共查询到20条相似文献，搜索用时 625 毫秒
1.
H. EDELMANN 《Geophysical Prospecting》1966,14(4):455-469
In order to obtain high resolution correlograms, it is of importance amongst other things to get reflection signals with large bandwidth. An advantage of the VIBROSEIS *** *** Trade Mark and Service book of the Continental Oil Company.
method is that the frequencies radiated by the vibrators can be matched to the transmission response of the subsurface involved. By choosing the right frequency range, the highest possible amplitude and most favourable form may be given to the reflection signals. In a reflection correlogram, individual signals cannot be considered in isolation. Signals of different origin are interfering with one another. They very often have different amplitudes, so that it may be desirable in many cases to filter out events of certain apparent velocity. With the VIBROSEIS method this may be achieved quite simply. All frequencies of the noise signal are uniformly suppressed. The advantage is that noise signals, e.g. refraction signals, which cannot be sufficiently attenuated by wavelength filtering, may be completely eliminated by this velocity filtering without affecting the bandwith of the desired signal. The total dynamic range of the tape recording can be used for the registration of wanted events. To perform this kind of filtering several vibrators are necessary in the field; each of them is controlled by an individual signal. There is an unavoidable error of static and dynamic corrections which causes the results of reflection measurements to deteriorate when using multiple coverage. High frequency components especially are seriously affected by destructive interference. This difficulty can be avoided by using a VIBROSEIS signal with high frequency component amplitudes supported. For the probability of error of corrections a normal distribution is assumed. A smoothed amplitude characteristic may be achieved after stacking. The amplitude characteristic of seismic devices is commonly reduced to about 100 cps bandwidth. For further improvement of resolution of VIBROSEIS correlograms it is necessary to apply special filtering methods. This is of particular interest when any kind of gain control is used to display weak events more clearly. With increasing amplification the sidelobes of the strong signals may reach the size of the weak events. In order to eliminate this effect, the amplitude characteristic of the VIBROSEIS signal is adjusted for optimum suppression of side-lobes. 相似文献
method is that the frequencies radiated by the vibrators can be matched to the transmission response of the subsurface involved. By choosing the right frequency range, the highest possible amplitude and most favourable form may be given to the reflection signals. In a reflection correlogram, individual signals cannot be considered in isolation. Signals of different origin are interfering with one another. They very often have different amplitudes, so that it may be desirable in many cases to filter out events of certain apparent velocity. With the VIBROSEIS method this may be achieved quite simply. All frequencies of the noise signal are uniformly suppressed. The advantage is that noise signals, e.g. refraction signals, which cannot be sufficiently attenuated by wavelength filtering, may be completely eliminated by this velocity filtering without affecting the bandwith of the desired signal. The total dynamic range of the tape recording can be used for the registration of wanted events. To perform this kind of filtering several vibrators are necessary in the field; each of them is controlled by an individual signal. There is an unavoidable error of static and dynamic corrections which causes the results of reflection measurements to deteriorate when using multiple coverage. High frequency components especially are seriously affected by destructive interference. This difficulty can be avoided by using a VIBROSEIS signal with high frequency component amplitudes supported. For the probability of error of corrections a normal distribution is assumed. A smoothed amplitude characteristic may be achieved after stacking. The amplitude characteristic of seismic devices is commonly reduced to about 100 cps bandwidth. For further improvement of resolution of VIBROSEIS correlograms it is necessary to apply special filtering methods. This is of particular interest when any kind of gain control is used to display weak events more clearly. With increasing amplification the sidelobes of the strong signals may reach the size of the weak events. In order to eliminate this effect, the amplitude characteristic of the VIBROSEIS signal is adjusted for optimum suppression of side-lobes. 相似文献
2.
