激光Doppler测流系统中光学参数的确定

本文着重讨论了双光束条纹型激光多普勒测流系统中,光学分束系统参数与散射信号的关系,列出了有关的公式。计算了园形截面的散射颗粒直径与干涉条纹周期呈不同比值时对信号的影响,其结果与以前采用矩型截面进行计算的结果差异较大。以设计一台激光海流计为例,推荐一种以选择与散射粒径相匹配的条纹周期为出发点的光学参数选择方法。最后介绍作者提出的为实现这种选择的光学布置。     

激光Doppler测流系统中光学参数的确定

本文着重讨论了双光束条纹型激光多普勒测流系统中。光学分束系统参数与散射信号的关系，列出了有关的公式。计算了园形截面的散射颗粒直径与干涉条纹周期呈不同比值时对信号的影响．其结果与以前采用矩型截面进行计算的结果差异较大。以设计一台激光海流计为例，推荐一种以选择与散射粒径相匹配的条纹周期为出发点的光学参数选择方法。最后介绍作者提出的为实现这种选择的光学布置。     

浅海波导中刚性球声散射特性研究

目标特性研究对军事及海洋开发具有重要意义。作者用Ingenito的简正波方法对浅海波导中刚性球的散射进行了理论研究。在理论推导中直接利用波导中简正波解,同时去掉文F．Izngenito等研究中的远场假设,使理论结果更具一般性。文中对浅海波导中刚性球的散射进行了数值计算,并进行了分析。结果表明,浅海波导中目标散射场特性与自由场中明显不同,海底、海面的存在使散射场在深度方向产生干涉,从而影响散射场的空间分布,海底声速及衰减系数对散射场空间分布有重要影响。     

拉曼后向散射在海面检测及海面与陆地区分中的应用

给出了光散射、后向散射以及拉曼后向散射等基本概念，推导了后向散射截面与后向散射微分截面的基本关系，以及散射微分截面的计算公式。同时还得出了振动拉曼散射、振动一转动拉曼散射、转动拉曼散射、瑞利散射之间的关系。提出了利用647nm红光的拉曼后向散射检测海面以及区分海面与陆地的方法，可以有效地提高机载激光海洋测深的精度。     

用星载微波散射计测量海洋风场的反演方法研究

Seasat-A卫星散射计(SASS)成功地测量了全球海洋上的风矢量场.其技术基础基于微波后向散射对由海表面风产生的海面厘米级波的敏感性.由于后向散射是各向异性的,所以可以从而个或更多的天线方位角的测量中反演出风速、风向由于散射物理模型函数的非线性及信号中噪声的存在,使得风场反演中存在风向多解.本文给出了一种从SASS测量的后向散射强度的数据中反演出大尺度海洋风场的新的方法,计算结果与Petecherych等[5]利用SASS表面风分析的结果比较在风向上是吻合的,在风速上我们得到的结果更接近于表面真实风速.     

深空背景下空间目标红外特性建模方法研究

针对空间目标红外特性提出了一种精确建模方法.根据空间目标的背景辐射环境,充分考虑到目标表面间的热传导及内热源的影响,建立了空间目标的热平衡方程.基于目标的结构特性和材料特性,利用节点网络法求解了目标表面的温度分布.根据光辐射定律、光散射定律建立了空间目标红外特性的数学模型.结合具体的参数,对深空目标资源一号卫星和风云三号卫星的温度场分布和辐照度分布进行了数值计算,仿真结果验证了理论分析的正确性.     

激光多普勒测流系统中光学参数的确定

本文着重讨论了双光束条纹型多普勒测流系统中，光学分束系统参数与散射信号的关系，列出了有关公式。计算了圆形截面的散射颗粒直径与干涉条纹周期呈不同比值时对信号的影响，其结果比以前采用矩型截面进行计算的结果更为合理。结合激光海流计的设计，分析了光学系统中各项参数的选择对测量结果的影响。     

碳纤维层合板有限元分析

碳纤维材料作为一种优良的复合材料,越来越广泛地应用于水下攻防领域。 主要研究了有限元法对碳纤维层合板的分析。 首先介绍层合板理论,基于该理论对碳纤维层合板模型进行理论分析,然后利用大型有限元软件 ANSYS 对同一模型进行有限元仿真计算。 最后,对二者计算结果进行比较,讨论有限元法对碳纤维层合板的强度计算的可行性,为工程设计运用提供参考。     

