further explained that the errors in the WMR estimation of zenith wet delay (ZWD) might be introduced in the retrieval algorithms, in the absorption models for water vapor emission at the WMR frequencies, and/or in the calibration of the radiometer. It is expected that IWV retrieval biases is 1mm for dry conditions (6.5 mm zenith wet delay) and 2.5 mm of IWV (16-20 mm ZWD) for very humid conditions