Retrieval of optical thickness of low-level water cloud using the MSG multi-channel data
| Inoue, Toshiro | MRI/JMA |
We studied the optical thickness of low-level water cloud using MSG ( Meteosat Second Generation) data. The multi-channel data of MSG are use for retrieval of cloud optical thickness. The brightness temperature difference between the split window (BTD) generally shows larger value for ice cloud due to differential absorption by ice. However, optically thin water cloud also shows the larger value of BTD (Lutz et al., 2003). The use of 8.7m m is effective in classifying the ice/water. Using the multi-channel of MSG, we can classify optically low-level thin water cloud. We found the BTD shows good relationship with optical thickness that is less than 6. Further, we construct the BTD-TBB diagram for water cloud that is similar to the diagram for cirrus cloud. Then we can estimate both optical thickness and effective radius. We compare the retrieval of optical thickness by the use of 8.7m m and split window and so-called solar reflectivity method which uses the visible, 3.7m m and 11m m. Both show reasonable agreement for optically thin water cloud. However, the diurnal variation of optical thickness shows slightly different characteristics.
