Determining C Factor of Universal Soil Loss Equation (USLE) Based on Remote Sensing

Abstract

Soil erosion is a serious environmental problem which causes degradation of soil and water environment. Thus, soil conservation is necessary for the areas where accelerated erosion occurs. At early stages of soil conservation, certain strategies should be implemented based on predicted soil erosion rate of the area. Soil erosion rate has been calculated using erosion models, such as Universal Soil Loss Equation (USLE), Revised Universal Soil Loss Equation (RUSLE), Water Erosion Prediction Project (WEPP), etc. However, the most common model is either Universal Soil Loss Equation (USLE) or Revised Universal Soil Loss Equation (RUSLE), as they are easy in handling by users. Attention has been paid to Cropping Management, factor C of USLE or RUSLE, since it is challenging to determine. The factor depends on the type of crop and the growing stage, however growing conditions would change locally and harvesting time are unpredictable. Also, vegetation could be changed unpredictably due to weather or farming conditions. Approaches based on remote sensing technology which has less temporal and spatial restrictions on detection of vegetation were applied to determine C factor using vegetation indices. However, it is not always successful in field application. Therefore, the objective of the study is to improve determination of C factor using vegetation indices. For clarification, experiments for identifying the relationship between C factor and vegetation indices such as Normalized Difference Vegetation Index (NDVI) and Soil-Adjusted Vegetation Index (SAVI) were carried out under several types of soil. Furthermore, the accuracy of determination of C factor using vegetation indices was discussed through an erosion model experiment. The results showed SAVI is more strongly correlated with C factor than NDVI. Estimation of C factor based on NDVI and SAVI have 30% and 36% of relative error in field application. Therefore, it was concluded that vegetation indices have high potential to determine C factor of USLE or RUSLE. Also, estimation of field C factor based on SAVI is more recommendable for determination of C factor in the field where there are several types of soil.