共查询到19条相似文献,搜索用时 125 毫秒
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鉴于低空大气波导对海上工作的雷达、通信系统的显著影响,提出了基于实测船舶自动识别系统(automatic identification system, AIS)信号的海上低空大气波导遥感新方法.首先讨论了不同大气折射环境下的AIS信号传播特性,验证了低空大气波导尤其表面波导对海上实际VHF频段AIS信号的显著影响;然后给出了2018年4月20日以及22日岸基AIS接收机接收功率平面位置分布图结果,利用接收站附近探空站的修正大气折射率剖面验证了大气波导是形成AIS信号远距离传播的主要原因;最后给出了基于AIS信号反演低空大气波导的步骤,采用粒子群优化算法得到根据单一方位接收功率的反演结果.该方法具有被动接收、时空分辨率高的优点,是当前雷达海杂波、卫星导航信号遥感探测大气波导的有益补充. 相似文献
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罗兰C信号在传播过程中受到路径影响,传播速度不可预测,降低了接收机的定位精度。采取时间比对方法解决二次相位因子(ASF)修正问题,有效改善定位准确度。 相似文献
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大气波导可陷获无线电波信号,使其发生超视距传播现象,影响无线电系统信号传播预测和性能评估应用。本文针对由探空数据诊断的悬空波导个例,利用对流层电波传播确定性方法模拟岸-船自动识别系统(automatic identification system, AIS)传播链路,定量研究了不同悬空波导环境影响下AIS信号的超视距传播特性。结果表明:波导强度50 M单位且底高约7 m的悬空波导环境下,AIS信号发生明显超视距传播现象;波导底高约700 m且强度较大的悬空波导环境也会对AIS信号传播产生影响;相比于单一悬空波导模型,复合悬空波导(文中指两个悬空波导层结构组成)环境对AIS信号传播影响更大。本文研究成果可为大气波导监测反演、无线电系统设计、装备效应评估等应用提供重要理论参考。 相似文献
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罗兰C信号在传播过程中受到陆地导电率和地形等因素的影响,传播速度不可预测,使信号传播时延增加,引起附加二次相位因子(ASF),降低了接收机的定位精度,因此在精确定位解算之前,需要用ASF对实测的罗兰传播时延进行修正。介绍了采取时间比对方法,利用现场实测和理论预测相结合建立起ASF修正数据库,提供给用户使用,解决ASF修正问题,使定位准确度得到有效改善。 相似文献
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收发相位同步是双基地雷达相参处理的前提,相位同步误差会对改善因子产生影响。首先建立了考虑相位同步误差的相参检波信号模型,在此基础上,导出了相位同步误差对改善因子影响的关系式,最后通过仿真分别给出了不同杂波类型,不同重复频率时相位同步误差对改善因子影响的结果。仿真结果表明,相位同步误差越大,对各类杂波改善因子的影响也越大,当误差为10 Hz时,地杂波改善因子下降十几分贝,且载波频率为1 GHz时,若要求MTI改善因子为50 dB,稳定本振的频率稳定度需满足10-8的数量级。 相似文献
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A comparison of 3, 9.6, and 18-GHz low-altitude over-the-horizon propagation (as influenced by the evaporation duct) is presented. Theoretical and experimental results are given for a 35-km over-water path, where the transmitters were located about 5 m above mean sea level and the receivers were located either 4-5 m or 18-19 m above sea level. Results are presented in terms of the one-way propagation factor in decibels at each frequency. Long-term cumulative frequency distributions of calculated and observed propagation factors are presented. Particular attention is given to the relative performance of each radio frequency to investigate frequency-diversity improvements that may be available on such paths. In most cases presented, there is a close agreement between theory and observations. It is concluded that substantial improvements in received signal levels are likely to be achieved in most areas of the world by a suitable choice of two frequencies in the 10-20-GHz range 相似文献
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Martorella M. Berizzi F. Mese E.D. 《Antennas and Propagation, IEEE Transactions on》2004,52(5):1193-1204
Fractal analysis of sea surface backscattering signal (sea clutter in radar terminology) represents a novel technique for the study of sea surface roughness. When Kirchhoff's assumption is satisfied, the fractal dimension of the signal is linearly related to the fractal dimension of the sea surface. Moreover, such a relationship is independent of transmitted frequency, polarization, time, space, sea wave propagation direction, incident angle (within the constraint of Kirchoff's assumption) and significant wave height. Nevertheless, for a low grazing angle, the Kirchhoff approximation does not hold and the behavior of the sea clutter fractal dimension cannot be theoretically predicted. The purpose of this paper is to investigate the fractal dimension of the sea clutter at low grazing angle, in order to extend the theoretical results. Moreover, the effects of the presence of a target on the sea surface are analyzed by means of the fractal dimension. Such an analysis is performed by using live recorded clutter data. In detail, the fractal dimension's dependence on space, time, sea wave propagation direction, sea wave height, transmitted polarization and presence of targets is investigated. A discussion on the use of the sea clutter fractal dimension for sea surface monitoring is addressed. 相似文献
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跨海微波超视距远距离传播深受探测和通信领域的重视,其机制分析和规律观测有重要意义. 本文对跨海微波超视距远距离传播的机制和有关原理进行了分析,对2019-09开展的C波段和X波段微波昼间跨海面超视距远距离传播试验进行了研究;利用试验测试记录和期间的气象站风观测数据,对试验期间观测到的C波段不同距离线路和X波段50 km线路上白昼的传播规律和机制做了总结分析. 本文结论可供对流层微波超视距远距离传播(大气波导传播和散射传播)研究或应用的系统设计、数据分析和机制研究等参考使用,特别是跨海的试验测试可以直接运用. 相似文献
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针对星载AIS(船舶自动识别系统)接收系统提出了实现信号有效接收的总体方案。重点提供星载AIS信号处理器的硬件电路设计和基于FPGA信号处理软件设计。以AIS接收机整机为测试平台,通过仿真和试验验证了星载AIS接收机整机设计的有效性和可行性,此信号处理器可以满足星载AIS接收机的需求。 相似文献
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A theoretical and numerical method is presented for the analysis of sea surface influence on the radar reflectivity of ships. The method of analysis is based on presentation of the field density scattered by the ship as a sum of echoes from different backscatterers located on the surface of the ship. The influence of sea surface is accounted for under the physical optics assumption. An analytical expression is obtained for the propagation factor with the ship in line-of-sight (LOS) range. Plots are illustrated for the dependence of the propagation factor on ship range for different heights of the radar antenna. The effect of microwave backscattering amplification from the ship is predicted for grazing angles of observation within LOS range 相似文献