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51.
We reformulate the equation of reverse‐time migration so that it can be interpreted as summing data along a series of hyperbola‐like curves, each one representing a different type of event such as a reflection or multiple. This is a generalization of the familiar diffraction‐stack migration algorithm where the migration image at a point is computed by the sum of trace amplitudes along an appropriate hyperbola‐like curve. Instead of summing along the curve associated with the primary reflection, the sum is over all scattering events and so this method is named generalized diffraction‐stack migration. This formulation leads to filters that can be applied to the generalized diffraction‐stack migration operator to mitigate coherent migration artefacts due to, e.g., crosstalk and aliasing. Results with both synthetic and field data show that generalized diffraction‐stack migration images have fewer artefacts than those computed by the standard reverse‐time migration algorithm. The main drawback is that generalized diffraction‐stack migration is much more memory intensive and I/O limited than the standard reverse‐time migration method. 相似文献
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Uncertainty assessment of ephemeral gully identification,characteristics and topographic threshold when using aerial photographs in agricultural settings 下载免费PDF全文
Alexandre Maugnard Hélène Cordonnier Aurore Degre Pierre Demarcin Nathalie Pineux Charles L. Bielders 《地球表面变化过程与地形》2014,39(10):1319-1330
Manual digitizing on aerial photographs is still commonly used for characterizing gully erosion over large areas. Even when automated detection procedures are implemented, manual digitizing is frequently being resorted to in order to constitute reference datasets used for training and validation. In both cases, manual digitizing entails some subjective decisions on behalf of the operator, which introduces uncertainty into the resulting datasets. To assess the magnitude of this uncertainty, 11 experienced operators were asked to digitize and classify ephemeral gullies (EGs) on cropland following a standardized methodology. The resulting 11 datasets were compared in terms of number, type and location of EGs. Furthermore, for EGs located on a well‐defined runoff flow concentration axis, the slope versus contributing area topographic thresholds required for initiating gully channels were assessed using four thresholding methods, and compared across the 11 datasets. The operators identified 259 different EGs. However, the number (52–139) and sum total length (8.9–23.7 km) of EGs varied widely across operators. Only 34% of the EGs were digitized by more than half of the operators, and 7% were identified by all. Identification of EGs located on a well‐defined flow concentration axis proved least subjective. The longer the EG and the more fields the EG crossed, the larger the number of operators that were able to identify it. EGs were also most easily identified when located in sugar beet fields as compared to other crops. EG classification and topographic threshold lines were also found to be strongly operator‐dependent. Quantile regression appeared to be one of the most robust thresholding methods. Operator subjectivity when digitizing EGs on orthophotographs introduces uncertainty that should be taken into account in future remote sensing‐based studies of EG erosion whenever they rely, in part or in full, on manual photograph interpretation. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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王乐洋 《大地测量与地球动力学》2013,33(3):106-110
??????????С????????о???????(??)??????????????????????????????????????????????????????????????????????????????ü???λ??????????????(??)????????????С???????????????????????????????????м???в??????????????????????????м???????????????????????????????????????????????????С??????????????????????????????????????????????????????С???????????С?????????????????????????????????С????????о???????????????????Ч??? 相似文献
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针对海表温度数据集的数据缺失,提出了一种基于自组织映射算法(SOM)和经验正交函数算法(EOF)有机结合的重构缺失值的新方法。该方法应用了SOM的非线性估计,能够很好的反映数据集的非线性结构,并把SOM估计的结果用于EOF算法的初始化,克服了EOF对数据集初始化敏感的问题。在处理过程中,对奇异值分解使用了lanczos算子分解矩阵,提高了程序运行效率。此外,该方法还引入蒙特卡罗交叉校正集,确定最佳重构的EOF模态数,最终高精度计算出重构误差。使用AQUA遥感卫星海表温度数据进行实验,结果表明该方法能够很好地重构出缺失率高达83.23%的数据集,且重构精度高。 相似文献
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???360???????????????????????????????????????????????·???????????в???????????????????????YCbCr???????????????????????????????????????????Ч??????????????????????????????????????????????????????????????????????????????????Ч?????????????????÷????????360?????????е??????????????????????????????????????????????Ч?????????á? 相似文献
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作为高精度波形反演或逆时偏移的重要组成部分,地震波数值模拟对计算速度和效率提出了更高要求.GPU通用计算技术的产生及其内在数据并行性,为高效地震波数值模拟应用和研究得以有效开展奠定了基础.本文借助交错网格的Fourier伪谱微分矩阵算子和GPU上高效矩阵乘法,实现了复杂介质中地震波模拟的高效算法.数值试验表明,优化后的GPU计算相比CPU单核计算在大规模二维地震波场计算中获得至少100x以上的加速比.这对我们快速分析目标反射层在地震剖面中同相轴位置,制定优化采集方案具有重要意义. 相似文献
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矢量地图空间信息度量及其变化分析方法 总被引:1,自引:0,他引:1
如何计算地图的空间信息含量是评价制图质量、地图综合算法以及实现空间信息有效传输的重要基础。论文在详细分析现有的空间信息度量方法的基础上,提出了一种空间信息度量的新方法。该方法分别从几何、专题、拓扑以及专题拓扑4个方面来度量地图空间信息。然后,提出利用膨胀和序贯膨胀形态学算子分析几何信息熵、专题信息熵、拓扑信息熵以及专题拓扑信息熵随地图符号影响范围不同而引起的变化。通过算例分析发现,利用Voronoi图计算得到的结果是论文方法的一个极值结果(即特例),并且该方法便于定量分析地图空间信息熵度量随符号影响范围(或大小)的变化情况。 相似文献