干涉技术在天体测量中的应用

介绍了射电、光学和红外波段地面干涉的仪器以及近期的进展,如厘米波段的VLBA、EVLA、SKA等;毫米波段的ALMA、CARMA等;光学波段的Keck、VLTI/PRIMA,CHARA、MarkⅢ、NPOI、LBTI等.叙述了目前干涉技术在空间天体测量中应用的一些研究项目。如射电波段的VSOP、iARISE、RadioAstro;光学波段的HST/FGS、SIM PlanetQuest等.探讨了干涉技术在天体测量中的有关研究课题,并概述了其在我国的发展和应用情况.     

第二代天体测量卫星及后依巴谷地面天体测量的进展

简述了后依巴谷的天体测量工作。首先给出了第二个天体测量卫星Gaia的最新进展、最近提出的JAMSE和OBSS计划的简介,以及包含天体测量内容的SIM PlanetQuest计划的情况; 叙述了多波段天体参考架的建立和维持,特别是依巴谷星表向暗星方向的扩充和数字巡天,以及其他地面观测计划,如双星和聚星、太阳系天体的观测等;介绍了天体测量与天体物理结合的几个研究课题的进展;最后对我国自然科学基金会“十一五”天体测量优先发展的方向与内容提出建议。     

未来的国际天球参考架

本文简述了国际天球参考架的发展历史和现在射电参考架的现状—基准源选择的标准和参考架的稳定性。描述了地面上光学观测在依巴谷参考架的维持和加密的一系列工作。介绍由天体测量卫星GAIA和SIM给出的天球参考架可能逵到的精度。详述了在今后十年中地面天体测量的作用以及正在开展有关天球参考架的研究课题 ,同时也列出了我国正在和即将开展天体测量的几个研究课题     

利用基本天体测量仪器开展天文测光研究

讨论有关天体测量中的测光问题，介绍一些地面天体测量仪器和空间天体测量望远镜的测光研究。给出一种测光资料的处理方法，并建议利用ＤＣＭＴ开展天文光课题研究。     

空间时代地面光学天体测量的意义

从基本天体测量的主要任务出发，介绍了绝对测定和相对测量之间的区别和不同用途，并针对河外射电源参考架和依巴谷参考架的高精度的不足之处，说明了地面光学天体测量的长期性和灵活性等优势正是克服这些不足之处所必须的，但这不应是传统的已有精度下的地面光学天体测量，而应是与空间测量精度可比的要求下的地面测量，两者配合起来，将能促进本学科和相关学科的发展。     

云南天文台基本天体测量工作的发展

介绍了云南天文台天体测量工作的发展过程，论述了在空间时代地面光学基本天体测量的必要性和应具备的条件，并且叙述了在新的要求和条件下，地面光学基本天体测量工作应该发挥的作用和广阔的发展前景。     

利用基本天体测量仪器开展天文测光研究(英)

讨论有关天体测量中的测光问题，介绍一些地面天体测量仪器和空间天体测量望远镜的测光研究。给出一种测光资料的处理方法，并建议利用DCMT开展天文测光课题研究。     

云南天文台基本天体测量工作的发展

介绍了云南天文台天体测量工作的发展过程，论述在空间时代地面光学基本天钵测量必要性和应具备的条件，并且叙述了在新的要求和条件下，地面光学基本天体测量工作应该发挥的作用和广阔的发展前景。     

依巴谷天体测量卫星的阶段成果

本文综合介绍依巴谷天体测量卫星自１９８９年１１月开始观测以来，由头两年获得的观测资料取得的空间天体测量的阶段性成果，以及空间天体测量结果与地面观测结果相互之间的比较，成功地用于解算天体测量参数的星数已达１１２４４颗，由依巴谷天体测量卫星的头两年观测资料进行归算处理，得到恒星位置，视差和年自行的预期精度分别为３、４和２ｍａｓ。由此从整体上合面地检验了依巴谷科学计划，包括观测纲要，输入星表，卫星本身及     

中国小望远镜观测太阳系小天体项目的回顾

回顾了中国用小望远镜进行的一些科研项目,如小行星的天体测量和测光观测,近地天体的观测和天然行星卫星的天体测量观测.介绍了小行星和近地天体轨道的测定,以及行星/月球历表的编制.简述了天体测量标准区的建立,从射电源光学对应体推算光学和射电参考架的联系,双星轨道的测定,以及星团成员星自行的测定.提出了改进GSC2.3的新项目...     

