| This article is one part of scientific plan project of Zhejiang Province----The technology research of dynamic monitoring water and soil erosion basedon SPOT5 data by remote sensing (2006C33056). Study the technology of extracting the vegetation coverage degree by SPOT5 image data which is one of most important factors to influencing water and soil erosion.In order to pick up high accuracy vegetation coverage degree, the article combines the high space resolution characteristic of SPOT5 image data, the article adopts the dimidiate pixel mode based on the NDVI vegetation index. Since the ascertaining of two parameters NDVIveg and NDVIsoil in dimidiate pixel model is rather important, the article puts forward two methods of ascertaining parameters in the dimidiate pixel model accordingly as to different land utilization types of Yu Hang District. By concrete experiment of Yu Hang District by SPOT5 image in November,2005 and combining vegetation coverage degree data that measures on the open country, the experiment has got high accuracy in picking up vegetation coverage degree data and the results can fit to the high accuracy need of vegetation coverage degree in water and soil erosion model which indicates that the dimidiate pixel model and two parameters NDVIveg and NDVIsoil of dimidiate pixel model are feasible to pick up the vegetation coverage degree in water and soil erosion model.At the same time, the article has further probed serviceability of the model which will be applied to remote sensing image data in different period. Making use of the TM image of Yu Hang District in May , 2000 and July , 2004, the experiment picks up vegetation coverage degree by the dimidiate pixel model and the result of different period is consistent mainly which indicates that the dimidiate pixel model adapts to pick up the vegetation coverage degree by image data of different period.The article puts the good foundation on withdrawing the water and soil erosion information further by the research.
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