Spatial Characteristics of Land Subsidence in Architectural Heritage Sites of Beijing’s Royal Gardens Based on Remote Sensing

Beijing’s royal gardens represent the highest artistry in the artificial modification and utilization of natural hill and lake landforms. They also encompass the most concentrated ancient Chinese royal architectural heritage complexes. Their sustainable development has drawn significant attention, particularly in detecting and identifying areas of land subsidence and analyzing its influencing factors, which are crucial for preserving Beijing’s royal architectural heritage. This study employed time-series interferometric synthetic aperture radar (InSAR) technology to collect 148 SAR datasets from 2019 to 2023. It compares the persistent scatterer (PS)–InSAR and small baseline subset (SBAS)–InSAR techniques for cross-validation analyses to systematically assess the spatial characteristics of land subsidence of the most valuable architectural heritage complexes in the four most representative Beijing’s royal gardens. The study identified several areas with concentrated subsidence. Further analysis of the types of ancient building locations reveals that buildings situated in hilly areas (Type C), waterside buildings (Type A1), and near-water buildings (Type A2) are more significantly affected by land subsidence. Through an analysis of the causes of subsidence, it was found that, affected by the “excavating lakes and piling hills” landscape modification method and the utilization of natural hilled terrain approach, the subsidence observed in most Type C architectural heritage complexes within the study area may be associated with the Holocene sediments in the underlying soils beneath the shallow foundations of architectural heritage, localized bedrock instability caused by exposure and weathering, and slope instability. Type A building complexes’ subsidence and localized uplift may be associated with Holocene sediments beneath their foundations. The cross-comparison between SBAS-InSAR and PS-InSAR provides a reference framework for exploring land deformation research in architectural heritage sites where detection methods are constrained.