The Research Of InSAR Phase Unwrapping Method In Low Coherence Region

Interferometric Synthetic Aperture Radar(InSAR)is a new type of ground measurement technology that has been rapidly developed in recent decades,it has the unique advantages of all-time and all-weather operations and is widely used in topography,ground subsidence,geological disaster monitoring and other fields.Using InSAR technology to measure the terrain can obtain a large area of surface elevation information at a relatively low economic and time cost.However,in the actual process of InSAR topographic surveying,its measurement accuracy will be limited by many factors and errors,the mainly error comes from the process of phase unwrapping.Due to changes in the backscattering conditions of the ground and the imaging geometry of the synthetic aperture radar itself,the generated interference phase map often contains low-coherence areas,and the low-coherence areas show obvious dark areas in the coherence coefficient map,and in the interference phase diagram,it appears that adjacent pixels generate random jumps or discontinuities,it brings great difficulties to the phase unwrapping process,which not only increases the complexity of phase unwrapping,but also transmits the error of its unwrapping phase to the subsequent step of InSAR data processing,the local topographic measurement results are very different from the actual,and even the generated digital elevation model is not available.Therefore,this paper studies the phase unwrapping method applicable to low-coherence areas,and there is practical significance for promoting the precision of InSAR topographic surveying.In the paper,the development process of InSAR technology and phase unwrapping is described in detail,the basic principles of InSAR topographic surveying are described,and several common phase unwrapping methods are introduced,then,an unwrapping method combining block interpolation and branch cut method is proposed.At last,the effectiveness of the proposed phase unwrapping method for phase unwrapping in low-coherence regions is experimentally verified.The main research contents of this paper are as follows:(1)The development context of InSAR technology is reviewed,and the current research status of phase unwrapping methods at home and abroad is reviewed.The importance of phase unwrapping for InSAR technology is pointed out.Phase unwrapping methods are mainly divided into three categories: phase unwrapping based on path integration,phase unwrapping based on minimum norm,and other phase unwrapping methods,several common phase unwrapping methods are introduced.(2)The advantages and disadvantages of the branch cut method are analyzed,and an improved idea is proposed.The purpose is that the improved branch cut method can be applied to phase unwrapping and provoke the accuracy in low-coherence regions.A phase unwrapping method is proposed based on the previous improved idea,and the applicable conditions of the method are given in simulation experiments.The results show that under the applicable conditions,the initial phase without wrapping is basically restored.(3)The actual data verification experiments on the phase unwrapping method which is proposed in this paper show that compared with several commonly used phase unwrapping methods,the proposed phase unwrapping method not only has the highest unwrapping accuracy in the low coherence region,but also takes relatively short time,and the timeliness is high.