错格实数傅里叶变换微分算子及其在非均匀介质波动传播研究中的应用

提出一种新的数值微分运算方法，即错格实数傅里叶变换微 分法. 该方法的运算速度 比错格复数傅里叶变换数值微分解法快0.33倍；因为该微分算法在整个微分运算过程中保留 了奈奎斯特分量，使得它比普通分格的实数傅里叶变换数值微分算法的精度高，稳定性好. 将该方法和Cagniard De Hoop解析法在求解半无限空间地震波动的问题中进行比较，结果 表明，新微分法的精度和解析方法的精度相同. 在非均匀介质中的地震波传播数值模拟的结 果表明，该方法是一种研究非均匀介质中地震波传播问题的有效的数值微分方法.     

Merging of Airborne Gravity and Gravity Derived from Satellite Altimetry: Test Cases Along the Coast of Greenland

The National Survey and Cadastre - Denmark (KMS) has for several years produced gravity anomaly maps over the oceans derived from satellite altimetry. During the last four years, KMS has also conducted airborne gravity surveys along the coast of Greenland dedicated to complement the existing onshore gravity coverage and fill in new data in the very-near coastal area, where altimetry data may contain gross errors. The airborne surveys extend from the coastline to approximately 100 km offshore, along 6000 km of coastline. An adequate merging of these different data sources is important for the use of gravity data especially, when computing geoid models in coastal regions.The presence of reliable marine gravity data for independent control offers an opportunity to study procedures for the merging of airborne and satellite data around Greenland. Two different merging techniques, both based on collocation, are investigated in this paper. Collocation offers a way of combining the individual airborne gravity observation with either the residual geoid observations derived from satellite altimetry or with gravity derived from these data using the inverse Stokes method implemented by Fast Fourier Transform (FFT).     

积分半径可控地形改正FFT算法的研究

地形改正等地球重力场元量的FFT算法(平面二维、球面近似二维、球面单带)研究已基本成熟,并广泛应用于科研与工程实践。但是FFT算法也有其固有的缺陷,即存在着频谱混迭、泄漏等现象。本文利用离散卷积分具有Toeplitz矩阵的性质,将其拓展为循环Toeplitz与拓展观测数据矢量的乘积,利用循环Toeplitz的Fourier表示,实现离散卷积分的快速算法。该算法与离散求和等价,当数据量较大时,可明显地提高计算速度。     

频率细化技术在超低频/极低频电磁信号检测中的应用

离散快速傅里叶变换算法在频谱分析中得到了广泛的应用，这种算法得到的计算结果是在整个频段上的频谱信息. 在一些应用中，需要了解的仅仅是某一窄带内的频谱精细结构，要求频谱的分辨率较高. 而要得到一个较高分辨率的频谱，直接采用快速傅里叶变换计算则会导致参加快速傅里叶变换运算的数据点数的增加，从而引起计算量和存储量的急剧增大，这样，快速傅里叶变换算法就不能满足要求了. 本文介绍了基于复调制的频率细化技术的原理及其在超低频/极低频电磁接收机研制中的应用，阐述了采用这种技术如何实现高分辨率频谱的计算，并给出了理论数据和实际观测数据的计算结果.      

利用FFT技术计算垂线偏差研究

首先导出了更加严密的二维平面FFT垂线偏差计算公式 ,在深入分析和比较二维平面和二维球面FFT算法特点和差异的基础上 ,给出了二维球面FFT计算公式的改进形式 ,并通过大量的数值计算 ,详细讨论了参考场选取、积分球冠半径确定、边缘效应、积分元离散化误差以及计算点奇异积分处理对垂线偏差计算结果的作用和影响。最后 ,利用全国 5′× 5′实测重力异常对我国海陆垂线偏差进行了试算 ,并将计算结果同实际观测值作了比较。     

The FFT Moving Average (FFT-MA) Generator: An Efficient Numerical Method for Generating and Conditioning Gaussian Simulations

A fast Fourier transform (FFT) moving average (FFT-MA) method for generating Gaussian stochastic processes is derived. Using discrete Fourier transforms makes the calculations easy and fast so that large random fields can be produced. On the other hand, the basic moving average frame allows us to uncouple the random numbers from the structural parameters (mean, variance, correlation length, ... ), but also to draw the randomness components in spatial domain. Such features impart great flexibility to the FFT-MA generator. For instance, changing only the random numbers gives distinct realizations all having the same covariance function. Similarly, several realizations can be built from the same random number set, but from different structural parameters. Integrating the FFT-MA generator into an optimization procedure provides a tool theoretically capable to determine the random numbers identifying the Gaussian field as well as the structural parameters from dynamic data. Moreover, all or only some of the random numbers can be perturbed so that realizations produced using the FFT-MA generator can be locally updated through an optimization process.     

新沂地电场日变化特征及频谱分析

通过对新沂地电场平静时段资料与地磁场资料对比分析,结果显示:新沂地震台地电场变化和变化磁场密切相关,其中NS向的主体变化和地磁场H分量的变化准同步;EW向主体变化虽与地磁场H分量变化有相同之处,但其变化形态与其反向,且不尽相同.运用快速傅里叶变换进行频谱分析,发现:新沂地电场NS向和EW向与地磁场H分量的优势周期存在不...     

海浪预报三维动画计算原理与制作方法

研究了基于线性海浪模型制作三维动画海浪预报产品的制作方法,并制作了首个三维动画海浪警报产品.基本步骤为:由线性海浪模型生成一系列不同波高和波长的二维海面高度场,以及这些波面高度场对应的反光系数场;根据海浪预报图中波高的空间分布情况将不同波高的波面高度场拼接成复合的波面高度场,同时拼接出与之对应的复合反光系数场;由复合的...     

nhanced Destriping of Satellite Data of Ice Surface in Antarctica

This paper briefly reviews the cause of the striping and then develops a tapered (Chebwin & Kaiser) window finite impulse response (FIR) filter and a constrained least squares FIR filter by reason of the striping of ASTER satellite data . Both filters minimize the stripes in the visible data and simultaneously minimize any distortion in the filtered data. Finally, the results obtained by using these new filtering methods are quantitatively compared with those produced by other destriping methods.     

汶川MS8.0级地震前后ULF电磁辐射频谱特征研究

本文基于电磁波频谱理论研究方法,对2008年四川汶川M_S8.0地震前后金河、剑阁及郑州二砂三个电磁波台站的观测资料进行FFT和小波变换分析,研究了电磁辐射数据快速傅里叶频谱变化特征和在不同尺度下小波变化的分解,发现在汶川地震前确实有异常信息存在.结果表明:(1) FFT动态谱图像说明,地震前电磁波频谱变化特征较明显,在时间、频段上均显示了阶段性进程特征,且随着震中距的增大,辐射能量越小,异常出现的时间越晚;(2) 小波分解显示了地震前电磁波异常信号低频部分出现的时间较早;距震中较近的台站,异常信息在高频部分相对明显;距震中稍远的台站,异常信息在低频部分相对明显.