| Beidou Satellite Navigation System(BDS)is an independently developed global satellite navigation system in China..It provides free and open services to the Asia-Pacific region at the end of 2012.Unlike the use of MEO orbits in GPS constellation and the fact that only some satellites broadcast three-frequency signals after modernization,BDS is the first satellite navigation system in the world to broadcast three-frequency signals in space constellation,which is constructed by three different orbits(MEO GEO IGSO).The appearance of multi-frequency signals not only increases the redundant observations and improves the stability and reliability of satellite positioning accuracy,but also provides the ability of forming more excellent combinations with longer wavelength ? smaller ionospheric delay coefficient and observation noise coefficient,which can detect cycle slips more quickly and accurately and fix ambiguity.In view of the advantages of multi-frequency combined observations,it is of great significance to study the Beidou three-frequency location algorithm.With Beidou system gradually providing free and open services to the whole world,and the upgrading of GNSS reference station of Crustal Movement Observation Network of China,some stations have accumulated abundant BDS observation data.Therefore,the feasibility of Beidou data in crustal deformation monitoring at present stage can be verified by the research on the quality evaluation and data processing of BDS observation data,and can better promote the application of BDS in the field of high-precision positioning.Based on the research of cycle slip detection and restoration of Beidou's three-frequency observations and the algorithm of three-frequency ambiguity fixing,this thesis carries out the processing,analysis and application of high-precision Beidou data in crustal deformation monitoring.The main research contents are as follows:(1)Two kinds of three-frequency cycle slip detection methods,code-pahse combination method and geometry-free phase combination method are studied.The mathematical principles of the two methods and the selection criteria of combination coefficients are introduced.The cycle slip detection of Beidou satellite with different sampling rates and three-frequency observation data of different orbits are analyzed in detail.The results show that when the sampling rate of observation data is low,the cycle slip detection accuracy will also decrease,and the MEO orbital data detectionaccuracy is slightly lower than IGSO and GEO orbits.Finally,two groups of code-phase combination and a group of geometry-free phase combination are used to correct the cycle slip of the original three-frequency data,and the shortcomings of cycle slip detection are overcome.(2)Based on the TCAR step-by-step ambiguity resolution principle,the Beidou three-frequency single-epoch ambiguity fixing algorithm is studied,and the error in the process of the step-by-step ambiguity fixing is analyzed.The results of ambiguity calculation for three groups of baselines with different lengths show that the success rate of ambiguity fixing is higher under medium and short baselines,while the success rate of ambiguity fixing for ultra wide-lane and wide-lane can still reach 100% when the baseline is longer,while the ambiguity of narrow-lane is difficult to fix directly.The ionospheric delay correction method is proposed,which can improve the fixed success rate of ambiguity in long baseline and narrow-lane to a certain extent.(3)Using GAMIT software as a tool,the high-precision baseline processing of BDS/GPS observation data accumulated over two years in Crustal Movement Network of China(CMONOC)is carried out,and the accuracy evaluation indexes of BDS solution results under ultra-long baseline are analyzed in detail.Aiming at the imperfection of BDS correlation error model in GAMIT software,the influence of antenna phase center correction on long baseline solution is analyzed.The results show that the NRMS values of BDS and GPS baselines are less than 0.25.The length and repeatability of BDS baselines are at mm level in horizontal direction and GPS,while the vertical difference is basically 1-2 cm.The accuracy of the two system in vertical direction is less than that in horizontal direction,and the effect of antenna phase center correction on vertical direction is greater than that in horizontal direction under long baseline.When the antennas at both ends of the station are identical,the effect of antenna phase center correction can be weakened to a certain extent.(4)Using GLOBK to adjust the result of baseline solutions,the coordinate time series of the station in ITRF08 frame are obtained,and the internal and external coincidence accuracy of BDS coordinate adjustment results is evaluated with the reference of GPS calculation results..After outliears are eliminated,the least square method is used to fit the horizontal velocity field of the station.The results show that the stability of BDS time series is slightly worse than that of GPS,and the repeatability of coordinates is slightly larger than that of GPS.The difference between BDS coordinates and GPS in horizontal direction is 3-7 mm,and the difference invertical direction is 1-2 cm.The estimated velocity field results are slightly different,the difference in N direction is 0.1-0.8 mm/a and E direction is 0.8-1.7 mm/a.The Beidou system is gradually applied to high-precision positioning fields such as crustal deformation. |
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