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41.
42.
Remote estimation of terrestrial evapotranspiration by Landsat 5 TM and the SEBAL model in cold and high‐altitude regions: a case study of the upper reach of the Shule River Basin,China 下载免费PDF全文
Evapotranspiration (ET) is an important expenditure in water and energy balances, especially on cold and high‐altitude land surfaces. Daily ET of the upper reach of the Shule River Basin was estimated using Landsat 5 TM data and the Surface Energy Balance Algorithm for Land (SEBAL) model. Based on observations made at the Suli station, the algorithms of land surface temperature and soil heat flux in SEBAL were modified. Land surface temperature was retrieved and compared with ground truth via three methods: the radiative transfer equation method, the mono‐window algorithm, and the single‐channel method. We selected the best of these methods, mono‐window algorithm, for estimating ET. The average error of daily ET estimated by the modified SEBAL model and measured by the eddy covariance system was 16.4%, with a root‐mean‐square error of 0.52 mm d?1. The estimated ET means were 3.09, 2.48, and 1.48 mm d?1 on June 9 (DOY 160), June 25 (DOY 176), and July 27 (DOY 208) of the year 2010, respectively. The average estimated ET on the glacier surface of all days was more than 3 mm d?1, a measurement that is difficult to capture in‐situ and has rarely been reported. This study will improve the understanding of water balance in cold, high‐altitude regions. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
43.
We performed an in-depth literature survey to identify the most popular data mining approaches that have been applied for raster mapping of ecological parameters through the use of Geographic Information Systems (GIS) and remotely sensed data. Popular data mining approaches included decision trees or “data mining” trees which consist of regression and classification trees, random forests, neural networks, and support vector machines. The advantages of each data mining approach as well as approaches to avoid overfitting are subsequently discussed. We also provide suggestions and examples for the mapping of problematic variables or classes, future or historical projections, and avoidance of model bias. Finally, we address the separate issues of parallel processing, error mapping, and incorporation of “no data” values into modeling processes. Given the improved availability of digital spatial products and remote sensing products, data mining approaches combined with parallel processing potentials should greatly improve the quality and extent of ecological datasets. 相似文献
44.
地表温度在全球能量平衡和气候变化研究中具有重要意义。中国新一代高分辨率卫星高分五号卫星(GF-5)搭载的全谱段成像光谱仪有4个40 m空间分辨率的热红外波段,可以提供高空间分辨率的地表温度信息。本文提出了适用于全谱段成像光谱仪的温度与发射率分离TES(Temperature and Emissivity Separation)算法同时反演地表温度和发射率,为了提高大气校正精度,算法加入了水汽缩放WVS(Water Vapor Scaling)大气校正方法。首先利用Seebor V5.0全球大气廓线库构建模拟数据对算法精度进行了评价;然后利用张掖地区11景ASTER影像作为替代数据和同步的地面实测数据对算法精度进行了验证。模拟数据结果表明加入WVS方法后TES算法反演地表温度的RMSE由2.59 K降低到1.54 K,4个波段地表发射率的RMSE分别从0.122、0.12、0.102和0.037降低到0.042、0.04、0.028和0.026;地表验证结果表明本文算法反演的地表温度与站点实测值具有更好的一致性,平均Bias由1.08 K降低到0.47 K,RMSE由2.17 K降低到1.7 K;反演的各波段地表发射率与地面实测结果误差均小于1%。因此,本文提出的温度与发射率分离算法具有较高精度,可以利用GF-5数据获取高精度高空间分辨率的地表温度和发射率数据,服务于其他相关研究。 相似文献
45.
