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1.
大地电磁测深数据的时频分析 总被引：1，自引：0，他引：1
大地电磁测深(MT)数据表现出非线性、非平稳、非最小相位特征,不符合以Fourier变化为基础的传统谱分析的基本要求.为寻求更好的谱分析方法,把最新发展的Hilbert-Huang变换(HHT)引入到大地电磁测深数据的时频分析当中来,针对湖北宜万线实测的MT信号,与短时Fourier变换(STFT)、Winger-Ville分布(WVD)和小波变换(WT)进行了时频分析比较.比较分析表明:HHT方法克服了其它一些方法的缺陷,完全取消了窗函数的作用,其结果不受核函数影响与时频测不准原理限制,具有完全的局部时频特性和更好的时频聚集性.分析认为HHT是一种全新而更优越的分析与处理大地电磁测深信号的时频方法,能更好地提取信号的时频本质特征,用于指导生产勘测实践. 相似文献
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Some natural substrates record environmental information and, as such, provide a means to reconstruct the environmental conditions
from the period these substrates were formed. Samples from environmental archives are not always equally spaced in distance.
When a periodic time series model is estimated from these unequally spaced proxy records, the search for reasonable starting
values is the main difficulty. In this work, a non-parametric method based on the regressive Fourier series is first presented,
which reduces averaging errors starting from unequally spaced records. The method is applied to synthetic data and generally
performs well in all circumstances. Secondly, a parametric method for the construction of a time base and the elimination
of averaging errors from unequally spaced records is presented. This parametric method uses the non-parametric method to produce
starting values for the parameters. The method is compared with the time series construction method with the averaging effect
taken into account and it is observed that only the current method produces acceptable results. The statistical performance
of the method is verified with a Monte Carlo simulation and the estimator is proven to be an efficient estimator. The applicability
of the method is demonstrated on the vessel density measurement in a mangrove tree, Rizophora mucronata, which is a proxy for the rainfall in tropical coastal regions. 相似文献
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广义S变换是目前比较新的一种非平稳信号分析的时频分析方法,其特点和优势为广义S变换的反变换与傅立叶变换有直接的联系,保证其是无损变换;线性变换保证其不存在交叉项;时频分辨率与信号的频率有关;基本小波不必满足容许性条件;尺度性质使得广义S变换有很好的频率聚集能力。基于这些特点和优势,在地震勘探中已经有了广泛的应用,如利用广义S变换进行瑞利面波频散分析、时频域波场分离与去噪、沉积相旋回以及地震波初至识别等。笔者总结了应用中比较有代表性的广义S变换类型,并结合实例,阐述了该方法在地震勘探中的研究进展。 相似文献
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随着致密油、页岩气等非常规能源领域勘探程度的加深,特别是水平井位的大规模部署,微小断层的准确识别比以往更加重要。本文利用扩散滤波技术在压制噪声的同时能够增强地震同相轴横向连续性、使断点更加清晰、以及微小断层在窄频带地震数据中断层特征明显的特点,提出了一种基于高精度快速匹配追踪的分频相干加强微小断层识别方法。与常规短时窗傅氏变换谱分解技术相比,基于匹配追踪的谱分解技术更适用于地震信号非平稳性的特点。为了在保证匹配追踪算法计算高效性的同时进一步提高计算精度,对其进行了相应的改进：采用可变尺度参数的Morlet小波构建时频原子库,利用二阶微分复数道分析技术得到高分辨率三瞬参数,最后给出了具体的实现步骤。实际数据应用表明,与常规相干体技术相比,分频相干加强技术对微小断层的反映更为清晰、准确,而且对河道边界和岩性发育区等地质信息也有更好的反映。这不但为非常规勘探（以水平井钻探及大规模压裂为核心技术）提供了更详细的地质信息,而且在高含水老油田的剩余油开发中也将发挥更大的作用。 相似文献
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预测滑坡地下水位的动态演变过程对滑坡稳定性分析具有重要意义, 三峡库区库岸滑坡地下水位时间序列受多种因素影响, 呈现出高度非线性非平稳的特征.为对其进行预测, 提出一种基于相空间重构的小波分析-粒子群优化支持向量机(wavelet analysis-support vector machine, 简称WA-PSVM)模型.该模型引入小波变换法对地下水位序列进行时频分解, 将非平稳的地下水位序列转变为多个不同分辨率尺度下的较平稳的地下水位子序列; 然后重构各子序列的相空间, 再利用PSVM(全称support vector machine)模型对地下水位各子序列进行预测, 最后将各子序列预测值相加得到最终预测结果.以三峡库区三舟溪滑坡前缘STK-1水文孔日平均地下水位序列为例, 首先分析滑坡前缘地下水位变化的影响因素, 再将WA-PSVM模型应用于地下水位预测, 并与单独PSVM模型和小波分析-BP网络模型(wavelet analysis-back propagation, 简称WA-BP)作对比.结果表明: 滑坡前缘地下水位受降雨和库水位影响较大, 利用WA-PSVM模型对STK-1水文孔地下水位进行预测的均方根误差为0.073m、拟合优度为0.966, WA-PSVM模型预测精度高于单独PSVM模型和WA-BP模型.WA-PSVM模型解决了地下水位序列非线性非平稳的问题, 在不考虑影响因素的情况下能获得满意的预测效果, 具有较高的建模效率和较强的实用性. 相似文献
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Identification of karst features with spectral analysis on the seismic reflection data 总被引：1，自引：0，他引：1
The use of high-resolution seismic tools to investigate karst terrain has had limited success due to the ambiguous seismic events caused by lateral heterogeneities of the sedimentary cover, as well as the superimposition of surface waves. To address these problems, a spectral analysis scheme is proposed on the seismic reflection data to characterize karst features in this paper. First, the S-transform is applied to suppress the ground roll. As a type of time–frequency transform, the S-transform provides frequency-dependent resolution while maintaining a direct relationship with the Fourier spectrum. Application of a filter based on the S-transform attenuates ground roll in a time–frequency domain. Then, the continuous wavelet transform is employed for the time–frequency mapping of potential karst features, which are featured as frequency differentiation anomalies. Synthetic model and real-data example validate the efficiency of the spectral analysis scheme for the detection of karst features. 相似文献
10.
