Retrieving surface secondary subsidence in closed mines with time-series SAR interferometry combining persistent and distributed scatterers

The groundwater recovery in closed mines causes surface secondary subsidence or uplift, which threatens the safety of buildings around the mines. However, due to the long-lasting surface subsidence in closed mines, the coherence points selected by permanent scatterer (PS) interferometric synthetic aperture radar (InSAR) are not enough to reflect the spatio-temporal evolution pattern of surface subsidence. Therefore, this study proposes a distributed scatterer (DS) InSAR method by integrating statistically homogeneous pixels selection and phase optimization into PSInSAR. To prove the effectiveness of DSInSAR, PSInSAR is employed synchronously to obtain the surface subsidence of closed mines in Xuzhou, Jiangsu Province, based on 88 scenes Sentinel-1A images from October 2016 to October 2019. The results show that the spatial heterogeneity of surface subsidence (− 35 mm/year to +\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$+$$\end{document} 35 mm/year) in closed mines is obvious, the coherent point density of DSInSAR is 13.3 times that of PSInSAR, and DSInSAR retrieves three subsidence areas that PSInSAR missed. Moreover, the results of DSInSAR and PSInSAR are consistent, with a correlation of 0.92. Compared with the leveling data shows that the root mean square error (RMSE) of DSInSAR monitoring results is 3.81 mm, which is slightly higher than that of PSInSAR (RMSE: 3.84 mm). Finally, the difference between the surface subsidence of closed and mining mines was analyzed, which shows that the surface secondary subsidence of closed mines is complex, uneven, and diverse. Therefore, obtaining the long-term and complete surface subsidence of closed mines is of great significance to predict and prevent surface subsidence disasters.