钟房时频服务自动化工作系统

钟房时频服务自动化工作系统已建立并投入运行。该系统具有守时、时间测量、数据处理和自动校正铷频标的能力。运行表明,该系统使XSR铷钟守时精度提高了一个数量级,其输出频率相对BPL时频标准台的频偏保持在2×10~(-12)以内。全文介绍了系统的构成及主要性能。     

区域GPS网实时计算可降水量的若干问题

目前地基GPS气象学测得的可降水量(PWV)精度好于2mm，但在利用区域GPS网实时计算每个测站上空的PWV时，要涉及到很多常规GPS资料处理时所忽略的问题，如需考虑数据处理软件和计算方式的选择、站坐标的确定和约束、轨道的使用方法、网外辅助站最佳数量的确定、海潮对实时计算PWV的影响以及实时应用于气象服务时的端部效应等问题。利用上海GPS综合应用网获取的2002年6、7月份长江三角洲地区人梅前后的数据，分析了利用区域性的GPS网实时计算高精度的PWV时要解决的各种问题，探讨了其数据处理方案。     

辛方法的校正公式

1996年Wisdom等提出了对辛方法进行校正的概念和实践，现在继续对辛校正进行详尽讨论和数值比较，尤其对哈密顿函数可分解为一个主要部分和多个次要部分的一般情形，用Lie级数推导任意阶的各种辛算法的一次和二次辛校正公式并对一些算法给出具体的辛校正公式。又以日、木、土三体问题为模型进行数值实验，结果表明一次辛校正能提高精度，改善数值稳定性。计算效率也比较高，因而值得推荐使用，辛方法通常用大步长数值积分，这时二次辛校正并没有显著提高结果的精度，却大大增加了计算时间，不应予以推荐。     

云台40m射电望远镜的指向误差校正

首先综述了射电望远镜指向误差校正的原理并对软件校准的两种方法进行了比较。其次阐述了利用软件校准的方法对云南天文台40m射电望远镜进行指向校正的过程,并给出其指向校正结果。结果是经过指向校正后该射电望远镜的指向精度达到观测要求。     

区域GPS网实时计算可降水量的若干问题

目前地基GPS气象学测得的可降水量 (PWV )精度好于 2mm ,但在利用区域GPS网实时计算每个测站上空的PWV时 ,要涉及到很多常规GPS资料处理时所忽略的问题 ,如需考虑数据处理软件和计算方式的选择、站坐标的确定和约束、轨道的使用方法、网外辅助站最佳数量的确定、海潮对实时计算PWV的影响以及实时应用于气象服务时的端部效应等问题。利用上海GPS综合应用网获取的 2 0 0 2年 6、7月份长江三角洲地区入梅前后的数据 ,分析了利用区域性的GPS网实时计算高精度的PWV时要解决的各种问题 ,探讨了其数据处理方案     

利用地基GPS技术反演武汉地区大气可降水分

利用武汉地区的探空资料和GPS实测数据，对对流层干分量延迟、对流层加权平均温度进行了检验分析．结果表明，对于武汉地区而言，常用的大气干分量延迟模型(SAAS Hopfield and Black)存在着1-2cm的系统误差，这在利用GPS资料估算大气可降水分(PWV)时会引入2-3mm的误差；对流层加权平均温度与常用的Bevis公式也存在着一定的差异，但这种差异对PWV结果影响很小．为此，提出了校正对流层干分量延迟的方法，并利用实测数据对该方法进行了检验．实践证明，这种校正方法基本上可以消除常用干分量模型的系统误差。     

基于CGGTTS的北斗3号系统时间性能评估

依据国际时间频率咨询委员会(Consultative Committee for Time and Frequency, CCTF) GNSS (Global Navigation Satellite System)时间比对工作组制定的时间传递标准(Common GNSS Generic Time Transfer Standard Version2E, CGGTTS_V2E), 针对GNSS接收机观测到的伪距信号开发了数据处理软件, 用于生成标准格式的CGGTTS文件, 并对其可靠性进行了验证. 结果表明, 与sbf2cggtts软件生成的CGGTTS文件相比, 在同一历元下, 分别利用相同GPS和BeiDou-2卫星观测值计算的星地钟差值基本一致, 互差绝对值不超过0.5ns的差值分别占总数的96%、94%. 以中国标准时间UTC(NTSC) (Coordinated Universal Time (National Time Service Center))为参考, 利用数据处理软件分别对BeiDou-2和BeiDou-3卫星的B1I和B3I双频消电离层组合观测值处理并生成标准格式的CGGTTS文件, 通过分析其星地钟差参数对BeiDou系统时间的性能进行评估. 结果表明, 与BeiDou-2相比, BeiDou-3系统时间的内符合精度提高约28%, 且1 d以上中长期频率稳定度明显优于BeiDou-2.     

