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261.
阐述了一起发生在用户作训期间的短波电台干扰类故障,在常规线路导通和串件试验均无法判定故障点的情况下,工程技术员根据故障现象,结合馈线图进行层层分析,剖析该故障产生的原因,得出问题的解决方案,给直升机大修及外场维护过程中解决该类故障提供参考. 相似文献
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M. Pietrella L. Perrone G. Fontana V. Romano A. Malagnini G. Tutone B. Zolesi Lj.R. Cander A. Belehaki I. Tsagouri S.S. Kouris F. Vallianatos J. Makris M. Angling 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
After a first oblique-incidence ionospheric sounding campaign over Central Europe performed during the period 2003–2004 over the radio links between Inskip (UK, 53.5°N, 2.5°W) and Rome (Italy, 41.8°N, 12.5°E) and between Inskip and Chania (Crete, 35.7°N, 24.0°E), new and more extensive analysis of systematic MUF measurements from January 2005 to December 2006 have been performed. MUF measurements collected during moderately disturbed days (17 ? Ap ? 32), disturbed days (32 < Ap ? 50) and very disturbed days (Ap > 50), have been used to test the long term prediction models (ASAPS, ICEPAC and SIRM&LKW), and the now casting models (SIRMUP&LKW and ISWIRM&LKW). The performances of the different prediction methods in terms of r.m.s are shown for selected range of geomagnetic activity and for each season. 相似文献
264.
R.R. Rosa M. Karlický T.B. Veronese N.L. Vijaykumar H.S. Sawant A.I. Borgazzi M.S. Dantas E.B.M. Barbosa R.A. Sych O. Mendes 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
We analyze the weak component of the localized temporal pattern variability of 3 GHz solar burst observed by the Ondrejov radiospectrograph. A complex, short and weak impulsive sample from the time series was analyzed by applying a method based on the gradient pattern analysis and discrete wavelet decomposition. By analyzing canonical temporal variability patterns we show that the new method can reliably characterize the phenomenological dynamical process of short time series (N ? 103 measurements) as the radio burst addressed here. In the narrowest sense, by estimating the mutual information distance in the gradient spectra, we show that the fluctuation pattern of the short and weak 3 GHz impulsive solar burst, with energetic amplitudes <350 SFU, is closer to the intermittent and strong MHD turbulent variability pattern. 相似文献
265.
L. van Driel-Gesztelyi C.P. Goff P. Démoulin J.L. Culhane S.A. Matthews L.K. Harra C.H. Mandrini K.-L. Klein H. Kurokawa 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
A series of three flares of GOES class M, M and C, and a CME were observed on 20 January 2004 occurring in close succession in NOAA 10540. Types II, III, and N radio bursts were associated. We use the combined observations from TRACE, EIT, Hα images from Kwasan Observatory, MDI magnetograms, GOES, and radio observations from Culgoora and Wind/ WAVES to understand the complex development of this event. We reach three main conclusions. First, we link the first two impulsive flares to tether-cutting reconnections and the launch of the CME. This complex observation shows that impulsive quadrupolar flares can be eruptive. Second, we relate the last of the flares, an LDE, to the relaxation phase following forced reconnections between the erupting flux rope and neighbouring magnetic field lines, when reconnection reverses and restores some of the pre-eruption magnetic connectivities. Finally, we show that reconnection with the magnetic structure of a previous CME launched about 8 h earlier injects electrons into open field lines having a local dip and apex (located at about six solar radii height). This is observed as an N-burst at decametre radio wavelengths. The dipped shape of these field lines is due to large-scale magnetic reconnection between expanding magnetic loops and open field lines of a neighbouring streamer. This particular situation explains why this is the first N-burst ever observed at long radio wavelengths. 相似文献
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为了模拟无线电引信中的Chirp信号,设计了一种基于DDS的无线电引信Chirp信号生成系统的方案。该方案采用PC输出波形控制参数,用DSP进行数字信号处理并控制DDS芯片的总体结构。对PC与DSP芯片的通信接口、DSP芯片与DDS芯片的接口以及软件处理流程进行了详细设计。 相似文献
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射频干扰(radio frequency interference, RFI) 对L波段综合孔径辐射计遥感数据造成了严重污染,降低了产品质量。RFI检测定位是处理RFI的关键步骤。传统的基于亮温图像的定位算法受到仪器角分辨率的限制,无法有效分离相邻的RFI。为了实现更高的空间分辨率,基于子空间分解技术的多信号分类(multiple signal classification, MUSIC)算法被提出。然而,当亮温图像的信噪比较低时,背景和噪声对子空间分解的准确性影响较大,进而降低了MUSIC算法的定位性能。文章通过结合亮温图像和子空间分解两种方法的优点,提出了一种融合改进定位方法。该方法通过在亮温图像域中消除背景场景、增强目标射频干扰,2次提高了图像信噪比,在频域中,利用子空间分解和MUSIC算法实现超分辨率和高精度定位。通过对土壤湿度和海洋盐度(soil moisture and ocean salinity, SMOS)卫星数据进行实验和仿真验证,证明了文章提出的方法在低信噪比情况下优于传统的MUSIC算法和基于亮温的定位算法。此外,在对多个弱RFI源的定位上,该方法的定位精度也优于基于点源波纹的弱RFI检测定位算法。 相似文献
270.
电磁散射场和雷达散射截面积的计算 总被引:2,自引:1,他引:1
薛晓春 《北京航空航天大学学报》1998,24(2):193-196
计算了绕二维物体的时域电磁散射场的空间分布和雷达散射截面积 (RCS).通常的电磁场计算是频域的,采用高频计算方法,而流场计算是时域的.由于以研究流场--电磁场优化设计计算为目的,需要统一采用时域计算,因此重点采用矢通量分裂法这种时域方法计算了RCS ,通过将特征值分裂为正负两部分,抑制了各自的误差.此外,采用LaxWendroff方法作为对照.两种方法的结果一致. 相似文献