## 4 Experimental Results and Analysis  
### Experimental and Results Analysis  
In the monitoring area of 590 km\({}^{2}\) in the main urban area of Fuzhou, based on TerraSAR-X data (image matrix of 14,500 \(\times\) 13,000 pixels), a dynamic rule grid partitioning strategy (grid size of 1200 \(\times\) 1200 pixels, overlap of 300 pixels, overlap rate of 25%) was applied to divide the entire region into 210 sub-blocks (Figure 4a). After an adaptive adjustment, the maximum height of the edge sub-blocks was 1900 pixels, and the maximum width was 1300 pixels, while the other sub-blocks maintained the standard size. Using a dual threshold selection method with amplitude deviation (\(D_{A}\leq 0.65\)) and average coherence (\(\overline{\gamma}\geq 0.5\)), the maximum number of candidate points in a single sub-block was 396,800 (Figure 5b), with the corresponding spatial density reaching 88,742 points/km\({}^{2}\). The total number of processed points reached 23,837,354, and after de-duplication in the overlapping regions, 13,867,836 PS candidate points were retained (Table 1), with an average density of 25,000 points/km\({}^{2}\) across the entire region. Under the 32 GB memory limitation of the machine, this method significantly surpassed the data-bearing limits of the traditional global methods. Based on the candidate point selection strategy described in Section 2.2.1, the distribution differences of the initial PS candidate points in the overlapping regions of each sub-block were significantly improved by global merging: after updating the overlapping regions through additional selection (Figure 5c), the number of candidate points in each sub-block increased by an average of 1600 points (a growth rate of 4.5%), providing sufficient redundant observations for subsequent stitching. By setting the overlap region validity threshold to \(\tau_{\text{overlap}}=500\), 494 valid overlap regions were selected (the valid overlap relationships of the sub-blocks are shown in Figure 6). For example, sub-block 75 (located in the sixth row and fifth column) had valid overlaps with seven adjacent sub-blocks (the overlapping sub-block indexes were 60, 61, 62, 74, 76, 89, and 90), indicating that it was in a core hub position within the connected components. Based on graph theory and connected component analysis, nine independent connected components were identified across the entire region. Among them, connected component 1 contained 19 isolated sub-blocks (which were not connected with other  
Figure 4: SAR data spatiotemporal baseline distribution: (**a**) TerraSAR-X; (**b**) Sentinel-1. sub-blocks due to PS point absence or invalid overlap regions), while connected component 3, the core connected domain, covered 157 sub-blocks (which accounted for 75.1% of valid overlapping sub-blocks) and formed the main deformation monitoring network for the entire region. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Initial Sub-Block Results** & \
\begin{tabular}{c} **Traditional Stitching** \\ **Method** \\ \end{tabular} &
\begin{tabular}{c} **Proposed Stitching** \\ **Method** \\ \end{tabular} \\ \hline Number of sub-blocks & 202 & 157 & 202 \\ (with PS points) & 12,921,707 & 12,204,302 & 12,921,707 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Statistics of sub-blocks and PS points for different stitching methods. Figure 5: Sub-block division and PS candidate point distribution results. (**a**) Global sub-block division and PS candidate point distribution map (green rectangles are sub-blocks, blue diagonal hatching areas are overlapping regions, and red dots are PS candidate points, with an enlarged view of the black rectangle area on the right). (**b**) Distribution map of the initial PS candidate points for each sub-block. (**c**) Distribution map of the increased PS candidate points for each sub-block. The independent PSInSAR processing of each sub-block yielded a total of 21,694,364 cumulative PS points.