The utilization of the double focal transformation for sparse data representation and data reconstruction          下载免费PDF全文

H. Kutscha  D.J. Verschuur 《Geophysical Prospecting》2016,64(6):1498-1515

In many cases, seismic measurements are coarsely sampled in at least one dimension. This leads to aliasing artefacts and therefore to problems in the subsequent processing steps. To avoid this, seismic data reconstruction can be applied in advance. The success and reliability of reconstruction methods are dependent on the assumptions they make on the data. In many cases, wavefields are assumed to (locally) have a linear space–time behaviour. However, field data are usually complex, with strongly curved events. Therefore, in this paper, we propose the double focal transformation as an efficient way for complex data reconstruction. Hereby, wavefield propagation is formulated as a transformation, where one‐way propagation operators are used as its basis functions. These wavefield operators can be based on a macro velocity model, which allows our method to use prior information in order to make the data decomposition more effective. The basic principle of the double focal transformation is to focus seismic energy along source and receiver coordinates simultaneously. The seismic data are represented by a number of localized events in the focal domain, whereas aliasing noise spreads out. By imposing a sparse solution in the focal domain, aliasing noise is suppressed, and data reconstruction beyond aliasing is achieved. To facilitate the process, only a few effective depth levels need to be included, preferably along the major boundaries in the data, from which the propagation operators can be calculated. Results on 2D and 3D synthetic data illustrate the method's virtues. Furthermore, seismic data reconstruction on a 2D field dataset with gaps and aliased source spacing demonstrates the strength of the double focal transformation, particularly for near‐offset reflections with strong curvature and for diffractions.  相似文献   

基于NDVI先验知识的LAI地面采样方法     

曾也鲁  李静  柳钦火  柏军华 《遥感学报》2013,17(1):107-121

针对非均质中低分辨率像元的叶面积指数LAI验证中如何布设基本采样单元ESU的问题,提出基于NDVI先验知识的ESU布设方法,并采用不同植被类型、不同均匀程度的地表作为模拟场,分析对比了方法的精度及稳定性。结果显示,本文方法用NDVI先验知识描述植被的生长空间分布信息,能相对准确地划分植被的不同生长水平,有效降低层内方差。在草地和森林地区的试验中,精度与稳定性均优于传统的随机采样、均匀采样和基于分类图的3种采样方法。因此,本文提出的采样方法为大尺度非均质区域LAI地面验证的采样方案提供了新的设计思路。  相似文献   

卫星钟差采样间隔对高频PPP-ZTD精度的影响     

李黎  李浩军  龙四春  沈军  张立亚 《大地测量与地球动力学》2015,35(1):77-80

高频对流层延迟（ZTD）的提取对于反映水汽含量的高时间分辨率瞬时变化及其在暴雨短临预报中的应用具有重要意义。基于精密单点定位技术（PPP）分析了不同采样间隔的卫星钟差对PPP-ZTD精度的影响。结果表明,卫星钟差的时间间隔小于30 s时,所获得的PPP-ZTD(RMS<4 mm)比5 min间隔的（RMS<6 mm）精度要高;而5 s与30 s采样间隔的卫星钟差所获得的ZTD精度相当。  相似文献   

边坡稳定分析的神经网络改进模糊点估计法     

舒苏荀  龚文惠 《岩土力学》2015,36(7):2111-2116

边坡稳定性分析中,模糊点估计法能同时考虑模糊不确定性和随机不确定性因素。针对传统模糊点估计法计算工作量大的缺点,提出一种神经网络改进模糊点估计法。利用拉丁超立方抽样法和径向基函数神经网络（RBF）建立边坡安全系数的预测模型;对黏聚力和内摩擦角等模糊随机变量取λ截集,并在各截集水平对参数进行组合;利用建立的预测模型对各参数组合的安全系数进行预测;最后由统计矩点估计法计算边坡的可靠度指标。实例分析表明：改进模糊点估计法使用方便、结果可靠,且能通过增加λ截集水平的数目来提高计算精度。对于含有2～4个模糊随机变量的边坡,采用改进模糊点估计法计算可靠度时λ截集水平的数目可近似取25。  相似文献   

Monitoring polycyclic aromatic hydrocarbons in the Northeast Aegean Sea using Posidonia oceanica seagrass and synthetic passive samplers     

