GNSS精密卫星单点定位技术(Precise Point Positioning，PPP)仅使用单台接收机便可获得全球范围内高精度的测站坐标、接收机钟差和大气延迟等多种信息，因此广泛应用于精密定位、导航、授时、大气监测等领域中。卫星钟差是制约精密单点定位精度的重要因素，但目前的卫星钟差产品仍存在以下问题：传统卫星钟差产品由于采用单日解算策略，天界处钟差相位模糊度的不重叠导致发生跳跃，使用这种钟差产品进行时间传递获得的钟差序列也会存在明显的天间跳变现象；预报卫星钟差产品虽然可以实时获取但精度不能满足高精度精密卫星单点定位的需求；各分析中心发布的钟差产品也存在粗差和部分历元卫星钟差缺失的问题。基于以上存在的问题，本文主要研究内容及成果如下：

     （1） 针对连续时间传递中天界处的跳变现象，采用一种基于多天观测数据估计的连续钟差产品解决。使用该连续钟差产品进行连续时间传递，天界处最大跳变仅为0.034ns，有效削弱了时间传递的天间跳变。

    （2） 针对近实时钟差估计计算耗时问题，提出了一种基于K-mean++聚类算法的全球跟踪站网选站策略。该选站策略不仅考虑了跟踪站的全球均匀分布而且顾及跟踪站的观测数据质量，仅需50个跟踪站便可解算出精度为0.016ns的事后卫星钟差产品。针对IGS超快产品（IGS Ultra-rapid products，IGU）预报钟差精度低，实测钟差发布时延长的问题，采用一种基于状态空间阈（State Space Representation，SSR）改正的近实时钟差产品，时延仅为1h，钟差精度优于0.09ns。使用该钟差产品进行PPP实验并与IGS周解坐标进行对比，GPS相位残差RMS值优于1cm，GALILEO相位残差RMS值在1cm左右。

    （3）针对钟差产品不可避免的会出现粗差和部分历元卫星钟差缺失的问题，对各分析中心钟差产品统一时间基准并剔除钟差产品中的粗差，使用多角帽定权法对各分析中心钟差产品进行加权平均生成一种可靠性更高的综合钟差产品。计算的GPS综合钟差与IGS最终 卫星钟差（IGS Final products，IGS)二次差的STD值优于40ps，GALILEO综合钟差与参与综合的钟差产品STD值均优于100ps。

    （4）东京海洋大学高须知二教授研发的开源软件GPSTools（GT）仅能对GPS卫星系统进行数据处理。本文对GT软件进行了二次开发，增加了计算GALILEO卫星系统、钟差二次差对比、跟踪站网选站等功能，并优化部分数据处理程序。

    GNSS Precise Point Positioning ( PPP ) technology only uses a single receiver to obtain high-precision station coordinates, receiver clock offset and atmospheric delay in the global range. Therefore, it is widely used in precision positioning, navigation, timing, atmospheric monitoring and other fields. Satellite clock error is an important factor restricting the precision point positioning accuracy, but the current satellite clock error products still have the following problems : the traditional satellite clock error products due to the use of one-day solution strategy, the clock phase ambiguity at the boundary does not overlap lead to jump, the clock sequence obtained by using this clock error product for time transfer will also have obvious sky jump phenomenon ; although the prediction satellite clock error products can be obtained in real time, the accuracy cannot meet the needs of high precision satellite single point positioning. The clock error products released by each analysis center also have the problems of gross error and missing clock error of some epoch satellites. Based on the above problems, the main research contents and results of this paper are as follows :

    (1) Aiming at the sky boundary jump phenomenon in continuous time transfer, a continuous clock error product based on multi-day observation data estimation is adopted. Using this continuous clock error product for continuous time transfer, the maximum jump at the sky boundary is only 0.034 ns, which effectively weakens the sky jump of time transfer.

    (2) Aiming at the time-consuming problem of near-real clock error estimation, a global tracking station network selection strategy based on K-mean + + clustering algorithm is proposed. The station selection strategy takes into account not only the global uniform distribution of the tracking station but also the quality of the observation data of the tracking station. Only 50 tracking stations can be used to calculate the post-satellite clock product with a precision of 0.016 ns. Aiming at the problem of low prediction accuracy of IGS Ultra-rapid products ( IGU ) and long release time of measured clock error, a near-real clock error product based on state space representation ( SSR ) correction is adopted. The delay is only 1 h, and the clock error accuracy is better than 0.09 ns. The PPP experiment was carried out using the clock error product and compared with the IGS circumferential solution coordinates. The RMS value of GPS phase residual is better than 1 cm, and the RMS value of GALILEO phase residual is about 1 cm.

    (3) In view of the inevitable problems of gross error and missing of some epoch satellite clock errors in clock error products, the time benchmark of clock error products in each analysis center is unified and the gross error in clock error products is eliminated. The multi-angle cap weighting method is used to weighted average the clock error products in each analysis center to generate a comprehensive clock error product with higher reliability. The STD of GPS integrated clock error and IGS final products ( IGS ) secondary error is better than 40ps, and the STD of GALILEO integrated clock error and integrated clock error products are better than 100ps.

    (4) The open-source software GPSTools ( GT ) developed by Professor Tomoji Takasu of Tokyo Ocean University can only process the data of GPS satellite system. In this paper, the secondary development of GT software is carried out, including the calculation of GALILEO satellite system, the comparison of clock error quadratic difference, and the selection of tracking station network, and some data processing procedures are optimized.

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