# C-SAR/02 Satellite Polarimetric Calibration and Validation Based on Active Radar Calibrators
## 4 Results and Discussion
### Polarization Calibration Accuracy Inspection and Analysis
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{2}{c}{**Device**} & \multicolumn{1}{c}{**HH**} & \multicolumn{1}{c}{**HV**} & \multicolumn{1}{c}{**VH**} & \multicolumn{1}{c}{**VV**} \\ \hline \multirow{8}{*}{Region 3} & CR-14 & 0.8902\(\angle\)0.66\({}^{\circ}\) & 0.0003\(\angle\)171.00\({}^{\circ}\) & 0.0004\(\angle\)58.51\({}^{\circ}\) & 1.0000\(\angle\)0.00\(\arcsin\) \\ \cline{2-6}  & CR-15 & 0.9800\(\angle\)1.47\({}^{\circ}\) & 0.0006\(\angle\)26.67\({}^Polarization isolation refers to the ratio of the image power of the cross-polarized channels (HV or VH) to the image power of the co-polarized channels (HH or VV) in the image after polarization calibration. \[\Delta\delta_{hv}=10*\log_{10}\left|\frac{\delta_{hv}}{\delta_{hh}}\right|\,or\, \Delta\delta_{vh}=10*\log_{10}\left|\frac{\delta_{vh}}{\delta_{hh}}\right| \tag{22}\]  
Amplitude imbalance refers to the power ratio between the corresponding ground targets acquired in the VV-polarization channel and the HH-polarization channel in the image after polarization calibration. \[\Delta f=10*\log_{10}\left|\frac{\delta_{vv}}{\delta_{hh}}\right| \tag{23}\]  
Phase imbalance refers to the phase difference between the CRs acquired in the VV-polarization channel and HH-polarization channel in the image after polarization calibration. \[\Delta\phi_{f}=phase\big{(}\hat{S}_{vv}\big{)}-phase\big{(}\hat{S}_{hh}\big{)} \tag{24}\] \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Device** & **SCR/dB** & \(\Delta\delta_{hv}\)/**dB** & \(\Delta\)/\(f\)/dB** & \(\Delta\phi_{f}\)\({}^{\circ}\) \\ \hline \multirow{4}{*}{Region 1} & CR-1 & 30.75 & \(-\)34.47 & 0.74 & \(-\)2.28 \\ \cline{2-6}  & CR-2 & 27.37 & \(-\)34.75 & 0.43 & \(-\)0.52 \\ \cline{2-6}  & CR-3 & 24.80 & \(-\)37.20 & 0.53 & \(-\)4.08 \\ \cline{2-6}  & CR-4 & 31.44 & \(-\)33.90 & 0.19 & \(-\)3.44 \\ \hline \multirow{4}{*}{Region 2} & CR-5 & 28.61 & \(-\)35.62 & 0.28 & \(-\)1.74 \\ \cline{2-6}  & CR-6 & 30.22 & \(-\)35.10 & 0.47 & 0.27 \\ \cline{2-6}  & CR-7 & 29.94 & \(-\)39.86 & 0.08 & \(-\)1.84 \\ \cline{2-6}  & CR-8 & 31.46 & \(-\)31.87 & 0.79 & \(-\)1.70 \\ \cline{2-6}  & CR-9 & 29.24 & \(-\)34.67 & 0.52 & \(-\)4.36 \\ \cline{2-6}  & CR-10 & 30.11 & \(-\)33.50 & 0.69 & \(-\)0.72 \\ \cline{2-6}  & CR-11 & 28.93 & \(-\)30.26 & 0.26 & \(-\)4.37 \\ \cline{2-6}  & CR-12 & 28.52 & \(-\)27.18 & 0.04 & \(-\)7.76 \\ \cline{2-6}  & CR-13 & 21.16 & \(-\)27.51 & 0.19 & \(-\)4.12 \\ \hline \multirow{4}{*}{Region 3} & CR-14 & 28.15 & \(-\)34.26 & 0.51 & \(-\)0.66 \\ \cline{2-6}  & CR-15 & 29.07 & \(-\)32.06 & 0.09 & \(-\)1.47 \\ \cline{2-6}  & CR-16 & 23.64 & \(-\)35.08 & 0.23 & \(-\)4.60 \\ \cline{2-6}  & CR-17 & 29.18 & \(-\)32.86 & 0.53 & \(-\)2.36 \\ \cline{2-6}  & CR-18 & 28.42 & \(-\)28.29 & 0.50 & \(-\)4.15 \\ \cline{2-6}  & CR-19 & 29.88 & \(-\)25.99 & 0.13 & \(-\)13.11 \\ \cline{2-6}  & CR-20 & 25.15 & \(-\)30.48 & 0.34 & \(-\)0.47 \\ \cline{2-6}  & CR-21 & 25.49 & \(-\)25.08 & \(-\)0.01 & 6.42 \\ \hline \multirow{4}{*}{Average} & 28.17 & \(-\)32.38 & 0.3 & \(-\)2.72 \\ \cline{2-6}  & \multicolumn{1}{c}{} & & & & \\ \end{tabular}
\end{table} 
Table 7: Polarization calibration accuracy for Group 1. By comparing the results obtained from polarization calibration using the two combinations (Tables 7 and 8), both polarization isolation and amplitude imbalance were improved when using Group 2 compared with Group 1. In Group 2, polarization isolation improved by 0.06 dB compared with Group 1, representing an increase of approximately 1.8%. The amplitude imbalance of Group 2 was enhanced by 0.06 dB compared with Group 1, showing an improvement of approximately 16%. However, the phase imbalance of Group 1 exhibited slightly better performance, approximately 0.08\({}^{\circ}\) higher than that of Group 2, or around 3.3%. Nonetheless, both were significantly better than the design specification of the C-SAR/02 satellite, which aims for a phase imbalance within \(\pm\) 10\({}^{\circ}\).