Evaluation of the Precision of Three Tropospheric Delay Correction Models

Using the annual GPS observational tropospheric zenith delay data and meteorological data obtained at 36 globally distributed IGS stations in 2003, we have estimated the accuracy and range of application of two often-used models of tropospheric delay correction (the Hopfield and Saastamoinen models), and of a more recent model (the EGNOS model). We point out some defects in the Hopfield model and show that the EGNOS model can be used as the correction model of the tropospheric zenith delay for the GNSS real-time positioning and navigation.     

Path Bending Correction for Refraction Delay of Electromagnetic Waves

Focusing on lowering the cut-off elevation in the neutral atmosphere refraction delay correction and on raising the accuracy of the correction, we derive the formulae for calculating the correction for the bending of the light path caused by atmospheric refraction. This is the sort of correction that is given after the principal term in theoretical models of neutral atmospheric refraction delay correction, but is often neglected because it is a small quantity. However, in practice, for a not too low elevation like 15°, this term reaches 1 cm order of magnitude and can not be neglected. Li Yan-xing et al. specially gave a derivation of this correction and a computational method by successive approximation and some calculated values. Yan Hao-jian also proposed a formula of direct calculation but his calculated result was more than 3 times smaller than that of Li Yan-xing, which shows that further study of this correction is called for. Here we give a simple, convenient and reliable formula for calculating the correction.     

基于VLBI资料的ERP高频变化求解方法的研究

在天测与测地VLBI资料分析软件CALC／SOLVE中，对地球自转参数(ERP)高频变化的解算采用了附加约束的连续分段线性拟合方法，即要求在两个历元节点之间ERP变化率小于某事先约定值，并要求ERP在历元节点上连续．实测资料分析表明，当资料点密度较低时，引入约束条件和要求连续均有助于提高解的稳定性，但也人为降低了解的客观性，使各历元节点ERP解算结果之间相关．为此，基于CALC／SOLVE的用户偏导功能，实现了ERP高频变化的直接求解模块，不附加约束，也不要求连续．实测资料分析表明对ERP高频变化的直接求解模式更为可取．对于长时段VLBI资料的ERP高频变化求解，需要考虑岁差和章动模型偏差(天极偏移)的影响，编写相应的求解模块，并成功实现了1979至2003年长时段ERP高频变化求解．比较表明，在考虑了岁差章动模型偏差的影响时能够显著提高解的精度．为此，在基于VLBI资料解算ERP高频变化时，建议采用直接求解模式，并考虑岁差章动模型偏差的影响．     

Excitation of Chandler Wobble by Pacific,Indian and Atlantic Oceans from 1980 to 2005

In addition to the atmosphere, the oceans play important roles in the excitation of the Chandler wobble. The contributions made by the Pacific Ocean, the Indian Ocean and the Atlantic Ocean from 1980 to 2005 to the excitation of the Chandler wobble are first and systematically researched by taking advantage of the data of the current velocity field and ocean floor pressure provided by the marine circulation model of the Estimating the Circulation and Climate of the Ocean (ECCO). Studies show that the contributions of the three oceans to the excitation of the Chandler wobble are different from one another: the excitation energy of the Pacific Ocean makes up about 22.2% of the observational excitation energy, the largest one among the three oceans, that of the Indian Ocean accounts for about 12.7% and that of the Atlantic Ocean amounts to about 7.1%, the smallest among the three great oceans. The remarkable increase in the excitation energy of the Chandler wobble by the Pacific Ocean may be possibly due to the effect of the strong ENSO event which occurred from 1982 to 1983.     

Calculated atmospheric color refraction and observed stellar positions

Astrometric observations at different zenith distances have been performed in Dresden in an area centered atNGC 6791 where there are some stars with reliable color information (widely dispersed spectral types in the MK systemand color indices B_T – V_T) as well as with accurate positions from Tycho‐2 catalog. The results are used to estimate how significant improvements in stellar positions may be when accurate corrections for color refraction are taken into account. We have treated two cases for refraction calculations: (1) a photometric case for color indices and (2) a spectral case for spectral types and luminosity classes. To calculate refraction we use Stone's modified computer code (Malyuto & Meinel 2000). To treat the photometric case we have calculated the synthetic color indices for the spectral energy distributions of Sviderskiene (1988). The positional improvements due to including color refraction corrections are significant and slightly larger in the spectral case. An improvement of about 15% is reached at a zenith distance of 65°. Our basic conclusion is that color refraction should be taken into account for obtaining accurate stellar positions from ground based observations at larger zenith distances. Reliable refraction corrections may be calculated from spectral and/or photometric data.     

