## 1 Introduction  
With the urbanization and economic development in coastal areas, land resources are becoming increasingly scarce. To meet the development needs of coastal cities, humans have to reclaim land from the seaside all over the world, such as Shenzhen (China), Shanghai (China), Urayasu (Japan), New Orleans (USA), and Venice (Italy). All of those cities [1; 2; 3; 4; 5] have suffered from the land subsidence hazards due to long-time and gradual soil compaction on reclaimed land, which would cause damage to important infrastructures (e.g., airports, roads, buildings, and metros) and pose a great threat to the environment and public safety [6]. Therefore, monitoring, analyzing, and controlling the subsidence on reclaimed land is a crucial task not only to ensure the safety of citizens' life and property, but also to support the sustainable development of coastal areas. Xiamen Xiang'an New Airport (XXNA), one of the most important international airports in China, is built on Dadeng Island in Xiamen, Fujian Province. XXNA was scheduled to start construction in 2016, enter service in 2020, and complete construction by 2045 [7]. The planning area of Dadeng Island reaches 43 km\({}^{2}\), and about 65% of the land is reclaimed from the sea. According to previous studies [7; 8], due to the soil consolidation of the underlying unconsolidated marine sediments [9], XXNA is undergoing significant and non-uniform subsidence on reclaimed land during its construction. Therefore, it is important and necessary to continuously monitor ground subsidence at XXNA and determine potential subsidence damage during its construction and for future airport operation. Traditional in-situ measurements, such as leveling and Global Navigation Satellite System (GNSS), have been widely employed in ground subsidence monitoring with high accuracy. However, they cannot acquire continuous and dense ground subsidence measurements with a large-scale coverage at a low cost [10; 11]. Over the past decades, interferometric synthetic aperture radar (InSAR) technique has been proven to be a powerful geodetic technique to measure surface displacements with high-accuracy. It has been successfully applied in city subsidence detection [12; 13; 14], landslides monitoring [15; 16; 17], earthquake displacements measurements [18; 19; 20], etc. With the advantage of weather independence, wide coverage, high resolution, and high accuracy [21; 22; 23], InSAR technique has made many achievements in airport and reclaimed land subsidence monitoring. To monitor the subsidence in airports, [PERSON] et al. [24] and [PERSON] et al. [25] investigated residual settlement of the reclaimed foundation at Hong Kong International Airport by InSAR technique. [PERSON] et al. [26] employed high-resolution TerraSAR-X images to study the subsidence characteristics and driving forces of subsidence on Pudong International Airport from 2011 to 2012. [PERSON] et al. [27] applied a multi-temporal InSAR method to investigate the subsidence on Kuala Lumpur International Airport with Sentinel-1 images from 2014 to 2017. [PERSON] et al. [28] used high-resolution Cosmo-SkyMed SAR data from 2017 to 2019 at Beijing Capital International Airport to diagnose the subsidence hazard. In terms of monitoring reclaimed land subsidence, [PERSON] et al. [1] applied multi-temporal InSAR method to investigate coastal reclaimed land subsidence in Shenzhen by an ENVISAT ASAR ascending and descending orbits dataset both acquired from 2007 to 2010. [PERSON] et al. [2] determined coastal subsidence in Shanghai combined with historical reclamation activities by TerraSAR-X, ALOS PALSAR, and ENVISAT ASAR images from 2007 to 2010. [PERSON] et al. [3] investigated land reclamation in the coastal city of Urayasu by combining the ERS-1/-2 and ALOS-2 PALSAR-2 datasets from 1993 to 2017. [PERSON] et al. [8] employed SBAS-InSAR technique to determine the temporal and spatial evolution of ground settlement at XXNA combined with land reclamation (with Sentinel-1 images from 2015 to 2018).