A comparison of time series deformation models based on Small Baseline Subset Interferometric Synthetic Aperture Radar for soft clay subgrade settlement

Roads and highways built on soft clay subgrade are more prone to subsidence and induced instability. Therefore, monitoring long term surface deformation near the highways over soft clay subgrade is crucial for understanding the dynamics of the settlement process and prevent potential hazards. The precision of deformation estimation using time series radar interferometry (InSAR) techniques is restrained by the temporal deformation model. In this study, a comparison of four widely used time series deformation models in InSAR, namely Linear Velocity Model (LVM), Permanent Velocity Model (PVM), Seasonal Model (SM) and Cubic Polynomial Model (CPM), was conducted in order to understand and assess long term deformation process after constructing road embankment. To assess and validate these four selected models, both simulation and real deformation data over Lungui highway (a typical highway built on soft clay subgrade in Guangdong province, China) have been investigated using Small Baseline Subset Interferometric Synthetic Aperture Radar (SBAS-InSAR) technique with TerraSAR-X satellite imagery. The scenario using the simulated data showed all four models achieved satisfactory results when using Singular Value Decomposition (SVD) algorithm to estimate different deformation coefficients. However, LVM showed the least accuracy among the four models. This suggested LVM has higher estimation error due to its higher number of unknowns in the model. While in real data experiment, three precision indices were used to measure the residual phase, mean temporal coherence, and the root-mean-square-error (RMSE) of high-pass deformation, respectively. The results showed LVM and SM had better performance. In conclusion, SM is more suitable for the surface subsidence modeling and monitoring for highways built on soft clay subgrade in this case study.