# On-Orbit Calibration Method for Correction Microwave Radiometer of the HY-2 Satellite Constellation
## 5 Inversion and Verification
In fact, HY-2B and HY-2D also have more crossovers than between HY-2B and HY-2C at high latitudes, and observations at high latitude contain more uncertainty. Therefore, RMS is always greater between HY-2D and HY-2B than between HY-2C and HY-2B. In this study, the AWV and WPD of crossovers are divided into two parts by high and low latitude, which are bounded by the 45\({}^{\circ}\) north-south latitude. The products are reprocessed by the new retrieval algorithm presented in Equations (7) and (8). In Table 5, it can be seen that after on-orbit calibration, mean bias and RMS for products of the HY-2 satellite constellation at low latitudes is smaller than that at high-latitudes, but the reduction of RMS for high-latitude products is greater than that for low-latitude products after calibration. This shows that on-orbit calibration is more effective for improving the relative accuracy of high-latitude products and the absolute accuracy of low-latitude products. The deviation between products from different CMRs has a significantly decreased after-orbit calibration in the HY-2 satellite constellation, but the absolute accuracy of products must be also validated. Since too few in-situ measurement points can be matched with the HY-2 satellite constellation, AMR products of the Jason-3 satellite are used as a reference for validation. The AMR in Jason-3 is a radiometer with a similar mechanism as CMR, and its BT data have a good accuracy after long-term and systematic on-orbit calibration [35]. After on-orbit calibration to the HY-2 satellite constellation, the CMR products of HY-2C and HY-2D (the first group in Table 2), obtained by the operational algorithm, are compared with AMR products to check AWV and WPD. For HY-2B, the CMR products of the operational algorithm and new algorithm are compared with AMR products. The checking result is shown in Table 6. The RMS between CMR products and AMR products is decreased, but the variation is less than the reduction of RMS before and after calibration inside the HY-2 satellite constellation. For the first dataset (see Table 2) in cross-checking, Figure 10 shows a very different distribution of crossovers, to match the three satellites to the Jason-3 satellite at the same \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Content**} & \multirow{2}{*}{**Marker**} & \multirow{2}{*}{**Number**} & \multicolumn{2}{c}{**Mean Bias (mm)**} & \multicolumn{1}{c}{**RMS (mm)**} \\ \cline{4-5}  & & & **Before/After** & **Before/After** \\ \hline \multirow{2}{*}{HY-2C} & AWV & \multirow{2}{*}{3863} & 0.421/ –0.215 & 1.290/1.087 \\  & WPD & & 2.411/ –1.197 & 7.736/6.842 \\ \multirow{2}{*}{HY-2D} & AWV & \multirow{2}{*}{5823} & 1.087/1.345 & 1.887/1.446 \\  & WPD & & 6.563/7.831 & 11.056/9.121 \\ \cline{4-5}  & & & \multicolumn{2}{c}{Operational/New} & \multicolumn{1}{c}{Operational/New} \\ \cline{4-5}  & & & \multicolumn{1}{c}{} & 0.471/ –0.779 & 1.442/1.172 \\ \multirow{2}{*}{HY-2B} & AWV & \multirow{2}{*}{4983} & 2.859/ –4.675 & 8.278/7.061 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Cross CMR and advanced microwave radiometers (AMR) to check before and after on-orbit calibration.