(Objective)Long-term monitoring of reservoir bank slopes in hydropower stations is essential for early warning of slope instability in the dam area. Interferometric synthetic aperture radar (InSAR) technology has been proven to provide long-term and efficient monitoring of reservoir bank slopes. The engineering experience shows that the surface deformation of the bank slope has a strong response to the reservoir water level change and rainfall, and the cyclic deformation is significant. However, the traditional InSAR deformation estimation method can only obtain the linear deformation rate of the monitored object, and ignoring the effect of reservoir water level change and rainfall on the slope will lead to large residual deformation, which seriously affects the accuracy of the InSAR deformation estimation of the reservoir slope.(Method)In this study, the cycle model and precipitation influence factor are introduced into the time series InSAR deformation modeling, and the InSAR deformation model taking into account the reservoir water level change and rainfall influence is constructed to replace the traditional mathematical empirical model, so as to better describe the deformation evolution law of slope of the reservoir bank in the process of InSAR deformation modeling. By directly estimating the unknown model parameters through the singular value decomposition (SVD) method and using the model parameters to calculate the deformation components caused by water level change and rainfall in the bank slope, the monitoring accuracy of the bank slope deformation can be improved and the prediction of bank slope deformation can be realized.(Result)Based on the improved method in this paper, the time-series deformation results of the Dawanzi-Qiluogou section of Baihetan Hydropower Station were obtained for a period of 31 months. The results show that the deformation in this area is dominated by a linear trend, and the maximum cumulative deformation reaches -155 mm during the period from January 2020 to July 2022, along with the change of the reservoir water level. The RMS of the residual high-pass deformation shows that the modeling accuracy of the improved model is improved by 12.5% compared with that of the traditional InSAR model. The in situ GNSS monitoring results show that the external accuracy of the deformation obtained by this method is ±2.9 mm.(Conclusion)In this paper, an improved time-series InSAR deformation estimation method is proposed for slopes in the bank area. Based on the new method, the time-series deformation results are obtained for a period of 31 months in the section of Dawanzi-Qiluogou. It is found that the slope deformation in the near-river area is larger than that in the far-river area, and the deformation is cyclic along with the change of reservoir water level, and there is a lag effect of 2 months relative to the date of the change of dry and rainy seasons. The method of this paper can replace the traditional InSAR method, and provide an important reference for the identification, monitoring and early warning of potential instability zones in the construction and operation of hydropower stations and other large-scale projects.

InSAR;deformation monitoring;Bank Slopes;Unstable;Time series modeling