# An InSAR Interference Fringe-Matching Algorithm Based on Mountain Branch Points
## 3 Results  
### Experimental Data  
For experimental verification in this study, we utilized interference fringes that were acquired during actual flight tests. These flight tests were conducted in Baotou, Inner Mongolia, China. Figure 14a shows the specific location of the experimental site. The aircraft model is Modern Ark 60. The radar model is X-band dual-antenna radar with a bandwidth of 300 MHz. The radar is shown in Figure 14b. The radar is located at the bottom of the aircraft. Figure 14c shows the DEM data of the experimental scene. It can be seen that the terrain of the experimental site fluctuates greatly, which can verify the extraction effect of the proposed algorithm for terrain features. Flight-related parameters are shown in Table 2, where \(R_{min}\) is the nearest slant distance, \(S_{a}\) is the azimuthal resolution, \(S_{r}\) is the range resolution, and the remaining parameters are described in Section 2.2. \begin{table}
\begin{tabular}{c c c c c c c} \hline \(\boldsymbol{\lambda}\)/(cm) & \(\boldsymbol{H}\)/(m) & \(\boldsymbol{B}\)/(m) & \(\boldsymbol{\alpha}\)/(\({}^{\circ}\)) & \(\boldsymbol{R}_{min}\)/(m) & \(\boldsymbol{S_{a}}\)/(m) & \(\boldsymbol{S_{r}}\)/(m) \\ \hline
3.125 & 4876.300 & 1.048 & 45.601 & 3618.380 & 0.976 & 0.681 \\ \end{tabular}
\end{table} 
Table 2: Flight parameters. Figure 13: Comparison of improvement effects of descriptors. (**a**,**b**) Homonymous points of valley. (**d**,**e**) Homonymous points of ridge. (**c**,**f**) Euclidean distances of SIFT and the proposal descriptor. Figure 15a shows an SAR image obtained in the experiment. The number of azimuth points is 16,384, and the number of range points is 5500. A pair of SAR echo data points obtained in the experiment are registered to obtain the interference phase, as shown in Figure 15b. Classic interference phase denoising technology [40] is used to remove the noise. The interference fringe image after noise removal is shown in Figure 15c. To make the terrain feature more obvious, the phases of flat earth of the interference fringe need to be removed [41], as shown in Figure 15d. It can be seen that the interference fringes caused by the phase of the flat ground were removed, but there are still some fringes in the image, which is caused by the excessive undulation of the terrain. Due to the low resolution of the reference interference fringes, the actual interference fringes were down-sampled to ensure that they have the same proportion as the actual interference fringes. Figure 14: Experimental information. (**a**) Experimental site. (**b**) Radar and antenna. (**c**) DEM as well as longitude and latitude information corresponding to experimental data. The reference interference fringes were generated using DEM data that were derived from the publicly available NASA/ALOS PALSAR dataset. The resolution of the DEM data used was 12.5 m. Assuming that there are no errors in the POS data during the actual flight of the aircraft, the reference interference fringes for the corresponding region are generated according to the method in [42], as shown in Figure 16a. Compared with Figure 14f, it can be seen that the phase winding of the reference interference fringe is different from the real data. This is because the positioning and orientation system (POS) data of the actual flight are not ideal. This situation is in line with the actual situation and also tests the effectiveness of the algorithm. To verify the effectiveness of the algorithm in correcting the errors accumulated by the inertial measurement unit (IMU) during the flight of a real aircraft, two reference interference fringe datasets are produced, corresponding to a position error experiment and an attitude error experiment. The first dataset is generated by artificially adding position errors in the process of simulating interference fringes. The real position errors that exist in flight are simulated. The azimuth errors range between plus and minus 500 m, with an error interval of 25 m. A total of 41 datasets is generated.