Development of topsoil grain size index for monitoring desertification in arid land using remote sensing

The grain size composition of topsoil characterizes the soil texture and other physical properties. The coarsening of topsoil grain size is a visible symbol of land degradation; thereby the change in topsoil grain size can be potentially used to monitor desertification using remote sensing. This study proposes a new index for detecting topsoil grain size composition through ground in situ soil spectral reflectance measurements and soil physical analysis in the laboratory. The proposed topsoil grain size index (GSI), which has a positive correlation with fine sand content, was then applied to detect desertification in Siziwang Banner, Inner Mongolia, China, using a Landsat TM (1993) image and a Landsat ETM+ image (2000). The result shows the fine sand content of topsoil increased in most places, indicating a coarsening process of the topsoil in the study area. The fast soil coarsening of degradation is largely caused by human activities.