Based on data collected over five years of monitoring the Lower Tarim River,we analyzed the variability of soil moisture content （SMC） and the relationship between SMC,groundwater table depth （GWD） and vegetation ...Based on data collected over five years of monitoring the Lower Tarim River,we analyzed the variability of soil moisture content （SMC） and the relationship between SMC,groundwater table depth （GWD） and vegetation by using the methods of coefficient of variation （Cv）,Pearson correlation and regression. The results of the variability of SMC indicate that it rose with increase in depth of soil layer -SMC in the soil layer of 0-60 cm was relatively small compared to SMC in the soil layer of 100-260 cm which showed a significant increase in variability. SMC and GWD before and after ecological water diversions exhibited significant differences at the site of the Yingsu transect and its vicinity of the watercourse,especially SMC in the soil layer of 100-260 cm increased significantly with a significant rise of GWD and reached maximum values at a GWD of about 4 m. Plant coverage and species diversity significantly improved with increases in SMC in the soil layer of 100-260 cm,both of them approached the maximum values and 92.3% of major plant species were able to grow when SMC was 〉 10%. To restore the ecosystem of desert riparian forest along the Lower Tarim River,the GWD must be maintained at 〈 4 m in the vicinity of the watercourse and at about 4 m for the rest of this arid region.展开更多
In this paper, a partially linear single-index model is investigated, and three empirical log-likelihood ratio statistics for the unknown parameters in the model are suggested. It is proved that the proposed statistic...In this paper, a partially linear single-index model is investigated, and three empirical log-likelihood ratio statistics for the unknown parameters in the model are suggested. It is proved that the proposed statistics are asymptotically standard chi-square under some suitable conditions, and hence can be used to construct the confidence regions of the parameters. Our methods can also deal with the confidence region construction for the index in the pure single-index model. A simulation study indicates that, in terms of coverage probabilities and average areas of the confidence regions, the proposed methods perform better than the least-squares method.展开更多
基于1998—2011年的SPOT VGT-NDVI数据,运用最大化均值法、提取植被覆盖度法和一元线性回归趋势分析法,对甘肃河东地区连续14 a的植被覆盖时空变化特征进行动态研究。结果表明:河东地区植被南多北少。在时间上,整体植被呈缓慢上升趋势,...基于1998—2011年的SPOT VGT-NDVI数据,运用最大化均值法、提取植被覆盖度法和一元线性回归趋势分析法,对甘肃河东地区连续14 a的植被覆盖时空变化特征进行动态研究。结果表明:河东地区植被南多北少。在时间上,整体植被呈缓慢上升趋势,增速为0.028·(10a)-1。其中,前4 a NDVI呈下降趋势,从1998年的0.392下降到2001年0.314;后10 a NDVI呈波动上升趋势,从2002年的0.330上升到2011年的0.378。在空间上,陇南山区中北部、陇中高原南部植被呈增加趋势;而陇东高原东南部、甘南草原区则有所下降。展开更多
基金National Basic Research Program of China (973 Program),No.2010CB951003National Natural Science Foundation of China,No.40871059CAS Western Light Program,No.XBBS 200804
文摘Based on data collected over five years of monitoring the Lower Tarim River,we analyzed the variability of soil moisture content （SMC） and the relationship between SMC,groundwater table depth （GWD） and vegetation by using the methods of coefficient of variation （Cv）,Pearson correlation and regression. The results of the variability of SMC indicate that it rose with increase in depth of soil layer -SMC in the soil layer of 0-60 cm was relatively small compared to SMC in the soil layer of 100-260 cm which showed a significant increase in variability. SMC and GWD before and after ecological water diversions exhibited significant differences at the site of the Yingsu transect and its vicinity of the watercourse,especially SMC in the soil layer of 100-260 cm increased significantly with a significant rise of GWD and reached maximum values at a GWD of about 4 m. Plant coverage and species diversity significantly improved with increases in SMC in the soil layer of 100-260 cm,both of them approached the maximum values and 92.3% of major plant species were able to grow when SMC was 〉 10%. To restore the ecosystem of desert riparian forest along the Lower Tarim River,the GWD must be maintained at 〈 4 m in the vicinity of the watercourse and at about 4 m for the rest of this arid region.
基金supported by the Natural Science Foundation of Beijing City(Grant No.1042002)Technology Development Plan Project of Beijing Education Committee(Grant No.KM2005 10005009)+1 种基金the Special Grants of Beijing for Talents(Grant No.20041D0501515)supported by a grant from the Research Grants Council of Hong Kong,Hong Kong(Grant No.HKU7060/04P).
文摘In this paper, a partially linear single-index model is investigated, and three empirical log-likelihood ratio statistics for the unknown parameters in the model are suggested. It is proved that the proposed statistics are asymptotically standard chi-square under some suitable conditions, and hence can be used to construct the confidence regions of the parameters. Our methods can also deal with the confidence region construction for the index in the pure single-index model. A simulation study indicates that, in terms of coverage probabilities and average areas of the confidence regions, the proposed methods perform better than the least-squares method.
文摘基于1998—2011年的SPOT VGT-NDVI数据,运用最大化均值法、提取植被覆盖度法和一元线性回归趋势分析法,对甘肃河东地区连续14 a的植被覆盖时空变化特征进行动态研究。结果表明:河东地区植被南多北少。在时间上,整体植被呈缓慢上升趋势,增速为0.028·(10a)-1。其中,前4 a NDVI呈下降趋势,从1998年的0.392下降到2001年0.314;后10 a NDVI呈波动上升趋势,从2002年的0.330上升到2011年的0.378。在空间上,陇南山区中北部、陇中高原南部植被呈增加趋势;而陇东高原东南部、甘南草原区则有所下降。
