Two decades of settlement of Hong Kong International Airport measured with multi-temporal InSAR

The Hong Kong International Airport (HKIA) was constructed on a platform mainly reclaimed from the sea. The platform has experienced some significant settlement since its operation in 1998 due mainly to consolidation of the materials used in the land reclamation. Although some studies have been carried out to measure the settlement with techniques such as Interferometric Synthetic Aperture Radar (InSAR), the past studies have each only covered some limited time periods. Therefore, a complete history of settlement since the operation of the Airport has never been available to aid the understanding of the spatiotemporal behavior of the land settlement. We attempt for the first time to make full use of most of the available SAR data from multiple SAR sensors (ERS-2, ENVISAT ASAR, COSMO-SkyMed (CSK), and Sentinel-1A) to generate a settlement time series of the HKIA over 1998-2018 with an improved multi-temporal InSAR technique. In order to fill the time gaps between the different SAR datasets, a settlement model is developed based on the InSAR measurements. The results reveal both the spatial and temporal variations of the land settlement. They also show for the first time that the accumulative settlement reaches up to 40 cm over the past two decades. The settlement is largely associated with the material types used in the landfill works and the underlying alluvial sediments as some earlier research has indicated, and the stages of the reclamation works. The results are validated through cross-validation between the datasets and with leveling and GPS measurements on the Airport platform.