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1.
Three‐dimensional seismic survey design should provide an acquisition geometry that enables imaging and amplitude‐versus‐offset applications of target reflectors with sufficient data quality under given economical and operational constraints. However, in land or shallow‐water environments, surface waves are often dominant in the seismic data. The effectiveness of surface‐wave separation or attenuation significantly affects the quality of the final result. Therefore, the need for surface‐wave attenuation imposes additional constraints on the acquisition geometry. Recently, we have proposed a method for surface‐wave attenuation that can better deal with aliased seismic data than classic methods such as slowness/velocity‐based filtering. Here, we investigate how surface‐wave attenuation affects the selection of survey parameters and the resulting data quality. To quantify the latter, we introduce a measure that represents the estimated signal‐to‐noise ratio between the desired subsurface signal and the surface waves that are deemed to be noise. In a case study, we applied surface‐wave attenuation and signal‐to‐noise ratio estimation to several data sets with different survey parameters. The spatial sampling intervals of the basic subset are the survey parameters that affect the performance of surface‐wave attenuation methods the most. Finer spatial sampling will reduce aliasing and make surface‐wave attenuation easier, resulting in better data quality until no further improvement is obtained. We observed this behaviour as a main trend that levels off at increasingly denser sampling. With our method, this trend curve lies at a considerably higher signal‐to‐noise ratio than with a classic filtering method. This means that we can obtain a much better data quality for given survey effort or the same data quality as with a conventional method at a lower cost. 相似文献
2.
Gary Barnes 《Geophysical Prospecting》2014,62(3):646-657
When anomalous gravity gradient signals provide a large signal‐to‐noise ratio, airborne and marine surveys can be considered with wide line spacing. In these cases, spatial resolution and sampling requirements become the limiting factors for specifying the line spacing, rather than anomaly detectability. This situation is analysed by generating known signals from a geological model and then sub‐sampling them using a simulated airborne gravity gradient survey with a line spacing much wider than the characteristic anomaly size. The data are processed using an equivalent source inversion, which is used subsequently to predict and grid the field in‐between the survey lines by means of forward calculations. Spatial and spectral error analysis is used to quantify the accuracy and resolution of the processed data and the advantages of acquiring multiple gravity gradient components are demonstrated. With measurements of the full tensor along survey lines spaced at 4 × 4 km, it is shown that the vertical gravity gradient can be reconstructed accurately over a bandwidth of 2 km with spatial root‐mean square errors less than 30%. A real airborne full‐tensor gravity gradient survey is presented to confirm the synthetic analysis in a practical situation. 相似文献
3.
— We propose an algorithm for local evaluation of weak anisotropy (WA) parameters from measurements of slowness vector components and/or of particle motions of q P waves at individual receivers in a borehole in a multi-azimuthal multiple-source offset VSP experiment. As a byproduct the algorithm yields approximate angular variation of q P-wave phase velocity. The formulae are derived under assumption of weak but arbitrary anisotropy and lateral inhomogeneity of the medium. The algorithm is thus independent of structural complexities between the source and the receiver. If complete slowness vector is determinable from observed data, then the information about polarization can be used as an independent additional constraint. If only the component of the slowness along the borehole can be determined from observations (which is mostly the case), the inversion without information about polarization is impossible. We present several systems of equations which can be used when different numbers of components of the slowness vector are available. The SVD algorithm is used to solve an overdetermined system of linear equations for WA parameters for two test examples of synthetic multi-azimuthal multiple-source offset VSP data. The system of equations results from approximate first-order perturbation equations for the slowness and polarization vectors of the q P wave. Analysis of singular values and of variances of WA parameters is used for the estimation of chances to recover the sought parameters. Effects of varying number of profiles with sources and of noise added to “observed” data are illustrated. An important observation is that although, due to insufficient data, we often cannot recover all individual WA parameters with sufficient accuracy, angular phase velocity variation can be recovered rather well. 相似文献
4.
Shear‐wave polarization and time delay are attributes commonly used for fracture detection and characterization. In time‐lapse analysis these parameters can be used as indicators of changes in the fracture orientation and density. Indeed, changes in fracture characteristics provide key information for increased reservoir characterization and exploitation. However, relative to the data uncertainty, is the comparison of these parameters over time statistically meaningful? We present the uncertainty in shear‐wave polarization and time delay as a function of acquisition uncertainties, such as receiver and source misorientation, miscoupling and band‐limited random noise. This study is applied to a time‐lapse borehole seismic survey, recorded in Vacuum Field, New Mexico. From the estimated uncertainties for each survey, the uncertainty in the difference between the two surveys is 31° for the shear‐wave polarization angle and 4 ms for the shear‐wave time delay. Any changes in these parameters greater than these error estimates can be interpreted with confidence. This analysis can be applied to any time‐lapse measurement to provide an interval of confidence in the interpretation of shear‐wave polarization angles and time splitting. 相似文献
5.
