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An Improved Two-Step Multitemporal SAR Interferometry Method for Precursory Slope Deformation Detection Over Nanyu Landslide

A major landslide in Nanyu township, Zhouqu county, Western China, occurred on July 12, 2018, causing widespread damage and blocking the Bailong river. As a widely used surface deformation measurement technique, persistent scatterer interferometry (PSI) method fails in the precursory slope deformation detection over Nanyu landslide for two reasons: the high rate slope deformation of the landslide body before the occurrence of the disaster and the low density of measurement points in the widespread nonurban regions over hillside area. To solve these problems, a two-step multitemporal interferometric synthetic aperture radar (MTInSAR) method is proposed in this letter. In the proposed method, first, a carefully designed small baseline subsets (SBASs) method is applied to extract the linear high rate deformation component, which is then subtracted from the wrapping interferogram to reduce the likelihood of signal aliasing. In the second step, a two-tier network-based MTInSAR method by exploiting both persistent scatterers (PSs) and distributed scatterers (DSs) is employed to retrieve the residual deformation. The proposed method is applied to 47 Sentinel-1 images acquired between December 2016 and July 2018 and successfully detects the precursory deformation over Nanyu landslide for the first time. Experiment results illustrate the advantage of the proposed method for measuring high rate deformation compared with the traditional PSI. By using the proposed algorithm, the deformation rate map shows a clear landslide boundary and precursors of the rapid slope movements with a maximum displacement rate of 483 mm/year along the line of sight of the satellite.