Seismic coherence is used to detect discontinuities in underground media. However, strata with steeply dipping structures often produce false low coherence estimates and thus incorrect discontinuity characterization r...Seismic coherence is used to detect discontinuities in underground media. However, strata with steeply dipping structures often produce false low coherence estimates and thus incorrect discontinuity characterization results. It is important to eliminate or reduce the effect of dipping on coherence estimates. To solve this problem, time-domain dip scanning is typically used to improve estimation of coherence in areas with steeply dipping structures. However, the accuracy of the time-domain estimation of dip is limited by the sampling interval. In contrast, the spectrum amplitude is not affected by the time delays in adjacent seismic traces caused by dipping structures. We propose a coherency algorithm that uses the spectral amplitudes of seismic traces within a predefined analysis window to construct the covariance matrix. The coherency estimates with the proposed algorithm is defined as the ratio between the dominant the constructed covariance matrix. Thus, we eigenvalue and the sum of all eigenvalues of eliminate the effect of dipping structures on coherency estimates. In addition, because different frequency bands of spectral amplitudes are used to estimate coherency, the proposed algorithm has multiscale features. Low frequencies are effective for characterizing large-scale faults, whereas high frequencies are better in characterizing small-scale faults. Application to synthetic and real seismic data show that the proposed algorithm can eliminate the effect of dip and produce better coherence estimates than conventional coherency algorithms in areas with steeply dipping structures.展开更多
Two gain forms of spectral amplitude subtraction are derived theoretically without neglecting the correlation of speech and noise spectrum during the period of a fralne. In the implementation, the constrained gain is ...Two gain forms of spectral amplitude subtraction are derived theoretically without neglecting the correlation of speech and noise spectrum during the period of a fralne. In the implementation, the constrained gain is expressed as a function of noncausal a priori SNR （Signal-to-Noise Ratio）. Noise and noncausal a priori SNR are estimated from the multitaper spectrum of the noisy signal with algorithms modified to be suitable for the multitaper spectruln. Objective evaluations show that in case of white Gaussian noise the proposed method outperforms some methods based on LSA （Log Spectral Amplitude） in terms of MBSD （Modified Bark Spectral Distortion）, segmental SNR and overall SNR, and informal listening tests show that speech reconstructed in this way has little speech distortion and musical noise is nearly inaudible even at low SNR.展开更多
An improved method based on minimum mean square error-short time spectral amplitude （MMSE-STSA） is proposed to cancel background noise in whispered speech. Using the acoustic character of whispered speech, the algor...An improved method based on minimum mean square error-short time spectral amplitude （MMSE-STSA） is proposed to cancel background noise in whispered speech. Using the acoustic character of whispered speech, the algorithm can track the change of non-stationary background noise effectively. Compared with original MMSE-STSA algorithm and method in selectable mode Vo-coder （SMV）, the improved algorithm can further suppress the residual noise for low signal-to-noise radio （SNR） and avoid the excessive suppression. Simulations show that under the non-stationary noisy environment, the proposed algorithm can not only get a better performance in enhancement, but also reduce the speech distortion.展开更多
The absorption–dispersion properties of a microwave-driven five-level atom embedded in an isotropic photonic bandgap(PBG) have been studied. Due to the singular density of modes(DOM) in the isotropic PBG and the dyna...The absorption–dispersion properties of a microwave-driven five-level atom embedded in an isotropic photonic bandgap(PBG) have been studied. Due to the singular density of modes(DOM) in the isotropic PBG and the dynamically coherence induced by the coupling fields, modified reservoir-induced transparency and quantum interference-induced transparency emerge simultaneously. Their interaction leads to ultra-narrow spectral structure. As a result of closed-loop configuration, these features can be manipulated by the amplitudes and relative phase of the coherently driven fields. The position and width of PBG also have an influence on the spectra. The theoretical studies can provide us with more efficient methods to control the atomic absorption–dispersion properties, which have applications in optical switching and slow light.展开更多
