排序方式： 共有47条查询结果，搜索用时 15 毫秒
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介绍了一种全新的对流临近预报外推算法——光流法。主要是通过计算雷达回波的光流场得到回波的运动矢量场,并基于运动矢量场对雷达回波进行外推从而达到预报的目的。光流法立足于变化,在计算光流场时既考虑连续时次回波的变化,又考虑相邻位置回波的变化。因此,基于该算法的外推临近预报具有一定的物理意义。利用中值滤波等方法对雷达资料进行质量控制,有效地抑制了噪声等的影响。个例对比分析表明:经过中值滤波等质量控制后回波更平滑,边沿更清晰,回波质量明显改善,能够获得比较真实的雷达回波,也得到了方向更加一致、更加平滑的回波运动矢量场。光流法给出的30、60 min内雷达回波的位置、形状的外推预报和对应时次实况较接近,预报结果具有较好的业务指示意义。对光流法和交叉相关法预报结果进行的定量对比评价表明,对移动型局地生成及强度和形状随时间变化很快的回波,光流法预报效果优于交叉相关法。光流法可以弥补传统的交叉相关法的缺陷,能提升对流临近预报系统的性能。 相似文献
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Analysis of water-level response to rainfall and implications for recharge pathways in the Chalk aquifer, SE England 总被引：2，自引：0，他引：2
Water table response to rainfall was investigated at six sites in the Upper, Middle and Lower Chalk of southern England. Daily time series of rainfall and borehole water level were cross-correlated to investigate seasonal variations in groundwater-level response times, based on periods of 3-month duration. The time lags (in days) yielding significant correlations were compared with the average unsaturated zone thickness during each 3-month period. In general, for cases when the unsaturated zone was greater than 18 m thick, the time lag for a significant water-level response increased rapidly once the depth to the water table exceeded a critical value, which varied from site to site. For shallower water tables, a linear relationship between the depth to the water table and the water-level response time was evident. The observed variations in response time can only be partially accounted for using a diffusive model for propagation through the unsaturated matrix, suggesting that some fissure flow was occurring. The majority of rapid responses were observed during the winter/spring recharge period, when the unsaturated zone is thinnest and the unsaturated zone moisture content is highest, and were more likely to occur when the rainfall intensity exceeded 5 mm/day. At some sites, a very rapid response within 24 h of rainfall was observed in addition to the longer term responses even when the unsaturated zone was up to 64 m thick. This response was generally associated with the autumn period. The results of the cross-correlation analysis provide statistical support for the presence of fissure flow and for the contribution of multiple pathways through the unsaturated zone to groundwater recharge. 相似文献
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Li Zhenjun 《大气科学进展》1998,15(2):277-282
This paper describes the estimation of cloud motion using lag cross-correlation. In order to compute the lag cross correlation,
the Bayes Decision method is used first to identify cloud and surface of earth. Then cloud motion vectors are retrieved at
a subset of points through multiple applications of a cross-correlation analysis. An objective analysis is used to define
displacement at every satellite pixel throughout the domain and smooth the local inconsistencies. Cloud motions are then produced
with a backward trajectory technique by using these displacement vectors. 相似文献
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The gravity solid tide signal includes daily wave, half-day wave and annual wave and moon wave harmonic component, but the energy of day wave and half-day wave component is relatively strong, and the energy of annual wave and moon wave component is relatively weak. In order to effectively extract these harmonic components with large energy differences and reveal the modulation relationship between them, according to the cause of gravity tide, a gravity solid tide signal decomposition model is used to compare the tidal harmonic components with different strengths. The form of the independent component is decomposed into different orthogonal directions. At the same time, a new optimization algorithm is used to improve the independent component analysis algorithm and separate the independent components of different orthogonal directions. In the spectral correlation analysis of the components of independent components, the autocorrelation operation will make the strong component stronger and the weak component weaker. For this problem, the cross-correlation spectrum between independent components is used to reveal the gravity tide signal., the modulation relationship between harmonic components. The experimental results show that the proposed algorithm not only effectively separates the independent components with large intensity difference in the gravity tide signal from the perspective of additive decomposition, but also reveals the multiplicative modulation relationship between the corresponding tidal harmonics based on the cross-correlation spectrum. 相似文献
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利用卫星资料制作天气系统移动预报 总被引：2，自引：1，他引：1
本文使用交叉相关及后向轨迹预报的方法,对未经人工处理的两张不同时次的卫星云图灰度进处理,在前一时次卫星云图上定义一个象素子集,并在后一时次卫星云图定义的区域内计算逐个象素子集的相关系数,然后找出与前一区域具有最大相关系数的象素子集,把这两个象素子集中心的连线看作是象素子集内云的移动。利用天气系统运动的连续性和保守的性质,找出其移动的规律,并由此客观地作出天气系统的移动趋势,预报取得了较为满意的结果。 相似文献
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Most studies of seismic noise cross-correlation (NCC) have focused on regional/continental scale imaging using empirical surface-wave Green’s functions extracted from primary (0.05–0.08 Hz) and secondary (0.1–0.16 Hz) microseisms. In this work, we present the NCC results at higher frequencies (>0.5 Hz) from 6 months seismic noise recorded by a local array (~4 km aperture) deployed along the Calico fault in the Mojave Desert, California. Both fast and slow propagating waves are observed from the NCC record-sections. We compare the NCCs from sensor pairs that share a common sensor with the records of a borehole shot located very close to this common sensor. The result shows a good match of the slow surface-wave arrivals, indicating that the NCC method is able to recover unbiased surface-wave Green’s functions at local scales. The strong body-wave NCC component is caused by the P waves generated offshore California. Along a SW–NE profile across the fault, we observe apparent P-wave arrivals and their reflections, which can be explained by a low-velocity-zone (LVZ) along the Calico fault. We calculate the LVZ width to be ~ 2.3 km, and the P-wave velocity reduction within the LVZ to be ~35 %. These estimates are consistent with other evidence for a relatively wide LVZ along the Calico fault. 相似文献
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模板匹配滤波技术在地震数据处理中的应用 总被引：1，自引：0，他引：1
模板匹配滤波技术(Matched Filter Technique,MFT)是一种近几年发展迅速的可用于检测遗漏信号的算法,在图像识别、行星探测等众多领域均有广泛应用。在地震学中,该技术通过扫描连续波形找出模板事件附近发生的、与模板事件相关性较好的遗漏地震事件,可用于完善地震目录,实现对地震活动性以及区域应力状态的更好刻画。本文综述了模板匹配滤波技术在地震数据处理中的应用,首先概述基本原理,其次介绍该方法用于探测各类地震事件的实例,包括前震和余震、远程动态触发地震、诱发地震和非火山震颤等,最后展望了用于提高算法效率及探测精度的一些改进方法。 相似文献
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