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161.
Surface nuclear magnetic resonance signals recovery by integration of a non‐linear decomposition method with statistical analysis
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Presence of noise in the acquisition of surface nuclear magnetic resonance data is inevitable. There are various types of noise, including Gaussian noise, spiky events, and harmonic noise that affect the signal quality of surface nuclear magnetic resonance measurements. In this paper, we describe an application of a two‐step noise suppression approach based on a non‐linear adaptive decomposition technique called complete ensemble empirical mode decomposition in conjunction with a statistical optimization process for enhancing the signal‐to‐noise ratio of the surface nuclear magnetic resonance signal. The filtering procedure starts with applying the complete ensemble empirical mode decomposition method to decompose the noisy surface nuclear magnetic resonance signal into a finite number of intrinsic mode functions. Afterwards, a threshold region based on de‐trended fluctuation analysis is defined to identify the noisy intrinsic mode functions, and then the no‐noise intrinsic mode functions are used to recover the partially de‐noised signal. In the second stage, we applied a statistical method based on the variance criterion to the signal obtained from the initial phase to mitigate the remaining noise. To demonstrate the functionality of the proposed strategy, the method was evaluated on an added‐noise synthetic surface nuclear magnetic resonance signal and on field data. The results show that the proposed procedure allows us to improve the signal‐to‐noise ratio significantly and, consequently, extract the signal parameters (i.e., and V0) from noisy surface nuclear magnetic resonance data efficiently. 相似文献
162.
P. Hosseinzadeh Talaee Mahdi Kouchakzadeh B. Shifteh Some’e 《Theoretical and Applied Climatology》2014,118(1-2):297-305
Assessment of the reliability and quality of historical precipitation data is required in the modeling of hydrology and water resource processes and for climate change studies. The homogeneity of the annual and monthly precipitation data sets throughout Iran was tested using the Bayesian, Cumulative Deviations, and von Neumann tests at a significance level of 0.05. The precipitation records from 41 meteorological stations covering the years between 1966 and 2005 were considered. The annual series of Iranian precipitation were found to be homogeneous by applying the Bayesian and Cumulative Deviations tests, while the von Neumann test detected inhomogeneities at seven stations. Almost all the monthly precipitation data sets are homogeneous and considered as “useful.” The outputs of the statistical tests for the homogeneity analysis of the precipitation time series had discrepancies in some cases which are related to different sensitivities of the tests to break in the time series. It was found that the von Neumann test is more sensitive than the Bayesian and Cumulative Deviations tests in the determination of inhomogeneity in the precipitation series. 相似文献
163.
Roghayeh Shamshiri Mahdi Motagh Marzieh Baes Mohammad Ali Sharifi 《Journal of Geodesy》2014,88(12):1171-1185
This paper presents deformation analysis of Lake Urmia causeway (LUC) embankments in northwest Iran using observations from interferometry synthetic aperture radar (InSAR) and finite element model (FEM) simulation. 58 SAR images including 10 ALOS, 30 Envisat and 18 TerraSAR-X are used to assess settlement of the embankments during 2003–2013. The interferometric dataset includes 140 differential interferograms which are processed using InSAR time series technique of small baseline subset approach. The results show a clear indication of large deformation on the embankments with peak amplitude of \(>\) 50 mm/year in 2003–2010, increasing to \(>\!\!80\) mm/year in 2012–2013 in the line of sight (LOS) direction from ground to the satellite. 2D decomposition of InSAR observations from Envisat and ALOS satellites that overlap in the years 2007–2010 shows that the rate of the vertical settlement and horizontal motion is not uniform along the embankments; Both eastern and western embankments show significant vertical motion, while horizontal motion plays a more significant role in eastern embankment than western embankment. The InSAR results are then used to simulate deformation using FEM at two cross-sections at the distance of 4 and 9 km from the most western edge of the LUC for which detailed stratigraphy data are available. Results suggest that consolidation due to dissipation of excess pore pressure in embankments can satisfactory predict settlement of the LUC embankments. Our numerical modeling indicates that nearly half of the consolidation since the construction time of the causeway 30 years ago has been done. 相似文献
164.
Rockfill is the most abundant building material. It is often used for water retention under different contexts, such as dams, embankments or drainage systems. Climate change may cause water levels to rise in reservoirs. As rockfill structures are not able to resist strong overtopping flow, rising water levels will constitute a danger for rockfill dam stability as well as for people living nearby. This work is aimed at the development of an empirical formula that enables calculation of the critical water level of overflow at the crest from the geometrical and physical parameters of a dam. To achieve these objectives, several experimental tests on a rockfill dam model with two different impervious cores, moraine with a sand filter and an empty wooden formwork, were conducted in a hydraulic channel at the hydro-environmental laboratory at École Polytechnique de Montréal. The purpose of these tests was to study the initiation of a riprap failure under the influence of different variables, such as rock size, riprap bank, downstream side slope and bed slope. Results showed linear trends between the critical water level and both the downstream side slope and bed slope. Also, a power trend was observed between the critical level and riprap grain size. A formula that gives the critical overtopping water level was developed from these results. 相似文献