《Marine pollution bulletin》2014,88(1-2):338-344

The concentrations of 22 polyaromatic hydrocarbons (PAH) in Posidonia oceanica seagrass, sediments, and seawater from the Alexandroupolis Gulf in the Aegean Sea, were investigated from 2007 to 2011. Temporal trends of total PAH contents in P. oceanica and sediments were similar. PAH levels in seawater, sediments, and seagrasses generally decreased with increasing distance from Alexandroupolis Port. Leaves and sheaths of P. oceanica had higher PAH levels than roots and rhizomes. P. oceanica accumulates PAHs and has good potential as a bioindicator of spatiotemporal pollution trends. PAH concentrations were also examined using in situ passive seawater sampling and were compared to results of passive sampling in the laboratory using local sediments and seawater. Levels of high molecular weight PAHs assessed using passive samplers confirmed the decreasing gradient of pollution away from Alexandroupolis Port. Passive sampling also proved useful for investigating sources of PAHs in P. oceanica meadows.  相似文献   

Sampling efficiency in Monte Carlo based uncertainty propagation strategies: Application in seawater intrusion simulations     

《Advances in water resources》2014

The implementation of Monte Carlo simulations (MCSs) for the propagation of uncertainty in real-world seawater intrusion (SWI) numerical models often becomes computationally prohibitive due to the large number of deterministic solves needed to achieve an acceptable level of accuracy. Previous studies have mostly relied on parallelization and grid computing to decrease the computational time of MCSs. However, another approach which has received less attention in the literature is to decrease the number of deterministic simulations by using more efficient sampling strategies. Sampling efficiency is a measure of the optimality of a sampling strategy. A more efficient sampling strategy requires fewer simulations and less computational time to reach a certain level of accuracy. The efficiency of a sampling strategy is highly related to its space-filling characteristics.This paper illustrates that the use of optimized Latin hypercube sampling (OLHS) strategies instead of the widely employed simple random sampling (SRS) and Latin hypercube sampling (LHS) strategies, can significantly improve sampling efficiency and hence decrease the simulation time of MCSs. Nine OLHS strategies are evaluated including: improved Latin hypercube sampling (IHS); optimum Latin hypercube (OLH) sampling; genetic optimum Latin hypercube (GOLH) sampling; three sampling strategies based on the enhanced stochastic evolutionary (ESE) algorithm namely φ_p-ESE which employs the φ_p space-filling criterion, CLD-ESE which utilizes the centered L₂-discrepancy (CLD) space-filling criterion, and SLD-ESE which uses the star L₂-discrepancy (SLD) space-filling criterion; and three sampling strategies based on the simulated annealing (SA) algorithm namely φ_p-SA which employs the φ_p criterion, CLD-SA which uses the CLD criterion, and SLD-SA which utilizes the SLD criterion. The study applies SRS, LHS and the nine OLHS strategies to MCSs of two synthetic test cases of SWI. The two test cases are the Henry problem and a two-dimensional radial representation of SWI in a circular island. The comparison demonstrates that the CLD-ESE strategy is the most efficient among the evaluated strategies. This paper also demonstrates how the space-filling characteristics of different OLHS designs change with variations in the input arguments of their optimization algorithms.  相似文献   

