Dust Environment Modelling of Comet 67P/Churyumov-Gerasimenko

Dust is an important constituent of cometary emission; its analysis is one of the major objectives of ESA’s Rosetta mission to comet 67P/Churyumov-Gerasimenko (C–G). Several instruments aboard Rosetta are dedicated to studying various aspects of dust in the cometary coma, all of which require a certain level of exposure to dust to achieve their goals. At the same time, impacts of dust particles can constitute a hazard to the spacecraft. To conciliate the demands of dust collection instruments and spacecraft safety, it is desirable to assess the dust environment in the coma even before the arrival of Rosetta. We describe the present status of modelling the dust coma of 67P/C–G and predict the speed and flux of dust in the coma, the dust fluence on a spacecraft along sample trajectories, and the radiation environment in the coma. The model will need to be refined when more details of the coma are revealed by observations. An overview of astronomical observations of 67P/C–G is given, because model parameters are derived from this data if possible. For quantities not yet measured for 67P/C–G, we use values obtained for other comets, e.g. concerning the optical and compositional properties of the dust grains. One of the most important and most controversial parameters is the dust mass distribution. We summarise the mass distribution functions derived from the in-situ measurements at comet 1P/Halley in 1986. For 67P/C–G, constraining the mass distribution is currently only possible by the analysis of astronomical images. We find that both the dust mass distribution and the time dependence of the dust production rate of 67P/C–G are those of a fairly typical comet.     

Changes in suspended sediments associated with 2004 Indian Ocean tsunami

The Sumatra tsunami on 26 December, 2004 in the Indian Ocean was generated by one of the largest earthquakes of the past 100 years. The present study investigated spatial and temporal changes of suspended sediment concentration (SSC) in North-East Indian Ocean (NEIO) after the Sumatra tsunami used satellite remote sensing data. The nLw551 products of MODIS-aqua data (using as indexing SSC) were analyzed for 5 years (2002–2006). Result shows SSC notably increased (55.6–200%) in large river estuaries along coast of the Bay of Bengal (BOB) in a short time (4 weeks) after the tsunami, especially the northwest coast of Indonesia, southeast coast of Myanmar, as well as the north offshore of BOB. Those increases were mainly caused by the re-suspension function induced by the initial surge of the tsunami. Monthly analysis indicates increases (4.26%) of SSC of the entire North-East Indian Ocean area in 2005; especially in November 2005 when increase of SSC increased by about 6.19% compared with other years; those may mainly be caused by the destruction of coastal vegetation and modifying of estuaries or wetlands by the 2004 tsunami. The increases of SSC have different mechanism in different region and period after the tsunami.     

侦察卫星星座覆盖性能仿真分析软件设计

为了快速、便捷分析天基侦察系统的对地覆盖性能,开展综合对比分析,设计开发天基侦察卫星星座对地覆盖性能仿真分析系统。仿真系统基于VS2010平台开发,通过软件交互接口调用STK引擎完成计算,使用Matlab编译的库函数完成仿真数据处理及可视化输出。仿真系统采用Redis数据库实现输入参数和仿真结果的存储,并提供与外部程序静态和动态交互功能。仿真系统提供独立仿真和协同仿真两种工作方式,可独立运行分析星座覆盖性能,也可作为其它仿真系统的一部分,在外部命令控制下运行。经应用测试,该系统可以快速、有效完成卫星星座对地面目标的覆盖性能对比分析,为天基侦察系统星座构型设计论证提供支撑。     

T 形焊缝超声相控阵检测的计算机辅助技术

超声相控阵技术在T形焊缝中的应用表现出其明显优势,但声波在T形焊缝中的辐射区域不能形象界定,且回波来源的位置得不到准确地判断。针对T形焊缝的结构编译了超声相控阵检测辅助软件,对试样中的人工孔检测表明:采用计算机辅助技术可以实现T形焊缝超声相控阵扇扫声束覆盖及回波信号的识别。     

基于北斗的ADS-B技术在我国通用航空中的应用

通用航空在我国发展迅速,但低空空域监视技术一直是其发展的瓶颈,提出了采用基于北斗的ADS—B技术作为解决问题的方法。介绍了ADS-B技术,分析了实现东北地区低空覆盖所需的地面站数量;设计了基于北斗的ADS—B通航监视系统,提出了发展该技术的建议措施。     

Advances on Technology and Application of Ocean Color Remote Sensing in China (2004 - 2006)

