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Acoustic behavior of gas-bearing sediments is significantly different from that of gas-free sediments. In situ velocity profiles and acoustic signal characteristics in gas-bearing sediments of the upper several meters of the sea floor in Kiel Bay are presented in this study. Observed velocities in gas-bearing sediments are both higher and lower than those of the gas-free sediments. Small amounts of gas appear to cause signal reverberation without much attenuation. whereas large amounts of gas cause substantial attenuation. 相似文献
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Sediment shear Q from airgun OBS data 总被引:2,自引:0,他引:2
P. D. Bromirski L. N. Frazer F. K. Duennebier 《Geophysical Journal International》1992,110(3):465-485
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Pairwise waveform (PWW) and pairwise spectrogram (PWS) processors for 3-D localization of unknown, continuous-wave, broadband sources in shallow water have been developed and implemented. The processors use sparse hydrophone arrays and are applicable to multiple sources, which can be unknown, continuous wave, and broadband. Here, we give new formulas for these two processors that significantly reduce computational requirements, making localization at longer ranges and higher frequencies feasible. The new processors are motivated by a demonstration that an incoherent version of the PWW (IPWW) processor (in which processor outputs at different frequencies are averaged after being processed independently) is the Bartlett processor without autoreceiver terms. The new PWW processor is mathematically equivalent to the original version, though much faster. The new PWS processor is mathematically equivalent to the original version only in the limit of infinite spectrogram window length, but for window lengths that are optimal with the old PWS processor, the new PWS processor gives essentially the same results with much greater speed. Simulations comparing PWS processing to Bartlett, PWW processing, and a time difference of arrival method indicate that the main advantage of PWS processing is for multiple sources in uncertain, high-noise environments at ranges many wavelengths long. With PWS, increased robustness with respect to mismatch is obtained at the expense of reduced resolution; varying PWS processor parameters (such as the size of windows used to create spectrograms) optimizes this tradeoff. This work is motivated by the problem of localizing singing humpback whales, and simulation results use whale sources. 相似文献
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Au et al.'s arguments against the hypothesis that humpback whale songs function as long-range sonar are based on questionable assumptions rather than on empirical data. Like other echolocating mammals (e.g., bats), singing humpback whales: 1) localize targets in the absence of visual information; 2) possess a highly innervated peripheral auditory system; and 3) modulate the temporal and spectral features of their sounds based on environmental conditions. The sonar equation is inadequate for determining whether humpback whale songs generate detectable echoes from other whales because it does not account for temporal variables that can strongly affect the detectability of echoes. In particular, the sonar equation ignores the fact that much of the noise encountered by singing humpback whales is spectrally and temporally predictable, and that audition in mammals is a dynamic and plastic process. Experiments are needed to test the hypothesis that singing humpback whales listen for and respond to echoes generated by their songs 相似文献
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L. Neil Frazer 《Geophysical Journal International》1982,70(2):529-533
Summary New formulae are obtained for the displacement potentials and displacements due to a point source with moment tensor, and for a fault with prescribed slip. These formulae, unlike previous formulae, are invariant, i.e. they are valid in any coordinate system, not just Cartesian coordinates or orthogonal curvilinear coordinates.
Apart from their invariance, these formulae have other advantages: they are exceedingly simple; the expressions for P -motion are nearly the same as those for S -motion; and the separation of far field motion from final static displacement is automatic. 相似文献
Apart from their invariance, these formulae have other advantages: they are exceedingly simple; the expressions for P -motion are nearly the same as those for S -motion; and the separation of far field motion from final static displacement is automatic. 相似文献