Evaluating erosion from space: um case study near Uberlândia

Resumo

Satellites can offer important spatial data for the assessment of soil erosion. This study was conducted to explore how satellite imagery could be used for evaluating erosion in a 10*10 km area in the Brazilian Cerrados. Products obtained from a variety of satellite sensors were analyzed for the purpose of (1) detecting erosion features; and (2) qualitatively mapping erosion risk. Erosion detection was done through visual image interpretation. Optical Terra ASTER images allowed for a better detection and delineation of major gullies as ENVISAT ASAR imagery. Gully dynamics could be assessed by jointly interpreting aerial photos of 1979 and a high-resolution QuickBird image of 2003. QuickBird also allowed for the detection of smaller erosion features, like rills. Erosion risk mapping was performed for the complete study area with a simple qualitative method integrating information on slope and vegetation cover. Slope was calculated from the SRTM DEM, and NDVI, being indicative of vegetation cover, was obtained from a wet-season ASTER image. Both factors were automatically classified based on their relative susceptibility to erosion. The erosion risk map was constructed by combining both classifications with the minimum-operator. The accuracy of the map was good (75 %) when compared to field estimates of erosion risk. The method presented therefore allowed for a quick and proper indication of spatial differences of erosion risk in the study area, particularly concerning rill and sheet erosion.