Recent Land Subsidence in the Vietnamese Mekong Delta derived from Advanced Sentinel-1 SAR Interferometry

The Vietnamese Mekong Delta (VMD) is facing several environmental challenges, including coastal erosion and land subsidence. Subsidence rates of up to several centimeters per year have been reported, which are an order larger than the regional sea level rise of about 3.3 mm/yr. The associated risks are an increased vulnerability to flooding, salinization of water resources and permanent inundation. Precise monitoring of land subsidence with high spatial and temporal resolution is essential to support the study of the associated causes and hazards as well as appropriate countermeasures. Here, we present results of land subsidence monitoring between 2017 and 2022 in the VMD based on Sentinel-1 Persistent Scatterer Interferometry (PSI). We used Sentinel-1 scenes from ascending and descending orbits and applied an advanced PSI approach. The advancements of the algorithm include the integration of Temporary Persistent Scatterers to derive the best possible Persistent Scatterer network for long time series. Furthermore, we developed a method to optimally integrate reference pixels in order to suppress spatially correlated noise in the subsidence time series. Due to a lack of well distributed geodetic references, we made use of an infrastructural reference network consisting of large bridges with deep foundation depths, which are nearly unaffected by subsidence. We present the derived subsidence rates and exemplary subsidence time series across the study area. Additionally, we highlight specific spatial and temporal features in the subsidence, which can be associated with land use characteristics and environmental influences.