A two scale nonlinear fractal sea surface model in a one dimensional deep sea

Using the theory of nonlinear interactions between long and short waves,a nonlinear fractal sea surface model is presented for a one dimensional deep sea.Numerical simulation results show that spectra intensity changes at different locations(in both the wave number domain and temporal-frequency domain),and the system obeys the energy conservation principle.Finally,a method to limit the fractal parameters is also presented to ensure that the model system does not become ill-posed.     

Methods for calculating low-frequency surface reverberation at known sea roughness characteristics

The problem of estimating the parameters of a reverberation signal generated due to scattering of acoustic waves on a rough surface is considered for a bistatic localization scheme using the example of tone and tone-pulse signals. Relatively simple calculation schemes that make it possible to recalculate three-dimensional space-time roughness spectra into angular-frequency reverberation characteristics and determine the positions of the surface regions that mainly contribute to the integral reverberation level are found. A reverberation spectrum is calculated for the wind waves typical for shallow-water closed basins, and the positions of the scattering regions forming the components of this spectrum are determined.     

Theoretical model of surface reverberation with allowance for interference of acoustic modes

We report on preliminary results of developing a theoretical model of surface reverberation with allowance for the interference structure of acoustic fields in oceanic waveguides. Basic expressions relating the intensity and two-dimensional frequency-time uncertainty function of the reverberation signals to the wind-wave parameters and the characteristics of sounding pulses are presented. Main physical effects determining the influence of intermode correlations on the reverberation are discussed. In this context, both narrow-and wideband emitted signals are analyzed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 5, pp. 391-398, May 2008.     

海底混响仿真研究

提出了一种新颖的海底混响仿真工程实现模型.它是基于单元散射的理论,通过模拟海底混响形成的物理过程实现仿真,具有仿真效果好,工程上易于实现的特点.根据该模型实现的多通道海底混响模拟器功能强、柔软性好,所产生的海底混响仿真信号无论是在形式上还是在统计特性方面与实测海底混响相比较都有很好的一致性.此外,该模拟器还可以作为目标模拟器或者相控/束控信号源使用.     

Experimental studies of low-frequency bistatic reverberation in a shallow sea

Experimental data are presented on time and frequency dependences of the reverberation level for bistatic transmission and reception at low acoustic frequencies. The data are obtained from the studies carried out in a coastal shallow-water region and in the central region of the Barents Sea with explosion-generated and pulsed cw signals. By using the simplest computational model, approximate estimates are obtained for the effective coefficient of spatial attenuation and the effective scattering coefficient in the frequency band 40–400 Hz.     

Room acoustical model of external reverberation

A theory of external reverberation in urban built-up environments is developed, based on a classical room acoustical model. In the model, external reverberation is analyzed as a special limiting case of internal reverberation in rooms. Explicit formulae are deduced for the statistical value of the external reverberation time, and the spatial distribution of the external sound field amplitude with distance from a fixed, constant power, sound source, for which comparison with published experimental results is possible. Predictions of the theory compare reasonably well with the experimental values. It is found that the external reverberation time in a built-up area depends chiefly on the average building height, and to a lesser extent on the packing fraction, and the ratio of surface area to cross-sectional area of buildings which make up the built-up environment, apart from the absorptive properties of the building and ground plane surfaces. For the spatial distribution of the steady state sound field amplitude in a built-up environment, it is found that the diffuse field amplitude attenuates with distance from a fixed, constant power source exponentially faster than the inverse square law.     

Anomalous scale transformations and functional integrals

A method is presented to analyse euclidean field theories starting from small volume subsystems. It bears resemblance with the real space renormalization group, but it is not limited to the lattice cutoff. An intuitive picture emerges for the role of perturbative results in asymptotically free models. There it is shown how to derive the one-loop β-function directly as a jacobian under scale transformations in a functional integral.     

The characteristics of acoustic line array prototypes for scale model experiments

The sound fields created by three different settings of a 5 m long linear loudspeaker array were studied experimentally in the present investigation in an attempt to find out a method to produce a reasonable sound field for scaled down model experiments. The first setting was with all the loudspeakers facing vertically upward, while the second setting was with all the loudspeakers facing the horizontal. The last one resembled the first setting but the loudspeakers were put inside a small partial enclosure whose opening was facing vertically upward. Results show that the last setting can produce a sound field with characteristics close to those of a two-dimensional sound field. The second setting results in a sound directivity pattern relevant to that of the measured A-weighted traffic noise.     

