An update global model of hmF2 from values estimated from ionosonde and COSMIC/FORMOSAT-3 radio occultation

In this paper, we present our recent work on developing an updated global model of the ionospheric F2 peak height hmF2 parameter by combining data from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC/FORMOSAT-3) radio occultation (RO) measurements and from the extended global ionosonde stations. In particular, 10 Chinese ionosonde stations’ data are newly introduced into this study. The modeling technique used is based on a two-layer empirical orthogonal function (EOF) expansion. Global distributions of hmF2 maps calculated using the newly constructed global model and the one provided by the International Reference Ionosphere model (IRI-ITU-R) are compared with the global distributions of hmF2 obtained by the COSMIC RO measurements and quantitative statistical analysis of the differences between the model results and those of the COSMIC RO measurements is made for the low (2008) and high (2012) solar activity years. The obtained average root-mean-square differences (RMSEs) for our model are 27.7 km (11.1%) and 31.0 km (9.8%), respectively for the years 2008 and 2012, whereas those for the IRI-ITU-R model are 39.9 km (16.9%) and 35.0 km (11.6%), respectively. Comparison of the results calculated both by our model and the IRI-ITU-R model with the digisonde observation is also made. The comparisons show that the newly constructed global hmF2 model can reproduce reasonably well the observations and perform better than IRI-ITU-R model.     

Tropopause analysis over the Iranian region using GPS radio occultation data

Near-tropopause phenomena like upper level fronts and cyclones, penetrative cumulus convection and mesoscale mechanisms of exchange make important contributions to the mixing processes in the atmosphere. Spatio-temporal monitoring of the tropopause height, temperature and pressure is an appropriate tool to show the running processes in the atmosphere. In this study, GPS radio occultation data is used to investigate the tropopause height fluctuations and the relation between the stratosphere–troposphere exchange and the aforementioned phenomena over the Iranian region. The paper shows how the position of the sub-tropical jet has changed with time, using GPS radio occultation observations. The tropopause height changes latitudinally, and three different bimodal probability distribution functions are observed. The results also show that the mixing region in the south of Iran is associated with the subtropical jet in winter. However, this region shifts north of Iran due to changes in the position of the subtropical jet during the summer. Consistency of the mixing region from the radio occultation data and the total ozone of TOMS over the Iranian region is also observed.     

浅析水平扭转M型下滑天线对入口高度及下滑角的影响

对于M型下滑天线,对天线作微调能改变近场DDM分布,从而对入口高度产生影响。本文阐述了扭动天线及调整辐射场形的原理。通过扭动上、下天线,定量分析入口高度和下滑角的改变量与扭动距离的依赖关系,并对飞行校验中的实例进行比较。对比扭动对近场(入口高度)和远场(下滑角)的影响。理论计算得出:上天线向跑道方向扭动一定角度,可以明显提高入口高度,向跑道外侧扭动后,入口高度减小;扭动下天线情况则相反,且两者基本都不影响下滑角。因此表明,扭动天线是一种有效改变近场的方法。     

Global empirical models of the density peak height and of the equivalent scale height for quiet conditions

Monthly average electron density profiles have been calculated from hourly electron density N(h) recorded in 26 digisonde stations distributed worldwide encompassing the time interval 1998–2006. The ionospheric electron density peak height of the F2 region, hmF2, and the effective scale height at the hmF2, Hm, deduced from average profiles have been analyzed to obtain the quiet-time behavior and have been analytically modeled by the spherical harmonic analysis (SH) technique using the modip latitude as the coordinate of the reference system. The coefficients of the SH models of hmF2 and Hm are bounded to the solar activity, and the temporal and seasonal variations are considered by Fourier expansion of the coefficients. The SH models provide a tool to predict hmF2 and Hm located anywhere in the range of latitudes between of 70°N and 70°S and at any time. The SH analytical model for hmF2 improves the fit to the observations by 10% in average compared to the IRI prediction, and it might improve the IRI prediction of hmF2 by more than 30% at high and low latitudes. The analytical model for Hm predicts the quiet behavior of the effective scale height with accuracy better than 15% in average which enables to obtain a good estimation of vertical profiles. These results could be useful to estimate information for the topside profile formulation.     

