Various methods have been used to study soil redistribution in the Loam Belt of Belgium. These methods have had contrasting levels of spatial coverage and time-scale. Ideally, a technique to assess soil redistribution patterns should provide the determination of dense networks of X, Y and Z terrain coordinates (digital elevation models) at different time intervals.
Sequential stereoscopic aerial photographs contain this information, which can be extracted with standard photogrammetric techniques. In this study, aerial photographs taken by the National Geographic Institute of Belgium in 1947 and 1991 were used to determine the soil redistribution pattern between these years. This was done by overlaying the two digital elevation models and subtracting the corresponding Z coordinate values (heights). The results indicate that most severe surface lowering occurs on the top of the hillslope and on the hillslope convexities. Important deposition occurs on the lowermost parts of the hillslope, in most hillslope concavities and in the topographically defined concentration line. The observed pattern differs markedly from that expected from water erosion processes, and suggests that the soil redistribution is dominated by tillage operations.