界面混响的耦合简正波理论研究

利用耦合简正波理论分析了粗糙界面散射引起的混响。引入了粗糙海底以及海面引起的各个模态间的耦合系数表述粗糙界面对声场的散射过程。结合风浪谱Pierson模型,仿真了不同海况下的海面混响,重点在于分析不同海况下海面起伏对海底混响的影响。利用耦合系数的求解从粗糙海面引起模态间能量耦合的角度对这种影响进行了机理性的探究。结果表明,尽管在浅海中海底混响占支配性地位,但随着海况等级的增加,海面散射对海底混响是有影响的,而这种影响可以从粗糙界面对声波模态间的耦合进行机理分析。      

Anomalous wave as a result of the collision of two wave groups on the sea surface

The numerical simulation of the nonlinear dynamics of the sea surface has shown that the collision of two groups of relatively low waves with close but noncollinear wave vectors (two or three waves in each group with a steepness of about 0.2) can result in the appearance of an individual anomalous wave whose height is noticeably larger than that in the linear theory. Since such collisions quite often occur on the ocean surface, this scenario of the formation of rogue waves is apparently most typical under natural conditions.     

波破碎下海洋表面微波辐射率的一种模式

利用有效介质近似理论方法，本文提出了计算强风驱动下海浪破碎的海洋表面微波辐射率的一种修正模式。该模式修正Pandey等人的经验模式，通过把海浪破碎的白冠层等效为海水和空气的复合介质，并利用复合介质有效介电常数的计算方法，在该模式中充分考虑了海洋表面水滴形态、白冠层厚度和覆盖率对海洋表面微波辐射率的影响。实验表明，该模式在不同风速、不同水滴形态以及微波频率下（6.6GHz,10.7GHz,37GHz）计算的海洋表面微波辐射率与实测结果一致。     

一种改进的水下爆炸声混响模型

为了研究水下爆炸声脉冲引起的混响,基于射线理论,利用椭球的几何性质,建立了改进的三维近程双基地混响平均强度模型,推导出爆炸深度任意的双基混响平均强度预报公式。计算分析了爆炸深度和脉冲宽度对混响强度的影响,并与实验结果进行了比较,结果表明:爆炸深度对混响强度的影响相对较小,脉冲宽度越大,混响强度越大。     

Anomalous roughness in dimer-type surface growth

We point out how geometric features affect the scaling properties of nonequilibrium dynamic processes, by a model for surface growth where particles can deposit and evaporate only in dimer form, but dissociate on the surface. Pinning valleys (hilltops) develop spontaneously and the surface facets for all growth (evaporation) biases. More intriguingly, the scaling properties of the rough one dimensional equilibrium surface are anomalous. Its width, W approximately Lalpha, diverges with system size L as alpha = 1 / 3 instead of the conventional universal value alpha = 1 / 2. This originates from a topological nonlocal evenness constraint on the surface configurations.     

一个L波段海表盐度遥感反演的新经验模式

海表盐度是描述海洋的一个重要参量，海表盐度的微波探测是海洋遥感研究的重要内容.利用黄海实测盐度数据和海表亮温资料，建立了一个适用于黄海近岸的盐度反演模式.在没有海浪破碎情况下，利用L波段的亮温资料反演海洋表层盐度.本模式充分考虑了海面粗糙度的影响，从海水亮温和海水的介电常数反演的表层盐度和实测的表层海水盐度基本一致，其平均绝对误差为0.288psu，与同类模式相比具有较高的精度. 关键词： 盐度 亮温 辐射率 介电常数     

Effect of surface reverberation on the selection of a diffracted signal

An experiment is described in which a wave scattered by a rough water surface is the factor by virtue of which the signal diffracted by a moving scatterer is received with confidence. Experimental corroboration of this fact is presented, and the origin of this phenomenon is revealed.     

Estimation of the underwater explosion depth from the modified cepstral analysis of sea reverberation

A mathematical model of the signal produced by an underwater explosion is used to obtain the dependence of the explosion depth on the argument T_k at which the cepstrum of the signal reaches its maximum. The algorithm evaluating the parameter T_k on the basis of the cepstral analysis of reverberation is substantiated. The proposed method of estimating the explosion depth is tested by experimental data to demonstrate its high accuracy.     

The time scale of Monte Carlo experiments

The time required to reach equilibrium in a standard Monte Carlo experiment is estimated on the basis of exact bounds on the longest time scale in one-dimensional models. The result implies the empirical law of Arrhenius at low temperatures if there are energy barriers.     

Anomalous surface photoconductivity in hydrogenated amorphous silicon

The intensity and time dependence of the source-drain photocurrent is measured on hydrogenated amorphous silicon (a-Si:H) field effect transistors as a function of gate bias. The photocurrent increases rapidly, becomes weakly dependent on excitation intensity, and exhibits long decay times. A model in which the relaxation of the space charge dominates the photocurrent quantitatively predicts the experimental data. The results show that anomalous surface photoconductivity is often the dominant photoresponse of a-Si:H.