导航卫星历书参数拟合算法研究

对导航卫星历书问题进行了综合研究,并结合J2项分析解,提出了两套新的历书参数拟合方法和用户算法,与正常算法不同的是:8参数历书拟合算法以Ω=-3/2J2R2t/p2n cos I隐性直接代替历书参数Ω1 ;在用户算法中对MEO卫星以ωk=ω0-ω1·(△t/2-tk),对高轨卫星以ωk=ω0-ω1·(△t/2-tk)/2修正历书参数ωk,其中ω1=A2/p2n(2-5/2sin2 I).9参数历书拟合算法在8参数的基础上增加了一个历书参数M=(T_Errn-T_Err0)/△t/a参数,在用户算法中以ωk=ω0-ω1·(△t/2-tk),Mk=M0 n·tk-M·(△t/2-tk)修正ωk和Mk·通过多组模拟轨道和IGS精密轨道的历书拟合实验,结果表明,新8参数历书拟合方法具有参数少、迭代收敛速度快、对MEO卫星拟合精度高等优点;新9参数历书拟合算法,迭代收敛快,拟合精度优于其他算法.     

用非差分方法确定单颗导航卫星的轨道

在导航系统中有时需要对单颗导航卫星进行定轨.此时由于无法组成常用的同历元单差或双差以消除卫星钟差或接收机钟差,有必要发展新的定轨策略和精度分析.该文以GPS为例,讨论在不依赖于星站间时间同步的情况下,对单颗导航卫星进行精密定轨.首先分析了GPS卫星钟差以及GPS接收机钟差的特性,发现在一定间隔内钟差主要表现为线性变化,而在去除这一线性项后,非线性钟差在3 m以内.利用GPS的伪距对单颗卫星定轨,在将钟差的主要部分作为测距的偏差和偏差变化率后,伪距测量量等价于常见的测距测量量.在利用等价的测距测量量定轨时可同时解算出偏差和偏差变化率参数.为验证该方案的可行性及其定轨精度,利用实测GPS观测数据进行了试验.结果表明,此种定轨方案定轨的径向精度优于4 m.考虑到GPS接收机的频率信号是由普通的晶振产生的,如果地面接收机采用原子钟提供的频率标准,其钟差的非线性部分将更小.模拟计算表明,采用本方案可以期望得到更高的定轨精度.     

卫星轨道理论的深入研究及其在定轨、预报和参数测定中的应用

自从1957年第1颗人造地球卫星Sputnik升空以来,人类进入空间时代已过半个世纪,这50多年中卫星技术日趋成熟.这篇论文根据作者在博士研究生阶段参加的3项课题撰写而成.这3项课题涉及了人造地球卫星轨道理论及应用的几个主要方面,具有一定的代表性,也能够展示目前卫星轨道研究的主要内容、手段以及在应用领域中的重要作用.     

用切比雪夫曲线拟合导航卫星广播星历

提出用一种基于切比雪夫曲线多项式拟合的方法,来拟合导航卫星广播星历。该方法对解决 GEO导航卫星的小倾角、小偏心率问题特别有效,并具有精度高、使用方便等特点。     

图像移位堆叠方法用于暗天然卫星的天体测量

暗弱天然卫星与主带小行星相比,具有亮度低、速度变化快的特点.在观测这类天体时,不能简单地延长曝光时间来提高其信噪比.尝试观测多幅短曝光的CCD (chargecoupled device)图像,采用移位堆叠(shift-and-add)方法,希望提高目标成像的信噪比,获得暗弱天然卫星的精确测量结果.使用2018年4月9—12日夜间,中国科学院云南天文台1 m望远镜(1 m望远镜)拍摄的木星5颗暗卫星的229幅CCD图像,实施了移位堆叠试验.为了验证结果的正确性,与相近日期中国科学院云南天文台2.4 m望远镜(2.4 m望远镜)观测的相同木卫图像的测量结果进行了比较和分析.位置归算采用了JPL (Jet Propulsion Laboratory)历表.结果表明,对CCD图像使用移位堆叠方法,通过叠加约10幅曝光时间100 s的图像, 1 m望远镜能观测暗至19等星的不规则天然卫星,而且测量的准确度与2.4 m望远镜的测量结果有良好的一致性.     

