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101.
The present study demonstrates the use of ambient noise for estimating the ocean depth in shallow waters of the Indian continental shelf. Ocean depth is estimated using a technique known as passive fathometer processing, which involves the correlation of surface-generated ambient noise with its reflection from the seabed. Ambient noise data collected using a vertical array from four locations (off Cochin, off Cuddalore, off Kakinada, and off Goa) along the Indian continental shelf were used for the study. The noise data recorded during windy conditions within the frequency band of 200–5000 Hz were used for analysis. Both conventional and adaptive beamforming techniques were applied for the passive estimation of the ocean depth. The estimated water column depth using the ambient noise measurement shows good agreement with the known depth from all the four locations. The advantages and limitations of the adaptive processing technique have also been discussed. The study clearly demonstrates the application of the surface-generated ambient noise in seabed image processing. 相似文献
102.
Ambient vibration tests of a seven-story reinforced concrete building in Van Nuys, California, damaged by the 1994 Northridge earthquake 总被引:3,自引:0,他引:3
S. S. Ivanovi M. D. Trifunac E. I. Novikova A. A. Gladkov M. I. Todorovska 《Soil Dynamics and Earthquake Engineering》2000,19(6):974
Results of two detailed ambient vibration surveys of a 7-story reinforced concrete building in Van Nuys, California, are presented. Both surveys were conducted after the building was severely damaged by the 17 January 1994, Northridge earthquake (ML=5.3, epicenter 1.5 km west from the building site) and its early aftershocks. The first survey was conducted on 4 and 5 February 1994, and the second one on 19 and 20 April 1994, about one month after the 20 March aftershock (ML=5.3, epicenter 1.2 km north–west from the building site). The apparent frequencies and two- and three-dimensional mode shapes for longitudinal, transverse and vertical vibrations were calculated. The attempts to detect the highly localized damage by simple spectral analyses of the ambient noise data were not successful. It is suggested that very high spatial resolution of recording points is required to identify localized column and beam damage, due to the complex building behavior, with many interacting structural components. The loss of the axial capacity of the damaged columns could be seen in the vertical response of the columns, but similar moderate or weak damage typically would not be noticed in ambient vibration surveys. Previous analysis of the recorded response of this building to 12 earthquakes suggests that, during large response of the foundation and piles, the soil is pushed sideways and gaps form between the foundation and the soil. These gaps appear to be closing during “dynamic compaction” when the building site is shaken by many small aftershocks. The apparent frequencies of the soil–foundation–structure system appear to be influenced significantly by variations in the effective soil–foundation stiffness. These variations can be monitored by a sequence of specialized ambient vibration tests. 相似文献
103.
多尺度CB形态学及其在线划图像噪声清除中的应用 总被引:1,自引:0,他引:1
介绍了基于轮廓结构元的形态学(简称CB形态学)的概念及其性质,讨论了CB形态运算的快速实现。由于CB形态学处理的对象不是基于目标的形状,而是基于目标的延伸度,因此它可以用来处理线划图像。在本文中,利用CB形态学的这一特性消除线划图像上的噪声,获得了满意的结果。 相似文献
104.
地震资料叠前去噪技术的现状与未来 总被引:26,自引:10,他引:26
地震资料叠前去噪是勘探地震资料处理的关键问题之一,但这个问题长期以来一直没有得到很好的解决,是提高地震资料分辨率的一个主要障碍,其中,如何有效地消除产生与地层间的多次反射波又是地震资料叠前去噪的核心问题。为此,人们进行了长期不懈的努力,以更好地消除多次波。本文着重概述现今实生常中常用的几种比较有效的消除多次波方法,包括拉冬变换,F-K方法和聚束滤波方法;同时也概述了预测反积消除水层混响和用K-L变换方法消除随机噪音提高信噪比等方法;最后,还讨论了近年发展的地震资料叠前去噪新方法及其发展趋势。 相似文献
105.
A. A. Panou N.P. Theodulidis P.M. Hatzidimitriou A.S. Savvaidis C.B. Papazachos 《Pure and Applied Geophysics》2005,162(5):891-912
In the framework of an ambient noise measurement project in the downtown district of the City of Thessaloniki (Northern Greece), several tests and evaluation of noise recordings were performed in selected sites. This data set was processed and compared with previous results for the same sites in terms of horizontal-to-vertical (H/V) spectral ratio obtained from weak and strong motion earthquake data. The recording system used was tested against a reference one. Finally, systematic ambient noise measurements were performed at eight sites in the citys downtown area, to evaluate diurnal and seasonal variations. It was concluded that the recording system used was reliable and the ambient noise H/V spectral ratios were in good agreement with relevant results previously obtained. Diurnal variation of the ambient noise H/V spectral ratio showed that it is preferable to perform measurements during the calm hours of the day, when man-made noise is relatively low. However, no systematic seasonal fluctuation effect on the ambient noise H/V spectral ratio was identified. 相似文献
106.
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109.
Efficiency of carrier-phase integer ambiguity resolution for precise GPS positioning in noisy environments 总被引:1,自引:0,他引:1
Precise GPS positioning relies on tracking the carrier-phase. The fractional part of carrier-phase can be measured directly
using a standard phase-locked loop, but the integer part is ambiguous and the ambiguity must be resolved based on sequential
carrier-phase measurements to ensure the required positioning precision. In the presence of large phase-measurement noise,
as can be expected in a jamming environment for example, the amount of data required to resolve the integer ambiguity can
be large, which requires a long time for any generic integer parameter estimation algorithm to converge. A key question of
interest in significant applications of GPS where fast and accurate positioning is desired is then how the convergence time
depends on the noise amplitude. Here we address this question by investigating integer least-sqaures estimation algorithms.
Our theoretical derivation and numerical experiments indicate that the convergence time increases linearly with the noise
variance, suggesting a less stringent requirement for the convergence time than intuitively expected, even in a jamming environment
where the phase noise amplitude is large. This finding can be useful for practical design of GPS-based systems in a jamming
environment, for which the ambiguity resolution time for precise positioning may be critical. 相似文献
110.
Paula Teves-Costa Carlos S. Oliveira M. Luisa Senos 《Soil Dynamics and Earthquake Engineering》2007,27(11):986-999
During the Mw=6.9 January 1, 1980 earthquake in the Azores, the damage distribution in the town of Angra do Heroísmo, in Terceira Island, had a non-homogeneous spatial character. In order to understand the observed pattern of damage a microtremor survey was carried out, using ambient vibrations, and the data were analysed with the J-Sesame software, following the H/V Nakamura methodology. The results are in good agreement with the surface geology and they show a good correlation with the observed damages. Two building surveys were performed, in 1980 on damage evaluation and in 2000 on characterization of few building parameters. With all these elements (surface geology type, soil peak frequency, building type, number of stories and damage level) for 2111 buildings it was possible to perform several interparameter analysis, which enabled the identification of indicators that could be used to improve the damage estimation for future events. 相似文献