## 3 Results  
### InSAR Results  
The results obtained using the PSI method for the time-series from 10 January 2023 to 30 November 2023 were divided into regional and local scales. We examined a 1 km buffer on each side of the study area at the regional scale to identify potential regional subsidence trends. Figure 9 shows the SAR image coherence, represented as gray and white pixels, where high coherence appears as white and low coherence as gray. The study area is marked with a blue square for reference. Due to vehicle movements on the road and nearby train construction activities, significant noise was introduced, leading to a loss of coherence. As a result, most pixels along the road failed to maintain coherence, and instead of the expected potentially high-resolution scatterers, only a limited number of coherent pixels were identified. Figure 10 shows the displacement velocity results from the PSI analysis along Road 431 with 811 PSI points. As observed in Figure 10, the average velocity across different sections of the road was \(-0.65\) cm/year at section A, with 408 PSI points; at section B, the average velocity was \(-1.09\) cm/year, with 88 PSI points; at section C, the average velocity was \(-0.69\) cm/year, with 35 PSI points; at section D, the average velocity was \(-0.062\) cm/year, with 212 PSI points. In the study area, the average velocity was \(-1.068\) cm/year, with 41 PSI points. While no clear regional trend was identified, an additional subsidence hotspot is noticeable in section B. The local scale: the study area in blue consists of 41 PSI points identified through the analysis, as shown in Figure 10. These points represent stable radar scatterers suitable for monitoring ground displacement. The eastern side of the study area demonstrates high coherence. In contrast, the western side suffers from significant decorrelation due to noise sources such as vehicle traffic on the road and nearby construction activities. These factors disrupt radar signals, limiting the reliability of measurements in the western section. As a result, the analysis was concentrated on the eastern side, where data quality is sufficient for accurate assessment. Figure 9: Coherence map of the study area with the road axis marked in red and the study area highlighted in blue. As highlighted in Figure 11, four representative points were selected at 30 m intervals along the road to represent the subsidence trends within the coherent section. The selection was based on maintaining coverage across the study area while capturing variations in subsidence. Figure 11: The distribution of coherent points in the study area highlights the eastern side, where coherence is maintained, and the representative points are selected for focused analysis at 30 m intervals. The yellow, red, and purple points exhibit vertical displacement of 0–1.5 cm, 1.5–2.5 cm, and 2.5–3.5 cm per year, respectively. The blue box is the study area. Figure 10: The displacement velocity map along Road 431 shows variations in surface subsidence, with the road axis marked in red. The yellow, red, and purple points exhibit vertical displacement of 0–1.5 cm, 1.5–2.5 cm, and 2.5–3.5 cm per year, respectively; the study area is highlighted in blue. The yellow boxes are the different sections A–D. Figure 12 illustrates the subsidence results for the selected points (A, B, C, D). Each scatter point in the graph corresponds to the ground's subsidence value, measured relative to previous acquisitions. The trends observed at these points indicate localized subsidence patterns, with variations in displacement magnitude over time. This focused analysis allows for a clear understanding of the subsidence behavior within the study area and highlights areas of concern for further investigation. As observed in Figure 12, a subsidence trend is shown at the representative points (A, B, C, D), with measured displacement rates of \(-1.1\) cm/year, \(-1.8\) cm/year, \(-2.7\) cm/year, and \(-0.6\) cm/year, respectively, during 2023, and relative to the reference point on 23 October 2023.