Correlation between molecular absorption spectral slope ratios and fluorescence humification indices in characterizing CDOM   总被引：2，自引：0，他引：2  

Hao Chen  Binghui Zheng  Yonghui Song  Yanwen Qin 《Aquatic Sciences - Research Across Boundaries》2011,73(1):103-112

Ultraviolet–visible absorption spectral slope ratios S_R (slope in 275–295 nm divided by slope in 350–400 nm) and humification index (HIX, integrated fluorescence emission in 435–480 nm divided by that in 435–480 and 300–345 nm) were compared when characterizing chromophoric dissolved organic matter (CDOM) in three humic acids and 44 whole water samples. HIX increased with increasing pH for humic acids, while their S_R showed much more complicated dependencies on pH. There was a negative correlation between S_R and HIX. S_R increased in the order terrestrial coal/peat < terrestrial soil/river < seawater, while HIX increased in the order seawater < terrestrial soil/river < terrestrial coal/peat. The comparative study in this work indicates that terrestrially derived CDOM has higher HIX and lower S_R than marine CDOM. Investigators may potentially use these two indices to compare qualitatively the character of CDOM in different sources (e.g., terrestrial vs. marine).  相似文献   

Monitoring global land surface drought based on a hybrid evapotranspiration model     

Yunjun Yao  Shunlin Liang  Qiming Qin  Kaicun Wang  Shaohua Zhao 《International Journal of Applied Earth Observation and Geoinformation》2011

The latent heat of evapotranspiration (ET) plays an important role in the assessment of drought severity as one sensitive indicator of land drought status. A simple and accurate method of estimating global ET for the monitoring of global land surface droughts from remote sensing data is essential. The objective of this research is to develop a hybrid ET model by introducing empirical coefficients based on a simple linear two-source land ET model, and to then use this model to calculate the Evaporative Drought Index (EDI) based on the actual estimated ET and the potential ET in order to characterize global surface drought conditions. This is done using the Global Energy and Water Cycle Experiment (GEWEX) Surface Radiation Budget (SRB) products, AVHRR-NDVI products from the Global Inventory Modeling and Mapping Studies (GIMMS) group, and National Centers for Environmental Prediction Reanalysis-2 (NCEP-2) datasets. We randomly divided 22 flux towers into two groups and performed a series of cross-validations using ground measurements collected from the corresponding flux towers. The validation results from the second group of flux towers using the data from the first group for calibration show that the daily bias varies from −6.72 W/m² to 12.95 W/m² and the average monthly bias is −1.73 W/m². Similarly, the validation results of the first group of flux towers using data from second group for calibration show that the daily bias varies from −12.91 W/m² to 10.26 W/m² and the average monthly bias is −3.59 W/m². To evaluate the reliability of the hybrid ET model on a global scale, we compared the estimated ET from the GEWEX, AVHRR-GIMMS-NDVI, and NECP-2 datasets with the latent heat flux from the Global Soil Wetness Project-2 (GSWP-2) datasets. We found both of them to be in good agreement, which further supports the validity of our model's global ET estimation. Significantly, the patterns of monthly EDI anomalies have a good spatial and temporal correlation with the Palmer Drought Severity Index (PDSI) anomalies from January 1984 to December 2002, which indicates that the method can be used to accurately monitor long-term global land surface drought.  相似文献   

基于非下采样Contourlet变换的极化SAR图像融合与去噪     

孙晓霞  张继贤  燕琴 《测绘科学》2011,36(3):70-72

针对非下采样Contourlet变换(NSCT)在处理噪声影像中具有的优势,以及同极化SAR图像(HH、VV)之间的相关性与互补性,本文实验了一种基于非下采样Contourlet变换的极化图像融合方法。该方法首先对每个极化图像进行多尺度、多方向分解,然后对不同分解子带系数分别采用有利于斑点噪声去除和信息增强的融合规则进行融合,最终通过NSCT反变换得到融合图像。通过信息熵、相关系数以及等效视数等指标的评价,验证了该方法可以有效地实现信息增强,同时该方法也在一定程度上降低了斑点噪声的负面影响。  相似文献   

利用目标点最小生成树的路面裂缝检测   总被引：1，自引：0，他引：1  

邹勤  李清泉  毛庆洲  陈龙 《武汉大学学报(信息科学版)》2011,(1):71-75

分析路面裂缝的成像特点,提出了一种基于目标点最小生成树的路面裂缝检测方法。最小生成树具有描述空间线性聚集特征的优点,有利于实现对裂缝的全局分析和提取。实验结果表明,对不连续裂缝的处理,本文方法优于传统方法。  相似文献   

Response of hydrological cycle to recent climate changes in the Tibetan Plateau   总被引：14，自引：0，他引：14  

Kun Yang  Baisheng Ye  Degang Zhou  Bingyi Wu  Thomas Foken  Jun Qin  Zhaoye Zhou 《Climatic change》2011,109(3-4):517-534

