共查询到20条相似文献，搜索用时 31 毫秒
1.
Woodon Jeong Constantinos Tsingas Mohammed S. Almubarak 《Geophysical Prospecting》2020,68(5):1523-1539
A number of deblending methods and workflows have been reported in the past decades to eliminate the source interference noise recorded during a simultaneous shooting acquisition. It is common that denoising algorithms focusing on optimizing coherency and weighting down/ignoring outliers can be considered as deblending tools. Such algorithms are not only enforcing coherency but also handling outliers either explicitly or implicitly. In this paper, we present a novel approach based on detecting amplitude outliers and its application on deblending based on a local outlier factor that assigns an outlier-ness (i.e. a degree of being an outlier) to each sample of the data. A local outlier factor algorithm quantifies outlier-ness for an object in a data set based on the degree of isolation compared with its locally neighbouring objects. Assuming that the seismic pre-stack data acquired by simultaneous shooting are composed of a set of non-outliers and outliers, the local outlier factor algorithm evaluates the outlier-ness of each object. Therefore, we can separate the data set into blending noise (i.e. outlier) and signal (i.e. non-outlier) components. By applying a proper threshold, objects having high local outlier factors are labelled as outlier/blending noise, and the corresponding data sample could be replaced by zero or a statistically adequate value. Beginning with an explanation of parameter definitions and properties of local outlier factor, we investigate the feasibility of a local outlier factor application on seismic deblending by analysing the parameters of local outlier factor and suggesting specific deblending strategies. Field data examples recorded during simultaneous shooting acquisition show that the local outlier factor algorithm combined with a thresholding can detect and attenuate blending noise. Although the local outlier factor application on deblending shows a few shortcomings, it is consequently noted that the local outlier factor application in this paper obviously achieves benefits in terms of detecting and attenuating blending noise and paves the way for further geophysical applications. 相似文献
2.
Xian Li Meiping Wu Kaidong Zhang Xiaofeng He Yangming Huang 《Surveys in Geophysics》2013,34(2):165-180
As a prerequisite of network differential global positioning system applications, the network ambiguity must be determined. Ambiguity resolution and validation are important aspects of this process. However, validation theory is still under investigation. This paper presents an improved network ambiguity validation method that incorporates additional knowledge measured from the network. This process involves the detection of outliers of the baseline measurement errors. By breaking the spatial correlation, incorrectly fixed ambiguities cause the corresponding baseline measurement errors to appear as outliers, which may be discovered and identified with the proposed outlier detection algorithm and outlier identification algorithm, respectively. These detection and identification procedures are iteratively performed until all of the wrong baseline ambiguities are corrected. Because the validation procedure is unconnected to the initial integer ambiguity estimation process, any available ambiguity resolution method may be used to obtain the initial integers, without algorithm correction. When the network ambiguity combinations do not pass the validation algorithm, the method uses a direct estimation algorithm to obtain the correct ambiguity. By using a direct estimation algorithm rather than a search process, this new method consumes less computational time than conventional methods. This study compares the performance of this new method with those of the conventional F-ratio and W-ratio test validation algorithms by using Monte Carlo simulation techniques. Results from a field experiment conducted on data from the United States continuously operating reference stations (US-CORS) reveal that this validation algorithm accelerates the convergence process of ambiguity determination. 相似文献
3.
Mohammad J. Tourian Johannes Riegger Nico Sneeuw Balaji Devaraju 《Studia Geophysica et Geodaetica》2011,55(4):627-640
Gravity measurements within the Gravity Recovery and Climate Experiment (GRACE) provide a direct measure of monthly changes
in mass over the Earth’s land masses. As such changes in mass mainly correspond to water storage changes, these measurements
allow to close the continental water balance on large spatial scales and on a monthly time scale within the respective error
bounds. When quantifying uncertainties, positive and negative peaks are detected in GRACE aggregated monthly time series (from
different data providers) that do not correspond to hydrological or hydro-meteorological signals. These peaks must be interpreted
as outliers, which carry the danger of signal degradation. In this paper an algorithm is developed to identify outliers and
replace them with hydrologically plausible values. The algorithm is based on a statistical approach in which hydrological
and hydro-meteorological signals are used to control the algorithm. The procedure of outlier detection is verified by evaluating
catchment based aggregated GRACE monthly signals with ground truth from hydrology and hydro-meteorological signals. The results
show improvement in the correlation of GRACE versus hydrometeorological and hydrological signals in most catchments. Also,
the noise level is significantly reduced over 255 largest catchments. 相似文献
4.
