交会对接成像软件的多目标跟踪改进

介绍交会对接成像敏感器的工作原理以及由单组条带预判窗口跟踪模式的单一目标敏感器组成的交会对接测量系统.从敏感器嵌入式软件的层面,提出多目标窗口计算、多目标条带预判、多目标匹配计算和多目标测量结果处理等4项改进方法,在硬件系统完全不变的情况下,改善多目标跟踪交会对接敏感器性能.该项改进将单机系统提升为多机热备份系统,提高系统安全性.实现不同目标器之间的自主跟踪切换,优化交会对接流程.此外,变不同敏感器之间切换为敏感器处理对象切换,提升交会对接过程的可靠性.改进后的算法已在我国交会对接各重点型号试验中顺利应用.     

新一代空间交会对接光学成像敏感器

摘要： 为满足中国未来空间交会对接任务对光学成像敏感器工作能力尤其是杂光抑制能力的更高需求,研制新一代空间交会对接光学成像敏感器.该产品多项指标优于其上一代产品神舟八号CCD光学成像敏感器,测量距离由原来的150~2 m范围提升为250~0.9 m范围;目标捕获时间由10 s缩短为0.32 s;抗杂光干扰能力大幅提升,实现准全天候工作.该产品已在中国神舟十一号载人飞船、天舟一号货运飞船与天宫二号的交会对接任务中成功验证,可在后续更好地服务中国空间站、探月三期等工程的交会对接任务.介绍该产品的测量原理、系统组成、地面试验和在轨工作表现等情况,并给出相应结论.     

人控交会对接九自由度半物理仿真试验系统设计及验证

以人控交会对接半物理仿真试验需求为背景,提出了可对人控交会对接控制系统单机敏感器性能和控制律设计方案进行仿真验证的人控交会对接九自由度半物理仿真试验系统的设计方法,给出了利用该设计方法对神舟九号飞船人控交会对接控制系统的仿真验证结果.神舟九号飞船与天宫一号目标飞行器首次在轨人控交会对接的工程实践结果表明,人控交会对接九自由度半物理仿真试验系统的设计方法正确.     

轨道维持与调相的综合优化策略研究

在交会对接飞行任务设计研究中必须首先确定目标航天器的轨道设计策略,研究了一种将目标航天器轨道维持和调相两种任务进行综合优化的策略.轨道维持的任务是使得目标航天器轨道的形状和位置符合交会要求,调相的任务是使目标航天器在轨道中的初始相位角符合交会要求.在考虑了交会对接发射窗口、交会终端约束条件下,将目标航天器轨道设计问题转化为一个非线性规划问题,应用序列二次规划方法对其进行了求解.仿真计算表明,这种方法既能以较少变轨次数满足交会对接任务要求,又能节省燃料,为空间交会对接任务规划提供了重要参考.     

交会对接光学成像敏感器遮光罩设计

遮光罩是交会对接光学成像敏感器中杂光抑制的重要组件,对有效提取目标点信息、保证敏感器定姿精度有重要作用.着重阐述了基于蒙特卡洛法的交会对接光学成像敏感器遮光罩设计,借助光学仿真软件进行仿真验证,并通过与试验结果进行对比,验证了遮光罩设计的有效性.     

交会对接光学成像敏感器中合作目标的分析与设计

交会对接技术是实现太空梭、太空平台和空间运输系统的装配、回收、补给、维修、太空人交换及营救等在轨服务的先决条件,交会对接光学成像敏感器是两航天器交会对接近距离平移靠拢段唯一能够提供六自由度相对导航信息的敏感器,由安装于追踪飞行器上的相机和安装于目标飞行器上的合作目标组成,采用角反射器作为合作目标标志,完成两飞行器间的相对位姿的解算.对其需求分析、设计方案、回光能量测试等进行了讨论,该方案已在神舟十一号载人飞船、天舟一号货运飞船与天宫二号的交会对接任务中成功验证,后续针对空间站及光学舱任务进行适应性修改.     

基于交会对接CCD光学成像敏感器的双目测量算法

在空间交会对接近距离逼近阶段,CCD光学成像敏感器作为相对导航信息获取的主要测量敏感器,其测量性能直接关系到空间交会对接能否成功.针对适用于空间交会对接过程中CCD光学成像敏感器的双目测量算法展开研究,推导了基于主像机坐标系的双目测量算法计算公式,并重点对其抗干扰能力进行研究,最后对该双目测量算法进行了仿真分析并给出了仿真结果.     

