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1.
At many sites on soft ground, spectral ratios (ratios of smoothed Fourier amplitude spectral ordinates at the site to those at a station on firm ground) for distant earthquakes are little sensitive to focal mechanism and coordinates and to magnitude. Spectral ratios furnish directly expected Fourier amplitude spectral ordinates at the site of interest. The corresponding response spectra can be estimated through the use of random vibration theory. This step is obviated by resorting directly to ratios of response spectral ordinates. Through comparisons for several sites on the Valley of Mexico we find that these ratios are as stable as those of Fourier amplitude spectral ordinates. 相似文献
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3.
A structural mode was used to characterize vegetation composition at the plant leaf level and a flourishing-withering ratio was developed. The spectral responses of vegetation with different flourishing-withering ratios were analyzed, the change rates of the chlorophyll and moisture content indices of vegetation with different flourishing-withering ratios were compared, and correlations between the chlorophyll and moisture content indices were analyzed. The results reveal that leaves with an intermediate flourishing-withering ratio can increase the absorption signatures of vegetation and that band ranges of 570–700 nm and 1300–1540 nm can play a role in indicating changes in the flourishing-withering ratios of vegetation; NPQI, NPCI, R695/R420, R695/R760, R750/R700, the peak-value area of red selvedge, the red selvedge amplitude, the ratio between the red selvedge amplitude and the minimum amplitude, and the NDVI of vegetation change regularly with the change in flourishing-withering ratios, and these nine vegetation indices are highly related to the chlorophyll content. Vegetation indexes of NDWI and PRI are very sensitive to the flourishing-withering change in vegetation and are closely related to the moisture content, and the correlation coefficient is higher than 0.9. The derivative of the spectra is more effective in describing changes in the structural mode of vegetation with different flourishing-withering ratios, especially at band ranges of 552–628 nm and 630–686 nm, and it is more sensitive to the mixed flourishing-withering ratios of leaves rather than to the vegetation indices. The red selvedge position in the spectrum is highly related to the chlorophyll content and is not sensitive to changes in the structural mode of mixed flourishing-withering leaves. The red selvedge parameters are sensitive to changes in the flourishing-withering ratio at the peak-value area of the red selvedge amplitude and the ratio between the red selvedge amplitude and the minimum amplitude. The effect of a sand background on the spectrum of withering leaves is higher than that of flourishing leaves; the effect of a sand background increases with increasing proportions of withering leaves, the superposition effect of the sand background on mixed flourishing-withering leaves is about 7% at visible light bands of 400–700 nm and 1300–1540 nm, and is over 10% at the near infrared band range of 700–1300 nm. 相似文献
4.
分频解释技术已经越来越多的应用到地震储层预测和油藏描述中,成为地震解释的一种常规技术手段,分频解释技术中分频RGB颜色融合显示方法因其独有的视觉效果也开始受到关注.本文介绍了分频混色技术在高精度地震解释中的应用以及在应用过程中应注意的几点问题,包括优选高精度频谱分解方法、RGB颜色融合技术应用中频率选择的原则等.在此基础上,进一步探讨了分频数据RGB混色方法能有效解决地震沉积学中地层切片精度不满足薄储层预测的问题.RGB颜色融合显示方法能充分发掘高精度地震数据宽频的优势,得到精度更高的储层预测结果. 相似文献
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Spectral phases of surface waves radiated at the seismic source are recovered by means of the Hilbert transform of spectral amplitudes. Through numerical simulations as well as the study of an earthquake with well known focal mechanism, it is shown that the recovered phases satisfy a criterion of coherency, so that they can be used in an inversion process for the retrieval of the seismic moment tensor. 相似文献
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nua m¶rt; nma aaua a, umua m nma, m n¶rt;um umau nuau un nmam. m¶rt; annua aaum nauu Pi2 u Pc3 u amu u u ¶rt;. ¶rt;a ma m ¶rt; nmam nuau aamumu u u auum m aum amumu. 相似文献
7.
A. R. Rao A. Durgunoglu 《Stochastic Environmental Research and Risk Assessment (SERRA)》1988,2(1):35-50
Autoregressive (AR) and Autoregressive-moving average (ARMA) methods of spectral analysis have been developed and are being increasingly used as alternatives to traditional methods of spectral analysis. Two of these methods developed by Marple and Friedlander are tested in this study by using generated data from models with known spectra. The Blackman-Tukey spectral estimates are also compared to the Marple and Friedlander estimates. The variability of the Marple and Friedlander estimates with sample sizes is investigated. Although both Marple's and Friedlander's methods are satisfactory, Friedlander's method is preferred because of its ability to handle a wider class of models. 相似文献
8.
