共查询到20条相似文献,搜索用时 46 毫秒
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The Global Positioning System (GPS) is a highly accurate navigation system that has a broad spectrum of military, civilian, and commercial applications. It uses a triangulation scheme based on the time delays of signals from the satellites to the user; these time delays are then equated to distances. However, as the timing signal passes through the Earth's atmosphere it undergoes an additional time delay due to the index of refraction. The time delay produced by the troposphere approaches a value corresponding to a range error of about 25 m for an elevation angle of 5° and decreases with increasing elevation angle to less than a few meters at zenith. It has been shown that there is a good correlation between the range error and the surface index of refraction. Worldwide statistics of surface refractivity have been analyzed and shown to be correlated with site latitude, height above sea level, and time of year. Regression lines for range-error corrections based on these parameters are derived. Range-error accuracies vary from about 8% down to 3.7% of the total range error, depending on the amount of information that is available 相似文献
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Ikegami F. Akiyama T. Aoyagi S. Yoshida H. 《Antennas and Propagation, IEEE Transactions on》1968,16(2):194-200
Measurements of the variation of the incident angle were made on several line-of-sight paths, together with the simultaneous observation of the refractive index gradient of the atmosphere. Statistics of incident angle variation andM -gradient and their relations were analyzed. Radio refraction is dependent on the atmospheric layer thickness in which radio waves are propagated. Considering the controlling layer thickness, a method of predicting refraction variation is presented for arbitrary radio paths and meteorological conditions. The measurements of the incident angle were found to agree well with the estimated refraction. 相似文献
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卫星编队构形是影响分布式卫星SAR系统性能的重要因素之一。该文主要研究满足绕飞轨道条件下的分布式卫星SAR编队构形设计问题,提出了基于高程测量误差最小的分布式卫星SAR编队构形设计方法。文中给出了分布式卫星SAR多组高程测量数据融合后的像素单元高程测量误差表示,并提出了给定观测区域的高程测量误差表达式。在此基础上,以观测区域的高程测量误差为优化目标,采用遗传算法对分布式卫星初始编队构形进行优化设计。仿真试验验证表明,通过该方法得到的初始卫星编队构形能够较好的降低给定观测区域内的分布式卫星SAR高程测量误差。 相似文献
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用于LED光源准直的紧凑型光学系统设计 总被引:7,自引:4,他引:3
设计了一种光学系统,用于发光二极管(LED)光源准直,并通过TracePro软件仿真进行了验证。该系统采取了折射和反射式自由曲面的组合,使LED光源的发散角从70°减少到约4°,效率在约85%,系统的高度为7.65mm,口径为8.73mm。分析了折射和反射的最佳分界角区域是41°~45°,最佳分角比例因子是0.4~0.5。 相似文献
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在对大气层采用球面分层的基础上,利用折射定律,阐述了球面分层大气折射模型的建立过程,得到了光束折射的光路方程.由此得出光束偏移与卫星高度和地面发射角间的关系,给出了光束偏移随卫星高度变化的计算公式,为地-空光通信链路的修正提供了重要的理论参考. 相似文献
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星光折射法是一种很有发展前途的导航方法。由于航天实验费用巨大,往往不可能进行实时的星空拍摄。为解决这个问题,文中提出了一种折射星的模拟方法,该方法结合大气折射模型和星光折射几何方程来计算星光折射角,进而得到折射星的赤经和赤纬。再利用星图模拟方法就可以模拟折射星在星敏感器像平面的位置,而且能够根据实际情况考虑星敏感器噪声、环境噪声的影响,仿真结果验证了本方法的正确行和实用性。 相似文献
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I. L. Raskovskaya 《Journal of Communications Technology and Electronics》2009,54(12):1445-1452
The main types of structured laser beams obtained using diffractive optical elements are presented. A new information and
measuring technique—the laser refractography based on the application of structured radiation—is proposed for the quantitative
diagnostics of inhomogeneous media. The relations for the analysis of geometrical-optical models and the refraction of structured
beams in the boundary temperature layer are presented. A solution to the inverse problem based on the Abel transform is adapted
to the flat beam in the case of a relatively strong refraction in a spherical inhomogeneous layer. The temperature profile
of the layer is reconstructed using the refractograms of flat and cylindrical beams. 相似文献
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《Antennas and Propagation, IEEE Transactions on》1992,40(4):439-442
