We present a satellite remote sensing technique to retrieve the cloud optical thickness (COT) which is
based on visible and shortwave infrared imagery from MSG-SEVIRI.
The semi-analytical cloud retrieval algorithm (SACURA) is implemented on a monthly dataset of SEVIRI
level 1.5 images. The background surface albedo (A) plays an important role for thin clouds. Thus, A is
calculated by the minimum composite approach of reflectance in the visible channel, at pixel level, during
the month. Cloud ice and cloud water discrimination scheme is made on the basis of ratio of reflectance in
channel 1.6 μm to 0.6 μ. Reflectance of semi-infinite (R 0 ∞) cloud is a function of cosines of solar azimuth
angle (vo), satellite azimuth angle (v) and relative azimuth angle (Ψ). Thus, reflectance values, R 0 ∞,
R 0 ∞, are
interpolated from a look up table of reflectance, calculated from radiative transfer model, to corresponding
sun-satellite angular values.
Hence, total scaled cloud optical thickness is calculated as summation of scaled cloud optical thickness of
water and scaled cloud optical thickness of ice.
The result is compared with that of Cloudsat and it shows good agreement.