Enhancement of Cloud-Associated Shadow Areas in Satellite Images Using Wavelet Image Fusion

Shadows created by small patches of clouds obscure ground features from satellite imagery. In this research, a new technique was developed to enhance cloud-associated shadow areas in satellite images while preserving details underneath these areas. The developed algorithm utilizes wavelet analysis to decompose cloudy images into several frequency level components. Image details underneath shadow areas are preserved in the output image by fusing the cloudy image with another cloud-free image. The developed technique is implemented on a cloudy Landsat7 Panchromatic subscene. The results showed that the developed technique was successful in enhancing the cloudy image through preserving the obscured details underneath the cloudassociated shadow. The ability to maintain such details under shadow areas and the amount of introduced artifacts increased with the increase of the wavelet decomposition level. Generally, two or three wavelet decomposition levels were found to be sufficient for the analysis used in this study. The results obtained when using two images with the same spatial resolution were found to be better than those obtained using images with different spatial resolution.