| At present,China's urban infrastructures are in full swing.As one of the most important infrastructures,urban bridges are subject to the complicated traffic impact of intensive traffic flow in daily operations,and are affected by the complex effects of subway construction and other surrounding environments.Therefore,the safety of urban bridge operations is becoming increasingly severe.Therefore,in order to ensure the safety performance of existing urban bridges,it is urgent to carry out t rapid assessment and safety assessment for urban bridges.The dynamic deflection of urban bridges is one of the important indicators for the assessment of bridge safety status.The rapid and accurate acquisition of bridge deflection has become a hot issue in current research.With the characteristics of high precision monitoring,long monitoring distance,non-contact,all-weather,real-time monitoring,Ground-based synthetic aperture radar(GB-SAR)technology has been widely used in bridge dynamic deflection monitoring in recent years.However,the accuracy of GB-SAR technology is often affected by the external environment in the scene,of which atmospheric effect is one of the most serious interference factors.In addition,GB-SAR technology depends on the emitted electromagnetic,and the electromagnetic wave energy varies with the propagation distance.The attenuation of electromagnetic wave energy will lead to a decrease in the accuracy of the monitoring data.In response to the above questions,the main contents of this paper are shown as follows:(1)First,clarify the three major technical principles of GB-SAR and the principle of atmospheric refracting of the electromagnetic troposphere.Secondly,collect the atmospheric disturbance data by the experimental method and further to correct the monitored data by using the atmospheric parameter model correction method.The experimental results show that the monitored data obtained by GB-SAR is more seriously affected by atmospheric factors,the atmospheric parameter model correction method can calculate and eliminate the atmospheric disturbance phase,so that the accuracy of the monitored data can be effectively improved,the field environment has an impact on urban bridge monitoring by GB-SAR,and it should avoid atmospheric disturbances for long-term monitoring.(2)Firstly,according to the characteristics of urban bridge dynamic deflection monitoring by GB-SAR,the Essen-Froome empirical formula is used as the basis model to theoretically analyze the influence mechanism of different meteorological factors on the temporal and spatial distribution.The results show that the water vapor in the atmosphere is the main factor for the accuracy of the monitored data by GB-SAR.Secondly,the monitoring data by GB-SAR and meteorological data are collected by using the experimental method,and the various analysis methods are used to verify the above theoretical results.Finally,the historical material and meteorological data are reviewed,the distribution law of water vapor at different time resolutions is analyzed and summarized,and the optimal time period is determined for the dynamic deflection monitoring of urban bridges by GB-SAR.(3)The mathematical relationship among the instrument layout,the geometric characteristics of the bridge structure and the atmospheric refractive index is studied and derived for urban bridge dynamic deflection monitoring by GB-SAR.In order to resolve the phenomenon that the accuracy of monitored data by GB-SAR decreases with the increase of monitoring distance.The experimental method is used to acquire the data to fit the above mathematical relation expression to construct the the Essen-Froome atmospheric parameter optimization correction projection model taking into account the transmission distance of microwave.The proposed model is applied in different types of bridge dynamic deflection monitoring experiments.The experimental results show that it can effectively improve the accuracy of monitoring data,and the average accuracy is increased by 5.8%. |
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