Retrieval And Analysis About Cloud And Precipitation Physical Properties Using FY-2C Satellite Data

The cloud microphysical parameters are important to the research of climate, weather, environment, and weather modification. Cloud particle effective radius and optical thickness are important micro-physical parameters; they can be retrieved by using satellite data together with radiation transfer model. According to the principle of non-absorption visible band contains information about cloud optical thickness and absorption mid-infrared (or near) band includes information about cloud effective radius, some retrieval works were conducted by using the VIS channel (0.5-0.99μm) and mid-infrared channel (IR4:3.5-4μm) data from FY-2C geostationary meteorological satellite which was launched by our country.Mid-infrared band's (about 3.7μm) radiation intensity of the sun and the earth is basically the same, so the mid-infrared channel of FY-2C is special; we should take into account not only the atmospheric scattering but also the thermal emission process when using it.In this paper, FY-2C mid-infrared radiation are simulated by using radiation transfer model SBDART, then analysis the sensitivity to cloud droplet effective radius of scatter, thermal and total radiation. The results show that scatter radiation is more sensitive to the cloud droplet effective radius and is more suitable for retrieving.The data provided by mid-infrared channel of FY-2C is total radiation, the scatter part of which is useful in this paper, so the thermal radiation from mid-infrared channel and the total part from split window I channel (IR1:10.3-11.3μm) of FY-2C satellite are calculated and then deal with the two channel's data, finally get an empirical relationship which use split window data to detect the infrared heat radiation part .The relationship is a function of cloud top height .Cloud top height can be got by using iterative method, and then the diffuse radiation can be concluded by using the experience relationship.Article presented the sensitivity to optical thickness of visible channel data and the effects of other factors(surface albedo, cloud bottom height, solar zenith angle, satellite zenith angle, relative azimuth angle) on the retrieval results besides cloud effective particle radius and cloud optical thickness are analyzed, and some sensitivity experiments are carried out for special aims, the results show the effects of other factors are smaller than those of cloud effective particle radius and cloud optical thickness on the two channel reflection function respectively.Finally with the retrieval method and the data calculated by SBDART, we retrieved some micro-physical parameters such as the optical thickness and particle effective radius of the cloud on some regions in China, compared the results with the corresponding MODIS cloud productions. The results showed that the distribution of the particle effective radius had better spatial and temporal coherence, but the optical thickness of FY-2C were smaller than that of MODIS, there were also some differences in liquid water paths.