A practical method is developed for outlier detection in autoregressive modelling. It has the interpretation of a Mahalanobis distance function and requires minimal additional computation once a model is fitted. It can be of use to detect both innovation outliers and additive outliers. Both simulated data and real data re used for illustration, including one data set from water resources. 相似文献
5.
地磁参量实时测量野值的在线辨识与改正是影响地磁导航算法定位概率和精度的重要因素.地磁导航定位的研究目前主要集中于匹配定位算法,地磁参量实时测量数据处理的研究较少.本文将多层递阶非平稳时间序列预测模型引入海洋地磁参量实时测量野值在线辨识与改正,利用多层递阶模型对实时测量值进行一步预测,根据迪克松准则进行野值辨识,利用中值滤波和一步预测值对野值进行改正.仿真数据和实测数据的实验室仿真结果表明,本文提出的野值在线辨识与改正算法不仅可以检测全部孤立型野值而且对多数斑点型野值也有较好的辨识效果,对产生野值处信号的复原误差小于5%. 相似文献
6.
Flood season segmentation, which partitions an entire flood season into multiple subseasons, constitutes a considerable water resources management task. Moreover, the risks associated with various schemes for flood season segmentation should be evaluated. Preliminary analysis in this study used the principal component based outlier detection (PCOut) algorithm to identify possible outlying observations to reduce the uncertainty involved in flood season segmentation. Then, a quantitative measurement, the seasonal exceedance probability (SEP), was proposed to evaluate various segmentation schemes. The SEP quantifies the risk that the maximum observation occurs outside the main flood season. Several findings were derived based on a case study of China’s Three Gorges Reservoir (TGR) and daily streamflow records (1882–2010). (1) The PCOut algorithm was found effective in identifying outliers, and the estimation uncertainty of the segmentation evaluation due to outliers decreased when the end date of main flood season (EDMFS) was postponed. (2) The proposed SEP measurement was shown capable of supporting quantitative evaluation of the segmentation schemes in the flood season. (3) The current flood segmentation scheme based on an EDMFS of September 10 is sufficiently safe for the TGR. The findings of this study could help in the proper operation of the TGR. 相似文献
7.
Evaluation of multi‐use stormwater detention basins for improved urban watershed management 
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下载免费PDF全文 Detention basins are used to capture postdevelopment runoff and control the peak discharge of the outflow using orifices and weirs. The use of detention basins is typical practice in the construction of new developments on the fringe of existing urban areas, such as the Ulsan–Hwabong district in the city of Ulsan, South Korea. In this study, the required volume and flooding area of a detention basin was determined to control development outflow peaks for 2‐year, 10‐year, and 100‐year design storms with type II rainfall distributions as characterized by the US Department of Agriculture's Soil Conservation Service method. The rainfall–runoff simulation model used was the US Environmental Protection Agency's Storm Water Management Model (EPA‐SWMM) 5, which is the latest version of the software, updated for Windows. We designed three cases of detention basins multi‐staged by 2‐year, 10‐year, and 100‐year design storms and verified the designs with the application of 49 years (1961–2009) of hourly historical rainfall data. The three detention basin designs were compared in terms of the total construction and land costs as well as the benefits associated with recreational facilities or parking lot use. As a result, the design sizes of the detention basins are slightly greater than the actual sizes needed based on the historical rainfall application. Multi‐use detention basins (MDBs) based on 2‐year and 10‐year design storms were found to yield 37.4% and 22.8% benefits, respectively, for recreational facility use compared with detention basins without multi‐use space, and the results also indicate that benefits accrue after 6.5 years for parking lot use. The results of this study suggest that an MDB based on a 2‐year design storm is the most cost‐effective design among the three cases considered for Ulsan, South Korea. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
8.
