Computing the Sensitivity Kernels for 2.5-D Seismic Waveform Inversion in Heterogeneous,Anisotropic Media

2.5-D modeling and inversion techniques are much closer to reality than the simple and traditional 2-D seismic wave modeling and inversion. The sensitivity kernels required in full waveform seismic tomographic inversion are the Fréchet derivatives of the displacement vector with respect to the independent anisotropic model parameters of the subsurface. They give the sensitivity of the seismograms to changes in the model parameters. This paper applies two methods, called ‘the perturbation method’ and ‘the matrix method’, to derive the sensitivity kernels for 2.5-D seismic waveform inversion. We show that the two methods yield the same explicit expressions for the Fréchet derivatives using a constant-block model parameterization, and are available for both the line-source (2-D) and the point-source (2.5-D) cases. The method involves two Green’s function vectors and their gradients, as well as the derivatives of the elastic modulus tensor with respect to the independent model parameters. The two Green’s function vectors are the responses of the displacement vector to the two directed unit vectors located at the source and geophone positions, respectively; they can be generally obtained by numerical methods. The gradients of the Green’s function vectors may be approximated in the same manner as the differential computations in the forward modeling. The derivatives of the elastic modulus tensor with respect to the independent model parameters can be obtained analytically, dependent on the class of medium anisotropy. Explicit expressions are given for two special cases—isotropic and tilted transversely isotropic (TTI) media. Numerical examples are given for the latter case, which involves five independent elastic moduli (or Thomsen parameters) plus one angle defining the symmetry axis.     

青海高原1961-2008年雪灾时空分布特征

利用青海高原45个气象站1961-2008年冬季（10月至翌年2月）和春季（3-5月）积雪深度资料,按照DB63雪灾标准分类的等级,并结合实际灾情研究了青海高原雪灾时空尺度、强度及发生频次等的变化。结果表明：近50年来青海高原除了特大雪灾发生频次变化趋势不明显外,其他等级的雪灾发生频次年际变化均呈现上升趋势。青海高原南部的玉树、果洛、黄南南部、海南南部及海西东部地区是雪灾发生的高频区,柴达木盆地和青海东部地区极少发生雪灾。雪灾发生频次从20世纪60年代到2008年呈现上升趋势。     

大深度潜航器水下空间运动建模与仿真

分析大深度潜航器水下空间运动特点,建立描述其空间运动的数学模型,并以数学模型为基础利用 MATLAB\Simulink 软件完成潜航器空间运动仿真模型的开发。在搭建的仿真模型基础上,通过数学仿真手段分析了潜航器在螺旋下潜、抛载过渡、定角爬升、稳定至水面航行状态下的水下运动全过程,给出了具有弧形翼板的潜航器外形设计方案的运动能力仿真评估,为后续潜航器运动能力优化设计提供仿真依据。     

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三门湾沉积记录中长链烯酮不饱和指数-海表温度和浮游动物群落对厄尔尼诺/拉尼娜的响应

应用沉积地层记录中长链烯酮不饱和指数(U3K7)估算1916—2003年三门湾表层海水温度(SST)与变化。SST波动范围为15.97~18.00℃,年平均为17.03℃。该值比当年实测海水全年平均温度低3.52℃,同时应用长链烯醇不饱和指数与SST的关系重建历史上的厄尔尼诺现象。研究显示三门湾的厄尔尼诺气候事件在大尺度上与东太平洋一样均受制于气候影响,在变化尺度上又受到地理位置和地方性气候(季风)的影响,厄尔尼诺事件在形式和年代上相互对应,但是其涛动幅度不如东太平洋的强烈。通过比较厄尔尼诺期间(2003/2002年)和非厄尔尼诺期间(2006/2005年)的浮游动物群落结构变动信号、生物量、密度以及物种多样性等,在厄尔尼诺时期浮游动物种类数、生物量和丰度呈现偏高的趋势,三门湾的暖水性浮游动物类群、数量变化与台湾暖流活动过程中携带的浮游性动物有密切的联系。     

The Derivation and Validation of TBM Disc Cutter Wear Prediction Model

The problem of disc cutter wear is inevitable when shield or TBM excavating hard rock for a long distance, thus, the study of disc cutter wear model has an important project value on predicting its service life and replacement opportunity. It is put forward by analyzing disc cutter wear mechanism that the main wear form is abrasive wear, which is based on plastic removal mechanism. Then, disc cutter wear rate and linear wear rate prediction models are obtained by approximate calculation and mathematical deduction, which are based on Rabinowicz equation and CSM model. At last, the two models are verified through field test data from three projects, and the results show that the prediction model can accurately reflect the real wear situation of disc cutter.     

一种利用GPS进行姿态估计的新算法

提出了一种基于向量化姿态矩阵的姿态解算方法,该方法顾及了观测量之间的相关性及姿态矩阵的正交性。首先将姿态矩阵作为未知参数的估计问题进行向量化,采用经典最小二乘得到无正交约束的姿态解,然后使用几何规则对姿态矩阵进行正交化。该方法不需要初值,不受天线个数及布局限制,在理论上具有广泛的适用性及更好的严密性。仿真结果表明,新的姿态解算方法可以提高GPS姿态解算精度。     

Study on the Infrastructure for Spatial Information in Germany

Infrastructure for spatial information is an important part of our national information construction that is the subject of essentials on the social of spatial information. As an EU member, Germany has...     

用超长基线解算分析汶川地震动态形变特征

以远距离的IGS武汉GPS站为参考站,用超长基线双差瞬时精密定位技术,获取汶川Ms8.0地震震时震区连续GPS站1 Hz动态形变序列。同时以较近距离的雅安站为参考站解算动态形变序列,结果显示,两者的形变结果具有很好的一致性。距离断层较近的郫县、成都、绵阳、中江等站形变较大（形变最大的郫县站最大振幅达1.034 m）;位于震中南侧的邛崃、雅安等站形变较小。利用动态时序的地震波到时和震中距离估计地震波地壳平均速度为3.1 km/s。