几种时频分析方法比较

地震信号由于各种原因,往往是一种非线性、非平稳信号,基于平稳信号理论的常规傅立叶变化方法不能刻画任一时刻的频率成分.时频分析能同时保留时间与频率信息,目前已经出现了很多时频分析方法.本文介绍了Hilbert变换、Hilbert-Huang变换、正弦曲线拟合、雷克子波匹配、短时傅立叶变换、小波变换、S变换以及Cohen类这八种方法,并从时间分辨率、频率分辨率,以及对多频率成份信号适应能力等各方面阐述了各种方法的优缺点,对其中的一些方法结合了理论记录进行了试算,进一步阐述了这些方法的长处和不足之处.     

广西钦防海槽迁移与沉积-构造转换面

广西的钦州－防城－带，素以钦防海槽称之，系指加里东期构造运动后，扬子与华夏陆块间的“残留海”。其两侧为古隆所夹持，西为大明山古隆起，东为云开大山古隆起，其间划分为四个构造单元，由东向西依次为：博白坳陷，六万大山隆起，钦州坳陷和十万大山坳陷。现构造形迹的排列，反馈防海槽在早古生代至中生代间深海盆或浅海深水盆地在构造和沉积上有自东向西迁移的特点。晚古生代盆地迁移过程至少有八个沉积－构造转换面可记录盆地的构造演化：第1转换面为早奥陶世与晚寒武世间的沉积界面；第2转换面为早志留世与晚奥陶世间的沉积界面；第3转换面为早泥盆世早期与晚志留世间的海侵上超面；第4转换面为中泥盆世的海侵上超面；第5转换面为中二叠世与晚二叠世间的沉积界面；第6转换面为早三叠世的海侵面；第7转换面为中晚三叠世与早三叠世间的沉积界面；第8转换面为早侏罗世与晚三叠世间的沉积界面。前两个界面为盆山转换面，与华南加里东构造运动过程相耦合，为挤压的构造背景；第3界面为水下间断面，下泥盆统与上志留统为不连续沉积，在构造上应是挤压机制下的破裂不整合，也是加里东期构造运动的响应；第4界为海西期的海侵上超面，与盆地走滑拉张同步；第5界面则反馈于印支期造山的初始阶段，第6界面为中生代盆地迁移转换面；第7界面为印支期造山过程的盆地转换面；第8界面为燕山期造山造盆转换面。其转换面性质的转化，代表钦防海槽可能是个复杂大陆边缘前陆盆地演化史。     

Study on ETKF-Based Initial Perturbation Scheme for GRAPES Global Ensemble Prediction

Initial perturbation scheme is one of the important problems for ensemble prediction. In this paper, ensemble initial perturbation scheme for Global/Regional Assimilation and PrEdiction System (GRAPES) global ensemble prediction is developed in terms of the ensemble transform Kalman filter (ETKF) method.A new GRAPES global ensemble prediction system (GEPS) is also constructed. The spherical simplex 14-member ensemble prediction experiments, using the simulated observation network and error characteristics of simulated observations and innovation-based in ation, are carried out for about two months. The structure characters and perturbation amplitudes of the ETKF initial perturbations and the perturbation growth characters are analyzed, and their qualities and abilities for the ensemble initial perturbations are given. The preliminary experimental results indicate that the ETKF-based GRAPES ensemble initial perturbations could identify main normal structures of analysis error variance and reflect the perturbation amplitudes.The initial perturbations and the spread are reasonable. The initial perturbation variance, which is approximately equal to the forecast error variance, is found to respond to changes in the observational spatial variations with simulated observational network density. The perturbations generated through the simplex method are also shown to exhibit a very high degree of consistency between initial analysis and short-range forecast perturbations. The appropriate growth and spread of ensemble perturbations can be maintained up to 96-h lead time. The statistical results for 52-day ensemble forecasts show that the forecast scores ofensemble average for the Northern Hemisphere are higher than that of the control forecast. Provided that using more ensemble members, a real-time observational network and a more appropriate inflation factor,better effects of the ETKF-based initial scheme should be shown.     

Coherent Structures Detected in Atmospheric Boundary-layer Turbulence using Wavelet transforms at Huaihe River Basin, China

The presence of coherent structures in turbulent shear flows suggests order in apparently random flows. These coherent structures play an important dynamical role in momentum and scalar transport. To develop dynamical models describing the evolution of such motion, it is necessary to detect and isolate the coherent structures from the background fluctuations. In this paper, we decomposed atmospheric turbulence time series into large-scale eddies, which include coherent structures and small eddies, which are stochastic by using Fourier digital filtering. The wavelet energy computed for the three components of the velocity fluctuations in the large-scale eddies appears to have local maximum values at certain time scales, which correspond to the scales or frequencies of coherent structures. We extract coherent signals from large-scale vortices at this scale by inverse wavelet transform formulae. This method provides an objective technique for examining the turbulence signal associated with coherent structures in the atmospheric boundary layer. The average duration of coherent structures in three directions based on Mexican hat wavelets are 33 s, 34 s and 25 s respectively. Symmetric andanti-symmetric wavelet basis functions give almost the same results. The main features of the structures during the day and night have little difference. The dimensionless durations for u, v and w have linear correlations with each other. These relationships are insensitive to the wavelet basis.     