交会对接步骤详解

神舟八号载人飞船与天宫一号目标飞行器整个交会对接过程分为交会对接准备段、交会段、对接段、组合体飞行段和撤离段。交会对接准备段:载人飞船发射前,天宫一号目标飞行器降低轨道并调整朝向,完成交会对接准备。交会段:飞船发射入轨后,首先     

月球轨道交会对接任务辅助预报系统设计与验证

针对月球轨道自主交会对接制导、导航与控制(GNC)系统任务特点,设计一种基于人机协同框架的月球轨道自主交会对接过程辅助预报系统.该系统包括利用机器学习方法构建交会对接安全性规则知识库和安全性辅助预报两个部分.首先,在地面半物理仿真试验环境中,对导航监视相机拍摄的图像进行特征提取和匹配,利用图像特征与交会对接偏差组成训练样本对,用决策树方法构建安全性规则知识库.然后,利用安全性规则知识库,根据交会对接飞行过程中监视相机拍摄的当前状态的图像预报交会对接后续过程的安全性,给出成功的概率.通过地面半物理实验表明,该系统能够提升飞行控制过程中的智能化水平,有效协助地面飞行控制人员进行数据监视与任务决策.     

交会对接敏感器总体设计要点分析

相对测量技术是完成在轨航天器交会对接的重要技术之一,设计能够完成相对位置、速度,以及近距离的相对角度、角速度测量的交会对接敏感器,用于确定交会的轨迹和控制对接时的相对运动,不仅要考虑实现功能、性能方面,还要考虑在工程实现中外太空杂光干扰、热环境等因素的影响．本文不涉及到交会敏感器的具体设计,而是从分系统的任务和技术总体设计角度,总结交会对接敏感器设计时应注意的几个方面．     

Longitudinal variation of the equatorial ionosphere: Modeling and experimental results

We describe a new version of the Parameterized Regional Ionospheric Model (PARIM) which has been modified to include the longitudinal dependences. This model has been reconstructed using multidimensional Fourier series. To validate PARIM results, the South America maps of critical frequencies for the E (foE) and F (foF2) regions were compared with the values calculated by Sheffield Plasmasphere-Ionosphere Model (SUPIM) and IRI representations. PARIM presents very good results, the general characteristics of both regions, mainly the presence of the equatorial ionization anomaly, were well reproduced for equinoctial conditions of solar minimum and maximum. The values of foF2 and hmF2 recorded over Jicamarca (12°S; 77°W; dip lat. 1°N; mag. declination 0.3°) and sites of the conjugate point equatorial experiment (COPEX) campaign Boa Vista (2.8°N; 60.7°W; dip lat. 11.4°; mag. declination −13.1°), Cachimbo (9.5°S; 54.8°W; dip lat. −1.8°; mag. declination −15.5°), and Campo Grande (20.4°S; 54.6°W; dip lat. −11.1°; mag. declination −14.0°) have been used in this work. foF2 calculated by PARIM show good agreement with the observations, except during morning over Boa Vista and midnight-morning over Campo Grande. Some discrepancies were also found for the F-region peak height (hmF2) near the geomagnetic equator during times of F₃ layer occurrences. IRI has underestimated both foF2 and hmF2 over equatorial and low latitude sectors during evening-nighttimes, except for Jicamarca where foF2 values were overestimated.     

Parameterized Regional Ionospheric Model and a comparison of its results with experimental data and IRI representations

We describe a Parameterized Regional Ionospheric Model (PARIM) to calculate the spatial and temporal variations of the ionospheric electron density/plasma frequency over the Brazilian sector. The ionospheric plasma frequency values as calculated from an enhanced Sheffield University Plasmasphere–Ionosphere Model (SUPIM) were used to construct the model. PARIM is a time-independent 3D regional model (altitude, longitude/local time, latitude) used to reproduce SUPIM plasma frequencies for geomagnetic quiet condition, for any day of the year and for low to moderately high solar activity. The procedure to obtain the modeled representation uses finite Fourier series so that all plasma frequency dependencies can be represented by Fourier coefficients. PARIM presents very good results, except for the F region peak height (hmF2) near the geomagnetic equator during times of occurrence of the F₃ layer. The plasma frequency calculated by IRI from E region to bottomside of the F region present latitudinal discontinuities during morning and evening times for both solar minimum and solar maximum conditions. Both the results of PARIM and the IRI for the E region peak density show excellent agreement with the observational values obtained during the conjugate point equatorial experiment (COPEX) campaign. The IRI representations significantly underestimate the foF2 and hmF2 compared to the observational results over the COPEX sites, mainly during the evening–nighttime period.     