H. A. K. EDELMANN 《Geophysical Prospecting》1982,30(6):774-785
The characteristic and information content of a seismic signal depends considerably on the bandwidth of the signal. The Vibroseis system gives the possibility of selecting a certain frequency range. This selection is mostly done in the field by visual comparison, mainly taking into account the characteristic of the signal and the signal/noise ratio. A signal with a good characteristic has, in some cases, an arbitrary amplitude and phase characteristic which is not by itself optimum for the transmission of the desired stratigraphic information. The different factors which influence the amplitude characteristic of a Vibroseis signal are discussed. The present situation is illustrated by some results of measurements of vibrators in different areas. An outlook of how the characteristic of vibrators may be improved is given. 相似文献
3.
Anton Ziolkowski 《Geophysical Prospecting》2010,58(1):41-54
The goal of vibroseis data acquisition and processing is to produce seismic reflection data with a known spatially-invariant wavelet, preferably zero phase, such that any variations in the data can be attributed to variations in geology. In current practice the vibrator control system is designed to make the estimated groundforce equal to the sweep and the resulting particle velocity data are cross-correlated with the sweep. Since the downgoing far-field particle velocity signal is proportional to the time-derivative of the groundforce, it makes more sense to cross-correlate with the time-derivative of the sweep. It also follows that the ideal amplitude spectrum of the groundforce should be inversely proportional to frequency. Because of non-linearities in the vibrator, bending of the baseplate and variable coupling of the baseplate to the ground, the true groundforce is not equal to the pre-determined sweep and varies not only from vibrator point to vibrator point but also from sweep to sweep at each vibrator point. To achieve the goal of a spatially-invariant wavelet, these variations should be removed by signature deconvolution, converting the wavelet to a much shorter zero-phase wavelet but with the same bandwidth and signal-to-noise ratio as the original data. This can be done only if the true groundforce is known. The principle may be applied to an array of vibrators by employing pulse coding techniques and separating responses to individual vibrators in the frequency domain. Various approaches to improve the estimate of the true groundforce have been proposed or are under development; current methods are at best approximate. 相似文献
4.
J. W. M. DANKBAAR 《Geophysical Prospecting》1983,31(6):873-887
A theoretical study is presented of the effect of source/receiver patterns with fixed phase difference on the radiation/receiving characteristics of the single elements of the pattern in linear elastic media. The radiation characteristic of two vertical vibrators in phase and in counterphase is investigated in detail. By introducing source/receiver patterns the characteristics become dependent on dimension of the pattern, frequency and angle of observation in the horizontal plane. The types of waves generated by source patterns are, independent of phase differences, equal to those generated by single sources. With two vertical vibrators in phase radiation of P-waves can be improved relative to that of SV-waves. With two vibrators in counterphase radiation of SV-waves in vertical directions is enhanced relative to that of P-waves; this may be a valuable method of SV-shear wave generation in exploration seismics. SV-wave amplitudes larger than P-wave amplitudes can be expected at angles larger than 5°–10° with the vertical. 相似文献
5.
In land seismic surveys, the seismic data are mostly contaminated by ground-roll noise, high amplitude and low frequency. Since the ground-roll is coherent with reflections and depends on the source, the spectral band of seismic signal and ground-roll always overlap, which can be clearly seen in the spectral domain. So, separating them in time or frequency domain commonly causes waveform distortions and information missing due to cut-off effects. Therefore, the combination of these factors leads to search for alternative filtering methods or processes. We applied the conventional Wiener–Levinson algorithm to extract ground-roll from the seismic data. Then, subtracting it from the seismic data arithmetically performs the ground-roll suppression. To set up the algorithm, linear or nonlinear sweep signals are used as reference noise trace. The frequencies needed in creating a reference noise trace using analytical sweep signal can be approximately estimated in spectral domain. The application of the proposed method based on redesigning of Wiener–Levinson algorithm differs from the usual frequency filtering techniques since the ground-roll is suppressed without cutting signal spectrum. The method is firstly tested on synthetics and then is applied to a shot data from the field. The result obtained from both synthetics and field data show that the ground-roll suppression in this way causes no waveform distortion and no reduction of frequency bandwidth of the data. 相似文献
6.
