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Study Of Differential Code Bias Estimation And Ionosphere Modeling Using Multi-Mode And Multi-Frequency GNSS Observations

Posted on:2022-02-06Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q S WangFull Text:PDF
GTID:1480306563959389Subject:Surveying the science and technology
Abstract/Summary:PDF Full Text Request
Ionospheric delay is an important error source of GNSS navigation and positioning,especially for single frequency users.Therefore,it is of a great significance to monitor and model the ionosphere.On the one hand,GNSS signal delay caused by the ionosphere seriously affects the accuracy of GNSS navigation and positioning.On the other hand,GNSS provides an effective means for the monitoring and modeling of ionosphere because of its wide coverage,long observation time and a high accuracy of TEC inversion.GNSS-based monitoring and modeling of ionosphere have become the focus of current research on ionosphere.The differential code bias is included in the observation of ionosphere,coupled with the ionospheric TEC parameters,which needs to be accurately separated and determined during the modeling of ionosphere.Therefore,an accurate processing of DCBs and the function fitting of ionospheric TEC are two important issues in the research on GNSS ionospheric modeling.With the rapid development of multi-mode and multi-frequency GNSS(including GPS,GLONASS,BDS,Galileo and QZSS),more observation for research on ionosphere can be provided,which also brings corresponding problems.In this paper,the following aspects of research work have been carried out for the processing of multi-mode and multi-frequency GNSS satellites,receiver DCB and ionospheric TEC modeling:(1)The influence of DCB estimation of BDS after adding the BDS-3 data is analyzed,and the stability of DCB of QZSS is evaluated.The observation of BDS from MGEX is used to analyze the impacts on BDS-2 satellites and receiver DCB that are unknown after adding BDS-3 data.The results show that the value of effects on BDS-2satellite DCB after combining with the observation of BDS-3 is close to 0.Therefore,it can be concluded that there is no evident systematic bias between the processed DCB before and after combining with the observation of BDS-3.In order to further analyze the stability of the BDS receiver DCB after adding observation data of BDS-3,a method based on the GIM of CODE is presented to estimate the BDS receiver DCB through epoch-by-epoch,which is validated by comparing with the DCB products provided by CAS and DLR.During the study period,more than 94% of the intra-day STDs are less than 1ns,indicating that most of the receiver DCBs show a relative stability within one day with an intra-day STD of less than 1ns.Besides,the intra-day stability of receiver DCBs calculated through the observation of BDS-3 and the BDS-2 is compared.The result shows that the intra-day stability of BDS-3 receiver DCB is higher than that of BDS-2 receiver DCB.Moreover,the DCB of QZSS is estimated through global ionospheric modeling method based on a 90-day combined observation of QZSS/GPS in a multi-GNSS experiment(MGEX).The day-to-day fluctuation of the DCB time series is less than 0.5ns in about 96% of the cases of all satellites.However,the receiver DCB is a little less stable than satellite DCB,whose standard deviation(STDs)is within1.9ns.The result shows that the stability of the receiver DCBs is not significantly related to the type of receiver or antenna.(2)A new method of multi-GNSS DCB estimation is proposed,namely Independent GNSS DCB Estimation(IGDE),which is validated by comparing with the DCB products provided by MGEX.In order to analyze the effectiveness of the IGDE method,the 19 types of multi-GNSS satellite DCBs are estimated through a 200-day observation of more than 300 multi-GNSS experimental(MGEX)stations,and the performance of the proposed method is evaluated by comparison between the estimated DCB and MGEX products.The results show that the mean RMS value of is 0.12,0.23,0.21,0.13 and 0.11 ns respectively for GPS,GLONASS,BDS,Galileo and QZSS DCBs with respect to MGEX products,and the stability of estimated GPS,GLONASS,BDS,Galileo and QZSS DCBs is 0.07,0.06,0.13,0.11 and 0.11 ns.The method proposed shows a good performance in multi-GNSS DCB estimation.(3)A method of GNSS single-station DCB estimation is developed,and the intra-day stability of the receiver DCB is analyzed.Based on the IGDE method proposed and the satellite DCB provided by MGEX,the method is developed to estimate the single-station receiver DCB of GNSS through daily and epoch-by-epoch estimates.The results of one-month experiment show that the RMS of the 19 types of receiver DCBs estimated daily is less than 1ns with respect to the MGEX DCB products.The result of DCB estimation shows a good agreement with the MEGE DCB products.The epoch-by-epoch estimates of receiver DCB are analyzed through a single-difference experiment among zero-baseline stations,which indicates that the intra-day variation of the receiver DCB can be better estimated through this method.The experimental data shows that the intra-day stability of GPS receiver DCB is the best,and the intra-day STD of less than 1ns is more than 90%,followed by GLONASS and BDS receiver DCB,most of whose intra-day STD is less than 2ns.However,Galileo and QZSS have a poor intra-day stability according to the observation.Moreover,with GPS as an example,we analyze the relationship among the intra-day variation of the receiver,the station location,receiver type and temperature.The results show that the epoch-by-epoch estimation variation(intra-day variation)of the receiver DCB has no obvious relationship with the station location or receiver type,but it has a strong correlation with the temperature variation.(4)The Global Ionospheric Maps(GIM)products are generated based on the observation of multi-mode and multi-frequency GNSS and the comparison with other GIMs provided by the ionosphere analysis center.Taking the CODE(Center of Orbit Determination in Europe)GIM as a reference during the 30 days in January 2019,for the GIM from JPL(Jet Puls Laboratory),UPC(Technical University of Catalonia),ESA(Europe Space Agency),WUH(Wu Han University),CAS(Chinese Academy of Sciences)and this paper,the mean bias with respect to CODE products is 1.87,1.30,-0.10,0.01,-0.02 and-0.71 TECu,and the RMS is 2.12,2.00,1.33,0.88,0.88 and 1.30 TECu respectively.(5)The observation of ionosphere is extracted by undifferenced and uncombined precise point positioning(PPP)for its modeling,and the influence of intra-day variation of receiver DCB on the modeling of ionosphere is analyzed.The data of 30 days from more than 400 globally distributed GPS+GLONASS stations is selected.The GIM and P1-P2 DCB of GPS/GLONASS are estimated through an undifferenced and uncombined PPP observable and spherical harmonic model of ionosphere.The result shows that the mean bias and RMS of our estimated GIM with respect to CODE GIM product are-0.41 and 1.32 TECu respectively.Moreover,the experimental results show that the residual error of observation value is reduced to a certain extent after considering receiver diurnal variation,but the final influence on ionospheric GIM is less.
Keywords/Search Tags:Global Navigation Satellite System (GNSS), Ionospheric, Global Ionospheric maps (GIM), Total ionospheric electron content (TEC), Differential Code Biases(DCB), Spherical harmonic model
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