Emergence of Acoustic Green's Functions from Time Averages of Ambient Noise

2011 ◽  
Vol 97 (1) ◽  
pp. 44-53 ◽  
Author(s):  
Nikolay A. Zabotin ◽  
Oleg A. Godin
Keyword(s):  
Ambient Noise ◽  
Green's Functions ◽  
Green’S Functions ◽  
Time Averages

scholarly journals An adapted eigenvalue-based filter for ocean ambient noise processing

Geophysics ◽  
2020 ◽  
Vol 85 (1) ◽  
pp. KS29-KS38 ◽  
Author(s):  
Guoli Wu ◽  
Hefeng Dong ◽  
Ganpan Ke ◽  
Junqiang Song
Keyword(s):  
Covariance Matrix ◽  
Ambient Noise ◽  
Green's Functions ◽  
Green’S Functions ◽  
Homogeneous Distribution ◽  
Noise Sources ◽  
Data Set ◽  
Recording Time ◽  
Receiver Array ◽  
Sample Covariance

Accurate approximations of Green’s functions retrieved from the correlations of ambient noise require a homogeneous distribution of random and uncorrelated noise sources. In the real world, the existence of highly coherent, strong directional noise generated by ships, earthquakes, and other human activities can result in biases in the ambient-noise crosscorrelations (NCCs). We have developed an adapted eigenvalue-based filter to attenuate the interference of strong directional sources. The filter is based on the statistical model of the sample covariance matrix and can separate different components of the data covariance matrix in the eigenvalue spectrum. To improve the effectiveness and make it adaptable for different data sets, a weight is introduced to the filter. Then, the NCCs can be calculated directly from the filtered data covariance matrix. This approach is applied to a 1.02 h data set of ambient noise recorded by a permanent reservoir monitoring receiver array installed on the seabed. The power spectral density indicates that the noise recordings were contaminated by strong directional noise over nearly half of the whole observation period. Beamforming and crosscorrelation results indicate that the interference still exists even after applying traditional temporal and spectral normalization techniques, whereas the adapted eigenvalue-based filter can significantly attenuate it and help to obtain improved crosscorrelations. The approach makes it possible to retrieve reliable approximations of Green’s functions over a much shorter recording time.

Estimation of surface wave Green's functions from correlation of direct waves, coda waves, and ambient noise in SE Tibet

2009 ◽  
Vol 177 (1-2) ◽  
pp. 1-11 ◽  
Author(s):  
Huajian Yao ◽  
Xander Campman ◽  
Maarten V. de Hoop ◽  
Robert D. van der Hilst
Keyword(s):  
Surface Wave ◽  
Ambient Noise ◽  
Green's Functions ◽  
Green’S Functions ◽  
Coda Waves ◽  
Se Tibet

Computing Green's Functions from Ambient Noise Recorded by Accelerometers and Analog, Broadband, and Narrow-Band Seismometers

2011 ◽  
Vol 82 (5) ◽  
pp. 661-675 ◽  
Author(s):  
I. M. Tibuleac ◽  
D. H. von Seggern ◽  
J. G. Anderson ◽  
J. N. Louie
Keyword(s):  
Ambient Noise ◽  
Green's Functions ◽  
Narrow Band ◽  
Green’S Functions

Application of temporal reweighting to ambient noise cross-correlation for improved seismic Green's function

2020 ◽  
Vol 221 (1) ◽  
pp. 265-272
Author(s):  
Jiangtao Li ◽  
Richard L Weaver ◽  
John Y Yoritomo ◽  
Xiaodong Song
Keyword(s):  
Seismic Data ◽  
Ambient Noise ◽  
Green's Functions ◽  
Cross Correlation ◽  
Green’S Functions ◽  
Signal To Noise Ratio ◽  
Alternative Measure ◽  
Signal To Noise ◽  
Cross Correlations ◽  
Noise Cross Correlation

SUMMARY Due to the partly diffuse character of ambient noise, the retrieval of amplitude information and attenuation from noise cross-correlations has been difficult. Here, we apply the temporal reweighting method proposed by Weaver & Yoritomo to seismic data from the USArray in the central-midwest US. The results show considerable improvements in retrieved Green's functions in both symmetry and causality. The reweighting is able to make the effective incident noise field more isotropic (though not yet truly isotropic). It produces more robust amplitude measurements and also makes both the causal and anticausal parts usable. This suggests that it could be widely applicable for retrieval of Green's functions from ambient noise for attenuation study. The results also suggest an alternative measure of signal-to-noise ratio that complements the conventional one.

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