# C-SAR/02 Satellite Polarimetric Calibration and Validation Based on Active Radar Calibrators
## 3 Experimental Procedures and Methods
### Equipment Deployment and Adjustment  
According to the requirements of [PERSON]'s method, three ARCs with different scattering matrices are needed to solve the distortion matrix together; therefore, three active calibrators were first deployed in positions close to each other without interference in the experiments. The default scattering matrix of the ARC was \(\begin{bmatrix}1&0\\ 0&0\end{bmatrix}\), and the scattering matrix of the ARC was set to different forms by adjusting the angles of the transmitting antenna and receiving antenna, as shown in Table 2.  
By rotating the transmitting antenna angle of ARC1 to \(0^{\circ}\) and the receiving antenna angle to \(90^{\circ}\), the transmitting antenna angle of ARC2 to \(90^{\circ}\) and receiving antenna angle to \(0^{\circ}\), and the transmitting antenna angle of ARC3 to \(45^{\circ}\) and receiving antenna angle to 45\({}^{\circ}\), the scattering matrix of ARC1 is \(\begin{bmatrix}0&0\\ 1&0\end{bmatrix}\), that of ARC2 is \(\begin{bmatrix}0&1\\ 0&0\end{bmatrix}\), and that of ARC3 is \(\begin{bmatrix}-1&-1\\ 1&1\end{bmatrix}\). In this way, the polarization calibration matrix of the C-SAR/02 satellite was solved using the combination of ARC1, ARC2, and ARC3.  
[PERSON] [30] observed that a single-point PARC calibration is limited because of the variation in crosstalk isolation across the swath. To address this problem, a fourth active calibrator, ARC4, was deployed at a location \(\sim\)1990 m away from ARC3 in the distance direction, and its scattering matrix was set to \(\begin{bmatrix}-1&-1\\ 1&1\end{bmatrix}\). The polarization calibration matrix was solved using the combination of ARC1, ARC2, and ARC3, which were defined as equipment Group 1, and the combination of ARC1, ARC2, and ARC4 (equipment Group 2). To check the calibration results, 21 trihedral CRs with a right-angle edge length of 1.4 m were deployed in three regions in the range direction, and were used to analyze the distribution pattern of the polarization calibration accuracy along the range direction. As shown in Figure 1, the ARCs and CRs 1-4 were placed in Region 1, CRs 5-13 were placed in Region 2, and CRs 14-21 were placed in Region 3; Region 2 was \(\sim\)70 km away from Region 1 in the range direction, and Region 3 was \(\sim\)7 km away from Region 2 in the range direction.  
During the transit of the SAR satellite, the pointing angle of the ground equipment must be aligned with the direction of the radar incident beam to ensure that the radar antenna receives the peak RCS signal from the ground point target. Therefore, before the satellite transit, the orbital parameters of the C-SAR satellite were used to predict its positional coordinates at the time of transit. Subsequently, using the spatial geometric relationship between the satellite and the ground, the azimuth and elevation angles required by the calculation device were calculated. After calculating the required angle values, the CR was manually adjusted to the corresponding angles. The ARC was then controlled through the uploaded commands to adjust the servo motor, which in turn controls the azimuth and elevation angles, ensuring that the direction of the ground calibration equipment aligns with the incident direction of the radar beam [47].  
The parameters that need to be set for the ARC also include the RCS value and delay time; here, the RCS value was set to 50 dB and the delay time was set to 2 \(\upmu\)s. The characteristics of the four ARCs on the experimental images with different polarization modes are shown in Figure 6. Among them, ARC-3 and ARC-4 are visible on the HH-polarization image, ARC-2, ARC-3, and ARC-4 are visible on the HV-polarization image, ARC-1, ARC-3, and ARC-4 are visible on the VH-polarization image, and ARC-3 and ARC-4 are visible on the VV-polarization image.  
Figure 6: _Cont._