# Surface Subsidence Monitoring in Kunming City with Time-Series InSAR and GNSS
## 5 Conclusions  
In this study, a total of 35 Sentinel-1A images during 22 March 2018-24 December 2020 were used for SBAS processing, and the observation data of 8 CORS stations during 2019-2020 were used to monitor surface deformation in the study area It can be seen from the data processing results that the two different monitoring methods have the ability to monitor the surface deformation no matter from the region or the site. This study can draw the following conclusions.  
1. The surface deformation of Kunming City was monitored by GACOS-assisted SBAS technology, and the standard deviation of STD was corrected by 76.8%. The overall subsidence rate of Kunming City was obtained in the range of \(-\)48 mm/year-26 mm/year.
2. The main settlement areas are Fuhai-Hewei village- Yuhu village, Convention and Exhibition Center, Xiaobanqiao-Guangwei village, Pingzheng village-Sanjieqiao area and Kunyang Phosphate Mine. Fuhai-Hewei Village- Yuhu Village area, Convention Center area, Xiaobanqiao-Guangwei Village area, Pingzheng Village-Sanjie Bridge area and Kunyang phosphate mining area. The maximum subsidence rate reached \(-\)35 mm/year. The subsidence factor is related to the compression of soft soil layer caused by large-scale development projects and the exploitation of groundwater.
3. The observation data of 8 CORS stations during 2019-2020 were calculated, and King interpolation was performed on them. The results were compared and verified with the SBAS results in the same period. The maximum _RMSE_ value was 6.20 and the minimum _RMSE_ value was 0.34.
4. Since the accuracy of SBAS and CORS inversion is not in the same order of magnitude, the jump of CORS solution is relatively clear. The settlement results of different time series have some systematic deviation.  
Considering the factors of surface deformation in Kunming city, it is mainly due to the excessive exploitation of groundwater, excessive urban construction load and underground mining of mineral resources. The deformation area is mainly distributed in the eastern and northeastern Dianchi Lake and Kunyang Phosphate Mine area, which seriously restricts the urban development process. Therefore, relevant departments should pay attention to the deformation area, strengthen the real-time monitoring and formulate relevant prevention and control measures.  
Designed the experiment, S.Z.; methodology, X.Z., S.G. and Y.L.; carried out the experiment. S.Z.; analyzed the experimental results, S.Z. and C.L.; participated in the discussion of the experimental conclusion, S.Z., Y.L. and S.G.; resources, X.Z. and K.S.; writing--original draft preparation, S.Z.; writing--review and editing, S.Z.; visualization, C.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (No: 42161067).  
Not applicable.  
The data used to support the findings of this study are available from the corresponding author upon request.  
We thank the European Space Agency for providing the Sentinel-1A SAR data freely. Thanks to [PERSON] of Yunnan Basic Surveying and Mapping Technology Center for providing Kunming city CORS data, which provides available validation data for this paper.  
The authors declare no conflict of interest.