CHARACTERISTICS OF THE NOAA NESDIS CLOUD RETRIEVAL ALGORITHM USING HIRS-MSU RADIANCE MEASUREMENTS/

A cloud retrieval algorithm using NOAA/National Environmental Satellit e, Data, and Information Service High-Resolution Infrared Radiation So under 2 Microwave Sounding Unit measurements from a polar-orbiting sat ellite, described in McMillin et al., uses multiple channel pairs with a two-pass procedure for enhancing accuracies. The current paper comp lements McMillin et al. in several ways. First it describes the charac teristics of the channel pairs used in the algorithm while documenting the logic of the channel selection. It shows that the cloud-top heigh ts and cloud fractions are dependent on the sensing channel pairs. The higher the altitude of the weighting function, the smaller the cloud fractions. Second, it adds an atmospheric attenuation correction and d isplays its effect on cloud-top heights. Without the attenuation corre ction, the cloud-top distributions are separated into two bands, possi bly as a result of the distance between the heights of the weighting f unctions of the sensing channel pair. The attenuation correction effec tively eliminates the gap, both by lowering the upper band and by elev ating the lower band. The cloud fractions from this experimental opera tion are compared with Air Force Real-Time Nephanalysis for 3 months, and they reveal its strength in detecting low-level stratus.