断层衍射波及其应用

本文从衍射波的物理定义出发,简化了Trorey提出的断层上Kirchhoff-Helmholtz衍射方程的解法;计算了不同深度、不同测线方向下的断层衍射波理论地震图;计算了衍射波振幅谱与相位谱,给出了利用衍射波求断层位置的公式;得出了一些新的结论,通过人工地震测深与地震勘探的实例,对断层衍射波的特性有了更明确的认识。 本文的结果表明:断层衍射波发生在地球介质剧烈变化处;衍射点两侧的衍射波走时曲线呈双曲线状;波初动清晰且半周期小;其优势频率振幅谱与反射波的相同,在衍射波与反射波走时曲线相切处附近,记录图中出现衍射波最大振幅,且波反相;视断点与真实断点一般不重合。上述特点可能为判定衍射波并确定断层位置提供判据。     

断层衍射波及其应用ht

本文从衍射波的物理定义出发,简化了Trorey提出的断层上Kirchhoff-Helmholtz衍射方程的解法;计算了不同深度、不同测线方向下的断层衍射波理论地震图;计算了衍射波振幅谱与相位谱,给出了利用衍射波求断层位置的公式;得出了一些新的结论,通过人工地震测深与地震勘探的实例,对断层衍射波的特性有了更明确的认识。 本文的结果表明:断层衍射波发生在地球介质剧烈变化处;衍射点两侧的衍射波走时曲线呈双曲线状;波初动清晰且半周期小;其优势频率振幅谱与反射波的相同,在衍射波与反射波走时曲线相切处附近,记录图中出现衍射波最大振幅,且波反相;视断点与真实断点一般不重合。上述特点可能为判定衍射波并确定断层位置提供判据。      

衍射CT技术和多源全息成象技术的比较研究

在本文中,我们从理论上比较研究了衍射CT技术和多源全息成象技术,讨论了在弱不均匀介质中多源全息成象技术失真的根源,推导出二维多源全息图象重建的快速算法,利用这些算法和计算机产生的非Born近似的正演数据,系统地研究了异常体的尺寸、异常程度的大小和数据采集方式对重建图象的影响.并且把它与衍射CT重建图象作了数值上的比较,所得到的许多结果（见正文结论部分）对于衍射地震CT技术和多源全息成象技术在生产中的应用有着指导意义.     

基于声光衍射原理的新型医学CT构想

根据声光衍射原理，提出一种全新扫描方式和图象重建方法的医学ＣＴ技术设想。在理论上给出了新技术的可行性研究，并提出新方法实用化实验的参数和条件。与现用的ＣＴ相比，交真有扫描时间短，重建图象速度快，对人体无害，图象分辨率高，成本大幅度降低等显著优点。     

一阶相衬CT重建算法的最新进展

本文简要地解释了衍射增强成像方法和光栅相衬成像方法的物理原理,详细地介绍了以这两种成像方法为基础的一阶相衬CT的物理模型及其重建算法的最新进展,着重分析这些重建算法的思路、特点和性能。这些重建算法基于相衬成像的物理原理,能够从一阶投影数据出发,直接重建样品内部的折射率分布,从而得到了弱吸收物质的高衬度CT图像。     

反假频非均匀地震数据重建方法研究

研究基于Fourier变换的数据重建方法,既能进行非均匀采样数据重建,又可以去除空间假频. 将不规则采样数据重建问题归结为信息重建的地球物理反演问题,采用最小二乘方法从观测的稀疏或不规则数据反演模型空间完全信息. 在求解信息重建反演问题时,引入DFT 加权范数规则化策略,采用预条件共轭梯度法（PCG）求解,保证解的稳定性和收敛速度. 处理线性同相轴假频问题时,根据采样定理,引入线性预测方法,采用Yule Walker方程由带限信号的无假频低频功率谱预测高频功率谱,达到反假频目的. 本文研究了均匀采样数据内插,非均匀采样数据重建,非均匀分布高频信息重建等方面问题,数值试验取得较好效果.     

