分布式天基雷达动目标检测性能分析

针对多部天基雷达采用分布式工作体制检测运动目标面临的杂波抑制困难问题,分析了沿航迹基线长度、有效基线长度、地面坡度、波束指向误差、图像配准误差、通道幅度和相位误差对杂波抑制和动目标检测性能的影响。仿真实验结果为以动目标检测为目的的卫星编队构形和雷达参数选择提供了一定依据。     

面向时间协同的多无人机队形变换最优效率模型

针对无人机（UAV）的编队集结、编队保持和编队重构等队形变换问题,从航迹规划的角度提出了一种面向时间协同的多无人机队形变换模型。在时间协同的条件下,选择队形变换的能源消耗与完成时间作为效率衡量指标,对编队集结、编队保持和编队重构进行规划,给出队形变换的最优空间位置。首先,分析了指定队形、无指定位置的编队集结问题,然后,将编队保持问题视为编队整体运动,最后,利用运动分解将编队重构问题分解为编队集结和编队整体运动。基于编队集结、编队保持和编队重构的不同特点,给出了这些具体队形变换下的最优效率计算公式,并进行了仿真实验,实验结果表明本模型可以实现预期的最优效率队形变换。     

医学CT的误差修正方法、图像重建及实现

医学Ｘ光ＣＴ作为一种诊断设备,对其图像质量要求很高,而在实际应用中各种误差都将会影响最终的图像质量,因而对误差进行修正是非常重要的,这一点在各厂家的ＣＴ 产品中表现得尤为突出。通过研究对医学Ｘ光ＣＴ 的探测器、Ｘ光射束硬化效应等所产生的误差进行修正,给出了在ＰＣ机上对误差进行修正和图像重建的方法和步骤,完成了对分辨率水模、对比度水模、病人头部和肺部的图像重建,证明该方法行之有效。     

近赤道卫星绕飞编队的运动学分析及轨道设计研究

首先对一般运动学方法在进行近赤道卫星编队相对运动分析和轨道设计时存在的问题进行了分析 ;其次介绍了一种基于零倾角轨道变换的运动学新方法 ,用其对近赤道卫星编队中参考卫星轨道倾角对环绕卫星轨道根数的影响进行了研究 ;最后对零倾角卫星编队相对运动方程的线性化误差进行了理论分析 ,并利用数值仿真对两种运动学方法的相对运动方程线性化误差进行了比较分析。数值仿真的结果表明 :由基于零倾角轨道变换运动学方法得到的相对运动方程的线性化误差不随参考卫星轨道倾角改变 ,而由一般运动学得到的相对运动方程的线性化误差随着卫星编队接近赤道而呈非线性增大。     

分离模块异构航天器集群松散队形设计

针对近地轨道分离模块航天器集群,考虑航天器之间面质比差异,提出一种能在较长时间内维持两星之间相对距离的松散队形设计方法。该方法以相对偏心率向量和相对轨道倾角向量描述松散队形,以两颗卫星之间的轨道长半轴之差和相对相位角之差为优化变量,并且通过设置虚拟空间圆解决避碰问题,保证在考虑气动力摄动的情况下,异构航天器松散编队能够有较长时间满足距离要求。仿真研究表明,针对轨道高度为500 km的参考轨道,当两星面质比分别为0.003 m 2/kg和0.0032 m 2/kg时,两颗卫星之间的距离能够在50天内处于200 m到20 km之间。     

一种适合于斜视TOPS SAR的改进PFA成像方法

针对斜视循序扫描地形观测(TOPS)合成孔径雷达(SAR)成像模式,对广义极坐标格式算法(PFA)进行改进,提出了一种先线性走动校正(LRWC)后PFA插值的成像方法。利用LRWC显著降低了距离向与方位向的耦合,简化了距离单元徙动校正过程。走动校正后方位向采样依然是均匀的,因此方位向插值可采用Chirp-Z变换快速实现。对于波束扫描及走动校正引起的多普勒调频率的方位空变问题,采用方位非线性变标(ANCS)的方法进行统一校正,大幅提高了方位向的聚焦深度,扩大了可良好聚焦的场景范围。仿真和实测数据处理结果验证了所提方法的有效性。     

Understanding Galaxy Formation with ISO Deep Surveys

We present the results obtained through the various ISO extragalactic deep surveys. Although IRAS revealed the existence of galaxies forming stars at a rate of a few tens (LIRGs) or even hundreds (ULIRGs) solar masses in the local universe, ISO not only discovered that these galaxies were already in place at redshift one, but also that they are not the extreme objects that we once believed them to be. Instead they appear to play a dominant role in shaping present-day galaxies as reflected by their role in the cosmic history of star formation and in producing the cosmic infrared background detected by the COBE satellite in the far infrared to sub-millimeter range. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands, and the United Kingdom), and with the participation of ISAS and NASA.     

Molecular Hydrogen

Observations of H₂ line emission in galactic and extragalactic environments obtained with the Infrared Space Observatory (ISO) are reviewed. The diagnostic capability of H₂ observations is illustrated. We discuss what one has learned about such diverse astrophysical sources as photon-dominated regions, shocks, young stellar objects, planetary nebulae and starburst galaxies from ISO observations of H₂ emission. In this context, we emphasise use of measured H₂ line intensities to infer important physical quantities such as the gas temperature, gas density and radiation field and we discuss the different possible excitation mechanisms of H₂. We also briefly consider future prospects for observation of H₂ from space and from the ground. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands, and the United Kingdom), and with the participation of ISAS and NASA.     

Large scale structure of the universe

The current situation with the cosmological model and fundamental constants is briefly reviewed. Here, we concentrate on evolutionary effects of large-scale structure formation, in particular, the relationship with the quasar distribution and dynamics is discussed. We argue that groups of bright quasars with few or more than dozen of members within regions l _LS(100–150)h ^–1 Mpc found atz<2 may belong to concentrations of young rich clusters of galaxies, and thus be distant Great Attractors like the local GA or the Shapley concentration. These early large-scale galactic structures (i) provide a natural way to bias the distribution of Abell clusters, and (ii) suggest that the spectrum of primordial density perturbations is nearly flat on scales encompassing both the cluster and GAs,l=k ^–1(10,100)h ^–1 Mpc: _k ² k ³ P(k) k , =1 _–0.4 ^+0.6 , whereP(k) is the power spectrum of density perturbations.     

无人机编队的高阶滑模控制方法研究

在未知干扰环境下,对无人机编队飞行的稳定性和精度提出了更高的要求,采用常规滑模控制的编队算法由于"抖振"等问题,不适应高精度和稳定性的要求.针对此问题,提出了一种基于高阶滑模控制的编队飞行控制方法,以三架无人机编队为例,建立了三维空间高阶滑模控制编队控制模型,实现了长机的航路跟踪及僚机的编队队形控制和保持.仿真结果表明...