| Ionospheric disturbances are one of the main tasks of the space weather forecast,and an important problem of ionospheric physics.Due to the particularity of the position of the ionosphere,the ionospheric disturbance presents multi-scale,irregular,and complex changes.When the ionospheric disturbance occurs,its electron density changes,which has a serious impact on satellite navigation,and positioning and communication.Studying the characteristics and modeling of ionospheric disturbances is necessary to maintain the safety of human space activities and avoid economic damage from space weather events.Ionospheric scintillation,as one of the important ionospheric disturbances,can not only reflect the irregular plasma structure and its physical characteristics in the ionosphere but also may cause distortion and error codes in the signal received by the ground receiver,thereby affecting satellite navigation and communication.The reliability and accuracy of the system.In recent years,with the increasing frequency of aerospace activities and the increasing dependence of global communication and navigation systems on the space environment,the monitoring and effects of ionospheric scintillation have become very important.In this context,the monitoring,modeling,and effects of ionospheric disturbances have become one of the international research hotspots.Based on the data from the space environment monitoring network established by Space Environment Prediction Center of the National Space Science Center and the Crust Movement Observation Network of China,this paper mainly discusses the effects of ionospheric disturbances caused by geomagnetic storms on the navigation positioning accuracy and analyzes the characteristic of GPS cycle slip related to ionospheric disturbances.Last,we generated the regional ionospheric scintillation maps over Southern China.The research results of this paper have a very high reference value for the space weather researchers and GNSS users.The main work of this paper includes the following specific aspects:(1)First,we analyze the impact of the ionospheric disturbances that occurred on GPS performance and Precise Point Positioning accuracy during 7-8,September2017.The results show that during the geomagnetic storm,the average positioning error in China increases significantly,and the maximum error is close to 2 m.Compared with the middle and high latitudes,the positioning error in the low latitudes is larger and the duration is longer.We note that the occurrence of strong plasma irregularities during the storm coincided with significant degradation of the performance of kinematic PPP,and such impacts vary at different time periods of the storm.The results of this part show that the geomagnetic storms occurring after sunset at local time enhance and lead to the development of ionospheric irregularities,which cause ionospheric scintillation.When the navigation signal passes through the irregularities,the quality of the signal will decrease,and the cycle slip will occur frequently,which will eventually lead to a decrease of system performance and positioning accuracy.The statistical analysis results show that when the ionospheric amplitude scintillation index S4 is greater than 0.4,the average kinematic PPP error calculated by the station is higher than 0.8 m.It is of theoretical reference and practical significance to predict the influence of ionospheric scintillation on the navigation system and will help engineers to determine margins necessary for navigation systems during times of severe ionospheric scintillation.(2)Based on the data of 260 GPS stations from the CMONOC monitoring network,we analyzed the temporal and spatial characteristics of cycle slip events using the GPS data detected from 260 observations in the China sector during the period of the year 2015 to 2018.The results show that the temporal variations of cycle slips are dependent on the local time,seasons,and solar activity.It occurs from20:00 LT to midnight and more frequently in the equinox months,especially in solar maximum years.The spatial distribution occurs mainly at southern sector below25°N,which should be associated with the solar condition and ionospheric irregularities in the equatorial region,and the case analyses reveal that the variation of cycle slips has a similar tendency with the ionospheric scintillation monitored at low latitude station Guangzhou explaining this relationship.Our results reflect the performance of the GPS signals monitored in the China area during the declining period of solar activity to some degree.(3)Last,Aiming at the precision problem of common scintillation models used in China cannot meet the requirements of research and application,and the common ionospheric scintillation monitoring products is relatively single.In this paper,we present the first time a technique to derive a near-real-time ionospheric scintillation index S4 regional mapping based on Kriging method using six low latitude stations in Southern China.The result is compared with the Global Ionospheric Scintillation Propagation Model(GISM)and ionospheric irregularity index represented by the rate of change total electron content index(ROTI)to assess the validation and accuracy of output of Kriging method.It shows that our map could reflect better the regional characteristic and variations of S4 in Southern China.The lower mean absolute errors and the mean square errors indicate that the results of Kriging method are relatively true and reliable,which could be considered monitoring and warning regional ionospheric scintillation activities under disturbed space weather conditions.This paper mainly studies the ionospheric scintillation and its effects on GNSS satellite navigation systems in China.It is of great significance and practical application prospects to deepen the research on the phenomenon of ionospheric scintillation in the GHz band in China,to carry out the current report and forecast of ionospheric scintillation,and to improve the design of navigation and communication systems in areas with high a incidence of ionospheric scintillation. |
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