共查询到18条相似文献，搜索用时 93 毫秒
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无论对于双基地海底混响仿真,还是混响预报,散射强度都是一个十分重要的物理量.针对小斜度模型和K扰动模型,根据试验结果,结合对比理论仿真计算,证明双基地散射强度模型计算的可行性,研究结果对双基地混响特性研究具有重要意义. 相似文献
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研究了收发分置声纳浅海近程混响的建模与仿真,模型主要基于单元散射理论,依据散射系数相关半径来划分海面、海底散射单元,通过模拟海面、海底混响形成的物理过程建立单接收与多接收模型。模型中考虑声纳设备参数(指向性、收发位置、发射信号)及环境因素(海面运动、海底粗糙程度)对混响建模的影响。设计程序实现浅海近程单接收与多接收混响信号模型并仿真计算出混响时间序列,提供GUI(Graphical User Interface)用户图形界面支持。对建模仿真的混响信号进行统计分析,验证了论文建立的浅海混响信号模型的正确性。 相似文献
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海洋测深中,海底混响信号是测深仪回波信号检测的主要内容。测深仪通常采用信号的相关处理方法对其进行检测,因此在设计测深仪的回波处理单元时,系统地分析海底混响信号的相关特性就显得尤为重要,对混响信号仿真是分析其特性的有效手段。基于单元散射理论,依据海底散射系数的空间相关半径划分散射单元,给出垂直分置海底混响信号的仿真方法。研究结果表明,该模型物理意义明确,计算简单。仿真得到的海底混响信号具有非常好的空间相关性和时间自相关性,与实测的海底混响信号相符,可用于对混响场特性的分析,改善测深仪的设计,从而有效提高测深仪的测量精度。 相似文献
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为了对海底声学参数反演中的估计精度做出预估,合理解释反演结果,本文基于Jackson海底声散射模型,利用Sobol算法,对该模型中的耗散系数、速度比等7个参数进行定量的敏感度分析。Sobol算法可以给出参数的一阶敏感度和参数间相互作用的敏感度,适用于分析散射强度的影响因子。仿真结果表明,所选择的声波频率对于参数的敏感度影响不大,模型各参数交互作用较为强烈,速度比的全局敏感度最大,而耗散系数敏感度很小。将参数划分为地声属性参数、粗糙度参数和非均匀性参数,地声属性参数敏感度最大。模型参数敏感度分析结果对于反演有一定的指导作用。 相似文献
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北极冰下声传播特性实验研究 总被引：1，自引：0，他引：1
通过2017年8月6日在北极海域开展的一次声传播实验，开展了冰下声传播特性实验研究。结合Burke-Twersky （BT）散射模型与射线模型，分析了冰下声传播的多途到达结构，研究了接收声强变化规律，解释了接收声强在30 min内衰减20 dB的现象，分析了接收信号的时间相关性，探讨了接收信号相关性较低的原因。实验结果表明，表面接收信号主要由小角度多次反转反射声线、一次海底反射声线和二次海底反射声线依次构成，表面声道到达信号显著强于海底反射信号。试验冰站在试验期间的运动导致了声传播信号强度和相关性的迅速衰减，并通过仿真得到了验证。 相似文献
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Possibilities and problems for the extraction of backscattering coefficients from airborne and spaceborne Synthetic Aperture Radar (SAR) data are discussed. Corrections for system errors and for imaging geometry are described. Examples are given for airborne SAR data acquired in theX - andC -bands over a test site in the Austrian Alps and for Seasat SAR data of glacierized areas in Iceland. From these data, backscattering coefficients have been derived on a relative scale for wet snow, glacier ice, and several ice-free surfaces. Data of in situ measurements on surface roughness and on dielectric parameters are presented for interpretation purposes and as the basis for backscatter modeling. The SAR-derived results are compared with theoretical backscattering calculations which were based on the Kirchhoff model for surface scattering and on the Born approximation for snow volume scattering. 相似文献
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海洋环流模式中不同近似假设下的海表高度 总被引：1，自引：1，他引：1
Boussinesq近似是现代海洋环流模式中经常采用的假设，但随着海洋模式的不断发展完善以及气候研究应用的需要，有必要估算Boussinesq近似造成的模式误差。分别利用一个非Boussinesq近似的海洋模式与另一个结构相同且采用Boussinesq近似的模式计算海表高度，并同时利用模式预报的温度、盐度资料计算了比容异常高度。分析结果显示，这3种不同定义的海表高度无论空间结构，还是时间演变，都基本类似，尤其在热带海区最接近，差值≤1cm。Boussinesq近似意味着在模式中以体积守恒代替质量守恒，通常的做法是对其进行简单的质量补偿来保持质量守恒。比较说明，以质量补偿方法进行的高度订正对减小Boussinesq近似带来的误差没有本质的意义。 相似文献
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海洋模式中Boussinesq近似误差讨论 总被引：4，自引：0，他引：4
根据全球增暖的特点,设计了一个理想的数值试验方案,用Boussinesq POP海洋模式和改进的非Boussinesq POP海洋模式定量讨论了Bousiinesq近似在海洋模式计算中的误差。结果发现,在只有热力驱动的热力环流背景下,由热膨胀引起的海平面上升在水平方向上是基本均匀的,在所给的初始边界条件下,这种由Boussinesq近似引起的最大海平面误差可以达到59％,在Boussinesq POP模式中,热源中心处的海面高度要远小于由非Boussinesq模式计算的海面高度,而其周围有虚假的海面高度下降;在只有加热引起的热盐环流过程中,当模式作了Boussinesq假设以后,计算的经向和纬向垂直环流都会产生虚假的加强,虽然这种误差只是在1％左右;在Bousiinesq近似假定下,热量经向通量在赤道上垂直剖面的积分误差比质量经向通量在赤道上垂直剖面的积分误差大一个量级;非Boussinesq模式计算的气压梯度所做功的垂向分布在3000m以下是有波动的,而Boussinesq模式计算的气压梯度所做功的垂向分布在3000m以下基本上是均匀的,它的误差在10％以上。 相似文献
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《Oceanic Engineering, IEEE Journal of》1989,14(1):17-75
