We studied a method to retrieve the optical thickness and effective particle radius of water clouds using the split-window
channels and the 8.7-μm channel of Meteosat-8. Valid ranges are approximately from 1 to 9 for optical thickness and
smaller than 18 micron for effective particle radius. The retrieval used the brightness temperature (TBB) and brightness
temperature difference (BTD) between the split windows, as computed with the radiation code RSTAR5b for various
properties of water clouds and vertical profiles of temperature and water vapor. The retrieved cloud parameters were then
compared to those retrieved by the solar reflection method, which employs the 0.6-, 3.9-, and 11- μm channels of
Meteosat-8. Comparison between the two methods revealed that the split-window technique could capture spatial
features for both optical thickness and effective particle radius. The BTD is a good indicator for optical thickness. The
diurnal variation of BTD shows the minimum value (thickest) before sunrise. Further precipitation and optical depth
estimated from TMI/TRMM are compared with optical properties.
A quasi real time system for estimate of the surface solar flux is introduced. The system will start to be operated in this year, and provide the solar flux until tomorrow’s morning. The system uses 0.09-degree resolution products from the GMS-5 image data of CEReS, Chiba Univ. It also uses the six-hourly atmospheric objective analysis data from the Japan Meteorological Agency. The solar flux is estimated at each pixel. This system includes four steps to estimate the surface solar flux. (1) The first step discriminates cloud pixel from clear one. The adopted method is similar to ISCCP, in which the reference Tbb for discrimination is created by data before and after the target day. In this system, it is impossible to use tomorrow’s data, because real time operation is needed. Therefore historical data is used to create the reference. (2) Cloud pixel is analyzed using 11/12 micron split window methods and 6.7 micron channel. The methods determine that the pixel is water or ice cloud, and derives the optical thickness for ice cloud. (3) The optical thickness for water cloud is retrieved from the reflection method using visible channel with assumption of the effective radius. (4) Cloud optical thickness and atmospheric information is converted to the surface solar flux from the package RSTAR5B for radiation transfer calculation. The surface solar flux using typical pixels from 0.5-degree grid area had been already derived. A comparison of satellite derived solar flux and the surface observation shows fair result in clear sky days, and overestimate in cloudy days.
Conference Committee Involvement (1)
Optical Remote Sensing of the Atmosphere and Clouds III
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