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161.
黑体为目标的能见度测量是从科西米德定律出发,通过工业相机对黑体目标物进行拍摄,建立黑体和背景天空的数学模型,求得能见度。分析表明:当能见度小于30 km,黑体黑度和CCD(change-coupled device)工业相机的面非均匀性对该方法测得的能见度造成的误差约为3.7%。该方法与前向散射能见度仪测量进行对比,能见度变化趋势上具有一致性;但在高能见度时,黑体能见度测量值大于前向散射能见度测量值,低能见度时,黑体测量值小于前向散射能见度测量值。 相似文献
162.
In this study, we investigate the impact of atmospheric convection over the western tropical Pacific (100–145°E, 0–20°N) on the boreal winter North Pacific atmosphere flow by analyzing National Center for Environmental Prediction Reanalysis 1, Extended Reconstructed Sea Surface Temperature and Global Precipitation Climatology Project data. The western tropical Pacific convection is not only the main energy source driving the local Hadley and Walker circulations, but it also significantly influences North Pacific circulation, by modifying a mid-latitude Jet stream through the connection with the local Hadley circulation. On the one hand, this strong convection leads to a northward expansion of local Hadley cells simultaneous with a northward movement of the western North Pacific jet because of the close correlation between the Jet and Hadley circulation boundaries. On the other hand, this strong convection also intensifies tropical Pacific Walker circulation, which reduces the eastern Pacific sea surface temperature, resembling a La Nina state through the enhanced equatorial upwelling. The cooling of the eastern tropical Pacific has an inter-tropical convergence zone located further north; thus, the local Hadley circulation moves northward. As a result, the jet axis over the eastern North Pacific, which also corresponds to the boundary of the local Hadley circulation, moves to higher latitude. Consequently, this northward movement of the Jet axis over the North Pacific is reflected as a northwest–southeast dipole sea level pressure (SLP) pattern. The composite analysis of SLP over the North Pacific against the omega (Ω) (Pa/s) at 500 hPa over the western tropical Pacific actually reveals that this northwest-southeast dipole structure is attributed to the intensified tropical western Pacific convection, which pushes the Pacific Jet to the north. Finally we also analyzed south Pacific for the austral winter as did previously to North Pacific, and found that the results were consistent. 相似文献
164.
互联网数据中蕴含丰富的地理信息,其无处不在、形式与结构多样的特征决定了感知和融合面临许多技术难题。本文在分析互联网泛在地理信息分类和特征的基础上,系统研究其感知和融合技术的总体现状,总结了服务快速准确发现、深层网络数据高覆盖度采集、非结构化文本中位置信息提取和关联图像空间语义提取等感知技术发展现状,分析了异源几何数据匹配关联、地址标准化处理、同名实体语义对齐、地理实体关系构建等融合处理关键技术;在此基础上,总结和展望了互联网泛在地理信息感知融合技术在开放地理数据网络、城市治理与应急管理、网络监测与地理空间情报等领域的应用前景。 相似文献
165.
For the last three decades, Northern China has been considered as one of the most sensitive areas regarding global environmental change. The integration of AVHRR GIMMS and MODIS NDVI data (1982–2011), of which for the overlapping period of 2000–2006 show good consistency, were used for characterizing land condition variability. The trends of standardized annually ΣNDVI, temperature, precipitation and PDSI were obtained using a linear regression model. The results showed that Northern China has a general increase in greenness for the period 1982–2011 (a = 0.05). Also, annually ΣNDVI is significantly correlated with temperature and precipitation data at the regional scale (p < 0.05), implying that temperature and precipitation are the dominant limiting factors for vegetation growth. Since the greening is not uniform, factors other than temperature and precipitation may contribute to greening in some areas, while the grassland and cropland ecosystem are becoming increasingly vulnerable to drought. The results of trend analysis indicate that greenness seems to be evident in most of the study areas. 相似文献
166.
Liang Wang Yuan-ping Cheng Feng-hua An Hong-xing Zhou Sheng-li Kong Wei Wang 《Natural Hazards》2014,71(1):85-107
The Huaibei coalfield is in the East China Economic Area, which is rich in coal and gas resources. However, hundreds of coal and gas outburst accidents have occurred because of the complex geological structures of the coalfield. Based on theoretical analysis and field statistics, the characteristics of regional geological structures and the coal measure strata evolution in the Huaibei coalfield were researched, and gas resource distribution and gas parameters were statistically analyzed to determine the dominant controlling factors of gas occurrence and gas dynamic disaster. The results indicated that the Huaibei coalfield has undergone complex tectonic evolution, causing obvious differences in gas storage in different blocks of different mining areas, which exhibits a pattern of high amounts of gas in the south and east, and low amounts of gas in the north and west. The coal seam and gas occurrence have a bipolar distribution in the coalfield caused by multiple tectonic movements, and they are deeply buried. Horizontal tectonic stress plays a dominant role in gas outburst, and the thermal evolution and trap effects of magma intrusion increase the possibility and extent of gas outburst. Considering coal seam and gas occurrence characteristics in the coalfield, we propose a new technology for deep coal reservoir reconstruction which combined present underground regional gas control methods and surface well extraction methods. The technology has three effects: developing gas resources, improving coal mining safety level and reducing greenhouse gas emissions, which has been practiced to be effective in coal mines in the Huaibei coalfield. 相似文献
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This paper proposes a numerical model for jointed rock masses within the 3‐D numerical manifold method (NMM) framework equipped with a customized contact algorithm. The strength of rock sample containing a few sets of discontinuities is first investigated. The results of models with simple geometries are compared with the available analytical solutions to verify the developed computer code, whereas models with complex geometries are simulated to better understand the fundamental behavior and failure mechanism of jointed rock mass. Furthermore, the stability of jointed rock mass in an underground excavation is studied, where rock failure process is determined by the 3‐D NMM simulation. The simulation results provide valuable guidance on excavation process design and stabilization design in rock engineering practice. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献