Robust reconstruction of aliased data using autoregressive spectral estimates

Autoregressive modeling is used to estimate the spectrum of aliased data. A region of spectral support is determined by identifying the location of peaks in the estimated spatial spectrum of the data. This information is used to pose a Fourier reconstruction problem that inverts for a few dominant wavenumbers that are required to model the data. Synthetic and real data examples are used to illustrate the method. In particular, we show that the proposed method can accurately reconstruct aliased data and data with gaps.     

插值公式、相关系数和采样间隔对GRACE Follow-On 星间加速度精度的影响

本文基于星间加速度法开展了插值公式、相关系数和采样间隔对GRACE Follow-On星间加速度精度影响的研究. 模拟结果表明:1)适当增加数值微分公式的插值点数可有效提高插值精度. 基于9点Newton插值公式,星间加速度的插值误差为4.401×10^-13 m·s^-2,分别基于7点、5点和3点插值公式,插值误差增加了1.192倍、6.912倍和274.029倍. 2)适当增大相关系数可有效降低星间加速度的误差. 基于相关系数0.99,星间加速度方差为3.777×10^-24 m²·s^-4,分别基于相关系数0.90、0.70、0.50和0.00,方差增加了9.780倍、22.404倍、26.217倍和26.820倍. 3)随着采样间隔增大,星间加速度方差逐渐降低,但卫星观测值的空间分辨率也同时降低,因此合理选取采样间隔有利于地球重力场精度的提高. 4)基于9点Newton插值公式、相关系数(K波段测量系统星间距离和星间速度0.85、GPS轨道位置和轨道速度0.95、星载加速度计非保守力0.90)和采样间隔10 s,利用预处理共轭梯度迭代法,精确和快速反演了120阶GRACE Follow-On地球重力场,在120阶处累计大地水准面精度为4.602×10^-4 m.     

Optimal implicit staggered‐grid finite‐difference schemes based on the sampling approximation method for seismic modelling

We propose new implicit staggered‐grid finite‐difference schemes with optimal coefficients based on the sampling approximation method to improve the numerical solution accuracy for seismic modelling. We first derive the optimized implicit staggered‐grid finite‐difference coefficients of arbitrary even‐order accuracy for the first‐order spatial derivatives using the plane‐wave theory and the direct sampling approximation method. Then, the implicit staggered‐grid finite‐difference coefficients based on sampling approximation, which can widen the range of wavenumber with great accuracy, are used to solve the first‐order spatial derivatives. By comparing the numerical dispersion of the implicit staggered‐grid finite‐difference schemes based on sampling approximation, Taylor series expansion, and least squares, we find that the optimal implicit staggered‐grid finite‐difference scheme based on sampling approximation achieves greater precision than that based on Taylor series expansion over a wider range of wavenumbers, although it has similar accuracy to that based on least squares. Finally, we apply the implicit staggered‐grid finite difference based on sampling approximation to numerical modelling. The modelling results demonstrate that the new optimal method can efficiently suppress numerical dispersion and lead to greater accuracy compared with the implicit staggered‐grid finite difference based on Taylor series expansion. In addition, the results also indicate the computational cost of the implicit staggered‐grid finite difference based on sampling approximation is almost the same as the implicit staggered‐grid finite difference based on Taylor series expansion.     

CST-based first order second moment method for probabilistic slope stability analysis

Correlated random variables are commonly involved in probabilistic slope stability analysis, such as reliability analysis of slopes with spatially variable soil properties. This paper proposes a simple Correlated Sampling Technique (CST) for generating samples of correlated random variables. The CST firstly produces correlated standard-normally distributed samples through linear combinations of independent standard-normally distributed samples. Correlated arbitrarily distributed samples can then be obtained by the Nataf transformation. The CST was combined with FOSM (named CST-based FOSM) for probabilistic slope stability analysis. The slope reliabilities of a single-layered cohesive soil slope and a high earth and rockfill dam were analyzed to illustrate the CST-based FOSM. These illustrative examples indicated that the CST-based FOSM can accurately estimate the slope reliability indices with considerably fewer simulations (especially in the case of low failure probability) compared with direct MCS, and the slope reliability was sensitive to the correlation of the strength parameters.     

亚洲象生境评价

本文阐述了通过外业抽样调查进行亚洲象生境因子定量分析，利用遥感技术提取生境专题信息建立数据库，在此基础上，应用ＧＩＳ对西双版纳勐养自然保护区亚洲象生境因子进行评价。同时，提出改善栖息地环境质量的治理方案。     

成矿预测中非参数蒙特卡洛模拟方法研究

非参数方法是在成矿预测中、当统计数据不服从或不完全服从现则分布时的一种蒙特卡洛模拟形式 非参数方法采用拉格朗日插值函数和三次条样函数,并均满足密度函数的条件.可以对统计数据进行拟合.借以建立各种抽样模型 即便是离散型数据.也可用牛顿插值法为其建立非参数抽样模型 因而.它具有算法统一.编程简单和有利于计算机自动化模拟等优点.具有广阔的应用前景     

A Monte Carlo study of rainfall forecasting with a stochastic model

A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities.     

Accuracy of two sampling methods used to estimate sediment concentrations in runoff from soil-loss plots

The use of a bottle sampler and a soil pipette to quickly and accurately sample soil-water mixtures of known sediment concentrations was tested. Both devices failed to sample adequately soil-water mixtures containing 1–187 gl^?1 of solid particles. Poor sampling ability was attributed to rapid settlement of larger particles and to innate deficiencies in the sediment trapping ability of the samplers. These sampling devices should not be used to estimate sediment loads in runoff from soil-loss plots, and erosion data from plot studies which have used a sediment sampling procedure should be treated with caution.     

估计迹长概率分布函数的新方法及其应用

本文提出一种估计迹长概率分布函数的新方法。该方法的优点是不需要有节理在测窗上出露长度的数据，有效的减少了野外工作量     

Radon变换的抽样取值与小波

Radon变换在实际应用中必须考虑抽样取值的问题,通信理论中常用的Shannon取样定理在地球物理学等领域中并不适用,因为它要求函数是频谱有限的.本义介绍利用小波理论建立新的取样定理的方法,这一方法的优点在于可以根据具体问题的要求选取适当的基本空间V_0,从而获得较佳的抽样插值效果.