磁共振探测技术（Magnetic Resonance Sounding,MRS）以其无损、定量、直接等优势,被广泛应用于地下水调查、水文环境评价以及灾害水源预警等领域.在实际应用中,强工频谐波和随机噪声等严重影响MRS信号的质量,导致后续水文参数解释不准确.针对这一问题,提出谐波建模和自相关相结合的方法进行消噪以及信号特征参数提取.首先构建工频谐波模型,针对建模算法严重依赖工频基频精度的问题,采用自适应扫描方式搜索方案,大幅提高搜索准确度和速度;其次推导了MRS信号自相关表达式,提出了自相关参数提取的非线性拟合方法.仿真数据结果表明,建模消噪方法有效消除了工频谐波,信噪比平均提升了17.03 dB;自相关处理后,信噪比进一步提升了16.10 dB,初始振幅和弛豫时间参数提取结果的准确度比处理前分别提高了3.8倍和2.8倍.通过不同信噪比和弛豫时间的重复实验,得到当噪声水平小于200 nV和弛豫时间大于200 ms时,自相关参数提取具有较高的稳定性.最后,通过野外实测数据处理实验,进一步验证了联合消噪和参数提取方法的有效性. 相似文献
6.
Gary J. Barnes John M. Lumley Phill I. Houghton Richard J. Gleave 《Geophysical Prospecting》2011,59(1):176-187
Noise levels in marine and airborne full tensor gravity gradiometer surveys together with conventional land, marine and airborne gravity surveys are estimated and analysed in gridded form, resulting in relations that detail how these different survey systems can be compared analytically. After defining survey parameters including line spacing, speed and instrument bandwidth, the relations estimate the noise levels that result on either grids of gravity (gz) or gravity gradient (Gzz) as a function of the spatial filtering often applied during geological interpretation. Such comparisons are believed to be a useful preliminary guide for survey selection and planning. 相似文献
7.
The prospecting of densely urbanized areas by the measurement of magnetic and electric natural fields is severely hampered by electromagnetic (EM) noise. Active man-made EM noise sources can generally be considered fixed in space, thus affecting the magnetotelluric (MT) signals of a measuring site mainly along their polarization directions. Taking advantage of the impulsive nature of polarized EM noise, a time-domain directional noise cancelling (DNC) technique is proposed. The comparison of noisy data with data predicted, using a low noise reference signal or with data interpolated whenever no reference is available, allows the detection of the most likely noise sources with prevailing directional patterns using a Bayes's criterion. The DNC approach is general and can be adapted, depending on the reference signal used (single-site or remote-reference). In field data, hodograms of the prediction residuals basically confirm the directional noise model assumed in DNC. An example is presented in which the DNC technique has been applied to a single-site MT survey carried out in northern Italy, where the signal was heavily corrupted by noise with prevailing directional properties due to the densely urbanized area. MT apparent resistivities and phases obtained at the site of the survey before and after DNC are presented and discussed. 相似文献
8.
地震勘探资料噪声压制及信噪比提高是整个地震勘探信号处理过程中的重要任务,随着地震勘探深度的增加及其复杂性,人们对地震数据质量的要求越来越高.勘探环境的复杂化使得采集到的地震资料中有效信号被大量噪声淹没,无法清晰辨识,严重影响后续的数据处理与解释.小波去噪是地震勘探中常用且发展较成熟的一种方法,但是其涉及到的阈值函数选取问题一直令人困扰,虽然已有多种阈值函数被提出,但仍存在各自的缺陷.本文利用小波分解在时域及频域良好的信号细节体现特性,引入模式识别中的非负矩阵分解(NMF)谱分离思想,针对小波系数阈值优化问题,提出了一种小波域图非负矩阵分解(GNMF)消噪算法.该方法首先在小波分解基础上,利用GNMF算法实现小波分解系数谱中信号分量与噪声分量的谱分离,然后通过反变换重构各分离子谱对应的子信号,最后利用K均值聚类算法将得到的多个子信号划分为信号类及噪声类,最终得到重构信号及分离噪声.合成记录和实际地震资料的消噪结果验证了新方法在提高信号与噪声分离准确性和精度方面的有效性,同时新方法避免了阈值选取造成的噪声压制不理想或有效成分损失问题.与小波消噪结果的对比及数值分析也说明了新方法在噪声压制及有效成分保持方面的优势. 相似文献
9.
