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基于射电观测的脉冲星导航验证及地面应用研究
Alternative TitleStudy on Pulsar Navigation and Terrestrial Application through Radio Observations
韩伟
Subtype博士
Thesis Advisor王娜
2020
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Name理学博士
Degree Discipline天体物理
Keyword毫秒脉冲星,射电观测,地面应用,导航
Abstract脉冲星作为宇宙中天然的灯塔,其脉冲到达时间具有高度的周期性和稳定性。在脉冲星到达时间换算至太阳系质心和到达时间残差的计算过程中,我们需要准确的测站坐标。如果测站坐标不准确,我们将得到错误的脉冲星计时残差。此时错误的计时残差中包含几方面的信息:到达时间的测量误差、未被模型化的物理过程或传播过程引入的计时残差,以及因测站错误坐标带来的误差。如果站点坐标误差较大,该误差会明显的反映在计时残差中。正因如此,我们可以使用脉冲星为观测站点或者航天器进行三维位置的测量。基于脉冲星导航的原理,本文利用了澳大利亚脉冲星计时阵观测数据,对帕克斯射电望远镜进行了定位实验。该实验的主要目的包括:一、基于射电观测,对脉冲星导航理论和精度进行验证;二、研究射电脉冲星用于地面导航的可行性。不同于以往脉冲星只能应用于深空导航的传统观念,脉冲星用于地面导航不仅是一种新的天文导航方式,也是脉冲星导航步入工程实践前的重要验证过程。本文分析了脉冲星的计时模型,基于国际地球参考系和国际天球参考系的相互转换,推导了射电望远镜在国际地球参考系中的测站坐标和脉冲星计时残差的关系,用于解算射电望远镜坐标。在文中我们称之为“解析法”。我们选取了9颗毫秒脉冲星进行了定位实验,这些脉冲星包括了白噪声脉冲星、弱红噪声脉冲星和红噪声脉冲星。考虑到不同脉冲星的计时残差的特性,如白噪声、弱红噪声和红噪声,分别使用了加权最小乘法和广义最小二乘法来获得最佳的位置估计。实验结果显示,对于红噪声的脉冲星,通过广义最小二乘法能取得更加可靠的位置估计。对于J0437-4715,使用475次观测数据,能达到几十米的定位精度。对于其它毫秒脉冲星,定位精度约在几十米至几百米不等。通过对定位结果进行分析,我们发现定位精度和脉冲星到达时间的观测精度有着正相关关系,与脉冲星本身的残差没有呈现明显的相关。对于这些脉冲星,我们也分别使用不同的数据跨度,以此研究时间跨度对于定位结果及精度的影响。除了解析法,我们还研究了使用格网搜索的方法进行射电望远镜的定位。格网搜索定位方法可概括如下:1、将三维空间分成若干单元格,生成射电望远镜的不同候选坐标;2、 将不同的候选坐标分别代入脉冲星的计时模型计算质心到达时间和计时残差;3、拟合脉冲星的参数,并得到各候选坐标在拟合参数后的约化卡方值和rms残差;4、选取最小约卡方值或rms残差值对应的候选坐标,将其作为射电望远镜的真实坐标。基于网格法,我们采取了不同的定位策略,包括:1、在国际地球参考系的X、Y和Z方向分别搜索;2、在X和Y的平面上搜索。网格法的定位精度显示,不同的脉冲星定位精度约在数十米到百米间不等,这与解析法的结果相吻合。我们在论文中重点分析了脉冲星的参考相位对于地面导航定位的影响。无论是解析法或者格网定位的方法,都需要绝对或者相对的脉冲星参考相位来准确的定位观测站在国际地球参考系中的Z坐标。由于目前脉冲星观测中并没有准确的测量脉冲星的绝对相位,我们提出了两种折衷的解决方案:1、使用相对脉冲星参考相位;2、 使用外部的地理信息。这两种方案都可以获得合理的测站Z坐标。为了研究毫秒脉冲星用于地面导航的可行性及其定位精度,我们使用选择PSR J0437-4715的进行了不同的实验,包括:(1)选取少量的不同次数的观测,使用解析法进行定位实验。我们验证了利用3 至4 次的计时数据,可以达到几百米的定位精度;同时,观测次数增加能明显提高定位精度。(2)使用大量观测次数,结合外部地理信息数据(数字高程模型),基于格网搜索法在大地坐标系中的经度和纬度的方向进行搜索定位,定位准确度可优于10米。(3)使用了少量观测次数和数字高程模型,基于网格法进行望远镜的定位,结果优于(1)中解析法的定位结果。
Other AbstractPulsars are thought to be natural beacons because of the extreme rotational stability and precise periodicity. To convert the time of arrival (ToA) of the pulse observed at the observatory to the Solar System Barycenter and then obtain reasonable timing residuals, the precise observatory coordinates are required. Wrong observatory coordinates will introduce extra errors in the timing residuals, which are composed of ToA measurement uncertainties, un-modeled physical effects or propagation delays, wrong Roemer delays. In this case, pulsar timing residuals reflect the errors of the coordinates and can be used to determine the position either for the observatory or the spacecraft. Based on the principle of pulsar navigation, we use the archival data of the Parkes Pulsar Timing Array to position the Parkes telescope in order to: (1) study on the possible positioning precision of the pulsar navigation for the spacecraft, and (2) investigate the feasibility of pulsar navigation for the terrestrial applications. The studies in this paper could be an attempt for the researches of pulsar navigation both for the users in the space or on the Earth. We derived the relations between the errors of the observatory coordinates and the timing residuals upon the pulsar timing models and transformation between the International Celestial