利用小波包分析在时域和频域同时具有良好的局部化特性,对信号进行小波包变换后,用谱矩阵法计算质点的空间运动特性,构造相应的滤波函数,对分解后的信号进行滤波,将滤波结果用逆小波包变换进行重构,实现了滤除干扰、保留有用信号的目的,取得了非常满意的效果。 相似文献
11.
Fracture set properties such as orientation, spacing, trace length, and waviness tend to be spatially correlated. These properties can be efficiently simulated by spectral analysis procedures that take advantage of the computational speed of the fast Fourier transform. The covariance function of each property to be simulated is obtained from the variogram function estimated from mapped fracture set data and is typically referenced to the mean vector of the set. Simulation procedures for normally and exponentially distributed data involve generating uncorrelated Fourier coefficients that are assigned proper variance according to the spectral density, which is the Fourier transform of the covariance function. These coefficients are then reverse Fourier transformed to produce simulated set properties that have the desired variance and variogram function. 相似文献
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Identifying non-stationary groundwater level response to North Atlantic ocean-atmosphere teleconnection patterns using wavelet coherence 总被引：1，自引：1，他引：0
Ian Paul Holman Monica Rivas-Casado John P. Bloomfield Jason J. Gurdak 《Hydrogeology Journal》2011,19(6):1269-1278
The first comprehensive use of wavelet methods to identify non-stationary time-frequency relations between North Atlantic ocean-atmosphere teleconnection patterns and groundwater levels is described. Long-term hydrogeological time series from three boreholes within different aquifers across the UK are analysed to identify statistically significant wavelet coherence between the North Atlantic Oscillation, East Atlantic pattern, and the Scandinavia pattern and monthly groundwater-level time series. Wavelet coherence measures the cross-correlation of two time series as a function of frequency, and can be interpreted as a correlation coefficient value. Results not only indicate that there are common statistically significant periods of multiannual-to-decadal wavelet coherence between the three teleconnection indices and groundwater levels in each of the boreholes, but they also show that there are periods when groundwater levels at individual boreholes show distinctly different patterns of significant wavelet coherence with respect to the teleconnection indices. The analyses presented demonstrate the value of wavelet methods in identifying the synchronization of groundwater-level dynamics by non-stationary climate variability on time scales that range from interannual to decadal or longer. 相似文献
14.
An accurate representation of permeability anisotropy is needed to model the rate and direction of groundwater flow correctly.
We develop a wavelet analysis technique that can be used to characterize principal directions of anisotropy in both stationary
and non-stationary permeability fields. Wavelet analysis involves the integral transform of a field using a wavelet as a kernel.
The wavelet is shifted, scaled, and rotated to analyze different locations, sizes, and orientations of the field. The wavelet
variance is used to identify scales and orientations that dominate the field. If the field is non-stationary, such that different
zones of the field are characterized by different dominant scales or orientations, the wavelet variance can identify all dominant
scales and orientations if they are distinct. If the dominant scales and orientations of different zones are similar, the
wavelet variance identifies only the dominant scale and orientation of the primary zone. In this paper, we present a combined
wavelet analysis and filtering approach to identify all dominant scales and orientations in a non-stationary permeability
field. We apply the method to permeability data obtained in the laboratory from the Massillon sandstone. 相似文献
15.
受到全球气候变化和大规模人类活动等变化环境的影响,特别是长江三峡水库、葛洲坝电站等大型水电工程的兴建,洞庭湖区各站点的洪水序列发生了变异,并引发了洪水频率分布的非一致性问题。以洞庭湖区内弥陀寺站为例,采用线性趋势、非线性趋势、小波分析及希尔伯特-黄变换四种考虑趋势变异的非一致性洪水频率计算方法推求了年最大洪峰流量的频率分布,并进行了四种方法的择优比较分析。结果显示弥陀寺站年最大洪峰流量序列的均值存在显著下降趋势变异,四种方法推求的过去和现状条件下频率曲线的差异较小,而对未来时期的预测差异较大;经择优度计算与比较分析,基于非线性趋势方法所得结果为最优,且进一步得出年最大洪峰流量的频率分布在过去、现状和未来三个时期存在显著的差异,将直接影响洞庭湖区内弥陀寺站附近堤防的安全评价和区域防洪规划。 相似文献
16.
