Prestack data enhancement with phase corrections in time-frequency domain guided by local multidimensional stacking

We present a new approach to enhancing weak prestack reflection signals without sacrificing higher frequencies. As a first step, we employ known multidimensional local stacking to obtain an approximate ‘model of the signal’. Guided by phase spectra from this model, we can detect very weak signals and make them visible and coherent by ‘repairing’ corrupted phase of original data. Both presented approaches – phase substitution and phase sign corrections – show good performance on complex synthetic and field data suffering from severe near-surface scattering where conventional processing methods are rendered ineffective. The methods are mathematically formulated as a special case of time-frequency masking (common in speech processing) combined with the signal model from local stacking. This powerful combination opens the avenue for a completely new family of approaches for multi-channel seismic processing that can address seismic processing of land data with nodes and single sensors in the desert environment.     

A high-precision time–frequency analysis for thin hydrocarbon reservoir identification based on synchroextracting generalized S-transform

Improving the seismic time–frequency resolution is a crucial step for identifying thin reservoirs. In this paper, we propose a new high-precision time–frequency analysis algorithm, synchroextracting generalized S-transform, which exhibits superior performance at characterizing reservoirs and detecting hydrocarbons. This method first calculates time–frequency spectra using generalized S-transform; then, it squeezes all but the most smeared time–frequency coefficients into the instantaneous frequency trajectory and finally obtains highly accurate and energy-concentrated time–frequency spectra. We precisely deduce the mathematical formula of the synchroextracting generalized S-transform. Synthetic signal examples testify that this method can correctly decompose a signal and provide a better time–frequency representation. The results of a synthetic seismic signal and real seismic data demonstrate that this method can identify some reservoirs with thincknesses smaller than a quarter wavelength and can be successfully applied for hydrocarbon detection. In addition, examples of synthetic signals with different levels of Gaussian white noise show that this method can achieve better results under noisy conditions. Hence, the synchroextracting generalized S-transform has great application prospects and merits in seismic signal processing and interpretation.     

Application of a cascading filter implemented using morphological filtering and time–frequency peak filtering for seismic signal enhancement

Inspired by the idea of the iterative time–frequency peak filtering, which applies time–frequency peak filtering several times to improve the ability of random noise reduction, this article proposes a new cascading filter implemented using mathematic morphological filtering and the time–frequency peak filtering, which we call here morphological time–frequency peak filtering for convenience. This new method will be used mainly for seismic signal enhancement and random noise reduction in which the advantages of the morphological algorithm in processing nonlinear signals and the time–frequency peak filtering in processing nonstationary signals are utilized. Structurally, the scheme of the proposed method adopts mathematic morphological operation to first preprocess the signal and then applies the time–frequency peak filtering method to ultimately extract the valid signal. Through experiments on synthetic seismic signals and field seismic data, this paper demonstrates that the morphological time–frequency peak filtering method is superior to the time–frequency peak filtering method and its iterative form in terms of valid signal enhancement and random noise reduction.     

利用惯容隔震系统的结构层间隔震研究

层间隔震技术对于结构竖向不规则以及结构增层等状况有良好的适用性。然而,层间隔震可能出现的较大隔震层变形会带来结构设计的困难。通过在隔震层中设置阻尼元件可以减少变形,但是过大的阻尼出力和过多的数量需求可能导致空间布置和安装不便。惯容元件为解决以上问题提供了一种新的途径。该研究提出采用惯容隔震系统作为层间隔震提高能量耗散效率的手段以控制地震响应,同时也给出了基于性能需求的惯容层间隔震的参数优化设计方法。并以一个标准钢结构模型验证了方法的有效性。结果表明:惯容元件的使用显著降低了上部子结构的地震响应和隔震层的变形,惯容系统实现了预期的耗能增效作用。     

