共查询到19条相似文献,搜索用时 156 毫秒
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对不规则地面低频地波传播预测中积分方程方法、Millington经验公式以及FDTD算法的性能进行了分析比较.首先介绍了三种方法的模型和理论;然后分别采用这几种方法预测了传播路径中有高斯形山脉时低频地波的场强和二次时延分布,对几种方法的优势、局限性及误差进行了比较分析.结果显示:在地形起伏较小的区域,积分方程方法和FDTD方法吻合较好,Millington方法不能反映地形起伏对地波传播影响规律;当地形起伏较大时,积分方程方法也不再适用,FDTD则可以在山前及山脉区域预测到由地形反射引起的振荡信号. 相似文献
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脉冲CO2激光水下致声声脉冲特性的实验研究 总被引:1,自引:0,他引:1
以分析水中的光声信号的特点为目的,采用实验的方法利用压电陶瓷球形水听器、数字存储示波器,对TEACO2脉冲激光在水中激发声波的幅度、频率等特性进行了测量,并用信号分析软件进行分析和处理。结果表明,TEACO2脉冲激光在水中产生的声信号幅度随脉冲能量增加而增大。实验中首次发现,激光声频率在100kHz以内有31kHz和62kHz两个峰值,且该两频率峰值随激光脉冲宽度增加而减小。光声信号的以上特性表明,可以通过调节激光脉冲的能量和宽度,选择或控制应用于水声通信、水下资源探测等技术的光声信号。 相似文献
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设计并实现了一种基于人眼安全波段的1550 nm全光纤化结构单频脉冲光纤激光器。激光器采用外腔稳频技术的单频半导体激光器作为种子源,其线宽1.8 kHz,功率20 mW。通过预放大器和声光调制器获得单频脉冲激光,并运用两级光纤放大器实现了线宽1.9 kHz、平均功率521 mW、脉冲宽度200 ns、重复频率10 kHz的单频脉冲光纤激光输出。输出脉冲峰值功率达260 W。输出端采用了双包层单模光纤,保证了输出激光的光束质量。整个激光器通过对种子光级联放大,结合放大器的增益控制,成功抑制了受激布里渊散射(Stimulated Brillouin Scattering,SBS)效应,消除了放大过程中噪声对线宽的影响,获得了线宽稳定的单频脉冲激光。 相似文献
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The Loran-C Navigation System is described in terms of its characteristics as a precise time and frequency dissemination system. The technique employed in timing a Loran-C chain is described, and user techniques are addressed including economic considerations. The accuracy available for both ground-wave and sky-wave transmission modes is shown to be a function of the low-frequency propagation factors and equipment delays involved. Phase and amplitude perturbations due to irregular terrain effects are shown to produce time difference discrepancies in inland service areas. Using broad assumptions, both ground-wave and sky-wave coverages are estimated. Experience shows that Loran-C provides an excellent medium for the dissemination of precise time and frequency on a continuous basis in both the ground-wave and sky-wave modes. The stability of the ground wave provides a submicrosecond precision capability, but the accuracy of the system is limited by propagation effects to about ± 1 µs. Loran-C sky-wave synchronization appears to be capable of ± 1 µs precision for one-hop daytime transmissions and an estimated ± 8 µs for one-hop nighttime transmissions. As distance is increased and more sky-wave hops are involved, nighttime synchronization precision is degraded to about ± 20 µs. Accuracy of sky-wave synchronization is limited to about ± 50 µs for both daytime and nighttime. 相似文献
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The propagation of the ground-wave pulse between points on the ground is of considerable practical importance, particularly in the application of the Loran-C navigation system to the absolute time synchronization of geographically separated clocks. Thus, the envelope of the pulse is frequently used to remove ambiguities which would otherwise result from the pulse synchronization at the characteristic or carrier frequency of the pulse. The propagation of the ground wave over finitely conducting ground modifies the propagation time of the tagged point-in-time on the envelope by amounts which may be sufficiently large as to cause cycle ambiguitypm pi radians at the carrier or characteristic frequency of the pulse. It is therefore the purpose of this paper to investigate the magnitude of this error by ascertaining the true signal velocity as determined by tagging a point-in-time on the leading edge of a groundwave pulse and calculating the time corrections for various ground conductivities and distances. These calculations can then be applied to resolve thepm pi radians ambiguity of the precision phase velocity instrumentation for Loran-C especially when the system is used for absolute-time synchronization. 相似文献
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D. V. Ivanov 《Journal of Communications Technology and Electronics》2006,51(7):759-766
The ionospheric propagation of shortwave signals with pseudorandom frequency shift are considered with allowance for their coherent and incoherent reception. The frequency ranges within which 1D propagation is realized over ionospheric radio links 2–8 Mm long are investigated, and the dispersion characteristics of these propagation channels are determined. The effect of the dispersion distortions on the reception of pseudorandom signals is investigated, and the maximal permissible signal parameters are estimated. 相似文献
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该文以非合作水声脉冲信号为对象,研究非合作条件下水声信号的单水听器匹配场定位。首先根据水声脉冲信号的短时瞬态非平稳特性,设计具有自适应径向高斯核函数的时频分布进行频率估计。然后利用声场传播模型计算声场,求解海洋信道脉冲响应。由计算出的信道脉冲响应和水听器上的接收信号,使用时域最小二乘的方法得到搜索网格区域上的拷贝场信号。最后通过建立误差代价函数,获得表征目标位置的模糊表面,实现利用单个水听器对非合作水声脉冲信号的匹配场定位。通过仿真实验和实际海试数据的验证,证明了该方法的有效性。 相似文献