The Application Of GB-SAR In The Deformation Monitoring Of Linear Structures

With the rapid development of economy,the linear structures such as cross sea bridges,overpasses,towers,buildings and so on have sprung up on the land of China,and have been integrated into people’s daily life.While they are bringing great convenience to people,their health is eroded by factors such as load,earthquake,wind force and flood.How to diagnose the health of these giants has become a hot topic in the current society.To diagnose the "health" status of linear structures,we need to get the deformation parameters and vibration parameters of linear structures,and then analyze the stability of linear structures,so as to get the overall "health" status of linear structures.The traditional deformation monitoring methods such as total station and GPS are very difficult to measure the large linear structures.The ground-based synthetic aperture radar(GB-SAR)technology has solved this difficult problem in recent years.Ground synthetic aperture radar(SAR)is a new remote monitoring system based on synthetic aperture radar(SAR),interferometry and FMCW.The synthetic aperture radar(SAR)improves the azimuth resolution by the synthetic aperture radar technology,and obtains the change of displacement by interferometry.The efficiency of the observation is improved by the FM continuous wave technology.It has the advantages of large coverage,high accuracy,all-weather,full automation,no contact and bad weather.It can be used for all-weather high frequency dynamic measurement of linear structures.It is the best way to diagnose the health status of linear structures at present.The foundation synthetic aperture radar system--Fast-GBSAR system,which is developed jointly by the Metasensing company and the European Space Agency(ESA),is presented in this paper.The introduction of microwave radar technology at home and abroad,the present situation of research and application,introduces the technology,synthetic aperture radar interferometry,FMCW technology of the three core technology,the test precision of GB-SAR radar design,the design and analysis of the influence factors of atmospheric correction test.In order to test the accuracy of the ground synthetic aperture radar(SAR),a slow deformation test is designed to test the accuracy of the GB-SAR radar.The corner reflector is fixed on the micrometer and rotated micrometer to move the corner reflector,and continuous observation is carried out through Fast-GBSAR.The observed displacement is compared with the movement of the micrometer.The results show that the measurement accuracy of Fast-GBSAR can reach submillimeter level and can accurately observe the tiny movement of the object.In the deformation monitoring of a linear structure,the results of the measurement are greatly influenced by the atmospheric factors.This paper introduces two methods of atmospheric correction is popular at home and abroad: meteorological parameter correction and permanent scattering correction method,analyzes their principle,and their correction formula,obtained through comparative analysis of Permanent Scatterers method can better eliminate the influence of atmosphere,improve the measurement accuracy of Fast-GBSAR.A new signal processing method,the extreme-point symmetric mode decomposition(ESMD)method,is introduced,which is based on the evolution of Hilbert-yellow method.The extreme-point symmetric mode decomposition method takes the difference of the internal pole symmetry instead of the envelope difference,and optimizes the screening times and trend functions to ensure that the decomposition result is the best.It can intuitively obtain the instantaneous amplitude and instantaneous frequency of the modal,and can also intuitively reflect the change of the total energy.The extreme-point symmetric modal decomposition method can effectively deal with and analyze the nonlinear and non-stationary data obtained by GB-SAR.The displacement of the object’s view line is obtained by Fast-GBSAR measurement,and the displacement of the vertical and horizontal direction of the object is often needed.In order to solve this problem,the mathematical principle is applied to the calculation model of lateral displacement and vertical displacement.In this paper,Fast-GBSAR system is used to monitor the deformation of a cross sea bridge and a landslide nearby,and get their shape and variable curves.The ESMD algorithm is used to analyze the change of instantaneous amplitude,instantaneous frequency and total energy,so as to identify the damage of the object and analyze the safety of the object structure.