基于线加速度计的高分辨率光学影像颤振检测与重建方法

卫星平台颤振条件下,推扫式高分辨率光学影像成像往往产生扭曲,从而影响影像的定位及信息提取精度。针对当前颤振下影像成像扭曲补偿的问题,提出一种基于线加速度计测量平台颤振下的稳态重成像模型实现高分辨率卫星颤振扭曲影像的重建。采用受平台颤振影响而扭曲变形的高分某型号卫星全色影像数据进行验证。分析结果表明:提出的线加速度计可以有效检测并测量出平台的颤振,设计的颤振影像地面重建模型可以有效提高光学影像成像质量,补偿后影像扭曲变形现象明显消除。     

非自旋弹头的无颤振滑模控制研究

将通道间的耦合项看作是不确定项,对非自旋弹头的姿态运动模型进行了变形和简化.为了解决滑模控制的消除颤振与控制精度之间的矛盾,提出了一种采用指数衰减型边界层的无颤振滑模控制器.它既可以有效地抑制颤振,又保证了较高的控制精度.采用简单的自适应算法来更新控制器参数,对不确定项的上界进行估计.仿真分析表明,所提出的无颤振滑模控制器是很有效的.     

强迫振动法大跨度桥梁节段模型气动导数辨识

研制了桥梁节段模型颤振导数测定的二维强迫振动实验装置,采用变频调速技术实现对振动频率的控制,模型惯性力、气动力的测量采用了特殊设计的测力元件,模型运动用压电式加速度计进行测量。实验时,模型分别作单自由度的竖弯或扭转的简谐运动,通过测量模型所受到的气动力及模型位移,应用谱分析方法和非线性曲线拟合算法实现了对八个颤振气动导数的辨识,并通过平板模型实验数据与Theodorsen理想平板数据及国外文献数据对比对实验装置及辨识算法进行了检验。     

光学成像侦察卫星威胁特性分析与仿真研究北大核心

为有效评估光学成像侦察卫星对地面目标的威胁,在对光学成像侦察卫星的成像过程以及影响其成像效果的成像条件进行分析的基础上,建立了基于目标检测概率的卫星威胁特性分析和预报模型,划分了威胁等级。通过STK/Matlab联合仿真,实时显示卫星在轨运行情况以及卫星对目标区域的覆盖信息,计算并输出在过境时间段内光学成像侦察卫星的威胁结果。仿真结果表明,该方法可提供更可靠和直观的光学成像侦察卫星威胁结果。     

光学成像侦察卫星威胁特性分析与仿真研究

为有效评估光学成像侦察卫星对地面目标的威胁,在对光学成像侦察卫星的成像过程以及影响其成像效果的成像条件进行分析的基础上,建立了基于目标检测概率的卫星威胁特性分析和预报模型,划分了威胁等级。通过STK/Matlab联合仿真,实时显示卫星在轨运行情况以及卫星对目标区域的覆盖信息,计算并输出在过境时间段内光学成像侦察卫星的威胁结果。仿真结果表明,该方法可提供更可靠和直观的光学成像侦察卫星威胁结果。     

运动补偿与UWB SAR中RD成像算法结合的实现方法

分析了机载合成孔径雷达(SAR)中载机运动误差对接收信号的影响,指出在运动补偿处理中可以将距离向误差分解为空不变项和空变项,在此基础上采用一阶和二阶运动补偿的方法来对两个误差项进行补偿.为了将测量的运动误差数据应用到高分辨率成像中,提出了一种与距离多普勒(RD)成像算法相结合的运动补偿方案.通过对仿真数据的测试,本文方法得到了验证.     

双轴平台动力调谐陀螺漂移补偿技术

在双轴平台动力调谐陀螺惯导系统中,动力调谐陀螺仪漂移与测量轴重力分量密切相关.根据动力调谐陀螺与重力相关漂移项的特点,提出了双轴平台陀螺漂移误差的补偿方法.通过安装在双轴平台上的加速度计测量载体姿态,并计算重力在陀螺两个测量轴的分量,建立了陀螺漂移模型,对方位漂移进行补偿.实验证明,该方法有效地提高了双轴平台方位漂移精度.     