Asok K. Sen 《Mathematical Geosciences》2009,41(1):43-49
Sedimentary records of Lake Edward in Central Africa from the late Holocene era exhibit submillennial-scale periodicities
in magnesium (Mg) and stable isotope compositions of endogenic calcite. Using multitaper spectral analysis, Russell et al. (Geology
31(8):677–680, 2003) detected a 725-yr cycle in the Mg data. We have analyzed the Mg data using a continuous wavelet transform and observed temporal
variations in the submillennial periodicities. These temporal variations can be discerned from a time-period representation
of the wavelet power spectrum by visual inspection. The multi-taper spectral analysis is based on the traditional Fourier
transform, which is a purely frequency domain technique, and therefore cannot detect temporal variability of the spectrum,
if any. In contrast, wavelet analysis offers a spectral-temporal approach by which both the dominant periodicities and their
time variations can be identified. In this regard, the results of our wavelet analysis extend those of Russell et al. (Geology
31(8):677–680, 2003). Our analysis reveals dominant periodicities around the 785-yr and 660-yr cycles, but these cycles persist over different
time spans within the late Holocene era. The 725-yr period identified by Russell et al. (Geology 31(8):677–680, 2003) with multitaper spectral analysis is very close to the average of the periods of these two cycles. For the purpose of accurately
reconstructing the climate history in Central Africa using Mg as a proxy, it would be important to take into consideration
the temporal variations of the submillennial periodicities. 相似文献
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In sedimentology, stratigraphic sequences and cycles are ordered by time spans and physical scales, such as thickness, and bounded by discontinuities, including unconformities or flooding surfaces. Spectral analysis based on wavelet transform (WT) maxima is proposed and used as a quantitative tool to identify multi-order stratigraphic boundaries and cycles in well log data. The proposed spectral analysis is based on quantitative analysis on the center frequencies and resolutions of Gaussian wavelets in time and frequency, and uses a combination of the WT maxima based on both the first order Gaussian wavelet having a high time resolution and the seventh order Gaussian wavelet having a high frequency resolution. WT maxima spectra, which can characterize the evolution of WT maxima across scales and periods along WT maxima lines concerned with sequence boundaries, are used to detect dominant spectral peaks corresponding to the time-period domain WT maxima and to determine WT maxima spectral slopes. The WT maxima spectral slopes are helpful for discriminating sequence boundaries from intrasequence cyclic variations in well log data, and the time-period domain WT maxima are used to relate the detected boundaries to relevant cycles. The interval WT maxima spectra and the stationary index, related to the WT maxima spectra, are introduced as indicators that can be used for the hierarchical ordering of the boundaries and cycles. Application of the proposed method to well log data shows that the suggested method is efficient in identifying multi-order sequences that relate well to the Milankovitch cycles.
相似文献18.
深度衰减效应对大型地下洞室群强震响应的影响分析 总被引：1，自引：1，他引：0
介绍了大型地下洞室群强震反应分析所需要输入地震波的选用原则,重点考虑了场地的深度衰减效应,同时提出了一种假设来确定地震危险性分析提供的峰值加速度的所在位置。选用了两组攀枝花实测地震记录,同时利用三角级数叠加法综合考虑了深度衰减效应,合成了一组人工地震动,使用ABAQUS软件对某水电站大型地下洞室群进行了二维非线性强震动力时程数值计算分析。结果表明：生成的地震波能较好地模拟地下洞室群的地震响应,深度衰减对地震响应结果有明显影响,不同频谱的地震波相对位移-时程差距较大,但频谱参数的影响还有待于深入研究。研究成果对大型地下洞室群地震动输入问题研究具有一定的指导意义。 相似文献
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地震信号在地下传播时会受到地层吸收衰减的影响,从而降低了地震资料的分辨率。因此地震波吸收衰减补偿是地震资料处理中的一项重要环节。本文研究的地层吸收衰减补偿方法主要基于局部时频变换(LTFT),该方法能够调节选取谱分解的频率范围和频率采样间隔,解决了短时傅里叶变换固定时窗和小波系数无法提供波形频率的精确估计值问题,适用于非平稳地震信号的时频分析。在求取地层Q值的方法中,频谱比值法具有高效简单的特点,有着广泛的应用范围。本文假设地下介质为层状变Q模型,使用局部时频变换将信号转换为时频域,通过频谱比值法求出各层的Q值,最后根据Kolsky衰减模型来补偿地震信号。理论模型测试和实际资料处理的结果表明,本文提出的方法能够有效恢复衰减信号,提高地震资料的分辨率。 相似文献