Research On Multi-frequency And Multisystem GNSS Medium And Long Baseline Solution Technology And Its Application Development

With the continuous improvement and development of the BDS and the Galileo system,combined with the already established GLONASS and GPS systems,the global satellite navigation system has entered the era of multi-constellation joint positioning.Multiple systems are integrated for positioning,which enriches the number of visible satellites at the measurement site,increases the graphic intensity of the observation satellites,and helps improve the accuracy and reliability of positioning.How to fuse the observations of multiple systems is the key to the successful realization of the baseline calculation of multiple systems;at present,China's BDS-3 generation system is in the final stage of networking.Its advantage of broadcasting three-frequency signals in full constellation is of great significance for the use of multi-frequency combined observations to quickly achieve ambiguity fixation.In view of this,the main research contents and conclusions of this paper are as follows:The basic theory of GNSS multi-system combined positioning is discussed in detail.The time and coordinate systems of each GNSS are compared and analyzed,and the unified methods of space-time reference of the four navigation systems are given.The basic observation equations of non-difference,single-difference and double-difference in GNSS combined positioning are described.The least square method and Kalman filter method are introduced in GNSS parameter estimation.The combination criteria of basic GNSS observations and some common linear combinations are given.Research on fixed method of ambiguity of wide lane with BDS three-frequency ultra-wide lane constraint.Taking advantage of the ease of fixing the ambiguity of the three-band ultrawide lane of Beidou,using the step-by-step ambiguity fixing strategy to preferentially fix the ambiguities of the two ultra-wide lanes of BDS-2 and BDS-3,and then using the BDS(1,0,-1)wide lane combination as a constraint condition,the analytic-based geometric model is used to constrain the GPS wide lane ambiguity.The test results show that the proposed method can achieve single epoch fixation of BDS/GPS wide lane ambiguity,and quickly achieve the wide lane combination positioning accuracy of level 3.5 cm and elevation 6.0 cm.Compared with the traditional MW method to solve the ambiguity of wide lanes,the proposed method reduces the number of epochs required to correctly fix the ambiguity of wide lanes,and effectively improves the timeliness of GNSS ambiguity solution.Research on the key technologies of GNSS multi-system medium and long baseline solution.The atmospheric delay error that affects the medium and long baseline solution were analyzed,and details how the conventional three-step method achieves fixed ambiguity.Based on this,considering the influence of tropospheric delay error,a multi-system combined baseline solution model applicable to different lengths is established.The test results show that the accuracy of multi-system combined positioning is better than that of single systems.Compared with the single BDS,the combined positioning accuracy of four-system combination has respectively improved by 51.1%,41.4%,and 71.0% in the three directions of N,E,and U;compared with single GPS,the combined positioning accuracy of BDS-2 and BDS-3 has respectively improved by 12.5%,39.0%,and 47.3% in the three directions of N,E,and U;in the GPS/BDS dual system combination,the 52 km,70 km,109 km,and 146 km long baselines have a plane positioning accuracy better than 1 cm and an elevation positioning accuracy better than 2.5 cm.The time required for the first fixation of ambiguity is less than 10 minutes.Development and testing of high-precision GNSS online monitoring data processing software.An online monitoring data processing software SEUMonitor that integrates real-time data access,data processing,results query and display functions was developed,and real-time measured data was used for verification,using the GNSS data processing theory described above,based on understanding the software development requirements,using object-oriented programming technology,detailed design of each functional module in the software.The test results show that in a small area(5 km),the real-time data processing software uses the Kalman filter method to calculate the point coordinates,the error in the plane is within 3 mm,and the error in the elevation direction is within 5 mm,which meet the needs of general small-scale slope deformation monitoring.