S. R. Taylor A. A. Velasco H. E. Hartse W. S. Phillips W. R. Walter A. J. Rodgers 《Pure and Applied Geophysics》2002,159(4):623-650
—?A fundamental problem associated with event identification lies in deriving corrections that remove path and earthquake source effects on regional phase amplitudes used to construct discriminants. Our goal is to derive a set of physically based corrections that are independent of magnitude and distance, and amenable to multivariate discrimination by extending the technique described in Taylor and Hartse (1998). For a given station and source region, a number of well-recorded earthquakes is used to estimate source and path corrections. The source model assumes a simple Brune (1970) earthquake source that has been extended to handle non-constant stress drop. The discrimination power in using corrected amplitudes lies in the assumption that the earthquake model will provide a poor fit to the signals from an explosion. The propagation model consists of a frequency-independent geometrical spreading and frequency-dependent power law Q. A grid search is performed simultaneously at each station for all recorded regional phases over stress-drop, geometrical spreading, and frequency-dependent Q to find a suite of good-fitting models that remove the dependence on m b and distance. Seismic moments can either be set to pre-determined values or estimated through inversion and are tied to m b through two additional coefficients. We also solve for frequency-dependent site/phase excitation terms. Once a set of corrections is derived, effects of source scaling and distance as a function of frequency are applied to amplitudes from new events prior to forming discrimination ratios. Thus, all the corrections are tied to just m b (or M 0) and distance and can be applied very rapidly in an operational setting. Moreover, phase amplitude residuals as a function of frequency can be spatially interpolated (e.g., using kriging) and used to construct a correction surface for each phase and frequency. The spatial corrections from the correction surfaces can then be applied to the corrected amplitudes based only on the event location. The correction parameters and correction surfaces can be developed offline and entered into an online database for pipeline processing providing multivariate-normal corrected amplitudes for event identification. Examples are shown using events from western China recorded at the station MAKZ. 相似文献
7.
考虑地铁环境振动噪声对未来城市地铁地震警报系统中地震信号识别的影响,以包含Ⅱ类和Ⅲ类2种场地土类型的哈尔滨市4个地铁站的上行线首部和尾部作为观测点,展开地铁环境振动噪声的测试、分析以及降噪处理研究。首先,对采集的列车振动数据进行统计分析;其次,基于滑动平均法,提出确定帕曾窗带宽b值的经验方法,并利用其对采集的地脉动数据进行平滑滤波处理;最后,采用本方法确定哈尔滨地铁地震P波预警的滤波频带,并与日本气象厅仪器地震烈度以及新干线地震预警系统的滤波频带进行对比。结果表明:①三轴向地铁列车振动信号中,竖向振动比水平向振动要大,切向振动比径向振动要大。②帕曾窗带宽b值为0.4 Hz时,平滑滤波处理后的频谱能较好地反映地脉动信号的频谱主频,且滤波后的地脉动信号的卓越频率和场地土类型有明显的对应关系,即水平向卓越频率和场地土类型的相关性较好,而竖向卓越频率的误差较大。③哈尔滨地铁地震P波预警的滤波频带为0.3~10 Hz时,能较好地滤除地震动信号中的地铁环境振动噪声,满足地震警报系统对地震记录信噪比的要求。 相似文献
8.
