Shadow extraction and correction from quickbird images

Shadows in remote sensing images often result in problems for many applications such as land-cover classification, change detection, and damage detection in disasters. Due to these reasons, it is very useful if the radiance of shadowed areas is corrected to the same radiance as shadow-free areas. In this study, a shadow detection and correction method is proposed. Shadowed areas are detected by object-based classification, using brightness values and a neighbor relationship. Then the detected shadowed areas are corrected by a liner function to produce a shadow-free image. The shadowed areas with different darkness are corrected with different ratios to improve the accuracy of the result. The spectral characteristics of sunlit and shadowed areas in several QuickBird images were studied and then the shadow-free radiance was obtained.