Improved precision of virtual height measurements with coherent radio pulse sounding based on the maximum likelihood method

The paper describes a new technique that improves precision of the virtual height measurements by a coherent pulse sounding of the ionosphere. Proposed technique is based on the method of maximum likelihood that matches expected and observed spectral domain signatures of the signal intermixed with the noise. Computer simulations show that our technique allows measurements of the echo virtual height with ∼100 m precision even at a much coarser step of the height sampling in the sounder. In experiment, we expect an average 300 m precision of the virtual height measurements for single echoes received during periods of little spread due to ionospheric irregularities.     

Storm time behavior of topside scale height inferred from the ionosphere–plasmasphere model driven by the F2 layer peak and GPS-TEC observations

The International Reference Ionosphere model extended to the plasmasphere, IRI-Plas, presents global electron density profiles and total electron content, TECiri, up to the altitude of the GPS satellites (20,000 km). The model code is modified by input of GPS-derived total electron content, TECgps, so that the topside scale height, Hsc, is obtained minimizing in one step the difference between TECiri and TECgps observation. The topside basis scale height, Hsc, presents the distance in km above the peak height at which the peak plasma density, NmF2, decays by a factor of e (∼2.718). The ionosonde derived F2 layer peak density and height and GPS-derived TECgps data are used with IRI-Plas code during the main phase of more than 100 space weather storms for a period of 1999–2006. Data of seven stations are used for the analysis, and data from five other stations served as testing database. It is found that the topside basis scale height is growing (depressing) when the peak electron density (critical frequency foF2) and electron content are decreased (increased) compared to the median value, and vice versa. Relative variability of the scale height, rHsc, and the instantaneous Hsc are inferred analytically in a function of the instantaneous foF2, median fmF2 and median Hmsc avoiding a reference to geomagnetic indices. Results of validation suggest reliability of proposed algorithm for implementation in an operational mode.     

歼击机高度分层试飞验证

针对采用气动补偿空速系统以改善测高系统精度的现代飞机 ,简要介绍了高度分层的要求 ;阐述了引起飞机空速系统位置误差的主要误差源并进行了分析 ;给出了通过 GPS速度法对歼击机高度分层试飞验证结果 ,并对试飞结果进行了分析和讨论 ;结果表明 ,所得到的试飞数据可为飞机气动补偿空速系统设计和高度分层试飞方法研究提供重要依据。     

基于LabVIEW的温度测量记录系统

论述用单片机和虚拟仪器通过串口通信实现温度测量记录系统的原理、硬件结构、软件设计及该系统对温度进行测量、存盘。     

一种基于Particle Filter的攻击目标高度估计算法

利用目标高度估计确定目标攻击要害点是精确制导武器信息处理中的一个重要内容。传统方法主要有直接利用几何方法估计和扩展卡尔曼滤波器方法,这两种方法精度都不高。Partic le F ilter是一种新出现的滤波方法,在解决非线性问题中得到了广泛应用。利用Partic le F ilter设计了一种新的目标高度估计算法。该算法通过贝叶斯递推方法,避免了在测量方程非线性很强的时候,扩展卡尔曼滤波器不合理的线性化所带来的误差。仿真结果表明,这种基于Partic le F ilter的目标高度估计算法提高了估计精度和收敛的鲁棒性。     

太阳活动对EUV辐射在大气中吸收过程的影响

本文利用A-E卫星在太阳活动21周峰年间观测到的EUV辐射资料,高层大气成分的吸收截面,以及MSIS-86热层大气模式,研究了EUV辐射在大气中的吸收过程;在透射比为1/e和0.1/100时分别计算了透射高度随波长及太阳活动的变化。在波长范围50—1050内对37个波段分别求出了透射高度随太阳天顶角的变化。结果表明,当太阳活动增强时各波段的透射高度均升高,而且透射比越大则透射高度随太阳活动的变化也越剧烈。当透射比为一定时,太阳天顶角越大则透射高度随太阳活动的变化也越大。除此之外还存在一个相反效应,即太阳活动会使Chapman函数变小,这反过来又促使透射高度降低。这两种效应的综合作用结果可较好地解释某些电离层观测中的日没效应。     

