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721.
722.
在柴达木盆地东部石炭系地震勘探过程中,地震层速度是一个重要的参数。层速度不仅仅可以应用于时深转换,还可以应用于反映地层岩性、构造和地层压力等方面的信息,地震剖面与地震速度也密切相关。柴达木盆地东部石炭系由于资料所限,速度问题一直未能很好地解决,时深转换过程中速度误差较大。因此,为了解决研究过程中速度误差较严重的问题,文章在前人工作基础上,探索性地提出了一种新的层速度求取方法,以提高柴达木盆地东部石炭系地震勘探过程中层速度的精度,从而更好的认识本区的构造和地质特征。通过对单井速度分析和二维地震叠加速度多次拾取,保证了速度谱拾取的精度,然后将地震叠加速度换算成均方根速度,进而利用基于单井速度趋势模型约束Dix反演层速度技术将均方根速度转换成层速度,拟合出全区的平均速度场。同时在拟合后,以井上测井速度为控制点,对平均速度进行了合理校正,从而建立比较合理的研究区层速度模型。利用新建立的层速度模型,对原来的构造重新进行时深转换,取得了较好的效果。新的改进Dix公式层速度求取方法求取的速度模型与前人成果相比较,利用了单井速度约束Dix公式进行速度反演,因而比前人成果更精确,更符合单井速度趋势,因而更符合地质认识规律。 相似文献
723.
L. E. Sjöberg 《Journal of Geodesy》2003,77(3-4):139-147
Assuming that the gravity anomaly and disturbing potential are given on a reference ellipsoid, the result of Sjöberg (1988, Bull Geod 62:93–101) is applied to derive the potential coefficients on the bounding sphere of the ellipsoid to order e
2 (i.e. the square of the eccentricity of the ellipsoid). By adding the potential coefficients and continuing the potential downward to the reference ellipsoid, the spherical Stokes formula and its ellipsoidal correction are obtained. The correction is presented in terms of an integral over the unit sphere with the spherical approximation of geoidal height as the argument and only three well-known kernel functions, namely those of Stokes, Vening-Meinesz and the inverse Stokes, lending the correction to practical computations. Finally, the ellipsoidal correction is presented also in terms of spherical harmonic functions. The frequently applied and sometimes questioned approximation of the constant m, a convenient abbreviation in normal gravity field representations, by e
2/2, as introduced by Moritz, is also discussed. It is concluded that this approximation does not significantly affect the ellipsoidal corrections to potential coefficients and Stokes formula. However, whether this standard approach to correct the gravity anomaly agrees with the pure ellipsoidal solution to Stokes formula is still an open question. 相似文献
724.
A computational scheme to model the geoid by the modified Stokes formula without gravity reductions 总被引:2,自引:1,他引:1
L. E. Sjöberg 《Journal of Geodesy》2003,77(7-8):423-432
In a modern application of Stokes formula for geoid determination, regional terrestrial gravity is combined with long-wavelength gravity information supplied by an Earth gravity model. Usually, several corrections must be added to gravity to be consistent with Stokes formula. In contrast, here all such corrections are applied directly to the approximate geoid height determined from the surface gravity anomalies. In this way, a more efficient workload is obtained. As an example, in applications of the direct and first and second indirect topographic effects significant long-wavelength contributions must be considered, all of which are time consuming to compute. By adding all three effects to produce a combined geoid effect, these long-wavelength features largely cancel. The computational scheme, including two least squares modifications of Stokes formula, is outlined, and the specific advantages of this technique, compared to traditional gravity reduction prior to Stokes integration, are summarised in the conclusions and final remarks.
AcknowledgementsThis paper was written whilst the author was a visiting scientist at Curtin University of Technology, Perth, Australia. The hospitality and fruitful discussions with Professor W. Featherstone and his colleagues are gratefully acknowledged. 相似文献
725.
