Shi Junbo, Wang Gaojing, Han Xianquan, Guo Jiming
School of Geodesy and Geomatics, Wuhan University, Wuhan 430079, China.
Key Laboratory of Precise Engineering and Industry Surveying, National Administration of Surveying, Mapping and Geoinformation, Wuhan University, Wuhan 430079, China.
Sensors (Basel). 2017 Jun 12;17(6):1363. doi: 10.3390/s17061363.
Satellite orbit and clock corrections are always treated as known quantities in GPS positioning models. Therefore, any error in the satellite orbit and clock products will probably cause significant consequences for GPS positioning, especially for real-time applications. Currently three types of satellite products have been made available for real-time positioning, including the broadcast ephemeris, the International GNSS Service (IGS) predicted ultra-rapid product, and the real-time product. In this study, these three predicted/real-time satellite orbit and clock products are first evaluated with respect to the post-mission IGS final product, which demonstrates cm to m level orbit accuracies and sub-ns to ns level clock accuracies. Impacts of real-time satellite orbit and clock products on GPS point and relative positioning are then investigated using the P3 and GAMIT software packages, respectively. Numerical results show that the real-time satellite clock corrections affect the point positioning more significantly than the orbit corrections. On the contrary, only the real-time orbit corrections impact the relative positioning. Compared with the positioning solution using the IGS final product with the nominal orbit accuracy of ~2.5 cm, the real-time broadcast ephemeris with ~2 m orbit accuracy provided <2 cm relative positioning error for baselines no longer than 216 km. As for the baselines ranging from 574 to 2982 km, the cm-dm level positioning error was identified for the relative positioning solution using the broadcast ephemeris. The real-time product could result in <5 mm relative positioning accuracy for baselines within 2982 km, slightly better than the predicted ultra-rapid product.
在GPS定位模型中，卫星轨道和时钟校正通常被视为已知量。因此，卫星轨道和时钟产品中的任何误差都可能给GPS定位带来重大影响，尤其是对于实时应用。目前，有三种类型的卫星产品可用于实时定位，包括广播星历、国际全球导航卫星系统服务（IGS）预测的超快产品和实时产品。在本研究中，首先将这三种预测/实时卫星轨道和时钟产品与任务后IGS最终产品进行评估，后者展示了厘米到米级的轨道精度和亚纳秒到纳秒级的时钟精度。然后分别使用P3和GAMIT软件包研究实时卫星轨道和时钟产品对GPS单点定位和相对定位的影响。数值结果表明，实时卫星时钟校正对单点定位的影响比轨道校正更为显著。相反，只有实时轨道校正会影响相对定位。与使用标称轨道精度约为2.5厘米的IGS最终产品的定位解相比，轨道精度约为2米的实时广播星历对于长度不超过216公里的基线提供了小于2厘米的相对定位误差。对于长度在574至2982公里之间的基线，使用广播星历的相对定位解的定位误差为厘米到分米级。对于长度在2982公里以内的基线，实时产品可实现小于5毫米的相对定位精度，略优于预测的超快产品。
