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141.
��������ƹ�������С�ⷨ�ĵ�ͼ����任 总被引:1,自引:1,他引:0
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This paper describes an improved algorithm for fuzzyc-means clustering of remotely sensed data, by which the degree of fuzziness of the resultant classification is decreased as
comparing with that by a conventional algorithm: that is, the classification accuracy is increased. This is achieved by incorporating
covariance matrices at the level of individual classes rather than assuming a global one. Empirical results from a fuzzy classification
of an Edinburgh suburban land cover confirmed the improved performance of the new algorithm for fuzzyc-means clustering, in particular when fuzziness is also accommodated in the assumed reference data. 相似文献
146.
G. Christakos V. Papanicolaou 《Stochastic Environmental Research and Risk Assessment (SERRA)》2000,14(6):471-478
Permissibility of a covariance function (in the sense of Bochner) depends on the norm (or metric) that determines spatial
distance in several dimensions. A covariance function that is permissible for one norm may not be so for another. We prove
that for a certain class of covariances of weakly homogeneous random fields, the spatial distance can be defined only in terms
of the Euclidean norm. This class includes commonly used covariance functions. Functions that do not belong to this class
may be permissible covariances for some non-Euclidean metric. Thus, a different class of covariances, for which non-Euclidean
norms are valid spatial distances, is also discussed. The choice of a coordinate system and associated norm to describe a
physical phenomenon depends on the nature of the properties being described. Norm-dependent permissibility analysis has important
consequences in spatial statistics applications (e.g., spatial estimation or mapping), in which one is concerned about the
validity of covariance functions associated with a physically meaningful norm (Euclidean or non-Euclidean). 相似文献
147.
Inter‐annual variations and factors controlling evapotranspiration in a temperate Japanese cypress forest
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This study was undertaken to evaluate the effects of climatic variability on inter‐annual variations in each component of evapotranspiration (ET) and the total ET in a temperate coniferous forest in Japan. We conducted eddy covariance flux and meteorological measurements for 7 years and parameterized a one‐dimensional multi‐layer biosphere‐atmosphere model (Kosugi et al., 2006 ) that partitions ET to transpiration (Tr), wet‐canopy evaporation (Ewet), and soil evaporation (Esoil). The model was validated with the observed flux data. Using the model, the components of ET were estimated for the 7 years. Annual precipitation, ET, Tr, Ewet, and Esoil over the 7 years were 1536 ± 334 mm, 752 ± 29 mm, 425 ± 37 mm, 219 ± 34 mm, and 108 ± 10 mm, respectively. The maximum inter‐annual fluctuation of observed ET was 64 mm with a coefficient of variance (CV) of 2.7%, in contrast to relatively large year‐to‐year variations in annual rainfall (CV = 20.1%). Tr was related to the vapour pressure deficit, incoming radiation, and air temperature with relatively small inter‐annual variations (CV = 8.2%). Esoil (CV = 8.6%) was related mainly to the vapour pressure deficit. Ewet was related to precipitation with large inter‐annual variations (CV = 14.3%) because of the variability in precipitation. The variations in Ewet were counterbalanced by the variations in Tr and Esoil, producing the small inter‐annual variations in total ET. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
148.
Variations of crop coefficient and its influencing factors in an arid advective cropland of northwest China
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Understanding the variation and magnitude of crop coefficient (Kc) is important for accurate determination of crop evapotranspiration and water use. In this study, we calculated Kc in an irrigated maize field with ground mulching by eddy covariance evapotranspiration measurements during the whole growing periods in 2009 and 2010 in an arid region of northwest China. A semi‐empirical practical approach for estimating Kc was proposed by introducing the dynamic fraction of canopy cover and incorporating the effect of leaf senescence as a function of days after sowing. The contribution of arid advection of sensible heat resulting from irrigation to Kc and the response of Kc to canopy conductance (Gc) were investigated. The averaged values of daily Kc were lower than typical values obtained previously without mulching due to decreasing effect of mulching on Kc, with 0.82 and 0.80 for the 2 years, respectively. The maximum average Kc occurred at the heading stage, with 1.21 and 1.04 for the 2 years, respectively. The difference of Kc was attributed to the difference of leaf area index. The semi‐empirical practical approach could well estimate the variations of Kc, thus could be a robust and useful tool for the practical users and water managers. The contributions to daily Kc from the arid advection were 4.4–28.0% of the measured Kc. The Gc had stronger control on daily Kc at the early and later stages than at the middle stage. When Gc, leaf area index and relative soil extractable water were lower than the respective threshold values of 20 mm s?1, 3.0 m2 m?2 and 0.5, the daily Kc increased significantly with the increase of the three factors, and almost remained constant when the three factors were beyond the threshold values. These results are helpful for quantifying contributions of individual factors to Kc, and subsequently improving water management practices according to Kc. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
149.
用涡度相关法对新疆塔里木河下游荒漠河岸柽柳(Tamarix chinensis)灌丛进行了1个生长季的实验观测,利用同步气象资料探讨了干旱胁迫环境下柽柳灌丛的近地面微气象和能量平衡特征,并运用普通最小二乘法线性回归及能量平衡比率法对比分析了不同天气条件下柽柳的日能量平衡变化和分配的差异。结果表明:观测期内柽柳灌丛的能量平衡闭合率为72.3%,地表能量通量和能量分配特征呈明显的单峰型二次曲线,地表净辐射通量和潜热通量是柽柳灌丛生长季的主要能量收入项和支出项;生长季内柽柳灌丛的能量平衡残差出现系统性、正负交替的日循环规律;在不同天气条件下,能量的分配转化和平衡程度均有明显差异,晴天的能量闭合状况好于阴天、降雨及扬沙天气,白天好于夜间;能量平衡比率在日出前与日落后的变化显著,且出现瞬时能量过闭合现象。受光合作用的影响,能量平衡闭合程度及碳通量的变化与不同天气下的温度及水分密切相关。 相似文献
150.
半干旱夏季放牧草地能量收支和地表蒸散量变化特征 总被引:1,自引:0,他引:1
以半干旱区域典型夏季放牧草地为研究对象,采用涡动相关法,获取了2012年5月至2013年5月水汽和能量通量观测数据,分析夏季近地层能量收支特征、地表蒸散量变化及其气象控制因子。观测结果显示:生长季有效能量的分配以潜热通量为主,非生长季则以感热通量为主;地表蒸散日总量最大值为3.0mm,日蒸散量大小主要取决于土壤温度、气温和净辐射;降雨量的季节分布是地表蒸散量季节变化的一个重要的影响因子。 相似文献