## 4 The Deformation Detection Experiment and Results
### The Deformation Detection Experiment Results
All remaining single-look SAR images serve as secondary images, which are processed separately with the reference image, resulting in 256 interferograms for each of the five scenarios. Subsequently, phase filtering and phase unwrapping are conducted on the interferograms to derive the absolute phase. The phase filtering technique employed is temporal multi-look filtering with a look number of 256, effectively reducing noise in the interferometric phase while preserving resolution. Figure 13 presents the Differential Interferometric Phase (DIP) for each scenario following multi-look processing (the target area is magnified within the red box, where the data labels X and Y represent the azimuth and range coordinates of the target in the SAR image, respectively, with units in meters, and Index indicates the phase value of the target point in radians). It can be observed that the DIP of the target area, where deformation is simulated, exhibits significant changes. Moreover, as the deformation value increases, the changes in the DIP become more pronounced, while other regions within the scene do not demonstrate this characteristic. Additionally, the DIP value at the location of the corner reflector is marked in the figure; the increment displayed by this value correlates with the preset deformation increment of 2 mm (corresponding to approximately 0.42 rad), thereby confirming the accuracy of the experimental results. Figure 14 illustrates the phase distribution of the corner reflector before and after multi-look filtering, where the blue line represents the single-look phase prior to filtering, and the red line denotes the multi-look phase subsequent to filtering. Figure 12: Coherence coefficient distribution of the corner reflector targets. The multi-look phase exhibits a higher SNR compared to the single-look phase, thereby ensuring the accuracy of deformation detection. Consequently, the LOS deformation value is calculated based on the multi-look phase, with the calculation method detailed in Section 3.4. Figure 15 compares the detected LOS deformation values obtained from the CBS with the actual LOS deformation values. Additionally, Table 3 presents the errors between these two sets of values. (The actual LOS deformation value displayed here is \(-1.977\) mm (rather than \(-2\) mm), which represents the projection of the corner reflector's horizontal displacement of \(2\) mm onto the LOS of the CBS.) Based on the processing results of the measured data, the CBS demonstrates excellent performance in deformation detection. In the experiment, the deformation value applied to the corner reflector exhibits a linear change, which aligns well with the linear distribution of the multi-look phases presented in Figure 14. Furthermore, although the SNR of the single-look phases prior to filtering is relatively low, the stepped changes corresponding to the deformation values remain observable. This observation confirms the accuracy of the CBS in capturing phase changes. The trend of the detected LOS deformation values illustrated in Figure 15 closely corresponds to the actual LOS deformation values, with a maximum error of only \(-0.3437\) mm. This result indicates that the CBS is capable of accurately detecting the displacement of the corner reflector. In the experiment, the CBS was able to continuously observe the ground area at an interval of just \(2.5\) ms. This not only ensured the acquisition of sufficient data for processing, thereby enhancing the reliability of the deformation monitoring results, but also met the demands of tasks requiring rapid deformation rate observations due to the CBS's ultra-high observation frequency. A total of \(1280\) echo data points were processed during the experiment, taking \(79\) s in total. This allowed for real-time processing of the data obtained by the CBS, ensuring the timeliness of the observation tasks. Therefore, it  
Figure 13: Differential Interferometric Phase for each scenario (the red box represents the locally amplified target area). (**a**) \(2\) mm displacement.