Adopting a simple model, a formulation is presented for the scattering from a circular island surrounded by an otherwise smooth sea. Both the surface impedance and the height profile of the island are functions of the radial distance. Employing the electromagnetic compensation theorem, an expression for the mutual impedance between two small ground-based vertical antennas is derived. To simplify the analysis these antennas are assumed to be located at distances that are large compared with the radius of the island. It is shown that the relative importance of the surface impedance and the height profile will depend on the scattering angle subtended, at the island center, by the direction to the source and receiving antennas. The results are relevant to the propagation of electromagnetic waves in the earth-ionosphere waveguide at very low frequencies (VLF) 相似文献
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基于WGS-84椭球模型的卫星测时差定位精度分析 总被引:1,自引:0,他引:1
针对采用WGS 84椭球模型的三星座测时差定位算法 ,分别对高程假设引起的系统误差和随机测量误差引起的定位精度分布进行了分析 ,给出了仿真结果。研究表明 ,该定位方法可以实现高定位精度 ,适合对接近大地水准面的目标定位。 相似文献
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Refraction of a microwave plane wave by a wedge with exact characterization of and is evaluated by a ray approach. Snell's Law is used for the lossless wedge, while exact formulations are used for the propagation constants and angle in the lossy wedge. The heavily lossy wedge produces negative refraction. Data are given on the loss factor that allows Snell refraction to be exactly reversed by lossy refraction, and the internal angle in the lossy wedge. 相似文献
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GongMin ZhangChuanwu HuangShunji 《电子科学学刊(英文版)》2005,22(3):294-300
The change of the equivalent baseline and interferometric phase of cluster SAR satellites is analyzed when the constellation circles around the Earth and the satellites rotate around the center at the same time. The letter provides assessment of baseline error and phase error which influence the precision of height measurement in the across-track interferometric mode. The mathematical model of cluster satellite movement is built, simulation analyses and the curve of height error are presented. The simulation results show that height measurement error can be compensated by the formulae derived in this letter, therefore, the Digital Elevation Models (DEM‘s) are recovered accurately. 相似文献
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靶场通常采用夜间静态拍星的方式检测光电经纬仪的静态测角总误差。受大气折射率变化的影响,俯仰方向测角数据通常采用大气折光差经验公式进行修正。不同地区和时间的大气环境差异使得该经验公式存在较大误差,导致拍星解算得到的俯仰方向测角误差偏大,且影响俯仰方向测角误差因素的进一步分离。为此,提出了一种基于多台光电经纬仪同步拍星数据相关性分析的大气折光差修正方法。基于经纬仪拍星方位角和俯仰角测量残差模型推导得到了大气折光差修正误差模型。根据该误差模型,利用分布在同一区域不同点位的多台光电经纬仪拍星俯仰角残差数据,采用最小二乘法拟合得到大气折光差的修正系数并修正俯仰角测量残差数据。实测数据表明:采用该方法对俯仰角测量残差进行大气折光差修正后,光电经纬仪俯仰角测角总误差显著降低,且由垂直轴倾斜误差修正错误引起的方位角和俯仰角残差特性得以显现。文中提出的方法无需使用探空气球等获取大气参数,即可对同一地域分布的多台光电经纬仪拍星俯仰角残差数据进行修正,修正后的数据可用于进一步分离其他误差因素,具有较强的工程应用价值。 相似文献
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复数折射角的物理内涵 总被引:1,自引:1,他引:0
当平面波入射到不同介质的分界面时.会产生反射与折射。对有耗介质,或在界面处产生全反射现象时,折射角为复数。复数折射角常使人感到困惑。本文将给出在不同情况下由复数折射角导出的等相面行进方向角和相速度以及等振幅面的衰减方向角和衰减常数的简洁计算公式,从而揭示复数折射角的物理意义。 相似文献
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针对海洋上空大气折射环境影响下岸基俯视雷达信号的舰载机动接收有效方法进行了系统研究.根据实际需求,建立俯视雷达信号在海洋上空传播的物理模型,通过射线追踪法结合Hopfield折射率剖面模型,仿真计算获得了大气折射影响下的电波实际传播路径,并与Ray-VT射线追踪软件的计算结果进行比对,四种发射参数下的水平距离相对偏差分别为-0.002%、-0.041%、-0.029%、-0.007%,初步说明了电波传播路径仿真的准确性.经过仿真,发现海洋上空大气折射环境对岸基俯视雷达信号的舰载接收有很大影响,必须对接收位置和接收仰角加以修正. 相似文献
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Poirier J.-R. Aubert H. David J. 《Microwave and Wireless Components Letters, IEEE》2008,18(5):299-301
This letter determines the dimensional profile of a periodic metallic surface that minimizes the electromagnetic energy scattering of an incident plane-wave back in the incident direction, irrespective of the plane-wave incidence angle. Simple Fourier series is used to describe the surface height variation and it is shown that a small number of design parameters are required to obtain the optimal profile of the surface. Experimental validations are presented and a very good agreement with electromagnetic simulation results is achieved. 相似文献