Studying On Ionospheric Modeling Using Multi Source Data And Ionospheric Responses To Magnetic Storms

Total Electron Content(TEC)is an important physical quantity for monitoring the temporal and spatial variation of ionosphere.Acquisition of TEC based on GNSS dual ?frequency observations has always been an important means to study the ionosphere.Ionospheric monitoring and modeling can use the relevant detection data to invert the structure of the ionosphere.It has important scientific significance and application value in the monitoring of space environment such as magnetic storm,ionospheric disturbance and ionospheric delay correction.The research and development of related technical methods have been paid more and more attention in fields such as geodesy and space physics.Ionospheric perturbation has always been the focus of the international researc,and is also an important part of the current study of space weather.Today,thanks to the development of multi-source ionospheric detection means,a new path is provided for people to better understand the ionospheric space environment.Based on the introduction of the basic theory of ionosphere,this paper mainly introduces the processing flow of multi-source ionospheric observation data acquisition,the delay estimation of satellite and receiver hardware,the construction of two-dimensional and three-dimensional ionospheric model,and the ionospheric disturbance monitoring during magnetic storm.Specifically,the main contents of this paper are as follows:(1)The Combination of Multisource Data Nowadays ground-based Global Navigation Satellite System(GNSS)stations of the International GNSS Service(IGS)are distributed unevenly around the world,Especially in the southern ocean area,which makes the ionospheric Pierce Points(IPP)cannot effectively cover the ocean and middle-high latitude areas of the southern hemisphere.As a result,many unreasonable negative Vertical Total Electron Content(VTEC)values appeared in corresponding areas referred above,similar problems also appeared in CODE and ESA IONEX products.At this stage,the ground-based GNSS is still one of the most important technical means of ionospheric detection.The application of cCOSMIC greatly improves and enhances the coverage of space-based TEC observations.Jason-1 and Jason-2,two altimeter satellites,can cover 90%of the global ocean surface,this unique advantage just to make up for the the ocean blank of GNSS observation data.In this paper,the ionospheric data of the space-based ltimeter satellites,COSMIC system and the GNSS observation are fused to greatly improve the distribution of ionospheric pierce points around the world.(2)Estimation of BDS Satellites and Receivers Differential Code Bias(DCB)DCB is an important error item for TEC calculation.As the limited number of the BeiDou Navigation Satellite System(BDS)satellites and tracking stations currently,it's difficult to attain daily DCBs solution with precisely high accuracy based on BeiDou single system.In order to overcome the weakness above,two different zero-mean constraints for BDS satellites,called constraint one and constraint two,respectively,are used to estimate DCBs of BDS based on BeiDou observations from the Multi-GNSS Experiment(MGEX)network and Global Ionosphere Maps(GIM)from the Center for Orbit Determination in Europe(CODE).The results show that the systematic difference of the overall trend under two different constraints is consistent,and the systematic difference of DCBC21-C71.and DCBC11-C61 is-3.3 ns and 1.2 ns.respectively.The systematic difference between BDS satellite DCBs and receiver DCBs has the same absolute value,but opposite signs instead.Compared to constraint one,The DCBs estimation of IGSO/MEO satellites under constraint two are more stable(the improvement of satellites DCBC21-C71 and DCBC21-C61 STD are up to 21%,13%,respectively),the stability of IGSO and MEO satellites(STDs are within 0.1 ns,0.2 ns,respectively)is better than that of GEO satellites(STDs are 0.15-0.32 ns).DCB estimation of constraint one is not only consistent with the CAS/DLR products(Bias:-0.4?0.2 ns),but also takes into account the stability of BDS satellites DCB.Under the two different constraints,there is no obvious change in BDS receiver DCBs,meaning that the selection of constraints has no obvious influence on the stability of BDS receivers DCBs.The overall stability of BDS receiver DCBs is better than 1 ns.Due to the accuracy discrepancy of GIM in different latitudes,the stability of BDS receiver DCBs in the middle-high latitude(STDs are within 0.4 ns)is better than that in low latitude region(STDs are 0.8?1 ns).(3)Two/Three Dimensional tomography Model After obtaining all kinds of observation data,the ionospheric two-dimensional model of multi-source data is constructed.Integration of space-based ionospheric data and ground-based GNSS observations can get high-precision GIM and improve the accuracy and reliability of the GIM in marine areas.The results show that after adding space-based data,GIM accuracy in the ocean has been greatly improved,which make up for the defects of the existing GIM.However,the two-dimensional model is based on the assumption of a single layer,only reflecting the overall of ionospheric electronic content changes.With the help of computerized ionosphere tomography,three-dimensional ionosphere structure can be reconstructed,which provides a new way for us to understand the ionosphere In this paper,we focus on optimizing the projection function of each layer,and propose a function base layer method considering the projection function,and apply it to the ionospheric disturbance monitoring during the magnetic storm.(4)Ionospheric Responses to Magneftic Storms The global ionospheric storm in March,2015 was investigated using data from over 3000 GPS stations worldwide.In this study,Total Electron Content(TEC),Rate of TEC(ROT)and ROT's standard deviation ROTI,as well as the second-order difference operator TECT,were considered as main characteristic methods to distinguish ionosphereic disturbances.The results show that,?Based on the multiple methods above,we all observed that,for the first time,there were three equatorward traveling ionospheric disturbances(TIDs)in the main phase of this storm.In North America,the disturbance zone expanded to-40°N;the disturbance periods and auroral electrojet(AE)peak stages were roughly synchronous.We suggest that these three TIDs were induced by the propagation of acoustic gravity waves(AGWs)to low latitudes under the action of AE.? The most intense positive storm occurred over South America and the South Atlantic(over 300%enhancement;00:00-05:00 UT March 18),whereas a negative storm was observed in the corresponding region of the NH.Such inverse hemispheric asymmetry in intensity and structure can be explained by the variations of the thermospheric composition,the IMF By component and the geomagnetic intensity.?On March 18,a negative storm dominated globally(except at certain low latitudes),and tended to propagate equatorward and decay with time,which could be largely attributed to the storm circulation theory.And the evolution of the negative storm was further characterized by the foF2 variations of ionosondes.