变分同化FY-3B红外分光计(InfraRed Atmospheric Sounder, IRAS)的通道亮温要求亮温观测模拟偏差满足高斯分布。由于卫星数据处理以及数值预报模式等包含的误差不服从高斯分布，因此需要对偏差进行订正。首先对IRAS资料进行云检测等初步质量控制；在统计了IRAS的20个通道亮温之后，发现扫描偏差具有星下点对称性；最后对扫描和气团偏差进行了订正。结果表明，订正后IRAS高层通道1、10以及近地面通道14的偏差绝对值有所增加，水汽通道13和地面通道20的偏差标准差有所增加，其它15个通道亮温观测模拟偏差均值从1.04 K减小到了-0.30 K，相应的标准差从2.28 K减小到了1.99 K。偏差概率分布更具高斯性。

The variational assimilation channel brightness temperature of the Infrared Atmospheric Sounder (IRAS) onboard FY-3B weather satellite requires its observation simulation deviation to satisfy Gaussian distribution. Because the deviations contained in satellite data processing and numerical forecast modes do not follow Gaussian distribution, it is necessary to correct them. First, the preliminary quality control such as cloud detection is performed for the data from IRAS. After the brightness temperatures in 20 channels of IRAS are counted, it is found that the scanning bias is symmetry at nadir. Finally, both the scanning bias and the air mass bias are corrected. The result shows that after correction, the absolute deviation valuesin top channels 1, 10 and near ground channel 14 are increased. The standard deviations of deviations in water vapor channel 13 and ground channel 20 are increased. The mean brightness temperature observation bias in other 15 channels are reduced from 1.04 K to 0.30 K. Their corresponding standard deviations are reduced from 2.28 K to 1.99 K. The bais probability distribution is more Guassian.