Applicability of satellite remote sensing for mapping hazardous state of land degradation by soil erosion on agricultural areas

摘要

This paper introduces two case studies of mapping hazardous state of land degradation appeared widely in Southeast Asian countries. One was a case for Keduang watershed in the upper stream of Wonogiri River in Central Java, Indonesia. The author developed a method to obtain 2.5 meters resolution landuse data by combination of Landsat/TM/ETM+ and ALOS/PRISM/AVNIR2 pan-sharpened data, which showed overall accuracy of 74.4% and 0.660 of kappa coefficient. This was converted to C factor of USLE equation and then multiplied by LS factor obtained from digital elevation data. This combined factor could depict detail distribution of hazardous area of soil erosion. Another case was for hilly land along Cagayan River in the Philippines. The author attempted to extract area suffered by gully erosion, which was ditch like feature presented on agricultural field, by using high spatial resolution satellite data. Edge enhancement of Sobel filter applied to WorldView panchromatic data was effective to screen candidate of gully erosion, only it remained falsely extracted area. Then he employed topographical and texture analysis to separate non-gully area from the candidate. As a result, 63.4% of gully was properly extracted by developed method.