Most GPS time-series exhibit a seasonal signal that can have an amplitude of a few millimetres. This seasonal signal can be removed by fitting an extra sinusoidal signal with a period of one year to the GPS data during the estimation of the linear trend.However, Blewitt and Lavallée (2002) showed that including an annual signal in the estimation process still can give a larger linear trend error than the trend error estimated from data from which the annual signal has been removed by other means. They assumed that the GPS data only contained white noise and we extend their result to the case of power-law plus white noise which is known to exist in most GPS observations. For the GPS stations CASC, LAGO, PDEL and TETN the difference in trend error between having or not having an annual signal in the data is around ten times larger when a power-law plus white noise model is used instead of a pure white noise model. Next, our methodology can be used to estimate for any station how much the accuracy of the linear trend will improve when one tries to subtract the annual signal from the GPS time-series by using a physical model.Finally, we demonstrate that for short time-series the trend error is more influenced by the fact that the noise properties also need to be estimated from the data. This causes on average an underestimation of the trend error. 相似文献
10.
航空电磁法作为一种地形复杂地区资源探测的有效方法,近年来得到了广泛的应用.然而,由于系统所处的动态环境,噪声干扰严重.为了改善航空电磁数据质量,提高地下电性反演的准确性,需要研发相关去噪技术.传统航电去噪大多针对特定噪声或单一测线上的信号进行处理,难以兼顾相邻测线之间观测信号的相关性.本文采用曲波变换进行二维航空电磁数据去噪.由于曲波变换具有多尺度和多方向性特征,可以在对噪声精细分析的基础上进行有效去除,同时还保证了整个测区内信号的相关性.进而,我们提出Sigmoid阈值函数对传统阈值函数进行改进,以进一步改善去噪效果.为了验证曲波变换方法对航空电磁数据去噪的有效性,将曲波变换和传统去噪方法分别应用于理论模型和实测数据进行对比.试验证明本文曲波变换用于航空电磁数据去噪具有明显的优越性. 相似文献
11.
An application of waveform denoising for microseismic data using polarization–linearity and time–frequency thresholding 
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下载免费PDF全文 Jubran Akram 《Geophysical Prospecting》2018,66(5):872-893
Noise suppression or signal‐to‐noise ratio enhancement is often desired for better processing results from a microseismic dataset. In this paper, a polarization–linearity and time–frequency‐thresholding‐based approach is used for denoising waveforms. A polarization–linearity filter is initially applied to preserve the signal intervals and suppress the noise amplitudes. This is followed by time–frequency thresholding for further signal‐to‐noise ratio enhancement in the S transform domain. The parameterisation for both polarization filter and time–frequency thresholding is also discussed. Finally, real microseismic data examples are shown to demonstrate the improvements in processing results when denoised waveforms are considered in the workflow. The results indicate that current denoising approach effectively suppresses the background noise and preserves the vector fidelity of signal waveform. Consequently, the quality of event detection, arrival‐time picking, and hypocenter location improves. 相似文献
12.
E. RIETSCH 《Geophysical Prospecting》1980,28(4):531-550
The amplitude of the signal and the energy of the noise on each of at least three traces can be estimated provided that the signal has the same form (but not necessarily the same amplitude) on these traces and that the noise on any trace is correlated with neither the signal nor the noise on any other trace. This estimation of signal amplitude and noise energy can be achieved by a rather simple algorithm. The accuracy of the estimate depends, of course, on the degree to which the assumption that signal and noise on the different traces are mutually uncorrelated is actually met. The accuracy tends to improve with increasing number of traces. 相似文献
13.
Hilbert-Huang变换(HHT)是近年出现的一种自适应的非平稳、非线性信号处理方法,该方法迄今已在许多非线性、非平稳信号处理的研究领域得到了很好的应用.本文简要介绍了Hilbert-Huang变换的基本实现原理与算法基础,通过仿真信号验证了该方法的有效性,并以实际数据为例,探讨了它在极低频(ELF)信号处理及噪声压制方面的应用.利用Hilbert-Huang变换对ELF信号进行频率域滤波,可以对噪声进行有效压制,从而提取已知频率的电磁信号,极大地提高信号质量. 相似文献
14.
主成分分析方法利用低阶主成分重构航空电磁数据,解决了航空电磁探测中噪声与数据在频谱重叠情况下的噪声压制问题,但是参与重构的低阶主成分仍包含高频空间噪声,影响数据成像精度.本文提出的主成分滤波重构去噪方法,根据自适应窗宽平滑算法,设计了主成分低通滤波器组,对参与重构的低阶主成分进行测线滤波,再将滤波后的低阶主成分重构为电磁信号,不仅可以去除低阶主成分中的高频空间噪声,而且去除了高阶主成分包含的不相关噪声.仿真数据的去噪结果表明,主成分滤波重构获得较高的信噪比,较常规测线滤波与主成分重构分别提高了10.96dB和2.52dB;电导率深度成像结果证明了主成分滤波重构方法能够提高地下深部异常体的识别能力.最后通过实测数据的成像结果进一步验证了本文研究的主成分滤波重构去噪方法的有效性. 相似文献
15.
