## 2 Materials and Methods  
### Study Area and Data  
The research domain chosen for this investigation was the initial excavation zone (110,801) situated in East Area 1 of the Banji Coal Mine, Anhui Province. The first mining face 110,801 extends over a strike distance of 1237 m and displays a dip width of 280 m. The angle of inclination of the coal seam varies from 0\({}^{\circ}\) to 15\({}^{\circ}\), with an average dip angle of 8\({}^{\circ}\). Additionally, the coal seam manifests a thickness ranging from 1 m to 3.7 m, averaging at 2.5 m. The thickness of the overburden bedrock spans from 30 m to 330 m, with an average thickness of 130 m. The depth of the lower boundary of the coal seam ranges from 650 m to 834 m, with an average depth of 767 m. To enable monitoring of surface deformation, two observation lines, one along the strike and the other along the dip, were established above the surface. The strike observation line accommodated a total of 98 monitoringpoints, spaced between 20 m and 60 m apart. Similarly, the dip observation line included 92 monitoring points, spaced between 20 m and 40 m apart. The precise geographical location of the research area is illustrated in Figure 1.  
The SAR data utilized in this study were acquired from ESA's Sentinel-1A satellite, equipped with a C-band microwave sensor that revisits the area every 12 days. A total of 38 SAR images from ascending orbits, spanning the period from 10 April 2021 to 28 June 2022, were carefully chosen for this study. All pertinent parameters related to these SAR images are presented in Table 1. Additionally, the external DEM used in this study was selected from the shuttle radar topography mission (SRTM) data, providing a resolution of 30 m. The UAV data were acquired on two specific dates: 10 April 2021 and 28 June 2022, utilizing the DJI Matrice 300 RTK UAV (DJI, Shenzhen, China) equipped with a five-lens V2 tilt camera(SHARE, Shenzhen, China). The outdoor data collection scenario for the drone is shown in Figure 2. The drone missions were carried out at a skyward elevation of 159.8 m, with a ground resolution of 2.5 cm. During the flights, an 80% heading overlap rate and a 70% side-to-side overlap rate were achieved, ensuring comprehensive coverage of the study area. The main parameters pertinent to the UAV data collection are listed in Table 2. The monitoring points were subjected to routine surveillance for surface settlement using precise level and GNSS measurement techniques, conducted on the respective dates of 10 April 2021 and 28 June 2022, thus obtaining the plane coordinates and elevations of the monitoring points for both phases. The leveling survey was conducted to meet the precision standards of a third-class leveling survey, ensuring that the average elevation error for each survey did not exceed 3.5 mm. Furthermore, the total error in elevation observations for each kilometer after leveling fell within the specified range of \(\pm\)6.0 mm, as stipulated by the requirements for a third-class leveling survey. The planar connection measurement was conducted using GNSS technology, with a maximum error in the planar point position not exceeding 2.0 cm and an average error remaining within 1.5 cm. These measurements align with the precision requirements of the subsidence observation project.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Datatype** & **Production Mode** & **Polarization Mode** & **Orbit Direction** & **Breadth (km)** & **Range Resolution (m)** & **Azimuth Resolution (m)** \\ \hline SLC & IW & VV & Ascending & 250 \(\times\) 250 & 5 & 20 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Parameters of Sentinel-1A images.  
Figure 1: The geographic position of study area, working face, and monitoring points.