The consistency of global atmospheric mass and water budget performance in 20 state-of-the-art ocean–atmosphere Coupled Model Intercomparison Project Phase 5 (CMIP5) coupled models has been assessed in a historical experiment. All the models realistically reproduce a climatological annual mean of global air mass (AM) close to the ERA-Interim AM during 1989–2005. Surprisingly, the global AM in half of the models shows nearly no seasonal variation, which does not agree with the seasonal processes of global precipitable water or water vapor, given the mass conservation constraint. To better understand the inconsistencies, we evaluated the seasonal cycles of global AM tendency and water vapor source (evaporation minus precipitation). The results suggest that the inconsistencies result from the poor balance between global AM tendency and water vapor source based on the global AM budget equation. Moreover, the cross-equatorial dry air mass ?ux, or hemispheric dry mass divergence, is not well represented in any of the 20 CMIP5 models, which show a poorly matched seasonal cycle and notably larger amplitude, compared with the hemispheric tendencies of dry AM in both the Northern Hemisphere and Southern Hemisphere. Pronounced erroneous estimations of tropical precipitation also occur in these models. We speculate that the large inaccuracy of precipitation and possibly evaporation in the tropics is one of the key factors for the inconsistent cross-equatorial mass ?ux. A reasonable cross-equatorial mass ?ux in well-balanced hemispheric air mass and moisture budgets remains a challenge for both reanalysis assimilation systems and climate modeling. 相似文献
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利用观测海温资料和CMIP5模式模拟结果分析西北太平洋(120°E~120°W,20~60°N)海表温度的气候态和年代际变化特征。结果表明,所选22个模式可以较好地模拟出西北太平洋海表温度的气候特征及其年际、年代际变化特征;模式模拟的海表温度总体标准偏差在黑潮延伸体区域最大;绝大多数模式能模拟出海表温度的第一EOF模态;西北太平洋海表温度具有较明显的年代际振荡现象,13/22的模式模拟的海表温度存在明显的年代际振荡,同时海表温度气候态的模拟偏差对其周期振荡模拟的影响较大,尤其在黑潮延伸体区域。 相似文献
48.
The Siberian high(SH)experienced a decline from the 1970s to 1990s and a recovery in recent years.The evolution of the SH under global warming is unclear.In this study,41 Coupled Model Intercomparison Project Phase 5(CMIP5)climate models are evaluated in terms of their ability to simulate the temporal evolution of the SH in the 19th and 20th centuries and the spatial pattern of the SH during 1981–2005.The results show that 12models can capture the temporal evolution of the SH center intensity(SHCI)for 1872–2005.The linear correlation coefficient between the SHCI from the Twentieth Century Reanalysis and the simulated SHCI from the multi-model ensemble(MME)of the 12 models is 0.3 on annual and inter-annual scales(above the 99%confidence level).On decadal and multi-decadal time scales,the MME also captures the pronounced reduction(between 1981–2000and 1881–1900 period)and the recovery(during1991–2005)of the SH intensity.Finally,the future evolution of the SH is investigated using the MME of the 12models under the+4.5 and+8.5 W m-2 Representative Concentration Pathway(RCP)scenarios(RCP4.5 and RCP8.5).It is shown that the SHCI,similar to the SHCI in the 20th century,has no significant long-term trend in the 21st century under global warming(RCP8.5 scenario).At the end of 21st century(2081–2100),the SH shows stronger interannual variability than the SH at the end of20th century(1981–2000).The increased interannual variability likely favors the increased interannual variability in winter air temperature over midlatitude Eurasia at the end of 21st century. 相似文献
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50.
The tropical Hadley circulation (HC) plays an important role in influencing the climate in the tropics and extra-tropics. The realism of the climatological characteristics, spatial structure, and temporal evolution of the long-term variation of the principal mode of the annual mean HC (i.e., the equatorially asymmetric mode, EAM) was examined in model simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5). The results showed that all the models are moderately successful in capturing the HC's climatological features, including the spatial pattern, meridional extent, and intensity, but not the spatial or temporal variation of the EAM. The possible reasons for the poor simulation of the long-term variability of the EAM were explored. None of the models can successfully capture the differences in the warming rate between the tropical Southern Hemisphere (SH) and Northern Hemisphere (NH), which is considered to be an important driver for the variation of the AM. Most of the models produce a faster warming in the NH than in the SH, which is the reverse of the observed trend. This leads to a reversed trend in the meridional gradient between the SH and NH, and contributes to the poor simulation of EAM variability. Thus, this aspect of the models should be improved to provide better simulations of the variability of the HC. This study suggests a possible reason for the poor simulation of the HC, which may be helpful for improving the skill of the CMIP5 models in the future. 相似文献