Phase errors in accelerometer arrays: An analysis based on collocated sensors and FEM     

《Soil Dynamics and Earthquake Engineering》2015

The error properties of arrays of accelerometers were studied on the basis of systematic experiments and analysis of the differences in the recordings of collocated sensors. Four identical tri-axial force-balance accelerometers with common recordings and time stamping, were set at symmetrical positions on a prototype oscillator, a T-type inverted pendulum, and were subject to controlled excitations. Based on Finite Element Modeling (FEM) the response of the oscillator was modeled and there were identified time series of acceleration of different collocated sensors predicted to be identical (“comparable”). The differences of the corresponding “comparable” measurement time series, which are functions only of noise, were found important, indicating that the accelerometer arrays are characterized by significant dynamic noise and not by low-amplitude Gaussian noise, as is widely assumed.Further analysis of time series of accelerometer noise was based on spectral analysis techniques in the frequency and the time domain and on coherence, on filtering and on cross-correlation, as well as on examination of the impact of noise in the drift (errors computation of displacements using double numerical integration).The output of this study is that phase noise (jitter, or phase instability) characterizes accelerometers, as in the case with all other array sensors and sensor networks and this is a main source of dynamic noise. The latter becomes significant especially at the level of sampling interval (0.005 sec in our experiments), characterizes strong motions, is not constant and may be regarded as instrument-specific noise. Strategies to overcome this dynamic noise important for the modeling of structural response are discussed.  相似文献   

Signal detectability of marine electromagnetic methods in the exploration of resistive targets          下载免费PDF全文

Mark Goldman  Vladimir Mogilatov  Amir Haroon  Eldad Levi  Bülent Tezkan 《Geophysical Prospecting》2015,63(1):192-210

We compare selected marine electromagnetic methods for sensitivity to the presence of relatively thin resistive targets (e.g., hydrocarbons, gas hydrates, fresh groundwater, etc.). The study includes the conventional controlled‐source electromagnetic method, the recently introduced transient electromagnetic prospecting with vertical electric lines method, and the novel marine circular electric dipole method, which is still in the stage of theoretical development. The comparison is based on general physical considerations, analytical (mainly asymptotic) analysis, and rigorous one‐dimensional and multidimensional forward modelling. It is shown that transient electromagnetic prospecting with vertical electric lines and marine circular electric dipole methods represent an alternative to the conventional controlled‐source electromagnetic method at shallow sea, where the latter becomes less efficient due to the air‐wave phenomenon. Since both former methods are essentially short‐offset time‐domain techniques, they exhibit a much better lateral resolution than the controlled‐source electromagnetic method in both shallow sea and deep sea. The greatest shortcoming of the transient electromagnetic prospecting with vertical electric lines and marine circular electric dipole methods comes from the difficulties in accurately assembling the transmitter antenna within the marine environment. This makes these methods significantly less practical than the controlled‐source electromagnetic method. Consequently, the controlled‐source electromagnetic method remains the leading marine electromagnetic technique in the exploration of large resistive targets in deep sea. However, exploring laterally small targets in deep sea and both small and large targets in shallow sea might require the use of the less practical transient electromagnetic prospecting with vertical electric lines and/or marine circular electric dipole method as a desirable alternative to the controlled‐source electromagnetic method.  相似文献   

Implementation aspects of eigendecomposition‐based high‐resolution velocity spectra          下载免费PDF全文

