某卫星平台多结构工况下的优化设计

采用航天器结构优化系统ESSOSⅡ(Engineering System of Structural Optimization for Spacecraft),对某复杂卫星结构进行了以重量最轻为目标、以其中复合材料板件的铺层厚度为设计变量的优化设计,考虑发射(收拢)和在轨(展开)2种结构工况下的基频和应力等约束条件.基于2种结构工况下的有限元模型,采用二级多点逼近寻优算法进行优化求解,每一次优化迭代过程中均需对各结构工况模型作有限元分析.优化后结构重量比初始设计有明显降低,且满足收拢、展开结构工况中的所有约束条件,为卫星结构分系统的改进设计提供了依据,同时进一步验证了ESSOSⅡ系统的有效性.     

Evaluating the IRI topside model for the South African region: An overview of the modelling techniques

The representation of the topside ionosphere (the region above the F2 peak) is critical because of the limited experimental data available. Over the years, a wide range of models have been developed in an effort to represent the behaviour and the shape of the electron density (Ne) profile of the topside ionosphere. Various studies have been centred around calculating the vertical scale height (VSH) and have included (a) obtaining VSH from Global Positioning System (GPS) derived total electron content (TEC), (b) calculating the VSH from ground-based ionosonde measurements, (c) using topside sounder vertical Ne profiles to obtain the VSH. One or a combination of the topside profilers (Chapman function, exponential function, sech-squared (Epstein) function, and/or parabolic function) is then used to reconstruct the topside Ne profile. The different approaches and the modelling techniques are discussed with a view to identifying the most adequate approach to apply to the South African region’s topside modelling efforts. The IRI-2001 topside model is evaluated based on how well it reproduces measured topside profiles over the South African region. This study is a first step in the process of developing a South African topside ionosphere model.     

不同电离层模型对北斗共视的精度影响分析

GNSS共视时间传递已成为远程高精度时间同步的主要技术手段之一,我国自主研制的北斗导航系统已经服务于亚太地区,基于北斗共视进行高精度时间传递已成为我国时频领域的研究热点。为了提高导航系统定位精度,需降低或消除导航定位过程中的各类误差,其中电离层为影响北斗共视的主要误差。研究了常用的几种电离层修正算法,利用2014年7月份的观测数据分析不同电离层模型对北斗共视钟差的精度影响,给出了残差标准差和稳定度值。分析结果表明:经各种电离层修正后,钟差精度都有所提高,其中双频电离层修正最优,比VTEC格网模型和Klobuchar模型分别提高22%和30%。对于不同星座,GEO卫星计算的钟差修正后精度明显优于MEO、IGSO卫星。     

电脑多功能计时计分大屏幕显示系统

本文简要介绍了电脑多功能计时计分大屏幕显示系统。其内容包括:系统的组成、显示原理和显示方式,系统中的微计算机以及驱动电路和屏幕显示的控制等。该系统是一个用汽车灯泡作发光元件,构成分块式点阵的假“满天星”屏面,并采用5台Z-80单板机进行分布控制的大屏幕显示系统,现已安装在南京航空学院体育馆内,经多次使用表明,它在汉字、西文、计时计分的显示以及技术资料统计等功能上均符合国际、国内篮、排球等比赛要求,在同类系统中已达到国内先进水平。采用多台Z-80微计算机间的通讯进行分布控制来实现多功能大屏幕显示,是本系统的一大技术特色。     

太阳活动低年广州地区地磁扰动与电离层闪烁的统计特征分析

基于肇庆地磁台的地磁监测数据和广州气象卫星地面站建立的华南地区GPS电离层闪烁监测网的监测数据, 统计分析了2008年7月至2010年7月太阳活动低年期间广州地区地磁扰动与电离层闪烁的关系. 用肇庆台地磁水平分量H的变化量换算出肇庆地磁指数K, 以此来代表广州地区地磁扰动情况.分析结果表明, 磁暴/强地磁扰动对广州地区电离层闪烁的发生总体表现为抑制作用, 电离层闪烁主要发生在低K值期间, 而在K ≥ 4时电离层闪烁的发生呈下降趋势. 电离层闪烁发生率随季节和地磁活动的变化规律表现在, 春季的弱闪烁发生率、夜间中等以上闪烁发生率和夏季中等以上闪烁的发生率明显与地磁活动指数K相关, 即随$K$指数的增大而减小; 在秋季和冬季闪烁发生率与K指数变化无明显关系. 同时还综合分析了地磁与太阳活动的变化对电离层活动的影响, 广州地区闪烁主要发生在太阳活动较低的磁静日期间.      

A different method to update monthly median hmF2 values

The height, h_mF2, and the electron density, N_mF2, of the F2 peak are key model parameters to characterize the actual state of the ionosphere. These parameters, or alternatively the propagation factor, M3000F2, and the critical frequency, f_oF2, of the F2 peak, which are related to h_mF2 and N_mF2, are used to anchor the electron density vertical profile computed with different models such as the International Reference Ionosphere ( Bilitza, 2002), as well as for radio propagation forecast purposes. Long time series of these parameters only exist in an inhomogeneous distribution of points over the surface of Earth, where dedicated instruments (typically ionosondes) have been working for many years. A commonly used procedure for representing median values of the aforementioned parameters all over the globe is the one recommended by the ITU-R ( ITU-R, 1997). This procedure, known as the Jones and Gallet mapping technique, was based on ionosondes measurements gathered from 1954 to 1958 by a global network of around 150 ionospheric stations (  and ). Even though several decades have passed since the development of that innovative work, only few efforts have been dedicated to establish a new mapping technique for computing h_mF2 and N_mF2 median values at global scale or to improve the old method using the increased observational database. Therefore, in this work three different procedures to describe the daily and global behavior of the height of the F2 peak are presented. All of them represent a different and simplified method to estimate h_mF2 and are based on different mathematical expressions. The advantages and disadvantages of these three techniques are analyzed, leading to the conclusion that the recommended procedure to represent h_mF2 is best characterized by a Spherical Harmonics expansion of degree and order equal to 15, since the differences between the h_mF2 values obtained with the Jones and Gallet technique and those obtained using the abovementioned procedure are of only 1%.     