浅水中浮体在波浪作用下运动的三维时域计算模型

港口中系泊船在波浪作用下运动问题的本质是浅水波浪与浮体的相互作用。与深水情况不同,浅水问题应当考虑水底、水域边界的影响及浅水波浪自身的特性,单一模型很难实现该模拟过程。为此,建立了Boussinesq方程计算入射波和Laplace方程计算散射波的全时域组合计算模型。有限元法求解的Boussinesq方程能使入射波充分考虑到水底、水域边界的影响和浅水波浪的特性;散射波被线性化,采用边界元法求解,并以浮体运动时的物面条件为入射波和散射波求解的匹配条件。该方法为完全的时域方法,计算网格不随时间变动,计算过程较为方便。通过与实验及其他数值方法的结果进行比较,验证了本模型对非线性波面、浮体的运动都有比较理想的计算结果,显示了本模型对非线性问题具有较好的计算能力。     

水下加筋圆柱壳结构声散射特性研究

采用有限元/边界元(FEM/BEM)方法对水下加筋圆柱壳结构的声散射特性进行分析。考虑入射声场激发弹性结构振动产生二次辐射声场,总声场为入射场与散射场之和。基于Mindlin理论建立结构受迫振动的有限元模型,考虑入射声场为简谐激励,采用模态叠加法求出结构振动表面速度。根据声学边界元相关理论,利用有限元方法计算得出的弹性结构表面动力相应,可求出弹性结构的散射声场。研究结果表明,在同一波数下,不加筋结构后向散射强于加筋结构;加筋结构的散射指向性图案分叉较为明显;同种结构在波数增加的时候后向散射强度逐渐增大,前向散射强度逐渐减弱。     

Extraction of Ocean Wave Spectra From Simulated Noisy Bistatic High-Frequency Radar Data

An algorithm is developed for the inversion of bistatic high-frequency (HF) radar sea echo to give the nondirectional wave spectrum. The bistatic HF radar second-order cross section of patch scattering, consisting of a combination of four Fredholm-type integral equations, contains a nonlinear product of ocean wave directional spectrum factors. The energy inside the first-order cross section is used to normalize this integrand. The unknown ocean wave spectrum is represented by a truncated Fourier series. The integral equation is then converted to a matrix equation and a singular value decomposition (SVD) method is invoked to pseudoinvert the kernel matrix. The new algorithm is verified with simulated radar Doppler spectrum for varying water depths, wind velocities, and radar operating frequencies. To make the simulation more realistic, zero-mean Gaussian noise from external sources is also taken into account     

Radar cross section analysis of marine targets using a combining method of physical optics/geometric optics and a Monte-Carlo simulation

In this paper, the radar cross section of flat plates on ocean surfaces is statistically investigated. A combining method of physical optics and geometric optics is applied to establish an effective backscattering analysis procedure. This method is a high-frequency analysis method originally derived from a simplified Stratton-Chu integral equation, assuming that the radar is far away from the target so that Kirchhoff approximation is valid. A Monte-Carlo simulation method is adopted to statistically analyze the effects of undulated ocean surfaces. The ocean surfaces are randomly generated by Pierson-Moskowitz ocean wave spectrum and a directional distribution function. Numerical investigations are carried out for flat plates, with the same height and width but with different inclined angles, on ocean surfaces of various significant wave heights.     

点源二维各向异性地电断面的直流电场有限元解法

本文给出点源二维各向导性地电断面的直流电场有限元解法。首先,用付氏变换将点源二维各向异性地电断面的三维边值问题转变成二维边值问题;然后导出与二维边值问题相应的变分方程;最后用有限元法解变分方程并用付氏反变换,就获得三维空间中的电位 本文用此方法给出二个算例,并与解析解进行对比。     

Retrieval of integral parameters of tropospheric aerosol from two-wavelength lidar sounding

A scheme of interpreting the data of two-wavelength lidar sounding is proposed. The scheme is based on functional relationships between the lidar ratios and between some integral characteristics of aerosol and the ratio of the backscattering coefficients at the sounding wavelengths. The AERONET data, results of contact aerosol measurements and multiwavelength lidar sounding, and the OPAC aerosol model are used to find these functional relationships, which are statistical in character. Analysis of data is made separately for continental, dust, oceanic, and smoke aerosols. Backscattering for mineral aerosol fractions are calculated for a model of randomly oriented spheroids. A numerical experiment shows that the errors in determining a number of integral parameters of aerosol (extinction coefficient, characteristic radius of particles, volume concentrations) that are due to the statistical straggling of lidar ratios and other specified integral characteristics are no greater than 32% if the optical thickness of the sounding layer is no greater than 1.     