On small active region filaments,fibrils and surges

High resolution Hα images and magnetograms (0.2 arc s) of an active region were obtained in alternating time series at 42 s cadences using the Swedish 1-m Solar Telescope on 2004 August 21. The Hα filtergrams reveal an active region filament and surges consisting of thread-like structures which have widths similar to the widths of chromospheric fibrils, both recorded down to the resolution limit in the best images. All observed structures in the active region appear highly dynamic. Fibrils show counterstreaming strongly resembling the counterstreaming threads in filaments.     

面向空中威胁的无人机动态碰撞区建模与分析

针对现有方法一般是基于时间或距离的定值来确定碰撞区域的问题,提出了一种基于入侵机和无人机(UAV)运动信息的无人机动态碰撞区建模方法.首先,根据无人机与入侵机的运动状态、两机之间的最小安全距离等信息,通过几何方法得出无人机不采取任何规避机动时两机将发生碰撞区域的解析表达式,即无机动碰撞区数学模型;其次,考虑无人机的机动能力约束,计算了无人机采取最大过载转弯机动(左转或右转)时两机恰好避免碰撞发生的边界,即最大机动碰撞区数学模型;在此基础上,提出了不可规避区的概念;进而定义了安全飞行包络,它是无人机能够规避入侵机威胁的分界线;最后通过理论和仿真结合分析了影响各区域的主要因素.仿真与分析结果表明所建碰撞区不仅可以帮助无人机选择规避机动方式,而且能够帮助无人机判定常规避撞机动是否失败,并使无人机及时采取最大过载转弯机动,对无人机安全避撞决策具有实际参考价值.      

基于邻接表的分水岭变换快速区域合并算法

针对图像分水岭变换存在的过分割问题,提出了一种快速区域合并算法.该算法先对梯度图像进行Lee滤波以降低分水岭变换的过分割程度,在传统分水岭变换初步分割的基础上,利用区域邻接图(RAG, Region Adjacency Graph)的邻接表数据结构描述过分割区域之间的关系,采用分级阈值合并的方式完成区域合并,以降低合并计算的复杂度.合并过程中,将基于区域相对边界强度和边界长度的相似度度量准则与传统的区域灰度均值差异度准则相结合,构成新的区域可合并度综合评价函数,以保证区域合并准确可靠.实验结果表明,与传统的分水岭变换区域合并算法相比,该算法有效地提高了区域合并的准确性,并大幅提升了运算速度.      

海南地区电离层闪烁监测及初步统计分析

为开展赤道区的电离层闪烁形态特性及相关物理过程的研究,空间中心海南台站建立了一套GPS电离层闪烁监测系统．该系统是利用Plessey GPS Builder-2系统开发的,对软件的源码进行了修改,使其能以高采样率(50／s)同时并行记录11个通道GPS信号强度数据．对2003年7—12月间L-波段电离层闪烁事件的初步统计分析结果表明,电离层闪烁主要发生在日落后到午夜附近,其中9—11月较7—8月闪烁发生和结束的时间明显提前;电离层闪烁发生的频率和强度在9—11月较其他月份明显增强,其中10月达到最大;电离层闪烁的逐日变化具有很强的随机性,闪烁的发生在秋分附近9月底到10月中旬的磁静日期间达到最大;太阳和地磁活动的增强通常会抑制电离层闪烁的发生,这种情形在秋分附近尤为明显．     

Quiet sun XUV and EUV spectroscopy

The two XUV–EUV spectrometers on SOHO have collected a large amount of data in the 6000–10⁶ K solar plasma temperature range. These data have allowed us to greatly enhance our knowledge of the processes acting in the solar atmosphere, from the chromosphere to the corona. Some results on the quiet Sun structure (network, quiet Sun versus coronal hole), on the dynamics (velocities, waves, transient events), and the main characteristics of the quiet Sun atmosphere are presented and discussed.     

