## 4 Results
### Deformation Results in The YRD  
Yellow River Delta (YRD), including Regions A-F and Guangrao city, has been undergoing the most severe land subsidence over the Shandong peninsula, so the SBAS technique was applied to both ascending and descending datasets individually to retrieve the annual deformation rate and deformation time series along the LOS direction (Figure 4). Figure 2: Vertical deformation velocity of the whole Shandong peninsula derived from Sentinel-1 datasets with different tracks and acquisition geometries (ascending and descending). The red rectangles labeled from A to K indicate the deformation areas along the coastline. The green rectangle box shows the Guangrao subsidence area. Figure 4a,b show the LOS annual deformation rate maps from March 2017 to June 2019 acquired from ascending and descending datasets, respectively. The two maps show similar deformation patterns with the maximum LOS deformation rate as large as 260 mm/a in Region C. Slightly different patterns and magnitudes can also be seen in some regions, which were caused by the different LOS imaging geometries of the ascending and descending tracks. Compared to the previous studies [10; 11; 14], there are two notable spatial changes: (1) before 2016, the subsidence mainly occurred in the Shengli oilfield and Gudong oilfield, located in the Xicheng district and the southeast of Region C, respectively. However, our measurements did not show any obvious deformation, as the two oilfields mentioned above had been closed since 2016; (2) Regions A, B, C and D are the newly detected deformation centers from this research. Figure 4: Annual LOS deformation maps spanning from 2016 to 2019 derived from (**a**) ascending Sentinel-1 (Path 69), and (**b**) descending Sentinel-1 (Path 76) datasets using SBAS technique. Figure 3: Histogram of deformation rate difference in the vertical direction derived from different Sentinel-1 SAR datasets. (**a**) Path 3 Frame 470 vs. Path 98 Frame 118. (**b**) Path 3 Frame 470 vs. Path 76 Frame 467. 2-D Deformation Result  
To estimate the 2-D deformation time series, i.e., vertical and east-west deformation components over the YRD, InSAR measurements from the ascending Path 69 and the descending Path 76 are calculated with the MSBAS technique. The north-south deformation component is negligible due to the low sensitivity of near-polar orbiting sensors. In this case, the satellite parameters for the heading angles of ascending and descending Sentinel-1 track are \(-13.2^{\circ}\) and \(-166.8^{\circ}\), respectively, and the average incidence angles of ascending and descending track are \(33.7^{\circ}\) and \(33.9^{\circ}\), respectively. The vertical and east-west deformation rate maps of the overlapped areas of ascending and descending SAR images are shown in Figure 5a,b, respectively. Nine typical feature points (a-i), located in the subsidence centers (Figure 5a), are selected to analyze the time series deformation from March 2017 to March 2019, which are shown in Figure 6. It can be found from Figures 5 and 6 that the vertical deformations are much larger than the east-west deformations, which confirms that the vertical movements dominate the deformation fields in the YRD. Points a and b are located in the subsidence center in Region B, points c and d are in Region C, points e, f and g are in Region D, and points h and i are in Region E. The 2-D deformation time series measurements show a moderate linear deformation during the two years. The maximum cumulative deformation reached \(-450\) mm in the vertical direction at point e and reached \(100\) mm in the east-west direction at point b during the observation interval (Figure 6).