deviation value is also larger.(2)Comparing the monthly average changes of IRI-2016 model and CODE TEC,there is a strong correlation between the IRI-2016 model of each station and CODE TEC.Basically,the IRI-2016 model TEC of all stations is less than CODE throughout the year.(3)The IRI-2016 model TEC and CODE TEC have good consistency.The six IGS stations in the low latitude area all show significant seasonal changes,the highest in spring,followed by autumn and winter,and the lowest in summer.The seasonal variation of the layer VTEC is obviously consistent with the law of solar activity.Due to the difference in longitude of each station,the peak time of the ionospheric VTEC at different stations is different.3.Based on the IGS central ionosphere products,the ARIMA model,ARMA model,Holt-Winter addition and multiplication models are used to conduct short-term forecast analysis of the quiet period and active period ionospheric TEC in different latitude regions.The experimental results show that: in the ionospheric quiet period,The average relative accuracy of the ARIMA model is better than 86%,and the relative accuracy of the Holt-Winter additive and multiplication models at low latitudes is about the same,and the relative accuracy of the forecast is about 91%.In the active period of the ionosphere,the average relative accuracy of the ARIMA model is better than 88%,and the relative accuracy of the Holt-Winter additive and multiplication models can be better than 89% and 90% in the middle and high latitudes,respectively.