基于嵌入式人工智能设备的流星光学监测系统

流星光学监测网是定位陨石和观测火流星的基础科研设施. 流星光学监测系统利用光学相机高速采集天空图像, 使用嵌入式系统实时处理数据, 能够快速识别流星并获取流星位置和陨石落点信息, 是构成流星监测网的关键仪器. 为提高流星光学监测系统获取信息的实时性及准确性, 提出了一种基于嵌入式人工智能设备的流星光学监测系统. 该系统由软件及硬件部分组成: 硬件部分包括观测设备(商用高空抛物摄像头)以及数据处理设备(嵌入式人工智能设备); 软件部分运行于数据处理设备内, 主要包括控制界面模块、流星监测模块、数据管理模块. 实际工作时, 摄像头采集天空视频信息, 流星监测模块从视频流中实时监测流星并存储包含流星视频的数据, 数据管理模块将流星位置信息实时传回数据中心用于预警. 观测结束后, 将原始观测数据同步至数据中心用于后续科学研究. 在整个系统中, 流星监测模块决定了整个监测系统的实时性及准确性. 该系统采用嵌入式人工智能设备与人工智能算法结合的方法构建流星监测模块. 通过使用实测数据对搭载监测模块性能进行测试, 结果表明: 流星监测模块能够达到0.28%的低误检率以及100%的召回率, 且数据处理速度达到了Mobilenetv2的8倍. 进一步将包含监测模块的整个流星光学监测系统部署于太原理工大学-张壁古堡远程天文台, 通过实测表明流星光学监测系统实用中能达到100%的召回率和较低的误检率.     

一种低噪声硅微条探测器读出电子学系统的设计

硅微条探测器空间分辨率高、工作性能稳定, 广泛地应用于空间高能粒子探测领域. 如费米gamma射线空间望远镜(Fermi Gamma-ray Space Telescope, FGST)以及阿尔法磁谱仪(Alpha Magnetic Spectrometer 2, AMS-02)的径迹探测器中都采用了高位置分辨率的硅微条探测器. 基于硅微条探测器在空间观测领域的应用前景, 针对硅微条探测器单元设计了一套低噪声的电子学读出系统. 整个电子学系统分为前端电子学、数据获取电路和上位机软件. 前端电子学为提高集成度, 采用了一款电荷读出芯片VATAGP8, 实现了多通道、低噪声的电荷信号测量; 数据获取电路使用现场可编程门阵列(Field Programmable Gate Array, FPGA)实现了对前端电子学的时序控制以及对测量信号的采集控制; 上位机用来接收、处理数据获取电路采集的信号数据. 在对电子学通道的线性、基线、噪声等性能进行测试之后, 得到系统在0--200fC电荷输入范围内的线性增益约为13.41bin/fC, 积分非线性小于1%, 噪声小于0.093fC. 为了验证电子学读出系统对硅微条探测器单元的读出能力, 将两者集成在一起并测试了宇宙线缪子的能量沉积, 得到读出电子学系统的信噪比大于32, 缪子的电离损失能谱与Landau-Gaussian分布符合较好, 能够满足硅微条探测器单元读出电子学的设计要求.     

一种基于主分量分析的减天光方法

天光是天体观测中的一种重要噪声源.减天光问题是制约多目标光纤光谱观测深度的重要因素.主分量分析(PCA)是统计学的一种分析方法,它可以用来寻找各个天光谱之间的关系,以进一步获得目标光谱中含有的天光成分.为了研究LAMOST的减天光方法,用SDSS的一组原始观测数据进行了仿真实验,实验结果表明,采用PCA方法比SDSS处理程序能够更有效地减天光.最后对PCA方法在LAMOST中的应用前景进行了展望.     