Seismic directional random noise suppression by radial‐trace time–frequency peak filtering using the Hurst exponent statistic 
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下载免费PDF全文 Radial‐trace time–frequency peak filtering filters a seismic record along the radial‐trace direction rather than the conventional channel direction. It takes the spatial correlation of the reflected events between adjacent channels into account. Thus, radial‐trace time–frequency peak filtering performs well in denoising and enhancing the continuity of reflected events. However, in the seismic record there is often random noise whose energy is concentrated in certain directions; the noise in these directions is correlative. We refer to this kind of random noise (that is distributed randomly in time but correlative in the space) as directional random noise. Under radial‐trace time–frequency peak filtering, the directional random noise will be treated as signal and enhanced when this noise has same direction as the signal. Therefore, we need to identify the directional random noise before the filtering. In this paper, we test the linearity of signal and directional random noise in time using the Hurst exponent. The time series of signals with high linearity lead to large Hurst exponent value; however, directional random noise is a random series in time without a fixed waveform and thus its linearity is low; therefore, we can differentiate the signal and directional random noise by the Hurst exponent values. The directional random noise can then be suppressed by using a long filtering window length during the radial‐trace time–frequency peak filtering. Synthetic and real data examples show that the proposed method can remove most directional random noise and can effectively recover the reflected events. 相似文献
9.
采用短时单频脉冲震源的浅地层剖面,记录的波形数据空间假频较严重。因其信号具有频率高、频带窄的特征,通常利用Hiibert变换提取瞬时振幅属性（信号包络）供解释使用。但瞬时振幅均为正值,在进行构造解释时不方便使用。本文提出在对浅层剖面资料提取瞬时振幅的基础上,计算瞬时振幅的微分并配合滤波的方法,实现高频窄带浅地层剖面资料的一种频移处理。该方法把高频窄带的多周期信号变为低频带宽的单周期信号,有效扩展了倍频程并消除假频。应用在南海浅地层剖面资料处理中,资料处理后更利于构造解释。 相似文献
10.
Emile A. Okal Jacques Talandier Dominique Reymond 《Pure and Applied Geophysics》2007,164(2-3):309-323
The 2004 Sumatra-Andaman tsunami was recorded by hydrophones of the International Monitoring System at Site H08 near Diego
Garcia, notably in frequency bands extending outside the range of the Shallow Water Approximation. Despite the severe high-pass
filtering involved in this instrumentation, we show that the spectral amplitudes recovered around T = 87 s can be successfully explained by generation from the seismic source, in the framework of the normal mode theory of
tsunami excitation. At the lower frequencies characteristic of more conventional tsunami waves (800 to 3200 s), the signal
is probably present in the hydrophone records, but reliable deconvolution of its spectral amplitude is precluded by the fact
that the instrumental filters lowered the tsunami signal to the level of resolution of the instrument digitizer. In the context
of distant tsunami warning, hydrophone records could provide useful insight into high-frequency tsunami components, and even
at lower, more conventional, frequencies, provided that an unfiltered channel could be recorded routinely. 相似文献
11.
In the paper, we propose a surface wave suppression method in time-frequency domain based on the wavelet transform, considering the characteristic difference of polarization attributes, amplitude energy and apparent velocity between the effective signals and strong surface waves. First, we use the proposed method to obtain time–frequency spectra of seismic signals by using the wavelet transform and calculate the instantaneous polarizability at each point based on instantaneous polarization analysis. Then, we separate the surface wave area from the signal area based on the surface-wave apparent velocity and the average energy of the signal. Finally, we combine the polarizability, energy, and frequency characteristic to identify and suppress the signal noise. Model and field data are used to test the proposed filtering method. 相似文献
12.
径向道变换(Radial Trace Transform)是将地震道集振幅值从偏移距一双程旅行时坐标系变换到视速度-双程旅行时坐标系,通过这种坐标系的变换,使相干噪声与有效信号在视速度和频率方面都有效分离.本文在介绍RT变换基本原理基础上,分析了RT变换中两种常用插值方法及其特点.并利用对模拟地震资料的处理,证明了RT域模拟-相减法较其带通滤波法在相干噪声压制与反射信号保持方面具有明显优势.最后,根据噪声特点,通过选择合理RT滤波参数,对实际地震资料进行处理试验,获得了较好的去噪效果,明显提高了资料信噪比,验证了研究方法的有效性. 相似文献
13.
