Wang Fuhong, Gong Xuewen, Sang Jizhang, Zhang Xiaohong
School of Geodesy and Geomatics, Wuhan University, Wuhan 430079, China.
Collaborative Innovation Center for Geospatial Technology, Wuhan 430079, China.
Sensors (Basel). 2015 Dec 4;15(12):30403-18. doi: 10.3390/s151229805.
Satellite remote sensing systems require accurate, autonomous and real-time orbit determinations (RTOD) for geo-referencing. Onboard Global Positioning System (GPS) has widely been used to undertake such tasks. In this paper, a novel RTOD method achieving decimeter precision using GPS carrier phases, required by China's HY2A and ZY3 missions, is presented. A key to the algorithm success is the introduction of a new parameter, termed pseudo-ambiguity. This parameter combines the phase ambiguity, the orbit, and clock offset errors of the GPS broadcast ephemeris together to absorb a large part of the combined error. Based on the analysis of the characteristics of the orbit and clock offset errors, the pseudo-ambiguity can be modeled as a random walk, and estimated in an extended Kalman filter. Experiments of processing real data from HY2A and ZY3, simulating onboard operational scenarios of these two missions, are performed using the developed software SATODS. Results have demonstrated that the position and velocity accuracy (3D RMS) of 0.2-0.4 m and 0.2-0.4 mm/s, respectively, are achieved using dual-frequency carrier phases for HY2A, and slightly worse results for ZY3. These results show it is feasible to obtain orbit accuracy at decimeter level of 3-5 dm for position and 0.3-0.5 mm/s for velocity with this RTOD method.
卫星遥感系统需要精确、自主且实时的轨道确定（RTOD）来进行地理配准。机载全球定位系统（GPS）已被广泛用于执行此类任务。本文提出了一种新颖的RTOD方法，该方法利用GPS载波相位实现分米级精度，这是中国HY2A和ZY3任务所要求的。该算法成功的关键在于引入了一个新参数，称为伪模糊度。这个参数将GPS广播星历的相位模糊度、轨道和时钟偏差误差结合在一起，以吸收大部分组合误差。基于对轨道和时钟偏差误差特性的分析，伪模糊度可以建模为随机游走，并在扩展卡尔曼滤波器中进行估计。使用开发的软件SATODS对来自HY2A和ZY3的真实数据进行处理实验，模拟这两个任务的机载操作场景。结果表明，使用双频载波相位，HY2A的位置和速度精度（3D均方根误差）分别达到0.2 - 0.4米和0.2 - 0.4毫米/秒，ZY3的结果略差。这些结果表明，采用这种RTOD方法获得分米级轨道精度是可行的，位置精度为3 - 5分米，速度精度为0.3 - 0.5毫米/秒。