A. Ian McLeod K. W. Hipel 《Stochastic Environmental Research and Risk Assessment (SERRA)》1995,9(3):171-205
Current methods of estimation of the univariate spectral density are reviewed and some improvements are made. It is suggested that spectral analysis may perhaps be best thought of as another exploratory data analysis (EDA) tool which complements, rather than competes with, the popular ARMA model building approach. A new diagnostic check for ARMA model adequacy based on the nonparametric spectral density is introduced. Additionally, two new algorithms for fast computation of the autoregressive spectral density function are presented. For improving interpretation of results, a new style of plotting the spectral density function is suggested. Exploratory spectral analyses of a number of hydrological time series are performed and some interesting periodicities are suggested for further investigation. The application of spectral analysis to determine the possible existence of long memory in natural time series is discussed with respect to long riverflow, treering and mud varve series. Moreover, a comparison of the estimated spectral densities suggests the ARMA models fitted previously to these datasets adequately describe the low frequency component. Finally, the software and data used in this paper are available by anonymous ftp from fisher.stats.uwo.ca. 相似文献
9.
Total ozone data series for 1957–82 at ten locations were subjected to Maximum Entropy Spectral Analysis. Besides the annual, semi-annual, and quasi-biennial oscillations, peaks were noticed at 3.5–4, 6–7, and 10–11 years. For Arosa, Switzerland, for a longer period (1932–71), an additional peak was indicated at about 16 years. 相似文献
10.
Summary The method of two-component spectral analysis is described in two versions: as the so-called static analysis, in which the pulsation sample being studied is treated as a whole, and as the dynamic analysis, in which the given sample is processed piecewise in order to determine the time variations of various parameters. Both versions were applied to geomagnetic pi2 pulsations. The pi2 oscillations are resolved into several frequency components. The properties of these components are studied in dependence on the frequency and local time. The time variation of the amplitude (attenuation) and the polarization characteristics (precession) of pi2's are also studied. 相似文献
11.
Spatial variation of the surface micro‐relief in a Sharkey clay soil was investigated. The micro‐relief measurements of the soil surface were obtained using an automated infrared laser system and evaluated with methods of Fourier analysis. The authors illustrate the spectral technique with a simple example and then use the technique to interpret the surface micro‐relief patterns of soil samples subjected to three simulated rainstorm intensities. The periodicity of the soil surface micro‐relief in the longitudinal direction was 80–120 mm. The periodic surface micro‐relief patterns immediately following the rainstorm are shown to be an early manifestation of the cracking pattern. Published in 2006 by John Wiley & Sons, Ltd. 相似文献
12.
Dr. F. Volz 《Pure and Applied Geophysics》1955,31(1):119-123
Summary The indices of the wavelength dependency of the haze extinction which were currently determined from measurements of solar radiation and visibility at Mainz, show pronounced seasonal variations. The summer values are in general definitely higher than in winter. There is no connection with the scatter light types of the sky-light or with the meteorological situation.
Zusammenfassung Die Wellenlängenexponenten der Dunstextinktion, die in Mainz laufend aus Messungen der Sonnenstrahlung und der Sicht bestimmt wurden, zeigen starke jahreszeitliche Variationen. Insbesonders sind die Werte im Sommer meist deutlich höher als im Winter. Ein Zusammenhang mit den Streulichttypen des Himmelslichts oder der meteorologischen Situation besteht nicht.
Sommaire L'exposant de la longueur d'onde de l'extinction brumeuse qui a été déterminé de façon continue des mesures de la radiation solaire et de la visibilité montre des fortes variations annuelles. Tout spécialement les valeurs sont d'été sensiblement plus élevées que celles en hiver. Une relation avec les types de lumière diffuse céleste et la situation météorologique n'existe pas.相似文献
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This study is to evaluate the applicability of estimating the one-dimensional horizontal hydraulic diffusivity of an unconfined
aquifer with time-dependent fluctuation of lateral head and vertical recharge boundaries using observed water level spectra.
