Erosion extension of indurated volcanic soils of Mexico by aerial photographs and remote sensing analysis

In the northern part of Michoacan State in Mexico, between the Patzcuaro and Cuitzeo lakes, we used aerial photographs and Spot satellite data, to define the spatial and temporal extensions of soil erosion over indurated volcanic material called tepetates. Segmentation techniques combined with graphic mask were applied over the aerial photographs in order to obtain the extension of eroded areas for 1975, 1995 and 2000. An unsupervised classification was performed over various band combinations of Spot. The eroded areas were checked and improved with ground control points. The results show that there are no more eroded areas today than 25 years ago. There is, however, an evolution of the eroded areas; some of them have disappeared while others have become larger. A change in land use intensity explains the regression of eroded area in the north and the augmentation of eroded surfaces in the south. The result obtained with Spot imagery classification allows discrimination of four different erosion degrees, where only one could be distinguish with aerial photographs. However, it is not possible to distinguish outcropping tepetates and outcropping andesit with Spot. As well, additional socioeconomic studies and studies over spectral signatures of eroded materials in relation with their mineral contents are in process.