最优可分表示法三维波场延拓

适于复杂介质的高精度波场延拓算子是叠前深度偏移研究的重要内容。本文采用最优可分表示方法,运用正反傅立叶变换构造了三维单程波场延拓算子,算子实现了波数域变量与空间(速度)域变量分离。波数域内进行相移计算,在空间域对因介质横向变速引起的时移作修正。脉冲响应显示在区域内各速度的脉冲计算值与理论值基本一致,说明最优可分表示法叠前深度偏移可适用于强变速条件下复杂介质的成像需求。SEG／EAGE模型和实测数据的成像结果验证了本文方法对复杂构造的成像能力。     

实现稀疏反褶积的预条件双共轭梯度法

地震勘探稀疏反褶积计算一般要导出一个Toeplitz矩阵的线性系统，通常可以用矩阵求逆、Levison递推及共轭梯度等方法直接求解。当Toeplitz矩阵的条件数很大时，数值稳定性差，甚至无法求解。使用共轭梯度法，在矩阵的对角元素上加入规则化因子，可以改善这种情况，但不能彻底解决数值稳定性和精度问题。若求解最小二乘问题的原始问题，结果会好些。线性系统形式的细微改变，将导致不同的数值计算特性。在规则化策略基础上，可巧妙地构造稀疏反褶积的问题原型，引入预条件，采用双共轭梯度法求解，从而实现稀疏反褶积，获得较好结果。数值算例表明，预条件双共轭梯度法比直接稀疏反褶积方法收敛快、精度高。     

三维电阻率正演计算中的Lanczos迭代算法

在三维电阻率的正反演计算中,快速、准确的正演计算是反演的关键。而正演计算往往涉及到求解大型线性方程组Ax=b的问题,通过Lanczos迭代构造出对称三对角阵方程组,并采用正交分解法进行求解,与传统算法相比,此算法占用内存少、收敛速度快、且稳定;针对大型稀疏矩阵的特点,采用简单地记录矩阵的非零元素值及其所在行、列值的方法,来存储大型稀疏矩阵,可大大节省机器内存,提高运算速度。通过理论分析和点电源三维地电场计算实例,阐述该法是地电三维正演计算的有效方法。     

大地电磁测深资料的超球逼近反演

超球逼近方法是一种全局搜索的二次优化方法。将该优化方法应用到大地电磁测深资料的反演中取得较好的效果。在介绍了超球逼近方法的基本原理后,应用数值结果对该方法的可行性进行了检验。     

Surface-wave polarization data and global anisotropic structure

In the past few years, seismic tomography has begun to provide detailed images of seismic velocity in the Earth's interior which, for the first time, give direct observational constraints on the mechanisms of heat and mass transfer. The study of surface waves has led to quite detailed maps of upper-mantle structure, and the current global models agree reasonably well down to wavelengths of approximately 2000 km. Usually, the models contain only elastic isotropic structure, which provides an excellent fit to the data in most cases. For example, the variance reduction for minor and major arc phase data in the frequency range 7–15 mHz is typically 65–92 per cent and the data are fit to within 1–2 standard deviations. The fit to great-circle phase data, which are not subject to bias from unknown source or instrument effects, is even better. However, there is clear evidence for seismic anisotropy in various places on the globe. This study demonstrates how much (or little) the fit to the data is improved by including anisotropy in the modelling process. It also illuminates some of the trade-offs between isotropic and anisotropic structure and gives an estimate of how much bias is introduced by neglecting anisotropy. Finally, we show that the addition of polarization data has the potential for improving recovery of anisotropic structure by diminishing the trade-offs between isotropic and anisotropic effects.     