This study employs the different approaches of the spectral decomposition techniques to evaluate the hydrocarbon potential of the reservoir and analyse to determine the most efficient spectral decomposition technique ...This study employs the different approaches of the spectral decomposition techniques to evaluate the hydrocarbon potential of the reservoir and analyse to determine the most efficient spectral decomposition technique with better resolution using the “BOMS” Field, coastal swamp depobelt Niger Delta, Nigeria. A good number of drilled wells have failed both in the Niger Delta Basin and other basins due to a poor understanding of the reservoir properties in advance of drilling and identifying the best approach will help to minimize this risk. Seismic and well logs data together with the Hampson Russel 10.3 software were used for the study. The target reservoirs were identified from the suite of well logs at the horizons with low gamma ray, high resistivity, and low acoustic impedance between TVD (ft) of 10,350 - 10,450 ft. The analysis of the amplitude spectrum of the seismic data revealed that the distortion of interest lies between 5 - 60 Hz. Seismic data were then spectrally decomposed into several frequencies such as low frequency (15 Hz), mid-frequency (31 Hz), and high frequency (46 Hz) where distortions were observed. Time- frequency slices of 15 Hz and 23 Hz provided clearer events (potential hydrocarbon sand) indicated by high amplitude envelope (2200 - 2400) and amplitude anomalies. While the amplitude dropped in the mid-frequency (31 Hz), the high amplitude envelope and the high energy completely disappeared in the high (46 Hz) time-frequency slice. A comparison of the Short- time Fourier transform and the Basic Pursuit algorithm revealed that the Basic Pursuit provided a better resolution of the reservoir characteristics than the former. The Red, Green and Blue (RGB) colour blending model indicated that the channel was consistent with the low-frequency section and amplitude anomaly.展开更多
基于浙江测震台网记录到的2017年2—9月磐安地区发生的地震序列资料,采用Brune震源模型理论和波谱分析方法,得到磐安震群序列的应力降、视应力等震源参数。利用台站的零频幅值,计算谱振幅相关系数。采用聚类分组,并结合Cut and Paste(C...基于浙江测震台网记录到的2017年2—9月磐安地区发生的地震序列资料,采用Brune震源模型理论和波谱分析方法,得到磐安震群序列的应力降、视应力等震源参数。利用台站的零频幅值,计算谱振幅相关系数。采用聚类分组,并结合Cut and Paste(CAP)反演方法得到ML4.0主地震事件的震源机制解,系统分析小地震的震源机制的一致性程度。结果显示:震源区应力降值在0.00~0.80 MPa之间,整体构造应力较低;谱振幅相关系数较低,在0.86~0.95之间,震源机制整体相似程度不高;应力积累没有形成一个优势方向,可能指示磐安序列为低摩擦应力的断层作用。研究结果表明:磐安地震序列为普通的小震序列,其震源机制类型与构造应力场基本一致;谱振幅相关分析法可为小震序列的震后快速判定提供重要依据。展开更多
在实际测向系统中,当弱信号和强干扰空间临近时,空间谱测向系统仅能对强干扰进行波达方向(Direction of Arrival,DOA)估计,弱信号DOA估计性能下降甚至失效。针对这一问题,研究了空间谱扩展噪声子空间算法结合通道幅相误差校正,在强干扰...在实际测向系统中,当弱信号和强干扰空间临近时,空间谱测向系统仅能对强干扰进行波达方向(Direction of Arrival,DOA)估计,弱信号DOA估计性能下降甚至失效。针对这一问题,研究了空间谱扩展噪声子空间算法结合通道幅相误差校正,在强干扰抑制条件下对弱信号进行DOA估计的方法。该方法对采样信号的噪声协方差进行去加权处理,并对空间谱扩展噪声子空间算法的空间谱导向矢量进行修正。基于通用软件无线电外设(Universal SoftwareRadioPeripheral,USRP)和印刷偶极子线形天线阵构建实验平台,实验结果证明空间谱扩展噪声子空间算法结合改进的通道幅相误差校正方法,能对临近干扰源进行空间谱抑制的同时,实现对弱信号的DOA估计。展开更多
在实际测向系统中,空间谱测向天线阵通道误差校正时,校正系数也对接收通道噪声进行加权,在较低信噪比和临近强干扰抑制时,将导致天线阵列波达方向(Direction of Arrival,DOA)估计性能下降甚至失效。因此,结合阵列互耦导致天线有源方向...在实际测向系统中,空间谱测向天线阵通道误差校正时,校正系数也对接收通道噪声进行加权,在较低信噪比和临近强干扰抑制时,将导致天线阵列波达方向(Direction of Arrival,DOA)估计性能下降甚至失效。因此,结合阵列互耦导致天线有源方向图发生畸变的实际情况,在单辅助源通道误差估计基础上,提出改进的空间谱幅相误差校正算法。该算法在通道误差模型中引入天线有源方向图畸变系数,并对噪声协方差加权项进行处理,得到噪声去加权的阵列接收数据协方差矩阵,并在谱峰搜索时修正导向矢量,实现幅相误差校正和空间谱测向。将所提校正算法应用于相干信号测向和临近强干扰空间谱抑制,改善了通道误差条件下的空间谱测向,计算机仿真结果证明所提算法的可行性。展开更多
In this study,the Beibu earth fissure site in the northeastern part of Weihe Basin,which contains four nearly parallel earth fissures,was studied.A long straight microtremor measuring line,containing 49 measuring poin...In this study,the Beibu earth fissure site in the northeastern part of Weihe Basin,which contains four nearly parallel earth fissures,was studied.A long straight microtremor measuring line,containing 49 measuring points across four earth fissures,was established to investigate the dynamic response of this site using Fourier spectrum,response acceleration spectrum,Arias intensity,and HVSR analyses.The main results are as follows:(1)The fundamental frequencies of 44 measuring points obtained from HVSR analysis are concentrated within 1.67 Hz-2.25 Hz,and the existence of the earth fissures has little effect on the fundamental frequency changes.(2)There is an amplification effect near a single earth fissure.The dynamic responses are large at the measuring points near the earth fissure,and the values decrease with increasing distance from the earth fissure.In areas between two adjacent earth fissures,these values decrease and are even lower than those in sites without amplification effects.(3)In this earth fissure site,the general area(or less affected area)and affected areas were delineated based on the amplification effect.In engineering applications,construction design should avoid these affected areas and existing structures should be reinforced to satisfy the seismic fortification requirements.展开更多