VLBI相位校正信号提取的软件实现方法

从VLBI相关处理结果中提取的延迟值包括了天线、终端等设备的时延,必须对其加以修正,最终结果才能达到精度要求。提取相位校正信号,可以消除这些设备引入的时延,从而校正同一波前信号到达基线两端的几何时延。该文介绍了提取相位校正信号的原理、算法及软件实现方法。软件采用多线程和SSE技术,具备4台站多通道全部相位校正信号提取能力。     

我国月球探测工程中的定轨和定位

<正>本论文以我国月球探测工程为研究背景,使用仿真分析和实测数据处理相结合的方法,结合多种VLBI(very long baseline interferometry)技术在深空探测中的应用,展开对探月飞行器精密定轨、定位的方法研究和精度分析.本文主要做了以下几个方面的研究和探讨:首先,利用CE-2(Chang’E-2)探测器实时任务期间的实测数据,分析在我国现有的测量条件下月球探测器的轨道确定精度,重点讨论了CE-2任务中观测精度有所提高的VLBI数据对提高探测器     

GP S数据处理策略对成果精度的影响及可靠性分析

高精度全球定位系统(Global Positioning System,GPS)数据处理的成果精度往往受海潮模型、卫星轨道约束模式、星历产品等数据类型及处理策略的制约.在考虑上述影响因素的前提下进行相关实验,并基于误差理论提出一种增加基线解算次数组合平差的方法,以提高基线解算精度.实验结果表明,数据处理中置入海潮模型较...     

Stellar photometry and astrometry with discrete point spread functions

The key features of the matphot algorithm for precise and accurate stellar photometry and astrometry using discrete point spread functions (PSFs) are described. A discrete PSF is a sampled version of a continuous PSF, which describes the two-dimensional probability distribution of photons from a point source (star) just above the detector. The shape information about the photon scattering pattern of a discrete PSF is typically encoded using a numerical table (matrix) or an FITS (Flexible Image Transport System) image file. Discrete PSFs are shifted within an observational model using a 21-pixel-wide damped sinc function, and position-partial derivatives are computed using a five-point numerical differentiation formula. Precise and accurate stellar photometry and astrometry are achieved with undersampled CCD (charge-coupled device) observations by using supersampled discrete PSFs that are sampled two, three or more times more finely than the observational data. The precision and accuracy of the matphot algorithm is demonstrated by using the c -language mpd code to analyse simulated CCD stellar observations; measured performance is compared with a theoretical performance model. Detailed analysis of simulated Next Generation Space Telescope observations demonstrate that millipixel relative astrometry and mmag photometric precision is achievable with complicated space-based discrete PSFs.     

New Semi-Automated Photometric Telescope at the Skalnate Pleso Observatory

A semi-automated photometric telescope built at the Skalnate Pleso Observatory is described. In December 2000, the 0.3-m f/5 Zeiss astrograph was replaced by a 0.61-m f/4.3 mirror telescope equipped with a CCD camera. The observing programme is created to conform to the photometry of asteroids which are suspected to be of binary nature; photometry of NEAs and MBAs; a long-term photometry for theoretical modelling of the shape of asteroids; and photometry and astrometry of active comets and asteroids. Some results concerning the binary character of the asteroids are described in the paper.     

低纬子午环配备科学CCD的必要性和可行性

从基本天体测量学科的发展趋势和低纬子午环的课题目标出发，叙述了该仪器配备科学ＣＣＤ的必要性和对仪器性能的相应要求，并根据仪器的各种误差的测定方法和测定精度的分析，论述了该仪器配备科学ＣＣＤ后对天体位置作高精度绝对测定的可行性，文中还提出了对配备科学ＣＣＤ的总体要求。     

Spanish Monitoring of Comets: Making Sense of Amateur Photometric Data

Amateur astronomers have always represented an important observing group in cometary astronomy. Much of our knowledge of cometary light curves has come from amateur data, initially in the form of total visual magnitude estimates and now increasingly in the form of CCD observations. The increasingly widespread use by amateur astronomers of CCD cameras of excellent sensitivity and good cosmetic quality has revolutionised astrometry, allowing far more intensive astrometric monitoring of comets to be carried out down to magnitude 18 and fainter, with a corresponding enormous increase in the quality of calculated orbits. Although amateur CCD photometry is extensively available in the Internet, its use has been less widespread. The reason is the lack of standardisation in the way that this data is taken that leads to amateur CCD light curves having enormous dispersion. All amateur CCD photometry is aperture photometry, but it is seen that neither does it represent well the equivalent of m1 (total visual magnitude), even with a large aperture, nor is it close to the definition of m₂ (the nucleus magnitude). The problem is examined using data from the Spanish Comet Observers Group archives to show that by careful standardisation of data acquisition amateur CCD data can produce high quality, well-sampled and physically meaningful light curves. Examples are presented of the results for recent comets including 19P/Borrelly, 51P/Harrington, C/2001 TU80 (LINEAR-NEAT), C/2000 WM1 (LINEAR) & C/2001 A2 (LINEAR).     

