## 3 Results
#### 3.1.2 Measured Data Experiment  
This subsection also uses the measured data to verify the difference between the multi-look compressive sensing method and the traditional L1 norm compressive sensing method. The measured data are from the airborne millimeter-wave dual-baseline InSAR system [27], as shown in Figure 3. This airborne millimeter wave InSAR system shown in Table 2 has three antennas with rigid connection, with an imaging resolution of 0.3 m, and InSAR's height accuracy meets the 1:5000 scale requirements for topographic mapping in difficult areas in China. In addition, more than 200 sorties were flown and more than 20,000 square kilometers of high-precision topographic mapping data were obtained with the airborne millimeter wave InSAR system, the multi-baseline mode of which has a unique advantage in processing InSAR data of complex topographies such as mountainous terrain and urban areas. The size of the measured data in Figure 3 is 1024 \(\times\) 1536, where 1024 represents the slant range direction (vertical axis in Figure 3), and 1536 represents the azimuth direction (horizontal axis in Figure 3). The SAR amplitude figure is shown in Figure 3a, the long baseline interferometric phase pattern is shown in Figure 3b, and the long baseline coefficient is shown in Figure 3c. In addition, the theoretical resolution of the height direction is \(\rho_{h}\approx\) 72.7m from [20]. The phase in the middle part of Figure 3b behaves phase flips in the opposite of the general phase fringes which is consistent with the same part of Figure 3c. Additionally, this part can be considered to be layover areas. The distribution of scattering points in the measured data is shown in Figure 4 using the information theory method [14]. The red parts in Figure 4a have two scatterers with one pixel, which is consistent with the same parts of Figure 3b,c. Two methods were used to process the same profile of data in the 700 th azimuth direction and the 600-800 th scope in the range direction, and the number of scatterers is shown in Figure 4b. Additionally, the number of views of the multi-look compressive sensing method is nine. The normalized amplitude result after processing is shown in Figure 5, and the height of the separated scatterers is shown in Figure 6. \begin{table}
\begin{tabular}{c c} \hline \hline
**Type of Radar** & **Millimeter-Wave InSAR** \\ \hline Radar frequency (GHz) & 35 \\ Off-nadir angle \(\theta\) (\({}^{\circ}\)) & 45 \\ Baseline length (m) & 0, 0.087, 0.313 \\ Baseline angle (\({}^{\circ}\)) & 10 \\ Slant range (m) & 3086 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: System parameters of airborne InSAR. Figure 3: Raw SAR data. (**a**) SAR amplitude figure; (**b**) Long baseline interferometric phase pattern; (**c**) Long baseline coefficients. The horizontal axes represent the azimuth direction, and the vertical axes represent the slant range direction. It can be seen from Figure 5 that the sparsity of the results solved by the traditional L1 norm compressive sensing method is significantly weaker than that of the multi-look compressive sensing method. However, it can be seen from Figure 6 that the scatterers solved by the traditional L1 norm compressive sensing method are disorganized and have poor reliability, while the scatterers solved by the multi-look compressive sensing method have a better degree of continuity, which is more consistent with the actual situation and provides higher reliability. Additionally, the difference in height of separated scatterers is lower than the theoretical resolution of the airborne InSAR system which has a certain high resolution in height direction estimation in layover areas. Figure 4: Number of scattering points. (**a**) Distribution of the number of scatterers, where the horizontal axes represent the azimuth direction, and the vertical axes represent the slant range direction.