In contrast to previous studies using a single study area with many classes and restricted topographic parameters this paper examines variations in image radiometry due to slope in relation to a single vegetation class growing on all azimuths (0 degree(s) to 360 degree(s)) and slopes from 10 degree(s) to 60 degree(s). It demonstrates that the non-Lambertian Minnaert model was able to produce substantially better results than more traditional approaches on the cypress and pine forests covering the gorges of southwest Crete. These landforms represent extreme geographic features and include the Samaria gorge which is the largest in Europe. To improve the understanding of the model, a sensitivity analysis to evaluate the effect of the main variables known to affect the Minnaert `K' constant was performed. Three gorges were studied using three SPOT images: SPOT-1, August 23, 1986; SPOT-1, April 9, 1987 and SPOT-2 August 30, 1991. The values 0.4, 0.5 and 0.6 were proposed as the K constants of the study class for SPOT bands 1, 2 and 3. Regardless of gorge, image and data, these values produced excellent results.