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排序方式: 共有150条查询结果,搜索用时 15 毫秒
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灰色系统理论在估产中的应用:以吉林省梨树县为例 总被引:5,自引:0,他引:5
以吉林省梨树县为例,阐述了利用灰色系统进行了玉米气象估产的方法,其中包括用GM(1,1)模型进行了趋势产量预测,用灰色关联度分析方法确定主气象因子群,以及利用GM(1,1)进行气象产量预测等。 相似文献
34.
全球农作物对大气CO2及其倍增的吸收量估算 总被引:15,自引:0,他引:15
根据农作物产量资料(FAO1992年),计算出中国和全球各种作物对CO2的吸收总量分别为5.5×108t/aC和28.9×108t/aC。同时以不同CO2浓度下小麦、玉米、大豆等全生育期光合速率实验数据直接计算的C吸收量为对照,与相应的中国产量资料计算结果比较,两者相差2.6%。从而进一步依据作物对CO2倍增反应诊断实验结果,推算出大气CO2浓度比目前倍增(700ppm)条件下,中国和全球农作物吸收CO2总量将增长21%-26%,分别为6.6×108t/a—6.9×108t/a和34.1×108t/a—36.2×108t/aC。研究还表明,单位面积作物年吸C量全球(3.2t/(hm2·8))比中国(4.2t/(hm2·a))低25.4%,而且C4作物普遍高于同类C3作物。 相似文献
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N. C. Lind H. P. Hong V. Solana 《Stochastic Environmental Research and Risk Assessment (SERRA)》1989,3(3):191-202
The cross-entropy method with fractile constraints has been developed to estimate a random variable when the data are a set of independent observations of the variable. The method can claim several advantages over existing methods. It uses a reference distribution like the prior distribution in Bayesian analysis and likewise generates a posterior distribution.The method is of interest, in particular, because it satisfies two fundamental requirements for selfconsistency in the analysis of a probabilistic system based on data: a principle of invariance and a principle of data monotonicity.The method is applied to flood analysis. Robustness of the minimum cross-entropy method is compared with other methods: the methods of moments and the maximum likehood. 相似文献
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土地利用生态安全评价指标的系统聚类分析 总被引:15,自引:0,他引:15
生态安全研究是目前中国土地资源可持续利用研究的前沿课题.本文利用系统聚类分析方法,以湖南省14个地州市为样本,从1999年社会经济和土地生态环境压力、土地生态环境质量、土地生态环境保护和整治能力等多方面的运行数据中选取人口密度、城镇化水平、人均耕地、人均GDP、森林覆盖率、水土流失等24个指标,对土地利用生态安全评价指标作了系统聚类和分析。 相似文献
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Three and four parameter distributions of events and intervals based on the Kummer and Tricomi functions are shown to be
statistically tractable. The Kummer distributions cover events less as well as more clustered than the Poisson while the Tricomi
distributions have two and three parameter negative binomials as special cases. This flexibility and the moment relations
between the parameters make them attractive in cases where the Poisson distribution proves inadequate. 相似文献
38.
Jean-Denis Taupin 《Comptes Rendus Geoscience》2003,335(2):215-225
Many earlier studies have shown the very large spatial variability of rainfall in the Sahel at all time steps, from the event to the season. Often, the meteorological network in these countries is sparse, with one to five rain gauges per 10 000 km2. It is thus difficult to calculate accurate estimates of the mean rainfall over such a large area. To improve the knowledge of Sahelian systems and the spatial distribution of rainfall, a dense network was set up in an area of 16 000 km2 in southwestern Niger between 1991 and 1996. The aim was to calculate accurate rainfall spatial means over an area of 12 000 km2 at different time steps (from the season to the ten-day period). With the spatialisation method used (kriging), it was possible to calculate curves of estimation errors of mean rainfall versus the rain-gauge network density. Operational abacuses of the standard estimation error as a function of the spatial mean of rainfall and the network density are proposed. 相似文献
39.
This paper addresses the application of a data‐based mechanistic (DBM) modelling approach using transfer function models (TFMs) with non‐linear rainfall filtering to predict runoff generation from a semi‐arid catchment (795 km2) in Tanzania. With DBM modelling, time series of rainfall and streamflow were allowed to suggest an appropriate model structure compatible with the data available. The model structures were evaluated by looking at how well the model fitted the data, and how well the parameters of the model were estimated. The results indicated that a parallel model structure is appropriate with a proportion of the runoff being routed through a fast flow pathway and the remainder through a slow flow pathway. Finally, the study employed a Generalized Likelihood Uncertainty Estimation (GLUE) methodology to evaluate the parameter sensitivity and predictive uncertainty based on the feasible parameter ranges chosen from the initial analysis of recession curves and calibration of the TFM. Results showed that parameters that control the slow flow pathway are relatively more sensitive than those that control the fast flow pathway of the hydrograph. Within the GLUE framework, it was found that multiple acceptable parameter sets give a range of predictions. This was found to be an advantage, since it allows the possibility of assessing the uncertainty in predictions as conditioned on the calibration data and then using that uncertainty as part of the decision‐making process arising from any rainfall‐runoff modelling project. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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