W. A. Woodward S. R. Sain H. L. Gray B. Zhao M. D. Fisk 《Pure and Applied Geophysics》2002,159(4):889-903
—?We consider the problem of multivariate outlier testing for purposes of distinguishing seismic signals of underground nuclear events from training samples based on non-nuclear seismic events when certain data are missing. We consider the case in which the training data follow a multivariate normal distribution. Assume a potential outlier is observed on which k features of interest are measured. Assume further that the available training set of n observations on these k features is available but that some of the observations in the training data have missing features. The approach currently used in practice is to perform the outlier testing using a generalized likelihood ratio test procedure based only on the data vectors in the training data with complete data. When there is a substantial amount of missing data within the training set, use of this strategy may lead to a loss of valuable information. An alternative procedure is to incorporate all n of the data vectors in the training data using the EM algorithm to appropriately handle the missing data in the training set. Resampling methods are used to find appropriate critical regions. We use simulation results and analysis of models fit to Pg/Lg ratios for the WMQ station in China to compare these two strategies for dealing with missing data. 相似文献
9.
Carlo Sguera Pedro Galeano Rosa E. Lillo 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(4):1115-1130
This paper proposes methods to detect outliers in functional data sets and the task of identifying atypical curves is carried out using the recently proposed kernelized functional spatial depth (KFSD). KFSD is a local depth that can be used to order the curves of a sample from the most to the least central, and since outliers are usually among the least central curves, we present a probabilistic result which allows to select a threshold value for KFSD such that curves with depth values lower than the threshold are detected as outliers. Based on this result, we propose three new outlier detection procedures. The results of a simulation study show that our proposals generally outperform a battery of competitors. We apply our procedures to a real data set consisting in daily curves of emission levels of nitrogen oxides (NO\(_{x}\)) since it is of interest to identify abnormal NO\(_{x}\) levels to take necessary environmental political actions. 相似文献
10.
由于存在各种地电干扰,电磁法勘探采集到的原始电场数据中往往包含粗大误差.电磁法勘探中信号量的测量与传统的精密测量在误差来源与特点、测量值分布等方面均存在较大差异.经试验,对电磁勘探采集到的原始电场数据采用传统的莱伊达、格拉布斯、狄克逊等准则进行粗大误差的自动判别和剔除,处理效果不好;采用Robust估计和中值滤波方法,也不能达到满意的效果;采用手工方式挑拣剔除粗大误差,处理效率太低,均不能满足电磁勘探数据预处理的要求.作者提出了一种自适应双向均方差阈值法实现电磁勘探数据粗大误差的自动判别和剔除,此方法对采集到的原始电场数据样本进行排序后,采用迭代或递归的方式,每次均以中点为界分别计算前后两部分数据的均方差,将较大的一个与预先设置的均方差阈值进行比较,若其大于阈值,则判断粗大误差存在于相应的一端,进而剔除相应端端点位置的数据点;若前后均方差值都小于阈值或样本数量小于3个时算法结束.此方法具有自适应优化、阈值参数化控制、适应小样本数据以及计算简单效率高等特点.大量实验结果表明:在选取均方差阈值在30至90范围内时(经验值),能够有效地剔除电磁勘探原始电场数据中的粗大误差,保留最可信数据.目前已在多个实际勘探生产项目中应用此方法处理粗大误差,取得了令人满意的处理效果. 相似文献
11.
Meta-heuristic maximum likelihood parameter estimation of the mixture normal distribution for hydro-meteorological variables 总被引：1，自引：0，他引：1
Ju-Young Shin Jun-Haeng Heo Changsam Jeong Taesam Lee 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(2):347-358
In the water resources field, there are emerging problems such as temporal changes of data and new additions of water sources. Non-mixture models are not efficient in analyzing these data because these models are developed under the assumption that data do not change and come from one source. Mixture models could successfully analyze these data because mixture models contain more than one modal. The expectation maximization (EM) algorithm has been widely used to estimate parameters of the mixture normal distribution for describing the statistical characteristics of hydro meteorological data. Unfortunately, the EM algorithm has some disadvantages, such as divergence, derivation of information matrices, local maximization, and poor accuracy. To overcome these disadvantages, this study proposes a new parameter estimation approach for the mixture normal distribution. The developed model estimates parameters of the mixture normal distribution by maximizing the log likelihood function using a meta-heuristic algorithm—genetic algorithm (GA). To verify the performance of the developed model, simulation experiments and practical applications are implemented. From the results of experiments and practical applications, the developed model presents some advantages, such as (1) the proposed model more accurately estimates the parameters even with small sample sizes compared to the EM algorithm; (2) not diverging in all application; and (3) showing smaller root mean squared error and larger log likelihood than those of the EM algorithm. We conclude that the proposed model is a good alternative in estimating the parameters of the mixture normal distribution for kutotic and bimodal hydrometeorological data. 相似文献
12.
