Studies on the imaging characteristics of Yohkoh Soft X-ray Telescope: Optical aberration and scattering

In order to better understand the characteristics of Yohkoh Soft X-ray Telescope (SXT) mirror, we have analyzed the in-flight overexposed image (the starburst image) obtained during the solar flare observation. It has been revealed from our study that the intensity distribution inside the shadows shown in the scattering difference image contains little of the scattered component of the PSF and matches almost correctly the extension of the PSF core profile. Also it is found that the scattering wing of the SXT PSF is connected smoothly to the PSF core within the distance of about 100–200 arcsec from the peak. With numerical simulations we have shown that an increase in energy affects not only the level of scattering wing, but also both the shape and the absolute level of the PSF core. The results have revealed, however, that the energy dependence for the SXT PSF cannot be easily estimated with the data obtained from one filter alone, which implies that the data analysis using multiple filters will enable us to determine the absolute amount of scattered component as well as the energy dependence of the SXT PSF. Details on the analysis of starburst image and the results from numerical simulations will be introduced and discussed thoroughly.     

High-precision RCS measurement of aircraft’s weak scattering source

The radar cross section(RCS) of weak scattering source on the surface of an aircraft is usually less than 40 d Bsm.How to accurately measure the RCS characteristics of weak scattering source is a technical challenge for the aircraft's RCS measurement.This paper proposes separating and extracting the two-dimensional(2D) reflectivity distribution of the weak scattering source with the microwave imaging algorithm and spectral transform so as to enhance its measurement precision.Firstly,we performed the 2D microwave imaging of the target and then used the 2D gating function to separate and extract the reflectivity distribution of the weak scattering source.Secondly,we carried out the spectral transform of the reflectivity distribution and eventually obtained the RCS of the weak scattering source through calibration.The prototype experimental results and their analysis show that the measurement method is effective.The experiments on an aircraft's low-scattering conformal antenna verify that the measurement method can eliminate the clutter on the surface of aircraft.The precision of measuring a 40 d Bsm target is 3–5 d B better than the existing RCS measurement methods.The measurement method can more accurately obtain the weak scattering source's RCS characteristics.     

Influence of aircraft surface distribution on electromagnetic scattering characteristics

In this paper, two typical stealth aircraft concepts (wing fuselage blended and flying-wing) were designed. Then three gradually changed surface distribution models with the same plan-form for each concept were created. Based on the multilevel fast multipole algorithm (MLFMA), the vertical polarization transmitting/vertical polarization receiving (VV) and horizontal polariza-tion transmitting/horizontal polarization receiving (HH) radar cross section (RCS) characteristics were simulated with five frequencies between 0.1 and 1.0 GHz. The influences and mechanisms of aircraft surface distribution on electromagnetic scattering characteristics were investigated. The results show that for the wing fuselage blended concept, the VV RCS of this frequency range is higher than the HH RCS in most cases, while it is just the opposite for the flying-wing concept. As for the two aircraft concepts, the RCS levels of HH and VV both decrease with the frequency increasing, but the HH RCS has a faster downward trend. The surface distribution has little influ-ence on HH RCS characteristics. On the contrary, it has a significant impact on VV RCS charac-teristics, and the amplitude of the VV RCS increases with the surface thickness.     

基于空域滤波的二维全极化散射中心快速提取

在全极化逆合成孔径雷达(ISAR)体制下,二维相干极化几何绕射(CP-GTD)模型能够精确描述雷达目标高频电磁极化散射特性。针对CP-GTD模型,提出了一种基于空域滤波的二维全极化散射中心参数快速提取方法。该方法利用空域滤波将二维全极化散射中心参数提取问题分解为多个一维全极化散射中心提取问题,进而利用一维旋转不变技术(1D-ESPRIT)分步对全极化散射中心各维参数进行联合估计,最后利用最小二乘方法获得相干极化散射矩阵的估计。此外,采用这样的分步估计过程,可以实现二维参数的自动配对。复杂度分析和仿真实验表明:该方法不仅能够显著降低运算量,并且还能获得较好的估计精度,可以有效地用于目标全极化散射中心提取。     

用契合方法求平面SH波对半圆形突起地形的散射

采用“契合”的方法，给出了一个求解平面SH波对半圆形凸起地形散射的新方法。利用包括半圆形凸起上边界在内的一个圆域中预先构造的满足其上半部应力为零，下半部应力任意的级数解和其余的具体半圆形凹陷的半空间中的解答，通过在其结合面上完成“契合”的过程中分别决定出出圆域和半空间中的解答，给出了问题的最终结果。利用上述方法，问题的求解仍归结为对一组无穷代数方程组的求解。最后，给出了数值结果并对其进行了讨论。     

近地空间航天员训练视景真实感渲染技术研究

载人航天任务中,地面模拟训练是培养提升航天员操作技能的重要手段。视景系统是航天飞行训练模拟的重要组成部分,高逼真度的仿真场景对提升航天员训练效果有重要的意义。针对空间视景仿真场景调度和渲染的特殊性,提出并设计实现视景仿真软件的总体架构。对影响空间场景真实感的地球纹理数据库的生成和调度技术、大气散射仿真技术、场景光照实时渲染等关键技术进行研究,融合各种方法,在视景仿真系统中基于GPU实现。试验验证表明,实现算法准确,模型设计合理,已经应用于航天员的训练中。     

三维复杂目标求解的多层快速多极子方法

采用多层快速多极子方法(Multilevel fast multipole algorithm,MLFMA)求解混合场积分方程(Combined field integral equation,CFIE),并选择RWG型基函数,对金属带缝锥球体、三面角反射器以及钻石体的单站RCS(Radar cross section)进行了计算,计算结果与试验吻合良好.在此基础上计算了F-22缩比模型的单站RCS,其计算量、存储量分别达到O(NlogN)量级和O(N)量级,此方法适用于带有尖点和特别细长曲面的三维复杂目标,如战斗机外形的RCS计算分析.     

快速声散射方法在变截面管道中的应用

 快速声散射方法(FSM)是一种基于无流动Helmholtz方程边值问题的声散射预测工具,具有快速、灵活的特点.以航空发动机消声短舱的声学设计为背景,用该方法对变截面管道声传播特性进行数值模拟研究,用直接边界元方法(DBEM)进行数值求解,避免了求解管口反射系数,有效地提高了计算速度.数值研究了刚性壁面和不同位置壁面声衬组合对变截面圆环管道形状声传播的影响,并分析了管道厚度对散射声场的影响,数值结果与声类比方法结果进行了相互验证.最后,还对一种真实转子声源进行了管道声散射的数值研究,结果表明本方法在航空发动机声学设计中具有工程应用价值.     

中子及中子散射特征

中子以它特有的性质,使它成为继X射线和电子衍射之后的又一研究微观物质结构的有效方法。由于中子散射技术的发展,人们才得以在声子色散曲线和同位素效应的研究等方面有所收获。中子散射可以说是对X射线衍射和电子衍射的一个重要的和不可缺少的补充。中子散射技术利用中子不带电、穿透力极强、能直接鉴别核素、较之X射线对轻元素灵敏、具有磁矩和波粒二象性等特点,使之成为一种独特的,从原子和分子尺度上研究各种物质结构和微观世界运动规律的高新技术。