基于斩波轮技术的K波段接收机噪声校准研究

接收机是射电天文中用于探测微弱射电信号的重要接收设备.接收机的强度校准就是将接收机对射电源的响应转换为天文意义上的流量密度.常规方法就是使用经典的冷热负载法,将接收机自身的强度响应转换为一个等效的温度值,之后再据此对射电源做进一步标定.通过搭建基于斩波轮技术的K波段接收机强度校准平台,使用斩波轮法测试K波段常温接收机的噪声温度,并与传统冷热负载法的测试结果进行比对.结果显示,在晴好天气条件下,斩波轮法在30°、90°仰角下噪声温度的最大测试误差为7.5%和8.4%,可以很好地应用于实际噪声温度测试中;但在5°仰角测试中,由于过低仰角引入了地面噪声,使得斩波轮法的测试误差上升至20%–30%之间而无法使用.希望在此基础上进一步开展K波段天空亮温度的理论计算与实测,从而完善斩波轮技术的应用,使之可以满足在不同气象条件下的噪声校准测试需求.     

一种基于元学习的大口径射电望远镜俯仰轴承故障辨识方法研究

在经过长期运行后大口径射电望远镜俯仰轴会出现微小扭曲, 滚动轴承作为承载俯仰轴的核心部件, 也会因长期承受交变载荷增加疲劳风险, 导致轴承寿命以及望远镜指向精度的下降, 极大影响望远镜的性能. 以俯仰轴承为研究对象, 开展故障辨识方法研究, 可为望远镜天线的高性能运行提供重要支撑. 为实现在有限数据和复杂工作条件下准确地辨识俯仰轴承故障, 提出了一种小样本条件下基于元学习的故障辨识方法(Few-shot Meta-learning Fault Identification, FMFI). 首先将不同工况下的原始信号转换为时频图像数据, 之后按照元学习协议将数据样本随机采样到不同的学习任务中. 在有限样本的条件下, FMFI可以通过训练任务中的样本信息获取通用的先验知识, 在未知的测试任务下实现准确快速的故障辨识. 选取了与望远镜俯仰轴承工况具有相似性的变负载轴承数据集进行实验, 实验结果表明, FMFI方法具有很高的准确性和可靠性, 为大口径射电望远镜俯仰轴承的主动运维和高质量服役提供了有力的技术支持.     

一种基于全天相机云图的云量测量指标

全天相机云图是监测云量的重要手段,提出了一种新的云量测量量化指标——云分布密度(Cloud Distribution Density of ASI Images,ASICDD),并基于该指标建立全天相机云图自动分类系统.首先对云图进行去噪,利用最大类间方差法(Otsu)分割云区域;然后对去除背景的云区域图像使用云分布密...     

红外天文观测中望远镜副镜的一种新调制方法

本文介绍一种称作三位调制的望远镜副镜调制新方法。在用望远镜作L和M波段的红外天文观测时,采用这种新调制方法,在一定条件下可以替代望远镜所做的双束转换运动而获得令人满意的结果。对于控制功能不是很强的望远镜,或者进行一些不允许望远镜摆动的特殊观测(如红外偏振测量),这种方法极为有用。本文介绍了这种新调制方法原理和电路,并且使用1.2米红外望远镜比较了用这种新调制方法和用通常的副镜二位调制方法对一组红外标准星的测量结果:在J和K波段;两种方法的结果大体相同,在L波段,新调制方法显示出明显的优越性。     

一种全天相机云图的自动处理方法

使用全天相机拍摄云图是现在天文界广泛使用的监测天空云量的方法。云量的估算结果对望远镜观测有重要的影响,目前对云量的估算完全由人工处理,费时、费力而且准确度不够高,判别过程也完全依赖个人的经验。为此,提出一种针对全天相机云图的云量自动计算方法。首先针对多云和少云云图分别使用时间分割法和差分法去除云图中月亮影响区域;然后对去除月亮影响区域后的多云云图进行二值化处理,将云与背景进行分割,并使用基于灰度值的聚类算法对少云云图的云的厚薄进行量化分类;最后计算总云量,并依据30 m口径望远镜(Thirty Meters Telescope,TMT)判读全天相机云图的方法对云图进行自动分类。实验结果表明,该方法可提高云图判读效率,在有效解放人工的同时,也达到了平均值为76. 67%的识别准确率。     

