求解弹性波解耦方程的一种优化拟解析方法

常规伪谱方法二阶时间差分格式时间精度较低,且对于大步长时间采样间隔,常规伪谱方法不稳定.拟解析方法对于速度变化剧烈的模型,在时间和空间上均有较大误差.本文提出了一种基于解耦的二阶位移弹性波方程波场模拟及矢量波场分解的优化拟解析方法,将归一化的拟拉普拉斯算子分别应用于P波和S波波场延拓,延拓矢量波场的同时,可分解并延拓纯纵波和纯横波波场.利用弹性波优化拟微分算子表示拟拉普拉斯算子,该拟微分算子不仅包括原始微分算子的谱估计,而且还包含一个时间补偿项,其可在波数-空间域精确地补偿波动方程在时间方向上采用二阶有限差分引起的误差.利用低秩分解近似求解弹性波优化拟微分算子,可有效提高计算效率.2D均匀模型、层状模型以及部分盐丘模型数值正演模拟结果表明:相比较于常规的伪谱法和拟解析法,本文方法在时间和空间上均有很高的精度,并且稳定性条件比较宽松.     

Balloon-borne polarimetry

For about two weeks in 1995, the balloon-borne Flare Genesis Experiment will continuously observe the Sun well above the turbulent, image-blurring layers of the Earth's atmosphere. The polarization-free 80 cm telescope will supply images to a liquid-crystal based vector magnetograph, which will measure magnetic features at a resolution of 0.2 arcsec. An electrically tunable lithium-niobate Fabry-Perot provides a spectral resolution of about 0.015 nm. In a follow-up series of Antarctic balloon flights, the Flare Genesis Experiment (FGE) will provide unprecedented details about sunspots, flares, magnetic elements, filaments, and the quiet solar atmosphere.     

Fourier transform summation of Legendre series and D-functions

The relation between D- and d-functions, spherical harmonic functions and Legendre functions is reviewed. Dmatrices and irreducible representations of the rotation group O(3) and SU(2) group are briefly reviewed. Two new recursive methods for calculations of D-matrices are presented. Legendre functions are evaluated as part of this scheme. Vector spherical harmonics in the form af generalized spherical harmonics are also included as well as derivatives of the spherical harmonics. The special dmatrices evaluated for argument equal to/2 offer a simple method of calculating the Fourier coefficients of Legendre functions, derivatives of Legendre functions and vector spherical harmonics. Summation of a Legendre series or a full synthesis on the unit sphere of a field can then be performed by transforming the spherical harmonic coefficients to Fourier coefficients and making the summation by an inverse FFT (Fast Fourier Transform). The procedure is general and can also be applied to evaluate derivatives of a field and components of vector and tensor fields.     

利用Intergraph地图出版系统进行地图的生产和制作

Intergraph地图出版系统是一套比较实用的地图生产系统 ,利用它 ,我们成功地生产了高质量的《江苏省水利地图集》。文中主要介绍了 Intergraph地图出版系统的构成以及用它来制作地图的方法和步骤。     

高频地波雷达生成海洋表面矢量流图

武汉大学研制的双站高频地波雷达系统OSMAR2000利用测得的两幅单站径向海流图生成矢量海流图。经典矢量流图生成方法不能直接应用到OSMAR2000系统中。本文提出一种先在极坐标系下用自然三次样条函数将径向流插值到公共网格上然后直接进行矢量合成的矢量海流图生成方法。OSMAR2000在东海的表面矢量流实测结果与作对比验证的传统海流计测量结果十分吻合。对比数据表明，该方法是可行的，且优于先进行径向流线性插值后矢量合成的矢量流图生成方法。这也是国内首次利用高频地波雷达实现海洋表面矢量流的实时监测。     

Vector methods to compute azimuth, elevation, ellipsoidal normal, and the Cartesian ( X , Y , Z ) to geodetic ( φ , λ , h ) transformation

Vector-based algorithms for the computation of azimuth, elevation and the ellipsoidal normal unit vector from 3D Cartesian coordinates are presented. As a by-product, the formulae for the ellipsoidal normal vector can also be used to iteratively transform rectangular Cartesian coordinates (X, Y, Z) into geodetic coordinates (φ, λ, h) for a height range from −5600 km to 10⁸ km. Comparisons with existing methods indicate that the new transformation can compete with them.     

Slope stability analysis: a support vector machine approach

Artificial Neural Network (ANN) such as backpropagation learning algorithm has been successfully used in slope stability problem. However, generalization ability of conventional ANN has some limitations. For this reason, Support Vector Machine (SVM) which is firmly based on the theory of statistical learning has been used in slope stability problem. An interesting property of this approach is that it is an approximate implementation of a structural risk minimization (SRM) induction principle that aims at minimizing a bound on the generalization error of a model, rather than minimizing only the mean square error over the data set. In this study, SVM predicts the factor of safety that has been modeled as a regression problem and stability status that has been modeled as a classification problem. For factor of safety prediction, SVM model gives better result than previously published result of ANN model. In case of stability status, SVM gives an accuracy of 85.71%.     

C波段紧缩极化SAR海冰探测能力评估

The C-band synthetic aperture radar(SAR) data from the Bohai Sea of China, the Labrador Sea in the Arctic and the Weddell Sea in the Antarctic are used to analyze and discuss the sea ice full polarimetric information reconstruction ability under compact polarimetric modes. The type of compact polarimetric mode which has the highest reconstructed accuracy is analyzed, along with the performance impact of the reconstructed pseudo quad-pol SAR data on the sea ice detection and sea ice classification. According to the assessment and analysis, it is recommended to adopt the CTLR mode for reconstructing the polarimetric parameters σ_(HH)~0,σ_(VV)~0, H and α,while for reconstructing the polarimetric parameters σ_(HV)~0, ρ_(H-V), λ_1 and λ_2, it is recommended to use the π/4 mode.Moreover, it is recommended to use the π/4 mode in studying the action effects between the electromagnetic waves and sea ice, but it is recommended to use the CTLR mode for studying the sea ice classification.