1.2m地平式望远镜指向模型的研究-测角编码器小周期模型的建立

介绍了1．2m地平式望远镜利用天文观测和图像采集处理的方法，通过建立测角编码器小周期模型，解决了数显部分的细分误差，提高了指向精度，对于空间目标高精度测轨、定轨及激光卫星的盲跟踪测距都是十分重要的。     

机架模型下指向误差数据的筛选与分析

对地平式望远镜机架模型拟合的指向误差数据进行分析,介绍了指向误差数据的获取方法.采用最小二乘法求解修正系数,结合方位轴和高度轴的位置拟合指向修正量.在显著性水平α=0.05下进行残差分析,剔除偏离过大的点以提高拟合精度.通过计算均方根误差、相关系数、F检验的P值验证了机架模型的有效性.结果说明增加测试数据后,未经残差检...     

斜轴式天文望远镜运动特性研究

相对于传统地平式或赤道式望远镜,斜轴式天文望远镜因其独特的机架结构形式更加适应例如南极等的极端台址环境.但由于这种望远镜形式的应用较少,针对其运动特性的研究还比较缺乏.首先详细讨论了斜轴式望远镜的优缺点,推导了斜轴坐标系与地平和赤道坐标系之间的坐标变换关系,在此基础上研究了斜轴式望远镜在进行恒星跟踪时的运动特性,并与地平式望远镜进行了比较.另外,还研究了斜轴式望远镜的像场旋转特性,并分析了像旋对望远镜天线全息测量的影响.最后,还针对斜轴式望远镜的特点,推导了一套包含7个误差项的指向误差改正模型.     

射电天线指向改正模型中轴系误差的完全表达式

为了提高射电天线的目标跟踪精度,采用直接法推导了射电天线轴系误差对指向的影响,并给出轴系误差指向改正模型的完全表达式,明确了指向改正模型中各轴系参数的定义,传统分项以及球谐函数所推导的轴系误差项为该模型的简化形式.基于此,评估得出基本参数改正模型中,因忽略轴系误差高次谐项而引起的指向精度损失可能达到1′′量级,具体需结合轴系误差大小而定;同时明确了基本参数改正模型(如22项指向模型)中与轴系误差有关的部分高次谐项系数的物理意义.为高精度轴系误差指向改正模型的建立提供了理论依据.     

全日面磁场与活动监测望远镜轴系升级

在天文观测中,需要望远镜能快速、准确地指向目标天体,并进行稳定跟踪。针对怀柔太阳观测基地(Huairou Solar Observing Station, HSOS)的全日面磁场与活动监测望远镜(The Solar Magnetism and Activity Telescope, SMAT)进行轴系升级,使用伺服电机轴上23位高精度绝对式编码器替代光栅钢带码盘,通过VSOP87行星理论实时计算日面中心位置,使用基于大面阵CCD的高精度导行系统不间断跟踪并记录太阳位置,利用最小二乘法分段拟合太阳实时位置与绝对式编码器数值,建立指向算法并实现日面中心指向。经实测,赤经方向的指向误差约为36.69″,赤纬方向的指向误差约为21.49″,满足全日面太阳磁场望远镜的指向要求,该方法成本低,兼容性高,对于其他赤道式望远镜的升级改造具有借鉴意义。     

30cm球载红外望远镜(BIT)的指向、偏置导星、跟踪的数学模型和仰角轴装置,偏置导星轴系及其驱动

30cm球载红外望远镜(BIT)是为中国科学院紫金山天文台的“原星的红外观测研究”课题面作。由紫金山天文台和南京天文仪器厂联合研制,是国内首创的点源观测,有偏置导星,能精密指向和跟踪的空间仪器。本文叙述了BIT的指向,偏置导星,跟踪,地平装置倾斜后的影响。几种误差分析,还叙述了BIT的仰角轴装置,偏置导星轴系,驱动系统,轴角指示,润滑等。这些内容对地面的地平式望远镜亦能适用,且可简化,仰角的工作范围为0°～90°,偏置量的工作范围皆为±10°;仰角轴的转速为0.08°/min～6.3°/min,偏置轴的转速皆为0.05°/min～3.75°/min。 1990年6月15日BIT首次飞行试观测。     

