基于CFD高精度算法的雷电电磁场研究

雷电空间电磁场一直是电磁领域研究的热门，成熟的算法例如有限时域差分法（FDTD），传输线矩阵法（TLM）以及频域的矩量法（MoM）在计算雷电问题方面都有广泛的应用。由于计算流体力学（CFD）中的Euler方程与电磁学中的Maxwell方程有着相同的守恒形式，而且采用间断伽辽金方法（DG）已经在流场问题上得到广泛的尝试，因此引入了基于计算流体力学的DG方法来离散时域Maxwell方程，并采用网格分区并行技术加速计算，使用基于DG的圆球雷达散射截面积（RCS）算例进行测试，数值结果一致表明DG算法在求解电磁场问题上的可行性，之后通过计算一段近场雷电通道的电场分布并与解析解、某算法仿真解对比，数据基本吻合，说明该方法适合于雷电电磁场的计算。     

导航卫星中断频次的分析方法

面向导航卫星中断频次的定量分析需求,该文分析导航卫星中断产生的主要原因,给出中断频次分析的流程,并针对分析过程中的三个关键问题,研究提出具体实施方法,包括通过相关性分析快速定位底层中断事件,通过中断树建立指标分析模型,并融合在轨数据、地面试验数据快速预估得到底层功能异常率等。最后通过示例进一步说明中断频次分析过程。该文方法已应用于北斗导航卫星工程。     

Mapping mean lake surface from satellite altimetry and GPS kinematic surveys

Lake water height is a key variable in water cycle and climate change studies, which is achievable using satellite altimetry constellation. A method based on data processing of altimetry from several satellites has been developed to interpolate mean lake surface (MLS) over a set of 22 big lakes distributed on the Earth. It has been applied on nadir radar altimeters in Low Resolution Mode (LRM: Jason-3, Saral/AltiKa, CryoSat-2) in Synthetic Aperture Radar (SAR) mode (Sentinel-3A), and in SAR interferometric (SARin) mode (CryoSat-2), and on laser altimetry (ICESat). Validation of the method has been performed using a set of kinematic GPS height profiles from 18 field campaigns over the lake Issykkul, by comparison of altimetry’s height at crossover points for the other lakes and using the laser altimetry on ICESat-2 mission. The precision reached ranges from 3 to 7 cm RMS (Root Mean Square) depending on the lakes. Currently, lake water level inferred from satellite altimetry is provided with respect to an ellipsoid. Ellipsoidal heights are converted into orthométric heights using geoid models interpolated along the satellite tracks. These global geoid models were inferred from geodetic satellite missions coupled with absolute and regional anomaly gravity data sets spread over the Earth. However, the spatial resolution of the current geoid models does not allow capturing short wavelength undulations that may reach decimeters in mountaineering regions or for rift lakes (Baikal, Issykkul, Malawi, Tanganika). We interpolate in this work the geoid height anomalies with three recent geoid models, the EGM2008, XGM2016 and EIGEN-6C4d, and compare them with the Mean Surface of 22 lakes calculated using satellite altimetry. Assuming that MLS mimics the local undulations of the geoid, our study shows that over a large set of lakes (in East Africa, Andean mountain and Central Asia), short wavelength undulations of the geoid in poorly sampled areas can be derived using satellite altimetry. The models used in this study present very similar geographical patterns when compared to MLS. The precision of the models largely depends on the location of the lakes and is about 18 cm, in average over the Earth. MLS can serve as a validation dataset for any future geoid model. It will also be useful for validation of the future mission SWOT (Surface Water and Ocean Topography) which will measure and map water heights over the lakes with a high horizontal resolution of 250 by 250 m.     

Evaluation of a regional real-time precise positioning system based on GPS/BeiDou observations in Australia

The performance of real-time (RT) precise positioning can be improved by utilizing observations from multiple Global Navigation Satellite Systems (GNSS) instead of one particular system. Since the end of 2012, BeiDou, independently established by China, began to provide operational services for users in the Asia-Pacific regions. In this study, a regional RT precise positioning system is developed to evaluate the performance of GPS/BeiDou observations in Australia in providing high precision positioning services for users. Fixing three hourly updated satellite orbits, RT correction messages are generated and broadcasted by processing RT observation/navigation data streams from the national network of GNSS Continuously Operating Reference Stations in Australia (AUSCORS) at the server side. At the user side, RT PPP is realized by processing RT data streams and the RT correction messages received. RT clock offsets, for which the accuracy reached 0.07 and 0.28?ns for GPS and BeiDou, respectively, can be determined. Based on these corrections, an accuracy of 12.2, 30.0 and 45.6?cm in the North, East and Up directions was achieved for the BeiDou-only solution after 30 min while the GPS-only solution reached 5.1, 15.3 and 15.5?cm for the same components at the same time. A further improvement of 43.7, 36.9 and 45.0 percent in the three directions, respectively, was achieved for the combined GPS/BeiDou solution. After the initialization process, the North, East and Up positioning accuracies were 5.2, 8.1 and 17.8?cm, respectively, for the BeiDou-only solution, while 1.5, 3.0, and 4.7?cm for the GPS-only solution. However, we only noticed a 20.9% improvement in the East direction was obtained for the GPS/BeiDou solution, while no improvements in the other directions were detected. It is expected that such improvements may become bigger with the increasing accuracy of the BeiDou-only solution.     

战术导弹折叠翼快速展开性能的测试技术

介绍某些战术导弹折叠翼快速展开特性测试技术。详细地介绍了测量方法、项目、数据处理和主要结果。试验是在北京空气动力研究所一座低速风洞中进行的。试验结果表明，获得的数据具有很高精度和可靠性，重复性也是令人满意的。     

浅谈如何以内部审计工作促进企业管理水平的提高

本文从内部审计的职能、作用入手,在强调审计监督职能的基础上,突出内部审计工作对企业经营管理的服务职能,试图建立以内部审计管理为核心的企业管理模式,促进企业管理水平的提高。     

一种卫星间跟瞄方向的控制策略与实现

进行自由空间的光通信或空间对抗，需要在卫星间实现精确的跟踪与瞄准。因为地面测控站的设置非常有限，指令与数据注入的范围受到很多限制，所以要求这种跟瞄在很多时候是无主控制状态下完成的。提出了一种利用在地面测控站的范围内向星上数管中心注入目标卫星、本体卫星的轨道参数，其它时间依靠自主导航飞行和GPS修正的方法，结合本体星的姿态测量、振动测量实现卫星瞄准指向的方位角与俯仰角的精确控制的方法，提高了在地面站无法注入指令与数据时卫星的捕获概率。通过仿真，将计算结果与卫星仿真工具软件STK的数据进行比较，结果一致。最后在嵌入式DSP平台上实现了这一策略。     

原子时自动测量及数据采集系统

介绍了普通的时间实验室的时频测量,实现自动测量和数据收集的基本系统方案,并以上海天文台原子时实验室为例介绍了实际可行的自动测量和数据收集系统,这个系统高性能、低价格,可应用于国内几乎所有的时间实验室。