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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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针对稳定条件下蒸发波导RSHMU模型过于敏感不便使用的问题,引入BH91关系式、CB05关系式和SHEBA07关系式给出了相关的改进方法,并对不同风速以及不同相对湿度的敏感性进行了分析. 结果发现引入稳定条件下的剖面稳定度函数对蒸发波导高度诊断的敏感性改善不大. 进一步地,借鉴Paulus给出的订正方法,给出了P-RSHMU蒸发波导模型改进预测方法,有效解决了已有模型稳定条件下的不合理诊断结果. 与渤海梯度塔实测数据对比分析表明:稳定条件下P-RSHMU蒸发波导模型预测蒸发波导高度的平均误差为?1.02 m,均方根误差为1.49 m,显著优于已有RSHMU模型. 相似文献
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短波电离层传播损耗的计算对电离层基础研究与短波通信、天波超视距雷达等应用有重要意义,以往主要采用半经验模型.文中基于电磁波传播的抛物方程方法,实现对短波电离层传播损耗空间分布的数值计算,该方法可同时考虑电磁波传播的折射、反射、绕射和吸收等效应.根据电子浓度剖面数据,仿真计算了不同频点和天线波束宽度情况下的电离层传播损耗,从折射效应引起的传播模式、反射点高度、地面落区位置方面,与射线描迹结果进行对比,两者具有一致性.此外,进一步仿真分析了电离层的吸收效应.研究结果初步表明了抛物方程方法预测电离层传播的有效性及其强大的功能. 相似文献
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大气波导引起的反常地物回波是影响天气雷达数据质量的重要因素,本文针对大气波导对天气雷达海面回波的影响及应用,利用青岛多普勒天气雷达资料,结合探空数据对2014年7月18和19日一次大气波导过程造成的超视距海面回波进行了分析.通过分析处理探空剖面数据,得到18日20时存在表面波导,而雷达资料显示该时刻雷达存在明显的超视距海面回波.此次大气波导超视距过程持续约24 h,雷达超视距海面回波总体趋势是先从弱到强,再变弱直至消失,其空间分布和时间变化非常复杂.进一步基于实测雷达回波数据,采用抛物方程和粒子群算法反演获得了水平不均匀的大气波导剖面,比较了实测回波功率和以反演剖面为输入的计算回波功率,两者之间相差较小,表明基于天气雷达回波的大气波导反演方法具有有效性. 相似文献
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提出基于支持向量机的地基单站GPS遥感大气剖面的反演方法,主要包括经典支持向量机、最小二乘支持向量机、相关向量机3种方法,利用青岛地区的历史数据进行了仿真反演对比研究,并与神经网络反演方法进行比较,结果表明支持向量机能够有效地应用于地基单站GPS大气遥感领域。 相似文献
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Objective To investigate the effect of minocycline on early brain injury (EBI) following subarachnoid hemorrhage(SAH) in rats. Methods SAH was induced by the filament perforation model in male Sprague Dawley rats. SD rats(n=77) were randomly assigned to sham (n=22), SAH+vehicle (n=28), and SAH+minocycline (n=27) groups. Minocycline (135mg/kg) or equal volume of vehicle was administered 1 h after SAH induction. Mortality, neurological scores, brain edema were evaluated 24 h after SAH. Cell apoptosis were examined by TUNEL staining, and the expression of caspase-3 and Bcl-2 was assayed by Western blot at the same time point. Results The mortality was 21.4% in SAH+vehicle group, 18.5% in the SAH+minocycline group, while no death was observed in sham-operated rats; there was no significant difference in mortality between SAH+vehicle and SAH+minocycline groups (P>0.05), but the mortality in these two groups was much higher than that in shamgroup(P<0.05). The water content of brain was significantly increased in the SAH+vehicle group (80.00±0.16)% compared with that in sham group [(79.13±0.08)%, P<0.05]. Minocycline treatment markedly reduced brain water content (79.36±0.07)% compared with that in SAH+vehicle group (P<0.05). Caspase-3 levels were markedly increased in SAH+vehicle group (1.53±0.24) compared with sham group (1.00±0.21). Minocycline treatment significantly reduced caspase-3 levels, compared to SAH+vehicle group (1.11±0.18, P<0.05). A significant decrease in Bcl-2 expression was observed in SAH+vehicle group(0.65±0.03) compared with the sham group (1.00±0.12). The treatment of minocycline upregulated the expression of Bcl-2,compared to SAH+vehicle group (0.93±0.13, P<0.05). TUNEL-positive cells were increased in the cortex of SAH+vehicle rats,compared to sham group [(31.50±3.70)%, P<0.05]. Minocycline treatment significantly reduced the number of TUNEL positive cells, compared to SAH+vehicle group [(14.25±2.50)%, P<0.05]. Conclusion Minocycline may reduce early brain injury after subarachnoid hemorrhage in rats by inhibiting cell apoptosis, which is associated with down-regulation of caspase-3 and up-regulation of Bcl-2. 相似文献
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