Vegetation fractional coverage （VFC） is an important index to describe and evaluate the ecological system. The vegetation index is widely used to monitor vegetation coverage in the field of remote sensing （RS）. In...Vegetation fractional coverage （VFC） is an important index to describe and evaluate the ecological system. The vegetation index is widely used to monitor vegetation coverage in the field of remote sensing （RS）. In this paper, the author conducted a case study of the delta oasis of Weigan and Kuqa rivers, which is a typical saline area in the Tarim River Watershed. The current study was based on the TM/ETM＋ images of 1989, 2001, and 2006, and supported by Geographic Information System （GIS） spatial analysis, vegetation index, and dimidiate pixel model. In addition, VBSl （vegetation, bare soil and shadow indices） suitable for TM/ETM＋ irrlages, constructed with FCD （forest canopy density） model principle and put forward by ITTO （International Tropical Timber Organization）, was used, and it was applied to estimate the VFC. The estimation accuracy was later prow^n to be up to 83.52%. Further, the study analyzed and appraised the changes in vegetation patterns and revealed a pattern of spatial change in the vegetation coverage of the study area by producing the map of VFC levels in the delta oasis. Forest, grassland, and farmland were the three main land-use types with high and extremely-high coverage, and they played an important role in maintaining the vegetation. The forest area determined the changes of the coverage area, whereas the other two land types affected the directions of change. Therefore, planting trees, protecting grasslands, reclaiming farmlands, and controlling unused lands should be included in a long-term program because of their importance in keeping regional vegetation coverage. Finally, the dynamic variation of VFC in the study area was evaluated according to the quantity and spatial distribution rendered by plant cover diigital images to deeply analyze the reason behind the variation.展开更多
Soil erosion by water under forest cover is a serious problem in southern China.A comparative study was carried out on the use of leaf area index(LAI) and vegetation fractional coverage(VFC) in quantifying soil loss u...Soil erosion by water under forest cover is a serious problem in southern China.A comparative study was carried out on the use of leaf area index(LAI) and vegetation fractional coverage(VFC) in quantifying soil loss under vegetation cover.Five types of vegetation with varied LAI and VFC under field conditions were exposed to two rainfall rates(40 mm h-1 and 54 mm h-1) using a portable rainfall simulator.Runoff rate,sediment concentration and soil loss rate were measured at relatively runoff stable state.Significant negative exponential relationship(p < 0.05,R2 = 0.83) and linear relationship(p < 0.05,R2 = 0.84) were obtained between LAI and sediment concentration,while no significant relationship existed between VFC and sediment concentration.The mechanism by which vegetation canopy prevents soil loss was by reducing rainfall kinetic energy and sediment concentration.LAI could better quantify such a role than VFC.However,neither LAI nor VFC could explain runoff rate or soil loss rate.Caution must be taken when using LAI to quantify the role of certain vegetation in soil and water conservation.展开更多
针对目前SIFT算法及其改进算法在多波段SAR图像匹配时匹配性能低下(普适性差、匹配精度低、时间复杂度高)的问题,在SIFT算法框架下分别从尺度空间构建和描述符构建两个方面进行改进。在构建尺度空间层面,提出将高斯引导滤波引入多尺度...针对目前SIFT算法及其改进算法在多波段SAR图像匹配时匹配性能低下(普适性差、匹配精度低、时间复杂度高)的问题,在SIFT算法框架下分别从尺度空间构建和描述符构建两个方面进行改进。在构建尺度空间层面,提出将高斯引导滤波引入多尺度空间构建和预处理阶段,采用双边滤波策略,充分利用高斯引导滤波的实时性和旋转对称性与双边滤波的边缘保持优势,高效地滤除斑点噪声并保持边缘信息。在构建描述符阶段,提出采用局部差分二进制(Local Difference Binary,LDB)算法描述特征,在保证不降低特征点描述符区分性的同时,减少特征的向量维度,从而缩短构建描述符的时间。在特征匹配阶段,首先采用最近邻算法进行粗匹配,然后采用稀疏向量场一致性(Vector Field Consensus,VFC)快速剔除错误匹配点。实验结果表明,所提算法在SAR图像配准时间复杂度和匹配概率评价上要优于原始BFSIFT算法和KAZE算法。总体上,文中提出的SAR图像匹配算法是具有实时性、鲁棒性与高匹配概率的高效算法。展开更多
