Research Progress of Phase Linking Method in Time-Series InSAR

Objectives:Interferometry synthetic aperture radar (InSAR) can acquire wide-area high-precision surface morphology, which is widely used in the field of geohazard monitoring, etc. However, its monitoring performance strongly depends on the correlation degree of scattering characteristics of scatterers between different imaging moments. The phase linking (PL) method utilizes multi-reference interferometric phase analysis to recover the systematic phase series, which is the key to solving the problem of time-series InSAR (TSInSAR) coherence-low surface monitoring. In recent decades, scholars have proposed a series of effective implementation methods, whose differences can be attributed to the inconsistency of the adopted weighting strategy. Methods:We introduce the research progress of the existing PL methods in the TSInSAR surface deformation monitoring and other fields from various aspects, including research motivation, statistical basis, method progress and result analysis, and then discuss the future development trend. First, from the perspective of the interferometric phase components and decorrelation sources, we analyze the differences in phase consistency between both persistent and distributed scatterers and their reasons, and point out the necessity of PL research. Second, based on the introduction of complex covariance matrices and their statistical distributions, we categorize and compare the existing PL methods and point out the advantages and limitations of the great likelihood estimator and its accuracy upper limit for phase optimization theory. Results:The simulated experiment uses the Monte Carlo simulation to generate the multilloking time-series covariance matrix under both exponential and seasonal temporal decorrelation models, and quantificationally compare five classical PL methods in terms of interferometric phase optimization, deformation measurement accuracy and algorithm computational efficiency. In the real experiment, the Daguangbao landslide triggered by the 5·12 Wenchuan Mw 7.9 earthquake and the 56 scenes of Senetinel- 1 synthetic aperture radar (SAR) images in VV polarization are selected as the experimetal data and the study area, respectively. In addtion to the persistent scatterer interferometry technology, three PL methods are qualitatively compared and analyzed in the three aspects, similar to the simulated experiment. Conclusions:The existing PL methods are summarized and their limitations in TSInSAR deformation monitoring, data compression and SAR tomography are pointed out. With the development of spaceborne SAR platforms towards multi-band, multi-polarization and high spatiotemporal resolution, the research hotspot, technical challenge and future development direction of the PL method are discussed.