# Spatial Baseline Optimization for Spaceborne Multistatic SAR Tomography Systems
## 5 Experimental Verification
### Baseline Optimization Method Verification  
As mentioned above, we can consider SMS-TomoSAR to be monostatic SAR, when \(N=1\). However, monostatic SAR does not exhibit the same-track vertical baseline length, which directly limits the baseline span of monostatic SAR. However, when given the number of flights \(M=7\), monostatic SAR has only six baselines, which is insufficient to image for high-precision height resolution. In Figure 11 and Table 4, based on the parameters in Table 1 and \(q=1.0,\ e=20\%\), the performance results of SMS-TomoSAR and monostatic SAR are given. The experiment showed only the results of monostatic SAR under \(S_{spun}=500\) m due to the limited baseline span for the same-track vertical baseline length. Figure 11: The imaging results of SMS-TomoSAR and monostatic SAR. Figure 10: Imaging performance results when \(e_{\max}=10\%,\ 20\%,\ 40\%\). From the results above, compared with SMS-TomoSAR, it is obvious that monostatic SAR had smaller height span and fewer baselines. This directly resulted in lower unambiguity height and worse PSLR and ISLR. For an urgent mission within a fixed time, monostatic SAR is not suitable. The proposed method could be used if monostatic SAR obtains the same number of baselines as SMS-TomoSAR by more flights. However, SMS-TomoSAR and monostatic SAR have different influences on some issues, such as spatial transmission error estimation and compensation, as well as deformation measurement. Consequently, in this paper, we focus mainly on the effect of the proposed method for SMS-TomoSAR. To further verify the validity, we used simulated data to provide tomographic images of scatterers located in the same cross-slant-range line, and obtained the image by inverting the model using the described techniques. Firstly, three isolated and coherent targets A, B, and C were simulated, and then an A and C simulated coherent targets located on the bottom and on the top, respectively, gave a distributed target B with a certain extension, but separated from the coherent target located on the bottom. The simulated target information is seen in Table 5 and Figure 12.  
According to the conclusion above, we selected \(q=0.8,\ 1.0,\ 1.2\) and \(e_{\max}=10\%,\ 20\%,\ 40\%\) based on Table 1. The simulation results are seen in Figures 13 and 14. \begin{table}
\begin{tabular}{c c c c} \hline
**Parameter (NDFT/CS)** & \begin{tabular}{c} **Monostatic SAR** \\ **(N = 1 \(B_{span}\) = 500 m)** \\ \end{tabular} & \
\begin{tabular}{c} **SMS-TomoSAR** \\ **(N = 3 \(B_{span}\) = 500 m)** \\ \end{tabular} &
\begin{tabular}{c} **SMS-TomoSAR** \\ **(N = 3 \(B_{span}\) = 1000 m)** \\ \end{tabular} \\ \hline Target height span (m) & \([-54.3,54.3]/[-53.2,53.2]\) & \([-184.7,184.7]/[-179.4,179.4]\) & \([-89.5,89.5]/[-89.4,89.4]\) \\ Rayleigh resolution (m) & \(16.02\) m/\(15.71\) m & \(16.36\) m/\(15.90\) m & \(7.93\) m/\(7.92\) m \\ Imaging height error & \((0.13\) m/\(45.0^{\circ})\) & \((0.49\) m/\(45.0^{\circ})\) & \((0.23\) m/\(45.0^{\circ})\) \\ and phase & \(/(0.08\) m/\(45.0^{\circ})\) & \(/(0.24\) m/\(45.0^{\circ})\) & \(/(0.21\) m/\(45.0^{\circ})\) \\ Unambiguity height (m) & \(108.5\) m/\(106.4\) m & \(369.4\) m/\(358.8\) m & \(179.0\) m/\(178.7\) m \\ PSLR (dB) & \(-0.000317-0.000282\) & \(-12.62468-12.31986\) & \(-13.60256/-13.40242\) \\ ISLR (dB) & \(-0.031460/-0.032658\) & \(-6.506870/-8.981114\) & \(-8.034666/-10.06845\) \\ \hline \end{tabular}
\end{table} 
Table 4: The imaging performance results of SMS-TomoSAR and monostatic SAR for the NDFT and CS algorithms. Figure 12: Simulated target. \begin{table}
\begin{tabular}{c c c} \hline
**Target** & **Complex Scattering Coefficient** & **Target nsr Height (m)** \\ \hline Target A & \(\gamma_{A}(s)=\exp(j\pi/4)\) & \(S_{0}=-100\) \\ Target B & \(\gamma_{B}(s)=\exp(j\pi/4)*\sin c(s)\) & \(S_{0}=0\) \\ Target C complex scattering coefficient & \(\gamma(s)=\exp(j\pi/4)\) & \(S_{0}=100\) \\ \hline \end{tabular}
\end{table} 
Table 5: Target information.