一种偏振定标单元方位角误差的约束非线性最小化优化定标方法

偏振定标单元(Polarization Calibration Unit, PCU)对于定标由偏振系统和天文望远镜产生的仪器偏振至关重要, 然而偏振定标单元 中偏振元件光轴的方位角误差是限制定标精度的主要因素之一. 为解决该问题, 提出了一种基于约束非线性最 小化优化的方位角误差定标方法, 该方法具有定标精度高、定标速度快的优点. 首先将偏振定标单元中的线性 偏振片和四分之一波片的光轴方位角误差设置为两个待优化的自由变量, 然后利用产生和测量的Stokes参数 以及偏振定标获得的响应矩阵定义优化目标函数, 最终使用约束非线性最小化优化方法来确定 两个偏振元件的方位角误差. 分别从理论模拟和实际测量两个方面对优化方法进行了验证, 实验结果表明, 该 优化方法能够成功获得上述两个方位角误差, 精度分别优于2.79$''$和2.72$''$. 此外, 从理论上 计算分析了不同方位角误差对各Stokes分量的影响情况. 该优化方法有望应用到我国太阳望远镜中偏振定标 装置的误差定标及研制之中.     

一种简而易制的二圆柱面反射式摄谱仪准直畸像系统

本文是对于摄谱仪准直畸像光学系统研究的继续和深入,认真分析了Wynne的卡焦摄谱仪畸像系统的设计思想,认为可以避免像他那样将畸像系统设置在卡焦前会聚光束中(致使畸像系统变得复杂),而设置在摄谱仪准直光路中更为合理.作者与蒋世仰教授曾首次提出了准直畸像系统的概念,现在对于其中所提的反射系统的工作有所推进,寻求得到了一种结构简单、易于制作的系统.它仅由两个圆柱面构成,是一种柱面的类Mersenne系统.文中说明了在一定的条件下可以由圆柱面代替柱面Mersenne系统的抛物柱面(该系统在中已被提出过)、这种类Mersenne系统既可置于折轴摄谱仪中,亦可置于卡焦摄谱仪中,且能在大直径准直光束中起较剧烈的畸像作用,当然也具有反射系统所固有的优点——接收更宽的波段,特别在非可见光区优于透射系统.给出的算例说明该系统的准直误差极小.     

Mining the ESO WFI and INT WFC archives for known Near Earth Asteroids. Mega‐Precovery software

The ESO/MPG WFI and the INT WFC wide field archives comprising 330 000 images were mined to search for serendip‐itous encounters of known Near Earth Asteroids (NEAs) and Potentially Hazardous Asteroids (PHAs). A total of 152 as‐teroids (44 PHAs and 108 other NEAs) were identified using the PRECOVERY software, their astrometry being measured on 761 images and sent to the Minor Planet Centre. Both recoveries and precoveries were reported, including prolonged orbital arcs for 18 precovered objects and 10 recoveries. We analyze all new opposition data by comparing the orbits fitted before and after including our contributions. We conclude the paper presenting “Mega‐Precovery”, a new online service focused on data mining of many instrument archives simultaneously for one or a few given asteroids. A total of 28 instrument archives have been made available for mining using this tool, adding together about 2.5 million images forming the “Mega‐Archive”     

