## 2 Instrument Characteristics
\(\mathrm{R_{qv}}\) and \(\mathrm{R_{qh}}\) represent the radiation for the Qv and Qh polarizations, respectively, and \(\mathrm{R_{v}}\) and \(\mathrm{R_{h}}\) are the radiative components at V and H polarizations, respectively. \(\mathrm{R_{3}}\) is the third Stokes component. \(\mathrm{R_{r}}\) is the radiation emitted from the reflector. \(\epsilon_{v}\) and \(\epsilon_{h}\) are the emissivity of reflectors for V and H polarization, respectively. It can be observed from the above equations that the Qv channel involves the square of a sine function, while the Qh channel involves the square of a cosine function. This explains the formation of the brightness temperature distribution as it varies with the scan angle. Previous research [22; 23] shows that changes in polarization may lead to scan-dependent biases. Additionally, the ocean emissivity is sensitive to polarization. The differences between observation and simulation (O-B) can describe the above phenomenon [24]. Therefore, this study conducts multiple analyses based on the O-B results obtained under the \"clear sky ocean\" scenario. ECMWF Reanalysis v5 (ERA5) data are served as the input of ARMS. Based on the polarization settings provided by the National Satellite Meteorological Center (NSMC), taking FY-3F MWHS as an example, when the polarization of channel 1 is Qh, the O-B can reach over 10 K. However, after reversing the polarization of channel 1, the O-B value stabilizes at around 2 K. It can be observed that the O-B results after polarization reversal are more stable and reasonable. To verify whether similar scenarios exist in other channels, Figure 1 presents the O-B results of both polarizations, Qv and Qh, for all channels of MWHS. The green line represents the results of Qv, while the red line represents the results of Qh. The x-axis indicates the scan angle of the instrument, with 0\({}^{\circ}\) in the middle corresponding to the nadir point. From the Figure 1, it is clear that in addition to channel 1, the O-B of channels 7-10 are also significantly influenced by the polarization. When the polarization is Qv, channels 7-9 exhibit an \"M\" shape, while channel 10 displays a wavy pattern. In contrast, the O-B of the remaining channels does not show a notable difference between the two polarizations. Additionally, it can be observed that the O-B of most channels exhibits an asymmetric phenomenon, with a noticeable deviation from the nadir point on one side as the scan angle increases. For channels other than channels 1, 7-10, the differences between the two polarizations are generally very small in magnitude. Figure 2 illustrates the differences between the two polarizations of the MWTS, where the O-B differences between the two polarizations are significant for channels 1-7. The main reason for this phenomenon is that the channels near the surface (MWHS channel 1 and MWTS channels 1-3) and in the lower layers (MWHS channels 7-10 and MWTS channels 4-7) are sensitive to changes in polarization. In summary, different polarizations have a significant impact on the simulation results. When channels 1, 7-9 of the MWHS are simulated based on the polarization information provided by NSMC, the O-B curve exhibits significant fluctuations. However, after reversing their polarizations, the O-B decreases significantly, and the curve becomes more stable. For subsequent simulation work, we recommend that the actual polarizations used for FY-3F MWHS and MWTS in ARMS be set according to the results shown in Table 3.  
Figure 1: FY-3F MWHS scan angle dependence of 98 FOVs for 15 channels (**a––o**). The simulations are from ARMS. The green solid line and the red solid line represent Qv and Qh, respectively (units: K). Figure 2: FY-3F MWTS scan angle dependence of 98 FOVs for 17 channels (**a–q**). The simulations are from ARMS. The green solid line and the red solid line represent Qv and Qh, respectively (units: K).