共查询到20条相似文献,搜索用时 16 毫秒
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Zh. S. Gevorkyan 《Radiophysics and Quantum Electronics》1993,36(1):33-40
A theory of the radiation emitted by a charged particle moving in a randomly inhomogeneous correlated medium is constructed. It is shown that the radiation is isotropic and unpolarized. The frequency dependence of the radiation intensity is investigated and a peak is predicted in the wavelength region of e2a (where e2 is the dielectricconstant fluctuation and a is the correlation radius of the random field).Institute of Radio Physics and Electronics, Academy of Sciences of Armenia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 1, pp. 51–64, January, 1993. 相似文献
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浅海混响的垂直相干性 总被引:7,自引:6,他引:1
浅海混响垂直相干特性是海洋混响研究中一个重要的课题。在射线简正波混响理论的基础上,给出了浅海混响垂直相关的一般表达式,并推导出了在均匀层浅海中混响垂直相关的简化解析表达式。同时,通过对数值计算及实验结果的讨论,研究了浅海混响垂直相关与混响时间、频率、声源深度、接收器深度、海底衰减特性及海底散射系数等参数的变化关系。研究表明,在海底散射满足可分离性的条件下,浅海海底混响的垂直相关与声源位置无关,随着混响时间和海底衰减的增加、或随频率、接收器间隔和海深的减小,混响的垂直相关增大。 相似文献
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The intensity and the time correlation function of radiation transmitted through a layer of a randomly inhomogeneous medium are determined by numerical simulation of the Bethe-Salpeter equation for scalar and electromagnetic fields. The results of simulation agree well with the available experimental data. The domain of validity is determined numerically for the hypothesis of the diffusion approximation on the replacement of the extinction length by the transport length as a characteristic spatial scale for systems with the anisotropic scattering cross section. The polarized and depolarized components of the time correlation function of the transmitted light are calculated for the first time for different anisotropy parameters. It is shown that, to describe the residual polarization of transmitted light taking into account anisotropy, it is insufficient to perform the scale replacement of the extinction length by the transport length. 相似文献
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Using numerical simulation, an analysis was conducted of the interference structure of a bottomscattered sound field generated by a wideband point source in shallow water under winter and summer conditions. The scattered signals were received from the place where the source was located and were subjected to Fourier transform with a sliding window. The paper demonstrates the possibility of estimating the waveguide invariant for backscattered signals when processing the sound intensity distributions in wide frequency and distance ranges up to the scattering area. A technique is proposed for reconstructing the twodimensional field of internal waves using variations of the interference pattern of reverberation signals. The influence of wind surface waves on the degree of interference band contrast is illustrated. 相似文献
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《Journal of sound and vibration》1987,119(2):215-223
In this paper, the general expressions of long-range reverberation intensity in shallow water have been developed on the basis of the normal mode theory. Because the effects of the complex eigenvalues on the mode incident field have been considered, the results are more accurate than those in previous former normal mode theories of reverberation. In addition, for the sake of simplifying the calculations and making the results convenient to compare with experiments, the reverberation intensity has been smoothed by space averaging. The expressions obtained have obvious physical meaning and concise form so that they can be used for numerical calculation and analytical discussion. These expressions are suitable for wider types of velocity profile, bottom-reflection and scattering coefficients. As an example, the average reverberation intensity in shallow water with a thermocline is evaluated. The result shows that when both the source and receiver are located above the thermocline, the long-range reverberation intensity is proportional to r−5. This result is in agreement with the experimental data. 相似文献
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浅海平均混响强度的数值模拟 总被引:1,自引:0,他引:1
海中混响是回声探测的严重干扰。利用本文给出的混响模型可较快地计算分层海洋中平均混响强度的衰减规律及深度结构。
对于近程混响,由于海水非均匀性的影响较小,使用均匀层的射线方法计算。对于远程混响,使用简正波方法计算,它保持了平滑平均后的深度结构。在中等距离上两者能很好地衔接起来,由于考虑了复本征值对简正波入射场的影响,提高了计算精度,通过比较不同散射模型对混响强度计算的影响,提出以分离型二元散射模型作为混响数值模拟的基础,使能由界面反向散射系数估算二元后向散射系数,并大大简化混响强度的数值计算。 相似文献
对于近程混响,由于海水非均匀性的影响较小,使用均匀层的射线方法计算。对于远程混响,使用简正波方法计算,它保持了平滑平均后的深度结构。在中等距离上两者能很好地衔接起来,由于考虑了复本征值对简正波入射场的影响,提高了计算精度,通过比较不同散射模型对混响强度计算的影响,提出以分离型二元散射模型作为混响数值模拟的基础,使能由界面反向散射系数估算二元后向散射系数,并大大简化混响强度的数值计算。 相似文献
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《中国科学:物理学 力学 天文学(英文版)》2010,(8)
The striations of the reverberation spectrum in the time-frequency distribution were observed in a shallow water acoustic experiment in 2002. A model following the coherent reverberation model developed in 2002 is presented to explain the observed striations. To examine the consistency between the measured data and numerical predictions, we have used a method based on Radon transform for determining the slope of the striations to the measured reverberation data and numerical predictions. The results indicate that the previously developed coherent reverberation model can predict the interference structure of the reverberation intensity in the time-frequency distribution. 相似文献
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Pacific Oceanological Institute, Far East Division, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 33, No. 11, pp. 1232–1236, November 1990. 相似文献
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Using the method of refractive scattering of radio waves (RSRW), we solve the problem of space correlation of scintillations
of radiation from an extended source in a randomly inhomogeneous medium. General expressions are obtained for the index and
radius of the space correlation of fluctuations of intensity of radiation from a source with finite angular dimensions as
it propagates though a multilayered medium with refractive index fluctuations. The RSRW method is similar to the diffraction
calculation of space correlation of scintillations of an extended source in a thick layer with inhomogeneities. We note that
under certain conditions an increase in the number of inhomogeneous layers on the radio wave propagation path leads to a pronounced
decrease in the scintillation index and an increase in the space correlation of fluctuations of intensity of received radiation
from an extended source. The results obtained have a simple geometric-optical interpretation. We indicate a specific feature
in determining the angular dimensions of extended radio sources using the known method of scintillations.
Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika,
Vol. 40, No. 5, pp. 586–593, May, 1997. 相似文献
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Ainslie MA 《The Journal of the Acoustical Society of America》2007,121(6):3363-3376
Multipath ocean reverberation originating from the seabed in shallow isovelocity water, with particular attention to its information content in the cylindrical spreading and mode stripping regions, is considered. The reverberation is evaluated using Weston's flux integral method, both analytically with various simplifying approximations and numerically with all but one of these approximations rescinded. The functional form of the analytical solution is used to infer which physical seabed parameters can be extracted from measurements of reverberation. Coarse- and fine-grained sediments (sand and clay) are both considered. The main purpose of the numerical solutions is to check the accuracy of the analytical approximations; they also serve as a convenient surrogate for measured reverberation. 相似文献
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The problem of scattering from a rough sea surface is considered for a harmonic low-frequency (200–400 Hz) acoustic signal propagating in a shallow water area. An experimental study of the azimuthal reverberation dependence is carried out on the basis of the bistatic location scheme with the use of linear phased arrays. By comparison with calculations, the formation of the frequency-angular characteristics of reverberation is investigated for various wind directions with respect to the path of acoustic signal propagation. 相似文献
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A numerical experiment is carried out to study the long-range surface reverberation in the presence of intense surface waves for the case of using vertical transmitting arrays providing sound field focusing at different depths. To focus the field, a phase conjugation of acoustic waves from a probe source positioned at the focusing point is used. It is demonstrated that surface waves considerably affect the focusing quality at a distance of several tens of kilometers from the transmitting array. This prevents the efficient suppression of long-range reverberation by increasing the focusing depth. 相似文献
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I.IntroductionUndcrwatersoundrevcrberationhasrccentlybecomeatopicofgreatinterestlI-3l.Sincethcrcverberationincludescombincdeffcctsofsoundpropagahonandscattering,andthesoundpropagationinshallowwaterismuchmorecomplicatedthanthatinthedeepsea,itisnecessarytOstudycarefullybothintheoryandexperimcnt.Fortheshortrangereverberationinshal1owwatcrtheray-basedmodelisavai1ab1e,whilefOr1ongrangethewave-basedmodelmustbeusedbecauscofcomp1icatcdmu1tipaths,refractioneffcctsandfrequencydependence.Thenorma1-mode… 相似文献
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Yu. N. Barabanenkov M. Yu. Barabanenkov 《Journal of Experimental and Theoretical Physics》1998,86(2):237-243
The propagation of a quasimonochromatic wave packet of acoustic radiation in a discrete randomly-inhomogeneous medium under
the condition that the carrier frequency of the packet is close to the resonance frequency of Mie scattering by an isolated
scatterer is studied. The two-frequency Bethe-Salpeter equation in the form of an exact kinetic equation that takes account
of the accumulation of the acoustic energy of the radiation inside the scatterers is taken as the initial equation. This kinetic
equation is simplified by using the model of resonant point scatterers, the approximation of low scatterer density, and the
Fraunhofer approximation in the theory of multiple scattering of waves. This leads to a new transport equation for nonstationary
radiation with three Lorentzian delay kernels. In contrast to the well-known Sobolev radiative transfer equation with one
Lorentzian delay kernel, the new transfer equation takes account of the accumulation of radiation energy inside the scatterers
and is consistent with the Poynting theorem for nonstationary acoustic radiation. The transfer equation obtained with three
Lorentzian delay kernels is used to study the Compton-Milne effect—trapping of a pulse of acoustic radiation diffusely reflected
from a semi-infinite resonant randomly-inhomogeneous medium, when the pulse can spend most of its propagation time in the
medium being “trapped” inside the scatterers. This specific albedo problem for the transfer equation obtained is solved by
applying a generalized nonstationary invariance principle. As a result, the function describing the scattering of a diffusely
reflected pulse can be expressed in terms of a generalized nonstationary Chandrasekhar H-function, satisfying a nonlinear integral equation. Simple analytical asymptotic expressions are found for the scattering
function for the leading and trailing edges of a diffusely reflected δ-pulse as functions of time, the reflection angle, the mean scattering time of the radiation, the elementary delay time, and
the parameter describing the accumulation of radiation energy inside the scatterers. These asymptotic expressions demonstrate
quantitatively the retardation of the growth of the leading edge and the retardation of the decay of the trailing edge of
a diffusely reflected δ-pulse when the conventional radiative transfer regime goes over to a regime of radiation trapping in a resonant randomly-inhomogeneous
medium.
Zh. éksp. Teor. Fiz. 113, 432–444 (February 1998) 相似文献