Spectral-decomposition techniques for the identification of periodic and anomalous phenomena in radon time-series
Spectral-decomposition techniques for the identification of periodic and anomalous phenomena in radon time-series
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DOI：
10.5194/nhess-10-559-2010
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发表时间：
2010-01-01
影响因子：
4.6
通讯作者：
Richon, P.
中科院分区：
文献类型：
--
作者：
Crockett, R. G. M.;Perrier, F.;Richon, P.
两个小时采样的时间序列的土壤气氡浓度的持续时间为一年的顺序进行了研究的周期性和异常现象。这些时间序列是在很少或没有常规人类行为的地点记录的，因此实际上没有重大的人为影响。一个测量点，Sur-Fretes，位于法国阿尔卑斯山，土壤饱和;第二个测量点，Syabru-Bensi，位于尼泊尔，在河流阶地上，土壤不饱和。在这样的条件下，周期从8小时到7天的周期分量往往是弱的和间歇性的，因此，即使在固定强迫的存在下，难以识别两个谱分解技术，经验模态分解（EMD）和奇异谱分析（SSA），已被应用到这些时间序列，并产生类似的结果。对于Sur-Fretes，EMD观察到弱的昼夜和半日分量，而SSA仅显示昼夜分量。在Syabru-Bensi，EMD和SSA都表现出较强的周日分量和较弱的半日分量。在Sur-Fretes中，EMD也建议了潮汐分量M1和M2，而在Syabru-Bensi中没有观察到这些频率。这种分析技术的发展可以帮助表征土壤气体的表面和地下动态的多个物理过程。
Two hourly-sampled time-series of soil-gas radon concentrations of durations of the order of a year have been investigated for periodic and anomalous phenomena. These time-series have been recorded in locations having little or no routine human behaviour and thus are effectively free of significant anthropogenic influences. One measurement site, Sur-Fretes, is located in the French Alps, with saturated soil conditions; the second site, Syabru-Bensi, is located in Nepal, in a river terrace with unsaturated soil conditions. In such conditions, periodic components with periods ranging from 8 h to 7 days are often weak and intermittent and therefore, even in the presence of stationary forcing, difficult to identify.Two spectral decomposition techniques, Empirical Mode Decomposition (EMD) and Singular Spectrum Analysis (SSA), have been applied to these time series and yield similar results. For Sur-Fretes, weak diurnal and semi-diurnal components are observed with EMD, while SSA reveals only a diurnal component. In Syabru-Bensi, both EMD and SSA reveal a strong diurnal component and a weaker semi-diurnal component. Tidal components M1 and M2 are also suggested by EMD in Sur-Fretes, while these frequencies are not observed in Syabru-Bensi. The development of such analytical techniques can help in characterising the multiple physical processes contributing to the surface and subsurface dynamics of soil gases.