A wavelet-based detection and characterization of damped transient waves occurring in geophysical time-series: theory and application to the search for the translational oscillations of the inner core
A wavelet-based detection and characterization of damped transient waves occurring in geophysical time-series: theory and application to the search for the translational oscillations of the inner core
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DOI：
10.1111/j.1365-246x.2007.03533.x
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发表时间：
2007-10
影响因子：
2.8
通讯作者：
S. Rosat;P. Sailhac;P. Gegout
中科院分区：
文献类型：
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作者：
S. Rosat;P. Sailhac;P. Gegout
摘要含有瞬变激励的非平稳行为的地球物理时间序列需要专门的工具进行分析。特别是，当瞬时激励的强度比噪声低时，很难检测和表征具有扩散衰减的瞬时激励。这是在寻找内核难以捉摸的平移运动时的一个典型问题，也就是所谓的Slichter三元组。这种检测仍然是一个不平凡的问题，因为Slichter三元组的幅度预计会很弱。此外，这些低强度衰减瞬变波的特性(周期、激发时间和品质因数)约束较差。为了更好地检测和表征这种因果衰减瞬变波，我们引入了一种新的基于连续小波的方法，该方法利用与因果衰减正弦波的相关性作为小波基。这种因果阻尼子波(CDW)方法具有直接估计暂态波品质因数的优点。通过一些综合试验，给出了该方法在超导重力仪记录的时变重力数据中寻找Slichter三元组的应用。在所考虑的一年重力数据中，没有发现Slichter三胞胎的证据。然而，我们表明，由于我们的CDW方法的3-D表示，可以对数据集内容有一个完整的概述，并在幅度、品质因数、频率和时间方面限制检测到的事件。
SUMMARY Geophysical time-series with non-stationary behaviour which contain transient excitations need specific tools to be analysed. Especially, it is difficult to detect and characterize transient excitations with attenuation by diffusion when their intensity is low compared to noise. This is a typical question in the search for the elusive translational motion of the inner core, the socalled Slichter triplet. This detection remains a non-trivial problem since the amplitude of the Slichter triplet is expected to be weak. Moreover, the characteristics (period, time of excitation and quality factor) of these low-intensity damped transient waves are poorly constrained. To improve the detection and characterization of such causal damped transient waves, we introduce a new continuous wavelet-based method using correlations with causal damped sinusoids that serve as the wavelet basis. This causal damped wavelet (CDW) method presents the advantage to give a direct estimate of the quality factor of the transient wave. After some synthetic tests, we present an application of the method to the time-varying gravity data recorded by superconducting gravimeters in the search for the Slichter triplet. No evidence of the Slichter triplet has been found in the 1-yr gravity data considered. However, we show that, thanks to the 3-D representation of our CDW method, it is possible to have a complete overview of the data set content and to constrain the detected events in terms of amplitude, quality factor, frequency and time.