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题名	单颗导航卫星定轨的钟差模型和精度分析
作者	胡轩宇
学位类别	硕士
答辩日期	2009-06-10
授予单位	中国科学院上海天文台
授予地点	上海天文台
导师	胡小工
关键词	导航卫星 定轨 钟差模型 协方差分析
其他题名	Orbit Determination for A Single Navigation Satellite: Clock Bias Models and Precision Analysis
中文摘要	The application of navigation satellites (NS) is seen in almost every aspect of the society and our daily life nowadays. The primary function of the navigation system is to provide accurate positioning for users. The user normal relies on a receiver to collect the pseudo-range measurements which are the observed transmitted time of the signal from space to the ground, likely to contain large errors due to biases from the satellite-borne and ground clocks. If we assume that the satellite-borne clock bias (CB) is known or corrected, observations from no less than NS at the same time can specify the user’s position and the ground CB simultaneously. Therefore, the performance of the NS largely depends on the precise determination of the satellite position as well as the CB (the satellite-born in particular). This thesis studies the orbit determination (OD) of the navigation satellite COMPASS-M1 (M1). The major concern at present is how to account for the CB which cannot be removed entirely when there is only one satellite to work with. In the study, we focus on the use of two types of CB models, characterizing the true CB effects as either linear functions within a few hours or quadratic functions in a few days, in the OD problem of interest. The basic idea is to solve for the associated CB parameters together with the satellite state in the OD process, hence the OD precision is subject to the choice of CB models. OD strategies based on different CB models were analyzed and tuned to improve their results to the extent possible. Some of the necessary conditions and procedures in the OD for obtaining reliable results were tested and described in our work. Particularly, it was observed that the quadratic model strategy yields the most satisfactory performance of all, with an estimated line-of-sight and overall orbit precision of better than 1 meter and 10 meters, respectively. Additionally, the OD strategy with the quadratic model is a more robust method when working with problematic observation data than the other. Secondly, a detailed analysis was carried out on the CB model precision and the precision of satellite CB prediction. In this part we presented a novel approach to evaluate the CB model precision via the use of the station CB measurements in our work. It showed in a very straightforward way that the precision of the quadratic CB model is around a few nanoseconds. Besides, our approach also revealed the shortcomings of the CB models, since the stochastic CB errors could not be represented by deterministic models. For the satellite CB prediction, the quadratic model is easier to work with, where the accuracy is the same order as that of the CB model precision. In the final section of the thesis the covariance analysis was carried out to verify the overall OD precision. Preliminary study indicated that the covariance tends to overestimate both the orbit and the CB precision which could be explained by the fact that simplified OD strategies were used. We showed in the next step that, for the M1 problem one feasible way to adjust the covariance is to simply multiply it with a scalar value so that the true CB error level and tuned covariance result would agree. Moreover, the tuned covariance also appeared to match the true orbit precision, and thus it serves as further numerical evidence towards the understanding of the overall precision of our OD problem.
英文摘要	导航卫星的应用已经渗透到社会生产和生活的各个方面。导航系统的一项最重要的服务是为装备接收机的用户提供定位功能。接收机测得的是自身到卫星的伪距信息，这种时延观测量最主要的误差源通常是卫星和接收机所存在的钟差。若卫星钟差已知，利用接收机同时刻对多颗卫星的伪距观测量便可以解算出自身的位置和接收机钟差。所以对导航卫星而言，位置精度和卫星钟差信息是直接关系其服务质量的两个重要参数。导航卫星的定轨问题很大程度上就是准确估计以上两个参数的过程。 本文研究了COMPASS-M1导航试验卫星的定轨问题。由于单星定轨时钟差无法直接消除，一种可行的办法是用模型近似实际钟差的影响、将模型相关参数与卫星轨道一起在定轨过程中加以确定。这实质上是在确定卫星轨道的同时将钟差的主要部分从伪距中分离了出来。钟差模型的选取决定了其对实际钟差的近似精度，也直接影响着卫星位置精度。从这一点出发，本文分析了多种钟差建模方法。以往有研究指出，钟差在几个小时的时段内基本上可以用线性函数进行拟合，这种分段的钟差模型可以被用来建立简化的定轨策略。在此基础上，本文还考察了钟差在较长时间内的行为，提出在几天的时段内将其近似为二次曲线，并讨论了如何将这种新的二阶钟差模型运用于定轨工作中。分析结果说明，二阶钟差模型可以被成功地运用于定轨，在修正其它如对流层延迟、电离层延迟等观测误差后，基于二阶钟差模型的定轨方案可以获得视向好于1米、三维好于10米的定轨精度。本文还具体比较了新的二阶钟差模型与过去分段钟差模型运用于定轨的效果差异。分析结果说明，使用二阶钟差模型不仅获得的定轨精度明显好于分段模型，且在定轨时对错误观测数据的抗差性也更好。 除了钟差模型对定轨精度的影响，本文还详细考察了二阶钟差模型的精度以及将它用来做卫星钟差预报的精度。本文提出了用一种实测的站间钟差数据分析钟差模型精度的办法，分析结果说明钟差模型曲线相对实际钟差还有量级有几个纳秒的误差。同时也揭示出了使用模型近似实际钟差行为存在的局限性，即钟差具有一定随机性的、高频的变化是无法由钟差函数曲线所描述的。二阶钟差模型用于作钟差预报十分方便，钟差预报的精度与钟差模型精度同在纳秒级的水平。 最后，本文引入了协方差分析的方法对M1卫星定轨结果作了更深入的分析。考虑到文中简化模型的使用必然损失了部分定轨精度，本文研究了协方差分析的钟差估计精度和定轨精度与实际精度之间的关系。分析说明，实际误差水平相对于协方差给出的结果近似存在一个几十倍的放大关系。在对原始失真的协方差作出调整后，它可以作为关于M1卫星定轨精度的的数值分析参考。
语种	中文
公开日期	2011-07-01
页码	86
内容类型	学位论文
源URL	[http://119.78.226.72//handle/331011/14730]
专题	上海天文台_中国科学院上海天文台学位论文
推荐引用方式 GB/T 7714	胡轩宇. 单颗导航卫星定轨的钟差模型和精度分析[D]. 上海天文台. 中国科学院上海天文台. 2009.

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