衍射地震CT技术的数值研究

本文首先解决了声波方程的非Born近似的正演计算问题,从而获得理论上不带近似的正演数据;然后,推导了井间（CBP）、垂直地震剖面（VSP）和地面反射（SRP）三种不同的数据采集方式下的衍射CT的重建公式;利用这些重建算法和正演数据,系统地研究了影响到地球物理CT成象质量的三种因素,即:（1）数据采集方式,（2）异常程度和（3）成象区域的尺寸,对重建图象的影响;并比较了衍射地震CT和射线地震CT的成象质量。     

二维变密度声波波动方程的衍射层析成像

本文将二维声波衍射层析成像原理推广到二维变密度声波波动方程中，导出了在线源激发条件下，不同观测系统的滤波反传播重建算法，取两个以上不同频率值可得到密度和体积模量的成像．数值实例表明，该方法能得到密度和体积模量较满意的成像。     

地震数据反假频规则化方法研究

由于诸多因素的影响,地震数据沿空间方向通常是稀疏采样的,因此引起较为严重的空间假频.本文提出一种反假频地震数据规则化的方法,采用Fourier变换域加权范数带限重建方法完成低频数据重建,利用自适应频谱加权范数的正则化项约束方程的解,将地震数据的带宽和谱形状作为先验信息,具有较好的低频重建特性.文中采用共轭梯度算法求解方程,而后利用重建的低频数据信息,应用频带延拓的方法重建高频数据,未知的高频带信息由重建的低频带信息构建.本方法在完成地震数据规则化的同时,可有效去除地震数据中的空间假频干扰.理论模型和实际资料处理均表明文中所提出的反假频地震数据规则化方法是有效可行的.     

用于灾后遥感的共位衍射卫星隔离方法

针对地震发生后对受灾地区高精度地图的获取需求,考虑到静止轨道轨位的紧张性,研究了一种基于共位衍射的卫星成像系统。该系统由两颗共位卫星构成,一颗为成像卫星,另一颗为薄膜衍射卫星,相比于传统的单颗成像卫星,该系统具有响应迅速以及空间分辨率高的优势。本文基于共位策略和隔离策略相结合的设计原则,采用倾角/偏心率协调隔离的方法,设计了一组轨位在10. 6E定点经度内的共位衍射成像系统轨道根数。通过仿真分析,将各个共位卫星之间相对距离与实际在轨卫星的相对距离做对比,仿真结果与实际数据间的误差满足一定的设计要求。因此,该组轨道根数在实际在轨应用中具备一定可行性,本文设计的共位衍射卫星系统为灾后应急响应提供重要参考。     

Spatial and temporal spectra of the geomagnetic field and their scaling properties

Many natural phenomena show a relationship between their spatial and temporal Fourier spectra. This paper discusses such a connection for the geomagnetic field, when some assumptions are made about the (exponential or power-law) behaviour of the spatial power spectrum of the field itself and that of its time derivative (the spatial spectrum of the secular variation) as estimated from global geomagnetic field models. It is shown that, under either assumption, the temporal spectrum of the geomagnetic field computed at the core–mantle boundary (CMB) would have a power-law behaviour with a negative spectral exponent of about 0.5. At the Earth’s surface, although the temporal spectrum obtained from the power-law spatial model assumes a slightly more complicated form, it can be practically approximated with a power law with a negative exponent of about 3.6. Analysis of magnetic observatory data confirms these results and that the starting hypotheses are reasonable, especially in view of the possibly chaotic state of the dynamical processes underlying the generation and maintenance of the geomagnetic field.     

地球主磁场空间功率谱的变化特征

根据第8代IGRF模型，计算分析了1900－2000年地球磁场和分量X，Y，Z的空间功率谱的变化特征。结果表明1900－2000年主磁场的空间功率谱呈减小趋势，由功率谱随谐波阶次n的变化关系得出的非偶极子场的等效磁源位于核幔边界附近，而且其位置随时间变化，用n=1,2两阶谐波的谱得到的等效磁源位于地球内核边缘，1900年以来离开地心一直向外增大。     

The use of near-antenna artificial density ducts for increasing the power of VLF radiation in space plasma

We investigate the radiation from an artificial density duct excited by an annular electric current in the VLF frequency range. It is assumed that the duct possesses the form of a quasi-cylindrical density enhancement which smoothly reduces with distance from the source. We have found that the field in the duct is represented with a good accuracy in terms of eigenmodes whose propagation is supported in density enhancements. The radiation field in the background medium arises due to reemission of these eigenmodes from the duct. We calculate the excitation coefficients of eigenmodes and study the characteristics of a radiation field. We show that the presence of a duct with enhanced density can cause a considerable increase in the power radiated from the source. In particular, we study the distribution of radiated power over the spatial spectrum of waves excited in a surrounding magnetoplasma. It is concluded that under certain conditions an appreciable increase in the power radiated into the long wavelength part of the spatial spectrum can be achieved. We give concrete estimations for the conditions appropriate to the Earth's ionosphere.     