祁连山青海云杉(Picea crassifolia)林土壤有机碳与化学性质的相互关系   总被引：4，自引：0，他引：4  

赵维俊  刘贤德  张学龙  车宗玺  齐鹏  牛赟 《冰川冻土》2014,36(6):1565-1571

通过对祁连山大野口流域的青海云杉林大样地进行土壤剖面取样, 分析了样地土壤有机碳与pH值、养分和阳离子交换量等基本化学性质的变化规律及其相互关系. 结果表明: 随土层深度不断增加, 土壤有机碳含量逐渐减小, 在20～30 cm以下趋于稳定(P > 0.05); 土壤pH值不断增大, 仅在0～10 cm与10～20 cm差异显著(P<0.05); 土壤全氮、速效氮、全磷和阳离子交换量不断减小, 全氮含量在30～40 cm以下趋于稳定(P > 0.05), 速效氮含量变化剧烈(P<0.05), 全磷含量差异性不显著(P > 0.05), 阳离子交换量与有机碳含量变化规律相同; 土壤速效磷、全钾和速效钾含量没有明显的变化规律, 速效磷和全钾含量差异性不显著(P > 0.05), 速效钾含量仅在0～10 cm与10～20 cm差异显著(P<0.05). 土壤有机碳与全氮、速效氮、全磷、速效磷、速效钾和阳离子交换量之间呈极显著和显著正相关, 与土壤pH值和全钾含量之间呈极显著和显著负相关. 土壤有机碳与其他基本化学性质的回归方程具有较高精度(R²=0.793), 影响土壤有机碳含量的主要化学因子依次为土壤阳离子交换量、速效钾和全磷含量.  相似文献   

基于遥感和GIS方法的科尔沁沙地边界划定   总被引：2，自引：0，他引：2  

闫妍  朱教君  闫巧玲  郑晓  宋立宁 《地理科学》2014,34(1):122-128

基于已有文献,依据科尔沁沙地的形成历史与早期分布,确定科尔沁沙地的核心区;以核心区为基础,采用生态学取样方法,选取与核心区边界相交的16个方向上的交叉点为样本,以Landsat-5 TM影像为主要数据源,采用光谱混合模型、穗帽变换等遥感和GIS方法,通过反复试验设定阈值,提取每个方向的分界特征,据此勾画出科尔沁沙地的分界线。此后,进行实地考察和Google Earth高清影像验证,最终确定科尔沁沙地生态区域的边界。结果表明,科尔沁沙地面积为52 300 ± 360 km²,验证后精度在94%以上。研究结果为科尔沁沙地生态恢复与环境整治提供确切基础范围。  相似文献   

4DSVD分析误差与样本选取方法和样本容量的关系初探   总被引：1，自引：0，他引：1  

王金成  李建平 《气候与环境研究》2010,15(6):729-742

分析误差与样本选取方法和样本容量的关系是4DSVD同化方法一个亟需研究的重要问题。获得支撑大气模式空间和观测空间吸引子的基向量是4DSVD研究的关键部分,样本的好坏和样本容量的范围是决定4DSVD基向量和分析结果质量的一个重要前提条件。首先利用Lorenz28变量模式,用4DSVD方法做了一些简单三维同化试验,探讨了Lorenz28变量模式的分析误差与样本容量和样本选取方法的关系。数值试验结果表明,对一个具体的模式,有限的样本容量就能够获得较高精度的分析结果;在模式系统和观测系统不变情况下,用一定样本容量得到的支撑模式空间和观测空间的基向量具有很好的稳定性,即一旦获得一组较好的基向量,在观测系统和模式系统不变的情况下,对同化任何时刻的观测适用;分析结果对选取方法没有太大的依赖性,但具体的样本容量要视不同模式和样本选取方法而定。用WRF模式做的4DSVD四维观测系统模拟试验结果表明,若样本选取方法得当,所需要的样本容量要远远小于模式自由度。4DSVD要真正获得较高精度的分析结果,需要的条件是尽可能的在吸引子上取样并选取充足的样本容量;间隔取样可以一定程度上减少计算量。根据数值试验结果提出了4DSVD在实际同化时样本选取的一些初步的方法。  相似文献   

沈阳春夏季大气冰核浓度的观测研究   总被引：2，自引：1，他引：1  

周德平  洪也  王扬锋  刘宁微  张云海  李丽光 《气候与环境研究》2012,17(6):719-726

为了解沈阳地区大气冰核浓度的时空分布状况,2010年起开始对沈阳地区的大气冰核浓度分布进行观测和研究.地面采用Bigg型混合云室法和滤膜法进行冰核气溶胶的采样测量,高空利用辽宁省人工影响天气办公室租用的人工增雨飞机进行滤膜法采样.采样滤膜的处理都是统一在活化温度-15℃及冰面过饱和度20％、水面过饱和度3％的湿度条件下进行的.根据取得的部分观测资料,给出了沈阳春夏季大气冰核的浓度及冰核温度谱分布参数,分析了冰核浓度在3～6月各月以及在不同天气状况下的分布特征,初步给出了大气冰核浓度的尺度谱分布及其随高度的变化.  相似文献