Stratospheric N2O5, CH4, and N2O profiles from IR solar occultation spectra

Stratospheric volume mixing ratio profiles of N₂O₅, CH₄, and N₂O have been retrieved from a set of 0.052 cm^–1 resolution (FWHM) solar occultation spectra recorded at sunrise during a balloon flight from Aire sur l'Adour, France (44° N latitude) on 12 October 1990. The N₂O₅ results have been derived from measurements of the integrated absorption by the 1246 cm^–1 band. Assuming a total intensity of 4.32×10^–17 cm^–1/molecule cm^–2 independent of temperature, the retrieved N₂O₅ volume mixing ratios in ppbv (parts per billion by volume, 10^–9), interpolated to 2 km height spacings, are 1.64±0.49 at 37.5 km, 1.92±0.56 at 35.5 km, 2.06±0.47 at 33.5 km, 1.95±0.42 at 31.5 km, 1.60±0.33 at 29.5 km, 1.26±0.28 at 27.5 km, and 0.85±0.20 at 25.5 km. Error bars indicate the estimated 1- uncertainty including the error in the total band intensity (±20% has been assumed). The retrieved profiles are compared with previous measurements and photochemical model results.Laboratoire associé aux Universités Pierre et Marie Curie et Paris Sud.     

带有多道相关的抛物线Radon变换法分离P-P、P-SV波

因为多波多分量地震勘探中P-P波和P-SV波通常混杂在一起,所以较好地分离P-P波和P-SV波能够提高数据处理和解释的质量.抛物线Radon变换法在分离P-P波和P-SV波时取得了一定效果,但是在离散叠加的计算过程中会带来假频,这些假频会干扰波场分离.本文针对这一问题,将多道相关算法引入抛物线Radon变换,发展了带有多道相关的抛物线Radon变换法.该方法利用叠加信号具有相似性的特点,依据多道相关中衡量多道信号相似性的能量比标准,对叠加过程加以控制,压制变换中出现的假频.本文用该方法对合成地震记录进行了波场分离,取得了较好的效果.     

阿尔金山各边界断裂的归属性

系统研究阿尔金山南缘断裂、西北缘断裂、北缘红柳沟-拉配泉断裂的构造属性, 对重新认识中国大陆西部构造格架具有非常重要的意义.在卫星遥感图像宏观解译和野外调查基础上, 充分参考了近年来的区域地质调查和前人研究成果, 分析了阿尔金山各边界断裂特征, 结果表明南缘断裂形成于元古宙, 早古生代中晚期是一条具有右行走滑性质的巨型陆内转换断层, 中新生代分段差异复活; 西北缘断裂系形成较晚, 中新生代以来发生强烈的左行走滑, 应属于亚洲共轭滑移系的组成部分; 红柳沟-拉配泉断裂属于塔里木地块中央构造带系统, 是一条蛇绿构造混杂带, 早古生代属于陆缘或陆间裂谷.它们三者分属于不同的断裂系统, 具有不同的形成演化史, 其活动形式和构造意义各有不同, 但又相互联系、相互制约.      

基于主成分分析与K-L变换的双重属性优化方法

利用主成分分析客观赋权原理计算地震属性在预测目标参数时贡献率的大小,通过去除权重系数较小的属性参数,实现了地震属性的敏感性分析,建立储层参数与有效属性之间的匹配关联;在此基础上,利用K-L变换将属性样本空间的高维属性映射为低维属性,去除了属性之间的相关性,有效地解决了属性组合的优化问题,表明了主成分分析和K-L变换相结合的属性双重优化方法克服了单纯使用每种方法时的局限性,充分发挥了各自的优点,有助于属性分析、关联以及组合优化问题的解决,提高了地震储层参数预测的运算速度和精度。     

地面核磁共振响应数值模拟研究

模型响应的数值计算是地面核磁共振勘探的一个重要组成部分，作者在本文中给出了地面核磁共振数值计算方法。在文中，作者借助直接数值积分方法，对回线源产生的磁场轴向和垂向分量进行计算，并采用不等间距空间坐标剖分技术，对地面核磁共振积分方程进行数值积分。利用这些计算方法，计算了在均匀导电半空间中的某一深度上，磁场的垂向分量沿轴向变化曲线，并给出了两层导电模型中存在一层含水层的地电模型的地面模磁共振响应的数值模拟结果。采用在本文中介绍的数值计算技术，可成功地进行一维含水模型地面核磁共振信号的数值计算。     

地震资料处理中小波函数的选取研究

本文给出了常见地震子波的一个模拟公式，可以很好地模拟零相位及混合相位子波，在一定意义上也可以近似模拟最大相位及最小相位子波．模拟出的子波加上适当的修正项后满足允许条件，可用作小波函数．与Ｍｏｒｌｅｔ小波类似，在实际应用中这些修正项在一定条件下可以略去，文中对Ｍｏｒｌｅｔ小波作了改造，使其能更好地适应于地震资料处理．研究了反射波能量及噪声等干扰波在时间－尺度域的分布特征与所选基本小波的关系．提出用地震子波（或与地震子波相近的函数）作为基本小波，对地震资料进行去噪及分频解释的方法．最后用实例证明方法的有效性．