A Novel Virtual Benchmark For GNSS Deformation Monitoring

GNSS technology has been widely used in deformation monitoring fields such as largescale engineering and crustal movement because of its advantages such as high measurement accuracy,all-weather operation,no need to see between stations,and high degree of automation.However,GNSS is affected by space-related errors.The distance between the benchmark station and the monitoring station can't be too long,and the physical benchmark station must be deformed by human activities and natural factors during long-term continuous operation,which will affect the monitoring results.In view of the above problems,this paper studies the GNSS deformation monitoring virtual benchmark construction technology based on the Augmentation Reference Station(ARS),and replaces the traditional physical benchmark station with a 3D position-invariant virtual benchmark for deformation monitoring.The main research contents and results are as follows:1.Analyze the process of generating virtual benchmark observations,explain the sources of error and processing methods in the process of constructing the virtual benchmark.And build a virtual benchmark based on the ARS/VENUS software,an Augmentation Reference Station system independently developed by the Southwest Jiaotong University Satellite Navigation and Positioning Research Center.It is proposed to divide the virtual benchmark deformation monitoring mode into target point monitoring mode and area monitoring mode according to the monitoring needs,and then determine the 3D construction position of one or more virtual benchmark so that the virtual benchmark and each monitoring point form an ultrashort baseline for deformation monitoring.2.The validity of the virtual benchmark was tested: Quantitatively analyze the error modeling accuracy and residual size of tropospheric delay,ionospheric delay,ephemeris error,etc.during the construction of the virtual benchmark.Using the virtual benchmark and actual station GNSS observation data to check the observation quality with TEQC software.The results show that the virtual reference is superior to the actual station in signal-to-noise ratio,multipath effect,and cycle slip.Establishing a virtual benchmark and conducting a baseline solution effect test.Experiments show that using the virtual benchmark for deformation monitoring can achieve good monitoring accuracy and correctly reflect the change of displacement at the monitoring point.3.The main factors affecting the accuracy of the virtual benchmark solution are analyzed and compared through experiments.The experimental results show that: The accuracy of the virtual benchmark baseline solution is closely related to the processing time.The longer the solution time under the same conditions,the higher the solution accuracy.6h baseline solution accuracy is better than 2mm in the plane direction and 7mm in the vertical direction,24 h baseline solution accuracy is 1.10 mm in the plane direction and 3mm in the vertical direction.The number of visible satellites,PDOP values,and positioning accuracy of the virtual benchmark under the Bei Dou/GPS fusion system are better than those of the single systems.In the single system,the Bei Dou system has the same accuracy as GPS.The CORS network structure is one of the main factors affecting the performance of network RTK positioning services,but when constructing a virtual benchmark,the network structure of the reference station has a small impact on its monitoring accuracy.The specific performance is that under the condition that the observation station's observation data quality is good,the virtual benchmark established according to different network structures can obtain comparable monitoring accuracy.When using a virtual benchmark to monitor deformation of users outside the network,users with short extension distances can still correctly obtain the displacement changes,and the monitoring accuracy is equivalent to that of users inside the network.4.An application example analysis of virtual benchmark deformation monitoring: Using observation data from three reference stations in the Chengdu area CORS network from March to April 2019,a monitoring network was constructed to construct a virtual benchmark to monitor the deformation of four uniformly distributed monitoring stations in the network to obtain the displacement time series of each monitoring station.Combined with the results of GAMIT / GLOBK software analysis and comparison,the results show that the two groups of displacement data have the same change trend and the same accuracy.The baseline accuracy(plane)of each monitoring station obtained by the virtual benchmark monitoring method is within 1.5mm,which has a high monitoring sensitivity.It is feasible to use a virtual benchmark for GNSS deformation monitoring.Deformation monitoring method based on virtual benchmark has uniform accuracy distribution in the monitoring network and is a highprecision position-independent GNSS deformation monitoring method.No matter where the monitoring user is located in the monitoring network,you can use the virtual benchmark monitoring method to obtain high-precision deformation monitoring services.