Evaluation And Algorithm Improvement Of The Cloud Phase Product Derived From FY-3A/VIRR

Cloud has a significant role in regulating energy balance between the earth and atmosphere.Different phases of cloud are of different absorption and scattering properties, and thetransformation associated with the thermal kinetic process will directly affect the formation andevolution of the weather system in various scales. Understanding the cloud microphysicalproperties can not only contribute to the monitoring and forecasting of weather phenomena, butalso will benefit the study of artificial weather modification.Currently, the basic theory of retrieving cloud phase by satellite remote sensing data ismature. Studies for detecting cloud phase have also been extensively developed in China, andthe cloud phase products derived from FY-3A/VIRR were launched. This study improved thecloud phase identification algorithms basing on the accuracy analysis of present products, whichmight exert a positive role in promoting cloud phase products application.Firstly, based on the theory of radiative transfer in the atmosphere, this paper exploited theStreamer Radiative Transfer model to simulate the cloud radiation by different thermodynamicphase, cloud optical thickness and particle size by using multi-spectral image parameters ofFY-3A/VIRR, such as the reflectance in visible channel, near infrared channel and the brightnesstemperature in infrared channel. The physical infrastructure of the cloud phase identificationfrom the multi-channel detective information was elaborated. For different observational angles,underlying surface types, atmospheric environment and other external conditions, we calculatedthe forward radiative value of satellite observation by radiative transfer model, investigated theimpact of these external environmental factors on the channel values, therefore laid thegroundwork for the threshold value extraction in retrieving cloud phase.Besides, FY-3A/VIRR cloud phase retrievals were evaluated by Terra/MODIS cloud phaseproducts in the adjacent observational time and the same coverage with consistent spatialresolution for both single and complex cloud conditions. In this study, consistency validations,discrepancy caparisons and overlay display methods were all employed. The analysis resultsshowed that two kinds of cloud phase products had good consistency for the simple cloudcondition; under the complex cloud condition, the consistency between two kinds of cloud phaseproducts decreased. What’s more, it was found by the cases study that FY-3A/VIRR cloud phase operational products were possessed of a certain ability to identify the undefined type cloud inTerra/MODIS products.For the spectral characteristics of different cloud phases in FY-3A/VIRR visible,near-infrared and infrared wavelengths, multi-detection channel data were integrated used in themiddle and low-latitude ocean regions. Threshold method was employed to design cloud phaseidentification. The cloud phase was categorized to ice, water, thin cirrus and mixed by creatingthe sample database, analyzing the characteristics of numerical distribution in the subject ofstudy and determining the threshold values by the human-computer interaction. Cloud phasedetection threshold values varied with the observational time and space. The validation resultsshowed that the consistencies between cloud phase identification algorithm and the true valuefrom the sample database were above95%. The stability of this algorithm was also verified byvisual comparison, the synthesis of three-channel color images and NCEP-FNL data in casestudy. The analysis showed that this algorithm, to a certain extent, could correct the misjudgmentcloud in FY-3A/VIRR cloud phase products.