## 1 Introduction  
Surface subsidence is a type of geological disaster caused by a slow decline in the ground surface due to the action of natural or human factors. Uneven urban land subsidence severely threatens the safety of buildings and infrastructure, and affects the health and sustainable development of cities. Kunming is one of the cities in western China exhibiting relatively obvious surface subsidence. Historical leveling results indicate that the subsidence reached \(-227.5\) mm from 1985 to 1998. The mean subsidence rate was approximately \(-17\) mm/a, and the maximum subsidence rate reached \(-30\) mm/a in the area surrounding Xiaobanqiao [1]. In recent years, large-scale subway line construction and intensive real estate development in the deposition area near Dianchi Lake has led surface settlement to become increasingly serious, causing cracking damage to houses, road surface damage and other damage phenomena [2, 3]. Therefore, monitoring and analyzing the spatiotemporal variation in the land surface subsidence activity in the main urban area of Kunming on the north bank of Dianchi Lake is essential for disaster prevention and mitigation and for healthy urban development [4].  
Compared to the traditional leveling method, InSAR technology can measure surface deformation throughout the day, under all weather conditions, over a large range and with a high precision. InSAR technology has gradually become one of the main technical means to monitor the health of urban infrastructure; it has been widely used to monitor surface deformation worldwide [5, 6]. This technique can effectively identify and monitor deformation signals indicating the endangerment of urban safety, such as subsidence funnels attributed to groundwater exploitation [7; 8; 9], uneven deformation caused by fault activity [10; 11; 12], and surface subsidence due to infrastructure construction [13; 14; 15].  
Previous studies have analyzed the surface displacement in Kunming. [PERSON] et al. retrieved the surface displacement of Kunming from 2007 to 2016 using Advanced Land-Observing Satellite-1 (ALOS-1) data from 2007 to 2011, COSMO-Skymed data from 2011 to 2016 and Sentinel-1A data from 2015 to 2016. Two serious subsidence areas have occurred in Kunming city, concentrated in Guandu District and Xishan District. The cumulative displacements reached \(-210\) and \(-98\) mm, respectively, during the period of 2007-2016, and the maximum deformation rate was \(-35\) mm/a [16]. [PERSON] et al. used Sentinel-1A data from 2014 to 2016 to obtain land subsidence time series for Kunming city. The results revealed that there were four subsidence areas in Kunming city, including Xiaobanqiao, Dongju Xincun-Yulong Village, Dianchi International Exhibition Center and Zongshuying area. The area with the most serious surface subsidence was Xiaobanqiao, where the deformation rate reached \(-30\) mm/a [17]. [PERSON] et al. employed the Small Baseline Subset InSAR (SBAS-InSAR) technique to monitor the surface deformation of the north shore of Dianchi Lake in Kunming using Sentinel-1A data from 2018 to 2019. The results showed that the mean displacement rate of the north shore of Dianchi Lake could reach \(-30\) mm/a [18].  
To study land subsidence in the main urban area of Kunming in recent years, in this paper, two Sentinel-1 datasets from ascending and descending orbits covering Kunming from February 2018 to May 2021 were collected. The spatiotemporal evolution of large-scale surface subsidence of the north shore of Dianchi Lake in Kunming was obtained by using time-series InSAR technology. The reliability of our InSAR results was cross-validated by comparing the results from both ascending and descending orbits. The possible reasons for subsidence were also discussed.