光学成像侦察卫星作战效能分析

为支持航天装备体系作战效能评估,建立了光学成像侦察卫星性能指标与卫星发现目标概率和定位精度的关系以及信息处理与传递模型.以支持导弹打击大型移动目标为例,以命中目标概率为作战效能指标,建立了光学成像侦察卫星作战效能模型.对模型进行了仿真,分析了影响卫星作战效能的主要因素.仿真结果表明所建模型能够合理反映光学成像侦察卫星对作战结果的影响,可用于从顶层分析航天装备.     

基于时间序无圈有向图的多准则优化成像调度

合理有效地利用遥感卫星资源获取更多高质量影像数据是卫星成像调度的重要工作。提出了一种新的成像调度解决方案。应用图论相关理论,建立卫星成像时间序无圈有向图模型,利用多项准则作为衡量标准对不同成像路径进行评价,提出时间序多准则最短路径算法求取优化成像路径。理论分析和实验表明,该解决方案可以在较短时间内获得多条pareto优化成像路径,具有良好的调度性能。     

光力学加速度计在海上平台惯性导航中的应用发展

对光力学加速度计这一新型超高精度惯性器件在海上平台惯性导航中的应用进行了综合评述,并对未来关键技术研究进行了展望。围绕未来海上平台对高精度惯性器件的应用需求,首先归纳了当前惯性加速度计的主要类别、性能等级划分与技术发展现状;然后,剖析了光力学加速度计在海上平台惯性导航中的实际应用场景;最后,对海上平台应用关键技术发展提出建议。综述表明,光力学加速度计的工程化技术和环境适应性需持续开展研究,基于其在海上重力测量、大型船只动态变形测量、平台升沉测量以及长航时自主导航等方面的应用还需进一步深入探索和发展。     

SpaceWire时延抖动的仿真

SpaceWire总线是欧洲空间局为航天应用而设计的一种高速、点对点、全双工的总线网络[1]。时延抖动是表征网络传输性能的关键参数,它度量了端到端的最大传输时延和最小传输时延的差。通过建模仿真,对于某特定应用场景下的SpaceWire总线的时延抖动进行了定量分析和研究。利用Opnet建立仿真模型,通过仿真得出最大传输时延和最小传输时延,从而统计出时延抖动。并且对时延抖动进行定性定量的分析,获得对时延抖动有影响的关键参数。跟据分析结论,提出了改善时延抖动的建议和方法。本文的研究成果对于构建低时延抖动的SpaceWire总线网络提供参考。     

振荡器相位噪声对GNSS接收机载波跟踪数字锁相环性能的影响

关于振荡器相位噪声引起的GNSS接收机载波跟踪数字锁相环相位抖动,目前的解析结论仍是基于模拟锁相环的,不能说明相位抖动大小与中频积累时间的关系,因此不能有效指导高灵敏度、高精度载波跟踪锁相环参数设计.本文首先推导中频积累输出的频率白噪声、频率游走噪声序列的功率谱,然后基于数字二阶锁相环离散线性模型导出了环路相位抖动公式并进行了仿真验证,最后对公式进行了解析和数值分析.分析结果表明:频率白噪声、频率游走噪声引起的二阶载波跟踪锁相环相位抖动,均随中频积累时间单调递增,随环路带宽先递减后递增.本文推得的相位抖动公式及其随参数变化特征的分析结论,可用于具体指导GNSS载波跟踪锁相环参数设计.     

