中文摘要：

分析重力场模型的截断误差及其影响因素，并用多颗不同轨道高度的低轨卫星GPS实测数据进行实时定轨仿真分析，提出实时定轨精度能够达到1．0m（伪距法实时定轨）和0．5m（相位法实时定轨）的重力场模型阶次的最优确定方法。使用CHAMP和TerraSAR—X2颗卫星实测数据，验证了重力场模型阶次的最优确定方法的可行性和有效性。该方法不仅避免了传统经验法确定重力场模型阶次不准确的问题，而且不需要借助精密轨道进行精度评估，便于实时定轨系统的工程应用。

英文摘要：

In this paper, the truncated error of the earth gravity model is analyzed with RTOD simulation experiments, using the space-borne GPS observation data from several LEO satellites at different orbit heights. The optimal degrees and orders of the earth gravity model are chosen to match with RTOD solutions about 1.0 m using pseudo-range measurements and 0.5 m using carrier-phase meas- urements. Finally, this method is tested using other space-borne GPS data from CHAMP and Terra- SAR-X satellites. The results show that our method can determine the optimal degree and order of the earth gravity model in RTOD, without the need of precise satellite orbit parameters. It is convenient to be applied to satellite missions for RTOD.