| Bei Dou Satellite Navigation System(BDS)is a GNSS system built and operated independently by China,following a "three-step" strategy.Completed in July 2020,the BDS-3satellite navigation system has been providing services to users worldwide.It is a fast-growing trend to provide GNSS services for various industries by leveraging the advantages of BDS system.The study of high precision crustal deformation and tectonic movement has been an important field of GNSS application,and the GPS has achieved rich results in this field.However,due to the short time of BDS-3 network completion,the lack of perfect external reference model,and the number of ground tracking stations is also in the stage of increasing deployment,the study of BDS relative positioning and its application in crustal deformation is relatively weak.With the upgrading of receiving equipment,some stations in the Crustal Movement Observation Network of China(CMONOC)and the China Seismic Experimental Site(CSES)have accumulated BDS data for more than 2 years,which provides an important platform and sufficient observational data guarantee for the application of BDS in geosciences.To investigate the accuracy of BDS data positioning and their performance in crustal deformation studies,the following studies are conducted in this thesis: 1)Quality assessment of BDS-3 data from the China Seismic Experimental Site.2)Processing of BDS-3 和 GPS data from the CSES using a relative positioning method to obtain station coordinate time series in the framework of ITRF14,with comparing and analyzing the positioning results of accuracy.3)Fit the BDS 3D velocity field and the period signal of the time series in the experimental field by the station coordinate time series model and compare with the GPS results.4)For the Luding earthquake of September 5,2022,use the BDS data within 200 km of the epicenter to obtained a precise horizontal coseismic displacement field and use it to estimate the coseismic slip distribution.The following main conclusions are obtained:(1)The BDS-3 data in the experimental field area are of comparable quality with GPS,and can be used independently for high-precision deformation monitoring after setting a suitable cut-off altitude angle.Its positioning results in the framework of ITRF14 have horizontal accuracy of about 4-5 mm and vertical accuracy of about 8-10 mm,which is larger compared with GPS results.The main influencing factors are the relatively low accuracy of orbital products,and the imperfection of models,such as empirical solar pressure and satellite antenna phase center correction.(2)Obvious trend signals and period signals can be observed in the time series of station coordinates obtained by BDS-3.Among them,the three-dimensional velocity field obtained by BDS-3 and GPS has a systematic difference of about 2 mm/yr in the E direction,but the velocity field and period signal differences do not have obvious regional distribution characteristics.The reason for the velocity field differences is mainly due to the regional errors and scale differences between the BDS and GPS positioning results,resulting in the inconsistence of the datum.(3)The coseismic displacement based on the BDS observation clearly reveals the sinistral strike slip pattern of the earthquake.The coseismic displacement field derived from BDS is close to GPS-derived results,which indicates that,based on current BDS observations,it is possible to obtain coseismic displacement field of large earthquake occurring within the area of China Seismic Experimental Site.However,the slip distribution model based on BDS coseismic displacement has some difference from the results of GPS,mainly because of the number of GNSS stations which have the ability to receive BDS data is much less than that of GPS.Besides,most of these stations cannot receive full BDS-3 satellite data,thus the BDS station distribution has a lower resolution to estimate the slip distribution than that of the GPS station distribution. |
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