Renato Lopes  Martin Tygel 《Geophysical Prospecting》2015,63(1):99-115

In this paper, we discuss high‐resolution coherence functions for the estimation of the stacking parameters in seismic signal processing. We focus on the Multiple Signal Classification which uses the eigendecomposition of the seismic data to measure the coherence along stacking curves. This algorithm can outperform the traditional semblance in cases of close or interfering reflections, generating a sharper velocity spectrum. Our main contribution is to propose complexity‐reducing strategies for its implementation to make it a feasible alternative to semblance. First, we show how to compute the multiple signal classification spectrum based on the eigendecomposition of the temporal correlation matrix of the seismic data. This matrix has a lower order than the spatial correlation used by other methods, so computing its eigendecomposition is simpler. Then we show how to compute its coherence measure in terms of the signal subspace of seismic data. This further reduces the computational cost as we now have to compute fewer eigenvectors than those required by the noise subspace currently used in the literature. Furthermore, we show how these eigenvectors can be computed with the low‐complexity power method. As a result of these simplifications, we show that the complexity of computing the multiple signal classification velocity spectrum is only about three times greater than semblance. Also, we propose a new normalization function to deal with the high dynamic range of the velocity spectrum. Numerical examples with synthetic and real seismic data indicate that the proposed approach provides stacking parameters with better resolution than conventional semblance, at an affordable computational cost.  相似文献   

信号隔离技术在海洋仪器中的应用     

赵宇梅 《海洋技术学报》2005,24(2):18-19,33

信号隔离可保证多参数仪器在海洋现场测试中不会受到外界干扰及各参数之间干扰,对整个系统的正常工作非常重要。ISO124是美国Burr-Brown公司生产的隔离放大器,论文介绍其工作原理及其在海水负二价硫传感器中的应用。  相似文献   

近钻头井斜动态测量重力加速度信号提取方法研究   总被引：1，自引：1，他引：0       下载免费PDF全文

张文秀  陈文轩  底青云  孙云涛  杨永友  郑健 《地球物理学报》2017,60(11):4174-4183

利用加速度计进行近钻头井斜动态测量时,钻具的高速旋转,井下强振动、强冲击环境给重力加速度测量带来极大干扰,如何从干扰噪声中有效提取重力加速度信号对于提高井斜角和工具面角的测量精度至关重要.根据重力加速度径向和切向分量为周期性信号,轴向分量为近似直流信号,离心加速度为缓慢变化信号,振动和冲击加速度为随机信号的特征,提出一种基于互相关检测的重力加速度信号提取方法,选择径向或切向磁力计信号作为参考信号.利用相关检测方法分别对仿真数据、实验室旋转测试数据和振动测试数据进行处理,并计算了井斜角和工具面角,结果表明相关检测方法可以有效提取重力加速度信号,基于MEMS加速度计的井斜角测量精度优于0.5°,工具面角变化连续平滑,满足井斜动态测量需求.通过进一步开展实际钻井环境测试,该方法有望应用于近钻头地质导向系统或旋转导向钻井系统等需要近钻头井斜动态测量的场合.  相似文献   

基于递归分析和聚类的大地电磁信噪辨识及分离   总被引：1，自引：0，他引：1       下载免费PDF全文

李晋  汤井田  燕欢  彭代鑫  徐志敏 《地球物理学报》2017,60(5):1918-1936

为了剖析大地电磁信号和强干扰的本质特征,进一步精细分离出微弱的大地电磁有用信号,提出基于递归分析和聚类的大地电磁信噪辨识及分离方法.首先,运用递归分析法扩展大地电磁一维时间序列的维数,分析了嵌入维数、延迟时间和判别阈值对递归图的性能,并研究了不同长度的序列对递归定量分析参数的影响情况,然后,构建典型的大地电磁强干扰类型和微弱的大地电磁有用信号样本库,针对样本库讨论了强干扰和微弱大地电磁信号之间的递归定量分析参数,分析了K均值聚类和模糊C均值聚类的信噪辨识效果.最后,对实测大地电磁数据进行信噪辨识处理,并仅对辨识为强干扰的时间段采用数学形态滤波进行噪声压制.实验结果表明,递归分析能定性及定量地描述大地电磁信号时间序列的非线性特征和原动力系统的本质规律,与聚类算法相结合能对矿集区实测大地电磁信号进行信噪辨识;处理后的卡尼亚电阻率-相位曲线更为光滑、连续,其结果更为精细地保留了大地电磁信号低频段的缓变化信息,整个低频段的大地电磁数据质量得到了明显改善.  相似文献   

Evolution of deghosting process for single‐sensor streamer data from 2D to 3D          下载免费PDF全文

Zhigang Zhang  Hassan Masoomzadeh  Bin Wang 《Geophysical Prospecting》2018,66(5):975-986