一种实用的有线电视加解扰方案

在分析了电视加扰技术中的模拟加扰方式和数字加扰方式后,对数字加扰时基处理中的行旋转、行置换、行变换等方法做了详细分析;为了保护有线电视加扰系统的安全,采用了随机数的产生、数据的加密等技术。最后详细介绍了一个包括加、解扰系统和用户控制的实验系统     

Helping hands: civil–military cooperation and Italy's military operation abroad

In the Post-Bipolar Era the growing complexity of the military operations requires a new approach for the resolution of international crises. Since the end of the Cold War, peace support operations (PSO) have become the mainstay and principal occupation of most Western armies. At the same time, Italy has been one of the most important actors in such an area. The article focuses on the cooperation between military and civil components (a process called CIMIC) as a key variable in the Italian PSOs. We will analyse in detail the main lessons learned from past military interventions as well as the general context in which new tendencies are taking place. The maintaining of a minimum security frame becomes essential to fulfil activities ‘collateral’ to the mission: reconstructing services and infrastructure, food distribution, water and medication, law and order, de-mining, training of local forces, and supporting local institutions. These are the main tasks to obtain thrust and support from the population.     

Terrorism,insurgency, kidnapping,and security in Africa's energy sector

Energy continues to serve as the bedrock of modern economies and the main driver of modern society. For Africa, the production and supply of energy resources such as crude oil, natural gas, uranium, coal, biomass, biofuels and other renewables are an important source of employment, rents, taxes, royalties and profits. This sector brings in several tens of billions of dollars of revenue annually. The production and delivery of such resources, however, depend on critical infrastructures such as pipelines, refineries, processing plants, terminals, rigs, electrical energy pylons, substations, pump stations, vessels, and tankers. These infrastructures have been attacked by terrorists, insurgents, vandals and saboteurs, all of whom see them as targets against which to register their grievances and extract concessions from the state. This paper is a chronological account of some of the documented incidents of terrorism, insurgency, kidnapping, destruction, sabotage, and human casualties suffered in the oil and gas sectors in Africa between 1999 and 2012. It is based on data extracted from the databases of the RAND Database of World Terrorism Incidents and the University of Maryland's Global Terrorism Database (GTD).     

Tacit support for terrorism: The rapprochement between the USSR and Palestinian guerrilla organizations following the 1967 war

This article demonstrates the inconsistent and wavering Soviet attitude towards national liberation movements in general and the Palestinian organizations in particular. Until the late 1960s, the Soviets viewed these organizations with suspicion, hesitating to engage in political dialogue with them. However, in the 1970s, political and military events in the region, as well as modifications in the Kremlin's Cold War strategies, led to a general shift towards the Middle East in Soviet foreign policy. Soviet leaders showed increased willingness to provide certain Palestinian organizations with arms with which to conduct terrorist activities against Israeli, pro-Israeli, Jewish and Western targets. The article explores the complex relations between Palestinian organizations and the USSR in the field of international terror. The study also exposes and analyzes the nature and content of Soviet–Palestinian arms dialogues and transactions. It provides clear evidence that Soviet policymakers and other luminaries were fully informed of, and sometimes directly involved in, these transactions and dialogues at the highest levels.     

A1 Qaeda and the radical Islamic challenge to western strategy

The September 11 global crisis prompted by the attacks on the World Trade Center and the Pentagon raises major questions concerning the nature and trajectory of terrorism in the post-Cold War global order. Hitherto, terrorism has been largely debated by analysts at the level of nation states. Terrorist and insurgent movements have also been largely anchored in nationalist and ethnic power bases even when they have sought to mobilise a transnational ideological appeal on religious or class grounds. There have been a few exceptions to this pattern such as the alliance between the German Baader-Meinhof group and the Japanese Red Army Faction, but even such international alliances as this did not, until at least the 1980s, presage anything like a global terrorist network necessitating a global strategic response. This study examines terrorism and global strategic responses.     

Helping hands: external support for the KNU insurgency in Burma

This article analyses to what extent the Burmese KNU insurgency made use of external support from states, refugees, and diasporas. Based on extensive fieldwork it is concluded that support from neighbouring states and refugees has for years kept the Karen rebellion alive. Western countries perceived forms of resistance to the illegitimate Burmese regime as just and have therefore played a crucial role in the continuation of conflict in Karen State. It is important that policymakers and donors as well as executing organizations continue to reflect critically on the way they exercise their work.