TOPOGRAPHYC SHADOW INFLUENCE ON SATELLITE IMAGE ACQUISITION PRODUCTS ON SOUTH HEMISPHERE1

During the acquisition of satellite imagery, less cloudy cover scenes are preferably chosen for a better spectral information of the targets. However, during the process of collecting training samples, shaded areas are commonly found. This problem is similar with clouds, since the spectral information of the "shadow" is the same in every band. This problem tends to be exacerbated in areas of mountainous relief. In this order, we simulated under the same relief conditions, the variation of shadows at different latitudes. We employed models of direct solar radiation for the dates of passage of the Landsat TM and ETM satellites in the southern hemisphere. We considered only the time at which the imaging was performed. It was verified that, at 30o and 40o S latitudes, the loss of area of the scene by shadowing ranged from 27% to 91% and images can be acquired, preferably between the months of October to March. In 0o and 10o S latitudes, the loss are negligible when a minimum threshold of occurrence is set in 10% of shading. With respect to radiation by solar exposure area, it was found that the South and West faces received the least amount of lighting throughout the year.