InSAR and GNSS collaborative monitoring of land surface deformation in the coal mining subsidence areas in the middle Yellow River Basin

To address the limitation of a single monitoring technique in balancing large-scale spatial coverage and high-precision deformation measurement for land surface deformation monitoring in coal mining subsidence areas of the middle Yellow River Basin, this paper proposes a progressive collaborative monitoring method of InSAR and GNSS following an “area first, point later” approach. A large coal mine on the Loess Plateau of Northern Shaanxi is selected as the study area, aiming to achieve complementary advantages of the two techniques and improve the timeliness and accuracy of deformation monitoring in coal mining subsidence areas. Firstly, SBAS-InSAR technology is applied to process 12 scenes of LuTan-1 （LT-1） L-band SAR data （from December 2023 to December 2024） to obtain a large-scale time-series deformation field, identify deformation zones, and analyze their spatiotemporal evolution patterns. Secondly, taking the key deformation zones delineated by InSAR as targets, high-precision daily monitoring data from 20 GNSS stations are used to finely classify the land surface deformation stages and quantitatively obtain key parameters including cumulative subsidence, subsidence rate, and duration of each stage. The results show that: ① three major deformation zones （A, B, and C） are identified by InSAR, with a total area of approximately 1.98 km². The spatial distribution of these zones is highly consistent with the active mining faces during the monitoring period, and the subsidence centers migrate regularly with the advancement of mining faces. ② Based on GNSS daily monitoring data, the entire deformation process can be divided into three stages: the initial stage （averaging 54 days）, the active stage （averaging 59 days, accounting for over 90% of the total subsidence）, and the recession stage （averaging 262 days）. The whole process lasts an average of 367 days, with a maximum cumulative subsidence of 1 984.06 mm. ③ Influenced by coal seam thickness, burial depth, and coal pillar protection effects, the active stage deformation in the western zones A and B is intense and concentrated （with peak subsidence rates of 1 264.86 mm/month and 1 134.51 mm/month, respectively）, while the active stage in the eastern zone C is prolonged but with reduced intensity, and coal pillars exert a significant buffering and barrier effect on mining-induced stress. ④ The collaborative monitoring improves data timeliness from approximately 20 days （conventional leveling） to the hourly level, and increases the accuracy of deformation zone identification by about 40% compared to empirical methods. The vertical monitoring accuracy in large-gradient deformation areas is better than ±5 mm, and the error in deformation stage division is ≤±2 days, which is more than one order of magnitude better than that of empirical formula estimations. This study demonstrates that the collaborative mode of “areal scanning + point-based precise measuring” fully utilizes the complementary advantages of large-scale continuous monitoring by InSAR and high-precision real-time point monitoring by GNSS, significantly improving the timeliness, accuracy, and refinement of land surface deformation monitoring in coal mining subsidence areas. It provides reliable technical support and scientific basis for disaster early warning and ecological restoration in similar mining areas of the middle Yellow River Basin.