基金sponsored by National Key S&T Project of China(No.2011ZX05004-003)the Research Program of RIPED(No.101002kt0b52135)
文摘Seismic coherence is used to detect discontinuities in underground media. However, strata with steeply dipping structures often produce false low coherence estimates and thus incorrect discontinuity characterization results. It is important to eliminate or reduce the effect of dipping on coherence estimates. To solve this problem, time-domain dip scanning is typically used to improve estimation of coherence in areas with steeply dipping structures. However, the accuracy of the time-domain estimation of dip is limited by the sampling interval. In contrast, the spectrum amplitude is not affected by the time delays in adjacent seismic traces caused by dipping structures. We propose a coherency algorithm that uses the spectral amplitudes of seismic traces within a predefined analysis window to construct the covariance matrix. The coherency estimates with the proposed algorithm is defined as the ratio between the dominant the constructed covariance matrix. Thus, we eigenvalue and the sum of all eigenvalues of eliminate the effect of dipping structures on coherency estimates. In addition, because different frequency bands of spectral amplitudes are used to estimate coherency, the proposed algorithm has multiscale features. Low frequencies are effective for characterizing large-scale faults, whereas high frequencies are better in characterizing small-scale faults. Application to synthetic and real seismic data show that the proposed algorithm can eliminate the effect of dip and produce better coherence estimates than conventional coherency algorithms in areas with steeply dipping structures.
基金Supported by 973 Project of China (No.2002 CB312102)and the National Natural Science Foundation of China (No.60272044).
文摘Two gain forms of spectral amplitude subtraction are derived theoretically without neglecting the correlation of speech and noise spectrum during the period of a fralne. In the implementation, the constrained gain is expressed as a function of noncausal a priori SNR （Signal-to-Noise Ratio）. Noise and noncausal a priori SNR are estimated from the multitaper spectrum of the noisy signal with algorithms modified to be suitable for the multitaper spectruln. Objective evaluations show that in case of white Gaussian noise the proposed method outperforms some methods based on LSA （Log Spectral Amplitude） in terms of MBSD （Modified Bark Spectral Distortion）, segmental SNR and overall SNR, and informal listening tests show that speech reconstructed in this way has little speech distortion and musical noise is nearly inaudible even at low SNR.
文摘An improved method based on minimum mean square error-short time spectral amplitude （MMSE-STSA） is proposed to cancel background noise in whispered speech. Using the acoustic character of whispered speech, the algorithm can track the change of non-stationary background noise effectively. Compared with original MMSE-STSA algorithm and method in selectable mode Vo-coder （SMV）, the improved algorithm can further suppress the residual noise for low signal-to-noise radio （SNR） and avoid the excessive suppression. Simulations show that under the non-stationary noisy environment, the proposed algorithm can not only get a better performance in enhancement, but also reduce the speech distortion.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11447232 and 11204367)
文摘The absorption–dispersion properties of a microwave-driven five-level atom embedded in an isotropic photonic bandgap(PBG) have been studied. Due to the singular density of modes(DOM) in the isotropic PBG and the dynamically coherence induced by the coupling fields, modified reservoir-induced transparency and quantum interference-induced transparency emerge simultaneously. Their interaction leads to ultra-narrow spectral structure. As a result of closed-loop configuration, these features can be manipulated by the amplitudes and relative phase of the coherently driven fields. The position and width of PBG also have an influence on the spectra. The theoretical studies can provide us with more efficient methods to control the atomic absorption–dispersion properties, which have applications in optical switching and slow light.
