AIUB-CHAMP02S: The influence of GNSS model changes on gravity field recovery using spaceborne GPS

The gravity field model AIUB-CHAMP02S, which is based on six years of CHAMP GPS data, is presented here. The gravity field parameters were derived using a two step procedure: In a first step a kinematic trajectory of a low Earth orbiting (LEO) satellite is computed using the GPS data from the on-board receiver. In this step the orbits and clock corrections of the GPS satellites as well as the Earth rotation parameters (ERPs) are introduced as known. In the second step this kinematic orbit is represented by a gravitational force model and orbit parameters.     

冲击加速度校准中低通滤波器的应用

介绍了在冲击加速度校准中,为了抑制电、机械等干扰和噪声对冲击加速度测量结果的影响,采用二阶巴特沃斯型低通滤波器,通过时间序列翻转、二次滤波等方式,实现零相移的低通滤波效果。并比较不同截止频率下,低通滤波器对衰减程度不同的冲击加速度波形产生的峰值偏差,给出不同加速度波形下,低通滤波器截止频率选择应注意的问题。     

IMPROVEMENT OF PHASE GRADIENT AUTOFOCUS ALGORITHM

ＩＭＰＲＯＶＥＭＥＮＴＯＦＰＨＡＳＥＧＲＡＤＩＥＮＴＡＵＴＯＦＯＣＵＳＡＬＧＯＲＩＴＨＭＬｉＬｉｗｅｉ（李立伟），ＭａｏＳｈｉｙｉ（毛士艺），ＡｓｉｆＲａｚａ，ＬｉｕＹｉｎｇ（刘莹）（ＤｅｐａｒｔｍｅｎｔｏｆＥｌｅｃｔｒｏｎｉｃＥｎｇｉｎｅｅｒｉｎｇ...     

Love Waves in Layered Graded Composite Structures with Imperfectly Bonded Interface

Theoretical analysis and numerical calculations of Love wave propagation in layered graded composites with imperfectly bonded interface are described in this paper. On the basis of WKB method, the approximate analytic solutions for Love waves are obtained. By the interface shear spring model, the dispersion relations for Love waves in layered graded composite structures with rigid, slip, and imperfectly bonded interfaces are given, and the effects of the interface conditions on the phase velocities of Love waves in SiC/Al lay- ered graded composites are discussed. Numerical analysis shows that the phase velocity decreases when the defined flexibility parameter is greater. For the general imperfectly bonded interface, the phase velocity changes in the range of the velocities for the rigid and slip interface conditions.     

一种基于分步过渡的再入段组合导引法

针对比例导引法在弹道导弹再入段误差修正时可能引起的导弹攻角和侧滑角变化剧烈的问题,提出了一种基于分步过渡的再入段组合导引法,并采用了一种考虑弹道倾角增量和弹道偏角增量变化范围的过渡段计算方法。仿真结果表明,改进的组合导引法减小了侧滑角和横向过载的变化范围,并减弱了两种导引法交班段的攻角、侧滑角和过载突变问题,在保证导弹末段飞行稳定控制的同时减小了再入段误差对导弹射击精度的影响。     

频率计数器在航天器信号频率测量中的适用性分析

从频率计数器的工作原理出发,分析了航天器测控通信中常用的调相信号、调频信号和相移键控信号的频率测量误差,给出了调相信号和调频信号的测量误差表达式。使用频率计数器对上述3种航天器信号进行了频率测量试验。理论分析和试验结果表明,频率计数器适用于航天器调相信号和调频信号的频率测量,不适用于相移键控信号的频率测量。在实际使用中,为保证测量精度,应根据被测信号的调制方式选择适当的测量方法。     

Seasonal variations of GPS derived TEC at three different latitudes of the southern hemisphere during geomagnetic storms

Data from the archive of the International GNSS Services (IGS) were used to study the seasonal variations of Total Electron Content (TEC) over three stations located at different latitudes in the southern hemisphere during the geomagnetic storms of 11 January, 6 April, 8 June, and 13 October 2000, representing storms that occurred in summer, autumn equinox, winter and spring equinox, respectively. The percentage TEC deviation with respect to reference values differs substantially from season to season. A strong seasonal anomaly and clear equinoctial asymmetry in TEC response to the storms were observed. Weak and short-lived positive TEC deviations as well as strong and long-lasting negative trends were observed in summer storm during the main and recovery phases respectively over the high and low latitudes whereas in winter storm, the highest positive TEC deviations was recorded during the main phase over the entire latitudes. TEC enhancement dominated all the stations during the autumn (March) equinox storm while TEC depletion was majorly observed during the spring (September) equinox. All these variations find their explanations in the thermospheric composition change and circulation. Future work with direct or modeled measurement of atomic Oxygen to molecular Nitrogen ratio (O/N₂), large number of storms and other possible factors such as variations in storm’s intensity and local time dependence of the storm onset is expected to validate the observations in this study.     

月面无人自主采样返回任务动力下降点确定及验证

动力下降点确定是实施月面软着陆的重要环节，是多系统间复杂迭代的过程，涉及轨道设计、制导律设计、着陆目标的采样区确定、着陆及起飞安全分析。其设计结果直接影响了最终着陆点的位置和着陆过程的着陆安全，也间接影响采样安全和采样工程目标的实现结果。针对嫦娥五号在实施月面软着陆前确定动力下降点的任务需求，提出了通过多次轨道控制与最优标称制导轨迹搜索联合控制策略的动力下降点确定方法。首先，根据月面无人自主采样返回任务设计总结了动力下降点确定原理和约束条件；然后，详细论述了月面无人自主采样返回任务软着陆过程动力下降点确定方法；最后，通过嫦娥五号在着陆前主要的几次轨控实施结果分析了其对动力下降点的影响，同时综合了着陆区地形分析及着陆、起飞安全性分析，对动力下降点进行确定并根据最终在轨飞行结果进行验证。验证结果表明，基于“逐次逼近寻优方法”的月面软着陆环节动力下降点的确定方法有效，可以为后续地外天体软着陆等任务提供参考和借鉴。     

某型干扰机干扰效果提升研究

通过研究某型干扰机对多普勒雷达速度跟踪系统的干扰方式，分析假多普勒频率产生的干扰工作机理，研究对抗科目训练中该模式干扰效果不佳的具体原因，提出了采用数字移向技术替代行波管移相，增大对雷达回波原载频的抑制度，增强干扰效果。通过对样机的测试验证，给出了两种移相电路的假多普勒干扰比较。     

一种用于 ACAS 的相位校准方法

校准是用于 ACAS 发射机的一项关键技术,本文给出了一种新的基于比相的实时校准方法,去除了发射通道幅度对通道相位差的影响,介绍了该方法的原理,并在 FPGA 硬件平台上完成了该方法的仿真和验证,通过实测数据的分析与处理,证明了这种方法的可行性