The Deformation Monitoring Of Bridge Based On GNSS Velocity Measurement

The bridge is easy to be affected by the natural and human factors and deforms.When the bridge structure deforms beyond the safety range,the safety of the bridge structure will be affected to a certain extent.Therefore,it is necessary to construct an observation scheme with timeliness and high precision to understand the health status of Bridges.Velocity information is one of the key information of an object,which directly reflects the motion state of an object.Based on the Time Difference Carrier Phase(TDCP)velocity measurement model,this paper carries out research,which includes the following aspects:(1)The principle and algorithm of GNSS carrier phase time difference velocimetry are studied,and the height Angle stochastic model is introduced.Then the error sources of the algorithm are analyzed and the influence of each error on the measurement accuracy is verified one by one.Completes the addition of the carrier phase differential velocity measurement function in the open source software GAMP,so that the velocity variation between epochal units can be calculated while positioning,for the purpose of subsequent experiments.The experimental results show that the accuracy of the velocity measurement algorithm can reach millimeter level in the east,north and sky directions.After the difference between elements,the influence of each error on the measurement accuracy is basically less than millimeter,and the error curve diverges over time.(2)Using precision ephemeris products with different precision to solve the high-frequency observation data provided by domestic IGS reference stations.When the observation conditions are good,the accuracy can be improved to 40% in X direction,30% in Y direction,and 3% in Z direction.The reason why the accuracy is improved is to eliminate the jump of the velocity measurement results when updating the ephemeris.Through experiments,it is proved that different precision ephemeris products have little influence on the precision of velocity measurement.Therefore,combined with the real-time characteristics of ultra-fast precision ephemeris products,it can be proved that the TDCP velocity measurement model based on precision ephemeris products has the ability of fast calculation,and is better than the precision and stability of broadcast ephemeris.(3)Based on the bridge observation data of different frequencies,the TDCP velocity measurement model is used to measure the speed of bridge vibration.Through experimental verification,the overall change curve of the velocity error of the mobile station with the observation frequency of 1Hz is reduced in x,y and z directions,reaching to cm/s.Therefore,TDCP used in bridge deformation monitoring can effectively measure the position variation between ependons above centimeter level.The results of base station velocity measurement with observation frequency of10 Hz are quite different from the theoretical results,so the influence of observation frequency should be taken into account in the measurement.After converting 10 Hz data to 1Hz,the measurement accuracy of the base station is in line with the reference accuracy.(4)A discrete linear system based on the TDCP velocity measurement model was established,and the RTS algorithm in fixed interval smoothing was used to smooth the velocity measurement results of different frequency data.Experimental results show that the algorithm can smooth the jump epoch,but can not eliminate it completely.The statistical results show that the impact of the mutation on the accuracy is reduced to 0.1mm/s.After smoothing the data with a frequency of 1Hz,the accuracy of static velocity measurement is improved by more than 1mm/s in all three directions.The velocity curve of the mobile station can accurately reflect the time period when the bridge deck generates excitation action,and can measure the peak velocity.For 10 Hz data,RTS can quickly converge abnormal velocity measurement results and give play to the advantages of higher sampling frequency data,so that the RMS value of base station and mobile station can reach within 1mm/s,which proves that the TDCP velocity measurement model combined with RTS smoothing can be more widely used and more accurate results can be solved.