LANCZOS迭代算法及其在三维地电场数值模拟计算中的应用研究

在三维电阻率的正演计算中往往涉及到快速、准确求解大型线性方程纽Ax=b的问题。通过采用有限差分法来构造出求解点电源三维地电场的大型稀疏对称线性方程组。并引入Lanczos迭代技术，构造出三对角阵方程组，然后采用正交分解法进行求解，它是Krylov子空间方法中的一种。与传统迭代算法相比，它占用内存少，收敛速度快且稳定。针对大型稀疏矩阵及MATLAB语言的特点，采用简单记录矩阵的非零元素值及其所在行、列值的方法存储大型稀疏矩阵，可大大节省机器内存，提高运算速度。理论分析和计算实例显示，此算法是地电三维正演计算的有效方法，为下一步的反演计算打好基础。     

The 3-D Truncation Filtering Methodology Defined for Planar and Spherical Models: Interpreting Gravity Data Generated by Point Masses

This paper focuses on one particular way of linear filtering the gravity data to facilitate gravity inversion or interpretation. With the use of integral transforms the gravity anomalies are transformed into new quantities that allow an easier interpretation with the help of pattern recognition. As the integral transforms are in fact filters, and as the regions of integration are caps with a variable radius, which can be systematically changed as a free parameter, we refer to such methodology as the truncation filtering. Such filters may be understood as weighted spherical windows moving over the surface, on which the gravity anomaly is defined, the kernel of the transform being the weight function. The objective of this paper is to define and deploy the truncation filtering for a planar model, i.e. for a homogenous horizontally infinite layer with embedded anomalous masses, and for a spherical model, i.e., for a homogenous massive sphere with embedded anomalous masses. Instead of the original gravity anomaly, the quantities resulting from the truncation filtering are interpreted/inverted. As we shall see, this approach has certain benefits. The fundamental concept of the truncation filtering methodology is demonstrated here in terms of the model consisting of one point mass anomaly.The relationship between the depth of the point mass and the instant of the onset of the dimple pattern observed in sequences produced by truncation filtering the synthetic gravity data generated by point masses is, for both the planar and spherical models, compiled by computer simulations, as well as derived analytically. It is shown, that the dimple pattern is a consequence of truncating the domain of the filter and is free of the choice of the kernel of the filter. It is shown, that in terms of the mean earth and depths of point masses no greater than some 100 km the spherical model may be replaced by a planar model from the perspective of the truncation filtering methodology. It is also shown, that from the viewpoint of the truncation filtering methodology the rigorous gravity anomaly may be approximated by the vertical component of the gravity disturbance. The relationship between the instant of the dimple onset and the depth of the point mass thus becomes linear and independent of the magnitude (mass) of the point mass.     

DYNAMICAL CHARACTERISTICS OF THE STREAM FIELD OF COLD FRONT IN BOUNDARY LAYER

The motion equation of atmospheric boundary layer with cold front surface under geostrophicmomentum approximation is solved and some characteristics of the stream field for the cold frontsurface in the boundary layer are derived,for example,the slope of the cold front surface increaseswith the increases of geostrophic vorticity and the temporal tendency of geostrophic wind speed,and also increases with the decrease of the component of thermal wind speed along the motiondirection of the front:the stream field above and below the cold front surface in the boundary layerdepends on the slope of the front surface,geostrophic wind speed and its temporal and spatialdistributions.A common characteristic is that there exist updraft motion above the cold frontsurface and downdraft motion below it.     

Examination of a Correction Procedure for the Flow Attenuation in Orthogonal Sonic Anemometers

In this study we examine the calibration of wind speed measured by a sonic anemometer, with an orthogonal probe configuration, with regard to the approximation of the flow angle, and the wind-speed dependence of the flow attenuation attributed to the transducer shadow. The flow angle should be calculated by the iterative method when the attenuation is relatively high. For a probe manufactured by Kaijo Co. TR-61C, the wind-speed dependence of the transducer shadow effect is formulated from the results of the wind-tunnel experiment. Assuming the equation is applicable to field observations, significant errors possibly remain especially when the wind speed is low, and /or the angle between the flow vector and the sonic path is small, if the wind-speed dependence in measurement errors is neglected.     

跨断层监测数据奇异值的发现

在跨断层多期复测整体平差基础上分析了一期数据对最小二乘结果之影响,探讨了跨断层监测中异常数据的发现问题。