Three-parameter Radon transform in layered transversely isotropic media

Radon transform is a powerful tool with many applications in different stages of seismic data processing, because of its capability to focus seismic events in the transform domain. Three-parameter Radon transform can optimally focus and separate different seismic events, if its basis functions accurately match the events. In anisotropic media, the conventional hyperbolic or shifted hyperbolic basis functions lose their accuracy and cannot preserve data fidelity, especially at large offsets. To address this issue, we propose an accurate traveltime approximation for transversely isotropic media with vertical symmetry axis, and derive two versions of Radon basis functions, time-variant and time-invariant. A time-variant basis function can be used in time domain Radon transform algorithms while a time-invariant version can be used in, generally more efficient, frequency domain algorithms. Comparing the time-variant and time-invariant Radon transform by the proposed basis functions, the time-invariant version can better focus different seismic events; it is also more accurate, especially in presence of vertical heterogeneity. However, the proposed time-invariant basis functions are suitable for a specific type of layered anisotropic media, known as factorized media. We test the proposed methods and illustrate successful applications of them for trace interpolation and coherent noise attenuation.     

Seismic receiver coupling to the seafloor

The presence of geophysical receivers on the seafloor changes the local wave field due to the receiver seafloor interaction. The resulting PP- and PS-wave distortion of the wave field is often referred to as receiver coupling to the seafloor and can make data processing challenging and sometimes impossible. This paper provides an overview of the mathematical approaches to describe receiver coupling, how to estimate receiver coupling and what the difficulties and possible solutions are. The first section shows how the mathematical approach developed from a simple model considering only the vertical receiver component to include all three receiver components and their interactions with the seafloor. In the second section, I show how receiver coupling can be measured and how it can be improved using mathematical and data-driven approaches.     

Prediction of signatures of airgun arrays using dual near-field hydrophones

Successful estimation of airgun-array signatures from near-field measurements depends on the accuracy of poorly controlled model parameters such as the effective sea surface reflection coefficient and source depth. We propose a method for prediction of robust source signatures, which are insensitive to fluctuations of the latter parameters. The method uses vertical pairs of near-field hydrophones to measure near-field pressure and its vertical gradient, combination of which eliminates sea surface reflections from the near-field data. This excludes the uncertainty related to the fluctuating sea state and source depth from the process of inversion of the near-field data for source signature. The method explicitly separates the recorded near-field pressure into its up and down going components, which allows one to measure the effective frequency- and angle-dependent sea surface reflection coefficient right at the source, as well as to estimate the actual source depth. Tests on synthetic and field data demonstrate robust performance of the method.     

用极轨气象卫星资料分析飞机增雨云层条件

综合应用NOAA卫星AVHRR／3和FY-1极轨气象卫星高分辨0．58～0．68μm可见光、1．58～1．64μm近红外和10．3～11．3μm红外多通道资料,充分考虑了云的厚度、云中粒子尺度和云顶亮温的信息,给出了适宜飞机增雨作业云层的卫星遥感判据,建立了云层作业条件分析模型。实际应用表明,卫星遥感分析图可以有效地监测、判识和分析云层的增雨作业条件,应用效果好,可作为飞机增雨航线设计、作业决策的重要依据。通过增雨个例的微波图像特征分析,初步分析了AMSU—B微波图像在人工增雨作业中的作用和应用前景。     

陕西省飞机增雨作业典型天气个例分析

在2002～2003年春秋季陕西省14次飞机增雨作业天气分析的基础上,对2002年9月13日飞机增雨作业典型天气个例的环流背景、影响系统以及500 hPaθse、温度、垂直速度、水汽通量散度等物理量场进行了分析,并结合飞机和雷达探测资料,得出飞机增雨作业需要的有利于层状云向降水转化的条件：有稳定的层状云,云系有一定冷层厚度和过冷云水量,供自然冰相降水元和人工催化形成的降水元增长;云系还应有一定厚度的暖层,供下落的自然和人工形成降水元融化再经碰并云水增长成雨滴形成降水.陕西省春秋季具有进行有效飞机增雨作业的天气系统和天气条件.     

山东沿海降雨云系宏观特征及人工增雨潜力的估算

针对山东省飞机人工增雨作业的实际情况，分析了山东沿海地区的降雨特征，统计了沿海云层的宏观物理量，分析了莱州湾、黄海北部和东南沿海３个地区云与降水的关系，对主要降雨天气系统计算了降雨效率及增潜力，增雨潜力在４２．５５％－６８．７９％。通过对天气系统中水汽垂直分布的分析，为飞机在山东沿海地区增雨作业最佳催化层次的选择提供了信。