Research Note: Frequency domain orthogonal projection filtration of surface microseismic monitoring data     

Anton V. Azarov  Aleksander S. Serdyukov  Denis N. Gapeev 《Geophysical Prospecting》2020,68(2):382-392

We address the problem of increasing the signal-to-noise ratio during surface microseismic monitoring data processing. Interference from different seismic waves causes misleading results of microseismic event locations. Ground-roll suppression is particularly necessary. The standard noise suppression techniques assume regular and dense acquisition geometries. Many pre-processing noise suppression algorithms are designed for special types of noise or interference. To overcome these problems, we propose a novel general-purpose filtration method. The goal of this method is to amplify only the seismic waves that are excited in the selected target area and suppress all other signals. We construct a linear projector onto a frequency domain data subspace, which corresponds to the seismic emission of the target area. The novel filtration method can be considered an extension of the standard frequency–wavenumber flat wave filtration method for non-flat waves and arbitrary irregular receiver-position geometries. To reduce the effect of the uncertainty of the velocity model, we suggest using additional active shot data (typically the perforation shots), which provide static travel time corrections for the target area. The promising prospects of the proposed method are confirmed by synthetic and semi-synthetic data processing.  相似文献   

Step-on versus step-off signals in time-domain controlled source electromagnetic methods using a grounded electric dipole     

Amir Haroon  Andrei Swidinsky  Sebastian Hölz  Marion Jegen  Bülent Tezkan 《Geophysical Prospecting》2020,68(9):2825-2844

The time-domain controlled source electromagnetic method is a geophysical prospecting tool applied to image the subsurface resistivity distribution on land and in the marine environment. In its most general set-up, a square-wave current is fed into a grounded horizontal electric dipole, and several electric and magnetic field receivers at defined offsets to the imposed current measure the electromagnetic response of the Earth. In the marine environment, the application often uses only inline electric field receivers that, for a 50% duty-cycle current waveform, include both step-on and step-off signals. Here, forward and inverse 1D modelling is used to demonstrate limited sensitivity towards shallow resistive layers in the step-off electric field when transmitter and receivers are surrounded by conductive seawater. This observation is explained by a masking effect of the direct current signal that flows through the seawater and primarily affects step-off data. During a step-off measurement, this direct current is orders of magnitude larger than the inductive response at early and intermediate times, limiting the step-off sensitivity towards shallow resistive layers in the seafloor. Step-on data measure the resistive layer at times preceding the arrival of the direct current signal leading to higher sensitivity compared to step-off data. Such dichotomous behaviour between step-on and step-off data is less obvious in onshore experiments due to the lack of a strong overlying conductive zone and corresponding masking effect from direct current flow. Supported by synthetic 1D inversion studies, we conclude that time-domain controlled source electromagnetic measurements on land should apply both step-on and step-off data in a combined inversion approach to maximize signal-to-noise ratios and utilize the sensitivity characteristics of each signal. In an isotropic marine environment, step-off electric fields have inferior sensitivity towards shallow resistive layers compared to step-on data, resulting in an increase of non-uniqueness when interpreting step-off data in a single or combined inversion.  相似文献   

Measuring accelerometer dynamic range from seismic data using Allan deviation          下载免费PDF全文

Matt McDonald  Patrik Stigborg 《Geophysical Prospecting》2018,66(5):934-941

We propose a new approach for calculating the dynamic range of an accelerometer based on an Allan deviation analysis of production seismic data. This test is intended as a field audit technique and does not require an unconditioned dataset from a low‐noise environment. We first show that Allan deviation can measure white noise levels using two commercial accelerometers. The analysis accurately captures the manufacturing noise density specifications and known relationships between white noise, preamplifier gain, and group forming. We then show that a production seismic dataset is suitable for an Allan deviation analysis because the results are not critically affected by a recording filter. Finally, we illustrate the proposed technique by calculating the dynamic range of an accelerometer channel in a seismic streamer using a production dataset.  相似文献   

环境负载对云南地区基准站时间序列的噪声模型特性研究     

管雅慧  胡顺强  王坦  杨振宇 《中国地震》2020,36(4):924-934

以云南地区27个GPS基准站坐标时间序列为研究对象，使用赤池信息量和贝叶斯信息量估计准则（AIC/BIC）对其进行噪声分析，计算并扣除时间序列中大气负载、非潮汐海洋负载和水文负载3种环境负载引起的位移量，得到各基准站分量在环境负载改正前后的最优噪声模型。结果表明，部分基准站分量经过负载改正后最优噪声模型会发生变化，改正前后的大部分基准站噪声特性均体现为闪烁+白噪声和幂律噪声。环境负载对基准站的垂向位移影响比水平向更为显著，水文负载成为影响基准站的最大因素，最大位移量达到厘米级。分析环境负载改正前后噪声特性的变化表明，环境负载改正在U分量上的影响最大，N分量次之，E分量最小，噪声模型的变化在地域上并未呈现明显规律。  相似文献   

河北永清M 4.3地震北京烈度仪台网记录分析     

白立新  成云辉  张杰  马士振  何荣帅  冯刚 《震灾防御技术》2019,14(1):210-219

2018年2月12日河北永清发生M 4.3地震，北京烈度仪台网共35个台站获得有效记录，记录最大峰值加速度的台站为丰台地震台（D0001），峰值加速度为10.76cm/s2，该台距震中约61km。本文对北京烈度仪台网获得的此次地震动记录进行了初步分析，并对3个同台址的强震动仪记录的数据进行了对比分析。结果表明，烈度仪记录计算得出的仪器烈度与强震动仪记录计算的仪器烈度结果具有较高的一致性，可用于烈度速报。  相似文献   

