| Satellite navigation and positioning technology has entered the era of multi system integration of Global Navigation Satellite System(GNSS),which brings new opportunities and challenges for the development of precision navigation and positioning technology,and it also brings opportunities and challenges for GNSS fusion positioning:which has significantly improved the constellation space geometry of satellites,and improved the accuracy and stability of satellite positioning.However,the differences between systems,the complexity of multi-frequency and multi-GNSS fusion have also increased,which is manifested in multi-frequencies,hardware delays,constellation design and differences in time and space benchmarks.With the continuous improvement of the requirements for deformation monitoring,the traditional deformation monitoring methods have become increasingly difficult to meet the current requirements.As the current mainstream deformation monitoring method,GNSS,if it can make full use of the advantages of multi-frequency and multi-mode for tight combination in the case of limited satellites reception,it will be of great significance to the application of deformation monitoring.The main work and research results of this paper are as follows:1.Taking full account of receiver hardware delays,time and space benchmark deviations and other deviations,according to basic equations,a unified GNSS observation equation based on Code Division Multiple Access(CDMA)technology is derived.2.From the perspective of post-processing parameter estimation ways,the Inter-system Bias(ISB)extraction method of the same/different frequency short baseline tight coupled model is introduced.The characteristics of ISBs of GPS L1-Galileo E1 co-frequency and GPS L1/L2-BDS B1/B2 are also analyzed.The results show that the ISBs at the receiver has certain stability in few hours or one whole day;The GPS L1-Galileo E1 co-frequency ISB parameters can be ignored when the receiver types at both ends of the baseline are the same,GPS L1/L2-BDS B1/B2 different frequency tightly-coupled combination ISBs must be considered regardless of whether the receivers are same or different,.3.Taking full account of the hardware delays,the Similar Single Difference Model(SSDM)considering hardware delays are re-derived,the impact of the hardware delays are analyzed.Taking advantage of the deformation in last epoch,the application range of SSDM for deformation is expanded.The results show that under the condition of a 3 km baseline,the hardware delay at CUT2 site in the multi-GNSS experiment(MEGX)can bring an error of 2.3 mm to the observation model.For common deformation monitoring with low accuracy requirement,this error can be ignored;Observation data for about 15 mins shows that most plane difference between the calculated deformation value using SSDM method and the true value of the platform is within 1 cm,and a small part is within 1.5 cm.Most vertical difference between the calculated deformation value using SSDM method and the true value of the platform is within 1.5 cm.SSDM plane accuracy can basically meet the normal monitoring requirements,but the elevation accuracy is still slightly insufficient;the improved SSDM method can meet the general deformation monitoring requirements.4.The relationship between Ratio value and ISB parameter are disscussed,the distribution characteristics of ISB and the influence of ISB error to positiong are analyzed,the insufficient accuracy of inter-frequency single-differenced bias is solved using the relationship between Ratio value and ISB parameter,the problem that ISB needs to be post-processed is also solved.The influence of single-epoch tightly-coupled combination on the success rate of ambiguity fixation is analyzed,the accuracy of single-frequency tightly-coupled combination model is evaluated.The results show that the difference between ISB extracted by the relationship between the Ratio value and the ISB estimated by post-processed ways can be ignored;although the accuracy of tightly-coupled combination between loosely-coupled combination is similar,the GNSS tightly-coupled combination can effectively improve the success rate of ambiguity resolution.Under the condition of 3 km baseline,the deviation of plane direction shall not exceed 0.45 cm and that of vertical direction shall not exceed 0.60 cm under the average value of RTK solution for 20 min,which can meet the general deformation monitoring requirements.Figure 20 table 19 reference 81... |
