共查询到18条相似文献，搜索用时 187 毫秒
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电离层垂直探测方法获得的频高图是电离层观测中历史最为悠久的资料,利用现代微电子和计算机技术对大量历史胶片频高图的数字化转换、分析和保存,已成为拯救保护和利用这些珍贵历史资料的十分紧迫和重要的工作.本文采用数字和图像处理等技术对胶片频高图像进行数字化、校正、修复和格式转换,并开发出胶片频高图分析与转换程序,结合常用的SAO Explorer软件对武汉地区的胶片频高图进行了实例的分析.结果表明,该方法具有较好的可靠性和通用性,对大量历史频高图的数字化转换和分析具有实用性. 相似文献
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电离层特征参数的实时获取和分析是电离层空间天气监测预报的重要内容.本文针对电离层频高图参数的实时自动度量和分析问题，提出了一种基于电子浓度高度剖面经验正交函数(Empirical Orthogonal Function, 简称EOF)分析的频高图参数自动度量方法，并将该方法应用到位于北京空间环境观测站(403°N，1162°E)的CADI(Canadian Advanced Digital Ionosonde)数字测高仪观测频高图的实时自动度量和分析上.结果表明，该方法具有较好的可靠性和通用性，能实时自动度量频高图的有关参数并反映相关的电离层变化，可作为电离层空间天气实时监测分析的一种有效手段. 相似文献
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垂测仪是研究电离层中最常用的仪器之一,目前各国在世界范围内布设了大量的垂测仪来对电离层进行常规观测.而这些垂测仪每天都会记录大量的频高图数据,因此自动度量频高图算法的研究则成为如何高效利用大量频高图数据来研究电离层的重要基础.由于频高图中O波描迹的提取,对于研究不同电离层高度反射回波的扰动特征具有重要的意义,因此本文提出一种新方法用于从频高图中自动提取O波描迹.该方法基于滑动窗口和图像投影技术,首先确定O波和X波描迹的交叉点,然后在此基础上利用O波X波在频高图中的不同分布特征,单独提取出O波描迹,并利用局部加权回归算法对提取的描迹进行拟合.通过云南普洱站记录的频高图数据对该算法进行验证,将自动提取的描迹与人工提取的描迹进行对比,可接受的比例大约85.3%.对比结果表明本文提出的算法能够较好的提取频高图中的O波描迹. 相似文献
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本文对电离层频高图换算为电子浓度垂直分布剖面图方法中的Titheridge联合换算方法作了适当的修正和补充,并对此方法的误差等问题进行了分析和讨论。 相似文献
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《地球物理学进展》2020,(2)
频高图F层异常分层(增层)是指在常规电离层结构的基础上,由于电子密度被扰动而在频高图中出现多层回波结构,该F层异常分层(增层)现象在白天和晚上均可观测到.电离层异常分层(增层)主要由某种电动力学或者突发电离源导致电子密度出现扰动而形成,已经引起国内外学者的广泛关注和研究.目前从频高图中识别F层异常分层(增层)主要还是通过人工的方法,海量的频高图数据使该方法在研究F层异常分层(增层)统计特征时变得非常困难.有别于传统的图像分类算法中需要对图像特征进行提取,本文通过引入卷积神经网络(Convolution Neural Network, CNN),设计开发出一种能够自动识别存在F层异常分层(增层)频高图的方法,该方法可以直接输入频高图样本数据,省去了复杂的图像特征提取过程.本文设计的卷积神经网络经过训练以后F层异常分层(增层)识别率为85.82%,准确率90.36%.实验结果表明该卷积神经网络可以较好地自动识别出F层异常分层(增层)的频高图. 相似文献
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A. J. Parsons 《地球表面变化过程与地形》1982,7(1):71-78
If the three-dimensional form of a hillslope is regarded as an infinite population of two-dimensional slope profiles, values for attributes of the form of the hillslope can be determined by sampling and estimating the means of the attributes of the population of slope profiles. Twelve attributes are examined in seven first-order drainage basins located on the South Downs in East Sussex to determine necessary sample sizes. Results show that if spatial randomness is assumed the size of sample required varies considerably from one attribute to another but is commonly very large. Of four alternatives to spatial randomness that are tested, consideration of both hillslope plan form and valley asymmetry are shown not to lead to reduction in sample size. However, results do suggest that maximum slope, percentage of profile length in the range 5° to < 10°, and mean angular difference between adjacent slope segments may all be dependent upon distance of the slope profile down valley. Furthermore, initial tests of the effect of spatial autocorrelation suggest that for some attributes consideration needs to be given to this factor when determining sampling strategies. 相似文献
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A boundary element formulation having discontinuous curved quadratic elements is presented for 2D elastodynamics. The first fundamental solution for static case is subtracted from and added to the first fundamental solution for dynamic case. As both kernels have the same order of singularity, the integral involving the regular expression arising from the subtraction can be calculated. matrix is calculated by employing the well-known rigid-body motion technique. The formulation is performed in Fourier transform space. Based on the formulation presented in this study, a general purpose computer program is developed for elastic or visco-elastic 2D elastodynamic problems. The program performs the analysis in Fourier transform space and can also be used for static analysis by assigning a very small value close to zero for the frequency. The results of some elastodynamic and dynamic soil–structure interaction problems obtained using the present study are compared with those in the literature. 相似文献
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An approach for measuring confinement and assessing the influence of valley setting on river forms and processes 
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下载免费PDF全文 Valley setting and confinement (or lack thereof) are primary controls on river character and behaviour. Although there are various proxies for valley confinement, direct measures that quantify the nature and extent of confinement are generally lacking and/or inconsistently described. As such they do not lend themselves to consistent analysis over large spatial scales. Here we clearly define forms of confinement to aid in quantification of degrees of confinement. Types of margin that can induce confinement are differentiated as a valley margin, valley bottom margin, and/or anthropogenic margin. Such margins sometimes overlap and share the same location, and in other situations are separated, giving immediate clues as to the valley setting. We apply this framework to examples from Australia, United States and New Zealand, showing how this framework can be applied across the spectrum of river diversity. This method can help to inform interpretations of reach‐scale river behaviour, highlighting the role of antecedent controls on contemporary forms and processes. Clear definitions of confinement are shown to support catchment‐scale analysis of river patterns along longitudinal profiles, and appraisals of the geomorphic effectiveness of floods and sediment flux in catchments (e.g. process zone distribution, lateral sediment inputs and (dis)connectivity). Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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ABSTRACT The distribution of environmental tritium, deuterium and oxygen-18 in the unsaturated zone and the underlying sandy phreatic aquifer was studied throughout 1981 in an area of high pine forests in the Rhine valley near Heidelberg. The observed vertical distribution of isotopes in the unsaturated zone can be satisfactorily explained by the combined use of a multi-cell model for moisture transport and an evapotranspiration model. The distribution in the underlying aquifer of the tracer input at the water table obtained using this method is found by replacing the total vertical diffusion coefficient in the diffusion equation with the dispersion coefficient. In this way observed tritium profiles are satisfactorily simulated for the period 1966–1981. The stable isotope profile in the unsaturated zone however remains largely unexplained due to inadequate data on the stable isotope content of precipitation over the investigated area. 相似文献
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Summary The purpose of the paper is to provide a statistical view of the role of circulation patterns and the origin of low stratospheric air in connection with vertical ozone distribution below the ozone maximum, and also with the total ozone amount. Ozonesonde data from the aerological observatory of the Czech Hydrometeorological Institute (CHMI) Prague-Libu (50·0N, 14·7E) for January to April during the period 1979–1990 have been analyzed using an objective method to find the distribution of laminae in the vertical profile of the ozone partial pressure related to the different types of circulation patterns. The synoptic classification following Grosswetterlagen (GWL) was used, the parameters of the ozone profile such as number, magnitude, thickness and height of laminae, or the appearance of the large laminae were obtained for the individual types of GWL and used in other procedures. The total ozone data from the ozone observatory of CHMI in Hradec Králové (50·2N, 15·8E) was also included together with the height of the tropopause and parameters of ozone profiles in the cluster analysis to investigate connections between the ozone distribution and circulation patterns (types of synoptic situation). The ozone low-level index (LLI), defined as the ratio of the integral amount of ozone in D.U. from the surface up to 50 hPa and total ozone were introduced to provide better information about ozone profile response to circulation patterns and thus provide a better grouping of similar types of GWL. The presented results imply the strong confirmation of the huge ozone laminae below the ozone maximum as the source of total ozone positive extremes under appropriate synoptic situations with the near location of the polar vortex edge, which could be used in common forecasts of atmospheric ozone as well as in remote sensing applications. 相似文献
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Qina Yan Toshiki Iwasaki Andrew Stumpf Patrick Belmont Gary Parker Praveen Kumar 《地球表面变化过程与地形》2018,43(1):218-228
Floodplains and terraces in river valleys play important roles in the transport dynamics of water and sediment. While flat areas in river valleys can be identified from LiDAR data, directly characterizing them as either floodplain or terraces is not yet possible. To address this challenge, we hypothesize that, since geomorphic features are strongly coupled to hydrological and hydraulic dynamics and their associated variability, there exists a return frequency, or possibly a narrow band of return frequencies, of flow that is associated with floodplain formation; and this association can provide a distinctive signature for distinguishing them from terraces. Based on this hypothesis we develop a novel approach for distinguishing between floodplains and terraces that involves transforming the transverse cross‐sectional geometry of a river valley into a curve, named a river valley hypsometric (RVH) curve, and linking hydraulic inundation frequency with the features of this curve. Our approach establishes that the demarcation between floodplains and terraces can be established from the structure of steps and risers in the RVH curves which can be obtained from the DEM data. Further, it shows that these transitions may themselves be shaped by floods with 10‐ to 100‐year recurrence. We additionally show that, when floodplain width and height (above channel bottom) are normalized by bankfull width and depth, the ratio lies in a narrow range independent of the scale of the river valley. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
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We study the reduction of peak velocity on the ground surface of a soil valley caused by loss of wave energy by large nonlinear strains and strain localization inside the valley, for excitation by a half-sine P-wave pulse. This study is a follow up to our previous study of out of plane response for excitation by an SH-pulse. In this paper, we consider the inplane response, and assume that the soil material does not support tension, but the normal stress at a point in the soil can be compression(negative) or zero. A point in the soil with zero stress behaves as a stress-free point, it does not transmit normal stress and appears as a crack point. Because of this, along with the nonlinear response associated with compression and shear, the in-plane response in this study is more complex than that of the out-of-plane SH response. We study the interplay of two opposing effects:(i) jump in impedance from a higher value(half-space) to a lower value(valley), which amplifies the linear motions at the free surface of the valley, and(ii) the occurrence of nonlinear zones in the valley, which reduce the motion at the valley surface. 相似文献