Modeling of spatially correlated,site-reflected,and nonstationary ground motions compatible with response spectrum

Seismic risk analysis and mitigation of spatially extended structures require the synthesis of spatially varying ground motions in the response history analysis of these structures. These synthetic motions are usually desired to be spatially correlated, site reflected, nonstationary, and compatible with target design response spectra. In this paper, a method is presented for simulating spatially varying ground motions considering the nonstationarity, local site effects, and compatibility of response spectra. The scheme for generating spatially varying and response spectra compatible ground motions is first established for spatial locations on the ground surface with varying site conditions. The design response spectrum is introduced as the “power” spectrum at the base rock. The site amplification approach is then derived based on the deterministic wave propagation theory, by assuming that the base rock motions consist of out-of-plane SH wave or in-plane combined P and SV waves propagating into the site with assumed incident angles, from which tri-directional spatial ground motions can be generated. The phase difference spectrum is employed to model ground motions exhibiting nonstationarity in both frequency and time domains with different site conditions. The proposed scheme is demonstrated with numerical examples.     

The limit properties of spatial coherence of seismic ground motion

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高频GPS坐标时序的噪声特性分析

为研究高频GPS坐标时序的噪声特性,对芦山地震前后三天,北京时间8:00—9:00,位于四川盆地8个CORS站50Hz的高频观测资料进行解算与分析。分析过程中,分别采用恒星日滤波和主成分滤波分析以及去除时空噪声,并采用功率谱分析经滤波后的坐标时序。结果表明,高频GPS坐标时序的谱指数在1.6~2.0间,符合白噪声+随机游走噪声模型特性。建议当利用高频GPS研究地表运动特性、监测大型建筑的运动结构或确定GPS动态实验平台姿态时,应考虑高频GPS坐标时序的这一噪声特性。     

太阳活动低年时太阳同步轨道电场高频(HF)波的观测特性研究

文章使用搭载在DEMETER卫星上的电场探测仪器(Instrument Champ Electrique,ICE)在太阳活动低年(2007年2月4日到2008年2月3日)所探测的数据,研究频率从10 kHz到3.33 MHz宽频段的高频(HF)电场波功率谱的空间分布特征.地磁宁静期间,从2.08 MHz到3.33 MH...     

Response spectrum analysis of structures subjected to spatially varying motions

An important aspect of earthquake loads exerted on extended structures, or structures founded on several foundations, is the spatial variability of the seismic motion. Hence, a rigorous earthquake resistant design of lifeline structures should account for the spatial character of the seismic input, at least in an approximate way. A procedure is proposed which enables addressing the problem of multiply supported structures, subjected to imperfectly correlated seismic excitations, by means of an extension to the response spectrum method. A modified response spectrum model is developed for the design of extended facilities subjected to single and multicomponent ground motion. The modification procedure is based on adjusting each spectral value of the given design response spectrum by means of a correction factor, which depends on the structural properties and on the characteristics of the wave propagation phenomenon. Finally, the theoretical model is validated through digital simulation of seismic ground motion, whereby model predictions are found to be in good agreement with exact results.     

THE P400 WATERGUN SOURCE IN THE QUEST FOR IMPROVED RESOLUTION AT ALL DEPTHS*

The low-frequency response of the P400 watergun is an improvement over that of the S80 version. It has been further enhanced by deployment in a vertically staggered array. The notch in the amplitude spectrum at about 35 Hz due to the interference between the precursor and main implosion pulse has been virtually eliminated, and depth notches due to the free surface interface at the upper end of the spectrum have been greatly reduced. The spectral band is thus very broad and well-shaped and corresponds to an even shorter signature. After convolution with the streamer ghost, the amplitude of the implosion pulse from the composite far-field signature is more than 30 times the composite precursor amplitude. Thus the signal approaches the minimum-phase condition. Shot-generated noise scattered back by diffractors located at or near seabed is the single greatest impediment to increased penetration, especially in high resolution surveys. Such noise decays much less rapidly than signal, particularly so with broad band data. Furthermore, back-scattered interference coming from a cone of bearings between 15–45° with respect to the line is particularly damaging since in these directions the stack enhances the interference and confuses the primary velocity analysis. The watergun source patterns are therefore element-weighted to maximize directivity within these critical directions in the frequency band 50–155 Hz. When spatial aliasing is reduced by increased streamer spatial sampling and by discrete anti-alias filters during the record cycle,f-k filtering can be applied to the field records as an effective supplement to the source and receiver patterns without the aliased ‘wrapped around’ noise alignments destroying the upper end of the spectrum of genuine reflectors. Furthermore, increased spatial sampling is a pre-requisite in thef-k-migration process if the valuable higher frequencies of broad band data are to be migrated in steep-dip situations without aliasing. Thus, spatial resolution is a necessary complement to temporal resolution if maximum advantage of the broad-band P400 watergun source is to be realized.