EURONEAR: Data mining of asteroids and Near Earth Asteroids

Besides new observations, mining old photographic plates and CCD image archives represents an opportunity to recover and secure newly discovered asteroids, also to improve the orbits of Near Earth Asteroids (NEAs), Potentially Hazardous Asteroids (PHAs) and Virtual Impactors (VIs). These are the main research aims of the EURONEAR network. As stated by the IAU, the vast collection of image archives stored worldwide is still insufficiently explored, and could be mined for known NEAs and other asteroids appearing occasionally in their fields. This data mining could be eased using a server to search and classify findings based on the asteroid class and the discovery date as “precoveries” or “recoveries”. We built PRECOVERY, a public facility which uses the Virtual Observatory SkyBoT webservice of IMCCE to search for all known Solar System objects in a given observation. To datamine an entire archive, PRECOVERY requires the observing log in a standard format and outputs a database listing the sorted encounters of NEAs, PHAs, numbered and un‐numbered asteroids classified as precoveries or recoveries based on the daily updated IAU MPC database. As a first application, we considered an archive including about 13 000 photographic plates exposed between 1930 and 2005 at the Astronomical Observatory in Bucharest, Romania. Firstly, we updated the database, homogenizing dates and pointings to a common format using the JD dating system and J2000 epoch. All the asteroids observed in planned mode were recovered, proving the accuracy of PRECOVERY. Despite the large field of the plates imaging mostly 2.27° × 2.27° fields, no NEA or PHA could be encountered occasionally in the archive due to the small aperture of the 0.38m refractor insufficiently to detect objects fainter than V ∼ 15. PRECOVERY can be applied to other archives, being intended as a public facility offered to the community by the EURONEAR project. This is the first of a series of papers aimed to improve orbits of PHAs and NEAs using precovered data derived from archives of images to be data mined in collaboration with students and amateurs. In the next paper we will search the CFHT Legacy Survey, while data mining of other archives is planned for the near future (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mining the CFHT Legacy Survey for known Near Earth Asteroids

The Canada‐France‐Hawaii Legacy Survey (CFHTLS) comprising about 25 000 MegaCam images was data mined to search for serendipitous encounters of known Near Earth Asteroids (NEAs) and Potentially Hazardous Asteroids (PHAs). A total of 143 asteroids (109 NEAs and 34 PHAs) were found on 508 candidate images which were field corrected and measured carefully, and their astrometry was reported to Minor Planet Centre. Both recoveries and precoveries (apparitions before discovery) were reported, including data for 27 precovered asteroids (20 NEAs and 7 PHAs) and 116 recovered asteroids (89 NEAs and 27 PHAs). Our data prolonged arcs for 41 orbits at first or last opposition, refined 35 orbits by fitting data taken at one new opposition, recovered 6 NEAs at their second opposition and allowed us to ameliorate most orbits and their Minimal Orbital Intersection Distance (MOID), an important parameter to monitor for potential Earth impact hazard in the future (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

All-sky search algorithms for monochromatic signals in resonant bar gravitational wave detector data

In this paper we design and develop several filtering strategies for the analysis of data generated by a resonant bar gravitational wave (GW) antenna, with the goal of assessing the presence (or absence) therein of long-duration monochromatic GW signals, as well as the eventual amplitude and frequency of the signals, within the sensitivity band of the detector. Such signals are most likely generated in the fast rotation of slightly asymmetric spinning stars. We develop practical procedures, together with a study of their statistical properties, which will provide us with useful information on the performance of each technique. The selection of candidate events will then be established according to threshold-crossing probabilities, based on the Neyman–Pearson criterion. In particular, it will be shown that our approach, based on phase estimation, presents a better signal-to-noise ratio than does pure spectral analysis, the most common approach.     

Analysis and Correction of the Influence of Track Irregularity on the Antenna Pointing

According to the influence mechanism of the antenna track irregularity on the telescope pointing accuracy, the distribution of the track errors and their influence on the pointing of the Urumqi Nanshan 26 m telescope are reanalyzed after the antenna track was reformed by using the whole-body welding technology, and hereby the pointing error model is correspondingly revised. By using the moving least-squares method, the measured height errors of the antenna track plane are fitted with a closed curve, and the tilt of the antenna azimuth axis caused by the track irregularity can be determined accordingly. Comparing it with the measured deviation of the antenna azimuth axis caused by the deformation of antenna pedestal, it can be found that both deviations are strongly correlated. A new pointing error model is established in view of the gravity deformation of antenna pedestal, which includes the north-south and east-west components, as well as the antenna track irregularity. Finally, by scanning a known calibration radio source at different positions in the sky, the measured pointing errors are fitted with the new pointing error model. The result shows that the sinusoidal component of the model error can be well constrained by the new pointing correction model, indicating that the new model can reflect very well the antenna pointing error, and can amend it to a certain extend.     