The problem of underwater acoustic scattering from truly composite wind-wave surfaces under zero-gradient conditions (Δc =0) is examined. Here the dominant small-scale component is postulated to be a soliton surface ensemble, produced by the nonlinear wind-wave interactions and associated with the wind-drift surface layer riding on the underlying, mostly large-scale gravity-capillary component of the composite surface. A general bistatic analysis, based on the Kirchhoff approximation, is presented, which includes arbitrary geometries, beam patterns, and general signals. Both low-frequency O(0.2-1 kHz) and high-frequency O(≳3 kHz) signals are considered, and far-field (Fraunhofer) geometries are assumed. Surface Doppler, including Doppler spread and the modulation effects of the large-scale component, are examined. Both forward-scatter and backscatter regimes are considered in the determination of the scattered field and received wave intensities, scattering cross-sections, and coherency measures of surface scatter. Particular attention is given to the high-frequency cases, with small grazing angles, moderate-to-strong mean surface winds, and essentially bubble-free regimes. Recent empirical data appropriate to these conditions are included, which support the soliton conjecture and illustrate the general results. Both coherent and incoherent scattering are examined, along with relevant surface Doppler data 相似文献
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An explicit and concise approximation to the wavelength in which the effect of nonlinearity is involved and presented in terms of wave height, wave period, water depth and gravitational acceleration. The present approximation is in a rational form of which Fenton and Mckee's (1990, Coastal Engng 14, 499–513) approximation is reserved in the numerator and the wave steepness is involved in the denominator. The rational form of this approximation can be converted to an alternative form of a power-series polynomial which indicates that the wavelength increases with wave height and decreases with water depth. If the determined coefficients in the present approximation are fixed, the approximating formula can provide a good agreement with the wavelengths numerically obtained by Rienecker and Fenton's (1981, J. Fluid Mech. 104, 119–137) Fourier series method, but has large deviations when waves of small amplitude are in deep water or all waves are in shallow water. The present approximation with variable coefficients can provide excellent predictions of the wavelengths for both long and short waves even, for high waves. 相似文献
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The Fresnel-corrected Kirchhoff approximation is applied to predict the impulse response of high-frequency signals forward-scattered from the under-ice surface. The theory predicts a sufficient dependence of the response on ice rms roughness and slope to permit estimation of these parameters from temporal response measurements. The predicted impulse response is then convolved with signal ambiguity functions for comparison with Arctic data. The theory is found to compare favorably with the data for ice characterized by relatively low rms slope and height 相似文献
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Using the recently developed expansion formulae for wave structure interaction problems, the scattering of surface water waves by a semi-infinite floating membrane due to abrupt change in bottom topography is analyzed. Both the cases of finite and infinite steps are analyzed. In the present paper, the analysis is based on the linearized theory of water waves and small amplitude membrane response. Combining the linearized kinematic and dynamic surface conditions on the water surface with the dynamic pressure condition on the membrane, a third order differential equation is derived to describe the membrane covered free surface condition. General wave energy relation for wave scattering by floating horizontal membrane is derived by the application of law of conservation of energy flux and alternately by the direct application of Green's second identity. In the floating membrane covered region, the wave energy density is a combination of the kinetic and potential energy density due to the surface gravity waves, and the surface energy density which is due to the existence of the floating membrane on the free surface. Gravity wave transformations due to an abrupt change in bottom topography in the presence of a floating membrane in finite water depth are analyzed based on shallow water approximation. Numerical results are computed and analyzed to understand the wave transformation due to the floating membrane when there is an abrupt change in topography in different cases. 相似文献