Reference System and International Terrestrial Reference System, which is used for the position determinations of the Parkes telescope, and is named ``analytic method” in this paper. Nine pulsars, including white noise pulsars, weak red noise pulsars and red noise pulsars, are selected for the positioning tests. Weighted least squares method is used to position the telescope with the white noise pulsars. In the presence of red timing noise, General Least Squares method is applied for better results. We obtained best positioning precision of about tens of meters with 475 observations from J0437-4715. For the other pulsars, the precision ranges from tens of meters to hundreds of meters. We demonstrate that the positioning precision has positive relation with the ToA uncertainties other than the rms timing residuals. Different data spans are also used to investigate the possible positioning precision. Besides, we use a grid searching method to position the radio telescope for comparison. The method divides the space around the radio telescope into small grids, from which we form the rms timing residuals and fit pulsar parameters to find the position with minimal chi-square values or rms timing residuals. We tried two positioning strategies including: (1) searching in the 3-dimensional space, (2) searching in the X-Y plane with a constant wrong Z coordinates. The results shows that precision of about tens to hundreds of meters is achievable depending on pulsars. We analyzed the impacts of pulsar reference phase in the pulsar timing model on the positioning results, especially on the Z coordinates. The reference phase is essential for the terrestrial position determinations both for the grid searching method and analytic method. Considering that the absolute pulsar reference phase is not available for the present pulsar timing analysis. We suggest to use the relative pulsar reference phase or external geographical data to obtain reasonable positioning results for terrestrial objects.In order to investigate the feasibility of pulsar terrestrial navigation and the possible positioning precision, we make use of different numbers of observations from J0437-4715 for our analysis. Assuming that the timing measurements are made on the Earth, we test the positioning precision in 3 cases including: (1) using a few observations based on analytic method, the results of which show an overall accuracy of about 300 meters with only three or four observations, and as more observations are involved, the positioning accuracy increases significantly; (2) hybrid data of the total pulsar timing observations and geographical information based on grid search in the geodetic coordinate system, whose results is better than 10 meters; (3) the same as (2) but smaller numbers of observations are used, in this case, better results than (1) are obtained. 
Pages86
Language中文
Document Type学位论文
Identifierhttp://ir.xao.ac.cn/handle/45760611-7/4146
Collection研究生学位论文
Affiliation中国科学院新疆天文台
First Author AffilicationXinjiang Astronomical Observatory, Chinese Academy of Sciences
Recommended Citation
GB/T 7714
韩伟. 基于射电观测的脉冲星导航验证及地面应用研究[D]. 北京. 中国科学院大学,2020.
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