Application And Estimation Of Tropospheric Delay For Base Station Stability By Using BDS/GPS Technology

With the strengthening of China’s comprehensive national strength,the modernization construction is getting faster and faster.The various engineering projects have emerged from the ground,and it is an indispensable task to carry out safety monitoring.The bigger engineering makes the more work.That makes traditional monitoring methods face the challenges.Since the birth of GNSS technology,it has been widely used in the field of deformation monitoring because of its high precision,no need for visibility,all-weather operation,and easy automation.As the scale of the project is getting larger and larger,and the environment is more and more complex,various problems in practical application are found.Hence,the higher requirements are imposed on the current GNSS deformation monitoring technology.Among them,the stability of the base station is the basis and key of the entire monitoring system.The base station location of the current GNSS monitoring system is close to the monitoring area.When the scale of the project is large,the stability of the base station is easily affected by monitoring area,making results unreliable.In this context,this paper designs a remote base station assisted deformation-monitoring program that makes the base station far away from the monitor area to avoid the problem of instability.Based on the high precision automatic deformation monitoring system developed by Professor Huang’s team,make tropospheric delay error processing module that makes the system to have the ability to monitor 200 km long baseline deformation.The main research contents of this paper are as follows:1.By summarizing the results of previous studies,it is determined that the key to solving this problem lies in the processing of tropospheric delay errors.The commonly used tropospheric delay estimation methods are compared and their differences and applicability are analyzed.The results show that: The tropospheric delay solution strategy with 2 hours interval of parameters can reflect the tropospheric delay variation well.Multi-parameter method and piecewise linear method have their pros and cons in practical applications.The piecewise linear method is sensitive to prior information,and the wrong information will make the deviation of the solution result.Piecewise linear method is more effective when the observed data quality is poor.Multi-parameter methods can more accurately reflect tropospheric changes when the observed data quality is good.Compared the accuracy of tropospheric delay estimation of BDS and GPS,the results show that the difference between the GPS estimation result and BDS can reach the centimeter level.2.The main factors affecting the baseline solution within 200 km of this system are analyzed through experiments.The results show that: Ephemeris accuracy has a slight effect on the north direction of the baseline solution,no more than 2 mm and there is no effect on the east direction.The length of observation will affect the accuracy of the solution.Compared with the 24-hour observation and the 72-hour,the longer observation will improve the accuracy of the result,but the effect is very limited.It is less than 1 mm in the E direction,1 mm in the N direction,and 2 mm in the U direction.Different tropospheric delay estimation methods only affect the baseline vertical direction results.In order to obtain more reliable elevation accuracy,it is recommended to use a multi-parameter method when VDOP is better,and a piecewise linear function method when VDOP is poor.The long baseline solution results of BDS and GPS are consistent,and the accuracy is similar.Multi-constellation fusion positioning can improve the accuracy of the elevation direction by 30%,and the improvement of the horizontal precision is small and can be ignored.This is because the VDOP improvement of Multiconstellation is more obvious,and the HDOP improvement is not obvious.3.Make GNSS tropospheric delay error processing module,so that the latest system has the capability of long baseline deformation monitoring.Test system long baseline solution accuracy: Baseline repeatability of 200 km baseline 24-hour solution,horizontal better than 4 mm,elevation better than 8 mm.This result means that it can be used to deformation monitoring for partial engineering.Aiming at the stability problem of close-range base station,a GNSS remote base station assisted deformation-monitoring program is designed.Experiment with the measured data of Guandi Dam to verify the feasibility and validity of this system long-baseline monitoring program.The results show that: The feasibility of using the baseline repeatability of long-distance base station monitoring results over a period to determine the stability of a close-range base station in this period is practical.Long baseline repeatability is used as the reference of weighting when multi-station integration,that can effectively improve the accuracy of results.Compared with the traditional scheme without considering baseline stability,the consistency between the monitoring results and the actual displacement can be increased significantly.This monitoring scheme can better avoid the adverse effects caused by instability of the close-range base station.