Improved Estimation of Earth Rotation Parameters Using the Adaptive Ridge Regression

The multicollinearity among regression variables is a common phenomenon in the reduction of astronomical data. The phenomenon of multicollinearity and the diagnostic factors are introduced first. As a remedy, a new method, called adaptive ridge regression (ARR), which is an improved method of choosing the departure constant θ in ridge regression, is suggested and applied in a case that the Earth orientation parameters (EOP) are determined by lunar laser ranging (LLR). It is pointed out, via a diagnosis, the variance inflation factors (VIFs), that there exists serious multicollinearity among the regression variables. It is shown that the ARR method is effective in reducing the multicollinearity and makes the regression coefficients more stable than that of using ordinary least squares estimation (LS), especially when there is serious multicollinearity. This revised version was published online in July 2006 with corrections to the Cover Date.     

导航卫星精密定轨与时间同步技术进展

全球卫星导航系统(Global Navigation Satellite System, GNSS)通过播发卫星钟差和精密轨道信息实现时间和空间基准信息向导航用户的传递.随着高精度原子钟等导航卫星载荷、星间链路等天基/地基监测手段以及数据处理方法等技术的不断更新,卫星轨道和钟差产品的精度和实时性也逐步提升. 2018年12月,北斗三号卫星导航系统正式开通,为"一带一路"国家提供实时高精度、高可靠的基本导航定位服务.综述了北斗导航系统从北斗二号区域系统到北斗三号全球系统精密定轨与时间同步处理面临的困难和挑战,针对上述问题,阐述了北斗运行控制系统的解决途径和实现指标.与GPS等其他GNSS系统进行比较,分析了不同导航系统技术特点.最后展望了精密定轨与时间同步技术未来的发展路线图,为更高精度的GNSS导航定位授时服务提供参考.     

双地下物质变化区参数解算方法研究

经典天体测量仪器以铅垂线为基准测量本地的天文经纬度,因而能探测到本地铅垂线的偏转.本地铅垂线的偏转代表着测站周围重力场的变化,而这一变化与地下物质的再分布相关,由此有望帮助了解地下物质变化的情况.将本地的铅垂线偏转(Plumb Line Variation, PLV)与地下物质变化联系起来,建立了双质量体模型.在97°E–107°E和21°N–29°N范围内,考虑了3480个包含正、负质量变化(相对地质背景)的质量体组合算例,并利用差分进化(Differential Evolutionary, DE)算法进行了解算.解算得到的质量体相对于模拟值的位置误差小于米量级,质量误差小于10¹¹kg,结果精度较高.     

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.     

导航战背景下的天文导航技术—天文导航技术的历史、现状及其发展趋势

综述近30年来我国内外天文导航技术及其相关理论和方法的进展，介绍世界各军事大国对天文导航的认识，并就天文导航在导航战背景下的显著优势进行论述。包括下列主要内容：（1）天文导航设备的历史和现状；（2）天文导航理论的新成果；（3）各军事大国对天文导航的态势；（4）天文导航的优势性；（5）天文导航自动化的主要关键技术，（6）天文导航自动化技术的发展趋势。     

HST astrometry of the closest brown dwarfs-II. Improved parameters and constraints on a third body

Located at less than two pc away, Luhman 16 AB (WISE J104915.57-531906.1) is the closest pair of brown dwarfs and the third closest “stellar” system to Earth. An exoplanet candidate in the Luhman 16 binary system was reported in 2017 based on a weak astrometric signature in the analysis of 12 HST epochs. An additional epoch collected in 2018 and re-analysis of the data with more advanced methods further increased the significance level of the candidate, consistent with a Neptune-mass exoplanet orbiting one of the Luhman 16 brown dwarf components. We report the joint analysis of these previous data together with two new astrometric HST epochs we obtained to confirm or disprove this astrometric signature. Our new analysis rules out the presence of a planet orbiting one component of the Luhman 16 AB system for masses $\mathrm{ℳ}$ $\gtrsim$ 1.5 M_♆ (Neptune masses) and periods between 400 and 5000 days. However, the presence of third bodies with masses $\mathrm{ℳ}$ $\lesssim$ 3 M_♆ and periods between 2 and 400 days ( $\sim$1.1 years) cannot be excluded. Our measurements make significant improvements to the characterization of this sub-stellar binary, including its mass-ratio 0.8305 $\pm 0.0006$, individual component masses 35.4 $\pm$0.2 M_Ꝝ and 29.4 $\pm$0.2 M_Ꝝ (Jupiter masses), and parallax distance 1.9960 pc $\pm$ 50 AU. Comparison of the masses and luminosities of Luhman 16 AB to several evolutionary models shows persistent discrepancies in the ages of the two components, but strengthens the case that this system is a member of the 510 $\pm$95 Myr Oceanus Moving Group.