In marine acquisition, reflections of sound energy from the water–air interface result in ghosts in the seismic data, both in the source side and the receiver side. Ghosts limit the bandwidth of the useful signal and blur the final image. The process to separate the ghost and primary signals, called the deghosting process, can fill the ghost notch, broaden the frequency band, and help achieve high‐resolution images. Low‐signal‐to‐noise ratio near the notch frequencies and 3D effects are two challenges that the deghosting process has to face. In this paper, starting from an introduction to the deghosting process, we present and compare two strategies to solve the latter. The first is an adaptive mechanism that adjusts the deghosting operator to compensate for 3D effects or errors in source/receiver depth measurement. This method does not include explicitly the crossline slowness component and is not affected by the sparse sampling in the same direction. The second method is an inversion‐type approach that does include the crossline slowness component in the algorithm and handles the 3D effects explicitly. Both synthetic and field data examples in wide azimuth acquisition settings are shown to compare the two strategies. Both methods provide satisfactory results.  相似文献   

地震资料自适应高分辨率处理方法定量研究          下载免费PDF全文

郭锐  林鹤  余刚  张宇生 《地球物理学报》2017,60(9):3587-3600

分辨率是地震资料处理的重要问题,常以子波能量展布和震荡长度来定量分析,决定于地震资料的主频和频宽.越来越复杂的勘探对象要求高分辨率算法提供更丰富的波形和相位信息.实践表明自适应滤波方法在提高地震资料分辨率的同时,处理结果表现出更丰富的信息.在对APES方法的自适应滤波原理进行理论探讨和模型分析基础上,提出了加权方式的改进算法(WAPES).通过统计实验,对改进前后的方法在信噪比和分辨率方面的表现进行了定量分析,同时设计典型模型试验来证明新方法的适用性.最后,改进后的方法应用于实际工区资料的处理,取得了很好的应用效果.  相似文献   

Comparison of migration‐based location and detection methods for microseismic events          下载免费PDF全文

Jacek Trojanowski  Leo Eisner 《Geophysical Prospecting》2017,65(1):47-63

Microseismic monitoring in the oil and gas industry commonly uses migration‐based methods to locate very weak microseismic events. The objective of this study is to compare the most popular migration‐based methods on a synthetic dataset that simulates a strike‐slip source mechanism event with a low signal‐to‐noise ratio recorded by surface receivers (vertical components). The results show the significance of accounting for the known source mechanism in the event detection and location procedures. For detection and location without such a correction, the ability to detect weak events is reduced. We show both numerically and theoretically that neglecting the source mechanism by using only absolute values of the amplitudes reduces noise suppression during stacking and, consequently, limits the possibility to retrieve weak microseismic events. On the other hand, even a simple correction to the data polarization used with otherwise ineffective methods can significantly improve detections and locations. A simple stacking of the data with a polarization correction provided clear event detection and location, but even better results were obtained for those data combined with methods that are based on semblance and cross‐correlation.  相似文献   

Structural complexity-guided predictive filtering     

Bin Liu  Chao Fu  Yuxiao Ren  Qingsong Zhang  Xinji Xu  Yangkang Chen 《Geophysical Prospecting》2020,68(5):1509-1522

Random noise attenuation utilizing predictive filtering achieves great performance in denoising seismic data. Conventional predictive filtering methods are based on fixed filter operators and neglect the complexity of structures. In this way, the denoised data cannot meet the requirement of balancing the signal preservation and noise removal. In this study, we proposed a structural complexity-guided predictive filtering method that utilizes an adapted filter operator to adjust the changes of structural complexity. The proposed structural complexity-guided predictive filtering mainly consists of two stages. A slope field information is acquired according to plane-wave destruction to assess the structural complexity. In addition, an adaptive filter operator is obtained to denoise the seismic data according to the adaptive factor. Both synthetic data and real seismic profiles are employed to examine the denoising capacity and flexibility of the refined predictive filtering using adaptive lengths. The analysis of the predicted results shows that adaptive predictive filtering is powerful and has the ability to eliminate random noises with negligible distortions.  相似文献