## 4 Discussion  
(1) Subsidence depth extraction based on D-InSAR technique  
In this paper, the cumulative surface collapse volume in the study area from 2017 to 2021 was extracted based on D-InSAR technology, and it was found that the maximum collapse volume was mainly concentrated in the southwestern and central part of the Zhaogu Mining Area and the southern part of the Zhaogu No. 2 Mine. Collapse basins occur in the central part of Zhaogu No.1 Mine and the southwestern and southern parts of Zhaogu No.2 Mine, and their extent exceeds that of the extraction zone. In particular, the collapse volume in the southwestern part of Jitun Township of Zhaogu No.1 Mine is also large, and the largest collapse basin is formed in the central part of Zhaogu Township. The southern part of Beiyunmen Township in Zhaogu No.2 Mine has the most serious collapse, in which the perennial collapse water accumulation area is out of coherence in D-InSAR processing, and the collapse volume cannot be obtained, considering that the scope of the collapse basin is usually larger than the scope of the air-mining area, especially in the multilayered horizontal mining method. Combined with the field surveys and research, it is possible  
Figure 12: Comprehensive management planning map of Zhaogu Mining Area subsidence area. to delineate all of these water accumulation areas and a certain range of areas around them as the collapse zone, but for these collapse zones, follow-up monitoring should be strengthened to observe the changes, especially the changes in water level and geological structure. In addition to this, this paper has certain advantages based on D-InSAR technology to extract the depth of collapse in the Zhaogu Mining Area. D-InSAR technology has the advantages of high spatial resolution, all-day, large coverage area, low cost, etc., which is especially suitable for large-area and rapid surface deformation monitoring. It fills the gap of traditional level measurement and GPS measurement technology, can monitor and record the cave-in process in the mine area in real time, and is more suitable for the 2017-2021 cave-in depth monitoring study of the Zhaogu Mining Area carried out in this paper, so as to provide an important indicator for the subsequent assessment of the degree of ecological environment damage in the mine area. (2) Evaluation of the degree of land destruction in the collapse zone based on a fuzzy comprehensive evaluation model with the improved G1 method  
At present, there are relatively mature methods for evaluating land damage in coal mining subsidence areas. For example, [PERSON] et al. [38] combined the limit condition method and the evaluable method to evaluate the degree of land damage in subsidence areas. However, the evaluation results derived from these methods are not scientific and intuitive enough, resulting in the results of the classification of the degree of land destruction within the subsidence area not being in line with the actual situation of the land and a lack of guidance for the actual management of the subsidence area. In order to evaluate the land destruction situation in the subsidence area more accurately and intuitively, this paper improves the weight determination method of the fuzzy comprehensive evaluation model and establishes a fuzzy comprehensive evaluation model based on the improved G1 method to evaluate the degree of land destruction in the subsidence area. Based on the results of the evaluation of the degree of land destruction in the subsidence area, and in combination with different land types, a subsidence area management model suitable for the Zhaogu Mining Area was formulated to provide a theoretical basis and data support for the management of the subsidence area in the Zhaogu Mining Area.