高精度星相机光学系统像质评价及实现

摘要： 高精度星相机光学系统是实现高性能星相机的关键技术.从工程实际出发，梳理星相机光学系统像质评价的指标，重点论述星点质心位置指标分解、光学系统评价指标分解过程.分析认为星相机光学系统设计过程中需关注质心位置偏差和质心位置与理想像高的偏差、温度分析需兼顾均匀温升及梯度温度变化.给出一个继承于双高斯结构形式的设计实例，结合像差理论进行消热设计和畸变控制，分析不同温度条件下不同类别恒星的质心位置一致性.设计结果表明该光学系统可满足高精度星相机指标要求.     

风雪运动数值模拟中自保持平衡边界条件研究

在目前风场自保持性研究的基础上,结合等效物理粗糙高度,给出一类近似满足自保持性的用于风雪运动数值模拟的边界条件.首先结合低温风洞实验室的风雪实验数据,把文献的方法应用于风雪运动数值模拟中.经对比验算发现,文献的方法应用于风雪数值模拟中不能很好满足自保持性.为了进一步满足自保持性要求,引入等效物理粗糙高度,建立起雪跃移高度与等效物理粗糙高度的关系.结果表明:通过引入等效物理粗糙高度,边界条件的自保持特性得到了进一步的提高.最后对该方法的应用进行了推广验证.     

高分辨率星载斜视SAR的姿态导引

高分辨星载斜视合成孔径雷达回波信号中,多普勒中心频率随距离向的变化通常是十分显著的.这种变化导致系统需要更高的脉冲重复频率来实现方位向无混叠采样.然而,过高的脉冲重复频率将引起严重的距离模糊、极大的数据率,并将限制成像区域大小.本文推导了一种新的全零多普勒导引方法,并在此基础上提出了一种最小化多普勒中心频率随距离变化的姿态导引方法,从而能够最大限度地降低系统脉冲重复频率.根据星地空间几何关系和姿态导引原理,文中推导了实现全零多普勒导引的偏航角和俯仰角的解析表达式,并进一步给出了最小化多普勒中心频率随距离变化的姿态导引规律.最后通过计算机仿真,验证了该方法的有效性.     

Variability of the ionosphere over Irkutsk at low solar activity

Statistical and spectral analyses are performed to investigate variations of two ionosphere F2 layer key parameters, the critical frequency (foF2) and the peak height (hmF2), that were measured over Irkutsk (52.5°N, 104.0°E) from December 2006 to January 2008 under solar minimum. The analyses showed that both parameters contain quasi-harmonic oscillations with periods of T_n = 24/n hours (n = 1–7), among which the diurnal (n = 1) and semidiurnal (n = 2) ones are the strongest. Seasonal variations are explored of mean and median values, spectrum, amplitude, and phase of the diurnal and semidiurnal components of foF2 and hmF2.     

Disturbances in the ionospheric F-region peak heights in the American longitudinal sector during geomagnetic storms of September 2005

In this paper, we use the modified GSM TIP model to explore how the thermosphere–ionosphere system in the American longitudinal sector responded to the series of geomagnetic storms on September 9–14, 2005. Comparison of modeling results with experimental data at Millstone Hill, USA (42.6°N, 71.5°W), Ramey, Puerto Rico (18.3°N, 66.8°W) and Jicamarca, Peru (11.9°S, 76.9°W) has shown a good agreement of ionospheric disturbances in the F-region maximum height. We examine in detail the formation mechanisms of these disturbances at different latitudes and describe some of the important physical processes affecting the behavior of the F-region. In addition, we consider the propagation of thermospheric wind surge and the formation of additional layers in the low-latitude ionosphere during geomagnetic storms.     

高动态下的星体目标质心提取方法

高动态情况下,星点像斑在星敏感器探测器上会呈现出拖尾现象,星点质心无法被准确提取。针对上述难点,本文提出了一种高动态条件下基于差异哈希算法的星点质心提取方法。该方法分为三步：第一,建立动态星斑的数学模型;第二,利用差异哈希算法和汉明距离实现星跟踪窗口内星体目标粗定位;第三,在粗定位区域使用阈值分割与连通域法提取星点质心。实验结果表明,该方法能够适应各种长度的曝光时间,并实现星敏感器在3（°）/s条件下的稳定跟踪。在曝光时间50ms,角速度3（°）/s的条件下,星对角距误差为13”,平均提取率为96%,相比于传统方法,分别提高了29.6%和22.9%。     

B样条技术在RPM切片数据处理中的应用

首先介绍了RPM切片数据的处理问题,其次阐述了B样条的基本原理,最后研究了用三次B样条的反求技术对切片数据进行插值修补处理,并用弦高差方法对插值点进行取舍,生成最终的轮廓数据。     

星载软件重用技术研究

介绍了软件重用技术、意义和实现途径,讨论了星载软件重用技术的形式,分析了影响星载软件可重用性的主要因素,并根据星载实时嵌入式系统特点,提出了基于标准化硬件和通信协议的层次框架软件重用方法。研究认为基于层次框架的星载软件可重用技术能提高效率、降低成本,同时也提高星载软件可靠性和安全性。     

Towards a new reference model of hmF2 for IRI

A numerical model of the peak height of the F2 layer, hmF2_top, is derived from the topside sounding database of 90,000 electron density profiles for a representative set of conditions provided by ISIS1, ISIS2, IK19 and Cosmos-1809 satellites for the period of 1969–1987. The model of regular hmF2 variations is produced in terms of local time, season, geomagnetic latitude, geodetic longitude and solar radio flux. No geomagnetic activity trends were discernible in the topside sounding data. The nighttime peak of hmF2_top evident for mid-latitudes disappears near the geomagnetic equator where a maximum of hmF2_top occurs at sunset hours when it can exceed 500 km at solar maximum. The hmF2 given by the IRI exceeds hmF2_top at the low solar activities. The hmF2_top, obtained by extrapolation of the first derivative of the topside profile to zero shows saturation similar to foF2 the greater the solar activity. The proposed model differs from hmF2 given by IRI based on M(3000)F2 to hmF2 conversion by empirical relationships in terms of foF2, foE and R12 with these quantities mapped globally by the ITU-R (former CCIR) from ground-based ionosonde data. The differences can be attributed to the different techniques of the peak height derivation, different epochs and different global distribution of the source data as well as the different mathematical functions involved in the maps and the model presentation.