Operational testing of the SBIG ST-6 CCD camera

The SBIG Model ST-6 CCD Imaging Camera was tested and found suitable for various kinds of astronomical observations on telescopes with apertures from 6 mm to 0.6 m. We discuss different noise sources, linearity, sensitivity, and other detector characteristics. Limits, which they set to the observations and accuracy of data evaluation process, are also discussed. Detection, accurate astrometry, and VR photometry limiting magnitudes are about 21, 20, and 17.5, respectively, with the 0.6-m telescope and 10-min integration time. Detection of 5th magnitude 1-second optical transients is possible with the 6-mm wide-field lens.     

Analysis of δ Librae including Hipparcos astrometry

New spectroscopy of the classical Algol system δ Lib, combined with high-quality optical and infrared photometry, provides the basis for a good understanding of the close binary system's main parameters. Detailed analysis of the photometry reveals the significant role of a third light source, pointing to the existence of a companion to the eclipsing system of mass  ∼1 M_⊙  .
We review the methodology of applying high-accuracy positional information, available from the Hipparcos Intermediate Astrometric Data archive, to stars that may have such companions. Analysis of the astrometry of δ Lib also points to a third star similar to the one already identified by Worek from radial-velocity data, although with slightly revised parameters. O–C data do not contradict this, but their general precision (while confirming the close pair's Algol status) fails to allow a decision on the third orbit parameters: Worek's or revised ones. Taking the photometry, spectroscopy and astrometry together, however, the existence of a third star of comparable mass to the Sun, as a relatively close companion to the eclipsing binary (∼4 au), is confirmed.     

Objectives of ground-based astrometry after HIPPARCOS

After a short summary of the results expected from the HIPPARCOS mission, the author gives several examples illustrating the needs that will arise afterwards in order to maintain the level of precision achieved and to extend it to many more objects. Three domains are particularly dealt with in this paper:

1. The maintenance of the HIPPARCOS reference system that will degrade at the rate of 2 mas per year. The instruments intended to contribute to this task should concentrate on observing a few stars as accurately as possible. The best candidates are astrolabes and optical interferometers.
2. The extension of the HIPPARCOS catalogue to more stars using astrographs, Schmidt telescopes, and photoelectric meridian circles. A particularly important objective would be to reduce the GSE catalogue to this system and determine its proper motions with second epoch plates.
3. The determination of new parallaxes and double star parameters in particular with CCD astrometry, astrometric photometry and various interferometric techniques.

     

Improved astrometry of space debris with image restoration

In order to implement an observing strategy,image degradation that occurs during optical observation of space debris is ineluctable and has distinct characteristics. Image restoration is presented as a way to remove the influence of degradation in CCD images of space debris,based on assumed PSF models with the same FWHM as images of the object. In the process of image restoration,the maximum entropy method is adopted. The results of reduction using observed raw CCD images indicate that the precision in estimating positions of objects is improved and the effects of degradation are reduced. Improving the astrometry of space debris using image restoration is effective and feasible.     

关于地平式反射望远镜的CCD平场(英文)

现有标准设计的反光望远镜在拍摄CCD平场时,绝大多数都受残留散射光的影响.但是赤道式与地平式反光镜所受影响是不同的.在赤道式上做时间序列较差测光时,只要待测星永远位于CCD的固定像元上,不太准确的CCD平场也能得到高精度的测光结果.当需要0.1%～0.3%精度的平场时,则可以采用夜天平场.地平式的特点是,它的CCD相机必须置于旋转器上,在跟踪天体时不停地旋转,以抵消地球自转的影响.上述用于赤道式的方法失效,因此,在CCD平场时,消除散射光的影响比赤道式更为重要.一个典型的地平式反光镜的例子是NAOC兴隆天文台的EOS 1米镜.虽然该台已附加了防散射光的装置,但是对所有B、V、R、I滤光片,在不同旋转器位置拍摄的CCD平场,仍然有2%～3%的差别(主要是梯度).该文给出了改进的建议,必须满足下面两个条件:Cij=C(r);旋转器的中心与反光镜的光学中心重合.此问题的解决对所有地平式反光望远镜都有普遍意义.     

全天相机在多设备巡天中的应用

天文观测站夜天空星像星等信息和天区分布信息可用于指导多设备巡天观测.建立全天相机监测系统(Monitoring all-sky system)对本地天区夜天空实时监测,获取的监测图像需要有效的方法进行处理以提取全天图像星像信息.由于全天图像视场大和高阶扭曲的影响,采用天顶等距投影与多项式函数组合的方法计算图像的底片常数.天文定位的均方根残差约为0.15个像素.通过对图像中亮星部分测光得到的星等差,改正大气消光误差.最后使用HEALPix (Hierarchical Equal Area isoLatitude Pixelation)方法实现天区划分和每个天区可观测极限星等值的存储.