时间域航空电磁数据往往在测量过程中受到天然和人文噪声的干扰.如果不能很好滤除这些电磁噪声,那么将会降低资料质量、影响反演的精度,甚至获得错误的解释结果.本文提出了一种基于核主成分分析的去噪方法,通过核主成分分析提取叠加后衰减曲线的主成分,然后使用能量占比方法分离反映地下介质的有效信号和噪声,最后使用反映地下介质的特定成分进行重构.本文所推荐的去噪方法不仅能剔除天然噪声,例如天电产生的尖脉冲或者振荡,而且能有效地抑制人文噪声.分别使用基于核主成分分析的去噪方法,以及AeroTEM软件的处理方法对同样的吊舱式时间域直升机航空电磁勘查系统实测数据进行处理,并比较其结果.处理结果表明：所推荐的去噪方法要优于AeroTEM软件. 相似文献
16.
Polarization analysis of multi-component seismic data is used in both exploration seismology and earthquake seismology. In
single-station polarization processing, it is generally assumed that any noise present in the window of analysis is incoherent,
i.e., does not correlate between components. This assumption is often violated in practice because several overlapping seismic
events may be present in the data. The additional arrival(s) to that of interest can be viewed as coherent noise. This paper
quantifies the error because of coherent noise interference. We first give a general theoretical analysis of the problem.
A simple mathematical wavelet is then used to obtain a closed-form solution to the principal direction estimated for a transient
incident signal superposed with a time-shifted, unequal amplitude version of itself, arriving at an arbitrary angle to the
first wavelet. The effects of relative amplitude, arrival angle, and the time delay of the two wavelets on directional estimates
are investigated. Even for small differences in angle of arrival, there may be significant error (>10°) in the azimuth estimate. 相似文献
17.
18.
V. A. Ryzhov 《Seismic Instruments》2009,45(1):105-109
A method is presented for filtering harmonic components of the signal while preserving background broadband noise. The method is widely applied for filtering quasi-harmonic disturbances in the technique of low-frequency seismic sensing (LSS), a useful signal that is background microseismic noise. The algorithm is based on subtracting the model’s harmonic signal from the real signal by selecting the signal parameters, i.e., frequency, phase, and amplitude. To do this, the parameters of the model harmonic signal, at which the energy of the difference signal is minimal, are estimated using the optimization algorithms adapted for the goal function. The proposed method successfully solves the problem of filtering the background microseism noise out of harmonic disturbances. 相似文献
19.
本文将时频峰值滤波(TFPF)去噪技术应用于共炮点地震资料的随机噪声压制.时频峰值滤波技术是通过频率调制将信号调制成解析信号的瞬时频率,利用解析信号的Wigner-Ville分布的峰值进行瞬时频率估计,恢复有效信号,与其它去噪方法相比,TFPF具有在较少的约束条件下压制强随机噪声的优点.本文针对实际地震资料的非线性特性,利用加窗的Wigner-Ville分布实现TFPF,使得地震信号在一个窗长内近似满足线性瞬时频率条件,减小由地震信号非线性引起的偏差.本文对共炮点地震记录做时频峰值滤波处理,滤波结果表明在地震勘探资料中存在强随机噪声的情况下,利用局部线性化处理的时频峰值滤波技术可以有效地压制地震资料中的随机噪声,恢复出湮没在随机噪声中的地震反射信号.信噪比提高3～6 dB. 相似文献
20.
Jing Liu Youcai Tang Kai Tao Chunquan Yu Jie Chen Jieyuan Ning Yongshun John Chen Yongge Feng 《地震科学（英文版）》2010,23(6):627-636
We have developed a new stacking technique in ambient noise tomography to obtain high-quality dispersion curves of Rayleigh waves.This technique is used to stack the vertical components of the Estimated Green Functions(EGFs) obtained respectively from cross correlation of the ambient noise data recorded by a remote seismic station and one of the short distance seismic stations of a seismic array.It is based on a phase-matched filter and is implemented by a four-step iterative process:signal compression,stacking,signal extraction and signal decompression.The iterative process ends and gives the dispersion curve of Rayleigh wave when the predicted one and the processing result converge.We have tested the method using the vertical components of synthetic Rayleigh wave records.Results show that this new stacking method is stable and it can improve the quality of dispersion curves.In addition,we have applied this method to real data.We see that the results given by our new technique are obviously better than the ones employing the traditional method which is a three-step process:signal compression,signal extraction and signal decompression.In conclusion,the new method proposed in this paper can improve the signal to noise ratio of EGFs,and can therefore potentially improve the resolution of ambient noise tomography. 相似文献