浅论回收型卫星气动外形设计

本文首先简要介绍回收型卫星重返大气层概貌。从工程设计角度出发论述卫星再入舱气动外形设计依据,评述美、苏两国现有空间再入飞行器外形的特点,然后论述卫星再入舱与导弹再入弹头的主要差别,指出再入舱特有的主要空气动力学问题。最后展望回收型卫星气动外形未来发展趋势,推荐一种有发展前途的新型再入舱气动外形—平头双锥体。     

高效率E类功率放大器在某调频电台发射机中的应用

高效率E类功率放大器是一种新型的开关模式功率放大器,由Sokals发明,Raab作了理论上的分析,但至今还不完善,近年来,工程应用研究是讨论的主要课题。本文根据某调频电台发射机的具体情况,讨论了它的设计方法和理论,并给出了试验结果。实验结果表明,应用了E类放大器之后,发射机的输出功率增加,整机效率提高,电池寿命延长,通信距离增加,效果明显改善,体现了应用高效率E类放大器的优越性。     

机舱内部超宽带确定性信道建模

将室内无线信道仿真中常用的几何光学和射线追踪技术,引入到对客机机舱内部的超宽带(Ultra-WideBand,UWB)信道研究当中。信道仿真的主要算法基于一种称为射线密度归一化(RayDensityNormalization,RDN)的方法。该方法使用射线密度的概念来计算每条射线对接收点处总信号强度的贡献。为了验证方法的有效性,实验构建了一个Boeing737-200客机机舱模型进行仿真。仿真将接收机设置在每个座位的顶部、扶手和底部,以研究不同水平高度信道的差别。仿真中对路径损耗和均方根(RMS)时延扩展两类大尺度信道参数进行了统计和分析,部分仿真结果与国外实测结果进行了对比。对比结果证明了仿真结果的保真度以及现有仿真工具的有效性。     

Synergetic retrieval of terrestrial AOD from MODIS images of twin satellites Terra and Aqua

Aerosol optical depth (AOD) is one of the most important indicators of atmospheric pollution. It can be retrieved from satellite imagery using several established methods, such as the dark dense vegetation method and the deep blue algorithm. All of these methods require estimation of surface reflectance prior to retrieval, and are applicable to a certain pre-designated type of surface cover. Such limitations can be overcome by using a synergetic method of retrieval proposed in this study. This innovative method is based on the fact that the ratio K of surface reflectance at different angles/geometries is independent of wavelength as reported by Flowerdew and Haigh (1995). An atmospheric radiative transfer model was then established and resolved with the assistance of the ratio K obtained from two Moderate Resolution Imaging Spectroradiometer (MODIS) spectral bands acquired from the twin satellites of Terra and Aqua whose overpass is separated by three hours. This synergetic method of retrieval was tested with 20 pairs of MODIS images. The retrieved AOD was validated against the ground observed AOD at the Taihu station of the AErosol RObotic NETwork (AERONET). It is found that they are correlated with the observations at a coefficient of 0.828 at 0.47 μm and 0.921 at 0.66 μm wavelengths. The retrieved AOD has a mean relative error of 25.47% at 0.47 μm and 24.3% at 0.66 μm. Of the 20 samples, 15 and 17 fall within two standard error of the line based observed AOD data on the ground at the 0.47 μm and 0.66 μm, respectively. These results indicate that this synergetic method can be used to reliably retrieve AOD from the twin satellites MODIS images, namely Terra and Aqua. It is not necessary to determine surface reflectance first.     

复合材料内传感光纤的埋置技术

对传感光纤在复合材料内的埋置技术进行了详细的实验研究,包括复合材料内光纤埋置工艺与布局原则,光纤内埋置部分在热压时的保护,光纤的引出及引出接头的保护,埋入光纤对材料性能的影响,复合材料内应变与损作的检测灵敏度与光纤阵列矶局的关系等,并成功地将传感光纤埋置入教－１１飞机的碳纤维／环氧复合材料垂直尾翼试件内。