Satellite radiance is generally considered to be biased with respect to a reference (e.g., background or analysis field in NWP assimilation) due to systematic error of the observation itself, the reference field, and RTM. Bias correction is a necessary step prior to assimilating radiance data. There are two ways of performing bias correction in WRFDA. One is based on the Harris and Kelly (2001) method, and is carried out using a set of coefficient files pre-calculated with an off-line statistics package, which was applied to a training dataset for a month-long period. The other is Variational Bias Correction (VarBC). Only VarBC is introduced here, and recommended for users because of its relative simplicity in usage.