共查询到19条相似文献,搜索用时 99 毫秒
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精确测量和确定同步卫星轨道是实现高精度导航、定位等应用的基础,光学测角定轨和卫星通信信号测时差定轨是两种最重要的无源测轨方法,各有优缺点.本文提出将光学测角与无线电通信信号测时差相结合,可实现对卫星的单次测量定位,多次测量提高定轨精度.推导得到卫星到光学站的距离表达式,实现对卫星位置的解析求解.通过GDOP方法,分析了光学站与无线电站的不同布站方式对定位精度的影响,据此提出了优化布站方式.通过计算机Monte-Carlo仿真,比较分析了联合测轨方法与单一光学测轨方法的测轨精度.仿真结果表明:若无系统误差时,24小时观测数据统计定轨位置误差为25 m,预报1周位置误差为200 m,约为单一光学方法的2/3;当存在系统误差时,需采用自校准方法估计系统误差,基于24小时观测数据的单一光学方法未能实现自校准定轨,而联合测轨方法定轨精度可达到约6 m,归一化系统误差估计精度优于0.1,预报1周的位置误差约为140m. 相似文献
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精确测量和确定同步卫星轨道是实现高精度导航、定位等应用的基础,光学测角定轨和卫星通信信号测时差定轨是两种最重要的无源测轨方法,各有优缺点。本文提出将光学测角与无线电通信信号测时差相结合,可实现对卫星的单次测量定位,多次测量提高定轨精度。推导得到卫星到光学站的距离表达式,实现对卫星位置的解析求解。通过GDOP方法,分析了光学站与无线电站的不同布站方式对定位精度的影响,据此提出了优化布站方式。通过计算机Monte-Carlo仿真,比较分析了联合测轨方法与单一光学测轨方法的测轨精度。仿真结果表明:若无系统误差时,24小时观测数据统计定轨位置误差为25m,预报1周位置误差为200m,约为单一光学方法的2/3;当存在系统误差时,需采用自校准方法估计系统误差,基于24小时观测数据的单一光学方法未能实现自校准定轨,而联合测轨方法定轨精度可达到约6m,归一化系统误差估计精度优于0.1,预报1周的位置误差约为140m。 相似文献
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天基光电望远镜对空间目标成像的模拟 总被引:10,自引:2,他引:8
提出了一种天基望远镜对空间目标成像的模拟方法。由卫星轨道参数计算得到卫星在地心赤道坐标系中的坐标,再通过平移、旋转和比例变换将其变换到望远镜坐标系中的坐标,模拟得到卫星的成像图。通过旋转和比例变换,将恒星坐标从地心赤道坐标系变换到望远镜坐标系,模拟得到星空成像图。两者合成得到总模拟图。将望远镜的位置矢量和光轴的方向矢量之间的夹角作为望远镜视场是否被地球遮挡的判断依据。以0星等和10星等为参考,用计算机模拟得到256级灰度图。仿真结果表明,该方法既能有效地模拟卫星的运动,又可以克服对相同星空背景的重复模拟。 相似文献
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美国天基红外低轨系统在探测弹道中段目标时,大气辐射和背景星体辐射可能远大于目标辐射,探测存在一定的困难.根据天基红外低轨系统的设计要求,本文估计出一种天基多波段弹道中段目标探测方法.该方法根据星体辐射光谱容易获得这一特点,在大气辐射和目标辐射光谱未知的条件下,对正交子空间(OSP)算法进行改进.采用主成分分析方法,提取大气辐射背景主成分.再结合星体的端元信息,构成新的背景端元矩阵.并采用全一向量替代目标端元.计算机模拟表明该方法在有效地抑制大气和星体背景同时,可靠地探测出中段小目标. 相似文献
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空间光学遥感器在航天对地观测、太空探测等领域均具有重要的科学和军事意义.未来战争的显著特点是精确打击、电子战、信息战,首要的是战场侦察、空间监视与测量信息的获取.航天、陆地、海洋资源气象探测、环境及灾害监测等对国民经济现代化有极其重要影响的活动,也需要获取一般手段难以得到的信息.总之,所有这些都要靠新一代的空间光学遥感器,即高分辨率空间环境适应性强的空间相机. 相似文献
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We studied the effectiveness of using polarized illumination and detection to enhance the visibility of targets buried in highly scattering media. The effects of background optical properties including scattering coefficient, absorption coefficient, and anisotropy on image visibility were examined. Both linearly and circularly polarized light were used in the imaging. Three different types of target were investigated: scattering, absorption, and reflection. The experimental results indicate that target visibility improvement achieved by a specific polarization method depends on both the background optical properties and the target type. By analyzing all polarization images, it is possible to reveal certain information about target or the scattering background. 相似文献
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The satellite for earth observation (Bhaskara) launched on 7 June 1979 has two TV cameras and a passive microwave radiometer for earth resources survey and meteorological
studies respectively. As it had to be a minimally modified version of the earlier spin-stabilised satelliteAryabhata, it is configured as a spin-stabilised satellite, with a spin rate of between 6 to 11 rev/min and a spin axis perpendicular
to the orbital plane within 3°. The cold gas system ofAryabhata was modified to provide a low and controlled thrust for spin-up and spin-axis orientation operations. Two horizon-crossing
sensors are used for automatic spin-axis control and attitude determination on ground. This paper presents a report on the
system evolution, design, simulation and on-orbit performance ofBhaskara. 相似文献
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中国对地观测技术发展现状及未来发展的若干思考 总被引:4,自引:3,他引:1
空间对地观测及应用是发展航天技术的核心使命之一。至今为止,国际上已发射了几千颗航天器。其中,对地观测卫星占有重要分量,是为经济发展、国家安全及环境、能源等领域的需求直接带来效益的、不可替代的航天技术领域。几十年的发展表明,国际上把对地观测技术作为重中之重技术发展。我国对地观测技术是上世纪70年代初开始,至今已走过四个发展阶段,已成为谱段齐全、数据获取技术有了较大发展、应用领域不断拓展、有较深入的基础研究及处理方法的初具规模的技术科学体系,几十年来在国民经济发展、国家安全建设中已发挥了重要作用。在我国中长期科技发展规划中,有多项相关对地观测的重大事项和研究项目。我国对地观测将以需求牵引、技术驱动,面向国际前沿,力争在对地观测领域跻身国际先进行列。 相似文献
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光电探测中空间目标和恒星目标运动特性分析 总被引:1,自引:0,他引:1