The Tibetan Plateau (TP) surfaces have been experiencing an overall rapid warming and wetting while wind speed and solar radiation have been declining in the last three decades. This study investigated how climate changes influenced the hydrological cycle on the TP during 1984??2006. To facilitate the analysis, a land surface model was used to simulate surface water budget at all CMA (China Meteorological Administration) stations on the TP. The simulated results were first validated against observed ground temperature and observation-derived heat flux on the western TP and observed discharge trends on the eastern TP. The response of evaporation and runoff to the climate changes was then analyzed. Major finding are as follows. (1) Surface water balance has been changed in recent decades. Observed precipitation shows insignificant increasing trends in central TP and decreasing trends along the TP periphery while evaporation shows overall increasing trends, leading to decreased discharge at major TP water resource areas (semi-humid and humid zones in the eastern and southern TP). (2) At the annual scale, evaporation is water-limited in dry areas and energy-limited (radiation and air temperature) in wet areas; these constraints can be interpreted by the Budyko-curve. Evaporation in autumns and winters was strongly controlled by soil water storage in summers, weakening the dependence of evaporation on precipitation at seasonal scales. (3) There is a complementary effect between the simulated actual evaporation and potential evaporation, but this complementary relationship may deviate from Bouchet??s hypothesis when vapor pressure deficit (or air temperature) is too low, which suppresses the power of vapor transfer.  相似文献   

Eigen analysis of tree-ring records: Part 1, a limited representativeness of regional curve     

Bao Yang  Dmitry M. Sonechkin  Nina M. Datsenko  Nadezda N. Ivashchenko  Jingjing Liu  Chun Qin 《Theoretical and Applied Climatology》2011,106(3-4):489-497

Based on a set of very long-living (2,000?years) Qilian junipers (Sabina przewalskii Kom.) from the north-eastern part of the Tibetan Plateau (the region of Dulan), we carefully consider the regional curve standardization (RCS) technique. For this goal, we correlate deviations of individual tree-ring width records from their regional mean age-dependent curve (RC). It turns out that these correlations keep their positivity for almost all shifts between ages compared (up to 500?years and even more) evidencing each Dulan juniper to be a unique ??thermometer??. Just the unification of these ??thermometers?? in the form RC creates a spurious positive trend in the Dulan chronology. We modify the RCS technique to closer attach RC to these ??thermometers?? in order to construct a new chronology in which the trend is absent.  相似文献   

遗传算法求解最大预报误差的可行性研究     

郑琴  张露  戴毅  陆小庆 《南京气象学院学报》2011,34(5):529-537

利用条件非线性最优扰动（conditional nonlinear optimal perturbation,CNOP）可以实现最大预报误差的上界估计。CNOP通常由基于梯度信息的约束优化算法进行求解,且其中的梯度信息由伴随模式提供。然而当非线性模式中含不连续＂开关＂时,传统伴随方法不能为优化过程提供正确的梯度方向,从而导致优化失败。为此,采用自适应变异和混合交叉的遗传算法,联赛选择机制和小生境技术的约束处理方法来求解最大预报误差上界。为检验新方法的有效性,以修改的Lorenz模型作为预报模式,对3个初始态分别用新方法和传统伴随方法进行比较,数值试验结果显示新方法求解出的最大预报误差的上界更加精确。  相似文献   

高空站后备电源维护方法     

覃晓玲  赵建吉  曾斌 《广西气象》2011,(4):74-76

对目前高空站所使用的后备电源的维护方面,参考有关资料,结合台站的工作经验,总结出备份电源的维护与保障方法,为各台站在日常使用备份电源时提供一定参考。  相似文献   

象山港余流特征数值研究     

万猛  姚炎明  陈琴  李丹 《海洋通报》2015,34(3):295-302

基于Delft3D-Flow模块建立了象山港海域的三维斜压潮流数值模型,结合实测水文资料,研究了象山港的潮(余)流特征,对欧拉余流场的时空分布进行了定量的比较和分析,并与潮流测站计算分析得到的欧拉余流分布对比,很好的模拟了象山港的余流特征。结果表明:由湾外至湾顶,余流呈减小的趋势,湾外余流最大为33 cm/s,湾顶最小,余流平均仅5 cm/s。垂向上,表层余流大于底层余流,表层余流指向湾外,而底层余流则指向湾内。对比斜压、正压两种模式下的欧拉余流分布,可以看出湾顶附近主要受径流控制,两种模式得到的结果基本一致,口门至西沪港区域受径流和潮流的共同影响,斜压模式更准确地模拟出了水体层化和垂向余环流结构。  相似文献   

数字滤波技术在潮汐观测中的应用研究     

闫秦  成方林  郭海  叶颖  王斌 《海洋技术学报》2015,34(4):28-32

潮汐是重要的海洋物理要素。瞬时变化的海面高度信息除了包含潮汐信息外,还包括波浪等高频干扰信息,因此需要对干扰信息进行滤除。如何从获取到的海面瞬时高度变化中提取出潮汐信息就成为一个关键问题。海洋学中通常是通过低通滤波来获取低频的潮汐信息。通过分析常用的3种低通数字滤波的方法,即滑动平均法、快速傅里叶变换法和小波变换法,对3种低通滤波方法应用于潮汐数据处理的效果进行了比较分析,得出滑动平均法在潮汐信息提取中具有较高应用价值的结论。  相似文献