# C-SAR/02 Satellite Polarimetric Calibration and Validation Based on Active Radar Calibrators
## 4 Results and Discussion
### Polarization Calibration Accuracy Inspection and Analysis
Therefore, considering these three indicators collectively, the Group 2 polarization calibration accuracy was considered to be the best. As shown in Figure 1, to systematically analyze the stability of polarization calibration accuracy in the range direction, the ground validation equipment was divided into three regions: Region 1, Region 2, and Region 3. Region 1 contained CRs 1 to 4, Region 2 contained CRs 5 to 13, and Region 3 contained CRs 14 to 21. Region 2 is approximately 7 km away from Region 1 in the range direction, and Region 3 is approximately 7 km away from Region 2 in the range direction. The polarization calibration accuracy for the two device groups was calculated and statistically analyzed for each of these three regions (Figures 8-10). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Device** & **SCR/dB** & \(\Delta\delta_{hp}\)/dB & \(\Delta\beta\)/dB & \(\Delta\phi\)/\(d^{\circ}\) \\ \hline \multirow{4}{*}{Region 1} & CR-1 & 30.75 & \(-\)34.65 & 0.56 & \(-\)2.55 \\ \cline{2-6}  & CR-2 & 27.37 & \(-\)34.92 & 0.25 & \(-\)0.79 \\ \cline{2-6}  & CR-3 & 24.80 & \(-\)37.38 & 0.35 & \(-\)4.35 \\ \cline{2-6}  & CR-4 & 31.44 & \(-\)33.72 & 0.36 & \(-\)3.17 \\ \hline \multirow{4}{*}{Region 2} & CR-5 & 28.61 & \(-\)35.80 & 0.11 & \(-\)2.01 \\ \cline{2-6}  & CR-6 & 30.22 & \(-\)35.28 & 0.29 & 0.00 \\ \cline{2-6}  & CR-7 & 29.94 & \(-\)40.04 & \(-\)0.10 & \(-\)2.11 \\ \cline{2-6}  & CR-8 & 31.46 & \(-\)32.05 & 0.61 & \(-\)1.97 \\ \cline{2-6}  & CR-9 & 29.24 & \(-\)34.85 & 0.35 & \(-\)4.63 \\ \cline{2-6}  & CR-10 & 30.11 & \(-\)33.68 & 0.51 & \(-\)0.99 \\ \cline{2-6}  & CR-11 & 28.93 & \(-\)30.08 & 0.43 & \(-\)4.10 \\ \cline{2-6}  & CR-12 & 28.52 & \(-\)27.00 & 0.22 & \(-\)7.49 \\ \cline{2-6}  &Figure 8: Polarization isolation metrics corresponding to different device groups. (**a**) Group 1. (**b**) Group 2. (The different colors are for differentiation, the hollow squares refer to the average value, and the diamonds indicate the value of each equipment indicator. The following are similar). Figure 9: Amplitude imbalance metrics corresponding to different device groups. (**a**) Group 1. (**b**) Group 2. From Figures 8-10 and Tables 9 and 10, for both Group 1 and Group 2, there was no significant difference in the amplitude imbalance \(\Delta f\) or phase imbalance \(\Delta\phi_{f}\) calculated using the trihedral CRs deployed at three different ranges. The values were all superior to the development requirements of the C-SAR/02 satellite, which specifies that the amplitude imbalance should be better than \(\pm\)0.5 dB and the phase imbalance should be better than \(\pm\)10\({}^{\circ}\). However, polarization isolation only met the requirement of 35 dB specified in the design requirements of the C-SAR/02 satellite when using equipment within Region 1 for validation. Moreover, as the distance between the CRs and ARCs used for calibration increased in the range direction, the error in the calculated polarization isolation \(\Delta\delta_{ln}\) also increased. This is consistent with the results of [PERSON] [30]. Therefore, in subsequent polarization calibration experiments, further research can be conducted to mitigate the effects of different ranges and eliminate this issue. The polarization response characteristics to some extent reflect changes in the radar receiving power of targets under different polarization transmit-receive combinations, and  
Figure 12 illustrates the polarization response characteristics of CR-1 before and after calibration using Group 1. After calibration, the polarization response of the trihedral CR closely resembled the ideal polarization response diagram shown in Figure 12. The co-polarization receiving power reached its maximum at an ellipticity angle of \(\chi=0\), indicating the maximum response to linearly polarized electromagnetic waves, while it reached its minimum at \(\chi=\pm\frac{\pi}{4}\), indicating the minimum response to circularly polarized electromagnetic waves. The situation was reversed for cross-polarization receiving power.