文摘This study employs the different approaches of the spectral decomposition techniques to evaluate the hydrocarbon potential of the reservoir and analyse to determine the most efficient spectral decomposition technique with better resolution using the “BOMS” Field, coastal swamp depobelt Niger Delta, Nigeria. A good number of drilled wells have failed both in the Niger Delta Basin and other basins due to a poor understanding of the reservoir properties in advance of drilling and identifying the best approach will help to minimize this risk. Seismic and well logs data together with the Hampson Russel 10.3 software were used for the study. The target reservoirs were identified from the suite of well logs at the horizons with low gamma ray, high resistivity, and low acoustic impedance between TVD (ft) of 10,350 - 10,450 ft. The analysis of the amplitude spectrum of the seismic data revealed that the distortion of interest lies between 5 - 60 Hz. Seismic data were then spectrally decomposed into several frequencies such as low frequency (15 Hz), mid-frequency (31 Hz), and high frequency (46 Hz) where distortions were observed. Time- frequency slices of 15 Hz and 23 Hz provided clearer events (potential hydrocarbon sand) indicated by high amplitude envelope (2200 - 2400) and amplitude anomalies. While the amplitude dropped in the mid-frequency (31 Hz), the high amplitude envelope and the high energy completely disappeared in the high (46 Hz) time-frequency slice. A comparison of the Short- time Fourier transform and the Basic Pursuit algorithm revealed that the Basic Pursuit provided a better resolution of the reservoir characteristics than the former. The Red, Green and Blue (RGB) colour blending model indicated that the channel was consistent with the low-frequency section and amplitude anomaly.
文摘基于浙江测震台网记录到的2017年2—9月磐安地区发生的地震序列资料,采用Brune震源模型理论和波谱分析方法,得到磐安震群序列的应力降、视应力等震源参数。利用台站的零频幅值,计算谱振幅相关系数。采用聚类分组,并结合Cut and Paste(CAP)反演方法得到ML4.0主地震事件的震源机制解,系统分析小地震的震源机制的一致性程度。结果显示:震源区应力降值在0.00~0.80 MPa之间,整体构造应力较低;谱振幅相关系数较低,在0.86~0.95之间,震源机制整体相似程度不高;应力积累没有形成一个优势方向,可能指示磐安序列为低摩擦应力的断层作用。研究结果表明:磐安地震序列为普通的小震序列,其震源机制类型与构造应力场基本一致;谱振幅相关分析法可为小震序列的震后快速判定提供重要依据。
文摘在实际测向系统中,当弱信号和强干扰空间临近时,空间谱测向系统仅能对强干扰进行波达方向(Direction of Arrival,DOA)估计,弱信号DOA估计性能下降甚至失效。针对这一问题,研究了空间谱扩展噪声子空间算法结合通道幅相误差校正,在强干扰抑制条件下对弱信号进行DOA估计的方法。该方法对采样信号的噪声协方差进行去加权处理,并对空间谱扩展噪声子空间算法的空间谱导向矢量进行修正。基于通用软件无线电外设(Universal SoftwareRadioPeripheral,USRP)和印刷偶极子线形天线阵构建实验平台,实验结果证明空间谱扩展噪声子空间算法结合改进的通道幅相误差校正方法,能对临近干扰源进行空间谱抑制的同时,实现对弱信号的DOA估计。
文摘在实际测向系统中,空间谱测向天线阵通道误差校正时,校正系数也对接收通道噪声进行加权,在较低信噪比和临近强干扰抑制时,将导致天线阵列波达方向(Direction of Arrival,DOA)估计性能下降甚至失效。因此,结合阵列互耦导致天线有源方向图发生畸变的实际情况,在单辅助源通道误差估计基础上,提出改进的空间谱幅相误差校正算法。该算法在通道误差模型中引入天线有源方向图畸变系数,并对噪声协方差加权项进行处理,得到噪声去加权的阵列接收数据协方差矩阵,并在谱峰搜索时修正导向矢量,实现幅相误差校正和空间谱测向。将所提校正算法应用于相干信号测向和临近强干扰空间谱抑制,改善了通道误差条件下的空间谱测向,计算机仿真结果证明所提算法的可行性。
基金National Natural Science Foundation of China under Grant No.41772275the Fundamental Research Funds for the Central Universities under Grant No.CHD300102268203。
文摘In this study,the Beibu earth fissure site in the northeastern part of Weihe Basin,which contains four nearly parallel earth fissures,was studied.A long straight microtremor measuring line,containing 49 measuring points across four earth fissures,was established to investigate the dynamic response of this site using Fourier spectrum,response acceleration spectrum,Arias intensity,and HVSR analyses.The main results are as follows:(1)The fundamental frequencies of 44 measuring points obtained from HVSR analysis are concentrated within 1.67 Hz-2.25 Hz,and the existence of the earth fissures has little effect on the fundamental frequency changes.(2)There is an amplification effect near a single earth fissure.The dynamic responses are large at the measuring points near the earth fissure,and the values decrease with increasing distance from the earth fissure.In areas between two adjacent earth fissures,these values decrease and are even lower than those in sites without amplification effects.(3)In this earth fissure site,the general area(or less affected area)and affected areas were delineated based on the amplification effect.In engineering applications,construction design should avoid these affected areas and existing structures should be reinforced to satisfy the seismic fortification requirements.
