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电离层对人类活动影响重大,涉及天气、通讯、军事应用和卫星运行等许多方面.电离层中各种粒子的发光辐射特性,特别是远紫外辐射特性,是电离层、热层和极光带等高层大气的物理化学信息重要来源.对电离层进行探测,主要是通过最先进的光谱成像技术对远紫外波段进行研究,提供充足的电离层分布的光谱信息和空间信息,建立精确的电离层模型.本文主要阐述了电离层远紫外波段光谱成像技术的发展和趋势,指出了影响这种技术的关键因素,即光学系统和探测器,分析了我国相关技术的薄弱环节.并结合我国目前的研制水平和技术,提出了发展星载电离层探测成像光谱技术的建议. 相似文献
885.
建水地下流体监测井水位骤降异常分析 总被引:2,自引:0,他引:2
2012年2月底至4月上旬,建水县地下流体监测站监测井水位出现了幅度近8m的显著下降变化.通过对该监测井与石屏—建水断裂带观测井同期水位进行对比分析,排除了监测井水位骤降异常是由构造活动引起的可能性.同时,调查了周边的抽水井,运用水文地质分析方法,结合当地水文地质情况,确定该监测井水位骤降异常是由附近的井孔抽水引起.充分了解当地的水文地质情况,根据地下水的运移规律,结合实地调查,可以对地下水异常给出相对合理的解释,并进一步判断地下水异常是否是构造活动引起的地震异常. 相似文献
886.
本文提出了一种初至纵波(P波)与瑞雷面波的交叉梯度联合反演策略.通过对初至P波进行全波形反演可以获得近地表P波速度结构;通过对仅含瑞雷面波信息的地震数据转换到频率-波数域进行加窗振幅波形反演(Windowed-Amplitude Waveform Inversion,w-AWI)可获得近地表横波(S波)速度结构.在二者反演的目标函数中均加入P波速度和S波速度的交叉梯度作为正则化约束项,使得在反演过程中P波速度和S波速度相互制约,相互约束,从而实现对地震初至P波与瑞雷面波的联合反演.数值模拟结果表明交叉梯度联合反演可以提高S波速度反演分辨率,而P波速度反演结果并没有得到提高.实际资料的反演结果表明,交叉梯度联合反演能够获得更加可信的近地表速度结构. 相似文献
887.
Elastic reverse-time migration (RTM) can reflect the underground elastic information more comprehensively than single-component Pwave migration. One of the most important requirements of elastic RTM is to solve wave equations. The imaging accuracy and efficiency of RTM depends heavily on the algorithms used for solving wave equations. In this paper, we propose an efficient staggered-grid finite-difference (SFD) scheme based on a sampling approximation method with adaptive variable difference operator lengths to implement elastic prestack RTM. Numerical dispersion analysis and wavefield extrapolation results show that the sampling approximation SFD scheme has greater accuracy than the conventional Taylor-series expansion SFD scheme. We also test the elastic RTM algorithm on theoretical models and a field data set, respectively. Experiments presented demonstrate that elastic RTM using the proposed SFD scheme can generate better images than that using the Taylor-series expansion SFD scheme, particularly for PS images. FurH. thermore, the application of adaptive variable difference operator lengths can effectively improve the computational efficiency of elastic RTM. 相似文献
888.
Flow in a single fracture (SF) is an important research subject in groundwater hydrology, hydraulic engineering, radioactive nuclear waste repository and geotechnical engineering. An abruptly changing aperture is a unique type of SF. This study discusses the relation between the values of the critical Reynolds number (Rec) for the onset of symmetry breaking of flow and the expansion ratio (E) of SF, which is defined as the ratio between the outlet (D) and inlet (d) apertures. This study also investigates the effect of inlet aperture d on Rec for flow in an SF with abruptly changing apertures (SF‐ACA) using the finite volume method. Earlier numerical and experimental results showed that flow is symmetric in respect to the central plane of the SF‐ACA at small Reynolds number (Re) but becomes asymmetric when Re is sufficiently large. Our simulations show that the value of Rec decreases with the increasing E, and the relationship between the logarithm of Rec and E can be described accurately using either a quadratic polynomial function or a logarithmic function. However, the relationship of Rec and d for a given E value is vague, and Rec becomes even less sensitive to d when E increases. This study also reveals that the hydraulic gradient (J) and flow velocity (v) follow a super‐linear relationship that can be fitted almost perfectly by the Forchheimer equation. The inertial component (Ji) of J increases monotonically with Re, whereas the viscous component (Jv) of J decreases monotonically with Re. The Re value corresponding to equal inertial and viscous components of J (named as the transitional point Re) decreases when E increases, and such a transitional point Re should be closely related to the critical Reynolds number Rec, although a rigorous theoretical proof is not yet available. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
889.
Imperviousness, considered as a critical indicator of the hydrologic impacts of urbanization, has gained increasing attention both in the research field and in practice. However, the effectiveness of imperviousness on rainfall–runoff dynamics has not been fully determined in a fine spatiotemporal scale. In this study, 69 drainage subareas <1 ha of a typical residential catchment in Beijing were selected to evaluate the hydrologic impacts of imperviousness, under a typical storm event with a 3‐year return period. Two metrics, total impervious area (TIA) and effective impervious area (EIA), were identified to represent the impervious characteristics of the selected subareas. Three runoff variables, total runoff depth (TR), peak runoff depth (PR), and lag time (LT), were simulated by using a validated hydrologic model. Regression analyses were developed to explore the quantitative associations between imperviousness and runoff variables. Then, three scenarios were established to test the applicability of the results in considering the different infiltration conditions. Our results showed that runoff variables are significantly related to imperviousness. However, the hydrologic performances of TIA and EIA were scale dependent. Specifically, with finer spatial scale and the condition heavy rainfall, TIA rather than EIA was found to contribute more to TR and PR. EIA tended to have a greater impact on LT and showed a negative relationship. Moreover, the relative significance of TIA and EIA was maintained under the different infiltration conditions. These findings may provide potential implications for landscape and drainage design in urban areas, which help to mitigate the runoff risk. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
890.
In high elevation cold regions of the Tibetan Plateau, suspended sediment transfer from glacier meltwater erosion is one of the important hydrological components. The Zhadang glacier is a typical valley‐type glacier in the Nyainqentanglha Mountains on the Tibetan Plateau. To make frequent and long period records of meltwater runoff and sediment processes in the very high elevation and isolated regions, an automatic system was installed near the glacier snout (5400 m a.s.l) in August 2013, to measure the transient discharge and sediment processes at 5‐min interval, which is shorter than the time span for the water flow to traverse the catchment from the farthest end to the watershed outlet. Diurnal variations of discharge, and suspended sediment concentration (SSC) were recorded at high frequency for the Zhadang glacier, before suspended sediment load (SSL) was computed. Hourly SSC varied from the range of 0.2 kg/m3 to 0.5 kg/m3 (at 8:00–9:00) to the range of 2.0 kg/m3 to 4.0 kg/m3 (at 17:00–18:00). The daily SSL was 32.24 t during the intense ablation period. Hourly SSC was linearly correlated with discharge (r = 0.885**, n = 18, p < 0.01). A digit‐eight hysteresis loop was observed for the sediment transport in the glacier area. Air temperature fluctuations influence discharge, and then result in the sediment variations. The results of this study provide insight into the responses of suspended sediment delivery processes with a high frequency data in the high elevation cold regions. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献