基金supported by the National Basic Research Program of China (2009CB421302)the Joint Fundsof the National Natural Science Foundation of China(U1138303)+4 种基金the National Natural Science Foundation of China(41261090,41161063)the Open Foundation of State Key Laboratory of Resources and Environment Information Systems (2010KF0003SA)Scientific Research Foundation for Doctor (BS110125)Xinjiang Natural Science Foundation for Young Scholars (2012211B04)Research Fund for Training Young Teachers (XJEDU2012S03)
文摘Vegetation fractional coverage （VFC） is an important index to describe and evaluate the ecological system. The vegetation index is widely used to monitor vegetation coverage in the field of remote sensing （RS）. In this paper, the author conducted a case study of the delta oasis of Weigan and Kuqa rivers, which is a typical saline area in the Tarim River Watershed. The current study was based on the TM/ETM＋ images of 1989, 2001, and 2006, and supported by Geographic Information System （GIS） spatial analysis, vegetation index, and dimidiate pixel model. In addition, VBSl （vegetation, bare soil and shadow indices） suitable for TM/ETM＋ irrlages, constructed with FCD （forest canopy density） model principle and put forward by ITTO （International Tropical Timber Organization）, was used, and it was applied to estimate the VFC. The estimation accuracy was later prow^n to be up to 83.52%. Further, the study analyzed and appraised the changes in vegetation patterns and revealed a pattern of spatial change in the vegetation coverage of the study area by producing the map of VFC levels in the delta oasis. Forest, grassland, and farmland were the three main land-use types with high and extremely-high coverage, and they played an important role in maintaining the vegetation. The forest area determined the changes of the coverage area, whereas the other two land types affected the directions of change. Therefore, planting trees, protecting grasslands, reclaiming farmlands, and controlling unused lands should be included in a long-term program because of their importance in keeping regional vegetation coverage. Finally, the dynamic variation of VFC in the study area was evaluated according to the quantity and spatial distribution rendered by plant cover diigital images to deeply analyze the reason behind the variation.
基金the support for this research from the National Basic Research Program of China(Grant No.2007CB407206)the National Natural Science Foundation of China(Grant No.40921061)The National Basic Research Program of China(Grant No.2010CB950702)
文摘Soil erosion by water under forest cover is a serious problem in southern China.A comparative study was carried out on the use of leaf area index(LAI) and vegetation fractional coverage(VFC) in quantifying soil loss under vegetation cover.Five types of vegetation with varied LAI and VFC under field conditions were exposed to two rainfall rates(40 mm h-1 and 54 mm h-1) using a portable rainfall simulator.Runoff rate,sediment concentration and soil loss rate were measured at relatively runoff stable state.Significant negative exponential relationship(p < 0.05,R2 = 0.83) and linear relationship(p < 0.05,R2 = 0.84) were obtained between LAI and sediment concentration,while no significant relationship existed between VFC and sediment concentration.The mechanism by which vegetation canopy prevents soil loss was by reducing rainfall kinetic energy and sediment concentration.LAI could better quantify such a role than VFC.However,neither LAI nor VFC could explain runoff rate or soil loss rate.Caution must be taken when using LAI to quantify the role of certain vegetation in soil and water conservation.
文摘针对目前SIFT算法及其改进算法在多波段SAR图像匹配时匹配性能低下(普适性差、匹配精度低、时间复杂度高)的问题,在SIFT算法框架下分别从尺度空间构建和描述符构建两个方面进行改进。在构建尺度空间层面,提出将高斯引导滤波引入多尺度空间构建和预处理阶段,采用双边滤波策略,充分利用高斯引导滤波的实时性和旋转对称性与双边滤波的边缘保持优势,高效地滤除斑点噪声并保持边缘信息。在构建描述符阶段,提出采用局部差分二进制(Local Difference Binary,LDB)算法描述特征,在保证不降低特征点描述符区分性的同时,减少特征的向量维度,从而缩短构建描述符的时间。在特征匹配阶段,首先采用最近邻算法进行粗匹配,然后采用稀疏向量场一致性(Vector Field Consensus,VFC)快速剔除错误匹配点。实验结果表明,所提算法在SAR图像配准时间复杂度和匹配概率评价上要优于原始BFSIFT算法和KAZE算法。总体上,文中提出的SAR图像匹配算法是具有实时性、鲁棒性与高匹配概率的高效算法。
