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传统CSEM一般只提取主频信号,或以谐波与主频的振幅比为依据提取部分低阶谐波信号,但缺乏判断标准,实际操作中存在很大的不确定性.本文基于小波变换和希尔伯特解析包络提出一种新的CSEM信号噪声评价方法,首先在时间域中基于混合基快速傅里叶变换获得原始信号准确功率谱;其次在频率域中根据CSEM频率位置相邻频率幅值进行频谱预处理,基于离散小波变换将预处理后的频谱分成低频部分和高频部分,基于希尔伯特变换识别高频部分的上包络线,并与低频部分重构得到频谱的整体上包络线;最后根据包络线与对应CSEM频率振幅的比值估计噪声的影响幅度,根据阈值筛选出高信噪比的主频和谐波信号.本方法不需增加野外工作量即可提取大量的频率信号,特别是高阶谐波信号,实现频率加密,提高CSEM的纵向分辨能力和能源利用率. 相似文献
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On the Earth and in its neighborhood, spherical harmonic analysis and synthesis are standard mathematical procedures for
scalar, vector and tensor fields. However, with the advent of multiresolution applications, additional considerations about
convolution filtering with decimation and dilation are required. As global applications often imply discrete observations
on regular grids, computational challenges arise and conflicting claims about spherical harmonic transforms have recently
appeared in the literature. Following an overview of general multiresolution analysis and synthesis, spherical harmonic transforms
are discussed for discrete global computations. For the necessary multi-rate filtering operations, spherical convolutions
along with decimations and dilations are discussed, with practical examples of applications. Concluding remarks are then included
for general applications, with some discussion of the computational complexity involved and the ongoing investigations in
research centers.
Received: 13 November 2000 / Accepted: 12 June 2001 相似文献
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Recent observations from the South China Sea have demonstrated that semi-diurnal tides sometimes generate a double-frequency harmonic. Similar harmonic generation has been found in laboratory experiments and numerical simulations of internal wave beams refracting into a pycnocline. Here, a weakly nonlinear theory of internal wave refraction is applied to oceanic internal tides in an idealized stratification profile. The steady state harmonic amplitude is calculated as a function of the tidal frequency and the pycnocline characteristics. The results indicate that harmonic generation by nonlinear refraction of semi-diurnal tides is consistent with the South China Sea observations. 相似文献
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