地基大视场天文光电观测系统获取的序列图像中,空间目标和数目众多的恒星目标成像特性相似,两者的区别主要是其运动特性差异.以圆轨道空间目标为例,并忽略地球自转的影响,分析了低轨道空间目标在不同仰角处的运动特性;在建立地平坐标系和时角坐标系这两种天球坐标系的基础上,分析了恒星目标·在不同方位不同仰角处的运动特性;比较了空间目标和恒星目标在视场中运动特性的差异,结果表明恒星目标的运动体现为慢速运动,而空间目标表现为明显的运动特性,且在短时间内可以认为是匀速直线运动. 相似文献
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James L. Hyde Eric L. Christiansen Justin H. Kerr 《International Journal of Impact Engineering》2001,26(1-10):345-356
The NASA/JSC Hypervelocity Impact Technology Facility (HITF) performed a meteoroid and orbital debris threat assessment on a low earth orbit satellite constellation. The results of the analysis will show that the risk from hypervelocity impact was significant enough to warrant design changes. The techniques used to significantly mitigate the risk from hypervelocity impact will be discussed. 相似文献
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Xiangting DONG Guangyan HONG College of Materials Chemical Engineering Changchun University of Science Technology Changchun China Key Laboratory of Rare Earth Chemistry Physics Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun China 《材料科学技术学报》2005,21(4):555-558
A series of rare earth hydroxide and oxide nanoparticles have been prepared by precipitation method with alcohol as the dispersive and protective reagent. Transmission electron microscope (TEEM) images indicate that the particles are spherical in shape and smaller than 100 nm in size. The crystallite sizes of cubic Ln2O3 have lanthanide shrinking effect, while average crystal lattice distortion rates possess lanthanide swelling effect. The diffraction peak intensity of heavy rare earth oxide nanometer powders is remarkably stronger than that of light rare earth oxide nanometer powders. The variation of diffraction intensity with atomic number presents an inverted W type, forming a double peak structure. Fourier transform infrared (FTIR) spectrums reveal that Ln2O3 nanopowders have higher surface activity than that of ordinary Ln2O3 powders. The UV-vis spectra show that Ln-O bond of these particles is slightly blue-shifted, and its absorption intensity decreases. 相似文献
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Ghulfam Zahra Muhammad Imran Abdulrahman M. Qahtani Abdulmajeed Alsufyani Omar Almutiry Awais Mahmood Fayez Eid Alazemi 《计算机、材料和连续体(英文)》2021,68(3):3465-3481
In recent years, video surveillance application played a significant role in our daily lives. Images taken during foggy and haze weather conditions for video surveillance application lose their authenticity and hence reduces the visibility. The reason behind visibility enhancement of foggy and haze images is to help numerous computer and machine vision applications such as satellite imagery, object detection, target killing, and surveillance. To remove fog and enhance visibility, a number of visibility enhancement algorithms and methods have been proposed in the past. However, these techniques suffer from several limitations that place strong obstacles to the real world outdoor computer vision applications. The existing techniques do not perform well when images contain heavy fog, large white region and strong atmospheric light. This research work proposed a new framework to defog and dehaze the image in order to enhance the visibility of foggy and haze images. The proposed framework is based on a Conditional generative adversarial network (CGAN) with two networks; generator and discriminator, each having distinct properties. The generator network generates fog-free images from foggy images and discriminator network distinguishes between the restored image and the original fog-free image. Experiments are conducted on FRIDA dataset and haze images. To assess the performance of the proposed method on fog dataset, we use PSNR and SSIM, and for Haze dataset use e, r−, and σ as performance metrics. Experimental results shows that the proposed method achieved higher values of PSNR and SSIM which is 18.23, 0.823 and lower values produced by the compared method which are 13.94, 0.791 and so on. Experimental results demonstrated that the proposed framework Has removed fog and enhanced the visibility of foggy and hazy images. 相似文献