J.M. Chuang 《中国海洋大学学报(英文版)》2005,4(4):357-365
Based on the Fourier transform, the analytical solution of boundary integral equations formulated for the complex velocity of a 2-D steady linear surface flow is derived. It has been found that before the radiation condition is imposed, free waves appear both far upstream and downstream. In order to cancel the free waves in far upstream regions, the eigenso-lution of a specific eigenvalue, which satisfies the homogeneous boundary integral equation, is found and superposed to the analytical solution. An example, a submerged vortex, is used to demonstrate the derived analytical solution. Furthermore, an analytical approach to imposing the radiation condition in the numerical solution of boundary integral equations for 2-D steady linear wave problems is proposed. 相似文献
726.
The analytical continuation bias in geoid determination using potential coefficients and terrestrial gravity data 总被引:1,自引:1,他引:0
J. Ågren 《Journal of Geodesy》2004,78(4-5):314-332
One important application of an Earth Gravity Model (EGM) is to determine the geoid. Since an EGM is represented by an external-type series of spherical harmonics, a biased geoid model is obtained when the EGM is applied inside the masses in continental regions. In order to convert the downward-continued height anomaly to the corresponding geoid undulation, a correction has to be applied for the analytical continuation bias of the geoid height. This technique is here called the geoid bias method. A correction for the geoid bias can also be utilised when an EGM is combined with terrestrial gravity data, using the combined approach to topographic corrections. The geoid bias can be computed either by a strict integral formula, or by means of one or more terms in a binomial expansion. The accuracy of the lowest binomial terms is studied numerically. It is concluded that the first term (of power H2) can be used with high accuracy up to degree 360 everywhere on Earth. If very high mountains are disregarded, then the use of the H2 term can be extended up to maximum degrees as high as 1800. It is also shown that the geoid bias method is practically equal to the technique applied by Rapp, which utilises the quasigeoid-to-geoid separation. Another objective is to carefully consider how the combined approach to topographic corrections should be interpreted. This includes investigations of how the above-mentioned H2 term should be computed, as well as how it can be improved by a correction for the residual geoid bias. It is concluded that the computation of the combined topographic effect is efficient in the case that the residual geoid bias can be neglected, since the computation of the latter is very time consuming. It is nevertheless important to be able to compute the residual bias for individual stations. For reasonable maximum degrees, this can be used to check the quality of the H2 approximation in different situations.Acknowledgement The author would like to thank Prof. L.E. Sjöberg for several ideas and for reading two draft versions of the paper. His support and constructive remarks have improved its quality considerably. The valuable suggestions from three unknown reviewers are also appreciated. 相似文献
727.
Prior to Stokes integration, the gravitational effect of atmospheric masses must be removed from the gravity anomaly g. One theory for the atmospheric gravity effect on the geoid is the well-known International Association of Geodesy approach in connection with Stokes integral formula. Another strategy is the use of a spherical harmonic representation of the topography, i.e. the use of a global topography computed from a set of spherical harmonics. The latter strategy is improved to account for local information. A new formula is derived by combining the local contribution of the atmospheric effect computed from a detailed digital terrain model and the global contribution computed from a spherical harmonic model of the topography. The new formula is tested over Iran and the results are compared with corresponding results from the old formula which only uses the global information. The results show significant differences. The differences between the two formulas reach 17 cm in a test area in Iran. 相似文献
728.
ZHANG Shuqing ZHANG Junyan & ZHANG Bai Northeast Institute of Geography Agricultural Ecology Chinese Academy of Sciences Changchun China Northeast Design Institute of China City Planning Engineering Changchun China 《中国科学D辑(英文版)》2004,47(8):749-759
Topological relation is one important characteris-tics of spatial data, and reflects the structural relation-ships among geographical objects, and is regarded as the core of spatial data processing[1,2]. Topological transformation has been widely used in diverse spatial studies, and in fact, the processing of geographical data is a kind of topological transformations[3]. There-fore, it is of significance to study the mathematical theory of generating and checking topological rela-tions in GIS… 相似文献
729.
730.