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141.
数据链作用距离的试飞结果受试验区电波传播衰减影响很大,需要对其进行精确计算,为分析试飞结果提供支持.Fock级数法是计算电波衰减的一种精确方法,本文详细讨论了应用该方法求解试验区电波传播衰减的工程计算问题. 相似文献
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Igor S. Veselovsky Serge Koutchmy 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
Several important issues are open in the field of solar variability and they wait their solution which up to now was attempted using critical ground-based instrumentations. However, accurate photometric data are attainable only from space. New observational material should be collected with high enough spatial and spectral resolution, covering the whole visible range of the electromagnetic spectrum as well infrared and ultraviolet to reconstruct the total solar irradiance: (1) the absolute contributions of different small-scale structural entities of the solar atmosphere from the white light flares and from micro-flares are still poorly known; (2) we do not know the absolute contributions of different structural elements of the solar atmosphere to the long-term and to the cyclic variations of the solar irradiance, including features of the polar regions of the Sun; (3) the variations of the chromospheric magnetic network are still poorly evaluated; (4) only scarce information is available about the spectral variations of different small-scale features in the high photosphere. Variability of the Sun in white light can be studied with higher spectral, spatial and time resolution using space-born telescopes, which are more appropriate for this purpose than ground based observatories because of better seeing conditions, no interference of the terrestrial atmosphere and a more precise calibration procedure. Scientific requirements for such observations and the possible experimental tools proposed for their solution. Suggested solar studies have broader astrophysical importance. 相似文献
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LIU Hua YANG Jia-ling LIU Kai-xin 《中国航空学报》2007,20(3):210-214
Theoretical analysis and numerical calculations of Love wave propagation in layered graded composites with imperfectly bonded interface are described in this paper. On the basis of WKB method, the approximate analytic solutions for Love waves are obtained. By the interface shear spring model, the dispersion relations for Love waves in layered graded composite structures with rigid, slip, and imperfectly bonded interfaces are given, and the effects of the interface conditions on the phase velocities of Love waves in SiC/Al lay- ered graded composites are discussed. Numerical analysis shows that the phase velocity decreases when the defined flexibility parameter is greater. For the general imperfectly bonded interface, the phase velocity changes in the range of the velocities for the rigid and slip interface conditions. 相似文献
146.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(4):1263-1278
Enhancing the dust storm detection is a key part for the environmental protection, human healthy and economic development. The goal of this paper is to propose a new Support Vector Machine (SVM)-based method to automatically detect dust storms using remote sensing data. Existing methods dealing with this problem are usually threshold-based that are of great complexity and uncertainty. In this paper we propose a simple and reliable method combining SVM with MODIS L1 data and explore the optimal band combinations used as the feature vectors of SVM. The developed method was evaluated by MODIS and OMI data qualitatively and quantitatively on three study sites located in the Arabian Desert, Gobi Desert and Taklimakan Desert, and it was also compared to three other traditional methods based on their accuracy, complexity, reliability and sensitivity to thresholds. The detection results demonstrated that the combination of (Band7 − Band3)/(Band7 + Band3) ((B7 − B3)/(B7 + B3)), Band20 − Band31 (B20 − B31), and Band31/Band32 (B31/B32) can detect the dust storms more precisely than other individual bands or their combination. The comparison among those cases indicated that the proposed automatic method exhibited an advantage of minimizing the uncertainty and complexity, which were the limits of defining thresholds based on the threshold-based methods. The conclusions can provide references for studies that focus on statistical-based dust storm detection. 相似文献
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