Time-frequency analysis based on curvelet transforms with time skewing     

Jiao Wang  Zhenchun Li  Lutz Gross  Stephen Tyson 《Geophysical Prospecting》2019,67(7):1838-1851

Oil and gas exploration gradually changes to the deep and complex areas. The quality of seismic data restricts the effective application of conventional time-frequency analysis technology, especially in the case of low signal-to-noise ratio. To address this problem, we propose a curvelet-based time-frequency analysis method, which is suitable for seismic data, and takes into account the lateral variation of seismic data. We first construct a kind of curvelet adapted to seismic data. By adjusting the rotation mode of the curvelet in the form of time skewing, the scale parameter can be directly related to the frequency of the seismic data. Therefore, the curvelet coefficients at different scales can reflect the time-frequency information of the seismic data. Then, the curvelet coefficients, which represent the dominant azimuthal pattern, are converted to the time-frequency domain. Since the curvelet transform is a kind of sparse representation for the signal, the screening process of the dominant coefficient masks most of the random noise, which enables the method to adapt for the low signal-to-noise ratio data. Results of synthetic and field data experiments using the proposed method demonstrate that it is a good approach to identify weak signals from strong noise in the time-frequency domain.  相似文献   

Most frequent value‐based factor analysis of direct‐push logging data          下载免费PDF全文

Norbert Péter Szabó  Gergely Pál Balogh  János Stickel 《Geophysical Prospecting》2018,66(3):530-548

An improved, iteratively re‐weighted factor analysis procedure is presented to interpret engineering geophysical sounding logs in shallow unsaturated sediments. We simultaneously process cone resistance, electric resistivity, and nuclear data acquired by direct‐push tools to give robust estimates of factor variables and water content in unconsolidated heterogeneous formations. The statistical procedure is based on the iterative re‐weighting of the deviations between the measured and calculated data using the most frequent value method famous for its robustness and high statistical efficiency. The iterative approach improves the result of factor analysis for not normally distributed data and extremely noisy measurements. By detecting a strong regression relation between one of the extracted factors and the fractional volume of water, we establish an independent method for water content estimation along the penetration hole. We verify the estimated values of water volume by using a highly over‐determined, quality‐checked interval inversion procedure. The multidimensional extension of the statistical method allows the estimation of water content distribution along both the vertical and the horizontal coordinates. Numerical tests using engineering geophysical sounding data measured in a Hungarian loessy–sandy formation demonstrate the feasibility of the most frequent value‐based factor analysis, which can be efficiently used for a more reliable hydrogeophysical characterisation of the unsaturated zone.  相似文献   

Noise suppression for microseismic data by non‐subsampled shearlet transform based on singular value decomposition          下载免费PDF全文

Xiaoqiang Liang  Yue Li  Chao Zhang 《Geophysical Prospecting》2018,66(5):894-903

The existence of strong random noise in surface microseismic data may decrease the utility of these data. Non‐subsampled shearlet transform can effectively suppress noise by properly setting a threshold to the non‐subsampled shearlet transform coefficients. However, when the signal‐to‐noise ratio of data is low, the coefficients related to the noise are very close to the coefficients associated with signals in the non‐subsampled shearlet transform domain that the coefficients related to the noise will be retained and be treated as signals. Therefore, we need to minimise the overlapping coefficients before thresholding. In this paper, a singular value decomposition algorithm is introduced to the non‐subsampled shearlet transform coefficients, and low‐rank approximation reconstructs each non‐subsampled shearlet transform coefficient matrix in the singular value decomposition domain. The non‐subsampled shearlet transform coefficients of signals have bigger singular values than those of the random noise, which implies that the non‐subsampled shearlet transform coefficients can be well estimated by taking only a few largest singular values. Therefore, those properties of singular value decomposition may significantly help minimise overlapping of noise and signals coefficients in the non‐subsampled shearlet transform domain. Finally, the denoised microseismic data are obtained easily by giving a simple threshold to the reconstructed coefficient matrix. The performance of the proposed method is evaluated on both synthetic and field microseismic data. The experimental results illustrate that the proposed method can eliminate random noise and preserve signals of interest more effectively.  相似文献   

基于谐波建模和自相关的磁共振信号消噪与提取方法研究          下载免费PDF全文

田宝凤  朱慧  易晓峰  杜官峰  蒋川东 《地球物理学报》2018,61(2):767-780

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   

Conflict of interest in research on anthropogenic noise and marine mammals: Does funding bias conclusions?     

Lucie Wade  Hal Whitehead  Linda Weilgart   《Marine Policy》2010,34(2):320-327

The U.S. Navy, whose sonars kill marine mammals, provides approximately 50% of the funds for marine mammal research worldwide. We examined six reviews of research on the effects of anthropogenic sound on marine mammals, as well as the primary papers cited in the reviews. These reviews cite references showing noise has no effect on marine mammals at an increasing frequency as their funding moves from a conservation organization to independent to partial U.S. military sources. Primary papers are 2.3 times more likely to be cited in the reviews as concluding no effect of noise if the research was militarily-funded than if not. Thus, conflict of interest may have led to a misrepresentation of the effects of noise on marine mammals in both the primary and secondary literature, and thus misinform public policy decisions.  相似文献