时频峰值滤波(TFPF)算法是一种非常有效的去噪方法.但是传统的TFPF采用的单一窗长,并且仅沿时间方向进行滤波,忽略了信号的空间信息,并且TFPF近似等效成一个时不变的低通滤波器,不能追踪快速变化的信号.针对这些问题,引入空间局部加权回归自适应TFPF(SLWR-ATFPF).鉴于随机噪声在各个位置的方向随机性,以及有效信号在各个位置的方向确定性,首先利用空间局部加权回归(SLWR),对含噪信号进行空间加权,从而使加权之后的信号包含空间信息.然后,再引入凸集和Viterbi的思想,对空间加权之后的信号进行自适应滤波.从而,完成时空域二维自适应滤波.将SLWR-ATFPF应用于合成记录和实际的共炮点记录,实验结果表明,改进的方法与原算法相比,能够在压制低信噪比(SNR)随机噪声的同时更好地保留有效信号. 相似文献
14.
I. Popova A. Rozhnoi M. Solovieva B. Levin V. Chebrov 《Izvestiya Physics of the Solid Earth》2016,52(2):305-317
In this paper, we suggest a technique for forecasting seismic events based on the very low and low frequency (VLF and LF) signals in the 10 to 50 Hz band using the neural network approach, specifically, the error back-propagation method (EBPM). In this method, the solution of the problem has two main stages: training and recognition (forecasting). The training set is constructed from the combined data, including the amplitudes and phases of the VLF/LF signals measured in the monitoring of the Kuril-Kamchatka region and the corresponding parameters of regional seismicity. Training the neural network establishes the internal relationship between the characteristic changes in the VLF/LF signals a few days before a seismic event and the corresponding level of seismicity. The trained neural network is then applied in a prognostic mode for automated detection of the anomalous changes in the signal which are associated with seismic activity exceeding the assumed threshold level. By the example of several time intervals in 2004, 2005, 2006, and 2007, we demonstrate the efficiency of the neural network approach in the short-term forecasting of earthquakes with magnitudes starting from M ≥ 5.5 from the nighttime variations in the amplitudes and phases of the LF signals on one radio path. We also discuss the results of the simultaneous analysis of the VLF/LF data measured on two partially overlapping paths aimed at revealing the correlations between the nighttime variations in the amplitude of the signal and seismic activity. 相似文献
15.
基于高灵敏度检波器数据的分频匹配滤波方法及其应用(英文) 总被引：1，自引：0，他引：1
具有较高自然频率的高灵敏度检波器在采集数据时可以通过压制低频信号来相对提高高频能量,但这也造成了其低频响应差的问题,如果将高灵敏度数据与常规数据进行优势组合,就可以达到拓宽频带的目的。为此,本文提出分频段匹配滤波的方法,即在保持常规数据低频优势的前提下,对其高频端进行匹配滤波,实现不同频带范围内的优势互补,从而改善地震记录。通过引入不同主频的雷克子波模拟得到具有常规数据和高灵敏度数据特点的理论模型,论证了分频匹配滤波方法的可行性。在对野外单炮地震记录处理中发现,分频匹配滤波方法拓宽了地震记录的有效频带宽度,提高了地震记录的分辨率。 相似文献
16.
The signal-to-noise ratio （SNR） of seismic reflection data in many areas is rather poor and conventional two-dimensional filters designed to suppress noise with different moveout from the signal tend to generate artifacts. We have extended a method of multichannel filtering, based on the hypothesis that signals on adjacent channels are similar, for enhancing the SNR on stacked sections. Using only the mid-range frequencies where the SNR is highest, the event trend is found for overlapping windows on the section and the average signal vector is calculated. Then the data from the full bandwidth section are projected onto the spatially varying unit similarity vectors and the results are merged for the overlapping windows. Application of the method to synthetic data containing steeply dipping events and to a stacked section for a marine 2D line has produced good results. The modifications we have introduced carry a small overhead in computing time but they should enable the method to be used effectively even on sections containing steep dips. 相似文献
17.
