Fig. 1. Flow chart for calculating cirrus optical thickness using RT3

Fig. 2. Change of cirrus reflectance under different optical thickness, surface reflectance,observation angle and effective particle radius.（a）Optical thickness；（b）surface reflectance；（c）observation angle；（d）effective particle radius

Fig. 3. Comparison on cirrus optical thickness between MODIS observation and LUT calculation

Fig. 4. MODIS observed and LUT calculated the optical thickness distribution of cirrus. (a) MODIS-UTC2020-07-17T03∶15∶00;(b) LUT- UTC2020-07-17T03∶15∶00; (c) MODIS-UTC2020-07-17T05∶00∶00; (d) LUT-UTC2020-07-17T05∶00∶00