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141.
M. D. Sharma 《Journal of Earth System Science》2001,110(3):205-213
Perturbations in elastic constants and density distinguish a volume inhomogeneity from its homogeneous surroundings. The equation
of motion for the first order scattering is studied in the perturbed medium. The scattered waves are generated by the interaction
between the primary waves and the inhomogeneity. First order scattering theory is modified to include the source term generating
the primary waves. The body force equivalent to the scattering source is presented in a convenient form involving the perturbations
in wave velocities and gradient of density perturbation.
A procedure is presented to study the scattering of a spherical pulse from a small inhomogeneity, in time domain. The size
of inhomogeneity is assumed small as compared to its distance from source and receiver. No restrictions are placed on the
positions of source, receiver and inhomogeneity. The dilatation and rotations are calculated for a pulse scattered from an
arbitrary point in a spherical volume. The aggregate of the scattered phases from all the points of the inhomogeneity, reaching
at a fixed receiver, gives the amount of scattering from the inhomogeneity. The interaction of bothP andS waves with inhomogeneity are considered. Dilatation and rotations for scattering are obtained as integral expressions over
the solid angle of inhomogeneity. These expressions are computed numerically, for hypothetical models. The effects of source
(unit force) orientations, velocity and density perturbations, and size of inhomogeneity, on the scattered phases, are discussed. 相似文献
142.
Susan W.S. Millar & Frederick E. Nelson 《Geografiska Annaler: Series A, Physical Geography》2001,83(3):145-156
Samples of macrofabric data obtained from colluvial deposits near the late-Wisconsinan glacial margin display widely divergent characteristics. Those from highly weathered and jointed sandstone plot as girdle distributions. Samples from red colluvium of early-Wisconsinan age form moderately strong clusters. Fabrics from shallow depth in medium-textured brown colluvium of late-Wisconsinan age generally have modes aligned with the local slope but are weak, and appear to have been modified by frost heaving. Clasts in the basal layers of an overlying loess unit were emplaced by frost heaving from the brown colluvium and have very weak or uniform fabrics. Particle shape exerts an influence on fabric strength in the brown colluvium, with samples composed of more elongated clasts displaying stronger fabrics. Fabrics from near-surface deposits show generally weaker shape and strength characteristics and higher inclinations than those at depth. Calculated seasonal frost penetration is consistent with the depth to which weaker, more steeply inclined fabrics are found. Sampling in relict periglacial deposits should be performed only below the level of disturbance by seasonal frost. 相似文献
143.
144.
145.
本文引用S.J.Duda所导出的吸收特征时间t~*与震中距离△的关系,由地震台网观测的地震波振幅A和周期T,求得观测的t_0~*,及t_0~*~△的关系函数,用以拟合不同周期范围地震波品质因数Q 值随深度的分布Q(h),从而计算理论的t~*,再由t~*的残差δt~*与δQ 的关系参照A.M.Dzjewonskj 拟合地幔地震波速度三维分布的方法运用球谐函数的关系拟合地幔地震波品质因数Q 值的三维空间分布。 相似文献
146.
Spectral analysis using orthonormal functions with a case study on the sea surface topography 总被引:1,自引:0,他引:1
Cheinway Hwang 《Geophysical Journal International》1993,115(3):1148-1160
b
Spherical harmonics are orthonormalized using the Gram-Schmidt process in a function space. The problem of linear dependence of spherical harmonics over the oceans is studied using the Gram matrices and consequently three sets of orthonormal (ON) functions have been constructed. For the process an efficient formula for computing inner products of spherical harmonics has been developed. Important spectral properties of the ON functions are addressed. The ON functions may be used for representing the sea surface topography (SST) in the analysis of satellite altimeter data. The geoid error can be transformed to a representation by the ON functions and hence the comparison of powers of the geoid error and the SST signal only over the oceans is possible, leading to a better way of determining the cut-off frequency of the SST in the simultaneous solution using satellite altimeter data. As a case study, the modified Levitus SST is expanded into the ON functions. The results show that 99.90 per cent of that signal's energy is contained within degree 24 of the orthonormal functions. Such expansions also render better spectral behaviour of oceanic signals as compared to that from spherical harmonic expansions. The study shows that these generalized Fourier functions are suitable for spectral analyses of oceanic signals and they can be applied to future altimetric mission where the geoid and the SST are to be recovered. 相似文献
Spherical harmonics are orthonormalized using the Gram-Schmidt process in a function space. The problem of linear dependence of spherical harmonics over the oceans is studied using the Gram matrices and consequently three sets of orthonormal (ON) functions have been constructed. For the process an efficient formula for computing inner products of spherical harmonics has been developed. Important spectral properties of the ON functions are addressed. The ON functions may be used for representing the sea surface topography (SST) in the analysis of satellite altimeter data. The geoid error can be transformed to a representation by the ON functions and hence the comparison of powers of the geoid error and the SST signal only over the oceans is possible, leading to a better way of determining the cut-off frequency of the SST in the simultaneous solution using satellite altimeter data. As a case study, the modified Levitus SST is expanded into the ON functions. The results show that 99.90 per cent of that signal's energy is contained within degree 24 of the orthonormal functions. Such expansions also render better spectral behaviour of oceanic signals as compared to that from spherical harmonic expansions. The study shows that these generalized Fourier functions are suitable for spectral analyses of oceanic signals and they can be applied to future altimetric mission where the geoid and the SST are to be recovered. 相似文献
147.
148.
149.
关于Stokes公式的球面卷积和平面卷积的注记 总被引:2,自引:0,他引:2
晁定波 《武汉大学学报(信息科学版)》2003,28(6):651-654
讨论了Stokes公式球面卷积和平面卷积形式的近似性和严密性问题,分析了Stokes函数球面卷积形式和平面卷积形式的关系,推导了其间的差值表达式,估算了最大差值及其对计算大地水准面差距的误差影响。同时指出,将顾及Stokes函数全项的平面卷积公式称为严密公式的提法,仅仅是相对仅顾及Stokes函数首项的简单平面卷积公式而言,认为更合理的提法应该是“高精度Stokes平面近似卷积公式”。理论分析表明,球面卷积不可能严格转化为等效的平面卷积。 相似文献
150.
NOC model of the earth's main magnetic field 总被引:1,自引:0,他引:1
徐文耀 《中国科学D辑(英文版)》2003,46(9):882-894
The international geomagnetic reference field (IGRF) is a standard model for describing the spatial structure and temporal variation of the earth抯 main magnetic field[1—3]. The first IGRF model, designated IGRF 1965, was adopted by IAGA in 1968[4]. In l… 相似文献