Creating soil degradation maps using gamma-ray signatures

The uplands of northwestern Thailand are highly susceptible to soil erosion. The high degree of soil degradation originates mainly from unsustainable farming practices on steep terrain. The situation could be improved by sustainable land use planning. Therefore information is needed about the location of erosionprone areas and the state of soil degradation. Our study aims to provide decision makers with maps containing these informations. As the determination of actual soil erosion rates can be time consuming, we tested if radio signatures (K, eTh) can be used as proxies. Therefore, we compared the data of topsoil thickness and erosion measurements by Gerlach troughs with the gamma-ray signatures of these sites in an upland rice field in Mae Hong Son province. The results show a significant correlation between the erosion measurements and the K/eTh ratio. As next step an interpolated erosion map will be created using the data collected from the Gerlach troughs. This map will be overlain with the interpolated radiometry map in order to calculate the goodness of their fitting. If the fitting is significant, such gamma-ray interpolation maps can be used to pinpoint erosion hot spots on field scale and give information about the actual state of soil degradation.