LAUSR

Chinese Fengyun 3 (FY-3) polar-orbiting satellites carry Microwave Humidity Sounders (MWHSs), including MWHS and MWHS-2 which are on board FY-3A/B and FY-3C/D, respectively. Understanding the quality of MWHS data is important for data assimilation and other applications. Examination of observed and simulated brightness temperatures and comparison with those of the NOAA-18 Microwave Humidity Sounder (MHS) reveal that the FY-3C MWHS-2 observations contain significant along-scanline noise. Similar noise exists in the humidity sounder data from FY-3 series satellites. In this study, the principal component analysis (PCA) method is used to identify and characterize the along-scanline noise, and a noise filter is also applied to the FY-3 series MWHS data by combining a PCA with a five-point smoother. The observation minus background or O-B biases of MWHS channels vary more smoothly with scan position after applying the filter, indicating that the along-scanline noise has been effectively reduced. Comparisons of O-B biases among all four FY-3 MWHS instruments show that biases for different channels have different asymmetric scan-angle features. As for along-scanline noise, FY-3A MWHS has the largest noise: 0.16, 0.27, and 0.89 K for channels 3–5, respectively. Noise in the FY-3D humidity channels is the smallest, of the order of 0.06–0.07 K. The along-scanline noise is also strongly correlated between channels.