Abstract: Time baseline plays an important role in temporal InSAR deformation extraction. Aiming at the problem of difficult extraction of deformation information in mountainous areas with high vegetation cover and water content and large topographic relief, the historical image data of Sentinel-1A radar satellite from January 2019 to December 2020 are acquired with Pingzhai Reservoir near Guiyang as the study area, and different time baseline sets are constructed to compare and analyse the extracted surface deformation information. The baseline conditions that are most suitable for the extraction of deformation in the study area are selected by the principle of shortest time baseline sum, and the subsidence rate of the study area for two years is obtained based on the SBAS-InSAR technique. The results show that the most accurate deformation information is extracted from the 60 d time baseline set in the study area, and there are fewer misjudgments and omissions than other time baseline sets. The relationship between the temporal variation of dam deformation and rainfall is also analysed in the context of the average rainfall data from 2019 to 2020 in Guiyang and geometric level monitoring data. It is concluded that there is a strong correlation between rainfall and dam deformation, and it is also concluded that the deformation information extracted based on the SBAS-InSAR technique is convergent with the level monitoring results.

Key words: time series InSAR, time basis, deformation monitoring, coherence, dam