Topographic correction based on sun-canopy-sensor (SCS) geometry is more appropriate than terrain-based corrections in forested areas since SCS preserves the geotropic nature of trees (vertical growth) regardless of terrain, view, and illumination angles. However, in some terrain orientations, SCS experiences an overcorrection problem similar to other simple photometric functions. To address this problem, we propose a new$hbox SCS+C$correction that accounts for diffuse atmospheric irradiance based on the$hbox C$-correction. A rigorous, comprehensive, and flexible method for independent validation based on canopy geometric optical reflectance models is also introduced as an improvement over previous validation approaches, and forms a secondary contribution of this paper. Results for a full range of slopes, aspects, and crown closures showed$hbox SCS+C$provided improved corrections compared to the SCS and four other photometric approaches (cosine,$hbox C$, Minnaert, statistical-empirical) for a Rocky Mountain forest setting in western Canada. It was concluded that$hbox SCS+C$should be considered for topographic correction of remote sensing imagery in forested terrain.