很多地区地震资料的信噪比较低,而用于压制与信号具有不同方向的随机噪声的常规二维滤波方法常常产生假信息。基于相邻信号具有相干性这一假设,本文提出了一种叠后衰减随机噪声的多道滤波方法。该方法利用信噪比最高的中频段信息(含有主频的这一频率区间)分时窗计算信号单位矢量,并将该时窗内全频段数据向信号单位矢量方向投影,对各时窗(包括时间方向和空间方向)重叠部分按比例进行加权。我们利用这种方法对含有陡倾角的合成地震数据和海上二维实际地震资料进行了处理,处理效果很好。这种方法较为费时,但不受倾角限制,应用范围广。 相似文献
18.
提出一种自适应协方差的时频域极化滤波方法。该方法在广义S变换时频方法的基础上,构造时频域自适应协方差矩阵,通过特征分析计算时频域瞬时极化参数,设计极化滤波器,实现多分量地震极化分析和滤波。其优势在于协方差矩阵的分析时窗的长度由多分量地震数据的瞬时频率确定,可以自适应于有效信号的周期,在每个时频点计算极化参数不需要进行插值处理;结合时间频率信息,解决在时间域或频率域波形或频率重叠的信号具有明显的直观性。模型数据及实际三分量台站地震数据处理结果表明,该极化滤波方法在台站地震资料分析和处理方面具有很好的直观性和较高的分辨率。 相似文献
19.
Neil R. Goulty 《Physics of the Earth and Planetary Interiors》1979,19(1):52-58
Matching signals have previously been identified from about eighty repeating deep moonquake sources. These moonquakes clearly display tidal periodicities in their histories of origin times and signal amplitudes; they are presumably triggered by the solid-body tide in the moon, raised primarily by the earth. The A1 hypocentre has been the most active and has also produced seismograms with signals of reversed polarity. In an attempt to deduce focal mechanisms for these events, we calculated various tidal stress functions at the Al hypocentre using a homogeneous moon model, and correlated them with the origin times of events. No good correlation was found, either for tidal stress peaks of consistent polarity, or for tidal stress peaks of opposite polarity at the times of “inverted” events. This could be due to an inaccurate moon model, but it has also been noted that the relative amplitudes of signals recorded at different seismic stations vary between events from the same hypocentre. Earthquake swarms often contain events with fault-plane solutions in very different orientations. A similar variation between events from each deep moonquake hypocentre would explain the different amplitude ratios and also the “inverted” events. 相似文献
20.
Utilizing spectral decomposition to determine the distribution of injected CO2 at the Snøhvit Field 下载免费PDF全文
下载免费PDF全文 Time‐lapse 3D seismic reflection data, covering the CO2 storage operation at the Snøhvit gas field in the Barents Sea, show clear amplitude and time‐delay differences following injection. The nature and extent of these changes suggest that increased pore fluid pressure contributes to the observed seismic response, in addition to a saturation effect. Spectral decomposition using the smoothed pseudo‐Wigner–Ville distribution has been used to derive discrete‐frequency reflection amplitudes from around the base of the CO2 storage reservoir. These are utilized to determine the lateral variation in peak tuning frequency across the seismic anomaly as this provides a direct proxy for the thickness of the causative feature. Under the assumption that the lateral and vertical extents of the respective saturation and pressure changes following CO2 injection will be significantly different, discrete spectral amplitudes are used to distinguish between the two effects. A clear spatial separation is observed in the distribution of low‐ and high‐frequency tuning. This is used to discriminate between direct fluid substitution of CO2, as a thin layer, and pressure changes that are distributed across a greater thickness of the storage reservoir. The results reveal a striking correlation with findings derived from pressure and saturation discrimination algorithms based on amplitude versus offset analysis. 相似文献