结合随机状态空间方程和极大似然法的期望最大EM算法进行了结构运行模态分析。EM算法以迭代的方式更新模型参数,进而得到状态空间方程的极大似然估计。模态参数通过状态空间模型参数求得。应用了平方根卡尔曼滤波方程提高EM迭代过程的计算稳健性。考虑到状态空间方程中激励噪声和测量噪声的相关性,建立了更完善的参数化状态空间方程。通过数值模拟对比分析,结果表明：考虑噪声相关性的EM算法比假设噪声不相关的EM算法具有更高的识别精度,EM算法在采样数据较少的情况下比随机子空间方法更有优势。 相似文献
13.
应用模式匹配算法研究建立水平层状非均质横向同性地层中多分量感应测井响应的快速算法.首先,利用Fourier级数展开法将多分量感应响应的数值模拟转化为三个轴对称问题,并利用电阻率径向导数的奇异表达式,引入两个附加奇异微分算子,用于描述柱状分界面上的积累面电荷对共面线圈系电磁响应的影响.然后通过模式匹配算法求解轴对称问题,得到水平层状非均质横向同性地层中多分量感应磁场的半解析解以及测井响应计算方法,最后通过数值模拟结果对该算法进行检验并进一步考察阵列多分量感应仪器的响应特征. 相似文献
14.
Here we present a new algorithm (StalAge), which is designed to construct speleothem age models. The algorithm uses U-series ages and their corresponding age uncertainty for modelling and also includes stratigraphic information in order to further constrain and improve the age model. StalAge is applicable to problematic datasets that include outliers, age inversions, hiatuses and large changes in growth rate. Manual selection of potentially inaccurate ages prior to application is not required. StalAge can be applied by the general, non-expert user and has no adjustable free parameters. This offers the highest degree of reproducibility and comparability of speleothem records from different studies. StalAge consists of three major steps. Firstly, major outliers are identified. Secondly, age data are screened for minor outliers and age inversions, and the uncertainty of potential outliers is increased using an iterative procedure. Finally, the age model and corresponding 95%-confidence limits are calculated by a Monte-Carlo simulation fitting ensembles of straight lines to sub-sets of the age data.We apply StalAge to a synthetic stalagmite ’sample’ including several problematic features in order to test its performance and robustness. The true age is mostly within the 95%-confidence age limits of StalAge showing that the calculated age models are accurate even for very difficult samples. We also apply StalAge to three published speleothem datasets. One of those is annually laminated, and the lamina counting chronology agrees with the age model calculated by StalAge. For the other two speleothems the resulting age models are similar to the published age models, which are both based on smoothing splines. Calculated uncertainties are in the range of those calculated by combined application of Bayesian chronological ordering and a spline, showing that StalAge is efficient in using stratigraphic information in order to reduce age model uncertainty.The algorithm is written in the open source statistical software R and available from the authors or as an electronic supplement of this paper. 相似文献
15.
利用数值模式匹配技术,研究并建立层状各向异性倾斜地层中多分量感应测井响应的快速数值模拟算法.首先将位于井轴上的三个相互正交磁偶极子转化成关于极角θ的三个谐变分量的叠加,以便将三个正交磁偶极子电磁场的正演问题完全简化成三个谐变分量电磁场的轴对称定解问题,并给出电磁场各个谐变分量在井轴上满足的边界条件,保证电磁场在井轴附近仍然可解.然后利用数值模式匹配技术建立电磁场各个谐变分量的正演过程,得到层状各向异性地层中磁流源并矢Green函数的半解析表达式,给出计算层状各向异性倾斜地层中多分量感应测井响应的具体方法,最后通过数值计算结果证明该算法的有效性并考察几种不同情况下多分量感应测井响应特征. 相似文献
16.
地震诱导电磁现象是国内外地学领域十分关注的前沿问题,前人对地震波和电磁场耦合波场的认识主要是基于规则模型获得的.为研究含起伏地表和地下界面的地层中震电波场激发、传播特性,本文采用有限元软件COMSOL Multiphysics模拟点震源激发的电磁场.首先给出频率域二维SHTE模式震电耦合方程组,然后利用COMSOL软件建立计算模型,并求解出点力源激发震电波场的频率域响应,最后利用FFT变换得到地震波场和电磁场的时间域波形.模拟结果表明,震电波场中存在三种类型的电磁信号,第一种是震源直接激发的电磁波;第二种是地震波在分界面处激发的电磁波(包括自由表面、地下不同介质分界面);第三种是伴随地震波的同震信号,前两种电磁波比地震波更早到达远处观测台站,对地震预警有重要意义.此外,研究还发现:当地震波传播至地表并沿着地表传播时,在地表附近空气层中同样记录到了伴随地震波传播的电磁扰动信号,该信号与相同水平源距条件下、地下观测点接收到的电磁信号相同,这与前人的一些观测结果相符.本文研究结果为今后地震电磁信号的解释提供了理论证据. 相似文献
17.