Precovery of near‐Earth asteroids by a citizen‐science project of the Spanish Virtual Observatory

This article describes a citizen‐science project conducted by the Spanish Virtual Observatory (SVO) to improve the orbits of near‐Earth asteroids (NEAs) using data from astronomical archives. The list of NEAs maintained at the Minor Planet Center (MPC) is checked daily to identify new objects or changes in the orbital parameters of already catalogued objects. Using NEODyS we compute the position and magnitude of these objects at the observing epochs of the 938 046 images comprising the Eigth Data Release of the Sloan Digitised Sky Survey (SDSS). If the object lies within the image bound‐aries and the magnitude is brighter than the limiting magnitude, then the associated image is visually inspected by the project's collaborators (the citizens) to confirm or discard the presence of the NEA. If confirmed, accurate coordinates and, sometimes, magnitudes are submitted to the MPC. Using this methodology, 3226 registered users have made during the first fifteen months of the project more than 167 000 measurements which have improved the orbital elements of 551 NEAs (6% of the total number of this type of asteroids). Even more remarkable is the fact that these results have been obtained at zero cost to telescope time as NEAs were serendipitously observed while the survey was being carried out. This demonstrates the enormous scientific potential hidden in astronomical archives. The great reception of the project as well as the results obtained makes it a valuable and reliable tool for improving the orbital parameters of near‐Earth asteroids. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

How selection and weighting of astrometric observations influence the impact probability. The case of asteroid (99942) Apophis

The aim of this paper is to show that in the case of a low probability of asteroid collision with the Earth, the appropriate selection and weighting of the data are crucial for the impact investigation and for analysing the impact possibilities using extensive numerical simulations. By means of the Monte Carlo special method, a large number of 'clone' orbits have been generated. A full range of orbital elements in the six-dimensional parameter space, that is, in the entire confidence region allowed by the observational material, has been examined. On the basis of 1000 astrometric observations of (99942) Apophis, the best solutions for the geocentric encounter distance of  6.065 ± 0.081 R_⊕  (without perturbations by asteroids) or  6.064 ± 0.095 R_⊕  (including perturbations by the four largest asteroids) were derived for the close encounter with the Earth on 2029 April 13. The present uncertainties allow for special configurations ('keyholes') during this encounter that may lead to very close encounters in future approaches of Apophis. Two groups of keyholes are connected with the close encounter with the Earth in 2036 (within the minimal distance of  5.7736−5.7763 R_⊕  on 2029 April 13) and 2037 (within the minimal distance of  6.3359–6.3488 R_⊕  ). The nominal orbits for our most accurate models run almost exactly in the middle of these two impact keyhole groups. A very small keyhole for the impact in 2076 has been found between these groups at the minimal distance of 5.97347   R_⊕  . This keyhole is close to the nominal orbit. The present observations are not sufficiently accurate to eliminate definitely the possibility of impact with the Earth in 2036 and for many years after.     

数字边带分离校准研究

边带分离(Sideband-separating, 2SB)接收可实现上边带(Upper Sideband, USB)和下边带(Lower Sideband, LSB)信号同时观测,观测效率高且上、下两边带不会出现混叠.因此在射电天文观测应用中越来越受到重视.由于全模拟边带分离接收机存在难以克服的幅度和相位误差,导致了边带抑制率较低,影响了系统的性能.数字边带分离接收机可通过数字信号处理方法,有效改善系统边带抑制率.在3–18 GHz频段构建数字边带分离接收机原理实验,并基于边带分离理论和数字校准方法,实现实验系统的边带不平衡度校准,大大改善了系统的边带抑制率.