“嫦娥二号”卫星CCD立体相机的关键技术

文章介绍了中国两次绕月探测中 CCD 立体相机所采用的技术与创新,并与国际同类相机所获取的图像进行了比较;在此基础上详细介绍了“嫦娥二号”(CE-2)卫星CCD立体相机的综合创新集成技术--“单镜头两视角同轨立体成像、时间延迟积分图像传感器（TDICCD）推扫、速高比补偿”,并从工程目标与科学目标出发进行探测灵敏度及成像动态范围的需求分析;根据需求分析确定了总体技术方案,包括光、机、电的优化设计以及对月探测中首次采用TDICCD的技术困难与对策;特别讨论了速高比补偿的方案及实施途径,并进行了在轨试验验证。文章最后分别给出了虹湾地区成像分辨率为1.3m以及全月面分辨率为7m 的代表性图像,图像清晰、层次丰富,显示出中国在对月立体成像技术上取得了显著进步。     

巡航导弹飞行撞地概率的一种计算方法

研究了巡航导弹飞行高度控制系统对应的高度控制误差和地形起伏误差,在综合这两种误差的基础上,提供了一种飞行撞地概率的计算方法,并给出了飞行高度与之对应的撞地概率计算实例。计算和分析得出,参考航迹高度取现行标准值的某型巡航导弹撞地概率太大,需通过减小高度探测控制系统的误差或者增大参考航迹的规划高度来降低撞地概率。     

基于Zernike矩的高精度太阳图像质心提取算法

在基于太阳观测的月球车天文导航系统中,针对太阳传感器中图像噪声以及典型图像退化的不良影响,提出了一种基于Zernike矩的高精度太阳质心提取算法。采用Sobel算子进行边缘检测,Zernike矩重定位亚像素边缘,用最小二乘法拟合圆心。而当图像存在退化时,进行有效圆边缘点检测后,再用该法提取质心。从理论上分析了Zernike矩亚像素边缘检测对圆拟合法的改进作用。利用仿真图像和地表实验图像,将本文方法与传统的重心法、带阈值的重心法和圆拟合法进行了比较。结果表明,本文方法精度更高,具有更好的稳定性,可以对月球车天文导航精度的提高起良好作用。     

用于变体翼梢小翼的伸缩栅格研究

翼梢小翼能抑制翼尖涡流形成、降低机翼的诱导阻力,翼梢小翼的高度是对减阻效果影响较大的参数之一.传统翼梢小翼仅针对巡航状态设计,而在起降、爬升等非设计状态减阻效果不佳.变体翼梢小翼能根据飞行状态主动改变几何外形和尺寸,实时优化减阻效果.为了实现变形,设计了一种用于变体翼梢小翼的伸缩栅格,通过步进电机驱动,可使翼梢小翼的高...     

高线三角形有向面积的定值定理及其应用

给出圆内接 2n +1边形中高线三角形有向面积的定值定理及其推论 ,其中包括著名的三角形的高线定理     

液体射流喷入横向气流混合特性研究进展简

 随着低污染燃烧技术的发展,液体射流在横向亚声气流中的液雾混合特性越来越受到关注。因此对液体射流在横向亚声气流中的研究进展进行了综述,综述内容主要包括3个方面：液体射流在横向气流中雾化破碎;液体射流的穿透深度;液雾在横向气流中的散布和输运。大部分研究工作是针对单个直射式液体射流喷入均匀横向气流中的,也有研究考察了燃油脉动、气流不均匀或者旋转气流条件下射流在横向气流中的混合特性,然而对多喷射点或气动雾化直射式喷嘴形成的液雾在横向气流中的混合特性的研究工作开展的相对较少。最后对液体射流在横向气流中的国内外试验研究工作进行了简要的概括。通过对国内外相关研究进展的概括,并且以先进航空发动机低排放燃烧室中的雾化方式为背景,提出了液体横向射流混合特性研究应进一步完善的工作内容。