In optical dating, especially single-grain dating, various patterns of distributions in equivalent dose (De) are usually observed and analysed using different statistical models. None of these methods, however, is designed to deal with outliers that do not form part of the population of grains associated with the event of interest (the ‘target population’), despite outliers being commonly present in single-grain De distributions. In this paper, we present a Bayesian method for detecting De outliers and making allowance for them when estimating the De value of the target population. We test this so-called Bayesian outlier model (BOM) using data sets obtained for individual grains of quartz from sediments deposited in a variety of settings, and in simulations. We find that the BOM is suitable for single-grain De distributions containing outliers that, for a variety of reasons, do not form part of the target population. For example, De outliers may be associated with grains that have undesirable luminescence properties (e.g., thermal instability, high rates of anomalous fading) or with contaminant grains incorporated into a sample when collected in the field or prepared in the laboratory. Grains that have much larger or smaller De values than the target population, due to factors such as insufficient bleaching, beta-dose heterogeneity or post-depositional disturbance, may also be identified as outliers using the BOM, enabling these values to be weighted appropriately for final De and age determination. 相似文献
18.
A dual-ship-towed marine electromagnetic (EM) system is a new marine exploration technology recently being developed in China. Compared with traditional marine EM systems, the new system tows the transmitters and receivers using two ships, rendering it unnecessary to position EM receivers at the seafloor in advance. This makes the system more flexible, allowing for different configurations (e.g., in-line, broadside, and azimuthal and concentric scanning) that can produce more detailed underwater structural information. We develop a three-dimensional goal-oriented adaptive forward modeling method for the new marine EM system and analyze the responses for four survey configurations. Oceanbottom topography has a strong effect on the marine EM responses; thus, we develop a forward modeling algorithm based on the finite-element method and unstructured grids. To satisfy the requirements for modeling the moving transmitters of a dual-ship-towed EM system, we use a single mesh for each of the transmitter locations. This mitigates the mesh complexity by refining the grids near the transmitters and minimizes the computational cost. To generate a rational mesh while maintaining the accuracy for single transmitter, we develop a goal-oriented adaptive method with separate mesh refinements for areas around the transmitting source and those far away. To test the modeling algorithm and accuracy, we compare the EM responses calculated by the proposed algorithm and semi-analytical results and from published sources. Furthermore, by analyzing the EM responses for four survey configurations, we are confirm that compared with traditional marine EM systems with only in-line array, a dual-ship-towed marine system can collect more data. 相似文献
19.
Abstract. This report summarizes results of monitoring programs for volatile synthetic organic chemicals (VOCs) in Nebraska's private and public water-supply wells conducted by two State agencies. Of 97 community water-supply systems sampled as of June 1984, 16.5 percent (16 systems) showed quantifiable levels of at least one VOC. Detectable amounts of one or more VOCs were measured in samples from 15.9 percent (10) of 63 private wells sampled in 1982. These percentages are consistent with results of other State and national surveys. 相似文献
20.
本文研究声电效应测井波场的有限差分模拟算法.忽略井外地层中诱导电磁场对孔隙弹性波的影响,将求解动电耦合波方程组的问题解耦,先计算孔隙弹性波,再计算其诱导电磁场.基于轴对称柱坐标系下的速度-应力交错网格,采用时域有限差分计算井孔流体声波和井外地层孔隙弹性波.将电磁场近似看作似稳场,基于轴对称柱坐标系下的5点式有限差分网格,求解不同时刻的电位Poisson方程,计算诱导电场.结果表明:本文算法可准确模拟频率6.0 kHz的声电效应测井全波;在声波测井频率范围内,电导率、动电耦合系数和动态渗透率的低频近似对伴随电磁场的计算影响不大;地层水平界面导致伴随反射斯通利波的电场和显著的界面电磁波,后者对于探测地层界面具有潜在的应用价值. 相似文献