## 1 Introduction  
Land subsidence caused by either natural or anthropogenic factors has become one of the serious environmental problems around the world regarding population expansion and economic growth, among which the coastal subsidence phenomenon is reported frequently in many countries, such as in Shenzhen and Xiamen (China), Urayasu (Japan), Sibari and Venice (Italy), Houston and New Orleans (USA) [1; 2; 3; 4; 5; 6; 7; 8]. Land subsidence makes coastal areas more vulnerable to coastal flooding, saltwater intrusion, shoreline erosion and infrastructure damage. Therefore, accurate measurements and detailed analyses are critical for natural hazard assessment and risk evaluation in the coastal regions. Shandong peninsula (36 deg12'-38 deg12'v, 119 deg30'-122 deg43' E), the largest peninsula in China, is located in the east of Shandong province. The peninsula is surrounded by the Bohai Sea to the north and the Yellow Sea to the east, occupying an area of 34,000 km\({}^{2}\). The Shandong peninsula consists of several cities with large populations and prosperous economies, including Binzhou, Dongying, Weifang, Yantai, Weihai, Qingdao and Rizhao (Figure 1). The Yellow River Delta (YRD), located between Laizhou Bay and Bohai gulf on the northern coast of Shandong peninsula, is the second largest river delta in China. However, due to the rapid urbanization, industrialization and economy growth, serious long-term subsidence of different magnitudes has occurred in this area. Firstly, overexploitation of natural groundwater resources, including fresh water and brine, has led to severe land subsidence for decades [9; 10; 11; 12]. Abundant natural brine deposits occur in the coastal zones where many salt factories were built along the coastline of Laizhou Bay and Jiaozhou Bay. Coastlines are dominated by numerous aquaculture factories created in the bays. Subivalence in the salt and aquaculture fields may intensify storm surges and river flooding, salinate groundwater, destabilize infrastructure, and accelerate shoreline retreat. Secondly, the YRD possesses the second largest oilfield in China, Shengli oilfield, where hydrocarbon exploitation since the 1970s [13] has resulted in severe land subsidence near oil exploitation centers [13; 14]. Thirdly, there are 31 bays with an area larger than 5 km\({}^{2}\) along the coast of the peninsula. Land reclamation activities over these bays caused new land subsidence, which has raised great public concerns for the safety of structures such as harbors, highways, airport runways, and underground facilities [2; 15; 16]. Interferometric Synthetic Aperture Radar (InSAR) measures various surface displacements by differentiating the phase observations between two complex radar images with a centimeter to millimeter accuracy over large area. It has been an excellent technique for investigating the distribution, magnitude, and temporal changes of the earth's surface deformation over the past two decades [17; 18]. Multi-temporal InSAR techniques, such as Persistent Scatterers InSAR (PSInSAR), Small Baseline Subset (SBAS) InSAR and SqueezeSAR, have been developed to map land surface displacements by  
Figure 1: Study area and coverage of radar data tracks superimposed on the Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) shaded topography map over Shandong peninsula, China. Black and blue rectangles indicate the Sentinel-1 coverage and the orange rectangle represents RADARSAT-2 coverage. Different colored lines represent different types of coastal zones alone the coastline. The right-bottom inset is the approximate location of Shandong Peninsula in China. minimizing temporal/spatial decorrelation and the artifacts inherent in conventional InSAR [19; 20]. The advanced time series InSAR techniques have facilitated coastal land subsidence monitoring in many regions [1; 21; 3; 4; 5; 20].