# High-Resolution and Wide-Swath 3D Imaging for Urban Areas Based on Distributed Spaceborne SAR
## 3 Experiments and Results
### The Results of Range Ambiguity Resolution and HRWS 3D Imaging
Then, the weighted vector of the radar corresponding to each range moment is calculated to make the center of the receiving beam point exactly to the target location, the correct beam direction is obtained, and multi-channel range ambiguity resolution is realized. Next, precise image registration is performed on the ambiguity resolution image. As shown in Figure 14b, the interferometric phase is uniform even after range ambiguity. After the interferometric phase, the phase quality map needs to be calculated to evaluate the quality of the interferometric phase, and the coherence coefficient map is the most commonly used, whose calculation formula is shown below:  
\[Q_{\text{corr}}=\frac{\left|\sum\limits_{m=1}^{M}\sum\limits_{n=1}^{N}s_{1}(m, n)s_{2}^{*}(m,n)\right|}{\sqrt{\sum\limits_{m=1}^{M}\sum\limits_{n=1}^{N}\left|s_{1}(m, n)\right|^{2}\sum\limits_{m=1}^{M}\sum\limits_{n=1}^{N}\left|s_{2}(m,n) \right|^{2}}} \tag{17}\]  
The Coherence coefficient before and after the range ambiguity resolution is shown in Table 2, where \"1-2\" represents the correlation coefficients of the interferometric phases of channel 1 and channel 2. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Channel** & **Before Range Ambiguity Resolution** & **After Range Ambiguity Resolution** \\ \hline
1–2 & 0.5357 & 0.9861 \\
2–3 & 0.4751 & 0.9860 \\
3–4 & 0.5692 & 0.9861 \\
4–5 & 0.5596 & 0.9861 \\
5–6 & 0.6005 & 0.9860 \\
6–7 & 0.6290 & 0.9860 \\
7–8 & 0.5897 & 0.9864 \\
8–9 & 0.5695 & 0.9867 \\
9–10 & 0.5887 & 0.9867 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The Coherence coefficient before and after range ambiguity resolution. Figure 10: The results of range ambiguity resolution and 3D imaging of area A: (**a**) the SAR image with range ambiguity; (**b**) the near scene after range ambiguity resolution; (**c**) the far scene after range ambiguity resolution; (**d**) the 3D imaging result of (**b**); and (**e**) the 3D imaging result of (**c**). Figure 11: The results of range ambiguity resolution and 3D imaging of area B: (**a**) the SAR image with range ambiguity; (**b**) the near scene after range ambiguity resolution; (**c**) the far scene after range ambiguity resolution; (**d**) the 3D imaging result of (**b**); and (**e**) the 3D imaging result of (**c**). Figure 12: The results of range ambiguity resolution and 3D imaging of area C: (**a**) the SAR image with range ambiguity; (**b**) the near scene after range ambiguity resolution; (**c**) the far scene after range ambiguity resolution; (**d**) the 3D imaging result of (**b**); and (**e**) the 3D imaging result of (**c**). Figure 13: The results of range ambiguity resolution and 3D imaging of area D: (**a**) the SAR image with range ambiguity; (**b**) the near scene after range ambiguity resolution; (**c**) the far scene after range ambiguity resolution; (**d**) the 3D imaging result of (**b**); and (**e**) the 3D imaging result of (**c**). It can be seen from Table 2 that before the range ambiguity resolution, the average coherence coefficient between the adjacent channels is 0.5845, and the interferometric phase quality is poor. After the range ambiguity resolution, the average coherence coefficient between the adjacent channels becomes 0.9864, which greatly improves the interferometric phase. After the range ambiguity resolution, image registration, channel imbalance calibration, sparse recovery, and high-dimensional focusing, the 3D imaging point cloud of the whole area is illustrated in Figure 15, where color represents height. It can be observed that the method proposed in this paper can realize HRWS 3D imaging of a large area. Figure 14: The interferometric phase before and after the range ambiguity resolution of the SAR image: (**a**) before range ambiguity resolution and (**b**) after range ambiguity resolution. Figure 15: HRWS 3D imaging result of the study area.