Cloud Shadow Removal Based on Cloud Transmittance Estimation

This paper proposes a method of cloud shadow removal for multispectral images to retrieve the ground reflectance of areas shadowed by clouds. Cloud shadows are cast when incident direct solar irradiance gets attenuated by clouds. To retrieve the ground reflectance of the shadowed pixels, it is required to estimate pixel-wise attenuation factor for the solar irradiance. Unlike conventional methods, the proposed technique takes the physical model of cloud shadow formation into account to accurately estimate the attenuation factors. According to the physical model, the factors are derived from the transmittance of an occluding cloud. Visual and quantitative results demonstrate that the proposed method outperforms the well-known de-shadowing algorithm. The average correlation coefficient of the corrected image with a reference image is improved from 0.45 to 0.75 by the proposed method as compared to the conventional method. Further, the average spectral angle with a reference image is improved by 10%.