Study on the earth and rock-filled dam settlement monitoring in multi-SAR interferometry

In China, there are nearly 100,000 earth and rock-filled dams, which are essential water conservancy facilities for agricultural irrigation, food security, flood controlling, and power generation and so on. The periodically deformation monitoring for those dams are the key criterion to evaluate their safety. However, traditional surveying technologies such as levelling, total station and GNSS and some inner sensors (like fibers) for continuous real-time monitoring are costly and require large amounts of human resources.

In this paper, we evaluate the ability of the currently operating X-band and C-band SAR sensors on dam deformation monitoring and propose a conversion parameter to retrieve the dam consolidation settlement. According to the earth and rock-filled dam post-construction settlement mechanism, a dam settles due to the compaction effect of filling earth in the dam. While in SAR geometry, only the line-of-sight projection of the slope surface deformation is visible along the radar beam. In order to convert the deformation from SAR geometry to real 3D geometry, we proposed a method for converting the dam post-construction deformation from SAR light of sight to vertical direction, based on the geometrical parameters of the dam and the SAR sensor.

The experiments by both simulated and real cases in the Gongming reservoir of Shenzhen city in china are utilized to compare the deformation monitoring capability of various SAR sensors with different resolutions and to demonstrate the applicability of deformation conversion method. The simulation results show that the foreshortening of the slope greatly affects the slope deformation retrieval, for the small earth-rock filled dams with axis being parallel to the SAR heading direction, the conversion parameter between two slopes of dam maybe differ than 2~3 times. The real experiments, by both the differential interferogram and time series analysis, based on TSX, CSK and Sentinel-1 data in Shenzhen Gongming reservoir show that the high-resolution data have more precise results. The time series analysis of multi-SAR data from 2017 to 2021 are used to show full processing of the dam post-construction settlement. For the small dam which is nearly 30 meters high and 200 meters long, With the 1~3 meters resolution of TSX and CSK data, we can retrieve the dam  settlement from both the cross-section profile and the axis section profile. The Sentinel TOPS data sets with low resolution cannot fully retrieve the dam settlement and the results are underestimated.