Oceanic sound speed profile inversion

A modal (full-wave) method has been developed to predict ocean sound speed profiles from propagated acoustic field data. The method assumes a point source of sound in the ocean and uses as data the values of the transmitted acoustic field at an array. The formalism for depth-dependent sound speeds consists of the standard Hankel integral transform of the depth solution. In the travel length coordinate, the latter is written exactly, using the Green's function, in terms of an integral equation whose kernel includes the sound speed profile correction. A Born approximation to this equation is used. This is just the WKB solution, and permits the use of a nontrivial input (or guess) profile, here chosen as bilinear. The use of asymptotic methods enables us to write the data as an integral transform over the profile correction. The transform can be inverted. An example is presented for full-bandwidth inversion.     

任意截面直渠中先锋孤立子生成问题中的生成周期和振幅(英文)

借助任意截面直渠中的ｆＫｄＶ方程,理论上确定了先锋孤立子生成的平均特性。基于任意截面直渠中的ＡｆＫｄＶ方程,求得了先锋孤立子生成问题中的理论生成振幅和周期。作为例子,文中预报和比较了正方形和等腰三角形断面直渠中的生成周期和振幅。并且,理论研究也证实,对于正方形渠,当渠宽ｂ＝１时,所得的结果可退化为Ｘｕ［１］等人的结果。     

背景场对变分方法海面风速反演结果的影响

利用前期提出的合成孔径雷达反演海面风场变分方法新解法,开展背景场对合成孔径雷达反演海面风场变分方法风速反演结果影响的模拟试验分析.模拟试验表明,变分方法有效解决了直接反演方法的两大缺陷:一是当背景场风速较大的时候,合成孔径雷达后向散射系数对风速不敏感,直接导致较大的风速反演误差;二是当背景场风向存在误差时,将导致后向散...     

Bragg scattering of centimeter electromagnetic radiation from the sea surface: The effect of waves longer than Bragg components

The effect of sea surface waves longer than Bragg components on the backscattering of centimeter electromagnetic radiation is studied on the basis of data on direct field measurements of sea-surface slopes. A situation in which waves with wavelengths greater than 10 cm are longer than the Bragg components is considered. The increase in the backscattering cross section that is due to the presence of long waves is numerically estimated for sounding at horizontal and vertical polarization. Nonlinear effects in the field of surface waves result in the departure of the distribution of sea-surface slopes from a Gaussian distribution and lead to a change in the backscattering cross section. At a sounding angle of 35°, this change may reach 15% with respect to the cross section calculated for a Gaussian surface.     

Measurement of ocean wave spectra using narrow-beam HE radar

A data interpretation algorithm is developed to extract ocean wave information from HF radar backscatter observed by a narrow-beam antenna system. The basis of this measurement is the inversion of the integral equation representing the second-order radar cross section of the ocean surface. This equation is numerically inverted by approximating it as a matrix equation and pseudoinverting the kernel matrix using a singular value decomposition. As a test of this algorithm, comparisons are made between wave spectrum estimates obtained from a WAVEC buoy and a pair of 25.4-MHz ground wave radars, using data collected during the 1986 Canadian Atlantic Storms Program (CASP). Overall, the results of this experiment have been positive and have demonstrated both the basic feasibility of the inversion algorithm and the wave sensing capability of HF radar. For example, significant wave height estimates deduced by two radars differed from the buoy, in an absolute value sense, by only 0.12 m on average. When using only one radar, the mean difference of this important parameter from the buoy was a reasonable 0.33 m     

A 3-D Numerical Model for the Calculation of Water Wave Transformation in Large Area

Based on the integral equation transformed from three dimensional Laplace equation and by the adoption of the division manner of sub- region boundary element method, the numerical computations of the velocity potential of each sub-region are given considering the continuity conditions of potential and normal derivatives at the interface of sub-regions. Therefore, computation of wave deformation in offshore flow field is realized. The present numerical model provides a good solution for the application of boundary element method to the calculation of wave deformation in large areas.