Different models of boundary condition are imposed to evaluate the statistical significance between the calculated hydraulic
diffusivity (ξ′) with the given hydraulic diffusivity (ξ). The auto-spectra of the water level in observation wells tapping the same aquifer
are closely related to those at the disturbed boundaries. For an aquifer with a constant hydraulic diffusivity, the water
level fluctuation in the monitoring wells is linearly related to the water level spectra observed at the boundaries. The spectral
density function of aquifer hydraulic head varies inversely with specific yield (S
y) and directly with recharge. Given small variation in water level spectra at the disturbed boundaries, the water level fluctuation
in the aquifer is affected by the recharge condition and the aquifer spectral density function is sensitive to S
y. Using an iterative technique to estimate ξ from 1400 sets of given parameters, 99% of the ξ′/ξ values deviated within only one order of magnitude with the model length (L) being equal to 1 km and 10 km. For L equal to 100 m, approximately 82% of the ξ′/ξ population falls within two orders of magnitude. Therefore, spectral analysis of aquifer hydraulic head response can be
used to estimate the hydraulic diffusivity of an unconfined aquifer which is affected by periodic variations in recharge and
head at boundaries. 相似文献
15.
谱分析在识别初至P波中的应用 总被引：1，自引：1，他引：0
崔东源 《地震地磁观测与研究》2008,29(4):91-94
由于台站周围环境噪声干扰的增强,台站人员无法识别被背景噪声淹没的初至P波。我们利用DIMAS分析软件包中的谱分析方法,寻找初至P波的卓越周期,改善台站人员识别地震波的能力。 相似文献
16.
The next generation of seismic design codes, especially those adopting the framework of performance‐based design, will include the option of design based on displacements rather than forces. For direct displacement‐based design using the substitute structure approach, the spectral ordinates of displacement need to be specified for a wide range of response periods and for several levels of damping. The code displacement spectra for damping values higher than the nominal value of 5% of critical will generally be obtained, as is the case in Eurocode 8 and other design codes, by applying scaling factors to the 5% damped ordinates. These scaling factors are defined as functions of the damping ratio and, in some cases, the response period, but are independent of the nature of the expected ground shaking. Using both predictive equations for spectral ordinates at several damping levels and stochastic simulations, it is shown that the scaling factors for different damping levels vary with magnitude and distance, reflecting a dependence of the scaling on the duration of shaking that increases with the damping ratio. The options for incorporating the influence of this factor into design code specifications of displacement response spectra are discussed. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
17.
The presence of noise during dynamic measurements is one of the main sources of errors during integration procedures. To overcome this problem a methodology involving spectral subtraction of the noise amplitude from the signal is presented where noise characteristics are specified during ‘silence’ periods. This technique has been used for speech enhancement, and in this paper it is used to improve the integration procedure. The performance of the method is evaluated by means of both synthetic and real applications and by comparison with standard integration procedures. The proposed method has proven to lead to improved results, being a convenient way to address the integration problem, when noise is a major source of errors in the signal. 相似文献
18.
The paper deals with the evaluation of non-stationary spectral moments of multi-degree-of-freedom (MDOF) line systems subjected to seismic excitations. The spectral moments of the response are evaluated in incremental form solution by means of an unconditionally stable step-by-step procedure. As an application, the statistics of the largest peak of the response are also evaluated. 相似文献
19.
For four years measurements of solar radiation have been made with an instrument which observes the sky radiance in two spectral regions. The measured incident radiation is independent of the direction. Formulas are derived which allow to conclude the daily sun intensity in one region, knowing the measured intensity in the other region. The effect of ozone is noticeable in the difference between the measured and computed values in an ozone-absorbing region. The optical behaviour of the atmosphere can be defined by parameterization of extinction effects. From this one can conclude the intensity of any other spectral region and thus define selective influences of other absorbing gases like air-polluting constituents. 相似文献
20.
D. C.-F. Shih 《Stochastic Environmental Research and Risk Assessment (SERRA)》1999,13(1-2):85-99
This study uses the cyclical frequency to develop the mathematical relationship between hydraulic diffusivity and spectral
density functions calculated from groundwater level variation. Such relationship can be applied to (1) unsteady state, one-dimensional
confined aquifer with time-dependent water level on both end boundaries, and (2) linearized unconfined aquifer with or without
vertical recharge. The spectral density functions of groundwater fluctuations are largely affected by the spectral density
functions obtained from time-dependent end boundaries and their cross-spectral density functions. Hydraulic diffusivity of
an aquifer can be solved by type-curve matching technique at a specified frequency band under the conditions of (1) confined
aquifer having equal time-dependent boundaries on both ends, (2) unconfined aquifer having equal time-dependent boundaries
on both ends with surface recharge, and (3) unconfined aquifer subjected to surface recharge but neglecting the water table
fluctuations on both end boundaries. 相似文献