# Performance Evaluation and Noise Mitigation of the FY-3E Microwave Humidity Sounder
## 6 Conclusions  
Detailed assessment of the bias and error characteristics is a prerequisite for effective satellite data assimilation. Data from the fifteen days of the Pacific Ocean clear-sky observations between 50\({}^{\circ}\)S and 50\({}^{\circ}\)N were used to quantitatively evaluate the bias and error characteristics of MWHS-2 onboard FY-3E, a newly launched satellite in the early-morning orbit. In general, the biases of all the channels were within a reasonable range of \(-4\) K to 2 K, most of which were negative. The standard deviations of all the channels were less than 2 K, most of which were within 1.5 K except for the two window channels. As a cross-track scanning instrument, the bias and standard deviation of the \"O\(-\)B\" for MWHS-2 varied with the scanning angles and latitude bands. The biases for water vapor detection channels were nonsymmetrical about the FOVs, which may be caused by antenna pointing error or polarization misalignment. The standard deviations of the window channels and low-level  
Figure 14: The standard deviations of “O\(-\)B” (unit: K) varying with the FOVs for **(a)** the 118-GHz channels and **(b)** the other channels after removing the along-scan noises. Figure 13: Observation biases (unit: K) varying with the FOVs for **(a)** the 118-GHz channels and **(b)** the other channels after removing the along-scan noises. sounding channels near 118.75 GHz increased with decreasing scanning angles, while the standard deviations of the other channels were relatively stable along the scanlines. The linear variation in the bias with the latitude is significant in the window channels, water vapor absorption channels and 118-GHz high-level sounding channels. The standard deviation increased with the latitude in the window channels, water vapor detection channels, and Channels 2 and 9. Such variations with latitude bands are obviously stronger than the microwave temperature sounder carried with the same satellite, which also indicates that special attention should be given to the bias correction and observation error setting with latitude bands in the application of MWHS-2 data assimilation. During the analysis of the bias characteristics, both striping noise and along-scan noise were found in FY-3E MWHS-2. To clarify the magnitude of the noises in the instrument, noise filtering methods developed by our predecessors were introduced in this study to extract the two kinds of noises. The results show that the noise filtering method can mitigate the observation noise well without losing the original weather signals. The striping noises and the along-scan noises are all approximately 0.2 K, which is much smaller than the noise equivalent temperature difference of the instrument. Due to the limitation of the data quantity, the results in this study are still uncertain, especially without considering the variation characteristics of the biases and errors with time (such as daytime or seasonal), geographical location, weather system and underlying surface (such as land, sea or ice) [19], which are the targets of subsequent research. Conceptualization, J.M. and Z.Q. ; methodology, J.M. ; software, J.M. ; validation, Z.Q., J.L. and J.H. ; formal analysis, J.M. and Z.Q. ; investigation, J.M. and Z.Q. ; resources, J.L. and Y.H. ; data curation, J.L. and J.H. ; writing--original draft preparation, J.M. ; writing--review and editing, J.M., Z.Q. and Y.H. ; visualization, J.M. ; supervision, Z.Q., J.L. and J.H. ; project administration, Z.Q. ; funding acquisition, Z.Q. All authors have read and agreed to the published version of the manuscript. This research was jointly funded by the National Key R&D Program of China (Grant 2018 YFC1507302), the Youth Project of the National Natural Science Foundation of China (41805076), the Natural Science Foundation of Jiangsu Province (BK20211396) and the Fengyun Application Pioneering Project (FY-APP-2021.0201). The data used for RTM simulations are available at [[https://cds.climate](https://cds.climate)]([https://cds.climate](https://cds.climate)).