China has great progress in the technology and application of ocean color remote sensing during 2004-2006. In this report, firstly, four major technical advances are displaying, including (1) the vector radiative transfer numerical model of coupled ocean-atmosphere system; (2) the atmospheric correction algorithm specialized on Chinese high turbid water; (3) systematical research of hyper-spectrum ocean color remote sensing; (4) local algorithms of oceanic parameters, like ocean color components, ocean primary productivity, water transparency, water quality parameters, etc. On the foundation of technical advances, ocean color remote sensing takes effect on ocean environment monitoring, with four major kinds of application systems, namely, (1) the automatic multi-satellites data receiving, processing and application system; (2) the shipboard satellite data receiving and processing system for fishery ground information; (3) Coastal water quality monitoring system, integrating satellite and airborne remote sensing technology and ship measurement; (4) the preliminary system of airborne ocean color remote sensing application system. Finally, the prospective development of Chinese ocean color remote sensing is brought forward. With Chinese second ocean color satellite (HY-1B) orbiting, great strides will take place in Chinese ocean color information accumulation and application.     

多无人机协同搜索区域分割与覆盖

多无人机覆盖搜索是无人机的一项主要任务,将搜索区域进行分割后,每个子区域内成为单机覆盖搜索问题,大大降低了任务难度.对无人机的平行搜索策略进行了详细的分析,针对平行搜索策略给出了搜索起始点、转弯关键点、搜索终点的判断依据,使得区域覆盖率达到100%.分析了最小转弯半径对搜索路径的影响.根据无人机初始位置和搜索面积对任意凸多边形搜索区域进行分割.针对无人机搜索的特点,以转弯次数作为主要依据对分割结果进行评估.对不同情况下无人机从初始位置到搜索起始点的路径进行了研究.最后通过仿真验证了方法的实用性.      

First quality assessment of the Cryosat-2 altimetric system over ocean

This paper presents the results of a Calval analysis performed for the Cryosat-2 mission over ocean. The data set used in this analysis consists of products generated by the Cryosat-2 Processor Prototype developed by CNES (Center National d’Etudes Spatiales). This data set has been analysed focusing on LRM (Low Resolution Mode) mode only. One major objective of this paper is to illustrate the potential of Cryosat-2 data over ocean, mainly for waves and Sea Level Anomaly applications. All the results indicate very good performances of the SIRAL (SAR/Interferometric Altimeter) altimeter over ocean. Crossover standard deviation is close to 6.5 cm over the analysed period (3 months) which is close to the Jason-2 and ENVISAT performance. All these results confirm that Cryosat’s altimeter can provide data almost as valuable as other flying altimetric missions, and that it has the potential to contribute to oceanography (e.g. multi-mission climate record, mesoscale monitoring in near real time) and to geodesy (e.g. mean sea surface, bathymetry).     

无线传感器网络覆盖质量问题

降低功耗、延长寿命是无线传感器网络的一个重要问题,同时,对监测区域保持一定的覆盖质量才能及时捕捉到目标的状态变化.一种广泛采用的策略是选出能够满足监测区域质量要求的最小节点集作为工作节点,关闭其他冗余节点.因此,传感器网络中控制节点休眠与保持覆盖质量是两个重要方面.提出了一个数学模型,求解满足任意给定覆盖服务质量下所需的最小节点数.实验表明,当监测区域与节点感知区域比值较大时,提出的方法更为准确地计算出所需最小工作节点数,且此方法复杂度低、传感器节点的感知区域可以为任意形状.网络覆盖质量与节点休眠率同时达到最大化是一个NP难问题,采用遗传算法进行仿真实验尝试性解决这一问题,为传感器网络实际应用带来重要意义.     

具有相反横向射流角的全覆盖气膜孔冷却特性

通过数值计算的方法对全覆盖气膜冷却结构的流场特性、壁面表面传热系数、绝热壁面气膜冷却效率以及考虑固体导热影响下的综合冷却效率进行了对比研究.结果显示:相反横向射流角产生的反肾形涡对使冷气侧向扩散能力更强;虽然表面传热系数升高,但是由于较高的绝热壁面气膜冷却效率降低了传入固体壁面的热量,提升综合冷却效率.吹风比为1.0时,45°相反横向射流角斜孔有最高的综合冷却效率.当吹风比为1.5和2.0时,30°相反横向射流角斜孔有最高综合冷却效率.与相同横向射流角斜孔作对比,15°相反横向射流角斜孔综合冷却效率不及15°相同横向射流角斜孔,45°,60°相反横向射流角斜孔综合冷却效率在不同流向长度上与相同横向射流角斜孔综合冷却效率相差不大,30°相反横向射流角斜孔综合冷却效率高于相同横向射流角斜孔.