Application of LAMBDA Method to the Calculation of Slant Path Wet Vapor Content of GPS Signals

With the improvement of the GPS data processing techniques and calculating accuracy, the GPS has been increasingly and widely applied to atmospheric science. In the research on GPS meteorology the slant path wet vapor content (SWV) is one of the significant parameters. In the light of the problem of poorer real time, which existed in the method proposed by Song Shuli et al. in 2004, for directly calculating the SWV by means of the precise ephemeris, IGS clock error and observed value of the LC combination after the cycle skip processing, the LAMBDA method which has more mature application to the city virtual reference station (VRS) is applied to the problem of the processing of ambiguity search. Through the trial calculation of data, it is tested and verified that the method is feasible and there is a better uniformity when the calculated result is projected into the zenith direction. The atmospheric delay in the vertical direction obtained by using this method is compared with the result of the GAMIT or the BERNESE, with the result showing that the accuracy of the coincidence of the result of the method with that of the BERNESE is generally smaller than 1.5 cm and the accuracy of the coincidence of the result of the method with that of the GAMIT is generally smaller than 10 cm.     

The Method of Differential Measurement of Astronomical Refraction and Results of Trial Observations

Because of the influence of atmospheric refraction the astronomical observations of the objects with the angles of elevation below 15° are generally avoided, but for the sake of the complete theoretical research the atmospheric refraction under the condition of lower angles of elevation is still worthy to be analyzed and explored. Especially for some engineering applications the objects with low angles of elevation must be observed sometimes. A new idea for determining atmospheric refraction by utilizing the differential method is proposed. A series of observations of the starry sky at different heights are carried out and by starting from the zenith with a telescope with larger field of view, the derivatives of various orders of atmospheric refraction function at different zenith distances are calculated and finally the actually observed values of atmospheric refraction can be found via numerical integration. The method does not depend upon the strict local parameters and complex precise observational instrumentation, and the observational principle is relatively simple. By the end of 2007 a simply constructed telescope with a larger field of view at Xinglong Observing Station was employed to carry out trial observations. The values of atmospheric refraction at the true zenith distances of 44.8° to 87.5° were obtained from the practical observations based on the differential method, and the feasibility of the method of differential measurement of atmospheric refraction was preliminarily justified. Being limited by the observational conditions, the accuracy of the observed result was limited, the maximal accidental error was about 6” and there existed certain systematic errors. The value of the difference between the result obtained at the zenith distance of 84° and that given in the Pulkovo atmospheric refraction table was about 15”. How to eliminate the cumulative error introduced due to the integration model error is the key problem which needs to be solved in future.     

Application of Grey-autoregressive Dynamic Model to Calculation of Atomic Time Scale

Because of the effects of various kinds of noises and other factors, the state of running of an atomic clock is quite complicated. In order to precisely predict the exact variation in frequency or clock rate of the atomic clock, it is necessary to study and make a reliable prediction model and via the model the clock rate of the atomic clock is predicted so as to be adopted in the monitoring of the coordinated local time and the calculation of the local atomic time. The problem how to utilize the grey model and autoregressive model to predict the clock rate of the atomic clock is discussed. The synthesized model of the two models is proposed and researched. It is tested and verified in combination with the actual data of the atomic clocks at National Time Service Center, and the computational methods of predicting the accuracies of the models corresponding to different atomic clocks are given.     

Excitation of Annual Polar Wobble by Global Oceans

A reasonable and quantitative result on the variation of polar wobble excited by the oceans is not available at present. Numerous researches have shown that atmospheric motion is the greatest excitation source for the seasonal variations in the polar wobble and that oceanic motion is one of the main remaining excitation sources. The excitation of variation in the annual polar wobble caused by oceans from 1992 to 2004 both globally and in latitude dependence, have been studied in depth by means of the new generation of SODA oceanic data assimilation (SODA-1.4.2 and SODA-1.4.3) and the ECCO oceanic data assimilation. The result shows that the variation in the seasonal polar wobble excited by the SODA oceans is very close to that of the residual after the action of the atmosphere and land water is deducted from the geodesic excitation function for a large part of the investigated time interval, and that there is overall agreement between the two as regards the annual amplitude and phase. In addition, in comparison with the result of early SODA-Bata 7, the new generation of SODA oceanic excitation has achieved obvious improvements. The latitude distributions of the excitations of the annual polar wobble by the SODA and ECCO oceans are consistent in the Greenwich direction, while having obvious differences in the direction of 90° E.