平均风作用对天马望远镜面形精度和指指向精度的影响

天马望远镜的最高工作频段为43 GHz。为保证高质量的观测结果,需要研究风载荷对天线精度的影响。首先对观测站实测的风速风向数据做了统计分析,结果显示:10 m高度处10min时距平均风速小于4 m·s^-1的占比超过80%,主导风向为北-西北方向。然后,通过将倾斜仪实测结果与有限元模拟结果进行对比,验证了模拟的有效性,并进一步分析了在不同迎风姿态、不同风速下天线结构的平均风荷载响应,以及天线面形精度和指向精度的变化。结果表明,平均风荷载对天线指向精度,尤其是俯仰角指向精度的影响较大,对面形精度的影响较小;在弹性范围内,天线面形精度和指向精度与风速间均为二次关系。研究结果可为天线面形精度和指向精度的评估提供参考。     

基于光学辅助指向测量的太赫兹望远镜指向误差模型研究

针对太赫兹波段天文点源目标较少, 指向测量相对困难的特点, 研究了利用与太赫兹天线共轴的小型光学望远镜来辅助太赫兹望远镜指向测量以及建立指向误差修正模型的方法. 依托紫金山天文台1.2 m斜轴式太赫兹天线开展了光学辅助指向测量的实验研究, 利用一台安装在天线背架上的100mm口径折射式光学望远镜获得了优于2$''$的指向测量精度. 此外, 通过对斜轴天线的结构分析以及大气折射和本地恒星时(Local Sidereal Time, LST)偏差等误差来源的分析, 建立了包含23个误差项的斜轴式光学指向修正模型, 实现了约3$''$的拟合精度. 最后, 借助高精度数字摄影测量对光电轴一致性进行了标定, 并针对其对指向模型精度的影响进行了讨论. 研究成果将为南极5 m太赫兹望远镜(The 5m Dome A Terahertz Explorer, DATE5)及其他太赫兹望远镜提供指向测量和指向修正模型方面的技术参考.     

1.2米地平式望远镜指向模型的研究 (1.全天指向模型的建立)

介绍了云南天文台1.2米地平式望远镜用于天文观测和图像采集处理的方法,建立了新的、独特的全天指向模型,大大提高了该望远镜的指向精度,达到1″,并在多年的实际应用中得到验证。     

AIMS太阳望远镜中像旋对稳像精度的影响分析

针对用于太阳磁场精确测量的中红外观测系统(Accurate Infrared Magnetic field measurements of the Sun, AIMS)太阳望远镜地平式机架在跟踪目标时像场旋转的现象,研究了像场旋转对稳像系统校正精度的影响。首先理论分析了互相关因子算法和绝对差分算法在不同湍流强度及不同探测窗口大小时由像场旋转引起的计算误差。随后在光学分析软件ASAP(Advanced Systems Analysis Program)中建立了包含装配误差的望远镜系统动态光学模型,统计了折轴系统装配误差在望远镜实时跟踪太阳运动时引起的像场平移及旋转。其中,图像在半小时内的最大平移约为0.3 mm,最大像旋约为200″。结果表明,在现有的误差分配情况下,装配误差引起的像旋对稳像精度的影响很小,而为了获得较高的稳像精度,互相关因子算法是首选的稳像算法,且在硬件处理速度允许的情况下,应该选择128×128像素的探测窗口。     

望远镜静态指向模型的基本参数

对地平式望远镜静态指出模型的基本参数进行了讨论，给出了一种参数较少，模型稳定的望远镜修正模型，与常用的球谐函修正模型相比较，基本参数模型具有对观测资料分布不敏感，模型的系随资料分布变化较小和修正精度较高优点，并且其残差序列服从正态分布，基本上能够满足高精度定轨的需要。     

采用光学指向系统建立天马13m望远镜指向模型

描述了采用光学望远镜辅助天马13m射电望远镜进行指向测量以及建立指向误差修正模型的方法. 对于小口径望远镜, 指向校准目标源比较少, 用射电法建立指向模型难以覆盖全天区. 利用上海天文台天马13m射 电望远镜进行光学望远镜辅助射电望远镜指向测量研究, 在13m天线背架上安装一套光学指向系统, 获得了优 于3''的重复测量误差. 此外, 通过对影响天线指向因素的分析, 建立了包含8个误差项的指向误差修正模型以及 光轴和电轴偏差模型. 将指向模型代入天线伺服控制系统, 对校准目标射电源进行十字扫描, 得到指向样本残差约 为5''. 该研究可以为实现高精度指向建模提供一种参考方法.     