The subauroral electron density trough: Comparison between satellite observations and IRI-2007 model estimates

We compare electron density predictions of the International Reference Ionosphere (IRI-2007) model with in situ measurements of the satellites CHAMP and GRACE for the years from 2005 to 2010 over the subauroral regions. The electron density between 58° and 68° Mlat are considered. The trough region Ne peaks during local summers and attain the valley during local winter. Around −100°E and 60°E, two larger electron density sectors features can be seen in both hemispheres during all three seasons, which attributed to the electron extending from middle latitude to trough region. From 2005 to the beginning of 2010, the model overestimates the trough region Ne by 20% on average and the decrease of Ne in this region can also be seen during the last solar minimum. In the southern hemisphere, the model prediction shows quite well consistence with the observation during all three seasons while the huge difference between observations and model estimation implies that the IRI-2007 model needs significant improvement to predict better the trough region in northern hemisphere.     

Where is the base of the Transition Region? Evidence from TRACE,SDO, IRIS and ALMA observations

Classic solar atmospheric models put the Chromosphere-Corona Transition Region (CCTR) at $～2$ Mm above the ${\tau }_{5000}=1$ level, whereas radiative MHD (rMHD) models place the CCTR in a wider range of heights. However, observational verification is scarce. In this work we review and discuss recent results from various instruments and spectral domains. In SDO and TRACE images spicules appear in emission in the 1600, 1700 and 304 Å bands and in absorption in the EUV bands; the latter is due to photo-ionization of H i and He i, which increases with wavelength. At the shortest available AIA wavelength and taking into account that the photospheric limb is $～0.34$ Mm above the ${\tau }_{5000}=1$ level, we found that CCTR emission starts at $～3.7$ Mm; extrapolating to $\lambda =0$, where there is no chromospheric absorption, we deduced a height of $3.0\pm 0.5$ Mm, which is above the value of 2.14 Mm of the Avrett and Loeser model. Another indicator of the extent of the chromosphere is the height of the network structures. Height differences produce a limbward shift of features with respect to the position of their counterparts in magnetograms. Using this approach, we measured heights of $0.14\pm 0.04$ Mm (at 1700 Å), $0.31\pm 0.09$ Mm (at 1600 Å) and $3.31\pm 0.18$ Mm (at 304 Å) for the center of the solar disk. A previously reported possible solar cycle variation is not confirmed. A third indicator is the position of the limb in the UV, where IRIS observations of the Mg ii triplet lines show that they extend up to $～2.1$ Mm above the 2832 Å limb, while AIA/SDO images give a limb height of $1.4\pm 0.2$ Mm (1600 Å) and $5.7\pm 0.2$ Mm (304 Å). Finally, ALMA mm-$\lambda$ full-disk images provide useful diagnostics, though not very accurate, due to their relatively low resolution; values of $2.4\pm 0.7$ Mm at 1.26 mm and $4.2\pm 2.5$ Mm at 3 mm were obtained. Putting everything together, we conclude that the average chromosphere extends higher than homogeneous models predict, but within the range of rMHD models..     

Upgrading CCIR's foF2 maps using available ionosondes and genetic algorithms

We have developed a new approach towards a new database of the ionospheric parameter $f_{o}F2$. This parameter, being the frequency of the maximum of the ionospheric electronic density profile and its main modeller, is of great interest not only in atmospheric studies but also in the realm of radio propagation. The current databases, generated by CCIR (Committee Consultative for Ionospheric Radiowave propagation) and URSI (International Union of Radio Science), and used by the IRI (International Reference Ionosphere) model, are based on Fourier expansions and have been built in the 60s from the available ionosondes at that time. The main goal of this work is to upgrade the databases by using new available ionosonde data. To this end we used the IRI diurnal/spherical expansions to represent the $f_{o}F2$ variability, and computed its coefficients by means of a genetic algorithm (GA). In order to test the performance of the proposed methodology, we applied it to the South American region with data obtained by RAPEAS (Red Argentina para el Estudio de la Atmósfera Superior, i.e. Argentine Network for the Study of the Upper Atmosphere) during the years 1958–2009. The new GA coefficients provide a global better fit of the IRI model to the observed $f_{o}F2$ than the CCIR coefficients. Since the same formulae and the same number of coefficients were used, the overall integrity of IRI’s typical ionospheric feature representation was preserved. The best improvements with respect to CCIR are obtained at low solar activities, at large (in absolute value) modip latitudes, and at night-time. The new method is flexible in the sense that can be applied either globally or regionally. It is also very easy to recompute the coefficients when new data is available. The computation of a third set of coefficients corresponding to days of medium solar activity in order to avoid the interpolation between low and high activities is suggested. The same procedure as for $f_{o}F2$ can be perfomed to obtain the ionospheric parameter M(3000)F2.