Modeling and observations of the north–south ionospheric asymmetry at low latitudes at long deep solar minimum

Using the physics based model SUPIM and FORMOSAT-3/COSMIC electron density data measured at the long deep solar minimum (2008–2010) we investigate the longitude variations of the north–south asymmetry of the ionosphere at low latitudes (±30° magnetic). The data at around diurnal maximum (12:30–13:30 LT) for magnetically quiet (Ap ? 15) equinoctial conditions (March–April and September–October) are presented for three longitude sectors (a) 60°E–120°E, (b) 60°W–120°W and (c) 15°W–75°W. The sectors (a) and (b) have large displacements of the geomagnetic equator from geographic equator but in opposite hemispheres with small magnetic declination angles; and sector (c) has large declination angle with small displacement of the equators; vertical E × B drift velocities also have differences in the three longitude sectors. SUPIM investigates the importance of the displacement of the equators, magnetic declination angle, and E × B drift on the north–south asymmetry. The data and model qualitatively agree; and indicate that depending on longitudes both the displacement of the equators and declination angle are important in producing the north–south asymmetry though the displacement of the equators seems most effective. This seems to be because it is the displacement of the equators more than the declination angle that produces large north–south difference in the effective magnetic meridional neutral wind velocity, which is the main cause of the ionospheric asymmetry. For the strong control of the neutral wind, east–west electric field has only a small effect on the longitude variation of the ionospheric asymmetry. Though the study is for the long deep solar minimum the conclusions seem valid for all levels of solar activity since the displacement of the equators and declination angle are independent of solar activity.     

Validation of the Neustrelitz Global Model according to the low latitude ionosphere

Empirical modeling including empirical model for the total electron content (TEC) is important for the study of the ionosphere and practical applications. In this paper goodness of new Neustrelitz Global Model (then NGM) at low latitudes is studied. The NGM model includes such parameters as the maximal electron density (NmF2) and altitude of the maximum (hmF2). As of today, besides NGM there are several empirical models for NmF2 and hmF2. Therefore, a comparison of these parameters of the NGM model, not only with the experimental data, but also with two versions of the International Reference Ionosphere (the IRI model): IRI2001 and IRI-Plas would be instructive. Because the NGM model incorporates special factor describing the equatorial anomaly, the comparison in lower latitude areas is particularly interesting. As one can see from the presented example of the data from low latitude stations located in the northern and southern hemispheres near the Greenwich meridian, the NGM model may have certain advantages over the IRI model versions. In particular, NGM TEC is preferable regardless of solar activity level while NGM NmF2 is only preferable under high solar activity conditions. Next, NGM equivalent slab thickness of the ionosphere: τ(NGM) = TEC(NGM)/NmF2(NGM) has been calculated and tested to answer the question whether τ(NGM) can be used as a proxy of the slab thickness of the ionosphere for an empirical modeling. The answer is positive for the near equatorial stations and periods of high solar activity, and under such conditions predicted τ(NGM) can be used for deriving NmF2 from the experimental values of TEC(CODE) in real time.     

Validation of FORMOSAT-3/COSMIC radio occultation electron density profiles by incoherent scatter radar data

Low Earth Orbiting satellites carrying a dual frequency GPS receiver onboard offer a unique opportunity to remote sensing of the global ionosphere on a continuous basis. No other profiling technique unifies profiling through the entire F2-layer with global coverage. The FORMOSAT-3/COSMIC data can make a positive impact on the global ionosphere study providing essential information about the height electron density distribution and particularly over regions that are not accessible with ground-based measuring instruments such as ionosondes and GPS dual frequency receivers. Therefore, it is important to verify occultation profiles with other techniques and to obtain experience in the reliability of their derivation. In the given study we present results of comparison of the electron density profiles derived from radio occultation measurements on-board FS-3/COSMIC and from the Kharkov incoherent scatter radar sounding.     

The response of the ionosphere over Ilorin to some geomagnetic storms

The effects of some geomagnetic storms on the F2 layer peak parameters over Ilorin, Nigeria (Lat. 8:53°N, Long. 4.5°E, dip angle, −2.96°) have been investigated. Our results showed that the highest intensity of the noon bite-out occurred during the March equinox and lowest during the June Solstice on quiet days. Quiet day NmF2 disturbances which appeared as a pre-storm enhancement, but not related to the magnetic storm event that followed were observed at this station. These enhancements were attributed to the modification of the equatorial electric field as a result of injection of the Auroral electric field to the low and equatorial ionosphere. For disturbed conditions, the morphology of the NmF2 on quiet days is altered. Daytime and nighttime NmF2 and hmF2 enhancements were recorded at this station. Decreases in NmF2 were also observed during the recovery periods, most of which appeared during the post-noon period, except the storm event of May 28–29. On the average, enhancements in NmF2 (i.e. Positive phases) are the prominent features of this station. Observations from this study also indicate that Dst, Ap and Kp which have been the most widely used indices in academic research in describing the behavior of geomagnetic storms, are not sufficient for storm time analysis in the equatorial and low latitude ionosphere.