An automatic method to extract traces of slope failures was established on the basis on the high accurate DEM of 2 meter mesh. The DEM was obtained using air laser scanning covering a rectangular area of 2 km x 1km, where numerous slope failures occurred triggered by heavy rainfall. Three criteria were used to determine concave slopes, which correspond to old slope failures. (i)existence of concave slopes, (ii)existence of scarplets, and (iii) circular shape of them, respectively. To obtain the fundamental data of slope changes, Laplacian values of elevations were calculated for the analyses. And "slit method" was used to judge circular topographic characteristics. Consequently, many concave topographies corresponding slope failures were effectively extracted using this method. Based on the topographic contour lines, this method was confirmed to be effective. This means that the method is more effective than that of air photo interpretation.

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Leakages from the soil waterway, improper irrigation, and incomplete drain system have raised the groundwater levels in arid areas and caused salinization, i.e. accumulation of salts in the top soils. Vulnerability of salinization is also controlled by topographic properties and soil conditions. This study focuses on a desert area in the northern Tarim Basin, northwest China, because the rapid progress of salinization has been reported. One main factor for the salinization in the study area is the excessive water supply in the agriculture lands. For clarifying the salinization process, 40 scenes of satellite imagery in total by Landsat T‚l/ETM+ (acquisition years: 1990 and 2000) and Terra/ASTER (acquisition years: 2003, 2004, and 2006) were selected. Three normalized difference indices on vegetation, soil, and water and a color composition of the indices were adopted to detect surface changes in the period from 1990 to 2006. As a result, the salinized soils were found to have extended in the downstream, and their area increased monotonously with the time while the area of fixed dunes decreased largely. We proposed a Salinity Index to extract correctly the salinized areas from the ASTER images by refereeing to the reflectance spectra of the soil samples. This Salinity Index clarified that the salinized soils have high salt concentrations over 30 ppt and the concentrations of the moving sands are also high. In addition, the high salinity accumulation in the downstream of farmlands was identified, which implied a strong effect of agricultural development on the salinization.

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