Assessments of FY-3A Microwave Humidity Sounder measurements using NOAA-18 Microwave Humidity Sounder

Abstract

[1] The measurements from FY-3 MicroWave Humidity Sounder (MWHS) are compared with the data from NOAA-18 Microwave Humidity Sounder (MHS) under various atmospheric and surface conditions. A quality control (QC) procedure is applied to allow the comparison be conducted separately for outliers and nonoutliers. The QC algorithm includes a gross error check, instrument noise spikes through noise equivalent differential temperature, and an O-B biweighting check, where O represents satellite observations and B is model-simulated brightness temperature by Radiative Transfer for TIROS-N Operational Vertical Sounder based on the 6 h forecast fields of the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS). It is found that (1) the global bias and standard deviation of O-B from MWHS brightness temperatures are comparable in magnitudes to those of MHS measurements, (2) positive O-B outliers prevail in channel 3 for both MWHS and MHS instruments, and (3) biases of channels 4 and 5 are predominantly negative over land for both MWHS and MHS. A series of sensitivity experiments are carried out to demonstrate that the large positive O-B biases could be due to the errors in the atmospheric water vapor profiles from the model forecast fields being too wet, and that the negative biases over land arise mostly from errors in surface emissivity, but smooth model terrain also contributes to negative biases over land.