Modeling and calibration of pointing errors with alt-az telescope

This paper presents a new model for improving the pointing accuracy of a telescope. The Denavit–Hartenberg (D–H) convention was used to perform an error analysis of the telescope's kinematics. A kinematic model was used to relate pointing errors to mechanical errors and the parameters of the kinematic model were estimated with a statistical model fit using data from two large astronomical telescopes. The model illustrates the geometric errors caused by imprecision in manufacturing and assembly processes and their effects on the pointing accuracy of the telescope. A kinematic model relates pointing error to axis position when certain geometric errors are assumed to be present in a telescope. In the parameter estimation portion, the semi-parametric regression model was introduced to compensate for remaining nonlinear errors. The experimental results indicate that the proposed semi-parametric regression model eliminates both geometric and nonlinear errors, and that the telescope's pointing accuracy significantly improves after this calibration.     

An improved astrometric calibration technique for space debris observation

An optical survey is the main technique for detecting space debris. Due to the specific characteristics of observation, the pointing errors and tracking errors of the telescope as well as image degradation may be significant, which make it difficult for astrometric calibration. Here we present an improved method that corrects the pointing and tracking errors, and measures the image position precisely. The pipeline is tested on a number of CCD images obtained from a 1-m telescope administered by Xinjiang Astronomical Observatory while observing a GPS satellite. The results show that the position measurement error of the background stars is around 0.1 pixel, while the time cost for a single frame is about 7.5 s; hence the reliability and accuracy of our method are demonstrated. In addition, our method shows a versatile and feasible way to perform space debris observation utilizing non-dedicated telescopes, which means more sensors could be involved and the ability to perform surveys could be improved.     

Pointing of HAGAR telescope mirrors

An array of seven atmospheric Cherenkov telescopes was commissioned at a high altitude site in Hanle in the Ladakh region of the Himalayas. The array called HAGAR has been designed to observe celestial γ-rays of energy >100 GeV. Each telescope is altitude-azimuth mounted and carries seven parabolic mirrors whose optic axes are co-aligned with the telescope axis. The telescopes point and track a celestial source using a PC-based drive control system. Two important issues in positioning of each HAGAR telescope are pointing accuracy of telescope axis and co-alignment of mirrors’ optic axes with the telescope axis. We have adopted a three pronged strategy to address these issues, namely use of pointing models to improve pointing accuracy of the telescopes, RA-DEC scan technique to measure the pointing offsets of the mirrors and mechanical fine-tuning of off-axis mirrors by sighting a distant stationary light source. This paper discusses our efforts in this regard as well as the current status of pointing and monitoring of HAGAR telescopes.     

The basic parameters of static pointing model of telescope

In this paper, models of the static pointing errors and their correction of an altazimuth telescope are discussed, and a stable model with a small number of basic parameters is given. Compared with the common spherical harmonics model, the present model is not sensitive to the distribution of observing data and has a much higher correction accuracy. The residuals from this model follow the normal distribution in statistics. It can meet the need of precise orbit determination.     

Isotropic and anisotropic pointing models

This paper describes an alternative approach for generating pointing models for telescopes equipped with serial kinematics, esp. equatorial or alt-az mounts. Our model construction does not exploit any assumption for the underlying physical constraints of the mount, however, one can assign various effects to the respective components of the equations. In order to recover the pointing model parameters, classical linear least squares fitting procedures can be applied. This parameterization also lacks any kind of parametric singularity. We demonstrate the efficiency of this type of model on real measurements with meter-class telescopes where the results provide a root mean square accuracy of 1.5?2 arcseconds.     

Lessons for new large telescopes from the AAT

When it began operating in 1975, the Anglo-Australian Telescope set new standards for pointing, tracking, and efficient observing. Since then, several large telescopes with more advanced control systems and on better sites have come into competition but the AAT retains the reputation of having the best overall observing efficiency.A number of organizational factors in the design and construction phase and in the Anglo-Australian Observatory's operational years have contributed to the AAT's success. Careful consideration of these factors should help groups planning the construction and operation of new telescopes.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.     

1m红外太阳望远镜光电导行系统中像场旋转的分析

云南天文台1m红外太阳望远镜(YNST)光电导行系统是基于检测太阳像在面阵CMOS图像传感器上的偏移量作为反馈控制信号的高精度闭环跟踪系统[1]。由于YNST是一个地平式装置,在太阳像偏移检测量中存在着像场旋转量,为了获取稳定清晰的太阳像,必须对检测量进行消旋[2]才能达到光电导行系统的跟踪要求。根据球面天文学及天体测量学的知识并结合导行镜的光学系统,推导了光电导行系统中像场旋转的变化规律并对其进行模拟分析。