Using Landsat Images for Studying Land Use Dynamics and Soil Degradation - Case Study in Tamduong District, Vinhphuc Province, Vietnam

要旨

Tamduong district, Vinhphuc province, is representative for vast areas in the north of Vietnam where soils are strongly degraded and erosion has led to patches of bare soil with exposure of parent material, and crop yields on these soils are strongly reduced. The aims of this study are to apply satellite imagery for the assessment of the extent of soil degradation and implementing the results to the whole middle altitude area of North of Vietnam. Satellite images Landsat MSS in 1984 (4 bands), TM 1992, 1996 and 2000 (6 bands) were used for creating maps of the Color Composite and Band Ratios. From these images, bare and degraded soils were identified and extracted. Classified maps of the Band Ratios G/R and R/NIR for the year 2000 were established on the basis of new soil maps and ground truth data. The best band ratio, R/NIR, was selected for further processing and classification base on visual interpretation. The classified map of degraded soils, based on the R/NIR band ratio, matched well with the soil survey map and the field checks with an overall accuracy of 73%. Land use and soil degradation dynamics were reconstructed for the period 1984 to 2000 and degraded soil areas in the district were established at 2440, 3280, 2190 and 2580 ha, for 1984, 1992, 1996 and 2000 respectively. Hot spots from the Band Ratio imagery appeared to accurately represent the degraded soil areas in the hilly land and the degraded sandy soils on the high terraces, but not in the agricultural lowland, because on hilly and sandy terraces soil organic matter and soil moisture content were very low. The study shows that satellite imagery is a very useful tool for soil degradation studies.