| Soil erosion status can directly affect the development of the regional social economy and the quality of social life and the living environment of the residents, so taking soil erosion investigation of the situation at regular intervals is of great significance for evaluation of soil and water loss control efforts. The present investigation methods commonly used in the world are sampling survey, comprehensive evaluation, experience statistical model, theoretical physics model, and so on. We have carried out soil erosion remote sensing investigation three times by using the comprehensive evaluation, and have completed the fourth national soil erosion survey by the combination of sampling survey and CSLE model for the first time in 2010-2012 years in our country. The survey obtain the national distribution of soil erosion by laying the national investigation points and using CSLE model calculation. S ince 2013, Ministry of Water Resources launched a project about national soil erosion dynamic monitoring and announcement to investigate the typical county in the national emphasis management region. Therefore looking for reasonable sampling density and ca lculation method in a county has become the technical problems to be solved.The study, taking Mengyin and Yishui as an example, explore the impact on the quantitative characteristics and spatial distribution of soil erosion in 1%、4% of the sampling density, using grid calculation on county, direct calculation on unit andkriging calculation on unit, compare the differences, analyze the causes, and propose the reasonable sampling density and calculation method, which can not only guarantee the accuracy but a lso to reduce the workload outside the industry, to provide technical support for the typical county emphasis management region.According to the results:(1)The results of different sampling ratio are similar when using grid calculation, but they are great different when using direct calculation and kriging calculation based on field survey units.When using grid calculation, the area of soil and water loss of 1% sampling ratio is 49.97km2 higher than that of 4% sampling ratio, only account for 3.14% of Mengyin County, and account for 9.23% of the area of Mengyin County soil and water loss, and the location of soil and water loss is similar between two kinds of densities. When using direct calculation on survey units, the area of soil and water loss of 1% sampling ratio is 140.39km2 higher than that of 4% sampling ratio, account for 8.82% of Mengyin county, and account for 19.04% of the area of Mengyin County soil and water loss. When using kriging calculation on survey units, the area of soil and water loss of 1% sampling ratio is 126.60km2 higher than that of 4% sampling ratio, only account for 7.96% of Mengyin County, and account for 17.43% of the area of Mengyin County soil and water loss. The soil and water loss area of 1% lies central and northern county, when that of 4% is scattered across the county.When using grid calculation, the area of soil and water loss of 1% sampling ratio is 21.11km2 lower than that of 4% sampling ratio, only account for 0.88% of Yishui County, and only account for 1.98% of the area of Yishui County soil and water loss, and the location of soil and water loss is similar between two kinds of densities. When using direct calculation on survey units, the area of soil and water loss of 1% sampling ratio is 157.10km2 lower than that of 4% sampling ratio, account for 6.49% of the county, and account for 15.86% of the area of Yishui County soil and water loss. When using kriging calculation on survey units, the area of soil and water loss of 1% sampling ratio is 186.10km2 lower than that of 4% sampling ratio, account for 7.69% of county, and account for 19.29% of the area of the county soil and water loss. The soil and water loss area of 1% and 4% lies in the West and Southwest, but the location of every soil erosion intensity is diffe rent.(2)Under the same kind of density, the results of direct calculation on unit and kriging calculation on unit are similar, but they are quite different from grid calculation.The area of soil and water loss using direct calculation is only 24.25km2 higher than using kriging calculation, account for 1.52% at 1%sampling density in Mengyin. But they are 288.14km2 and 263.89km2 higher than using calculation on county, account for 18.12% and 16.60%. The area of soil and water loss using direct calculation is only 10.46km2 higher than using kriging calculation account for 0.66% at 4%sampling density in Mengyin. But they are 197.72km2 and 187.26km2 higher than using calculation on county, account for 12.43% and 11.77%. But the soil erosion spatial distribution between grid calculation and Kriging calculation is obviously different.The area of soil and water loss using direct calculation is only 20.99km2 higher than using kriging calculation accounting for 0.87% at 1%sampling density in Yishui. But they are 220.13km2 and 241.12km2 higher than using calculation on county, account for 9.09% and 9.96%. The area of soil and water loss using direct calculation is only 8.01km2 lower than using kriging calculation, account for 0.33% at 4%sampling density in Mengyin. But they are 84.14km2 and 76.13km2 higher than using calculation on county, account for 3.48% and 3.15%. But the soil erosion spatial distribution between grid calculation and Kriging calculation is obviously different.(3)The main influence factors are geological and soil, topography, land use, and engineering measures that result in the differences between divided sampling density and various calculation methods.Because of geological and soil, topography, land use, and engineering measures, the area of soil and water loss of 1% is higher than that of 4% using direct calculation and Kriging calculation, and the area of soil and water loss using direct calculation and Kriging calculation on unit is higher than using grid calculation in Mengyin. Because of topography, the area of soil and water loss of 1% is higher than that of 4% using direct calculation and Kriging calculation in Yishui.In the survey of soil and water loss at county scale, if equipped with a high resolution remote sensing images, we suggest to take 1% sampling density and use grid calculation on county for the soil erosion investigation; otherwise, we suggested to take 4% sampling density by direct calculation on unit or kriging calculation on unit to carry out the investigation.(4) In the survey of soil and water loss in a county, if equipped with a high resolution remote sensing images, we suggest to take 1% sampling density and use grid calculation on county for the soil erosion investigation; otherwise, we suggested to take 4% sampling density by direct calculation on unit or kriging calculation on unit to carry out the investigation. |
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