# Surface Subsidence Monitoring in Kunming City with Time-Series InSAR and GNSS
###### Abstract  
Kunming city is located in the middle of Yunnan Province. Due to large-scale groundwater exploitation and urban development in recent years, this area has been affected by surface subsidence. In this paper, Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS) data are used to monitor the surface subsidence in Kunming city area for better analysis and understanding. The study used data of Sentinel-1A from 2018 to 2020 with atmospheric correction based on GACOS to calculate the average annual subsidence rate in Kunming city area, and the results show that the maximum subsidence rate is 48 mm/year. The subsidence obtained by InSAR is compared with the vertical deformation information obtained by eight GNSS stations in continuous operation in the study area. The subsidence rate trend show by the two methods is consistent, which further verifies the validity of InSAR data to reflect the local deformation. Experimental results shown that the eastern and northeastern Dianchi lake areas were affected by underground resources mining, and the induced surface subsidence characteristics were obvious, with the surface subsidence rate reachable 48 mm/year and 37 mm/year respectively. The Kunyang Phosphate Mine also had different degrees of mining subsidence disaster, with the maximum subsidence rate reached 36 mm/year. The subsidence rate of InSAR and GNSS has the same trend on the whole. However, GNSS sites are generally located in stable areas, the settlement amount obtained in the same time period is somewhat different from that of InSAR. InSAR; subsidence; time series; GNSS; GACOS 2022122752022122122122212  
regional subsidence, [PERSON] et al. monitored the subsidence velocity of the Karapinar Basin by using Sentinel-1 and COSMO-SkyMed SAR data [17]. [PERSON] et al. used TerraSAR-X data to obtain the monitoring results of surface subsidence in the coastal areas of Venice [18]. [PERSON] et al. used ENVISAT ASAR data to monitor the surface deformation around the Toktogul reservoir in Kyrgyzstan [19]. [PERSON] et al. used RADARSAT-2 data to monitor Wuhan and concluded that the surface subsidence was related to three factors: groundwater exploitation, subway excavation and urban construction [20]. In these cases, InSAR technology provides researchers with a reliable means of monitoring. introduction should briefly place the study in a broad context and highlight why it is important. Differential InSAR (D-InSAR) uses external DEM or three-track/four-track differential to monitor surface deformation. However, D-InSAR technology is prone to the interference of time and space discoherence, and its measurement accuracy is affected due to atmospheric factors, which is difficult to eliminate [21; 22; 23]. In order to overcome the shortcomings of D-InSAR, many scholars in China and other countries have carried out a series of researches on time series InSAR, such as Small Baseline Subset (SBAS) InSAR technology. This method is a time-series insar surface deformation inversion technique proposed by [PERSON] [24] in 2002. SBAS technique can reduce the influence of space-time discoherence by setting time and space thresholds, so as to screen out interference pairs with high coherence. This technique can make use of highly coherent targets of persistent scatterers (such as buildings) in the region to monitor the deformation of the region in a wide range, with accuracy up to millimeter [25]. Based on the above advantages, SBAS technology has been successfully applied to urban surface subsidence monitoring, landslide monitoring and mining subsidence monitoring [26; 27; 28; 29; 30; 31]. Although the SBAS-InSAR has made remarkable progress in monitoring subsidence accuracy, the observation data based on only one InSAR is too single. Based on the above background, this paper uses SBAS-InSAR method and adds GACOS for atmospheric correction to analyze the correction effect of GACOS on interference pairs delay error.