露天试车台选址对海拔高度的需求初探

本文简要分析了露天试车台的功用和建设对选址的要求，重点探讨了海拔高度对露天试车台基准试车性能的影响和确定该影响的研究方案。已有研究结果初步表明，当海拔高度在3km以下或环境压力在70kPa以上条件下．露天试车台试验的发动机换算性能与在标准大气海平面静止空气条件下的发动机试验性能是一致的．即在海拔高度3km以下选址建设露天试车台都是可行和合理的。     

压气机叶片辊轧模具型腔前滑补偿方法

辊轧模腔是叶片无余量辊轧成形的关键,然而压气机叶片辊轧成形过程中存在前滑现象,造成叶片沿辊轧方向精度偏差,需要在模具型腔设计过程中补偿前滑量,以实现叶片沿积叠高度的精确成形。针对叶片辊轧前滑现象,本文提出并研究了基于辊轧前滑补偿的压气机叶片辊轧模具型腔优化设计方法。首先,在分析前滑成因及叶片截面前滑表征模型的基础上,研究了前滑补偿机理并建立了前滑补偿模型,即型腔中心角与叶片积叠高度的对应关系。在此基础上,通过提取表征叶片的工艺模型截面线族,顺次计算截面前滑值并基于前滑补偿模型对辊轧模具型腔中心角进行修正。然后,基于修正后的型腔中心角,建立叶片工艺模型截面线族到型腔截面线族的空间扇态映射法则并进行截面线映射变换,进而基于型腔截面线重构了基于前滑补偿的叶片辊轧模具型腔。最后,通过高置信度数值计算方法比较了前滑补偿模腔和直接空间几何映射模腔辊轧成形叶片的积叠高度。结果表明,优化后的模具型腔能够有效提高叶片积叠轴方向上的成形精度。     

Sensing snow height and surface temperature variations in Greenland from GPS reflected signals

The in situ measurements of snow surface temperature (SST) and snow height (SH) are very difficult with high costs, particularly in Greenland Ice Sheet (GrIS). Since the snow depth variations coupling with surface temperature are related to GPS multipath, it is possible to estimate the snow depth and surface air temperature variations by incorporating GPS-Reflectometry (GPS-R). In this paper, the reflected signals from ground GPS receivers are used to sense the SST and SH variations based on the thermophysical behavior and variations of snow layer from April to June 2010 at SMM1 site and from March to December 2010 at MARG site in Greenland. The results show that the mean daily changes in the ionospheric geometrical-free linear combination (GPS-L4) of dual-frequency GPS signals are related to daily SST and SH variations. The nonparametric bootstrapping model in direct (forward) and inverse models are developed and applied to estimate the SST and SH variations. The mean biases of SST and SH estimates are 0.18 °C and 0.23 m at SMM1 site, respectively, and 3.8 °C and 0.13 m at MARG site, respectively.     

基于PLM的网络DNC平台的研究

近十年来,随着装备制造业网络、数控、企业信息化等技术的不断深入推广和完善,使流程化管理、角色访问、柔性加工和实时诊断监控等技术,在提高企业竞争力的过程中起着十分重要的作用。它们都以计算机辅助制造与计算机集成制造系统为技术支撑。作为生产的终端,数控设备的管理就成了一个核心的环节。较早开发的CAD,CAM,PLM及PDM主要侧重于文档、角色、流程的管理,由于一些客观的原因,企业内部对数控生产线和数控设备的管理却又相对落后,尤其是对数控代码的管理和维护十分混乱,为此尝试在PLM的基础上搭建一个DNC平台来解决这一问题。