On the Effect of Thr Drop Size Distribution (dsd) and Melting Lyaer to the Brightness Temperature of a Spaceborne Passive Microwave Radiometer

Since the TRMM launch in 1997, global rain estimation by microwave radiometer has been improved referring the PR data. The microwave radiometer observation becomes the major observation tool for the Global Precipitation Measurement (GPM). However, there are still gaps of global rainfall distribution between PR and TMI (e.g. Berg et al., 2002). One of the major issues for rain retrieval algorithms for spaceborne microwave radiometers is to introduce an appropriate drop size distribution (DSD) model and melting layer (bright band, BB) model. Most of the algorithms assume Marshall-Palmer type DSD because it is one of the typical DSD model and it is easy to convert rain rate to DSD. However, recent studies using the TRMM data indicates that difference of DSD model used in the PR and the TMI algorithm causes the difference in rainfall estimation between the PR and the TMI. In this study, sensitivity to a DSD model is examined using plane parallel radiative transfer model by Liu (1998).